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:
1. Trace Elements:
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.
2. Chemical Impurities and Water:
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 discharges of drilling wastes, metal refineries etc. This is found in ground and surface waters in small amounts and also in waters associated with oil fields. This is a muscle stimulant.
There is evidence of toxicity by ingested soluble barium salts and it causes irreversible changes in the body. It accumulates in bones, muscles, kidney etc. Tolerance limit is not well established. Considering the serious toxic effects of barium on heart, blood vessels and nerves the maximum limit is fixed at 2.0 ppm by EPA.
Cadmium is used in chemicals, textiles, electronics, auto and aircraft industries. Mines, smelters and electroplating can also pollute with cadmium. It is also seen during corrosion of galvanised pipes, metal refineries, waste battery and point runoffs.
Cadmium is likely to be present in natural waters in minute traces. This is a powerful emetic and gastrointestinal irritant and causes chronic poisoning. Cadmium in insoluble form is food contaminant and incidents are reported with 530 ppm. Coffee and lemonade that held in cadmium plated containers for periods of 1½ to 14 hours produced several large. poisoning outbreaks among military personnel. Groundwater contamination was also reported due to percolation near waste dumps containing cadmium.
Cadmium accumulates in liver, kidney and in soft tissues. The tolerance to human is fixed at 0.005 ppm. By ingestion 2 to 6% of cadmium is absorbed by gastrointestinal track. Kidney and liver retain highest concentrations upto 50% of the total cadmium of the body. Ingestion of food contaminated with cadmium at concentrations exceeding 15 mg/l give rise to food poisoning and the symptoms are nausea, vomiting, abdominal pains, diarrhoea.
Cyanide contamination is common in industrial wastes. Gold extraction from ore also discharges cyanide wastes. Dosages beyond 5 to 10 mg/day are toxic to human beings. The level that normally detoxifies these compounds may not be able to do so beyond this dosage. Smaller dosages are lethal to fish and other life. Proper chlorination under neutral or alkaline condition forms cyanogen chloride which is 1/20 toxic than that of hydrogen cyanide.
Cyanide ion of cyanide compounds is rapidly absorbed from all routes of entry into body i.e., by ingestion, respiratory, skin, etc. Cyanide retards the ability of the cells and inhibits enzymes required for the respiration of cells. It prevents the uptake of oxygen by tissues as it readily combines with methaemoglobin leading to death due to asphyxia. EPA fixes maximum contamination level of 0.2 ppm as free cyanide.
V. Flouride (F):
This is an element of vital importance as it has good effects in small doses and bad in larger doses. Doses upto 1 ppm has beneficial effects while excessive amounts have irreversible and serious effects. Fluoride, most commonly occurs as calcium fluoride (CaF2 and calcium fluorapatite [(CaF2)3 Ca3(PO4)2]. Fluoride is absorbed after ingestion by digestive tract and afterwards, it is distributed throughout the body 98% of the total fluoride accumulates in skeletal and dental tissues.
Growing bones absorb more fluoride rapidly. Only 10% of the fluoride is excreted through kidney and faeces. Concentration of fluoride in urine is a good index for total fluoride accumulation in the body. Fluoride in limited quantities (less than 1.5 ppm) prevents dental caries, whereas higher concentrations (more than 2 ppm) may initiate mottling of teeth. It is very essential especially for children for the healthy growth of teeth. The effects of fluoride are tabulated.
Fluoride is also injurious to plant and animal life especially for insectivorous and carnivorous plants. In optional amounts, stimulation in the growth and yield of many plants, in the presence of fluoride has been reported. Excessive fluoride interferes and affects the plant metabolism, Carbon-dioxide assimilation and oxygen uptake by plant tissues. EPA fixes 2.0 ppm as Maximum Contamination Level (MCL).
This is often found in soils especially in arid areas. Discharges from mines and petroleum refineries also contain Selenium. This is an essential trace element in humans and animals. It is toxic in high concentrations.
It is seen that natural surface water contains Selenium upto 2.5 ppm and natural groundwater upto 1,600 ppm. Plants accumulate Selenium and contaminate livestock when consumed. Plants growing in soils affected by Selenium contain Selenium and cause “alkali disease” in the livestock when concentration is 25 ppm.
When the concentration in plants is between 100 to 1000 ppm an acute disease “blind staggers” is caused. Selenium affects liver and kidneys. It has carcinogenic effect on humans.
Hair or fingernail loss, numbness in fingers or toes, circulatory problems is observed due to Selenium contamination. Selenium is used in the manufacture of electronics equipment, production of steel, pigments, glass and ceramics. EPA fixes 0.05 ppm as MCL.
Silver is widely used in electroplating, photography and other chemical uses. Silver is not found in natural waters. Silver has disinfecting effect on water. On excessive dosage it is reported to have shown changes in kidneys, liver and spleen.
Silver nitrate is the most toxic among its compounds. Deposition of silver in body results in argyria and is incurable. Certain vegetables react with silver and enter the body by ingestion. The limit in drinking is fixed at 1.0 ppm by EPA.
Lead enters human body by ingestion and inhalation. Most ingested lead is excreted and 60% of inhaled is exhaled. Lead accumulates in body slowly. Lead poisoning results in stomachache and physical weakness and at final stages leads to the collapse of central nervous system.
Lead accumulation in the human body is quick and is more rapid in growing children. It damages nervous system, bones and kidneys even at low concentrations. The maximum contaminant level is zero while achievable treatment level is 0.015 ppm.
Mercury is used in the production of caustic soda, chlorine, electric lights, batteries, switches, thermometers, barometers, paints, paper, etc. It is also used in nuclear weapons. Mercury enters watercourses by various ways.
Chlor alkali industry is the main contributor to mercury poisoning. The effect of mercury poisoning is numbness, impairment of speech paralysis, deformity, coma and death. Mercury ingested fish is another potential source for mercury poisoning. MCL is 0.002 ppm
Copper enters into water through domestic wastes and also as mineral compounds. Most of the living organisms contain copper in one form or other. Copper is beneficial to human metabolism, and the deficiency results in nutritional anaemia. Copper supplementation in livestock feed in agricultural operations. Excessive doses lead to nausea, vomiting, diarrhea, sweating, coma and death.
Drinking of carbonated water, citrus fruit juices that were in contact with copper vessels, pipes etc., lead to gastrointestinal irritation and are seldom serious. Normal diet of human contains 2-5 mg of copper and is excreted. The retention in the body is always constant and is about 100-150 mg. MCL is 1.0 ppm to 1.3 ppm.
This is an abundant constituent of soil, rock etc., and is normally found in water. Iron is also a common constituent of plant matter and is often washed into streams and lakes from catchment. Iron is undesirable for both domestic and industrial use of water. It imparts brown colour in laundry goods, stains plumbing and imparts tastes in beverages. It forms incrustation in pipes.
The upper limit of removal is fixed depending on the feasibility for its removal. Iron is essential for metabolic activity of mammals and is supplemented through vegetables. Absorption of iron by human body is poor and an adult can retain 2.0 mg/day. Hence, when larger quantities of iron are taken, the excess is excreted through faeces. MCL is fixed at 0.3 ppm.
Manganese is found in natural water and more in waters received from mining and industrial operations. Manganese contaminates everything that it touches producing gray to black strains. Like iron, it forms incrustations in pipes. Like iron, mammals require it as an essential food element. Deficiency interferes with growth, reduction in the formation of bone and blood and their reproduction. Absorption and excretion is similar to iron and the human body can take 10 mg/day. MCL is 0.05 ppm.
Zinc enters into water through fertilizers, galvanized pipes especially from acidic water sources. Zinc is a beneficial element for human metabolism as well as plants. But it normally occurs as traces except in mine baled waters. Zinc salts are gastrointestinal irritants.
Zinc gives milky appearance when contained in 3.0 ppm or more. Though it does no harm, it is not accepted for aesthetic reasons. Zinc protects the body from toxic effects of Cadmium and lead. Very high doses more than 40 ppm may result in stiffness of muscles, loss of appetite etc. MCL fixed is 5.0 ppm.
Nitrogen and its compounds occur in water depending on the level of oxidation but nitrate is its completely oxidised state. These are very important chemicals that have concern over health than other compounds. Sources of nitrates are the domestic effluents and animal discharges from farms, runoff from agricultural lands and lands containing nitrified products and decayed vegetation and animal matter.
Thus presence of nitrogen compound indicates pollution from animal and human source. Infants are more affected by these compounds. Methemoglobulinemia is caused, when food containing nitrates and/or nitrites is taken. Nitrites when taken, try to get oxidised to form nitrates absorbing oxygen, thus depleting oxygen content in the body. Nitrates are readily absorbed in gastrointestinal track.
It forms methaemoglobin with the hemoglobin in the blood and gradually accumulates in the body. In infants below six months the foetal hemoglobin, which is present in them, oxidises more readily to form methemoglobin poison and accumulates.
Further the stomach of infants is less acidic than adults and encourages the growth of bacteria and the effect accelerates as the volume of blood in infants is much less. Organisms like Clostridium are capable of reducing nitrates into nitrites. The diet of infants that is mostly carbohydrate accelerates the poisoning and leads to death.
The infants have the following risks when they take water containing high nitrate:
1. Higher fluid intake per body weight.
2. Inability to produce gastric acid to a pH, below which nitrate producing bacteria cannot survive.
3. Infants contain hemoglobin ‘A’ in blood whereas adults contain hemoglobin ‘A’ in blood, which is more resistant to methemoglobin formation.
4. Water is normally boiled to feed the infants, which increases nitrate concentration and decreases oxygen content.
5. Lack of enzymes.
6. Water may be contaminated bacteriologically.
7. There is always a tendency to feed infants with vegetables rich in nitrate.
Cresols and xylenols are present in water, which receive industrial wastes. Phenols are readily absorbed and eliminated through urine and considerable amount is metabolized or lost. Phenols have repulsive taste even at very low concentrations. MCL for total xylenes is fixed at 10 ppm.
XVI. Total Dissolved Solids (TDS):
The major contents in normal water are chlorides and sulphates. They are acceptable in reasonable limits. Modern water purveyors do trade in the name of mineralised water, which contain these salts in acceptable limits. Water with high dissolved solids is likely to act as a laxative. Coffee made with high TDS is less acceptable in taste. The maximum limit fixed is 500 ppm.
With the development of nuclear industry and utilisation of radioactive materials, contamination of water with radioactive wastes has become a concern in recent years. Even at low concentration, exposure to radiation from radioactive materials like radium and strontium act on the functioning of body’s lining cells and damage bone marrow. They are known to promote increased risk as carcinogens, mutagens and teratogens.
Normal ways of contamination into drinking water occur through the decay of man-made deposits, corrosion of natural deposits, and other nuclear fallouts. The maximum contaminant level goals for Beta/Proton emitters, Alpha emitters and combined Radium (226/228) are fixed at zero while the MCL are 4m rem/yr, 15 pCi/l respectively.
Sodium enters into water from natural salt, decomposition of rock and salt-water aquifers. Sodium is essential to good health but mostly humans get 10 times more than their requirements through food. Consumption of sodium in higher quantities leads to blood pressure.
Levels of sodium with more than 20 mg/l can be bad for humans as it interferes with the osmotic process in the body physiology. Reasonable levels of SAR are recommended for human consumption and irrigation. Water classification of India recommends SAR at 26 for ‘E’ type use.
Sulphate enters water from rain contaminated by air, weathering rocks, steel mills, pulp mills, textile plants and municipal sewage. Water containing more than 75 ppm acts as a laxative in humans. EPA standard is 250 ppm and that of C.P.H.E.E.O., India is 400 ppm.
3. Pollutants Coming from Treatment & Distribution System:
Deteriorating asbestos cement pipes in water distribution adds asbestos in drinking water systems. Asbestos also enters from the water tapped from acquifers containing asbestos such as serpentine rock. Asbestos is a proven carcinogen. It can cause stomach and intestine cancers. MCL for asbestos (>10 mm) is 7 MFL. (Million Fibres per Litre)
Chloromines form by combining chlorine with ammonia. They are used as disinfectants. This remains for longer duration in water than free chlorine. They cause unpleasant tastes and odors. Chloramines can cause anaemia and are harmful to dialysis patients.
Chlorine is used as disinfectant universally in drinking water systems. Though it is reported to be carcinogenic, its usage could not be dispensed as disinfectant in water industry due to the easiness in application and measurement for its residual effect compared to others like O3 and UV radiation.
Chlorine-dioxide is used for bleaching of paper & pulp and flour. Chlorite, which is produced in water when treated with chlorine dioxide, is suspected to cause blood disorders.
(e) Dimethylformamide (DMF):
This is used as a solvent in the production of synthetic textiles, paints, dyes, as a paint stripper and as gasoline additive. This is suspected to be carcinogenic.
(f) Methylene Chloride:
Methylene Chloride is used in production of paint, varnish remover, insecticides, fumigants solvents, cleaners, pressurised spray products, fire extinguishers. Methylene Chloride is converted into carbon monoxide inside the body causing imbalances in the carrying capacity of oxygen and carbon dioxide by hemoglobin. This impairs nervous system and presence of ethanol may increase its toxicity to liver.
This is produced by electrical currents and by the reaction of some chemicals with sunlight. This is being held as a substitute for chlorine as disinfectant. It breaks down relatively quick as it enters into the water and is used as disinfectant.
(h) Bromoform (Tribromomethane):
This is used in fire retardant and as a solvent. It is found in water as a result of chlorination. Bromoform is suspected to be mutagen and teratogen in humans. It is estimated that 1.9 ppb in lifetime is sufficient to cause cancer.
(i) Chloroform (Trichloro-Methane):
Chloroform (Trichloro-methane) is used widely in production of drugs, plastics, as a refrigerant, propellant, pesticide and as a solvent. Primary source of Chloroform in drinking water is the reaction between chlorine and humic materials in the water.
This is suspected to be carcinogenic. This also causes damage to kidneys, liver and thyroid and hinders development of embryo and foetus. Chronic exposure exceeding 1.9 ppb is supposed to be risky.
Aluminium is the most common element on the earth. It is widely used as utensils, in cosmetics, deodorants and medicines. There is some evidence that Aluminium causes damage to nervous system, brain disorders (Alzheimer’s disease). It is also harmful for dialysis patients. Aluminium has shown to cause epilepsy and other nervous disorders in animals. MCL is 0.05-0.2mg/l.
Beryllium is used in nuclear power industry, rocket fuel and in use of ceramics and metal alloys. This is a proven carcinogen in animals. It causes disorders in respiratory system, heart, liver, spleen and suspected cause of bone cancer. MCL is 4.00 ppb.
Boron compounds are used in the manufacture of steel alloys, glass and pottery, in photography and used as wood preservative. Compounds of boron cause mild irritation in stomach and intestines, loss of appetite, rashes and kidney disorders.
This is used in the production of metals, ceramics, electrical equipment, chemicals and fertilizers. Molybdenum is an essential metal for humans and animals. Overdose causes gout and bone disorders. Cows fed on molybdenum can become severally diarrhetic and may die.
Other symptoms are loss of appetite, anemia, loss of hair and colour, bone effects. It is used for corrosion resistance in metal alloys and fungicides. It is an essential trace nutrient. High concentrations effect central nervous system, stomach disorders, heart, brain, liver, kidneys etc.
Vanadium is found in petroleum. It tends to accumulate in human liver and bones. No adverse effects have been studied or demonstrated.
4. Industrial Chemicals:
It is used in production of chemicals. Tobacco and auto smokes contain acetaldehyde. This is proved to be mutagen, teratogen.
This is used in production of plastics and textiles. This causes disorders in central nervous system in animals (MCLG- 0).
This is found in petroleum products and is widely used in paints, inks, oils and plastics, paint removers and rubber cement. This is widely used as a solvent and also in detergents, explosives and drugs.
It is a suspected carcinogen, mutagen and teratogen. Benzene is responsible for blood related disorders in humans. Chronic exposure leads to headaches, fatigue, anemia, loss of weight, dizziness, nose bleeds, bone-marrow damage etc. (MCL — 5 ppb).
It is used in chemicals and as additive to gasoline and motor oil. It is also found in traces in water treated with chlorine. It acts on the nervous system of humans.
It is a volatile chemical primarily used as solvent. It is used as dry cleaning fluid, fire retardant, in pesticides. It is a proven carcinogen in animals. It damages embryo/foetus, nervous system, liver, kidneys etc. (MCL—5 ppb).
This is widely used as a solvent and also in the manufacture of dyes, drugs and chemicals. This is a mutagen and carcinogen for animals.
This is used as fumigant, dyes, degreasers, etc. This is suspected to cause hemolytic anemia and carcinogen for animals. This also causes damage to nervous system, kidneys and liver (MCL — 75 ppb for para-dichlorobenzene).
Dichlorodifluoromethane is used as refrigerant, aerosol propellant, foaming agent, etc. This causes heart disorders and cancer. EPA put the chromic dose as 1.9 ppb.
This is used as a solvent and degreaser. It is also used in production of paints, chemicals and in processing of ores. This is a mutagen, carcinogen and causes damage to nervous system besides creating liver problems (MCL — 5 ppb).
This is used as a solvent, a major component in gasolene, used in insecticides. This is widely found in auto emissions. This leads to disorders in kidneys, liver and a carcinogen. MCL is 0.70 ppm.
xi. Fluoro Trichloro Methane or Trichloro Fluoro Methane:
This is used as a refrigerant (Freon), in fire extinguishers, as cleaning agent. This is found to cause disorders in heart and causes damage to ozone.
xii. Methyl Tertiary Butyl Ether (MTBE):
This is a widely used component of gasoline and is suspected to be a carcinogen.
This is used in the production of additives, a chemical used in dyes, rubber and solvents. Nitrobenzene is also used in explosives and as a solvent. This is readily absorbed by skin and by lungs. Nitrobenzene undergoes changes in stomach to form compounds leading to methemoglobulinemia. The other effects are fatigue, vertigo, vomiting, severe depression and lack of energy.
xiv. Poly Nuclear Aromatic Hydrocarbons (PAHS):
This comes under a family of toxic chemicals produced by incomplete combustion of fuels in the presence of little oxygen. They get into drinking water by air pollution, contaminated rain, and also from industrial runoff. Benzo(a)pyrene is the most common form of PAHS. They are suspected mutagens and carcinogens. MCL is 0.0 to 0.5 ppb.
xv. Polychlorinated Biphenols (PCB):
Water contaminated with PCBs has been found in many parts. They are normally associated with electronic industry and electric power transformers. They cause damage to chromosomes, the nervous system, liver etc. They are found to be carcinogenic, teratogenic and mutagenic. PCBs break down into dibenzofurans, which are more potent. MCL is 0.0 to 0.5 ppb.
Styrene is widely used in resins, plastics including resins used in water treatment. This acts on nervous system and is mutagenic. Tests on animals show that they can cause biochemical changes in brain and are carcinogenic. MCL is 0.1 ppm.
This is a product of refined petroleum or distilled coal tar. Toluene is also used in the production of chemicals, perfumes, dyes, solvents, drugs, Tri Nitro Toluene (TNT) and detergents. Exposure to toluene has a narcotic effect and results in nervous intoxication and finally paralysis, miscarriage, cancer etc. MCL is 1.0 ppm.
xviii. Trichloro Ethane (TCA):
This is used as a solvent, degreaser and as a cleaning agent in industries. This acts on nervous system, kidneys and is a mutagen. MCL is 3.0 to 5.0 ppb.
xix. Trichloro Ethylene (TCE):
This is an industrial solvent and also used for cleaning sanitary appliances. This is a carcinogen, mutagen and acts on kidneys and liver. MCL is 5.0 ppb.
This is widely used in the production of polyvinylchloride (PVC) resins. This is also used as a propellant in aerosols and was banned in 1974. It can find its way into drinking water systems, due to the deterioration of plastic pipes. This is a carcinogen, causes disorders in nervous system, brain, liver, lungs etc. MCL is zero to 2 ppb.
This is formed during distillation of petroleum, coal tar, coal gas and is used in solvents, aviation gasoline, rubber cement and in reduction of some chemicals. Xylene is found to cause birth defects, damage to nervous system, liver, kidneys etc. MCL for total xylene is 10.0 ppm.
This is a herbicide. This finds way into drinking water through the runoff and seepage from fields. This is a proven carcinogen (MCL-0).
This is a carbamate pesticide under trade name ‘Temik’. This is used for potatoes, peanuts, sugar beets, citrus crops and cotton. This is highly toxic (MCL — 9 ppb).
3. Aldrin and Dieldrin:
This is highly toxic. It is also a carcinogen, teratogen and acts on nervous system (MCL is 0.017 mg/l).
4. Chlordane (Kepone):
This is used on bananas, tobacco etc., for control of ants and roaches. This acts on nervous system, speech, sterility and liver. MCL is 2.0 ppb.
This is widely used as pesticide and is highly toxic. It is a proven carcinogen, reduces fertility and impairs nervous system. MCL is 2.0 ppb.
6. DDT (Dichloro Diphenyl Trichloro Ethane):
This is a chlorinated hydrocarbon insecticide and widely used as insecticide and pesticide. Its usage is banned by entire world because of its bad effect on the environment and run-off. This accumulates in the fat of humans and animals and is moderately toxic. It is a carcinogen in mice (0.042 mg/l).
This is used as mothballs. Anaemia and disorders of liver, kidneys can result from chronic exposure.
This is a most toxic organo-phosphate insecticide. It causes damage to nervous system and can penetrate through skin.
MCL – Maximum Contamination Level
ppm – Parts per million
ppb – Parts per billion
4. Examples of Industrial Water Pollutants:
Mercury is a rare element that occurs naturally in the earth and has been reported to vary from 5 to 1,000 ppb in common natural materials. In rock and soils it averages about 80-100 ppb, although some shales have been as high as 10 ppm. The oceans appear to average about 0.1 ppb with a range that typically occurs from 0.03-2 ppb. Mercury in nature is found tightly bonded to organic and inorganic suspended materials or sediments.
Mercury ore, called cinnabar, is mercury sulfide (HgS), and has been mined in Spain for 2,700 years. Most mercury was produced by roasting the ore in air, which separates the mercury from the sulfide. The symbol for mercury is Hg and is derived from the Latin name “hydargyrum,” which means liquid silver.
Mercury is the only common metal that is liquid at room temperature, although four other elements—gallium, francium, cesium and bromine—also exhibit this characteristic. Due to its uniform coefficient of expansion and large liquid range, it has found much use in commercial and industrial applications. Mercury is very dense, weighing 112.9 pounds per gallon. It has the highest volatility of all the metals and a low vapor pressure. Many metals dissolve in mercury to form amalgams (alloys).
Mercury has three oxidation states. The familiar elemental mercury has no charge, mercurous compounds of mercury carry a +1 charge, and the mercuric forms have a +2 charge. It is neither a required element nor is it a beneficial one for biological systems.
However, its special properties and resultant varied uses have led to its widespread occurrence in the environment. In this century, perhaps 200 million pounds of mercury have been used and much of it cannot be accounted for. It is estimated that 41.5 million tons are lost in the soil, water, and atmosphere.
Distribution and Occurrence:
Lead has been known to man for more than 3,000 years, and its softness and low melting point have enabled a wide variety of uses. Archaeologists have found lead pigments on structures built in 3,000 B.C., on which the residual colors are still visible. The crust of the earth does not contain large quantities of lead, averaging about 15 ppm. However, lead is concentrated in ores and certain soils.
The most common ore is galena, which is lead sulfide (PbS). Other forms include lead carbonate or cerussite (PbCO3), lead sulfate or anglesite (PbSO4), and lead chlorophosphate (pyromorphite). In living organisms, it bonds with the sulfhydryl, carboxyl, and amine sites on organic molecules. As a pollutant, it exists in air, water, and soil, but is particularly an air pollutant problem.
Like mercury, it use and distribution in the products of society have been the major source of pollution in the environment.
The principal categories of use are or were:
(ii) Metal products (cable covering, ammunition),
(iii) Chemicals (including gasoline additives),
(iv) Paints and pigments, and
(v) Miscellaneous processes and products.
As a water pollutant, the major inputs are from the atmosphere, runoff, hunting, leaching from landfills, and plumbing fixtures.
Airborne lead results from the burning of fossil fuels for energy, from commercial and industrial incinerators, and smelting (copper and lead) processes. It also can result from boilers used for heating, such as apartment buildings, which burn “used oil” as a fuel. It is much more of a problem in urban areas than elsewhere.
Formerly, the use of leaded gasoline was the biggest input, but since this process has all but stopped in the United States, atmospheric lead levels have dropped. However, Europe has not yet adopted the practice of using lead-free gasoline. A significant exposure can result from airborne dust containing lead.
Runoff from the land is probably the single largest input to aquatic systems. The lead is the residual material from vehicles and other sources. Some estimates put the amount of lead from leaded gasoline at 5.7 × 109 pounds since 1923 with peak use during the 1970s. Because the quantity of lead used is so staggering, it is important to understand how it ends up in aquatic systems from its origin in gasoline.
Lead in the form of tetraethyl lead (Pb(C2H5)4) and tetramethyl lead (Pb(CH3)4) were antiknock additives in gasoline. Upon combustion, the lead combined with scavenger chemicals in the gasoline to form gaseous compounds and exit the system. (Scavenger chemicals are designed to combine with and remove impurities from a host substance.) To facilitate this, the scavenger chemicals were commonly ethylene dibromide, C2H4Br2, and ethylene dichloride, C2H4C12.
The car exhausts products deposited on the walls of the exhaust system as lead carbonates, oxides, and oxycarbonates. They were then periodically ejected onto the road surface. From there they would be ground up by traffic, become airborne as a fine dust and redeposited on or near the road.
In fact, it is estimated that about half the lead would be redeposit within 100 feet of the roadway. Precipitation and runoff would then convey the lead to aquatic systems. Lead also was taken up by plants growing along the roadways. It is usually stored within the plants in nontoxic forms, such as lead phosphates.
Another significant introduction of lead into water occurs from hunting. Lead shot is often used in shotgun shells. Hunting of waterfowl has resulted in much lead being deposited from spent shot in the sediments. Waterfowl such as ducks—e.g., pintails, mallards, and geese—bottom-feed and ingest the lead shot. The lead changed into soluble salts that paralyze the bird’s gizzard and lead to death by starvation.
It is now estimated that two to three million ducks and geese die each year from ingestion of lead shot obtained from the bottom of lakes, ponds, and streams. In addition to these, predatory birds that feed on the waterfowl also can get lead poisoning; many bald eagles died due to this. In 1987, the use of lead shot for hunting was banned in the continental United States because of this problem.
While some lead will precipitate due to the low solubility it has when it reacts with carbonates, sulfates and sulfides, it is most effectively removed from natural waters by sorption. This is particularly true when natural organics, such as humic and fulvic acids are present, with which it complexes. This reaction increases its affinity for clays and other mineral substances. Therefore the concentration of lead markedly decreases with distance from its input source.
Microorganisms appear to be able to methylate lead precipitated in bottom sediments as tetramethyl lead, which, as in most cases with inorganic metals, is more toxic than the elemental form. Volatile tetramethyl lead can be produced from inorganics such as lead nitrate and lead chloride and organics such as (CH3)3PbOOCCH3. The importance of this process is not exactly known. However, the methylation process does appear to be an important way in which lead locked in the sediments can be available for reintroduction into the water column.
Solid waste landfills and places where lead-containing materials are dumped or stored (e.g., junk yards) can be an appreciable local source of lead. The somewhat acidic characteristics of rainwater facilitate the leaching of lead into groundwater and surface waters. Lead also can be found in or on the land or water; anywhere structures have been painted with lead-based paint.
This was commonly used on water towers, bridges, electric transmission towers, fuel tanks, and other structures. Many ships also were painted with it. If it doesn’t fall directly into the water, on land it can be leached to groundwater or be carried by runoff to surface water.
The last source of lead contamination in water is especially important to people because it can occur in our drinking water. The source is associated with the former use of lead piping and copper piping with lead solder. The problem becomes more serious with a more corrosive or acidic and soft water supply. Lead levels can become much higher if the water remains undisturbed for six hours or more.
Treatment controls applied at the process end of a water treatment system are used to lower the corrosivity/acidity. They include raising the pH with sodium hydroxide and adding sodium hexametaphosphate. New York City has begun using calcium orthophosphate to cause chemical deposition in pipes, resulting in covering the potential sources of lead with a scale coating.
The problem is very widespread. In the late 1980s, an EPA report on lead in the Colorado potable supply system was leaked. A conclusion in the report indicated that based on the findings, it estimated that 30 to 40 million Americans had too much lead in their water supply and that the standard was too high.
The present standard is 0.05 ppm (50 μ/l) for domestic water supply. The EPA is likely to significantly lower this standard soon. The World Health Organization has an upper limit standard of 0.1 ppm (100 μ/l). Surface waters used for drinking water supplies vary greatly in lead content, from non-detectable to 55 ppm.
As a metal, cadmium is soft and ductile, and related in its properties to mercury and zinc. It occurs in nature associated with zinc, copper, and lead ores mostly as cadmium sulfide (CdS) salt and also as cadmium carbonate (CdCO3). Near the mines and smelters of these ores, higher concentrations in soils probably cause observable concentrations in the water.
Other than from mining and industrial sources, cadmium occurring naturally in water in more than trace levels is very rare. Most freshwaters will contain less than 1 ppb and marine waters typically average around 0.15 ppb, where it occurs mostly in the +2 state. Unlike mercury, it does not form volatile compounds.
Cadmium also occurs as cadmium oxide (CdO), which can form cadmium hydroxide (Cd(OH)2) in water, and as cadmium sulfate, (CdSO4). The solubility of cadmium in water increases as pH decreases; significantly so as the pH goes below pH 8. Cadmium can, therefore, be seen as fairly mobile in the aquatic environment.
Because there is no cadmium ore, cadmium appears in the environment as a product of industrialization and is found only near man’s activities.
Cadmium is released to the environment in several ways:
1. Processing/smelting of ores (zinc and copper) containing cadmium.
2. Reclamation of scrap metals containing cadmium. (Steel is often coated with cadmium, which vaporizes when heated to high temperatures.)
3. Mining of metal ores containing cadmium.
4. Incineration for disposal of waste products containing cadmium, e.g., plastics and paints.
5. Runoff carrying fertilizers and fungicides containing cadmium.
6. Combustion of fossil fuels that contain cadmium, arsenic, and lead in minute quantities.
Some of these release mechanisms result in cadmium as an air pollutant. It can then be inhaled into a biological system or be deposited on land and water. On land, it can be taken up by plants for subsequent ingestion and incorporation into biological systems. Other inputs to soil include fertilizers, fungicides, land disposal of sewage sludge, and possibly irrigation water.
The allowable level, or “tolerance,” of cadmium in irrigation water is 5 μg/l. If a normal amount of irrigation water is applied, say 5 acre-feet, one acre would receive about 5 grams. This is equivalent to land disposal of 10 tons of sewage sludge from a large, fairly industrialized city where you could expect 0.5 grams of cadmium per ton. If the source of cadmium is not taken up by plants, it is then available for leaching to groundwater for potential ingestion or being transported by runoff to surface waters.
As described, the distribution of cadmium is caused by man’s activities. Because of this, downstream of large population centers and industrial complexes, the cadmium levels will be highest, generally decreasing with increasing distance from such locations. Cadmium is greatly adsorbed by organic materials, which may be the most important control over its fate and transport.
Selenium is a naturally occurring, nonmetallic element found in varying concentrations around the world and typically ranges from 0.03-0.8 ppm. However, in certain areas it may naturally occur much higher, up to 200 ppm in certain limestones. It also can be found in a few ppm in fossil fuels, being more abundant in coal than oil. Higher concentrations are generally associated with the Rocky Mountain States.
In the aerobic aquatic environment, it is usually found in the selenite (H2SeO3, selenious acid) forms (+4 oxidation state), and in the selenate (H2SeO4 selenic acid) forms (+6 oxidation state), which are the most dangerous forms. These types are very soluble and it is in these forms that it is mostly transported and taken in by plants.
Selenium also occurs in two other oxidation states. Elemental selenium is very sorptive and insoluble and can be released by fossil fuel combustion. It is relatively inert and nontoxic in the elemental form. The selenide form (-2 oxidation state) is the type found within plants and can be incorporated into amino acids and proteins. It is taken up through plant roots in the selenite or selenate forms. In reducing environments, metal selenides are formed by reaction with a metal or substitution for sulfur in metal sulfides.
Most of the selenium found in water is probably the result of the weathering of rock containing selenium. However, as an air pollutant from the combustion of fossil fuels, this anthropocentric source may bring selenium to areas where it does not naturally occur.
The ability of animals, plants and bacteria to transform and volatilize selenium through methylation has been documented. One study found that microbes could methylate selenium in lake sediments in Sudbury, Ontario. This forms, and H2Se found in reducing environments, are the volatile forms.