Benchmark dose of cadmium concentration in rice for renal effects in a cadmium-polluted area in Japan.

The aim of this study was to estimate the reference level of cadmium in rice as the benchmark doses (BMD) and their 95% lower confidence limits (BMDL) for various renal effects by applying an updated hybrid approach. The participants were 1120 men and 1274 women aged 50 years or older who lived in the environmentally exposed Kakehashi river basin for at least 30 years. As indicators of renal dysfunction, glucose, protein, aminonitrogen, metallothionein and β(2) -microgrobulin in urine were measured. Cadmium concentration was determined for rice samples stored in warehouses of the farmers in all of the polluted hamlets. The BMD and BMDL that corresponded to an additional risk of 5% were calculated with background risk at a zero exposure set at 5%. The obtained BMDLs were 0.39 (aminonitrogen), 0.26 (metallothionein), 0.25 (β(2) -microgrobulin) mg kg(-1) in men and 0.44 (glucose), 0.32 (protein), 0.33 (aminonitrogen), 0.28 (metallothionein) and 0.24 (β(2) -microgrobulin) mg kg(-1) in women. The lowest BMDL was 0.25 and 0.24 mg kg(-1) (β(2) -microgrobulin) in men and women respectively. These values were lower than the maximum level (0.4 mg kg(-1)) determined by the Codex Alimentarius Commission, indicating that these BMDLs may contribute to further discussion on the health risk assessment of cadmium exposure.