Spatial Distribution and Risk Management of Heavy Metal Contamination in Japan

Soil pollution and crop contamination by cadmium (Cd) and Arsenic (As) are widely-known and recognized as a global threat to sustainable life and the environment. Various factors contribute to soil pollution, including pollutants factor: sources of pollutants, pollutant pathways, the medium of pollution, and soil factor. Japanese agricultural soils in some region, have been heavily polluted with cadmium (Cd) and various other heavy metals, owing to fast industrialization during the 1960s. The Japanese government urgently enacted the Agricultural Land Soil Pollution Prevention Law in 1970 to cope with the heavy metal pollution, in which Cd, arsenic (As), and copper (Cu) were designated as the targeted hazardous substances for regulation. 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. Flooded cultivation for 3 weeks before and after ear emergence has been recommended to reduce cadmium (Cd) concentrations in rice grains to below permitted values (0.4 mg kg) in some regions of Japan. In 2014, the Codex Alimentarius Commission proposed a maximum permitted concentration for inorganic As in polished rice of 0.2 mg kg. However, in contrast to Cd uptake, As uptake by rice plants is markedly increased by flooded cultivation. Thus, there is a tradeoff between As and Cd uptake by rice depending on the type of water management. Promising practical techniques to simultaneously attenuate As and Cd in rice grain are urgently required. The presentation will provide an overview of heavy metal contamination in Japan and state of the art technologies to alleviate Cd and As contamination in soils and crops, which include; (1) breeding of low adsorptive cultivar, (2) phytoremediation of the polluted soil by rice plant, (3) chemical remediation of Cd-polluted soil by soil-washing and, (4) promising methods simultaneously decrease concentrations of As and Cd in rice grains.