The Mystery Of Arsenic Poisoning In India’s Bengal Delta Groundwater Deepens
A new study has deepened the mystery over the source of arsenic in India’s groundwater.
AsianScientist (Nov. 14, 2011) – The source of arsenic in India’s groundwater has eluded scientists for more than a decade after the toxin was discovered in the water supply of the Bengal delta.
But a recent study by researchers at Kansas State University and Tulane University has added a twist – and furthered the mystery.
Arsenic is a naturally occurring trace element, and it causes skin lesions, respiratory failure and cancer when present in high concentrations in drinking water. The environmental crisis began after large traces of the element were detected in the groundwater in the Bengal Basin, an area inhabited by more than 60 million residents.
The arsenic contamination caused a water shortage, illness, and death in the region, leaving residents unable to even use the water for ordinary tasks like washing dishes or ablution.
Though no definitive arsenic source has been determined, many geologists have claimed that recent man-made ponds in the region are a major contributor, as the heavy rainfall and erosion have created high amounts of organic material – containing arsenic – in the ponds.
From there, they believed that the pond’s water and organic material subsequently seeped into the groundwaters.
Saugata Datta, a Kansas State University assistant professor of geology recently completed a study looking at the ponds with his colleagues, and their findings were published in Geophysical Research Letters in late October.
“Our study suggests that ponds are not contributing substantial amount of water or this old organic matter into the groundwaters in the shallow aquifer in this region,” Datta said.
“These very high arsenic levels are actually coming from something else, possibly from within the organic matter contained in these Holocene sedimentary basins,” he said.
Datta, along with Tulane University colleague Karen Johannesson – the study’s other lead investigator, came to this conclusion after modeling the transport of the pond’s organic matter through the meters of sand and clay to the aquifers below.
Because of the organic matter’s highly reactive nature to minerals such as arsenic, researchers found that this organic matter actually serves as a retardant and causes minerals to absorb more slowly into the aquifer sediments.
“Characteristically the organic matter is very sticky and likes to glom onto mineral surfaces,” Johannesson said. “So it takes much longer for the organic matter to move the same distance along a groundwater flow path than it does through just the water itself.”
According to their model, it would take thousands of years to reach roughly 30 meters into the aquifers in the Bengal delta, which is where we see this peak of arsenic.
In the near future, the research team plans to travel to the region to collect groundwater and aquifer sediment samples for an extensive study that accounts for various valleys and ponds.
In addition to arsenic, the team will also monitor for high concentrations of manganese, as scientists are finding that the two metals often appear together.
The article can be found at: Datta S et al. (2011) Perennial ponds are not an important source of water or dissolved organic matter to groundwaters with high arsenic concentrations in West Bengal, India.
Source: Kansas State University.
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