The high concentration of arsenic in the groundwater of Cambodia is due to rapid burial of sediment and specific chemical conditions in rivers, including the Makong, explained Dartmouth professor and geochemist Ben Bostick during Tuesday’s weekly Geolunch lecture.

Arsenic levels in the Lvea Aem district in Cambodia are over 200 times greater than the EPA’s safe drinking limit. Rapid burial and high organic content create the low-oxygen conditions necessary for the reduction of iron oxides and subsequent mobilization of arsenic into the groundwater. The Makong River is one such example, where sediment is annually accreted and eroded from the meandering riverbanks, leading to high concentrations of arsenic in solution.

Normally under reducing conditions, sulfate takes the place of iron as the primary electron receptor, producing arsenic-sulfide minerals; however, arsenic-sulfides in Cambodia are limited by the low amount of sulfate, leaving high concentrations of arsenic in solution, Bostick said.

In September 2006, the first confirmed case of arsenicosis occurred in Lvea Aem region in Cambodia. Arsenicosis is a water-related skin disease causing discoloration, hard boils, and cancer. Similar health problems have been recognized elsewhere in Southeast Asia for the past 20 years. For instance, 20 million people in Bangladesh alone suffer from arsenic-related diseases. The disease develops over a minimum course of two years with consumption of contaminated water. The high concentrations of arsenic in groundwater are non-intuitive because it is not anthropogenic; arsenic in Lvea Aem is naturally occurring and typical of background levels anywhere on earth. But the chemical conditions associated with river sedimentation, not natural abundance, are responsible for the health crisis in Lvea Aem.

The problem is serious: the Makong River is home to the world’s largest freshwater fisheries, and today nearly 50 percent of the 72,000 people that live along the banks Makong River in Lvea Aem have arsenicosis. Two million Cambodians, 7 percent of the total population, have arsenic-related diseases.

The solution, says Bostick, is to prevent locals from building wells that tap into contaminated ground water. Surface water is much safer than groundwater located beneath rapidly buried sediment. However, surface water must be boiled, and that is not easy since fuel is scarce in the low-lying floodplains of Cambodia.

Bostick has been working in Cambodia for five years and continues to make biannual trips. Local residents in areas like Lvea Aem are the driving force behind his research.

“It’s not often that you can measurably improve the lives of people in the course of a few weeks,” he said.