Metals like cobalt, copper, manganese, zinc, iron and nickel are essential micro nutrients at trace level, but are toxic if present in higher concentrations. Whereas, heavy metals like lead, cadmium and chromium and arsenic are toxic to the environment and their higher concentrations beyond their permissible limits may affect adversely the living organisms.

Heavy metals are dangerous because they tend to bioaccumulate. Bioaccumulation is a process in which chemical substances are concentrated, accumulated and magnified in the body tissue of living organisms either directly from surrounding environment or indirectly through the food chain. The increasing contamination of aquatic water bodies with pollutants bearing trace metals cause deleterious impact not only on the immediate aquatic ecosystem but also on the well being of human population. Heavy metals are toxic elements with lipophilic affinities and bioaccumulation tendencies in biotic tissue. In aquatic organisms, trace metals uptake occurs directly from the surrounding water across the permeable body surface, along with food and water. The metallic ions are accumulated in biotic tissue in critical ranges due to the imbalance of absorption and elimination mechanism in living system.

Fish, which occupy the highest trophic level of food pyramid in aquatic ecosystem are an important target of bio-magnification of trace metals and also act as possible bio-transfer route to human beings.

Heavy metals can enter a water supply by industrial and consumer waste, or even from acidic rain breaking down soils and releasing heavy metals into streams, lakes, rivers, and groundwater.

Industries generate a significant quantity of wastewater, which ultimately finds its way to water bodies. Industrial discharges containing toxic and hazardous substances contribute to severe kind of pollution in the aquatic systems. The industrial effluents are generally varied in nature while the pulp and paper, dairy, distillery and cotton textile industries generate dyes and pigments. Paints and varnish, non-ferrous metals, steel and chlor-alkali generate toxic and hazardous wastes.

Industrial effluents, though comparatively lesser in volume, cause more menace to aquatic environment and the biotic communities, including fish, and ultimately effect man through food chain. Non-biodegradable and persistent types of pollutants like heavy metals, chlorinated hydrocarbon pesticides, oil components having high boiling points and radio-nuclides get more concentrated at higher trophic levels through bio-magnification and pose threat to human health. The industrial effluents include a wide variety of chemical toxicants and heavy metals apart from contributing substantially to the BOD load.

In India, although industrial development has not reached the level attained in the developed countries, more toxic compounds, hitherto unknown, are being detected in increasing numbers in our water courses. It is largely because the production of chemicals resulting in the generation of toxic and hazardous substances has been continuously on the increase for the last three decades.

A preliminary survey of mercury in fish from the Bombay and Thane environments revealed the presence of this highly toxic metal in muscles, brain and bones in thirty species of fish from seven different sources.

Several studies from water bodies near coastal Bombay, Baroda, Chandigarh, Lucknow, Madras, Khetri complex, Raipur, Kanpur and River Cauvery have shown incidence of heavy metal accumulation in living matter.

Recent studies on Gandhisagar reservoir, Chambal river near Nagda and Kota, Khan river near Indore, Kshipra river near Ujjain and lower lake of Bhopal have shown accumulation of metals such as zinc, manganese, copper, nickel, mercury and lead in water, sediments and fish.

In the past, the river Yamuna used to be the main source of drinking water, transportation and irrigation. The pollutants were limited to storm water drains. But post independence, India witnessed massive deforestation leading to soil erosion and related problems. Simultaneously industrialization and emphasis of modern living gained momentum. All the major industries are on the bank of some river or the other. Yamuna outnumbers any other river in the number of industries on its banks. This is because it passes through many major (post Independence) industrial cities.

The entire Yamuna , right from its origin to confluence with the Ganga and its tributaries is subject to human activities, which directly or indirectly affect the water quality. The pollution caused due to heavy metal sources is mainly due to point sources.

Point sources of pollution

The point sources of pollution are contributed at a single point in significant amount such as wastewater drains joining a water body. The point source pollution covers two major categories: Domestic and Industrial pollution.

Sewage is discharged into the river without any treatment from the cities located along the banks of river and its tributaries. This affects aquatic life and depletes oxygen level resulting into bad odours and turbidity. The river water does not remain suitable due to pollution, for uses like drinking, outdoor bathing, propagation of aquatic life, irrigation and industrial purposes.

Industrial pollution affects water quality in many ways i.e., dissolved oxygen, temperature, pH etc. Some industrial effluents cause toxicity. Large and medium industrial units - 22 in Haryana, 42 in Delhi and 17 in Uttar Pradesh have been identified as directly discharging and polluting the Yamuna under the Action Plan area. These industries include paper, sugar, chemical, leather, distillery and pharmaceuticals. The industries are contemplating to adopt adequate pollution control measures under the existing environment laws to ensure that treated effluent conforming to the prescribed standards should only be discharged into the river.