Prenatal Arsenic Exposure May Cause Cancer Later

This is the first time evidence of such genome-wide changes resulting from prenatal exposure has ever been documented from any environmental contaminant, say the MIT scientists.

Even when water supplies are cleaned up and the children never experience any direct exposure to the pollutant, they may still suffer lasting damage, the findings suggest.

The evidence comes from studies of 32 mothers and their children in a province of Thailand that experienced heavy arsenic contamination from tin mining.

Similar levels of arsenic are also found in many other regions, including the U.S. Southwest, the researchers say.

Pregnant woman, United States. (Photo courtesy USDA)

Exposure to higher than average levels of arsenic occur mostly in the workplace, near hazardous waste sites, or in areas with high natural levels, according to the U.S. Agency for Toxic Substances and Disease Registry. At high levels, the agency says, inorganic arsenic can cause death. Exposure to lower levels for a long time can cause a discoloration of the skin and the appearance of small corns or warts.

The research was led by Mathuros Ruchirawat, director of the Laboratory of Environmental Toxicology of the Chulabhorn Research Institute in Thailand, working with Leona Samson, director of MIT’s Center for Environmental Health Sciences and the American Cancer Society professor in the departments of Biological Engineering and Biology.

The team analyzed blood that had been collected from umbilical cords at birth. The exposure of mothers to arsenic during their pregnancy was independently determined by analyzing toenail clippings, "the most reliable way of detecting past arsenic exposure," said Ruchirawat and Samson.

The team found a collection of about 450 genes whose expression had been turned on or turned off in babies who had been exposed to arsenic while in the womb.

That is, these genes had either become significantly more active, as occurred in most cases, or less active, than in unexposed babies.

"We were looking to see whether we could have figured out that these babies were exposed in utero" just by using the gene expression screening on the stored blood samples, Samson says. "The answer was a resounding yes."

This is the first time such a response to prenatal arsenic exposure has been found in humans. But it is not entirely unexpected, Samson explains, because "in mice, when mothers are transiently exposed to arsenic in the drinking water, their progeny, in their adult life, are much more cancer-prone."

Recognizing the damaging effects of the arsenic exposure, "the government has provided alternative water sources" to the affected villages," although many people are still using the local water for cooking, says co-author Rebecca Fry, a research scientist at the MIT environmental health sciences center.

She intends to follow these toddlers as they grow older to show how long-lasting the effects of the prenatal arsenic exposure may be.

Fry suggests that studies of possible ways of reversing or mitigating the damage, perhaps through dietary changes, nutritional supplements, or drug treatments might show how to counteract the dangerous changes in genetic expression.

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