Heavy metal pollution of soil and a new approach to its remediation: research experiences in Japan

Fast industrialization in the 1960s brought about serious soil pollution by heavy metals such as cadmium (Cd) in Japan. The Agricultural Land Soil Pollution Prevention Law was enacted in 1970 to cope with the heavy metal pollution. Cd, in particular, has been recognized as one of the most detrimental elements in Japan because of the so-called itai-itai disease caused by Cd uptake. Recently, Codex Alimentarius Commission proposed the maximum permissible concentration of Cd in polished rice and other relevant crops. Therefore, it is a matter of urgency for the Japanese government to evaluate the Cd uptake risk for Japanese nationals and to minimize the Cd risk in terms of decreasing soil Cd contamination for food safety, hence human health. This paper is to overview the soil contamination of heavy metals in Japan, in general, and Cd contamination, in particular. The natural abundance level of heavy metals in Japanese soil is discussed in reference to the regulations of soil heavy metal pollution. In addition, appropriate technologies to minimize soil Cd contamination are to discuss and propose on; (1) water management to reduce bioavailability of soil Cd to rice plants, (2) addressing of, and/or replacement of contaminated soil with non-polluted soil, (3) phytoremediation of the polluted soil by rice and promising other crops, and (4) chemical remediation of Cd-contaminated soil by soil-washing with chemicals such as iron salts. This paper is to detail the chemical remediation by iron chloride to alleviate the Cd contaminated soil.