Arsenic Risk In China’s Groundwater Mapped

Researchers have developed a new statistical model to estimate the risk of arsenic contamination in China’s groundwater.

Asian Scientist (Aug. 28, 2013) – Researchers have developed a new statistical model to estimate the risk of arsenic contamination in China’s groundwater.

The model, based on geological, soil, and topological data, helps identify high risk areas for groundwater quality monitoring.

Since the 1960s, it has been known that groundwater resources in certain provinces of China are contaminated with arsenic and estimates of the numbers of affected people have risen year by year.

In the most recent survey – conducted by the Chinese Ministry of Health between 2001 and 2005 – more than 20,000 (5%) of the 445,000 wells tested showed arsenic concentrations higher than 50 µg/L.

According to official estimates, almost 6 million people consume drinking water with an arsenic content of more than 50 µg/L and almost 15 million are exposed to concentrations exceeding 10 µg/L (the guideline value recommended by the WHO).

Given the sheer size of China and the time and expense involved in testing for arsenic contamination, several more decades would probably be required to screen all of the millions of groundwater wells.

To help identify high risk areas for groundwater testing, researchers from China and Switzerland have developed a statistical risk model making use of existing data on geology, soil characteristics and topographic features.

To test their model, the researchers made use of available arsenic measurements. They found that actual arsenic measurements and their predictions of unsafe or safe areas showed a high level of agreement.

In addition, large areas have now been identified as potentially at risk, such as the basins of the Tarim (Xinjiang), Ejina (Inner Mongolia) and Heihe (Gansu), or the North China Plain (Henan and Shandong).

Arsenic concentrations above 10 µg/L are predicted for a total area of 580,000 square kilometers. When these results were combined with the latest available population data, it was found that almost 20 million people across China live in high-risk areas.

“This figure may be an overestimate, as we lack reliable information on the number of people with treated water sup-plies,” concedes geochemist Annette Johnson.

But in the long term, she adds, China will remain dependent on groundwater as a source of drinking water, particularly in the arid provinces.

The risk model shows where conventional groundwater quality monitoring efforts are best focused: “Our method permits more targeted sampling campaigns and saves time in identifying populations at risk. The Chinese authorities are adopting our maps in the national monitoring program.”

Johnson is convinced that the model could also be used in other countries where groundwater is known or suspected to be contaminated with arsenic – for example, in Africa or in central Asia, where risk assessments for arsenic contamination have not yet been performed.


Source: Eawag.
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