Sources of Heavy Metal Contamination in Surface Waters of Indian Freshwater Ecosystems and Their Effect on Aquatic Biota: A State of the Art Review.

The ecological integrity of several freshwater ecosystems has been disrupted by the rapid and unrestrained accumulation of toxic heavy metals (HMs) from various sources. Changes in land use and land cover, in the form of urbanization and industrialization, have significantly affected the surface-water quality of freshwater ecosystems by causing an upsurge in pollutant loads. In addition, agricultural runoff has contributed to the decrease in water quality. Almost 70% of India's surface-water resources have become polluted owing to the discharge of untreated sewage and industrial effluents, according to a recent report by the Central Water Commission (CWC) of India, with 42 rivers containing at least two HMs in concentrations above the permissible limit. The aquatic biota inhabiting contaminated sites can accumulate HMs from the surface water. In high concentrations, these HMs can damage biotic components, predominantly by triggering oxidative stress and becoming bioaccumulated in different trophic levels of freshwater ecosystems. Heavy metal contamination in the aquatic environment can also cause direct potential hazards to humans, mostly through their consumption of fish and waterfowl. Thus, it is recommended that the untreated wastewater discharge from industry, agricultural fields, and households be curtail to improve surface-water quality. In this systematic review, we investigated the probable sources of the HMs, the HM contamination in the important rivers and wetlands of India, the effects of HM toxicity on freshwater food chains, and potential remediation measures. The findings of the present study will improve our knowledge about the spectrum of HM toxicity and the effects of HM contamination on the biota in freshwater bodies throughout India, and will also aid policymakers in building strategic and sustainable freshwater management plans around the globe. [ABSTRACT FROM AUTHOR]