Water Pollution
Water resources are sources of water that are useful or potentially useful to humans. Water is essential for all forms of life, and this is no different for people. Many uses of water include agricultural, industrial, household, recreational and environmental activities. Virtually all of these human uses require fresh water. 88.7% of water on the Earth is salt water, and over two thirds of fresh water is frozen in glaciers and polar ice caps, leaving only 0.9% available for human use. Fresh water is a renewable resource, yet the world's supply of clean, fresh water is steadily decreasing. Water demand already exceeds supply in many parts of the world, and as world population continues to rise at an unprecedented and unsustainable rate, many more areas are expected to experience this imbalance in the near future. The framework for allocating water resources to water users (where such a framework exists) is known as water rights.
Surface water
Surface water is water in a river, lake or fresh water wetland. Surface water is naturally replenished by precipitation and naturally lost through discharge to the oceans, evaporation, and sub-surface seepage.
Although the only natural input to any surface water system is precipitation within its watershed, the total quantity of water in that system at any given time is also dependent on many other factors. These factors include storage capacity in lakes, wetlands and artificial reservoirs, the permeability of the soil beneath these storage bodies, the runoff characteristics of the land in the watershed, the timing of the precipitation and local evaporation rates. All of these factors also affect the proportions of water lost.
Human activities can have a large impact on these factors. Humans often increase storage capacity by constructing reservoirs and decrease it by draining wetlands. Humans often increase runoff quantities and velocities by paving areas and channelizing stream flow.
The total quantity of water available at any given time is an important consideration. Some human water users have an intermittent need for water. For example, many farms require large quantities of water in the spring, and no water at all in the winter. To supply such a farm with water, a surface water system may require a large storage capacity to collect water throughout the year and release it in a short period of time. Other users have a continuous need for water, such as a power plant that requires water for cooling. To supply such a power plant with water, a surface water system only needs enough storage capacity to fill in when average stream flow is below the power plant's need.
Nevertheless, over the long term the average rate of precipitation within a watershed is the upper bound for average consumption of natural surface water from that watershed.
Natural surface water can be augmented by importing surface water from another watershed through a canal or pipeline. It can also be artificially augmented from any of the other sources listed here, however in practice the quantities are negligible. Humans can also cause surface water to be "lost" (i.e. become unusable) through pollution.
Sub-surface water
Sub-Surface water, or groundwater, is fresh water located in the pore space of soil and rocks. It is also water that is flowing within aquifers below the water table. Sometimes it is useful to make a distinction between sub-surface water that is closely associated with surface water and deep sub-surface water in an aquifer (sometimes called "fossil water").
Sub-surface water can be thought of in the same terms as surface water: inputs, outputs and storage. The critical difference is that due to its slow rate of turnover, sub-surface water storage is generally much larger compared to inputs than it is for surface water. This difference makes it easy for humans to use sub-surface water unsustainably for a long time without severe consequences. Nevertheless, over the long term the average rate of seepage above a sub-surface water source is the upper bound for average consumption of water from that source.
The natural input to sub-surface water is seepage from surface water. The natural outputs from sub-surface water are springs and seepage to the oceans.
If the surface water source is also subject to substantial evaporation, a sub-surface water source may become saline. This situation can occur naturally under endorheic bodies of water, or artificially under irrigated farmland. In coastal areas, human use of a sub-surface water source may cause the direction of seepage to ocean to reverse which can also cause soil salinization. Humans can also cause sub-surface water to be "lost" (i.e. become unusable) through pollution. Humans can increase the input to a sub-surface water source by building reservoirs or detention ponds.
Water in the ground is in sections called aquifers. Rain rolls down and comes into these. Normally an aquifer is near to the equilibrium in its water content. The water content of an aquifier normally depends on the grain sizes. This means that the rate of extraction may be limited by poor permeability.
a)What are the sources of water pollution?
Some of the principal sources of water pollution are: Geology of aquifers from which groundwater is abstracted, Industrial discharge of chemical wastes and byproducts, Discharge of poorly-treated or untreated sewage, Surface runoff containing pesticides or fertilizers, Slash and burn farming practice, which is often an element within shifting cultivation agricultural systems, Surface runoff containing spilled petroleum products, Surface runoff from construction sites, farms, or paved and other impervious surfaces e.g. silt, Discharge of contaminated and/or heated water used for industrial processes.
Acid rain caused by industrial discharge of sulphur dioxide (by burning high-sulphur fossil fuels), Excess nutrients are added (eutrophication) by runoff containing detergents or fertilizers, Underground storage tank leakage, leading to soil contamination, and hence aquifer contamination, Inappropriate disposal of various solid wastes and, on a localized scale, littering, Oil spills.
There are many causes for water pollution but two general categories exist: direct and indirect contaminant sources.
Direct sources include effluent outfalls from factories, refineries, waste treatment plants etc.. that emit fluids of varying quality directly into urban water supplies. In the United States and other countries, these practices are regulated, although this doesn't mean that pollutants can't be found in these waters.
Indirect sources include contaminants that enter the water supply from soils/groundwater systems and from the atmosphere via rain water. Soils and groundwaters contain the residue of human agricultural practices (fertilizers, pesticides, etc..) and improperly disposed of industrial wastes. Atmospheric contaminants are also derived from human practices (such as gaseous emissions from automobiles, factories and even bakeries).
Contaminants can be broadly classified into organic, inorganic, radioactive and acid/base. Examples from each class and their potential sources are too numerous to discuss here.
b)What are the effects of water pollution?
The effects of water pollution are varied. They include poisonous drinking water, poisionous food animals (due to these organisms having bioaccumulated toxins from the environment over their life spans), unbalanced river and lake ecosystems that can no longer support full biological diversity, deforestation from acid rain, and many other effects. These effects are, of course, specific to the various contaminants.
Contaminants may include organic and inorganic substances.
Some organic water pollutants are: Insecticides and herbicides, a huge range of organohalide and other chemicals, Bacteria, often is from sewage or livestock operations, Food processing waste, including pathogens, Tree and brush debris from logging operations, VOCs (Volatile organic compounds), such as industrial solvents, from improper storage, Petroleum Hydrocarbons including fuels (gasoline, diesel, jet fuels, and fuel oils) and lubricants (motor oil) from oil field operations, refineries, pipelines, retail service station's underground storage tanks, and transfer operations. Note: VOCs include gasoline-range hydrocarbons.
Some inorganic water pollutants include: Heavy metals including acid mine drainage,
Acidity caused by industrial discharges (especially sulfur dioxide from power plants), Pre-production industrial raw resin pellets (an industrial pollutant), Chemical waste as industrial by products : Fertilizers, in runoff from agriculture including nitrates and phosphates. Silt in surface runoff from construction sites, logging, slash and burn practices or land clearing sites.
The sources of water pollution typically fall into one of two categories: point-source pollution and non-point-source pollution.
The term point-source pollution refers to pollutants discharged from one discrete location or point, such as an industry or municipal wastewater treatment plant. Pollutants discharged in this way might include, for example, fecal coliform bacteria and nutrients from sewage, and toxics such as heavy metals, or synthetic organic contaminants.
The term non-point-source pollution refers to pollutants that cannot be identified as coming from one discrete location or point. Examples are oil and grease that enter the water with runoff from urban streets, nitrogen from fertilizers and pesticides, and animal wastes that wash into surface waters from agricultural lands. Natural and unknown causes of pollutants also can impact water quality and may be related to human activities. For example, highway or housing construction may help precipitate the runoff of natural pollution sources, such as sediment.
Potability of Water – Water for drinking
Regular testing is important to identify existing problems, ensure water is suitable for the intended use, ensure safe drinking water, and determine the effectiveness of a treatment system. The quality of a water source may change over time, even suddenly. Changes can go unnoticed as the water may look, smell, and taste the same.
Basic Water Potability Test packages include tests for coliform bacteria, nitrates, pH, sodium, chloride, fluoride, sulphate, iron, manganese, total dissolved solids, and hardness.
• Coliform bacteria tests indicate the presence of microorganisms in the water that are potentially harmful to human health.
• Nitrate is a common contaminant found mainly in groundwater. High nitrate concentrations can be particularly dangerous for babies under six months, since nitrate interferes with the ability of blood to carry oxygen.
• Ions such as sodium, chloride, sulphate, iron, and manganese can impart objectionable taste or odour to water.
• Excessive amounts of sulfate can have a laxative effect or cause gastrointestinal irritation.
• Fluoride is an essential micro-nutrient, but excessive amounts can cause dental problems.
• Total dissolved solids represent the amount of inorganic substances (i.e. sodium, chloride, sulphate) that are dissolved in the water. High total dissolved solids (TDS) can reduce the palatability of water.
Other tests may be appropriate if a particular contaminant is suspected in the water. For instance, groundwater sources are sometimes tested for arsenic, selenium, and uranium. Both surface and groundwater sources may also be tested for pesticide contamination. Domestic water supplies should be tested a minimum of once per year. Drinking water supplies obtained from shallow wells and surface water sources should be tested more frequently (i.e. seasonally), as they are more susceptible to contamination.
The following terms are commonly used test parameters:
pH - represents the intensity of the acid or alkaline condition of a solution. A pH of 7 indicates neutral conditions on a scale of 0 (acidic) to 14 (alkaline).
Conductivity - measures the ability of water to conduct an electrical current, and is directly related to the total dissolved salts (ions) in the water.
Coliforms (Total) - bacteria found in faeces, soil, and vegetation, which is used to indicate the bacteriological quality of water. Coliforms indicate the possible presence of pathogenic bacteria and viruses.
Nitrate (NO3) - the most completely oxidized state of nitrogen found in water. High nitrate levels can occur naturally, but may indicate biological wastes in the water, or run-off from heavily fertilized fields. High nitrate levels reduce the ability of blood to transport oxygen to body tissues.
Total Hardness - mainly caused by the presence of calcium and magnesium in water, and is expressed as the equivalent quantity of calcium carbonate. Scale formation and excessive soap consumption are the main problems associated with hardness.
Total Dissolved Solids (TDS) - the total dissolved substances (i.e. salts and minerals) in water remaining after evaporating the water and weighing the residue.
Turbidity - represents the clarity of water. It is measured by the degree to which light is blocked because the water is muddy or cloudy.
Following are common questions and answers regarding the basic concepts of the bacterial indicator system used to monitor drinking water.
Q. Are there bacteria in properly treated potable water?
A. Yes. Drinking water regulations require that potable waters, water for human consumption, be free from human-disease-causing bacteria and specific indicator bacteria that are indicative of the presence of these pathogens. This does not mean that drinking water should be sterile. Keep in mind that not all bacteria are harmful to humans.
Q. What bacteria are harmful to the consumer?
A. There are some bacteria that have a greater probability of causing disease in humans. These bacteria are classified as pathogens. Examples of bacterial pathogens and their related diseases are Salmonella typhi (typhoid fever), Shigella dysenteriae (dysentery), and Legionella pneumophilia (Legionnaire's Disease).
There are other bacteria that will cause disease in humans, but this usually occurs in situations where the individual has been immuno-compromised. An immuno-compromised person can be very young or elderly, under antibiotic or chemotherapy treatment, undernourished, and so forth. Bacteria that cause disease in these individuals are classified as opportunistic pathogens. These bacteria take advantage of the compromised condition of the individual as an opportunity to develop disease symptoms. However, under normal or healthy conditions, the individual's own body defenses would prevent the disease from developing.
Q. How are bacteria indicative of contamination in drinking water?
A. Originally, the bacterial species and bacterial groups that are of regulatory concern were considered to be strictly associated with feces. However, it is now known that some of these bacteria can be isolated not only from human feces but also from the environment where no human fecal contamination has occurred. There is no easy or inexpensive way to differentiate the source of these bacteria when isolated from a drinking water sample. Therefore, erring on the side of safety, the regulations are based on the concept that the presence of these specific bacteria, regardless of their source, is indicative of fecal contamination from human or natural sources such as septic seepage, soils, and warm-blooded animals. This may seem unfair to the water treatment plant operator, but if the plant is operated efficiently and the distribution system is maintained properly, the probability of introducing these bacteria into the distribution system drinking water is minimal.
Q. What is coliform?
A. By definition, the term coliform group includes those bacteria that are aerobic and facultatively anaerobic, gram-negative, nonsporeforming, rod-shaped bacteria capable of fermenting lactose with gas and acid production within 48 h ± 4 h at 35°C ± 0.5°C.
Q. How does the technical definition of coliform group (previous answer) relate to a water treatment plant operator whose responsibility is the processing of water samples and interpretation of the results?
A. Admittedly, there is more information given in the definition of coliform group than is required to understand the basic concepts of the coliform indicator system. However, the descriptive terms used in the definition are necessary for classification of coliforms in relation to other bacteria and go beyond the intention of this handbook. The characteristic used for diagnostic purposes that you should be familiar with is the fermentation or utilization of lactose that produces gas bubbles and acid in the media.
Specific examples on how to interpret diagnostic results when using different types of media follow in later chapters. Also, depending on the technique used to analyze the water sample, such as multiple tube fermentation (MTF), presence-absence (PA), or membrane filter (MF), the definition for a coliform must be modified appropriately. Therefore, it is not important to memorize this definition. However, to understand why the definition must be modified when evaluating test results from the MTF technique versus the MF technique, it will be helpful to refer to this definition.
Q. What are fecal coliforms?
A. Fecal coliforms are defined in the same way as total coliforms except that fecal coliforms can ferment lactose at an elevated temperature when using standard media (44.5°C ± 0.2°C). This increase in incubation temperature inhibits the growth and lactose fermentation of the other total coliforms, which ferment lactose optimally at 35°C ± 0.5°C.
Q. Does the previous definition of fecal coliform apply to E. coli since it is a fecal coliform?
A. Yes. The only difference is in the standard media used to isolate E. coli.
Q. Why is E. coli considered to be more specific for indicating potable water contamination than the other total and fecal coliforms?
A. E. coli is more often directly associated with fecal contamination and disease outbreaks in potable waters than any of the other total or fecal coliforms. Recent developments in the technology for isolating, recovering, and identifying E. coli have made a once difficult task relatively simple, affordable, and dependable. Having a test that identifies the presence of a bacterium that is known to indicate the likelihood of fecal contamination gives the bacteriologist another technique for ensuring bacteriologically safe drinking water to the consumer.
Eutrophication
Eutrophication is a process whereby water bodies, such as lakes, estuaries, or slow-moving streams receive excess nutrients that stimulate excessive plant growth (algae, periphyton attached algae, and nuisance plants weeds). This enhanced plant growth, often called an algal bloom, reduces dissolved oxygen in the water when dead plant material decomposes and can cause other organisms to die. Nutrients can come from many sources, such as fertilizers applied to agricultural fields, golf courses, and suburban lawns; deposition of nitrogen from the atmosphere; erosion of soil containing nutrients; and sewage treatment plant discharges. Water with a low concentration of dissolved oxygen is called hypoxic.
Eutrophication is caused by the decrease of an ecosystem with chemical nutrients, typically compounds containing nitrogen or phosphorus. It may occur on land or in the water. Eutrophication is frequently a result of nutrient pollution such as the release of sewage effluent into natural waters (rivers or coasts) although it may occur naturally in situations where nutrients accumulate (e.g. depositional environments) or where they flow into systems on an ephemeral basis (e.g. intermittent upwelling in coastal systems).
Eutrophication generally promotes excessive plant growth and decay, favors certain weedy species over others, and is likely to cause severe reductions in water quality. In aquatic environments, enhanced growth of choking aquatic vegetation or phytoplankton (that is, an algal bloom) disrupts normal functioning of the ecosystem, causing a variety of problems. Human society is impacted as well: eutrophication decreases the resource value of rivers, lakes, and estuaries such that recreation, fishing, hunting, and aesthetic enjoyment are hindered. Health-related problems can occur where eutrophic conditions interfere with drinking water treatment.
Although traditionally thought of as enrichment of aquatic systems by addition of fertilizers into lakes, bays, or other semi-enclosed waters (even slow-moving rivers), terrestrial ecosystems are subject to similarly adverse impacts. Increased content of nitrates in soil frequently leads to undesirable changes in vegetation composition and many plant species are endangered as a result of eutrophication in terrestric ecosystems, e.g. majority of orchid species in Europe. Ecosystems (like some meadows, forests and bogs that are characterized by low nutrient content and species-rich, slowly growing vegetation adapted to lower nutrient levels) are overgrown by faster growing and more competitive species-poor vegetation, like tall grasses, that can take advantage of unnaturally elevated nitrogen level and the area may be changed beyond recognition and vulnerable species may be lost. Eg. species-rich fens are overtaken by reed or reedgrass species, spectacular forest undergrowth affected by run-off from nearby fertilized field is turned into a thick nettle and bramble shrub.
Eutrophication was recognized as a pollution problem in European and North American lakes and reservoirs in the mid-20th century. Since then, it has become more widespread. Surveys showed that 54% of lakes in Asia are eutrophic; in Europe, 53%; in North America, 48%; in South America, 41%; and in Africa, 28%.
Concept of eutrophication
Eutrophication can be a natural process in lakes, as they fill in through geological time, though other lakes are known to demonstrate the reverse process, becoming less nutrient rich with time. Estuaries also tend to be naturally eutrophic because land-derived nutrients are concentrated where run-off enters the marine environment in a confined channel and mixing of relatively high nutrient fresh water with low nutrient marine water occurs.
Phosphorus is often regarded as the main culprit in cases of eutrophication in lakes subjected to point source pollution from sewage. The concentration of algae and the tropic state of lakes correspond well to phosphorus levels in water. Studies conducted in the Experimental Lakes Area in Ontario have shown a relationship between the addition of phosphorus and the rate of eutrophication. Humankind has increased the rate of phosphorus cycling on Earth by four times, mainly due to agricultural fertilizer production and application. Between 1950 and 1995, 600,000,000 tonnes of phosphorus were applied to Earth's surface, primarily on croplands. Control of point sources of phosphorus have resulted in rapid control of eutrophication, mainly due to policy changes.
Human activities can accelerate the rate at which nutrients enter ecosystems. Runoff
from agriculture and development, pollution from septic systems and sewers, and other human-related activities increase the flux of both inorganic nutrients and organic substances into terrestrial, aquatic, and coastal marine ecosystems (including coral reefs). Elevated atmospheric compounds of nitrogen can increase soil nitrogen availability.
Chemical forms of nitrogen are most often of concern with regard to eutrophication
because plants have high nitrogen requirements so that additions of nitrogen compounds stimulate plant growth (primary production). Nitrogen is not readily available in soil because N2, a gaseous form of nitrogen, is very stable and unavailable directly to higher plants. Terrestrial ecosystems rely on microbial nitrogen fixation to convert N2 into other physical forms (such as nitrates). However, there is a limit to how much nitrogen can be utilized. Ecosystems receiving more nitrogen than the plants require are called nitrogen-saturated. Saturated terrestrial ecosystems contribute both inorganic and organic nitrogen to freshwater, coastal, and marine eutrophication, where nitrogen is also typically a limiting nutrient. However, in marine environments, phosphorus may be limiting because it is leached from the soil at a much slower rate than nitrogen, which are highly insoluble.
Ecological effects
Adverse effects of eutrophication on lakes, reservoirs, rivers and coastal marine
waters
• Increased biomass of phytoplankton
• Toxic or inedible phytoplankton species
• Increases in blooms of gelatinous zooplankton
• Increased biomass of benthic and epiphytic algae
• Changes in macrophyte species composition and biomass
• Decreases in water transparency
• Taste, odor, and water treatment problems
• Dissolved oxygen depletion
• Increased incidences of fish kills
• Loss of desirable fish species
• Reductions in harvestable fish and shellfish
• Decreases in perceived aesthetic value of the water body
Many ecological effects can arise from stimulating primary production, but there are
three particularly troubling ecological impacts: decreased biodiversity, changes in species composition and dominance, and toxicity effects.
Decreased biodiversity
When an ecosystem experiences an increase in nutrients, primary producers reap the benefits first. In aquatic ecosystems, species such as algae experience a population increase (called an algal bloom). Algal blooms limit the sunlight available to bottom-dwelling organisms and cause wide swings in the amount of dissolved oxygen in the water.
Oxygen is required by all respiring plants and animals and it is replenished in daylight by photosynthesizing plants and algae. Under eutrophic conditions, dissolved oxygen greatly increases during the day, but is greatly reduced after dark by the respiring algae and by microorganisms that feed on the increasing mass of dead algae. When dissolved oxygen levels decline to hypoxic levels, fish and other marine animals suffocate. As a result, creatures such as fish, shrimp, and especially immobile bottom dwellers die off. In extreme cases, anaerobic conditions ensue, promoting growth of bacteria such as Clostridium botulinum that produces toxins deadly to birds and mammals. Zones where this occurs are known as dead zones.
Sources of high nutrient runoff
Characteristics of point and nonpoint sources of chemical inputs
Point sources
• Wastewater effluent (municipal and industrial)
• Runoff and leachate from waste disposal systems
• Runoff and infiltration from animal feedlots
• Runoff from mines, oil fields, unsewered industrial sites
• Overflows of combined storm and sanitary sewers
• Runoff from construction sites >20,000 m²
Nonpoint Sources
• Runoff from agriculture/irrigation
• Runoff from pasture and range
• Urban runoff from unsewered areas
• Septic tank leachate
• Runoff from construction sites <20,000 m²
• Runoff from abandoned mines
• Atmospheric deposition over a water surface
• Other land activities generating contaminants
Point sources are directly attributable to one influence. In point sources the nutrient waste travels directly from source to water. For example, factories that have waste discharge pipes directly leading into a water body would be classified as a point source. Point sources are relatively easy to regulate.
Nonpoint source pollution (also known as 'diffuse' or 'runoff' pollution) is that which comes from ill-defined and diffuse sources. Nonpoint sources are difficult to regulate and usually vary spatially and temporally (with season, precipitation, and other irregular events). It has been shown that nitrogen transport is correlated with various indices of human activity in watersheds, including the amount of development. Agriculture and development are activities that contribute most to nutrient loading.
There are three reasons that nonpoint sources are especially troublesome:
• Soil retention
• Runoff to surface water and leaching to groundwater
• Atmospheric deposition
Prevention and reversal
Eutrophication poses a problem not only to ecosystems, but to humans as well. Reducing eutrophication should be a key concern when considering future policy, and a sustainable solution for everyone, including farmers and ranchers, seems feasible. While eutrophication does pose problems, humans should be aware that natural runoff (which causes algal blooms in the wild) is common in ecosystems and should thus not reverse nutrient concentrations beyond normal levels.
Cleanup measures have been mostly, but not completely, successful. Finish phosphorus removal measures started in the mid-1970s and have targeted rivers and lakes polluted by industrial and municipal discharges. These efforts have had a 90% removal efficiency. Still, some targeted point sources did not show a decrease in runoff despite reduction efforts.
Impact of farming
Farming is what makes possible the production of food surpluses and settled living. It also brings about big changes in the relationships between living things and in their habitats. Farming - especially modern, intensive farming can damage the environment in many different ways.
Effect of fertilizers
Fertilisers containing plant nutrients are sprayed onto fields to make plants grow faster and boost crop yields. When it rains the nutrients may get washed down from the fields and into rivers and lakes (this is called run-off). The result is eutrophication – which can kill almost everything living in the aquatic environment. It works like this:
Effect of pesticides
Pesticides are chemicals used to kill insects, weeds and microorganisms that might damage crops. However, pesticides damage other organisms apart from those they are intended to kill - for example, depriving insect-eating birds of food. Pesticides can also enter local food chains. Organisms that ingest them cannot break them down, so they persist in their bodies. (Substances that cannot be broken down are called persistent substances: the pesticide DDT is an example.) The pesticides may then build up at ever-higher levels until they become toxic to much larger organisms.
Other impacts of farming
Agriculture can impact on the environment in many other ways. For example:
• farming takes up land, reducing habitats and wildlife
• monocultures (large amounts of one type of food) provide lots of food for
pests as well as humans
• irrigation (watering of crops) may take too much water from rivers, depriving
downstream habitats of water
• clearing land for farming may result in soil erosion, damaging ecosystems
and leaving land barren
• Intensive livestock farming produces huge amount of faeces, which may
pollute waterways
Soil Pollution
Soil is the thin layer of organic and inorganic materials that covers the Earth's rocky surface. The organic portion, which is derived from the decayed remains of plants and animals, is concentrated in the dark uppermost topsoil. The inorganic portion made up of rock fragments, was formed over thousands of years by physical and chemical weathering of bedrock. Productive soils are necessary for agriculture to supply the world with sufficient food.
Definition of soil pollution: Soil pollution is defined as the build-up in soils of persistent toxic compounds, chemicals, salts, radioactive materials, or disease causing agents, which have adverse effects on plant growth and animal health.
There are many different ways that soil can become polluted, such as:
• Seepage from a landfill
• Discharge of industrial waste into the soil
• Percolation of contaminated water into the soil
• Rupture of underground storage tanks
• Excess application of pesticides, herbicides or fertilizer
• Solid waste seepage
The most common chemicals involved in causing soil pollution are:
• Petroleum hydrocarbons
• Heavy metals
• Pesticides
• Solvents
Types of Soil Pollution
• Agricultural Soil Pollution
i) pollution of surface soil
ii) pollution of underground soil
• Soil pollution by industrial effluents and solid wastes
i) pollution of surface soil
ii) disturbances in soil profile
• Pollution due to urban activities
i) pollution of surface soil
ii) pollution of underground soil
Causes of Soil Pollution
Soil pollution is caused by the presence of man-made chemicals or other alteration in the natural soil environment. This type of contamination typically arises from the rupture of underground storage links, application of pesticides, percolation of contaminated surface water to subsurface strata, oil and fuel dumping, leaching of wastes from landfills or direct discharge of industrial wastes to the soil. The most common chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead and other heavy metals. This occurrence of this phenomenon is correlated with the degree of industrialization and intensities of chemical usage.
Soil pollutant
A soil pollutant is any factor which deteriorates the quality, texture and mineral content of the soil or which disturbs the biological balance of the organisms in the soil.
Effect of soil pollution
Pollution in soil has adverse effect on plant growth.
· Pollution in soil is associated with
· Indiscriminate use of fertilizers
· Indiscriminate use of pesticides, insecticides and herbicides
· Dumping of large quantities of solid waste
· Deforestation and soil erosion
· Indiscriminate use of fertilizers
Soil nutrients are important for plant growth and development. Plants obtain carbon, hydrogen and oxygen from air and water. But other necessary nutrients like nitrogen, phosphorus, potassium, calcium, magnesium, sulfur and more must be obtained from the soil. Farmers generally use fertilizers to correct soil deficiencies. Fertilizers contaminate the soil with impurities, which come from the raw materials used for their manufacture. Mixed fertilizers often contain ammonium nitrate (NH4NO3), phosphorus as P2O5, and potassium as K2O. For instance, As, Pb and Cd present in traces in rock phosphate mineral get transferred to super phosphate fertilizer. Since the metals are not degradable, their accumulation in the soil above their toxic levels due to excessive use of phosphate fertilizers, becomes an indestructible poison for crops. The over use of NPK fertilizers reduce quantity of vegetables and crops grown on soil over the years. It also reduces the protein content of wheat, maize, grams, etc., grown on that soil. The carbohydrate quality of such crops also gets degraded. Excess potassium content in soil decreases Vitamin C and carotene content in vegetables and fruits. The vegetables and fruits grown on overfertilized soil are more prone to attacks by insects and disease.
Indiscriminate use of pesticides, insecticides and herbicides
Plants on which we depend for food are under attack from insects, fungi, bacteria, viruses, rodents and other animals, and must compete with weeds for nutrients. To kill unwanted populations living in or on their crops, farmers use pesticides. The first widespread insecticide use began at the end of World War II and included DDT (dichlorodiphenyltrichloroethane) and gammaxene. Insects soon became resistant to DDT and as the chemical did not decompose readily, it persisted in the environment. Since it was soluble in fat rather than water, it biomagnified up the food chain and disrupted calcium metabolism in birds, causing eggshells to be thin and fragile. As a result, large birds of prey such as the brown pelican, ospreys, falcons and eagles became endangered. DDT has been now been banned in most western countries. Ironically many of them including USA, still produce DDT for export to other developing nations whose needs outweigh the problems caused by it.
The most important pesticides are DDT, BHC, chlorinated hydrocarbons, organophosphates, aldrin, malathion, dieldrin, furodan, etc. The remnants of such pesticides used on pests may get adsorbed by the soil particles, which then contaminate root crops grown in that soil. The consumption of such crops causes the pesticides remnants to enter human biological systems, affecting them adversely.
An infamous herbicide used as a defoliant in the Vietnam War called Agent Orange (dioxin), was eventually banned. Soldiers' cancer cases, skin conditions and infertility have been linked to exposure to Agent Orange.
Pesticides not only bring toxic effect on human and animals but also decrease the fertility of the soil. Some of the pesticides are quite stable and their bio- degradation may take weeks and even months. Pesticide problems such as resistance, resurgence, and heath effects have caused scientists to seek alternatives. Pheromones and hormones to attract or repel insects and using natural enemies or sterilization by radiation have been suggested.
Dumping of solid wastes
In general, solid waste includes garbage, domestic refuse and discarded solid materials such as those from commercial, industrial and agricultural operations. They contain increasing amounts of paper, cardboards, plastics, glass, old construction material, packaging material and toxic or otherwise hazardous substances. Since a significant amount of urban solid waste tends to be paper and food waste, the majority is recyclable or biodegradable in landfills. Similarly, most agricultural waste is recycled and mining waste is left on site.
The portion of solid waste that is hazardous such as oils, battery metals, heavy metals from smelting industries and organic solvents are the ones we have to pay particular attention to. These can in the long run, get deposited to the soils of the surrounding area and pollute them by altering their chemical and biological properties. They also contaminate drinking water aquifer sources. More than 90% of hazardous waste is produced by chemical, petroleum and metal-related industries and small businesses such as dry cleaners and gas stations contribute as well.
Solid Waste disposal was brought to the forefront of public attention by the notorious Love Canal case in USA in 1978. Toxic chemicals leached from oozing storage drums into the soil underneath homes, causing an unusually large number of birth defects, cancers and respiratory, nervous and kidney diseases.
Deforestation
Soil Erosion occurs when the weathered soil particles are dislodged and carried away by wind or water. Deforestation, agricultural development, temperature extremes, precipitation including acid rain, and human activities contribute to this erosion. Humans speed up this process by construction, mining, cutting of timber, over cropping and overgrazing. It results in floods and cause soil erosion.
Forests and grasslands are an excellent binding material that keeps the soil intact and healthy. They support many habitats and ecosystems, which provide innumerable feeding pathways or food chains to all species. Their loss would threaten food chains and the survival of many species. During the past few years quite a lot of vast green land has been converted into deserts. The precious rain forest habitats of South America, tropical Asia and Africa are coming under pressure of population growth and development (especially timber, construction and agriculture). Many scientists believe that a wealth of medicinal substances including a cure for cancer and aids, lie in these forests.
Deforestation is slowly destroying the most productive flora and fauna areas in the world, which also form vast tracts of a very valuable sink for CO2.
Pollution Due to Urbanization
Pollution of surface soils Urban activities generate large quantities of city wastes including several Biodegradable materials (like vegetables, animal wastes, papers, wooden pieces, carcasses, plant twigs, leaves, cloth wastes as well as sweepings) and many non-biodegradable materials (such as plastic bags, plastic bottles, plastic wastes, glass bottles, glass pieces, stone / cement pieces). On a rough estimate Indian
cities are producing solid city wastes to the tune of 50,000 - 80,000 metric tons every day. If left uncollected and decomposed, they are a cause of several problems such as
• Clogging of drains: Causing serious drainage problems including the burst / leakage of drainage lines leading to health problems.
• Barrier to movement of water: Solid wastes have seriously damaged the normal movement of water thus creating problem of inundation, damage to foundation of buildings as well as public health hazards.
• Foul smell: Generated by dumping the wastes at a place.
• Increased microbial activities: Microbial decomposition of organic wastes generate large quantities of methane besides many chemicals to pollute the soil and water flowing on its surface
• When such solid wastes are hospital wastes they create many health problems: As they may have dangerous pathogen within them besides dangerous medicines, injections.
Pollution of Underground Soil
Underground soil in cities is likely to be polluted by
• Chemicals released by industrial wastes and industrial wastes
• Decomposed and partially decomposed materials of sanitary wastes
Many dangerous chemicals like cadmium, chromium, lead, arsenic, selenium products are likely to be deposited in underground soil. Similarly underground soil polluted by sanitary wastes generate many harmful chemicals.These can damage the normal activities and ecological balance in the underground soil
Causes in brief:
• Polluted water discharged from factories
• Runoff from pollutants (paint, chemicals, rotting organic material) leaching out of landfill
• Oil and petroleum leaks from vehicles washed off the road by the rain into the surrounding habitat
• Chemical fertilizer runoff from farms and crops
• Acid rain (fumes from factories mixing with rain)
• Sewage discharged into rivers instead of being treated properly
• Over application of pesticides and fertilizers
• Purposeful injection into groundwater as a disposal method
• Interconnections between aquifers during drilling (poor technique)
• Septic tank seepage
• Lagoon seepage
• Sanitary/hazardous landfill seepage
• Cemeteries
• Scrap yards (waste oil and chemical drainage)
• Leaks from sanitary sewers
Effects of Soil Pollution
Agricultural
• Reduced soil fertility
• Reduced nitrogen fixation
• Increased erodibility
• Larger loss of soil and nutrients
• Deposition of silt in tanks and reservoirs
• Reduced crop yield
• Imbalance in soil fauna and flora
Industrial
• Dangerous chemicals entering underground water
• Ecological imbalance
• Release of pollutant gases
• Release of radioactive rays causing health problems
• Increased salinity
• Reduced vegetation
Urban
• Clogging of drains
• Inundation of areas
• Public health problems
• Pollution of drinking water sources
• Foul smell and release of gases
• Waste management problems
Environmental Long Term Effects of Soil Pollution
When it comes to the environment itself, the toll of contaminated soil is even more dire. Soil that has been contaminated should no longer be used to grow food, because the chemicals can leech into the food and harm people who eat it. If contaminated soil is used to grow food, the land will usually produce lower yields than it would if it were not contaminated. This, in turn, can cause even more harm because a lack of plants on the soil will cause more erosion, spreading the contaminants onto land that might not have been tainted before.
In addition, the pollutants will change the makeup of the soil and the types of microorganisms that will live in it. If certain organisms die off in the area, the larger predator animals will also have to move away or die because they've lost their food supply. Thus it's possible for soil pollution to change whole ecosystems.
Effects of soil pollution in brief:
· pollution runs off into rivers and kills the fish, plants and other aquatic life
· crops and fodder grown on polluted soil may pass the pollutants on to the consumers
· polluted soil may no longer grow crops and fodder
· Soil structure is damaged (clay ionic structure impaired)
· corrosion of foundations and pipelines
· impairs soil stability
· may release vapours and hydrocarbon into buildings and cellars
· may create toxic dusts
· may poison children playing in the area
Control of soil pollution
The following steps have been suggested to control soil pollution. To help prevent soil erosion, we can limit construction in sensitive area. In general we would need less fertilizer and fewer pesticides if we could all adopt the three R's: Reduce, Reuse, and Recycle. This would give us less solid waste.
Reducing chemical fertilizer and pesticide use
Applying bio-fertilizers and manures can reduce chemical fertilizer and pesticide use.
Biological methods of pest control can also reduce the use of pesticides and thereby minimize soil pollution.
Reusing of materials
Materials such as glass containers, plastic bags, paper, cloth etc. can be reused at domestic levels rather than being disposed, reducing solid waste pollution.
Recycling and recovery of materials
This is a reasonable solution for reducing soil pollution. Materials such as paper, some kinds of plastics and glass can and are being recycled. This decreases the volume of refuse and helps in the conservation of natural resources. For example, recovery of one tonne of paper can save 17 trees.
Reforesting
Control of land loss and soil erosion can be attempted through restoring forest and grass cover to check wastelands, soil erosion and floods. Crop rotation or mixed cropping can improve the fertility of the land.
Solid waste treatment
Proper methods should be adopted for management of solid waste disposal. Industrial wastes can be treated physically, chemically and biologically until they are less hazardous. Acidic and alkaline wastes should be first neutralized; the insoluble material if biodegradable should be allowed to degrade under controlled conditions before being disposed.
As a last resort, new areas for storage of hazardous waste should be investigated such as deep well injection and more secure landfills. Burying the waste in locations situated away from residential areas is the simplest and most widely used technique of solid waste management. Environmental and aesthetic considerations must be taken into consideration before selecting the dumping sites.
Incineration of other wastes is expensive and leaves a huge residue and adds to air pollution. Pyrolysis is a process of combustion in absence of oxygen or the material burnt under controlled atmosphere of oxygen. It is an alternative to incineration. The gas and liquid thus obtained can be used as fuels. Pyrolysis of carbonaceous wastes like firewood, coconut, palm waste, corn combs, cashew shell, rice husk paddy straw and saw dust, yields charcoal along with products like tar, methyl alcohol, acetic acid, acetone and a fuel gas.
Anaerobic/aerobic decomposition of biodegradable municipal and domestic waste is also being done and gives organic manure. Cow dung which releases methane into the atmosphere, should be processed further in 'gobar gas plants' to produce 'gobar gas' and good manure.
Natural land pollution:
Land pollution occurs massively during earth quakes, land slides, hurricanes and floods. All cause hard to clean mess, which is expensive to clean , and may sometimes take years to restore the affected area. These kinds of natural disasters are not only a problem in that they cause pollution but also because they leave many victims homeless.
Water resources are sources of water that are useful or potentially useful to humans. Water is essential for all forms of life, and this is no different for people. Many uses of water include agricultural, industrial, household, recreational and environmental activities. Virtually all of these human uses require fresh water. 88.7% of water on the Earth is salt water, and over two thirds of fresh water is frozen in glaciers and polar ice caps, leaving only 0.9% available for human use. Fresh water is a renewable resource, yet the world's supply of clean, fresh water is steadily decreasing. Water demand already exceeds supply in many parts of the world, and as world population continues to rise at an unprecedented and unsustainable rate, many more areas are expected to experience this imbalance in the near future. The framework for allocating water resources to water users (where such a framework exists) is known as water rights.
Surface water
Surface water is water in a river, lake or fresh water wetland. Surface water is naturally replenished by precipitation and naturally lost through discharge to the oceans, evaporation, and sub-surface seepage.
Although the only natural input to any surface water system is precipitation within its watershed, the total quantity of water in that system at any given time is also dependent on many other factors. These factors include storage capacity in lakes, wetlands and artificial reservoirs, the permeability of the soil beneath these storage bodies, the runoff characteristics of the land in the watershed, the timing of the precipitation and local evaporation rates. All of these factors also affect the proportions of water lost.
Human activities can have a large impact on these factors. Humans often increase storage capacity by constructing reservoirs and decrease it by draining wetlands. Humans often increase runoff quantities and velocities by paving areas and channelizing stream flow.
The total quantity of water available at any given time is an important consideration. Some human water users have an intermittent need for water. For example, many farms require large quantities of water in the spring, and no water at all in the winter. To supply such a farm with water, a surface water system may require a large storage capacity to collect water throughout the year and release it in a short period of time. Other users have a continuous need for water, such as a power plant that requires water for cooling. To supply such a power plant with water, a surface water system only needs enough storage capacity to fill in when average stream flow is below the power plant's need.
Nevertheless, over the long term the average rate of precipitation within a watershed is the upper bound for average consumption of natural surface water from that watershed.
Natural surface water can be augmented by importing surface water from another watershed through a canal or pipeline. It can also be artificially augmented from any of the other sources listed here, however in practice the quantities are negligible. Humans can also cause surface water to be "lost" (i.e. become unusable) through pollution.
Sub-surface water
Sub-Surface water, or groundwater, is fresh water located in the pore space of soil and rocks. It is also water that is flowing within aquifers below the water table. Sometimes it is useful to make a distinction between sub-surface water that is closely associated with surface water and deep sub-surface water in an aquifer (sometimes called "fossil water").
Sub-surface water can be thought of in the same terms as surface water: inputs, outputs and storage. The critical difference is that due to its slow rate of turnover, sub-surface water storage is generally much larger compared to inputs than it is for surface water. This difference makes it easy for humans to use sub-surface water unsustainably for a long time without severe consequences. Nevertheless, over the long term the average rate of seepage above a sub-surface water source is the upper bound for average consumption of water from that source.
The natural input to sub-surface water is seepage from surface water. The natural outputs from sub-surface water are springs and seepage to the oceans.
If the surface water source is also subject to substantial evaporation, a sub-surface water source may become saline. This situation can occur naturally under endorheic bodies of water, or artificially under irrigated farmland. In coastal areas, human use of a sub-surface water source may cause the direction of seepage to ocean to reverse which can also cause soil salinization. Humans can also cause sub-surface water to be "lost" (i.e. become unusable) through pollution. Humans can increase the input to a sub-surface water source by building reservoirs or detention ponds.
Water in the ground is in sections called aquifers. Rain rolls down and comes into these. Normally an aquifer is near to the equilibrium in its water content. The water content of an aquifier normally depends on the grain sizes. This means that the rate of extraction may be limited by poor permeability.
a)What are the sources of water pollution?
Some of the principal sources of water pollution are: Geology of aquifers from which groundwater is abstracted, Industrial discharge of chemical wastes and byproducts, Discharge of poorly-treated or untreated sewage, Surface runoff containing pesticides or fertilizers, Slash and burn farming practice, which is often an element within shifting cultivation agricultural systems, Surface runoff containing spilled petroleum products, Surface runoff from construction sites, farms, or paved and other impervious surfaces e.g. silt, Discharge of contaminated and/or heated water used for industrial processes.
Acid rain caused by industrial discharge of sulphur dioxide (by burning high-sulphur fossil fuels), Excess nutrients are added (eutrophication) by runoff containing detergents or fertilizers, Underground storage tank leakage, leading to soil contamination, and hence aquifer contamination, Inappropriate disposal of various solid wastes and, on a localized scale, littering, Oil spills.
There are many causes for water pollution but two general categories exist: direct and indirect contaminant sources.
Direct sources include effluent outfalls from factories, refineries, waste treatment plants etc.. that emit fluids of varying quality directly into urban water supplies. In the United States and other countries, these practices are regulated, although this doesn't mean that pollutants can't be found in these waters.
Indirect sources include contaminants that enter the water supply from soils/groundwater systems and from the atmosphere via rain water. Soils and groundwaters contain the residue of human agricultural practices (fertilizers, pesticides, etc..) and improperly disposed of industrial wastes. Atmospheric contaminants are also derived from human practices (such as gaseous emissions from automobiles, factories and even bakeries).
Contaminants can be broadly classified into organic, inorganic, radioactive and acid/base. Examples from each class and their potential sources are too numerous to discuss here.
b)What are the effects of water pollution?
The effects of water pollution are varied. They include poisonous drinking water, poisionous food animals (due to these organisms having bioaccumulated toxins from the environment over their life spans), unbalanced river and lake ecosystems that can no longer support full biological diversity, deforestation from acid rain, and many other effects. These effects are, of course, specific to the various contaminants.
Contaminants may include organic and inorganic substances.
Some organic water pollutants are: Insecticides and herbicides, a huge range of organohalide and other chemicals, Bacteria, often is from sewage or livestock operations, Food processing waste, including pathogens, Tree and brush debris from logging operations, VOCs (Volatile organic compounds), such as industrial solvents, from improper storage, Petroleum Hydrocarbons including fuels (gasoline, diesel, jet fuels, and fuel oils) and lubricants (motor oil) from oil field operations, refineries, pipelines, retail service station's underground storage tanks, and transfer operations. Note: VOCs include gasoline-range hydrocarbons.
Some inorganic water pollutants include: Heavy metals including acid mine drainage,
Acidity caused by industrial discharges (especially sulfur dioxide from power plants), Pre-production industrial raw resin pellets (an industrial pollutant), Chemical waste as industrial by products : Fertilizers, in runoff from agriculture including nitrates and phosphates. Silt in surface runoff from construction sites, logging, slash and burn practices or land clearing sites.
The sources of water pollution typically fall into one of two categories: point-source pollution and non-point-source pollution.
The term point-source pollution refers to pollutants discharged from one discrete location or point, such as an industry or municipal wastewater treatment plant. Pollutants discharged in this way might include, for example, fecal coliform bacteria and nutrients from sewage, and toxics such as heavy metals, or synthetic organic contaminants.
The term non-point-source pollution refers to pollutants that cannot be identified as coming from one discrete location or point. Examples are oil and grease that enter the water with runoff from urban streets, nitrogen from fertilizers and pesticides, and animal wastes that wash into surface waters from agricultural lands. Natural and unknown causes of pollutants also can impact water quality and may be related to human activities. For example, highway or housing construction may help precipitate the runoff of natural pollution sources, such as sediment.
Potability of Water – Water for drinking
Regular testing is important to identify existing problems, ensure water is suitable for the intended use, ensure safe drinking water, and determine the effectiveness of a treatment system. The quality of a water source may change over time, even suddenly. Changes can go unnoticed as the water may look, smell, and taste the same.
Basic Water Potability Test packages include tests for coliform bacteria, nitrates, pH, sodium, chloride, fluoride, sulphate, iron, manganese, total dissolved solids, and hardness.
• Coliform bacteria tests indicate the presence of microorganisms in the water that are potentially harmful to human health.
• Nitrate is a common contaminant found mainly in groundwater. High nitrate concentrations can be particularly dangerous for babies under six months, since nitrate interferes with the ability of blood to carry oxygen.
• Ions such as sodium, chloride, sulphate, iron, and manganese can impart objectionable taste or odour to water.
• Excessive amounts of sulfate can have a laxative effect or cause gastrointestinal irritation.
• Fluoride is an essential micro-nutrient, but excessive amounts can cause dental problems.
• Total dissolved solids represent the amount of inorganic substances (i.e. sodium, chloride, sulphate) that are dissolved in the water. High total dissolved solids (TDS) can reduce the palatability of water.
Other tests may be appropriate if a particular contaminant is suspected in the water. For instance, groundwater sources are sometimes tested for arsenic, selenium, and uranium. Both surface and groundwater sources may also be tested for pesticide contamination. Domestic water supplies should be tested a minimum of once per year. Drinking water supplies obtained from shallow wells and surface water sources should be tested more frequently (i.e. seasonally), as they are more susceptible to contamination.
The following terms are commonly used test parameters:
pH - represents the intensity of the acid or alkaline condition of a solution. A pH of 7 indicates neutral conditions on a scale of 0 (acidic) to 14 (alkaline).
Conductivity - measures the ability of water to conduct an electrical current, and is directly related to the total dissolved salts (ions) in the water.
Coliforms (Total) - bacteria found in faeces, soil, and vegetation, which is used to indicate the bacteriological quality of water. Coliforms indicate the possible presence of pathogenic bacteria and viruses.
Nitrate (NO3) - the most completely oxidized state of nitrogen found in water. High nitrate levels can occur naturally, but may indicate biological wastes in the water, or run-off from heavily fertilized fields. High nitrate levels reduce the ability of blood to transport oxygen to body tissues.
Total Hardness - mainly caused by the presence of calcium and magnesium in water, and is expressed as the equivalent quantity of calcium carbonate. Scale formation and excessive soap consumption are the main problems associated with hardness.
Total Dissolved Solids (TDS) - the total dissolved substances (i.e. salts and minerals) in water remaining after evaporating the water and weighing the residue.
Turbidity - represents the clarity of water. It is measured by the degree to which light is blocked because the water is muddy or cloudy.
Following are common questions and answers regarding the basic concepts of the bacterial indicator system used to monitor drinking water.
Q. Are there bacteria in properly treated potable water?
A. Yes. Drinking water regulations require that potable waters, water for human consumption, be free from human-disease-causing bacteria and specific indicator bacteria that are indicative of the presence of these pathogens. This does not mean that drinking water should be sterile. Keep in mind that not all bacteria are harmful to humans.
Q. What bacteria are harmful to the consumer?
A. There are some bacteria that have a greater probability of causing disease in humans. These bacteria are classified as pathogens. Examples of bacterial pathogens and their related diseases are Salmonella typhi (typhoid fever), Shigella dysenteriae (dysentery), and Legionella pneumophilia (Legionnaire's Disease).
There are other bacteria that will cause disease in humans, but this usually occurs in situations where the individual has been immuno-compromised. An immuno-compromised person can be very young or elderly, under antibiotic or chemotherapy treatment, undernourished, and so forth. Bacteria that cause disease in these individuals are classified as opportunistic pathogens. These bacteria take advantage of the compromised condition of the individual as an opportunity to develop disease symptoms. However, under normal or healthy conditions, the individual's own body defenses would prevent the disease from developing.
Q. How are bacteria indicative of contamination in drinking water?
A. Originally, the bacterial species and bacterial groups that are of regulatory concern were considered to be strictly associated with feces. However, it is now known that some of these bacteria can be isolated not only from human feces but also from the environment where no human fecal contamination has occurred. There is no easy or inexpensive way to differentiate the source of these bacteria when isolated from a drinking water sample. Therefore, erring on the side of safety, the regulations are based on the concept that the presence of these specific bacteria, regardless of their source, is indicative of fecal contamination from human or natural sources such as septic seepage, soils, and warm-blooded animals. This may seem unfair to the water treatment plant operator, but if the plant is operated efficiently and the distribution system is maintained properly, the probability of introducing these bacteria into the distribution system drinking water is minimal.
Q. What is coliform?
A. By definition, the term coliform group includes those bacteria that are aerobic and facultatively anaerobic, gram-negative, nonsporeforming, rod-shaped bacteria capable of fermenting lactose with gas and acid production within 48 h ± 4 h at 35°C ± 0.5°C.
Q. How does the technical definition of coliform group (previous answer) relate to a water treatment plant operator whose responsibility is the processing of water samples and interpretation of the results?
A. Admittedly, there is more information given in the definition of coliform group than is required to understand the basic concepts of the coliform indicator system. However, the descriptive terms used in the definition are necessary for classification of coliforms in relation to other bacteria and go beyond the intention of this handbook. The characteristic used for diagnostic purposes that you should be familiar with is the fermentation or utilization of lactose that produces gas bubbles and acid in the media.
Specific examples on how to interpret diagnostic results when using different types of media follow in later chapters. Also, depending on the technique used to analyze the water sample, such as multiple tube fermentation (MTF), presence-absence (PA), or membrane filter (MF), the definition for a coliform must be modified appropriately. Therefore, it is not important to memorize this definition. However, to understand why the definition must be modified when evaluating test results from the MTF technique versus the MF technique, it will be helpful to refer to this definition.
Q. What are fecal coliforms?
A. Fecal coliforms are defined in the same way as total coliforms except that fecal coliforms can ferment lactose at an elevated temperature when using standard media (44.5°C ± 0.2°C). This increase in incubation temperature inhibits the growth and lactose fermentation of the other total coliforms, which ferment lactose optimally at 35°C ± 0.5°C.
Q. Does the previous definition of fecal coliform apply to E. coli since it is a fecal coliform?
A. Yes. The only difference is in the standard media used to isolate E. coli.
Q. Why is E. coli considered to be more specific for indicating potable water contamination than the other total and fecal coliforms?
A. E. coli is more often directly associated with fecal contamination and disease outbreaks in potable waters than any of the other total or fecal coliforms. Recent developments in the technology for isolating, recovering, and identifying E. coli have made a once difficult task relatively simple, affordable, and dependable. Having a test that identifies the presence of a bacterium that is known to indicate the likelihood of fecal contamination gives the bacteriologist another technique for ensuring bacteriologically safe drinking water to the consumer.
Eutrophication
Eutrophication is a process whereby water bodies, such as lakes, estuaries, or slow-moving streams receive excess nutrients that stimulate excessive plant growth (algae, periphyton attached algae, and nuisance plants weeds). This enhanced plant growth, often called an algal bloom, reduces dissolved oxygen in the water when dead plant material decomposes and can cause other organisms to die. Nutrients can come from many sources, such as fertilizers applied to agricultural fields, golf courses, and suburban lawns; deposition of nitrogen from the atmosphere; erosion of soil containing nutrients; and sewage treatment plant discharges. Water with a low concentration of dissolved oxygen is called hypoxic.
Eutrophication is caused by the decrease of an ecosystem with chemical nutrients, typically compounds containing nitrogen or phosphorus. It may occur on land or in the water. Eutrophication is frequently a result of nutrient pollution such as the release of sewage effluent into natural waters (rivers or coasts) although it may occur naturally in situations where nutrients accumulate (e.g. depositional environments) or where they flow into systems on an ephemeral basis (e.g. intermittent upwelling in coastal systems).
Eutrophication generally promotes excessive plant growth and decay, favors certain weedy species over others, and is likely to cause severe reductions in water quality. In aquatic environments, enhanced growth of choking aquatic vegetation or phytoplankton (that is, an algal bloom) disrupts normal functioning of the ecosystem, causing a variety of problems. Human society is impacted as well: eutrophication decreases the resource value of rivers, lakes, and estuaries such that recreation, fishing, hunting, and aesthetic enjoyment are hindered. Health-related problems can occur where eutrophic conditions interfere with drinking water treatment.
Although traditionally thought of as enrichment of aquatic systems by addition of fertilizers into lakes, bays, or other semi-enclosed waters (even slow-moving rivers), terrestrial ecosystems are subject to similarly adverse impacts. Increased content of nitrates in soil frequently leads to undesirable changes in vegetation composition and many plant species are endangered as a result of eutrophication in terrestric ecosystems, e.g. majority of orchid species in Europe. Ecosystems (like some meadows, forests and bogs that are characterized by low nutrient content and species-rich, slowly growing vegetation adapted to lower nutrient levels) are overgrown by faster growing and more competitive species-poor vegetation, like tall grasses, that can take advantage of unnaturally elevated nitrogen level and the area may be changed beyond recognition and vulnerable species may be lost. Eg. species-rich fens are overtaken by reed or reedgrass species, spectacular forest undergrowth affected by run-off from nearby fertilized field is turned into a thick nettle and bramble shrub.
Eutrophication was recognized as a pollution problem in European and North American lakes and reservoirs in the mid-20th century. Since then, it has become more widespread. Surveys showed that 54% of lakes in Asia are eutrophic; in Europe, 53%; in North America, 48%; in South America, 41%; and in Africa, 28%.
Concept of eutrophication
Eutrophication can be a natural process in lakes, as they fill in through geological time, though other lakes are known to demonstrate the reverse process, becoming less nutrient rich with time. Estuaries also tend to be naturally eutrophic because land-derived nutrients are concentrated where run-off enters the marine environment in a confined channel and mixing of relatively high nutrient fresh water with low nutrient marine water occurs.
Phosphorus is often regarded as the main culprit in cases of eutrophication in lakes subjected to point source pollution from sewage. The concentration of algae and the tropic state of lakes correspond well to phosphorus levels in water. Studies conducted in the Experimental Lakes Area in Ontario have shown a relationship between the addition of phosphorus and the rate of eutrophication. Humankind has increased the rate of phosphorus cycling on Earth by four times, mainly due to agricultural fertilizer production and application. Between 1950 and 1995, 600,000,000 tonnes of phosphorus were applied to Earth's surface, primarily on croplands. Control of point sources of phosphorus have resulted in rapid control of eutrophication, mainly due to policy changes.
Human activities can accelerate the rate at which nutrients enter ecosystems. Runoff
from agriculture and development, pollution from septic systems and sewers, and other human-related activities increase the flux of both inorganic nutrients and organic substances into terrestrial, aquatic, and coastal marine ecosystems (including coral reefs). Elevated atmospheric compounds of nitrogen can increase soil nitrogen availability.
Chemical forms of nitrogen are most often of concern with regard to eutrophication
because plants have high nitrogen requirements so that additions of nitrogen compounds stimulate plant growth (primary production). Nitrogen is not readily available in soil because N2, a gaseous form of nitrogen, is very stable and unavailable directly to higher plants. Terrestrial ecosystems rely on microbial nitrogen fixation to convert N2 into other physical forms (such as nitrates). However, there is a limit to how much nitrogen can be utilized. Ecosystems receiving more nitrogen than the plants require are called nitrogen-saturated. Saturated terrestrial ecosystems contribute both inorganic and organic nitrogen to freshwater, coastal, and marine eutrophication, where nitrogen is also typically a limiting nutrient. However, in marine environments, phosphorus may be limiting because it is leached from the soil at a much slower rate than nitrogen, which are highly insoluble.
Ecological effects
Adverse effects of eutrophication on lakes, reservoirs, rivers and coastal marine
waters
• Increased biomass of phytoplankton
• Toxic or inedible phytoplankton species
• Increases in blooms of gelatinous zooplankton
• Increased biomass of benthic and epiphytic algae
• Changes in macrophyte species composition and biomass
• Decreases in water transparency
• Taste, odor, and water treatment problems
• Dissolved oxygen depletion
• Increased incidences of fish kills
• Loss of desirable fish species
• Reductions in harvestable fish and shellfish
• Decreases in perceived aesthetic value of the water body
Many ecological effects can arise from stimulating primary production, but there are
three particularly troubling ecological impacts: decreased biodiversity, changes in species composition and dominance, and toxicity effects.
Decreased biodiversity
When an ecosystem experiences an increase in nutrients, primary producers reap the benefits first. In aquatic ecosystems, species such as algae experience a population increase (called an algal bloom). Algal blooms limit the sunlight available to bottom-dwelling organisms and cause wide swings in the amount of dissolved oxygen in the water.
Oxygen is required by all respiring plants and animals and it is replenished in daylight by photosynthesizing plants and algae. Under eutrophic conditions, dissolved oxygen greatly increases during the day, but is greatly reduced after dark by the respiring algae and by microorganisms that feed on the increasing mass of dead algae. When dissolved oxygen levels decline to hypoxic levels, fish and other marine animals suffocate. As a result, creatures such as fish, shrimp, and especially immobile bottom dwellers die off. In extreme cases, anaerobic conditions ensue, promoting growth of bacteria such as Clostridium botulinum that produces toxins deadly to birds and mammals. Zones where this occurs are known as dead zones.
Sources of high nutrient runoff
Characteristics of point and nonpoint sources of chemical inputs
Point sources
• Wastewater effluent (municipal and industrial)
• Runoff and leachate from waste disposal systems
• Runoff and infiltration from animal feedlots
• Runoff from mines, oil fields, unsewered industrial sites
• Overflows of combined storm and sanitary sewers
• Runoff from construction sites >20,000 m²
Nonpoint Sources
• Runoff from agriculture/irrigation
• Runoff from pasture and range
• Urban runoff from unsewered areas
• Septic tank leachate
• Runoff from construction sites <20,000 m²
• Runoff from abandoned mines
• Atmospheric deposition over a water surface
• Other land activities generating contaminants
Point sources are directly attributable to one influence. In point sources the nutrient waste travels directly from source to water. For example, factories that have waste discharge pipes directly leading into a water body would be classified as a point source. Point sources are relatively easy to regulate.
Nonpoint source pollution (also known as 'diffuse' or 'runoff' pollution) is that which comes from ill-defined and diffuse sources. Nonpoint sources are difficult to regulate and usually vary spatially and temporally (with season, precipitation, and other irregular events). It has been shown that nitrogen transport is correlated with various indices of human activity in watersheds, including the amount of development. Agriculture and development are activities that contribute most to nutrient loading.
There are three reasons that nonpoint sources are especially troublesome:
• Soil retention
• Runoff to surface water and leaching to groundwater
• Atmospheric deposition
Prevention and reversal
Eutrophication poses a problem not only to ecosystems, but to humans as well. Reducing eutrophication should be a key concern when considering future policy, and a sustainable solution for everyone, including farmers and ranchers, seems feasible. While eutrophication does pose problems, humans should be aware that natural runoff (which causes algal blooms in the wild) is common in ecosystems and should thus not reverse nutrient concentrations beyond normal levels.
Cleanup measures have been mostly, but not completely, successful. Finish phosphorus removal measures started in the mid-1970s and have targeted rivers and lakes polluted by industrial and municipal discharges. These efforts have had a 90% removal efficiency. Still, some targeted point sources did not show a decrease in runoff despite reduction efforts.
Impact of farming
Farming is what makes possible the production of food surpluses and settled living. It also brings about big changes in the relationships between living things and in their habitats. Farming - especially modern, intensive farming can damage the environment in many different ways.
Effect of fertilizers
Fertilisers containing plant nutrients are sprayed onto fields to make plants grow faster and boost crop yields. When it rains the nutrients may get washed down from the fields and into rivers and lakes (this is called run-off). The result is eutrophication – which can kill almost everything living in the aquatic environment. It works like this:
Effect of pesticides
Pesticides are chemicals used to kill insects, weeds and microorganisms that might damage crops. However, pesticides damage other organisms apart from those they are intended to kill - for example, depriving insect-eating birds of food. Pesticides can also enter local food chains. Organisms that ingest them cannot break them down, so they persist in their bodies. (Substances that cannot be broken down are called persistent substances: the pesticide DDT is an example.) The pesticides may then build up at ever-higher levels until they become toxic to much larger organisms.
Other impacts of farming
Agriculture can impact on the environment in many other ways. For example:
• farming takes up land, reducing habitats and wildlife
• monocultures (large amounts of one type of food) provide lots of food for
pests as well as humans
• irrigation (watering of crops) may take too much water from rivers, depriving
downstream habitats of water
• clearing land for farming may result in soil erosion, damaging ecosystems
and leaving land barren
• Intensive livestock farming produces huge amount of faeces, which may
pollute waterways
Soil Pollution
Soil is the thin layer of organic and inorganic materials that covers the Earth's rocky surface. The organic portion, which is derived from the decayed remains of plants and animals, is concentrated in the dark uppermost topsoil. The inorganic portion made up of rock fragments, was formed over thousands of years by physical and chemical weathering of bedrock. Productive soils are necessary for agriculture to supply the world with sufficient food.
Definition of soil pollution: Soil pollution is defined as the build-up in soils of persistent toxic compounds, chemicals, salts, radioactive materials, or disease causing agents, which have adverse effects on plant growth and animal health.
There are many different ways that soil can become polluted, such as:
• Seepage from a landfill
• Discharge of industrial waste into the soil
• Percolation of contaminated water into the soil
• Rupture of underground storage tanks
• Excess application of pesticides, herbicides or fertilizer
• Solid waste seepage
The most common chemicals involved in causing soil pollution are:
• Petroleum hydrocarbons
• Heavy metals
• Pesticides
• Solvents
Types of Soil Pollution
• Agricultural Soil Pollution
i) pollution of surface soil
ii) pollution of underground soil
• Soil pollution by industrial effluents and solid wastes
i) pollution of surface soil
ii) disturbances in soil profile
• Pollution due to urban activities
i) pollution of surface soil
ii) pollution of underground soil
Causes of Soil Pollution
Soil pollution is caused by the presence of man-made chemicals or other alteration in the natural soil environment. This type of contamination typically arises from the rupture of underground storage links, application of pesticides, percolation of contaminated surface water to subsurface strata, oil and fuel dumping, leaching of wastes from landfills or direct discharge of industrial wastes to the soil. The most common chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead and other heavy metals. This occurrence of this phenomenon is correlated with the degree of industrialization and intensities of chemical usage.
Soil pollutant
A soil pollutant is any factor which deteriorates the quality, texture and mineral content of the soil or which disturbs the biological balance of the organisms in the soil.
Effect of soil pollution
Pollution in soil has adverse effect on plant growth.
· Pollution in soil is associated with
· Indiscriminate use of fertilizers
· Indiscriminate use of pesticides, insecticides and herbicides
· Dumping of large quantities of solid waste
· Deforestation and soil erosion
· Indiscriminate use of fertilizers
Soil nutrients are important for plant growth and development. Plants obtain carbon, hydrogen and oxygen from air and water. But other necessary nutrients like nitrogen, phosphorus, potassium, calcium, magnesium, sulfur and more must be obtained from the soil. Farmers generally use fertilizers to correct soil deficiencies. Fertilizers contaminate the soil with impurities, which come from the raw materials used for their manufacture. Mixed fertilizers often contain ammonium nitrate (NH4NO3), phosphorus as P2O5, and potassium as K2O. For instance, As, Pb and Cd present in traces in rock phosphate mineral get transferred to super phosphate fertilizer. Since the metals are not degradable, their accumulation in the soil above their toxic levels due to excessive use of phosphate fertilizers, becomes an indestructible poison for crops. The over use of NPK fertilizers reduce quantity of vegetables and crops grown on soil over the years. It also reduces the protein content of wheat, maize, grams, etc., grown on that soil. The carbohydrate quality of such crops also gets degraded. Excess potassium content in soil decreases Vitamin C and carotene content in vegetables and fruits. The vegetables and fruits grown on overfertilized soil are more prone to attacks by insects and disease.
Indiscriminate use of pesticides, insecticides and herbicides
Plants on which we depend for food are under attack from insects, fungi, bacteria, viruses, rodents and other animals, and must compete with weeds for nutrients. To kill unwanted populations living in or on their crops, farmers use pesticides. The first widespread insecticide use began at the end of World War II and included DDT (dichlorodiphenyltrichloroethane) and gammaxene. Insects soon became resistant to DDT and as the chemical did not decompose readily, it persisted in the environment. Since it was soluble in fat rather than water, it biomagnified up the food chain and disrupted calcium metabolism in birds, causing eggshells to be thin and fragile. As a result, large birds of prey such as the brown pelican, ospreys, falcons and eagles became endangered. DDT has been now been banned in most western countries. Ironically many of them including USA, still produce DDT for export to other developing nations whose needs outweigh the problems caused by it.
The most important pesticides are DDT, BHC, chlorinated hydrocarbons, organophosphates, aldrin, malathion, dieldrin, furodan, etc. The remnants of such pesticides used on pests may get adsorbed by the soil particles, which then contaminate root crops grown in that soil. The consumption of such crops causes the pesticides remnants to enter human biological systems, affecting them adversely.
An infamous herbicide used as a defoliant in the Vietnam War called Agent Orange (dioxin), was eventually banned. Soldiers' cancer cases, skin conditions and infertility have been linked to exposure to Agent Orange.
Pesticides not only bring toxic effect on human and animals but also decrease the fertility of the soil. Some of the pesticides are quite stable and their bio- degradation may take weeks and even months. Pesticide problems such as resistance, resurgence, and heath effects have caused scientists to seek alternatives. Pheromones and hormones to attract or repel insects and using natural enemies or sterilization by radiation have been suggested.
Dumping of solid wastes
In general, solid waste includes garbage, domestic refuse and discarded solid materials such as those from commercial, industrial and agricultural operations. They contain increasing amounts of paper, cardboards, plastics, glass, old construction material, packaging material and toxic or otherwise hazardous substances. Since a significant amount of urban solid waste tends to be paper and food waste, the majority is recyclable or biodegradable in landfills. Similarly, most agricultural waste is recycled and mining waste is left on site.
The portion of solid waste that is hazardous such as oils, battery metals, heavy metals from smelting industries and organic solvents are the ones we have to pay particular attention to. These can in the long run, get deposited to the soils of the surrounding area and pollute them by altering their chemical and biological properties. They also contaminate drinking water aquifer sources. More than 90% of hazardous waste is produced by chemical, petroleum and metal-related industries and small businesses such as dry cleaners and gas stations contribute as well.
Solid Waste disposal was brought to the forefront of public attention by the notorious Love Canal case in USA in 1978. Toxic chemicals leached from oozing storage drums into the soil underneath homes, causing an unusually large number of birth defects, cancers and respiratory, nervous and kidney diseases.
Deforestation
Soil Erosion occurs when the weathered soil particles are dislodged and carried away by wind or water. Deforestation, agricultural development, temperature extremes, precipitation including acid rain, and human activities contribute to this erosion. Humans speed up this process by construction, mining, cutting of timber, over cropping and overgrazing. It results in floods and cause soil erosion.
Forests and grasslands are an excellent binding material that keeps the soil intact and healthy. They support many habitats and ecosystems, which provide innumerable feeding pathways or food chains to all species. Their loss would threaten food chains and the survival of many species. During the past few years quite a lot of vast green land has been converted into deserts. The precious rain forest habitats of South America, tropical Asia and Africa are coming under pressure of population growth and development (especially timber, construction and agriculture). Many scientists believe that a wealth of medicinal substances including a cure for cancer and aids, lie in these forests.
Deforestation is slowly destroying the most productive flora and fauna areas in the world, which also form vast tracts of a very valuable sink for CO2.
Pollution Due to Urbanization
Pollution of surface soils Urban activities generate large quantities of city wastes including several Biodegradable materials (like vegetables, animal wastes, papers, wooden pieces, carcasses, plant twigs, leaves, cloth wastes as well as sweepings) and many non-biodegradable materials (such as plastic bags, plastic bottles, plastic wastes, glass bottles, glass pieces, stone / cement pieces). On a rough estimate Indian
cities are producing solid city wastes to the tune of 50,000 - 80,000 metric tons every day. If left uncollected and decomposed, they are a cause of several problems such as
• Clogging of drains: Causing serious drainage problems including the burst / leakage of drainage lines leading to health problems.
• Barrier to movement of water: Solid wastes have seriously damaged the normal movement of water thus creating problem of inundation, damage to foundation of buildings as well as public health hazards.
• Foul smell: Generated by dumping the wastes at a place.
• Increased microbial activities: Microbial decomposition of organic wastes generate large quantities of methane besides many chemicals to pollute the soil and water flowing on its surface
• When such solid wastes are hospital wastes they create many health problems: As they may have dangerous pathogen within them besides dangerous medicines, injections.
Pollution of Underground Soil
Underground soil in cities is likely to be polluted by
• Chemicals released by industrial wastes and industrial wastes
• Decomposed and partially decomposed materials of sanitary wastes
Many dangerous chemicals like cadmium, chromium, lead, arsenic, selenium products are likely to be deposited in underground soil. Similarly underground soil polluted by sanitary wastes generate many harmful chemicals.These can damage the normal activities and ecological balance in the underground soil
Causes in brief:
• Polluted water discharged from factories
• Runoff from pollutants (paint, chemicals, rotting organic material) leaching out of landfill
• Oil and petroleum leaks from vehicles washed off the road by the rain into the surrounding habitat
• Chemical fertilizer runoff from farms and crops
• Acid rain (fumes from factories mixing with rain)
• Sewage discharged into rivers instead of being treated properly
• Over application of pesticides and fertilizers
• Purposeful injection into groundwater as a disposal method
• Interconnections between aquifers during drilling (poor technique)
• Septic tank seepage
• Lagoon seepage
• Sanitary/hazardous landfill seepage
• Cemeteries
• Scrap yards (waste oil and chemical drainage)
• Leaks from sanitary sewers
Effects of Soil Pollution
Agricultural
• Reduced soil fertility
• Reduced nitrogen fixation
• Increased erodibility
• Larger loss of soil and nutrients
• Deposition of silt in tanks and reservoirs
• Reduced crop yield
• Imbalance in soil fauna and flora
Industrial
• Dangerous chemicals entering underground water
• Ecological imbalance
• Release of pollutant gases
• Release of radioactive rays causing health problems
• Increased salinity
• Reduced vegetation
Urban
• Clogging of drains
• Inundation of areas
• Public health problems
• Pollution of drinking water sources
• Foul smell and release of gases
• Waste management problems
Environmental Long Term Effects of Soil Pollution
When it comes to the environment itself, the toll of contaminated soil is even more dire. Soil that has been contaminated should no longer be used to grow food, because the chemicals can leech into the food and harm people who eat it. If contaminated soil is used to grow food, the land will usually produce lower yields than it would if it were not contaminated. This, in turn, can cause even more harm because a lack of plants on the soil will cause more erosion, spreading the contaminants onto land that might not have been tainted before.
In addition, the pollutants will change the makeup of the soil and the types of microorganisms that will live in it. If certain organisms die off in the area, the larger predator animals will also have to move away or die because they've lost their food supply. Thus it's possible for soil pollution to change whole ecosystems.
Effects of soil pollution in brief:
· pollution runs off into rivers and kills the fish, plants and other aquatic life
· crops and fodder grown on polluted soil may pass the pollutants on to the consumers
· polluted soil may no longer grow crops and fodder
· Soil structure is damaged (clay ionic structure impaired)
· corrosion of foundations and pipelines
· impairs soil stability
· may release vapours and hydrocarbon into buildings and cellars
· may create toxic dusts
· may poison children playing in the area
Control of soil pollution
The following steps have been suggested to control soil pollution. To help prevent soil erosion, we can limit construction in sensitive area. In general we would need less fertilizer and fewer pesticides if we could all adopt the three R's: Reduce, Reuse, and Recycle. This would give us less solid waste.
Reducing chemical fertilizer and pesticide use
Applying bio-fertilizers and manures can reduce chemical fertilizer and pesticide use.
Biological methods of pest control can also reduce the use of pesticides and thereby minimize soil pollution.
Reusing of materials
Materials such as glass containers, plastic bags, paper, cloth etc. can be reused at domestic levels rather than being disposed, reducing solid waste pollution.
Recycling and recovery of materials
This is a reasonable solution for reducing soil pollution. Materials such as paper, some kinds of plastics and glass can and are being recycled. This decreases the volume of refuse and helps in the conservation of natural resources. For example, recovery of one tonne of paper can save 17 trees.
Reforesting
Control of land loss and soil erosion can be attempted through restoring forest and grass cover to check wastelands, soil erosion and floods. Crop rotation or mixed cropping can improve the fertility of the land.
Solid waste treatment
Proper methods should be adopted for management of solid waste disposal. Industrial wastes can be treated physically, chemically and biologically until they are less hazardous. Acidic and alkaline wastes should be first neutralized; the insoluble material if biodegradable should be allowed to degrade under controlled conditions before being disposed.
As a last resort, new areas for storage of hazardous waste should be investigated such as deep well injection and more secure landfills. Burying the waste in locations situated away from residential areas is the simplest and most widely used technique of solid waste management. Environmental and aesthetic considerations must be taken into consideration before selecting the dumping sites.
Incineration of other wastes is expensive and leaves a huge residue and adds to air pollution. Pyrolysis is a process of combustion in absence of oxygen or the material burnt under controlled atmosphere of oxygen. It is an alternative to incineration. The gas and liquid thus obtained can be used as fuels. Pyrolysis of carbonaceous wastes like firewood, coconut, palm waste, corn combs, cashew shell, rice husk paddy straw and saw dust, yields charcoal along with products like tar, methyl alcohol, acetic acid, acetone and a fuel gas.
Anaerobic/aerobic decomposition of biodegradable municipal and domestic waste is also being done and gives organic manure. Cow dung which releases methane into the atmosphere, should be processed further in 'gobar gas plants' to produce 'gobar gas' and good manure.
Natural land pollution:
Land pollution occurs massively during earth quakes, land slides, hurricanes and floods. All cause hard to clean mess, which is expensive to clean , and may sometimes take years to restore the affected area. These kinds of natural disasters are not only a problem in that they cause pollution but also because they leave many victims homeless.
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