Types of Water Pollutants
Waterpollutants are of different types, viz. biological agents, chemical agents and physical agents.
6.2.1 Biological Agents
These include bacteria, parasitic fungi and protozoa.
The main source of biological agents include human sewage, animal and plant wastes, decaying organic matter, industrial wastes (oil refineries, paper mill, food processing units etc.) and natural land and urban runoffs and waste water discharge from slaughter houses. Some of the contributory factors include over population, unplanned industrial and human settlements and lack of civic amenities.The oxygen requiring bacteria feed on the biological wastes and this results in depletion of oxygen in the water bodies. Life is destroyed in the absence of oxygen. The water acquires foul odour.
6.2.2 ChemicalAgents
These can be inorganic chemicals and minerals, organic chemicals and radioactive substances. The inorganic chemical agents may be acids, salts (nitrates, phosphates etc.), metals like lead and mercury. The main sources include natural run off from land, industrial wastes, leaded gasoline, lead smelting, agricultural chemicals run off from agricultural lands, mining, oil fields, food processing units etc. These pollutants in water are toxic to various forms of life and human beings and can cause genetic defects. The water is rendered unfit for human consumption (domestic, agricultural and industrial use). It upsets the ecosystem of water bodies and causes eutrophication.
The organic chemicals include agrochemicals (pesticides, herbicides), detergents, and chlorine containing compounds, oil, grease and plastics. The main sources include agriculture, forestry, pest control industries, home and industrial wastes, paper industry, bleaching process etc. Such polluted water is toxic to aquatic life and other organisms that are dependent on such water bodies. It may also cause eutrophication of water bodies.
The radioactive substances are released into water bodies as a result of nuclear wastes from research laboratories and hospitals. These are also released by processing of uranium ores and nuclear plants. The radioactive substances enter the food chain and are responsible for birth and genetic defects. They are also the causative agents for cancer.
6.2.3 Physical Agents
The physical agents include suspended solids, particulates and heat. The main source is soil erosion, run offs from the agriculture, mining and power plants. Suspended organic and mineral solids absorb toxic substances like heavy metals and pass them through food chain. Aquatic animals face problems in breathing through gills in such waters. Thermal pollution occurs when hot water enters the water body. Increase in temperature lowers the solubility of oxygen in water, there by affecting the aquatic life.
6.3