Arsenic is poised to become even more notorious. Scientists have found that if a pregnant woman is exposed, the deadly contaminant can alter the activity of several genes in her fetus, potentially increasing the child's risk of cancer later in life. The find puts new urgency on keeping arsenic out of expectant mothers' drinking water.
Arsenic contaminates drinking water the world over, entering from both naturally occurring deposits and industrial activities. To meet World Health Organization (WHO) standards for safety, arsenic must not be present in drinking water at concentrations greater than 10 parts per billion, but in some countries, such as Bangladesh, the levels far exceed that danger point. Scientists have linked low, chronic exposure to a host of illnesses including diabetes and cancer. In addition, recent work suggests that arsenic exposure before birth can raise cancer risks later in life, but the mechanism has remained unclear.
Wondering whether genes might play a role, researchers at the Chulabhorn Research Institute in Bangkok, Thailand, led by environmental toxicologist Panida Navasumrit focused on the country's Ron Pibul district. Tin mining from the 1960s to the 1980s contaminated groundwater there with arsenic at levels up to 50 times the WHO limit. The team took blood and fingernail clippings from newborns and their mothers in the region and sent 21 samples to Leona Samson, a molecular biologist at the Massachusetts Institute of Technology in Cambridge. Samson compared the samples to those from 11 babies in Bangkok whose mothers had not been exposed to arsenic. After analyzing blood samples from 13 exposed and unexposed babies, she found that the expression levels of 11 genes were significantly different in newborns with arsenic-exposed mothers. When Samson used these genes as a guide, she could predict with 83% accuracy whether the remaining 19 babies had been exposed to the environmental contaminant via their mothers.
The 11 genes play roles in cell growth and death as well as in inflammation, the group reported online 23 November in PLoS Genetics. Although it's not yet known exactly how arsenic causes cancer, Samson notes that chronic inflammation has been linked to stomach cancer. "It therefore seems likely that the arsenic-induced inflammatory response plays at least some role in arsenic-induced cancer," she says.
The paper "opens up potentially very interesting avenues of research" into the fetal effects of environmental contaminants, says Michael Waalkes, a toxicologist at the U.S. National Cancer Institute and the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina. Still, he notes that the predictive power of the gene set is low, and "because of the experimental design we can't really say that other exposures might [not] be an issue."