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How safe is our drinking water? Baby mice have severe growth problems when their mothers were given water containing arsenic – at levels considered safe for humans – when they were pregnant and lactating.

Arsenic in drinking water has been linked to many health problems. The US Environmental Protection Agency (EPA) states that water containing up to 10 parts per billion (ppb) of arsenic is safe. As many as 25 million people in the US, and many more worldwide, get their water from unregulated wells and so drink water with an arsenic concentration that exceeds this level.

Joshua Hamilton at the Marine Biological Laboratory in Woods Hole, Massachusetts, and his colleagues gave water containing arsenic at 10 ppb to pregnant and lactating mice, then monitored the development of their pups.


The pups grew more slowly than those in a control group containing mother mice that drank arsenic-free water. The arsenic was not passed to the pups through their mother’s milk, but it limited the nutrients that the milk contained.

Humans and mice show significantly different responses to arsenic, but the results are still important, says David Polya at the University of Manchester, UK, who was not involved in the work. “The adverse health effects observed here add support to concerns over the adequacy of the 10 ppb recommendation.”

Level drop

The EPA last reduced the recommended limit in 2001. Until then, it had been set at 50 ppb. It was lowered to 10 ppb after concerns about cancer risks.

“Since then, research at lower and lower exposure levels have been performed,” says Clark Lantz at the University of Arizona in Tucson.

The EPA is convening an advisory panel to evaluate the human and animal data on arsenic risk for non-cancer diseases to determine whether the 10 ppb limit is adequate to protect human health, says Aaron Barchowsky at the University of Pittsburgh in Pennsylvania.

“An important question is whether reducing the current limit further would be an improvement for public health that is economically sustainable,” he says, adding that reducing the limit to 2 ppb could cost trillions of dollars to enforce in the US.

Journal reference: PLoS One, DOI: 10.1371/journal.pone.0038249