Arsenic levels in drinking water deemed safe in the U.S. have negative health effects on pregnant mice and their offspring, according to a new study, and the findings could have implications for people, the researchers say.

Pregnant and lactating mice that drank water with 10 parts per billion (ppb) of arsenic had disruptions in their fat metabolism, leading to a reduction of nutrients in the mice’s blood and breast milk. The Environmental Protection Agency limits arsenic levels in drinking water to 10 ppb.

The reduction in nutrients had little effect on the offspring's birth weight and whether they were born on time, but it did lead to growth and developmental deficits in the young mice. Right before weaning, the pups were smaller than normal, and malnourished.

“We have to think again about whether 10 ppb arsenic as a U.S. drinking water standard is safe and protective of human health,” said study author Joshua Hamilton, a senior scientist in the Marine Biological Laboratory in Woods Hole, Mass.

The study also adds to the evidence that pregnant women and their offspring are uniquely sensitive to chemicals in their environments, Hamilton said. The researchers said that it may be that exposure to arsenic is more harmful when there is also a second source of stress on the body, such as pregnancy or lactation.

Researchers have linked arsenic with negative health effects in people, such as increased risks of respiratory infections and cancer. However, most work has been done in countries with markedly high arsenic levels, in the range of several hundred ppb, according to the study.

The female body has a protective mechanism that fully nourishes her offspring, even at her own expense, if necessary. But in mice that were exposed to arsenic in the study, this mechanism was compromised, and lower levels of nutrients were found in the breast milk, the researchers said.

The study showed that the nursed pups received fewer nutrients, and also were exposed to some arsenic, which is particularly problematic for young animals that are rapidly growing.

“It's not hard for very low doses of a chemical to have big effects on a developing animal,” Hamilton said.

When the researchers moved the pups, so they were nursed by a female who had no arsenic exposure, they grew quickly enough to make up for their growth deficits, although only male pups made a complete recovery.

The mice exposed to arsenic also saw abnormal accumulation of in their livers, a condition known as hepatic steatosis.

The researchers noted that in U.S. regions where water comes from private wells, arsenic levels are higher than the EPA limit — they can be over 100 ppb — due to high abundance of arsenic in the environment. Parts of New England, the upper Midwest, the Rockies, Florida and the Southwest are affected.

For municipal water sources, information on arsenic levels is publicly available, and tests can measure arsenic levels in private wells, the researchers said.

Because the study was performed on mice, it is not known whether the results apply to humans.

Still, Hamilton said, “the message here is, ‘Pay attention to your total arsenic exposure, both in drinking water and also in food.'” Hamilton said. “Pregnant women, especially, need to be very careful and protective of their health.”

The study was published today (May 31) in the journal PLOS One.

Pass it on: Exposure to arsenic during pregnancy might affect developmental and physical growth, a new study on mice suggests.

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