Current Status of Cadmium Exposure among Japanese, Especially Regarding the Safety Standard for Cadmium Concentration in Rice and Adverse Effects on Proximal Renal Tubular Function Observed in Farmers Exposed to Cadmium through Consumption of Self-Grown Rice

Abstract

Because the staple food in Japan is rice, which absorbs cadmium (Cd) from the soil efficiently, rice is the main source of exposure to Cd in the Japanese population. In addition, there have been many Cd-contaminated farming areas in Japan. Therefore, a safety standard for the Cd concentration in rice was set as 0.4 ppm by the Japanese government. This safety standard has been followed for decades without any appropriate scientific or legal basis. However, recent epidemiological studies of female Japanese farmers exposed to Cd through self-grown rice, that is, a series of Japanese Multi-centered Environmental Toxicant Study (JMETS), showed evidence that the safety standard is appropriate. Therefore, general Japanese consumers are unlikely exposed to Cd excessively with the application of this safety standard, considering the trend of decreasing amount of rice consumed among the Japanese population. On the other hand, Japanese farmers were found to be at risk of Cd exposure through the consumption of self-grown rice with a high Cd concentration. Actually, the JMETS showed that female farmers at 70 years of age or older had a decreased proximal renal tubular function due to the high renal accumulation of Cd. On the basis of these findings, "medical examinations for Cd exposure" have recently been implemented for farmers residing in Cd-polluted areas in northern Japan. Because it has been estimated that such Cd-polluted areas are actually larger, it is necessary to implement medical examinations of more farmers there, particularly the elderly.