Studies of selenium distribution in soil, grain, drinking water and human hair samples from the Keshan Disease belt of Zhangjiakou District, Hebei Province, China. (WC/96/052)
Abstract
Selenium (Se) is a naturally occurring essential trace element for human, animal and plant health. In China, an endemic selenium-responsive cardiomyopathy known as Keshan disease and an endemic osteoartbropathic disease, which causes deformity of affected joints, are associated with areas with extremely low environmental selenium concentrations.
A UK Government Overseas Development Administration (ODA) Technology Development and Research (TDR) programme (R6227) entitled \"Prediction and remediation of human selenium imbalances\" is being carried out in China by the British Geological Survey in collaboration with the Institute of Rock and Mineral Analysis (IRMA), based in Beijing, and county Public Health Bureaux and Endemic Disease Prevention Departments. The objective of this project is to develop a methodology for delineating areas where selenium deficiency or toxicity may pose a health risk. The environmental geochemical controls on the distribution of Se-responsive diseases are also being evaluated. This information will be used to help mitigate problems of natural Se imbalances by designing and implementing land-use planning, crop and dietary supplementation methods.
This report is the first of a series which will document investigations of selenium imbalances in several areas of China. It focuses on deficiency of selenium in the environment and its effect on human health, particularly Keshan disease. The district of Zhangjiakou in Hebei Province was chosen for the investigations reported here because of the availability of comprehensive epidemiological data and because co-operation already existed between IRMA and the Institute of Endemic Diseases in Zhangjiakou. The objective of the project was to study villages with varying incidence of Keshan disease and to compare the selenium status of the local environment (as indicated by cultivated soils, grain samples and drinking water) with the selenium status of the local population (as indicated by human hair samples).
All the villages studied in this investigation can be considered to have low levels of selenium in the environment. Between the three categories of Keshan disease incidence (high, moderate and none), expected trends in selenium were found in hair, water, and grain, and also for water-extractable selenium in soil. That is, villages with highest incidence of Keshan disease had the lowest selenium whilst the villages without Keshan disease had higher levels of selenium.
The results for total selenium in soils were contrary to what might be predicted - the highest levels of selenium were found in soils around the villages with the highest incidence of Keshan disease. Total Se closely reflects the amount of organic matter in the soil to which the Se is strongly adsorbed and not, therefore, readily available to plants. The soil organic matter is therefore a major factor controlling the incidence of Keshan disease in the Zhangjiakou area. Adsorption of selenium by hydrated iron oxides in the soil may also restrict its bioavailability. When levels of selenium in the environment are low, any factor that is responsible for reducing the bioavailability of selenium has a critical effect which would not be so significant in an area richer in selenium. This serves to emphasise that it is not the total selenium in soil but its availability that is most important.
Although selenium in hair broadly reflects the environmental Se status of an area, results for individuals are very variable reflecting the complexity of factors (environment, diet and lifestyle) that contribute to the selenium content of human hair. In general, it appears that grain Se is the most reliable indicator of local environmental Se concentrations and also of Keshan disease incidence.
All the villages with a high incidence of Keshan disease are remote with limited accessibility. The remoteness is an additional factor that has to be considered alongside geochemical factors when considering the criteria that make onevillage more prone to Keshan disease than another. The remoteness hinders communication and makes individuals more dependent on their local Se deficient environment for food.
This investigation has indicated a close relationship between topographic slope, soil colour and soil organic content. Dark black and brown-black organic-rich meadow soils developed on steeper slopes are more likely to be associated with high Keshan disease incidence than are the lighter and yellower sandy alluvial soils from flat lying areas. The dry soil colour is a very useful indicator of soil type and in the Zhangjiakou area is probably the best visual environmental indicator of Keshan disease risk.
It is recommended that investigations should be carried out of agricultural practices which could be used to help release selenium held by organic matter in the soil, thereby making it more readily available to crops. Raising the soil pH by liming should lead to desorption of Se adsorbed onto goethite and may also release Se adsorbed onto organic matter.
Citation
Johnson, C.C.; Ge, X.; Green, K.A.; Liu, L. Studies of selenium distribution in soil, grain, drinking water and human hair samples from the Keshan Disease belt of Zhangjiakou District, Hebei Province, China. (WC/96/052). (1996)