Current status of heavy metal contamination in Asia’s rice lands

Abstract

Major contribution (over 90 %) to the world’s rice production is coming from Asia, where metal contamination of agricultural lands is often reported. Thus the present paper reviews the sources and current status of heavy metal contamination of paddy lands in the region. Apart from the natural sources, agrochemicals, wastewater irrigation, sewage sludge application, livestock manures, mining and fly ash etc., could be identified as the key sources of metal contamination in Asia. Accumulation of heavy metals and metalloids (Cd, Zn, Cu, Pb, Cr, Ni, Fe, Zn, Co, Hg and As) in different parts of the rice plant (roots, straw, hull and grain) is reported at varying degrees. Rice grain accumulates the least amount of toxic metals compared to hull, straw and roots. Most importantly, a greater number of investigations confirmed that the metal contents in rice grains are within the permissible limits of Codex recommendations of joint Food and Agriculture Organization/World Health Organization Food Standards Programme and/or food regulations imposed by the respective governments. However, due to the fact that rice is a main route of human exposure to heavy metals, appropriate preventive and remedial measures should be enforced in the areas with potential risk of metal contamination.