- 1 What is Water Pollution? – Sources and Causes of Water Pollution That Affect Our Environment
- 1.1 Types of Water Pollution
- 1.2 Sources of Water Pollution
- 1.3 Ecology of Water Pollution
- 1.4 Sewage Pollution
- 1.5 Eutrophication
- 1.6 Occurence of Eutrophication
- 1.7 Industrial Pollution
- 1.8 Fertilizers, Pesticides and Herbicides of Agriculture
- 1.9 Biomagnification or Bioamplification
- 1.10 Thermal Pollution
- 1.11 Ecological Effects of Hot Water
- 1.12 Ecological Effects of Cold Water
- 1.13 Silt Pollution
- 1.14 Marine Pollution
- 1.15 Control of Water Pollution
- 1.16 1. Control of Agrochemical Pollution
- 1.17 2. Control of Industrial and Sewage Pollution
- 1.18 Sewage Treatment
- 1.19 3. Control of Groundwater Pollution
- 1.20 4. Control of Thermal Pollution
- 1.21 5. Control of Water Pollution Through Law
- 1.22 Arsenic Poisoning
One of the most fascinating Biology Topics is the study of genetics and how traits are passed down through generations.
What is Water Pollution? – Sources and Causes of Water Pollution That Affect Our Environment
According to Southwick (1976), “When the physical, chemical and biological changes of our natural water reach such a stage that it becomes unfit for human consumption, then the water is said& to be polluted.” The term water pollution is referred to any type of aquatic contamination between two extremes:
- A highly enriched, overproductive biotic community, such as a river or lake with nutrients from sewage or fertilizer is called cultural eutrophication.
- A body of water is poisoned by toxic chemicals that eliminate living organisms or even exclude all forms of life (Southwick, 1976).
Types of Water Pollution
Water pollution can be broadly classified into:
- Biological Pollution: When the water is polluted with various pathogens, e.g., viruses, bacteria, protozoa, helminths, and algae.
- Chemical Pollution: When the source of water becomes polluted with organic wastes like sewage, organic biocides like DDT, BHC and polychlorinated biphenyls (PCBs), inorganic chemicals like As, Pb, Cd, Ni, Hg, phosphates, nitrates, etc.
- Physical Pollution: When the water resources get polluted with oil spills or face thermal pollution, is termed as physical pollution.
Water Pollution can also be classified as
Sources of Water Pollution
Two types of sources of water pollution are observed. They are:
1. Natural Sources
It includes the leaching of minerals, rotting of dead animals and plants in ponds, clay and silt from soil erosion.
2. Anthropogenic or Man-Made Sources
It includes the following:
- Municipal Waste Water: It is the chief component of pollution from cities. It consists of sewage, domestic wastes, detergents, and animal wastes. These wastes are mostly biodegradable.
- Industrial Waste Water: Industrial waste water contains very harmful chemicals, both organic as well as inorganic. Industries using water as steam and as coolant, discharge hot water in the sources of water, also causing thermal pollution.
- Surface Run-Off: Water run-off is a common phenomenon, but if the water from lands using chemical fertilizers and pesticides falls into ponds and rivers, it may cause severe toxicity as they take with them the pesticides too. This kills many aquatic plants and animals.
- Oil Spills: Accidental discharges from oil tankers, oil refineries, and oil drilling industries can lead to oil spills. These extend to a large area of the oceans. Oil is lighter than water, therefore, floats over the top layer of water, and cuts off the air supply. This extensively kills aquatic life.
Ecology of Water Pollution
Each and every type of water pollution has an effect on the biotic and abiotic components of an aquatic ecosystem. Some of the well-known effects of water pollution are given in the following:
Pollution forms due to wastewater that flows after being used for industrial, domestic, and other purposes, called as sewage pollution. Wastewater that often contains feces, urine, and other laundry wastes is released in water. Sewage is a biodegradable pollutant that breaks down in the environment.
All fresh water and shallow offshore seas are seriously polluted by sewage. According to Simmons (1974), domestic sewage is composed of 99.9% water, 0.02-0.04% solids of which proteins and carbohydrates comprise 40-50% and fats 5-10%. Domestic sewage contains mostly biodegradable pollutants, such as human feces, urine, paper, animal parts, and certain dissolved organic compounds (e.g., proteins, carbohydrates, fats, urea, etc.) and inorganic salts, such as nitrates and phosphates of detergents and Na+, K+, Ca++, Cl– ions. Sewage water treatment is carried out by several engineering systems, such as septic tanks, oxidation ponds, filter beds, wastewater treatment plants municipal sewage treatment plants, etc.
Sewage wastes also contain different pathogenic bacteria and other harmful microbes that are responsible for human health hazards. Sewage wastes increase BOD (Biological Oxygen Demand), decrease D.O. (Dissolved Oxygen), and influence phytoplankton bloom or Eutrophication.
Composition of Sewage:
- Water is more than 95%.
- Soluble inorganic material: Ammonia, road salt, sea salt, cyanide, hydrogen sulfide, thiocyanate, thiosulfates, etc.
- Animals: Protozoa, parasitic worms, insects, arthropods, small fish, etc.
- Macrosolids such as sanitary napkins, diapers, needles, children’s toys, condoms, dead animals, or plants.
- Gases: Hydrogen sulfide, carbon dioxide, methane, etc.
- Emulsions: Paints, adhesives, emulsified oils, hair colorants, etc.
- Toxins: pesticides, poisons, herbicides, etc.
- Pharmaceutical products and hormones.
Domestic Sewage Characteristics:
|Solids precipitate||5-20 (ml/l)|
|Alkalinity (as CaCO3)||50-200|
Effects of Sewage Discharge on River and other Water bodies:
- Water becomes unfit for consumption due to stench, turbidity, coloration, or particulate matter or oil floating on it.
- pH level gets affected.
- With eutrophication due to toxicity, disturbance in pH, biological oxygen demand, etc. the water becomes unable to support life.
Biodegradation of Sewage:
Sewage mainly consists of biodegradable organic matter. The microbial decomposition of sewage is called the putrescibility. Such decomposition is an aerobic process requiring oxygen. Therefore, the amount of organic impurities present is measured in terms of B.O.D.
B.O.D (Biological Oxygen Demand):
B.O.D. is the amount of dissolved oxygen needed by aerobic biological organisms to break down the organic material present in a given water sample at a certain temperature over a specific time period. It is the amount of oxygen required for biological oxidation by microbes in any unit volume of water. B.O.D test is done at 20°C for 5 days or 3 days, called B.O.D5 and B.O.D3 respectively. If the B.O.D. level is below 1500 mg/L it indicates low pollution; if it is between 1500-4000 mg/L, pollution is medium, and if it is above 4000 mg/L, it indicates high pollution.
Generally, the B.O.D. test is taken as an indirect measure of water quality. It is a measure of the amount of oxygen required by microbes while decomposable organic matter stabilizes. Two bottles are filled with stream water, measuring the D.O. (Dissolved Oxygen) in one and placing another in the stream. In a few days, the second bottle is retrieved and the D.O. is measured. The difference in the oxygen levels was the B.O.D (as mg of O2 used per liter of the sample). Domestic sewage, if discharged into a river, increases B.O.D. Decomposition, in turn, consumes the Dissolved Oxygen. There will be very less amount of oxygen left for the respiration of aquatic organisms and thus they will get killed. However, it is observed that, as the river flows downstream, the sewage is decomposed gradually, and the D.O. increases with a fall in the level of B.O.D. Clean water along with the organisms reappears gradually.
B.O.D. directly affects the amount of dissolved oxygen in rivers and streams. The rate of oxygen consumption is affected by a number of variables: temperature, pH, the presence of certain kinds of microorganisms, and the type of organic and inorganic material in the water. The greater the B.O.D., the more rapidly oxygen is depleted in the stream. This means less oxygen is available to higher forms of aquatic life. The consequences or significance of high B.O.D. are the same as those for low dissolved oxygen: aquatic organisms become stressed, suffocate, and die. Sources of B.O.D. include topsoil, leaves, and woody debris; animal manure; effluents from pulp and paper mills, wastewater treatment plants, feedlots, and food-processing plants; failing septic systems; and urban stormwater runoff.
Quality of Water (According to the level of BOD):
BOD in River
|Types||BOD Level (mg dm-3)||Quality|
|D||BOD-10||Bad or Polluted Water|
BOD in Sewage Treatment Plant
|BOD Level (mg dm-3)||Quality|
C.O.D (Chemical Oxygen Demand):
In environmental chemistry, the chemical oxygen demand (C.O.D.) test is commonly used to indirectly measure the amount of organic compounds in water. Most applications of C.O.D., determine the amount of organic pollutants found in surface water (e.g., lakes and rivers) or wastewater, making C.O.D. a useful measure of water quality. It is expressed in milligrams per liter (mg/L), which indicates the mass of oxygen consumed per liter of solution.
C.O.D. or Chemical Oxygen demand is the amount of oxygen needed to oxidize all the reducing substances in sewage. It includes reducing chemicals produced during decomposition, oxygen-demanding chemicals, and also B.O.D. The more the B.O.D. or C.O.D. lesser the Dissolved Oxygen. If it is below 8.0 mg/L, the sewage is polluted, while if it is below 4 mg/L, it is highly polluted. The B.O.D. test is run using a standard B.O.D. bottle in the dark.
Chemical oxygen demand (C.O.D.) is a measure of the capacity of water to consume oxygen during the decomposition of organic matter and the oxidation of inorganic chemicals such as ammonia and nitrite. C.O.D. measurements are commonly made on samples of wastewater or natural waters contaminated by domestic or industrial wastes. Chemical oxygen demand is measured as a standardized laboratory assay in which a closed water sample is incubated with a strong chemical oxidant under specific conditions of temperature and for a particular period of time. A commonly used oxidant in C.O.D. assays is potassium dichromate (K2Cr2O7) which is used in combination with boiling sulfuric acid (H2SO4). As this chemical oxidant is not specific to oxygen-consuming chemicals that are organic or inorganic, both of these sources of oxygen demand are measured in a C.O.D. assay.
Chemical oxygen demand is related to biochemical oxygen demand (B.O.D.), another standard test for assaying the oxygen-demanding strength of wastewaters. However, biochemical oxygen demand only measures the amount of oxygen consumed by microbial oxidation and is most relevant to waters rich in organic matter. It is important to understand that C.O.D. and B.O.D. do not necessarily measure the same types of oxygen consumption. For example, C.O.D. does not measure the oxygen-consuming potential associated with certain dissolved organic compounds such as acetate. However, acetate can be metabolized by microorganisms and would therefore be detected in an assay of B.O.D. In contrast, the oxygen-consuming potential of cellulose is not measured during a short-term B.O.D. assay, but it is measured during a C.O.D. test.
Difference between BOD and COD:
|1. BOD is the amount of oxygen consumed by bacteria while decomposing organic matter under aerobic conditions.||1. COD is the amount of oxygen required for the oxidation of total organic matter in water.|
|2. Value is lower than COD value.||2. Value is always greater than BOD value.|
Eutrophication is a kind of response of the ecosystem to the addition of artificial or natural nutrients, mainly phosphates through the use of detergents, fertilizers, or sewage to an aquatic ecosystem. As an example algal bloom or rapid increase of phytoplankton population in a waterbody as a response to increased level of nutrients can be seen.
Formation of Eutrophication:
It arises from the excessive supply of nutrients which includes the massive growth of phytoplanktons or algae. When such organisms die, they consume oxygen in the body of water, thereby creating the state of hypoxia. The presence of phosphorus induces massive plant growth and decay, favouring simple algae and plankton t over other complicated plant species. This element is a necessary nutrient for plants to live. The source of this excessive phosphate is detergents by the industrial as well as domestic runoff and use of fertilizers. This industrial, domestic, and agricultural part has emerged as the dominant contributors to eutrophication. Sodium triphosphate is a major component of many detergents and a major contributor to eutrophication.
Occurence of Eutrophication
1. In Lakes and Rivers:
In lakes and rivers enhanced growth of aquatic vegetation (like phytoplankton, and algae) disrupts the normal functioning of the ecosystem, causing a variety of problems such as lack of oxygen needed for fishes to survive. Due to eutrophication, the water becomes turbid, filled with the coloured shade of green, yellow, brown, or red. Eutrophication also decreases the value of rivers, lakes, and other aesthetic enjoyment. Due to eutrophication health problems can occur where eutrophic conditions interfere with drinking water treatment.
2. In Nature:
Naturally, eutrophication is commonly caused by the activities of humans in lakes. Current research states that climate change, geological abnormalities, and other external influences are critical in regulating the natural productivity of lakes.
3. In Ocean Waters:
In the coastal areas, eutrophication is a major issue. In contrast to freshwater systems, nitrogen is more commonly the key limiting nutrient of marine waters; thus, nitrogen levels have greater importance to understanding eutrophication problems in salt water. Estuaries tend to be naturally eutrophic because land-derived nutrients are concentrated where run-off enters a confined channel. Upwelling in coastal systems also promotes increased productivity by conveying deep, nutrient-rich waters to the surface, where the nutrients can be assimilated by algae.
4. In Terrestrial Ecosystems:
The terrestrial ecosystems are affected by the adverse impacts of eutrophication. Due to soil eutrophication, the majority of terrestrial plant species become endangered. Due to low nutrient content and slowly growing plant species, the number of meadows, forests, etc decreases.
Effects of Eutrophication:
- Due to eutrophication, the biomass of phytoplankton become increased.
- Production of toxic phytoplankton species.
- The blooms of gelatinous zooplankton become increased.
- Increased biomass of benthic and epiphytic algal species.
- Due to decreased water transparency, and dissolved oxygen depletion, there is a loss of desirable fish species and also a reduction in the number of harvestable fishes.
- Eutrophication also decreases in perceived aesthetic value of the water body.
- Due to eutrophication, biodiversity is hampered, and ecological balance is lost. 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 aerobically 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.
- The extreme anaerobic conditions are favorable for the rapid growth of bacteria such as Clostridium botulinum which produces toxins deadly to birds and mammals. Zones where this occurs are known as dead zones.
According to Hutchinson (1969), eutrophication is a normal process that literally means “well-nourished or enriched”. However premature enrichment occurs due to the addition of domestic sewage, which contains phosphate, nitrates, and other organic wastes. The waterbodies become highly productive or eutrophic, and such a phenomenon is called Eutrophication. With the addition of nutrients, the luxuriant growth of algae in these waterbodies enhances and starts forming algal blooms. The algal blooms compete with other aquatic plants for light, for photosynthesis. Thus oxygen level or D.O. is depleted. Moreover, these blooms also release some types of toxic substances. Both oxygen depletion and toxic chemicals kill zooplanktons, fishes, and other aquatic organisms, and thus waterbody is turned into a stinking drain.
Several ponds, rivers, lakes canals, etc. are seriously polluted by industrial effluents of different industries, such as fertilizer factories, oil refineries, petrochemicals, pulp, paper, textile and sugar mills, tanneries, distilleries, coal washeries, synthetic material plants for rubbers, fibers, drugs, plastics, etc. Industrial waste contains metals, acids, alkalis, phenols, cyanide compounds, many inorganic ions, detergents, petroleum, and many different types of toxicants which may cause the death of aquatic organisms as well as terrestrial organisms indirectly through the food chain. Heavy metal pollution is posing a great problem globally. Toxicity of heavy metals can cause serious health hazards. Some metal pollutants and their effects are given below:
It is an extremely harmful metal pollutant. It is discharged in the form of water-soluble dimethyl mercury. It is persistent in nature and undergoes biomagnification. Therefore, the tertiary consumers including humans are the worst sufferers. It causes Minamata disease, named so for it was first reported in 1952 due to eating of fish captured from mercury-contaminated Minamata Bay of Japan. It can also cause impairing of senses, numbness of lips, tongue, and limbs, deafness, diarrhea, blurring of vision, meningitis, and even death. In Japan, illness and even death occurred in the 1950s among fishermen, who consumed fish, crabs, and shellfish contaminated with methylmercury (CH3Hg) from Japanese paper and pulp industries. This mercury poisoning causes Minamata disease.
It can cause fever, uremia, hypertension, and coma.
Mainly emitted from the burning of leaded petrol, it interferes in the synthesis of haeme of haemoglobin. It also inhibits oxygen and glucose metabolism. The harmful effects of lead can be vomiting, loss of appetite, and damage to the liver, kidneys, and even the brain.
It can cause damage to bones, cause diarrhea, and even paralysis.
Causes ulcers in gastrointestinal cavities, nephritis, and damage to the nervous system.
It is another very toxic metal, causing anaemia, damage to the liver, testicular atrophy, and cancer of the liver and lungs. It can cause itai-itai, (reported from Toyoma city of Japan in 1947) which is a serious, painful skeletal deformity.
Industrial pollution not only affects humans but can cause harm to all forms of living organisms. Therefore, it is the duty of industries to remove the polluting agents from their discharges, and if it fails to do that, the Pollution Control Board is authorized to close down the concerned industry.
Some Industry and Industrial Wastes are:
|Chemical Industry||Inorganic acid, Phenol, Ammonia, organic acid|
|Oil Refineries||Hydrocarbon, Phenol, Oil, Grease|
|Battery Production||Lead, Acid|
|Nuclear Power Plant||Fluoride|
|Leather Industry||Tannic Acid, Phenol, Cromium, Sulphide|
|Engineering Industry||Oil, Grease|
|Paint Industry||Phenol, Lead|
|Fertilizer Production||Phosphate, Chloride|
|Gas, Coke Production||NH3, Cyanide, Phenol, Sulphide|
|Alcohol Industry||Inorganic Acid|
Fertilizers, Pesticides and Herbicides of Agriculture
Agrochemicals, such as inorganic fertilizers, pesticides, and herbicides create heavy water and soil pollution. These agrochemicals are added to the soil to increase crop yield, and are washed down into water reservoirs and water sources during rains. Fertilizers promote eutrophication whereas, toxic chemicals like pesticides, herbicides, and weedicides create health hazards for aquatic organisms, birds, and mammals including man.
Biomagnification or Bioamplification
Gradual increase in the concentration of harmful non-biodegradable substances at successive trophic levels in the food chain is called biomagnification or bioamplification or bioaccumulation. Biological magnification is the increasing concentration of a substance, such as a toxic chemical in the tissues of organisms at successively higher levels in a food chain. Many non-biodegradable pesticides (such as DDT, aldrin, dieldrin, PCB, BHC, etc.), heavy metals (like lead, mercury, etc.), and radioactive substances (strontium, uranium, etc.) have a long lifetime in the environment. They get incorporated into the food chain and ultimately get deposited in the fatty tissues of organisms. These compounds are very much soluble in fats.
Aquatic microorganisms absorb them in fat and oil, where they accumulate to form concentrations many times greater than in water. Zooplankton that feed on countless contaminated phytoplankton cells, the concentration of these toxic substances still further rises in their tissues. Fishes feeding on zooplanktons accumulate further, and concentrations rise in their body. Birds feeding on fish concentrate the compounds further manifold. The increased accumulation of toxic substances in the food pyramid is called biological magnification or biomagnification.
It was observed in an island in the USA, that spraying DDT regularly for a few years resulted in a drastic decline in the population of fish-eating birds. The concentrations increased shockingly. It was 0.003 ppb in water, 30 ppb or 0.003 ppm in phytoplanktons, 0.04 ppm in zooplanktons, 0.5 ppm in small fishes, 2.00 ppm in bigger fishes feeding on smaller ones, and finally reached upto 25 ppm in seagulls which fed on fishes. Harmful effects of such pesticides include liver thinning of eggshells in birds, cirrhosis, and cerebral hemorrhage in men. The extinction of the Bald Eagle is an effect of the biomagnification of pesticides.
Biological magnification often refers to the process whereby certain substances such as pesticides or heavy metals move up the food chain, work their way into rivers or lakes, and are eaten by aquatic organisms such as fish, which in turn are eaten by large birds, animals, or humans. The substances become concentrated in tissues or internal organs as they move up the chain. Bioaccumulants are substances that increase in concentration in living organisms as they take in contaminated air, water, or food because the substances are very slowly metabolized or excreted.
The line drawing of biological magnification in the food chain is
According to this equation, the BCF of DDT is 54,000, the BCF of PCB is 1,00,000, and the BCF of heptaclore is 15,700. The major focus of biomagnification, however, is the accumulation of certain non-essential chemicals, especially certain chlorinated hydrocarbons that are persistent in the environment. These compounds are insoluble in water, but highly soluble in fats. Because almost all fats within ecosystems occur in the living bodies of organisms, chlorinated hydrocarbons such as 4, 4’-(2, 2, 2-trichloroethane-1, 1-diyl)-bis (chlorobenzene) (DDT) and polychlorinated biphenyls (PCBs) tend to selectively accumulate in organisms. This can lead to ecotoxicological problems, especially for top predators at the summit of ecological food webs, who ingest the toxic prey.
Biomagnification and Food-Web Accumulation:
Organisms are exposed to a myriad of chemicals in their environment. Some of these chemicals occur in trace concentrations in the environment, and yet they may be selectively accumulated by organisms to much larger concentrations that can cause toxicity. This tendency represents biomagnification.
Some of the biomagnified chemicals are elements such as selenium, mercury, nickel, or organic derivatives such as methyl mercury. Others are in the class of chemicals known as chlorinated hydrocarbons (or organo-chlorines). These are extremely insoluble in water, but are freely soluble in organic solvents, including animal fats and plant oils (these are collectively known as lipids). Many of the chlorinated hydrocarbons are also very persistent in the environment because they are not easily broken down to simpler chemicals through the metabolism of microorganisms, or by ultraviolet radiation or other inorganic processes. Common examples of bioaccumulating chlorinated hydrocarbons are the insecticides DDT and dieldrin, and a class of industrial chemicals abbreviated as PCBs. Food-web accumulation is a special case of biomagnification, in which certain chemicals occur in their largest ecological concentration in predators at the top of the food web.
Biomagnification of Inorganic Chemicals:
All of the naturally occurring elements occur in the environment. Some occur at very low concentrations, while others are more abundant. This contamination is always detectable, as long as the analytical chemistry method of detection is sensitive enough to detect even trace amounts of the target chemical. About 25 of the elements are required by plants and/or animals, including the micronutrients copper, iron, molybdenum, zinc, and rarely aluminum, nickel, and selenium. However, under certain ecological conditions, these micronutrients can biomagnify to very large concentrations and even cause toxicity to organisms. One example is serpentine soil and the vegetation that grows in it. Serpentine minerals contain relatively large concentrations of nickel, cobalt, chromium, and iron. Soils derived from this mineral can be toxic to plants. However, some plants grown on serpentine soils are physiologically tolerant of these metals and can bioaccumulate them to very large concentrations.
Biomagnification of Chlorinated Hydrocarbons:
Chlorinated hydrocarbons such as some insecticides (examples include DDT, dieldrin, and methoxychlor), PCBs and dioxin have a low solubility in water. In other words, they tend not to dissolve in water to form a solution. As a result, these chemicals cannot be diluted into a larger volume of water. However, chlorinated hydrocarbons are highly soluble in lipids. Because most lipids within ecosystems occur in biological tissues, the chlorinated hydrocarbons have a strong affinity for living organisms, and they tend to biomagnify by many orders of magnitude from vanishingly small aqueous concentrations. Furthermore, because chlorinated hydrocarbons are persistent in the environment, they accumulate progressively as organisms grow older, and they accumulate in especially large concentrations in top predators, as described previously. In some cases, older individuals of top-predator animals such as raptorial birds and fish-eating marine mammals have been found to have thousands of ppm of DDT and PCBs in their fatty tissues. The toxicity caused by these animals’ accumulated exposures to DDT, PCBs, and other chlorinated hydrocarbons is a well-recognized environmental problem.
It is caused by the addition of hot effluent in water bodies. Warm water contains less oxygen (14 ppm at 0°C, 1 ppm at 20°C). Therefore, there is a decrease in the rate of decomposition of organic matter. Green algae are replaced by less desirable blue-green algae. Many animals fail to multiply, some eggs fail to hatch while salmon does not spawn at higher temperatures.
Ecological Effects of Hot Water
A common cause of thermal pollution is the use of water as a coolant, especially in power plants. Warm water typically decreases the level of D.O. (Dissolved Oxygen) in the water, which harms aquatic animals. The temperature changes of even 1-2°C can cause significant changes in metabolism and other adverse cellular and biological effects (like mortality, reproduction, BMR). Warm water promotes plant growth rates, resulting in a shorter life span and species overpopulation. It can cause an algal bloom. Warm water may also increase the metabolic rate of aquatic animals, meaning that these organisms will consume more food in a shorter time than they would if their environment were not changed. This leads to competition for fewer sources which disturbs food chains.
Ecological Effects of Cold Water
Cold water released from reservoirs can dramatically change the fish and macroinvertebrate fauna of rivers and reduce the productivity of water bodies. In Australia, due to cold water thermal pollution, native fish species have been eliminated and microvertebrate fauna was drastically altered and impoverished.
Sources and Methods of Thermal Pollution:
|Major Sources||Methods of Pollution|
|Power Plant Creating Electricity from Fossil Fuel||Electricity is generated by heat/thermal energy stored in the fossil fuels and the stored energy creates a heat flow that runs the turbine. Turbines in this process produce more heat energy.|
|Water as Cooling Agent||Heat Exchangers: Exchange heat with other streams in the factory because these steps need heat while other steps generate heat.
Evaporate Cooling: Stream is used in many heating processes. Cooling by condensation generates a great amount of waste heat from the factory. Cooling comes from evaporation because ambient air is not saturated with water. Air discharged from cooling towers is a direct contribution to global warming.
|Deforestation of Shoreline||It further contributed to the problem in two ways:
|Soil Erosion||Sedimentation at lakes and streams makes water muddy. Muddy water or turbid water containing microbes and dissolved minerals increases the light absorption from the atmosphere, resulting in a rise in the temperature of water bodies.|
Wrong agricultural and forestry practices cause soil erosion or removal of top fertile soil during rain or flood and this makes the water bodies muddy. This load of particulate matter cuts down primary productivity by dredging the depth of light penetration. Animal population correspondingly gets depleted. The waterways get choked due to the deposition of mud and silt.
Coastal industries dump industrial wastes straight into marine ecosystems (i.e., seas, oceans, and estuaries). Sewage of coastal cities and distant places also reaches the sea. Oil spills, grease, petroleum products, garbage, sewage, and detergents from ships also pollute marine ecosystems.
Some Water Borne Diseases Caused by Polluted Water:
|1. Viral Diseases||Hepatitis A||This virus attacks mainly the liver, bile pigments increase, and skin & urine become yellow, creating jaundice.|
|Hepatitis B||It causes serious damage to the liver. Sometimes it turns to cancer of the liver.|
|Ruta Virus||It creates a serious type of diarrhea.|
|2. Bacterial Diseases||Cholera (Vibrio Cholerae)||It causes vomiting and the passing of liquid stool.|
|Typhoid (Salmonella typhi)||It causes bloodstained stool, ulceration in the gut, etc.|
|Paratyphoid (Salmonella paratyphi)||Symptoms: Fever & diarrhea.|
|Bacillary dysentery (Shigella sp.)||Abdominal pain, mucous, and bloodstained stool are the symptoms.|
|3. Protozoan Diseases||Dysentery (Entamoeba histolytica)||Dysentery and abdominal pain, mucous, and bloodstained stool are the symptoms.|
|Giardiasis (Giardia intestinalis)||Loss of appetite, abdominal pain, loose motion, etc.|
|4. Worm Diseases||Hook Worm (Ancylostoma duodenale)||Creates intestinal diseases, abdominal pain, anal irritation, loss of appetite, etc.|
|Round worm (Ascaris lumbricoides)||Creates intestinal diseases, abdominal pain, acute anaemia, loss of appetite, etc.|
|Pinworm (Enterobius Vermicularis)||Creates intestinal diseases, abdominal pain, anal irritation, etc.|
Control of Water Pollution
The various methods for the control of water pollution are discussed below:
1. Control of Agrochemical Pollution
Water pollution due to agrochemicals (e.g., fertilizers, pesticides, herbicides, etc.) can be reduced by using organic fertilizers instead of inorganic fertilizers, using very specific and less stable chemicals in the manufacture of insecticides or herbicides, and biological control. If such control is applied simultaneously, desired results can be obtained.
2. Control of Industrial and Sewage Pollution
Several methods and engineering techniques are used by which bacteria, microbes, organic debris, and other pollutants are removed from the polluted water. These methods involve the establishment of septic tanks, oxidation tanks, filter beds, water treatment plants, municipal sewage treatment plants, etc. In India, NEERI (National Environmental Engineering Research Institute) has proposed two very simple methods for controlling water pollution.
- Establishment of a Large Oxidation Tank: Domestic or industrial wastes should be stored in a large but shallow pond for several days. Due to the sunlight and presence of organic wastes, there will be mass-scale growth of those bacteria which will digest the harmful waste matter. Thus, this water can be reclaimed by proper sewage treatment plants and/or by a simple purification process the same water can be reused in factories and even in irrigation. The latter will be ideal because this water is rich in nitrogen, phosphorus, and potash.
- Control by Water Hyacinth: Water hyacinth is popularly known as Kaloli and Jalkhumbhi, which can purify water polluted by biological and chemical wastes. It can also filter out heavy metals like cadmium, mercury, lead, and nickel as well as other toxic substances found in the industrial wastewater.
Sewage pollution can also be prevented by setting up Sewage Treatment Plants. They perform the following treatments:
- Primary Treatment: It is the first step of treatment, which targets removing most of the undissolved wastes. It involved churning, screening, sedimentation, and floatation.
- Secondary Treatment: It involves the removal of organic matter or sludge by microbial decomposition. It is done by employing the trickling filter method by passing through a bed of gravel or activated sludge method by aeration followed by oxidation of sludge in huge oxidation tanks.
- Tertiary Treatment: After the removal of suspended matter and sludge, the partially cleared water is treated to remove pathogenic microorganisms. It can be done by chlorination, using chlorine or perchlorate salts, or by irradiating with UV. Salts dissolved in the water are precipitated by alum, ferric chloride, and lime. These can precipitate 90% of suspended solids and phosphates. Such water can be used in fields as manure water. Further clearing of dissolved organic matter occurs by activated carbon. It is followed by the removal of nitrates and special compounds like DDT and pesticides. Finally, the water is fit to be discharged into rivers and other water sources.
3. Control of Groundwater Pollution
To control underground water pollution, surface water should be kept pollution-free. By implementing several methods, this underground water pollution can be controlled.
4. Control of Thermal Pollution
Thermal pollution can be reduced by employing various techniques through cooling, cooling ponds, evaporative or wet cooling towers, and dry cooling towers. The purpose is that the water in the rivers and streams should not get hot.
5. Control of Water Pollution Through Law
Suitable strict legislation should be enacted to make it obligatory for industries to treat wastewater before being discharged into rivers or seas. [The Water Prevention and Control of Pollution Act, 1974]
Intermittent incidents of arsenic contamination in groundwater and the consequent ill health of people from arsenic poisoning have been widely reported. There are many clinical manifestations but the most commonly observed symptoms of chronic arsenic poisoning are keratosis, leucomelanosis, melanosis, and hyperkeratosis. In severe cases, gangrene in the limbs and malignant neoplasm are found.
Arsenic poisoning kills by allosteric inhibition of essential metabolic enzymes, leading to death from multisystem organ failure. In West Bengal of India and in Bangladesh, according to research, the incidents of arsenic contamination of groundwater have been reported as the biggest arsenic calamity in the world. Several districts and millions of people were affected by drinking arsenic-contaminated water and many of them had been suffering from arsenicosis disease.
Symptoms of Arsenic Poisoning:
- In Plants: Small concentrations of arsenic are known to stimulate plant growth, larger concentrations present in irrigation water may cause a reduction in the overall yield of crop plants.
- In Humans: Symptoms include violent stomach pains in the region of the bowels, retching, vomiting, a sense of dryness and tightness in the throat, thirst, hoarseness, and difficulty in speech. Symptoms of arsenic poisoning start with mild headaches and can progress to lightheadedness. Darkening of skin in the body or in the palm is the earliest symptom. Spotted melanosis is usually seen on the chest, back, and limbs. The combination of pigmentation and nodular rough skin is due to arsenic toxicity. It causes black sores on the foot called the black foot disease.
How to Combat the Situation:
In most villages of West Bengal, 40-50% of tubewells contain arsenic below 0.05 mg/l (which is safe). Safe tubewells are immediate to be marked green, while unsafe is to be marked red. Villagers are to be informed and safe tubewells to be tested every 3 months. An awareness campaign with videos/photographs should be launched. The risk of young children and women exposed to arsenic contamination should be highlighted. Methods to reduce arsenic levels in water sources should be implicated. Solar oxidation and removal of arsenic (SORAS) is a simple method that uses irradiation of water with sunlight to reduce arsenic levels in drinking water. The SORAS is based on photochemical oxidation of As (III) followed by precipitation or filtration of As (V). Proper watershed management is necessary to utilize these water resources.
Quality of Drinking Water:
According to United States Public Health (USPH), the quality of drinking water must be like the table.
|Parameter||ppm according to the upper level|
|Dissolved O2||4.00 – 6.00|