Serial changes in urinary cadmium concentrations and degree of renal tubular injury after soil replacement in cadmium-polluted rice paddies

Targeting persons requiring observation in the Cd-polluted Kakehashi River basin a serial observation study was conducted. Namely we followed the serial changes in 50 subjects who ingested household rice for 10 years after replacement of Cd-polluted soil in rice paddies. The serial changes in urinary substance levels in individuals were determined adjusting for the potential effect of age using a general linear mixed model.Cd excretions decreased with increasing number of years elapsed, with the partial regression coefficients of the number of years elapsed statistically significant in the women. The ratio of the Cd excretion theoretical values at the completion of soil replacement and 10 years later was 0.60 and the reduction rate was calculated as 5.0% per year in women. However, it was surmised that in practice a decrease to the level of inhabitants of non-polluted districts would not be achievable.The indices of renal tubular injury (β2-microglobulin, retinol binding protein (RBP), total protein, amino-N and glucose) with the exception of amino-N in men showed increased excretion in both sexes with increasing number of years elapsed with statistically significant differences in RBP and total protein in both sexes and glucose in men.In this study using a general linear mixed model, which is an appropriate statistical method to perform a follow-up study, Cd concentrations in rice and urine were found to decrease after Cd exposure was reduced, but the degree of renal tubular injury was not found to improve, leading to the conclusion that the renal tubular injury induced by environmental Cd exposure is irreversible.