“I think it is impossible to dump 17,000 metric tons plus of mercury in a community or release it into the air and not have significant consequences,” he said.
To investigate those consequences, Robins enlisted Nicole Hagan, who is now a doctoral candidate in environmental science and engineering at the University of North Carolina.
In 2009, using historical records, Robins and Hagan mapped the main colonial-era smelting zones in Potosí and Huancavelica, then modeled airflow patterns. Based on those results, they laid out transects and took soil samples.
High mercury concentrations were found in soil samples from both towns, although they were higher in Huancavelica, where the cinnabar ore was smelted.
Hagan said the soil levels are consistent with measurements near mercury mines in other parts of the world. The difference, however, is that over the years, many Huancavelica residents have constructed their homes from adobe bricks made with the contaminated soil.
In about 20 percent of 60 houses tested by the scientists, the indoor air concentration of mercury is between 1 and 10 micrograms per cubic meter, which exceeds levels considered safe under U.S. guidelines.
The U.S. Centers for Disease Control and Prevention sets a maximum of 1 microgram per cubic meter for residential exposure and recommends isolating residents from the source at a level of 10.
In addition, about three-quarters of the dirt floor and adobe brick samples taken inside the homes were higher than the Environmental Protection Agency’s screening level for mercury in soil. Many houses, like Salazar’s, have dirt floors where children play.
For Robins and Hagan, the next question is whether the contaminated building materials are affecting residents’ health. “It is not clear how volatile or bioavailable the mercury from historical depositions is and to what extent the mercury presents a health hazard,” Hagan said. “All forms of mercury are toxic, but the species of mercury and the exposure route will determine the extent of the toxicity.”
Methylmercury affects the neurological system, especially in children, and it has been linked to IQ reductions of children exposed in the womb. High levels can affect the kidneys and brain, causing tremors, irritability, and vision, hearing and memory problems.
Despite the long history of mercury pollution in Huancavelica, no health studies have ever been done there, according to Enrique Ecos, who heads the local hospital’s epidemiology department and collaborates with Robins and Hagan.
Government officials say they are busy trying to address the town’s urgent concerns like potable water and sanitation.
Last July, the team returned to Huancavelica to inform the residents of their results to date. They also took more than 100 hair samples from adults living in many of the homes they sampled in 2010, and also from people in brick houses with concrete floors, where mercury exposure is likely to be lower. They are awaiting the results.
Hair samples might not be conclusive about the risks posed by the homes because they could be contaminated with other airborne mercury, according to Philippe Grandjean, adjunct professor of environmental health at the Harvard School of Public Health, who recommended measuring mercury in urine. Nevertheless, Grandjean said, Robins’ and Hagan’s findings point to the need for further study.
Their main goal is to assess possible health impacts and recommend measures for reducing exposure. That could mean finding an effective, low-cost, culturally acceptable way to seal or shield the adobe bricks, Hagan said. A brick-making cooperative using uncontaminated clay is another option, Robins said. Soil cleanup, if necessary, could be costly, but might create jobs while improving public health.