Cadmium Exposure in General Populations in Japan: a Review

Abstract

Cadmium (Cd) intake via diet (Cd-D) has been a long-standing focus of administrative as well as public concern in Japan after the endemic of Itai-itai disease (chronic cadmium poisoning). The aim of this report was to review cadmium exposure in Japan by introducing publications from our study group and related articles. Literature survey disclosed that Cd-D was high (up to 100 µg/day) in 1960s even in non-polluted areas. Such high Cd-D levels were followed by gradual decreases in 1970s-1980s to current level of well below 20 µg/day. Once, a very high Cd-D (600 µg/day) was reported for a Cd-polluted area. Replacement of Cd-polluted rice paddy soil with clean soil resulted in substantial reduction in rice-associated Cd-D. In large-scale surveys in 10 prefectures all over Japan conducted early in 2000s, the geometric mean (GM) of Cd-U_cr (Cd in urine as corrected for creatinine concentration) was 1.26 µg/g cr, but was higher in one north-west sea coast prefecture in Honshu Island (>3 µg/g cr). Supplemental survey in 6 neighboring prefectures on the sea coast disclosed that Cd-U_cr in some prefectures were higher as compared with the national average. It was reported that Cd in brown rice was also high. However no clear-cut indication was detected to suggest renal tubular dysfunctions. Surveys in major cities in East and South-East Asia in 1980s-1990s made it clear that Cd-D was substantially lower there than in Japanese cities; Cd exposure of general populations was almost exclusively from foods. Statistical analysis revealed that tubular dysfunction markers increased sharply when Cd-U_cr exceeded 10–12 µg/g cr. The Cd-U_cr level of 11 µg/g cr corresponded to Cd-D level of 59 µg/day. This level was in agreement with the tolerable weekly intake of 7 µg/kg body weight/week, the value recommended by the Food Safety Commission of Japan.