Exposure to Low Doses of Arsenic Leads to Development of Cancer

Exposure to low levels of arsenic in drinking water can lead to development of lung cancer, a new study finds.

Arsenic exists in two forms-organic and inorganic-in the environment. In developing countries almost 100 million people are exposed to dangerously high levels of arsenic in drinking water. The U.S. environmental Protection Agency's standard is   arsenic levels in public drinking water must not exceed 10 parts per billion (ppb). But there are no established standards for private wells, from which millions of people get their drinking water.

An animal study conducted by researchers at the National Institute of Health found that mice exposed to low doses of arsenic in drinking water, similar to what people consume, developed lung cancer. In this study, the researchers exposed the mice to 50 ppb, 500 ppb and 5,000 ppb of arsenic in their drinking water. 50ppb is the lowest concentration that has been tested in animals. Due to the changing rate of metabolism, mice need to be exposed to higher concentrations of arsenic in their drinking water than humans in order to achieve similar health effects.

A model was used that replicated how humans are exposed to arsenic throughout their entire lifetime. Just three weeks before breeding and throughout pregnancy and lactation, the mice were give arsenic. After weaning even the offsprings were exposed to arsenic and also throughout adulthood at concentrations relevant to human exposure. The scientists then observed the tumors that developed in the adult offsprings.

"This is the first study to show tumor development in animals exposed to very low levels of arsenic, levels similar to which humans might be exposed," said Michael Waalkes, Ph.D., lead author on the paper and director of the National Toxicology Program (NTP) Laboratory. "The results are unexpected and certainly give cause for concern."

About 50 percent of the male mice developed both benign and malignant lung tumors on being exposed to lower doses of arsenic. Even at lower concentrations, female offsprings developed benign tumors. They, however, did not find significant rise in lung tumors in either sex at highest dose.

"Although this is only one study, it adds to a growing body of evidence showing adverse health effects from very low exposures to arsenic, raising the possibility that no level of arsenic appears to be safe," said Linda Birnbaum, Ph.D, director of the National Institute of Environmental Health Sciences (NIEHS) and NTP.

The study appears in Archives of Toxicology.