Soil & Water Conservation Engg.

Lesson 29 Water Pollution

29.1 Types of Water Pollution

Different types of water pollution can be listed as below.

1. Surface water pollution

2. Groundwater pollution

3. Microbial pollution

4. Oxygen depletion pollution

5. Nutrient pollution

6. Suspended matter pollution

7. Chemical pollution

1) Surface Water Pollution: Surface water pollution is the most visible form of pollution and can be seen floating on the water surface in lakes, streams, and oceans. Trash from human consumption, such as water bottles, plastics and other waste products, is most often evident on water surfaces. It also originates from oil spills and gasoline waste, which floats on the surface and affects the water and its inhabitants.

2) Groundwater Pollution: Groundwater pollution is becoming more and more relevant because it affects our drinking water obtained from the aquifers. Groundwater pollution is usually caused by highly toxic chemicals and pesticides that leak through the ground to contaminate the wells and aquifers below the surface.

3) Microbial Pollution: Microbiological pollution is the natural form of water pollution that is caused by microorganisms in uncured water. Most of these organisms are harmless but some bacteria, viruses, and protozoa can cause serious diseases such as cholera, typhoid, etc. This is a significant problem in third world or developing countries where many people have no clean drinking water and/or facilities to purify the water.

4) Oxygen Depletion Pollution: Microorganisms that thrive in water feed on biodegradable substances. When there is an influx of biodegradable material from sources such as waste or erosion from farming, the numbers of these microorganisms increase and utilize the usable oxygen. When the oxygen level is depleted, beneficial aerobic microorganisms die and anaerobic microorganisms thrive. Some of these organisms produce damaging toxins like sulfide and ammonia.

5) Nutrient Pollution: Nutrients are usually found in wastewater and fertilizers. Excess concentration of nutrients in water bodies can cause increased vegetation in the water bodies such as algae and weeds, using up the oxygen in the water and affecting the surrounding marine life and other organisms in the water.

6) Suspended Matter Pollution: It occurs when pollutants enter the water and do not mix with the water molecules. These suspended particles form fine silt on the waterbed, harming the marine life by taking away the nutrients, restricting oxygen diffusion into the water body and disturbing their habitat.

7) Chemical Pollution: From industrial plants and farms, chemical runoff flows into the nearby rivers and water sources. Metals and solvents flow out of factories into the water, polluting the water and affecting wildlife. Pesticides from farms also endanger the aquatic life. These dangerous pesticides and toxins can get transferred through infected fish and affects human health. Petroleum is also a type of chemical pollutant that dramatically affects the aquatic life.

29.2 Sources of Water Pollution

Based on the sources, water pollution is broadly divided into two groups (Fig. 29.1):

1. Point Sources Pollution

2. Non-Point Sources Pollution

1) Point Sources Pollution: Contamination that enters a waterway from a single, identifiable source, traced to a specific source is considered as point source pollution of water. Point source pollution comes directly from a known source like an industrial or sewage outfall pipe. Point sources are typically associated with manufacturing processes. Point source contamination includes leaking chemical tanks, effluents coming from a waste treatment of industrial plant, manure spill from a hog confinement lagoon, discharge from a sewage treatment plant, factory, city storm drain, industrial storm water, discharge from construction sites, leakage of oil tankers in the sea, septic tank systems, storage lagoons for polluted waste, municipal landfills, underground storage tanks containing pollutants such as gasoline, public and industrial wastewater treatment plants etc.

2) Non-point Sources Pollution: Contamination that does not originate from a single discrete source is called non-point source pollution. It is the cumulative effect of small amounts of contaminants gathered from wide spread area. They can’t be tracked to a single point or source. They come from many miscellaneous or diffuse sources rather than from an identifiable, specific point. It includes soil erosion, chemical runoff, animal waste pollution, leaching out of fertilizers from agricultural lands and nutrient runoff in storm water from agricultural field and forest. It also includes contaminated storm water washed off from parking lots, roads and highways, also called urban runoff. Other significant sources of non-point source pollution include litter; disposal of wastes in catch basins; hazardous waste improperly stored or discarded; improperly operating septic systems; erosion from construction sites, farms or home sites; acid deposition including acid rain and fog; pollution from roadways and road salting activities; leaking sewer lines; storm-water runoff from city and suburban streets (oil gasoline, dog faeces, litter); pesticides and fertilizers from croplands; and salt on roads for snow and ice control.

Fig. 29.1. Point and Non-Point Source Pollution. (Source : Calhoun, 2009)

29.3 Effects of Water Pollution

Physio-Chemical Effects: A large number of pollutants can impart colour, tastes and odors to the receiving waters thus, making them unaesthetic and even unfit for domestic consumption. The changes in oxygen, temperature and pH affect the chemistry of waters resulting in the formation of unwanted products. The addition of organic matter results in depletion of oxygen. The direct addition of nutrients through various sources enhances the algal and other biological growths which when die and decompose, further deplete the oxygen. The decomposition of excessive organic matter when undergoes in absence of oxygen results in odorous and unaesthetic conditions due to accumulation of several obnoxious gases like ammonia, hydrogen sulphide and methane etc.

Biological Effects: The addition of pollutants leads to the shift in flora and fauna due to homoeostatic (self-regulating) factors operating in the aquatic systems. Most freshwater algae are highly sensitive to pollutants and their elimination modifies the prey-predatory relationships by breaking down the food chains. This results in change of the whole plant and animal communities. The diversity of organisms increases due to encouragement of the growth of only a few tolerant forms in the polluted conditions.

Toxic Effects: These are caused by pollutants such as heavy metals, biocides, cyanide and other organic and inorganic compounds having detrimental effects on organisms. These substances have usually very low permissible limits in waters and their presence beyond these limits can render the water unfit for aquatic biota and even for human use.

Pathogenic Effects: In addition to the chemical substances, polluted water has several pathogenic, nonpathogenic microorganisms and viruses. The clostridium, perfingersans, staftoculus, ficaliris cause various types of food poisoning. Apart from this, many waterborne diseases like cholera, typhoid, paratyphoid, colitis and infective hepatitis (jaundice) are spread by consumption of sewage contaminated waters.

There could be big list of pollutants and their specific effects. A few of the effects of specific pollutants present in water are summarized in Table 29.1.

Table 29.1. Effects of Specific Pollutants Present in Water

Pollutants	Effects
Zinc (Zn)	It is an important cell component in several metalloenzymes. Heavy doses of Zinc salt (165 mg/l) for consecutive 26 days cause vomiting, renal damage, cramps, etc.
Copper (Cu)	Excess of Cu in human body (more than 470 mg) is toxic, may cause hypertension, sporadic fever, uremia and coma. Copper also produces pathological changes in brain tissue.
Barium (Ba)	Excess of Ba (more than 100 mg) in human body may cause excessive salivation, colic, vomiting, diarrhoea, tremors, paralysis of muscles or nervous system, damage to heart and blood vessels.
Iron (Fe)	It is a component of blood cells and liveral metalloenzymes. However, more than 10 mg per kg of body weight causes rapid respiration and pulse rates, congestion of blood vessels, hypertension and drowsiness. It increases hazard of pathogenic organisms, as many of them require Fe for their growth.
Cadmium (Cd)	50 mg may cause vomiting, diarrhoea, abdominal pains, loss of consciousness. It takes 5–10 years for chronic Cd intoxication. During first phase, discolouration of teeth, loss of sense of smell and mouth dryness occurs. Afterwards it may cause decrease of red blood cells, impairment of bone marrow, lumber pains, disturbance in calcium metabolism, softening of bones, fractures, skeletal deformations, damage of kidney, hypertension, tumor formation, heart disease, impaired reproductive function, genetic mutation, etc.
Mercury (Hg)	Excess mercury in human body (more than 100 mg) may cause headache, abdominal pain, diarrhoea, destruction of haemoglobin, tremors, very bad effects on cerebral functions and central nervous system, paralysis, damage of renal tissues, hyper coagulability of blood, mimamata disease, inactivates functional proteins and even causes death. It may cause impairment of vision and muscles and even coma. It disturbs reproductive and endocrine system. It also causes insomnia, memory loss, gum inflammation, loosening of teeth, loss of appetite, etc.
Lead (Pb)	More than 400 mg of lead in human body can cause brain damage, vomiting, loss of appetite, convulsions, uncoordinated body movements, helplessly amazed state, and coma. It is retained in liver, kidney, brain, muscle, soft tissues, and bones. It leads to high rate of miscarriages, affects skin, and respiratory system, damages kidney, liver and brain cells. It also disturbs endocrine system, causes anaemia, and long term exposure may cause even death.
Arsenic (As)	It is poisonous to fishes, animals and humans. More than 25 mg of arsenic in human body causes vomiting, diarrhoea, nausea, irritation of nose and throat, abdominal pain, skin eruptions inflammations and even death. It binds globulin of blood haemoglobin in erythrocytes. It may cause cancer of skin, lungs and liver, chromosomal aberration and damage, gangrene, loss of hearing, injury to nerve tissue, liver and kidney damage. Minor symptoms of As poisoning, are weight loss, hair loss, nausea, depression, fatigue, white lines across toe nails and finger nails.
Vanadium (V)	It is very toxic, may cause paralysis.
Silver (Ag)	It causes pathological change in kidney, liver and may even damage kidney. and may cause Argyria (discolouration of skin). It affects mucous membranes and eyes. In high doses, it may be fatal to humans.
Radioactive materials/ metals/ substances	These generally cause ‘Gene’ mutation, ionization of body fluids, chromosomnal mutations and cancers. It destroys body cell tissue, and adversely affects reproductive system. If the mother is exposed to radiation during pregnancy, it causes severe mental retardation and leukaemia in infants. Radioactive metals like heavy metals are nephrotoxic and damage kidneys.
Fluoride	Excess fluoride intake in body results in progressive crippling scourge (sponging)/fluorosis of bones, and teeth. It may cause metabolic alternations in soft tissues and their functional mechanism.
Selenium (Se)	Signs of Se poisoning (more than 4 mg) are fever, nervousness, vomiting and low blood pressure. It causes damage to liver, kidney and spleen, loss of nails and hair and blindness to animals. It affects enzyme systems and interferes with sulphur metabolism. It can cause growth inhibition, skin discolouration, bad teeth, psychological problem, and gastro intestinal problems, but trace amount of Se is protective against poisoning by Hg, Cd, and Ag.
Chromium (Cr)	Any chromium compound is toxic but hexavalent Cr greater than 70 mg is very toxic. It causes cancer, anuria, nephritis, gastrointestinal ulceration, and perforation in partition of nose. It penetrates cell membrane and badly affects the central nervous system. It causes respiratory trouble and lung tumors when inhaled. It may cause complications during pregnancy. and has an adverse effect on aquatic life. Trace amount of CrIII is essential for normal glucose, protein and fat metabolism and hence it is an essential trace element in diet.
Manganese (Mn)	Mn is essential for mammals but in concentration greater than 100 ppm, is toxic and causes growth retardation, fever, sexual impotence, muscles fatigue, and eye blindness.
Cobalt (Co)	High dose (27 mg or above) can cause paralysis, diarrhoea, low blood pressure, lung irritation and bone defects.
Nickel (Ni)	More than 30 mg may cause changes in muscle, brain, lungs, liver and kidneys and can also cause cancer, tremor, paralysis and even death.
Boron (B)	Boron in traces is essential for plant growth. In higher concentration it is harmful to crops and affects metabolic activities of plants. It also affects central nervous system.
Alkalinity and Acidity	Permissible range of pH value if violated may cause health problems to human and animals and loss of productivity in agriculture.
Phosphate and nitrates	Phosphates and nitrates are soil nutrients and not toxic in low concentration. They deplete oxygen by promoting excess algae production in water and -giving bad odour and taste of water which are detrimental to aquatic life. They are toxic for human and animal life if concentration is beyond the permissible limits. Nitrates also cause cyanosis or blue body disease.
Chlorine (Cl)	It destroys plant and aquatic life and is a biocide.
Sulphide	It gives bad odour, toxic to many aquatic organisms and animals.
Salinity	Salinity is very harmful for soils as it destroys agricultural land.
Oil/Grease/ Oil Sludge	Petroleum products in general are very harmful for soils, aquatic life, animal, human and plant life. They are very toxic. Agricultural land may suffer accumulation of oily waste affecting aeration and fertility. Many constituents of oily sludge are even carcinogenic and potent immunotoxicants.
Surfactants and detergents	They are toxic and harmful for aquatic life, animals and humans. They inhibit self-purification of water.
Phenols	They are toxic and impart objectionable odour. They generally subdue plant growth. Some phenols (nitrophenyl etc) are carcinogens.
Cyanides	Cyanide poses a serious health hazard. Apart from acute toxicity and chronic toxicity, it leads to development of iodine deficiency disorders.
Pesticides/ Insecticides	They are highly poisonous for humans and animals. Also they lower seed germination, play a role in the development of Parkinson’s disease, destruction of nerve cells in certain regions of brain resulting in loss of dopamine which is used by nerve cells to communicate with brain. Some of these are physical poisons, some are protoplasmic poisons causing liver damage, some are respiratory poisons and some are nerve poisons.
Aluminium (Al)	It is especially toxic for brain and sometimes may lead to Alzheimer’s disease in humans.

 

Keywords: Types of Pollution, Sources of Pollution, Effects of Pollution.

References

Calhoun, Y. (2009). Water Pollution. Infobase Publishing.

Suggested Readings

Calhoun, Y. (2009). Water Pollution. Infobase Publishing.

Harrison, R. M. (Ed.). (2001). Pollution: causes, effects and control. Royal Society of Chemistry.