Soil, grain and water chemistry in relation to human selenium-responsive diseases in Enshi District, China

Selenium deficiency (Keshan Disease) and toxicity diseases in humans occur within 20 km of each other in Enshi District in China and have been linked to environmental levels of Se. Low concentrations of Se are associated with Jurassic siltstones and sandstones, whereas high concentrations occur in a reas underlain by Permian carbonaceous strata. Although these broad relatio nships between Se in the environment and the human population have been est ablished previously, not all villages underlain by the carbonaceous strata suffer Se toxicity problems and the precise controls on Se distribution and availability have not been quantified. In the present study, soil, grain, drinking water and human hair samples are examined to determine the control s on Se availability in 3 Se environments in Enshi District. Five low-Se an d Keshan Disease villages, 5 high-Se and no toxicity villages and 5 high-Se and toxicity villages were selected for the study. Results show that the m ajority of samples in the low-Se villages are deficient or marginal in Se, and that Se availability to plants is inhibited by adsorption onto organic matter and Fe oxyhydroxides in soil. Therefore, remediation strategies invo lving the application of Se fertiliser direct to the soil may not increase plant Se levels as expected. In the high-Se villages, localised lithologica l variations result in considerable ranges in Se concentrations in all samp le types. Deficient and excessive levels of Se are recorded in samples from the same village. Selenium bioavailability in the high-Se toxicity village s is controlled by the total soil Se concentration and pH. A greater propor tion of the Se is plant available in villages where the carbonaceous strata are interbedded with limestone. Villagers should be advised to avoid plant ing crops in these areas if possible. (C) 1999 Elsevier Science Ltd. All ri ghts reserved.