Arsenic Field Tests May Lead to Mislabeled Wells
WASHINGTON, DC, November 25, 2002 (ENS) - Thousands of people in Bangladesh and India may be drinking arsenic contaminated water from wells that are falsely labeled safe, warn researchers from Jadavpur University in Calcutta, India. Inaccurate arsenic test kits are leading villagers to avoid safe water and drink from unsafe wells in countries where untainted water is among the most precious of commodities.
Researchers analyzed 2,866 water samples from wells that had been tested and labeled by field workers. They found that a large percentage of the wells were mislabeled, marked safe when they contained dangerous levels of arsenic, or marked as contaminated when more sensitive analyses showed them to be safe.
Shallow wells, known as tubewells, are used in Bangladesh and India to avoid the region's surface water, much of which contains bacteria that can cause waterborne diseases like cholera. Starting in the 1970s, international aid organizations dug millions of tubewells to provide bacteria free water.
But officials soon found that the tubewells were reaching groundwater containing high levels of arsenic.
By 1993, the Bangladesh Department of Public Health Engineering had reported widespread signs of arsenic poisoning, and blamed water from tubewells. Similar problems have also surfaced in other countries in the region, including India, Vietnam, Cambodia, Nepal and Myanmar (formerly Burma).
WHO has called the region's arsenic problem the largest mass poisoning of a population in history.
In 1997, the World Bank, WHO, UNICEF and other international organizations undertook a massive project to test every tubewell in Bangladesh and the surrounding area using field kits. Many wells were labeled with paint to indicate their viability: green for safe water, containing under 50 micrograms per liter of arsenic, and red for unsafe water.
"We have been surveying in arsenic affected areas of Bangladesh since 1996," said Dr. Dipankar Chakraborti, head of the School of Environmental Studies at Jadavpur University, and lead author of the paper. A print version of the paper is scheduled for publication in the December 15 edition of "Environmental Science & Technology."
The villagers then proceeded to assault the workers, Chakraborti said, because both samples had been taken from the same well.
The researchers began testing tubewells themselves with a technique called flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS), a fast and sensitive method performed in a laboratory setting. They found random errors in the labeling of tubewells, which led them to begin the systematic study reported in the current paper.
The team found that almost 50 percent of the wells painted red by field workers contained safe drinking water, according to their lab technique. In contrast, just 7.5 percent of the green painted wells, which had been dubbed safe, turned out to be unsafe.
The field kits are difficult to read with precision, the team said, and the majority of the analyses done in Bangladesh were performed before 2000, using a test kit with a minimum detection level of 100 micrograms per liter.
Chakraborti recommends using the FI-HG-AAS analysis because it not only provides more accurate readings, but also has fewer environmental impacts. The field kits require large quantities of toxic chemicals that must be disposed of, he said, but the laboratory technique uses a micro-assay technique with much less need for chemicals.
The lab technique can also be less expensive than the field kit method, Chakraborti added.
"Cost is an important consideration, but [it] requires comparison with the even higher cost of falsely labeling a well as unsafe," the researchers write. "Given the scarcity of uncontaminated water, the mislabeling of 50 [percent] of safe wells has a major socioeconomic impact."
Harvey and his colleagues argue that irrigation pumping draws down the levels of underground aquifers, which are then replenished by monsoon rains and other surface waters. As these surface waters percolate through the rich soil of farmlands, they carry organic carbon into the upper levels of the aquifers, where it reacts with arsenic bearing rock to release arsenic into the water.
The "Science" article suggests that drilling wells into the deeper, older waters of ancient aquifers could avoid much of this newly released arsenic and provide safer drinking water.