Arsenic contamination: groundwater study redux

Ezine

Published: Dec 15, 2010
Author: David Bradley
Channels: Atomic

thumbnail image: Arsenic contamination: groundwater study redux

Chronic toxicity

Chronic arsenic poisoning is perhaps one of the most insidious environmental disaster affecting tens of millions of people on the Indian subcontinent and elsewhere. An ongoing study of the problem of arsenic-contaminated drinking water uses atomic absorption spectroscopy to underpin its analytical data. The studies, dating back to the mid-1990s, has now revealed that some 36 million people in Bangladesh alone are affected by drinking water above arsenic safety limits. However, during the last five years exposure levels seem to have fallen in some places with 5 million people now drinking safe water. The improvement is partly due to the awareness campaign wrought from the science and pressure on government to block contaminated tubewells.

In the early to mi-1990s, Dipankar Chakraborti and colleagues at the School of Environmental Studies at Jadavapur University, Kolkata, recognised that chronic poisoning of villagers in West Bengal, Bangladesh and other parts of the Indian subcontinent was taking place. They began testing the tubewells on which most villagers rely across the region for their drinking water. Over the course of several years arsenic contamination was shown to be the cause of the poisoning of "the devil's water", attendant cancer incidence and many fatalaties across thousands of villages.

The source of the devil's water

Chakraborti and colleagues suggested that intensive farming was to blame. The industrial-scale extraction of water from aquifers exposed to the air a bedrock rich in insoluble arsenic salts, which gradually oxidise and become soluble, thus contaminating the water once the monsoon refills the aquifers. The researchers suggested that the best solution would be to encourage farmers to store the vast quantities of water available to them during the monsoon season rather than simply draining the aquifers in the dry season. However, convincing governments to make this a legal requirement was always likely to be an impossible task given inherent corruption and inefficiencies.

In the intervening years Chakraborti and colleagues have campaigned internationally bringing the problem to the attention of the global scientific community and raising the issue in other areas, such as China, Thailand, Laos and Cambodia and desert regions of the USA, where the problem of arsenic contamination of drinking water is also a potential problem. International pressure and a slow realisation that it might be possible to address the problem on the Indian sub-continent saw government carrying out its own tests of tubewells. Unfortunately, false positives deprived many villagers of a safe drinking water supply as wells that were not contaminated were closed off and false negatives left many exposed to unsafe water. During the last five years, however, this problem has been addressed more effectively in some places and the number of people with safe drinking water is increasing.

Arsenic solution?

Chakraborti and his colleagues have sampled and tested more than 52,200 water samples from hand tubewells in all 64 districts of Bangladesh. About 95% of those samples were collected and analyzed between 1996 and 2002 while additional samples were taken during the team's epidemiological work from 2003 to 2009. The team used ﬂow injection hydride generation atomic absorption spectrometry (FI-HG-AAS) to test for arsenic and found that almost a third had arsenic levels above 50 milligrams per litre (the Bangladesh safe limit) and 2 in every 5 wells had concentrations above 10 mg/l (the World Health Organization's safe limit on drinking water). Almost one in ten tubewells were contaminated to above 300 mg/l, a concentration that causes overt arsenicalskin lesions and chronic health problems due to organ toxicity and cancer.

"In Bangladesh and West Bengal, India the crisis is not having too little water to satisfy our needs, it is the challenge of managing available water resources," explains Chakraborti. "The development of community-speciﬁc safe water sources coupled with local participation and education are required to slow the current effects of widespread arsenic poisoning and to prevent this disaster from continuing to plague individuals in the future."

"The thoughtless exploitation of groundwater for irrigation without any effective watershed management is in retrospect widely viewed as a terrible mistake. The effects of groundwater arsenic contamination in Bangladesh have intensified throughout long periods of neglect, resulting in mistakes that must not be repeated," Chakraborti and colleagues assert. "Countries where groundwater extraction proceeds in a similarly uncontrolled manner may be in the future faced with arsenic or other contaminants."