17 April 2000
Possible Solution For Arsenic Crisis In Bangladesh
by Kate Melville
Technology developed at the Department of Energy's Sandia National Laboratories to remove toxins from groundwater contaminated by nuclear waste may offer clues about how to resolve a catastrophic environmental crisis in Bangladesh where arsenic-polluted wells are slowly poisoning and killing hundreds of thousands of people.
This spring Sandia geochemist Pat Brady will travel to Vienna to meet with scientists from the International Atomic Energy Agency (IAEA) and help them understand the origins of the arsenic in the Bangladeshi wells. The IAEA is one of several world organizations striving to put an end to the poisoning.
Brady was invited to join in the IAEA scientists' efforts because of his work in natural attenuation, a naturally occurring process that adsorbs soluble heavy metals onto a mineral surface, thus eliminating it from water or soil. Scientists speculate that the mirror-image of the process is providing arsenic to the wells in Bangladesh, and that mineral uptake might conceivably be used to remove arsenic from drinking water -- if the right mineral can be found.
The water contamination, which The New York Times has described as "the biggest mass poisoning in history," began innocently in the late 1970s when the United Nations International Children's Emergency Fund (UNICEF) dug about one million wells to provide clean water in rural areas of Bangladesh. Most of the surface water was polluted, and the new wells were seen as the solution to the water dilemma. Villagers dug an additional three million wells at their own expense, mostly used for crop irrigation. No one knew the new wells were polluted because they were not tested for arsenic contamination.
Arsenic poisoning started showing up in the mid-1980s, and today it is estimated that hundreds of thousands of people throughout Bangladesh are suffering from it and millions more are at great risk. It can cause breathing difficulties, skin discoloration, lesions, cancer, and ultimately death. The World Bank surveyed 10 percent of the four million wells in Bangladesh and found that 40 percent contained significant contamination.
Scientists have been struggling to determine the cause. Originally they believed arsenic might be coming from pyrite (iron sulfide -- "fool's gold") in groundwater. More recently they concluded the arsenic originated in iron oxide coatings of rocks lining the aquifer. Arsenic may be on surface coatings, whereupon fresh water can easily wash it off. Or it may be buried deep inside the mineral coating with the arsenic seeping out at weak points, like cracks, in the coatings.
"It's important to understand the origins of the arsenic," Brady says. "Once we do that, we can figure out how persistent the problem is likely to be, and it might give clues as to how to get it out."
In the meantime the quest continues to find a way to eliminate the arsenic from the water. Brady and several other Sandia scientists have been designing "getters" -- mineral solids that "suck" much of a particular contaminant out of the water. The getters would be external to the wells. Contaminants are attracted to a specific type of mineral and then eventually become entrapped in it, freeing the water or soil of the metal molecules.
The Sandia researchers have been successful in using this technique to remove iodide -- a contaminant emitted by nuclear waste -- from groundwater. Both iodide and arsenic are anions, negatively charged ions. In theory, similar methods could be used to clean up both.
Brady says the team has identified at least two types of minerals that they believe might pull out arsenic. This was accomplished through molecular modeling of arsenic interaction with mineral surfaces.
"This helped us rule out certain minerals and told us which ones might be getters," Brady says. "As a result, we don't have to test every mineral."
Brady says the next step will be to run arsenic-contaminated water through the selected minerals and determine if and how fast the arsenic sorbs.
If this works, they will have found a cheap and easy way to remove arsenic from drinking water.
"Existing methods of arsenic cleanup, including distillation, would cost hundreds of millions of dollars," Brady says. "That is well out of the price range of Bangladesh, a country where the per capita income is roughly $250. A less expensive method of cleanup must be found. Maybe the Sandia-designed getters will be the one."