Estimating arsenic risks in China

Two weeks after Earth pages featured arsenic in groundwater below the Mekong Delta another important paper has emerged about modelling risk of arsenic contamination throughout the People’s Republic of China (Rodriguez-Lado, L. et al. 2013. Groundwater arsenic contamination throughout China. Science, v. 341, p. 866-868). Scientists based in the Swiss Federal Institute of Aquatic Science and technology and the China Medical University follow up the results of geochemical testing of groundwater from almost 450 thousand wells in 12% of China’s counties; part of a nationwide aim to test millions of wells. That is a programme likely to last for decades, and their work seeks to develop a predictive model that might better focus such an enormous effort and help in other large regions where well sampling is not so advanced.

As well as the well-known release of arsenic-containing ions through the dissolution of iron oxy-hydroxides in aquifers that exhibit reducing conditions, aridity that causes surface evaporation can create alkaline conditions in groundwater that also desorbs arsenic from similar minerals. The early results from China suggested 16 environmental  factors available in digital map form, mainly geological, topographic and hydrogeochemical, that possibly encourage contamination; a clear indication of the sheer complexity of the problem.  Using GIS techniques these possible proxies were narrowed down to 8 that show significant correlation with arsenic levels above the WHO suggested maximum tolerable concentration of 10 micrograms per litre (10 parts per billion by volume). Geology (Holocene sediments are most likely sources), the texture of soils and their salinity, the potential wetness of soils predicted from topography and the density of surface streams carrying arsenic correlate positively with high well-water contamination, whereas slope, distance from streams and gravity (a measure of depth of sedimentary basins) show a negative correlation. These parameters form the basis for the predictive model and more than 2500 new arsenic measurements were used to validate the results of the analysis.

Estimated probability of arsenic in Chinese groundwater above the WHO acceptable maximum concentration (Credit:Rodriguez-Lado, et al. 2013)

Estimated probability of arsenic in Chinese groundwater above the WHO acceptable maximum concentration (Credit:Rodriguez-Lado, et al. 2013)

The results graphically highlight possible high risk areas, mainly in the northern Chinese provinces that are partly confirmed by the validation. Using estimated variations in population density across the country the team discovered that as many as 19.6 million people may be affected by consumption of arsenic contaminated water. In fact if groundwater is used for irrigation, arsenic may also be ingested with locally grown food. It seems that the vast majority of Chinese people live outside the areas of risk, so that mitigating risk is likely to be more manageable that it is in Bangladesh and West Bengal.

As well as being an important input to environmental health management in the PRC the approach is appropriate for other large areas where direct water monitoring is less organised, such as Mongolia, Kazakhstan and Kyrgyzstan in central Asia, and in the arid regions of South America.

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2 responses to “Estimating arsenic risks in China

  1. Let us hope that this will provide awareness worldwide. There could be more areas around the world that could possibly be experiencing the same thing.

    • Thanks for the comment
      This kind of revelation about arsenic is worrying. The first news of the arsenic poisoning in West Bengal and Bangladesh didn’t surface until the late 1980s. The awful thing is that it began after public health campaigns to encourage people to dig wells because groundwater was believed to be free of biological hazards that had caused epidemics linked to use of surface water supplies for drinking and hygiene. So in some respects, the arsenic crisis is a modern phenomenon. However, in hazardous semi-arid areas where people have always depended on wells and springs, generation after generation may have been exposed to the risks of various cancers linked to arsenic as well as chronic arsenic poisoning. The vast survey in China seems to be exposing such a situation. But at least it is easily possible to remove arsenic cheaply using filters of various kinds. SD

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