1. Nriagu, J.O. (1988) A silent epidemic of environmental metal poisoning? Environmental Pollution, 50, 139–61.
2. Shacklette, H.T. and Boerngen, J.G. (1984) Element concentrations in soils and other surface materials of the coterminous United States. US Geological Survey Professional Paper, No. 1270, US Geological Survey, Washington, DC.
3. Trelease, S.F. (1945) Selenium in soils, plants and animals. Soil Science, 60, 125–31.
4. Yang, G., Zhou, R., Yin, S., et al. (1989) Studies of safe maximal daily dietary selenium intake in a seleniferous area in China. Journal of Trace Elements and Electrolytes in Health and Disease, 3, 77–87.
5. Finch, M. and Ryan, P. (1966) Soils of County Limerick. Soil Survey Bulletin, No. 16, Irish Agricultural Institute, Dublin.