Biological effects of heavy metals: an overview.

Heavy metals constitute a very heterogeneous group of elements widely varied in their chemical properties and biological functions. Heavy metals are kept under environmental pollutant category due to their toxic effects on plants, animals and human being. Heavy metal contamination of soil results from anthropogenic as well as natural activities. Anthropogenic activities such as mining, smelting operation and agriculture have locally increased the levels of heavy metals such as Cd, Co, Cr, Pb, As and Ni in soil up to dangerous levels. Heavy metals are persistent in nature, therefore get accumulated in soils and plants. Heavy metals interfere with physiological activities of plants such as photosynthesis, gaseous exchange and nutrient absorption, and cause reductions in plant growth, dry matter accumulation and yield. Heavy metals also interfere with the levels of antioxidants in plants, and reduce the nutritive value of the produce. Dietary intake of many heavy metals through consumption of plants has long term detrimental effects on human health.