Arsenic contamination in the groundwater in India is not a result of arsenic coming from man-made ponds, says a new study. The study suggests instead that the contamination originates in sediments in aquifers.
Arsenic is a naturally occurring trace element that causes skin lesions, respiratory failure and cancer when present in high concentrations in drinking water.
Though no definitive arsenic source had been determined in the past, many geologists claimed that recent man-made ponds in the Bengal delta are a major contributor, as the heavy rainfall and erosion have created high amounts of organic material in the ponds.
Saugata Datta from Kansas State University and his colleague Karen Johannesson from Tulane University recently completed a study looking at the ponds and reached this conclusion after modelling the transport of the pond's organic matter through the meters of sand and clay to the aquifers below.
"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.
Due to the organic matter's highly reactive nature to minerals like arsenic, the 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," Datta 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," he added.
The study has been published in Geophysical Research Letters and also appeared in the journal Nature.