Heavy Metal Pollution of Soil and a New Approach to Its Remediation: Research Experiences in Japan

Rapid industrialization in the 1960s caused heavy metals such as cadmium (Cd) to severely pollute soil 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 through Cd uptake. Recently, the Codex Alimentarius Commission proposed the maximum permissible concentration of Cd in polished rice and other relevant crops. Therefore, it is urgent for the Japanese government to evaluate the Cd uptake risk for Japanese citizens, and to minimize the Cd risk by decreasing soil Cd contamination for food safety and for human health. This paper is an overview of the soil contamination of heavy metals in Japan, particularly of Cd. The natural abundance level of heavy metals in Japanese soil is discussed referring to the regulations of soil heavy metal pollution. In addition, appropriate technologies to minimize soil Cd contamination were discussed and proposed on the following: (1) water management to reduce bioavailability of soil Cd to rice plants; (2) addressing and/or replacement of contaminated soil with non-polluted soil; (3) phytoremediation of the polluted soil by rice and other promising crops; and (4) chemical remediation of Cd-contaminated soil by washing it with chemicals such as iron salts. This paper also contains details on chemical remediation using iron chloride to alleviate the Cd contaminated soil.