Compilation of answers we got on the examples of water pollutants.
1. Examples of Water Pollutants:
Pollutants of streams and lakes come from many sources:
1. Nutrients and Eutrophication:
Excessive nutrients, such as, nitrates and phosphates commonly originate from waste materials from animal feedlots and industrial effluents. These nutrients cause excessive growth of algae in water bodies. These algae are generally not utilised by zooplanktons, rather they compete with other aquatic plants for light for photosynthesis, which leads to depletion of dissolved oxygen.
Moreover these algae also release some toxic chemicals which is harmful for aquatic organisms and further the action of bacteria decomposing the algae finally results in killing of fish and other aquatic organisms due to lack of oxygen. This whole series of events is called eutrophication.
Shallow lakes are most vulnerable to eutrophication. Deep lakes that lack or are poor in these plant nutrients are called oligotrophic (poorly nourished).
Thus in a poorly oxygenated water with higher CO2 levels, the water body is converted into a stinking drain.
2. Infectious Agents:
Several disease causing organisms like bacteria, protozoans, parasites and viruses pollute the water.
The major sources of infectious agents include:
(i) Untreated or improperly treated sewage,
(ii) Tanneries releasing untreated animal wastes,
(iii) Animal wastes, and
(iv) Some wildlife species transmit waterborne disease.
Due to accumulation of sewage and other wastes that enter the water bodies due to uncontrolled dumping of wastes of rural areas, towns and cities, the water bodies are not able to recycle them and their self-regulatory capability is lost. These water bodies no longer remain fit for drinking or for any other domestic use.
Water polluted with sewage is a major source of illness and death in developing countries. Each year, diarrhea kills more than 4 million people, mostly children. Other diseases spread by human waste in water include typhoid which afflicts 70 million people in developing countries; amoebiasis, 500 million; hepatitis A (an unknown number of people affected but 14,000 deaths annually); giardiasis, 250 million; gastroenteritis, 1000 million; and cholera, 300,000.
3. Organic Compounds:
Many toxic synthetic organic compounds ultimately find their way into the water. These include polychlorinated biphenyls (PCBs) (widely used in plastics, electrical insulation and carbonless printing paper), phenols (produced from rotting vegetation and sewage treatment plants, iron and steel factories, oil refineries, and coal and wood distillation facilities) and chlorinated hydrocarbons like DDT.
The concern for these pollutants has been mainly due to their being:
(a) Non-bio degradable or slowly degradable properties,
(b) Bio magnification,
(c) Carcinogenic nature,
(d) Toxicity to fish and other organisms, and
(e) Offensive smell or taste to water and fish.
4. Inorganic Compounds:
Toxic inorganic substances include a wide range of chemicals like acids, salts and metals. Acids may enter water from acid precipitation, various industrial sources and underground coal mines. Chlorine is used as a disinfectant in drinking water, and sewage treatment plants.
Nitrates come from fertilised crops, septic tanks and sewage treatment plant. Metals are produced in mining, air pollution fall out, industrial effluents, sewage effluents, and many natural resources.
Sediment is a by-product of agriculture, mining, silviculture, and construction of roads and buildings. Agricultural practices increase erosion rates 4-8 times whereas poor construction may increase the rate of erosion 10-200 times. Sediment is limiting to fish and decreases light penetration and thus killing vegetation.
Chemical fertilizers and pesticides, used in the agricultural practice, get washed away from the fields and enter the water bodies. In the form of nitrites and nitrates they not only make the water unfit for drinking but also cause diseases. The mostly known disease caused is methaemoglobinaemia.
In the form of pesticides, a wide range of chemicals are used, which are hazardous and toxic. They are harmful because they either do not degrade or degrade very slowly in nature. Thus, they form a chronic accumulation of pesticides and play a role in kidney malfunctioning, excess of amino acids in blood and urine, electroencephalogram abnormalities of brain tissues, and blood abnormalities.
Two chief pollutants are in the form of thermal discharge and nuclear wastes. Other industrial pollutants are various chemicals, inorganic and organic pollutants all of which can be called as industrial effluents.
Varieties of inorganic and organic pollutants are present in industrial effluents that come out from breweries, tanneries, dying textiles, paper and pulp mills. These also include oils, greases, plastics, metallic wastes, suspended solids, phenols, toxins, acids, salts, dyes, cyanides, DDT, etc. All these pollutants, which are not readily susceptible to degradation, cause serious pollution problems.
2. Examples of Water Pollutants:
The various types of water pollutants can be broadly classified into the following four major categories:
(i) Organic Pollutants:
The organic pollutants may be further categorised as follows:
(a) Oxygen-Demanding Wastes:
These include domestic and animal sewage, bio-degradable organic compounds and industrial wastes from food-processing plants, meat-packing plants, slaughter-houses, paper and pulp mills, tanneries etc., as well as agricultural run-off.
(b) Disease-Causing Wastes:
These include pathogenic micro-organisms which may enter the along with sewage and other wastes and may cause tremendous damage to public health. These microbes, comprising mainly of viruses and bacteria, can cause dangerous water-borne diseases such as cholera, typhoid, dysentery, polio and infectious hepatitis in humans. Hence, disinfection is the primary step in water pollution control.
(c) Synthetic Organic Compounds:
These are the man-made materials such as synthetic pesticides, synthetic detergents (syndets), food additives, pharmaceuticals, insecticides, paints, synthetic fibres, elastomers, solvents, plasticisers, plastics and other industrial chemicals. These chemicals may enter the hydrosphere either by spillage during transport and use or by intentional or accidental release of wastes from their manufacturing establishments. Most of these chemicals are potentially toxic to plants, animals and humans.
(d) Sewage and Agricultural Run-Off:
Sewage and run-off from agricultural lands supply plant nutrients, which may stimulate the growth of algae and other aquatic weeds in the receiving water body. This unwieldy plant-growth results in the degradation of the value of the water body, intended for recreational and other uses.
Oil pollution may take place because of oil spills from cargo oil tankers on the seas, losses during off-shore exploration and production of oil, accidental fires in ships and oil tankers, accidental or intentional oil slicks.
The oil pollution leads to unslightly and hazardous conditions which are deleterious to marine-life and sea-food.
(ii) Inorganic Pollutants:
Inorganic pollutants comprise of mineral acids, inorganic salts, finely divided metals or metal compounds, trace elements, cyanides, sulphates, nitrates, organometallic compounds and complexes of metals with organics present in natural waters.
(iii) Suspended Solids and Sediments:
Sediments are mostly contributed by soil erosion by natural processes, agricultural development, strip mining and construction activities. Suspended solids in water mainly comprise of silt, sand and minerals eroded from the land. Soil erosion by water, wind and other natural forces are very significant for tropical countries like India.
(iv) Radio-Active Materials:
The radio-active water pollutants may originate from:
(a) Mining and processing of ores, e.g., Uranium tailings.
(b) Increasing use of radio-active isotopes in research, agricultural, industrial and medical (diagnostic as well as therapeutic) applications.
(c) Radio-active materials from nuclear power plants and nuclear reactors.
(d) Radio-active materials from testing and use of nuclear weaponry.
3. Examples of Water Pollutants:
Trace elements play a vital role in the health of human as well as other life on the planet. Trace elements enter the human body by ingestion and inhalation. Food and water consumed are the main entries into the body and they supply other major nutrients besides minerals.
Intake of food and water balances and maintain nutritional levels. Analysis made on food bought and eaten shows the difference in contribution to these elements. The difference between these two is due to losses (or occasionally gains) in trace elements in food during cooking.
On an average human beings take about two to two and a half litres of water every day through food or direct drinking. Even if the elements are in low concentrations, the total amounts ingested will be appreciable.
The minerals in water are in a free, ionic, easily absorbable form. The minerals required for the body are never as per the requirements, either they are in excess or less.
There is scientific evidence to prove that presence of certain inorganic elements in drinking water results in health or disease.
Health associated problems of some substances are presented here:
This is a mood stabilizer and is commonly used in treatment of behavioral disorders. People drinking water with sufficient quantity of lithium are seen to be less aggressive and less competitive. Studies made at Texas (up to 100 mg/litre) showed lower cardiovascular mortality rates and less mental disorders and less homicides and suicides.
Studies at Arizona showed low prevalence of coronary heart disease and of gastro-duodenal ulcers. Lithium occurs normally at 0.001 — 0.3 µg/litre in natural waters. It is potentially toxic to plants. In natural waters such toxic concentrations to irrigation are not normally encountered.
Chromium is used in plating of metals, photography and other industrial processes. Its usage in tanning industry is causing highest concern for its removal.
This is an essential element, which acts as a cofactor with insulin to maintain normal glucose tolerance. Studies at Jordan showed that lack of chromium showed increased frequency of juvenile diabetes. This is based on the studies made on the villagers with two different doses of 0.5 mg/litre and 1.6 mg/litre.
When chromium chloride was given to the children in the low-chromium village, the juvenile diabetes syndrome quickly disappeared. Chromium has been found to be protective against atherosclerotic lesions in experimental animals. Chromium may give protection against coronary heart disease as per the studies made in Finland at 2.6 mg/litre. It also showed high rate of coronary heart disease rate on populations that consumed water with 8.6 mg/litre.
A higher dose of chromium has harmful effects both by inhalation and ingestion. The form in which it is more dangerous is not known. Trivalent chromium is believed to be less harmful than the hexavalent. Chromium has carcinogenic effect on nasal track, skin and other sensitive organs and glands. Trivalent chromium is not readily absorbed from the digestive system, but combines with proteins in the superficial layers of skin to form stable complexes.
The hazards in industries and their discharges were seem to be more harmful than where trivalent are involved. Besides the effects on respiratory and skin, it penetrates deeply into soft tissues and forms ulcers. Liver, kidney and circulatory disorders are also common. Chromium has both short- and long-term effects. EPA fixed the Maximum Contaminant Level (MCL) at 0.10mg/ litre.
Goiter is associated with the deficiency of iodine in drinking water. Studies in Greece showed that goiter is absent where the concentrations of iodine in drinking water are 25 mg/litre and 10 mg/litre in areas with endemic goiter. Drinking water may contribute 20% of the daily requirements of iodine. In Finland, heart diseases appeared where the concentration was less than 3 mg/litre.
Accidental ingestion of iodine of 2 to 3 mg may be fatal to human being. Iodine and its compounds are more fatal than bromine and chlorine. Chronic absorption of iodine causes “iodism”, a disease characterised by tremor, weight loss, diarrhea, conjunctivitis, bronchitis, etc. Iodine is concentrated in the thyroid gland and is often used.
This is an essential element for animals as well as human beings. There is no difficulty in meeting the daily requirements. Findings in UK and Finland showed that death rates due to coronary heart disease were less in communities which used water containing 1.7 mg/litre of silicon as against higher rates which used 7.6 mg/l, 4.8 mg/l and 7.7 mg/litre.
The chemical environment in which a human being is living now-a-days has become extremely complex. About 4 million chemicals have been isolated from natural products out of which 60,000 are in frequent use. About 1500 ingredients are used in pesticides, 4000 in drugs and 2000 in excipients. More than 5000 are used as additives in food industry. Wastes from manufacture and disposals after use in case of consumer goods such as cleaning agents, pesticides, cosmetics and drugs reach water bodies besides solid waste dumps.
Contamination of water with these wastes create myriad of problems. Chemicals like organo-metallic mercury, organo-chlorine cause intoxication. Animals too get affected by many of these chemicals. Certain chemicals cause chronic diseases while some lead to death and/or deformity. Some are carcinogens or teratogens and cause lesser disease resistance.
Human exposure to them can occur through skin contact ingestion, air, water or food. Methyl mercury reaches high concentrations in fish and enter human body. Certain chemicals have irreversible affects and bring about structural and physiological changes in human and animal life due to continued usage or exposure.
The effect of many chemicals depends on the type of exposure (i.e., inhalation, ingestion and skin contact) and their physical and chemical properties. Further it also depends on the frequency, duration, metabolism of the chemical in the organism, absorption, distribution, bio-transformation, excretion and capacity to resist the toxicity. Fish-kills at many places of the world are attributed to agricultural and industrial wastes.
Depending on the toxicity and dangers associated, certain limits of concentration of these contaminants are permitted in drinking water. Further, the maximum contaminant levels for certain contaminants were fixed taking into consideration the available treatment techniques. However, they are classified into categories where no toxicity is allowed and for others certain allowable limits are permitted.
Traces of arsenic are common in natural water as arsenate from hot springs. Industrial and mining activities also contribute to surface waters. Certain pesticides used in agricultural operations also contribute to arsenic contamination. Arsenic contamination is also found from the discharges of semiconductor manufacture, petroleum refining, wood preservatives etc.
Arsenic compounds are very toxic even at 1.0 mg/l concentration. Excretion is very slow and the cumulative effect is dangerous. Death of cattle is reported in New Zealand. There is evidence that arsenic is carcinogenic. There was evidence that employees of an arsenial powder manufacturing plant were subjected to skin and lung cancer. The permissible limit is fixed as low as 0.05 ppm.
The long-term or chronic poisoning by arsenic, ingestion is partly different from those by inhalation. Vague abdominal symptoms, diarrhea or constipation are generally associated with arsenic poisoning while Anemia and leucocytopenia are reported to occur with chronic poisoning.
Barium is widely used in paints, paper, pesticides, caustic soda manufacture. It is also used in purification of beet sugar, animal and vegetable oils, in electric industry and also found from the discharg