First it was apple juice. Now researchers say there is inorganic arsenic in rice, and that it could particularly affect pregnant women, CBS News reports. Arsenic is able to cross the placenta and may harm a developing baby.

For the study, researchers measured arsenic levels in the urine of 229 pregnant women in New Hampshire, a state where 40% of people get their water from wells. (Well water sometimes has higher arsenic levels than tap water, which must meet federal safety standards.)

Researchers checked the women's tap water for arsenic. They also asked the women to write down what food they had eaten in the three days before their urine tests.

Even after accounting for arsenic in drinking water, researchers found that women who had recently eaten rice had slightly higher levels of inorganic arsenic — the toxic form — in their urine, compared to women who had not eaten rice.

“Rice, which I think a lot of people would think of as very healthy, may be a real source of exposure to inorganic arsenic, above and beyond drinking-water arsenic,” Michael S. Bloom, PhD, an assistant professor at the University at Albany in New York, told CBS.

Bloom, who is studying the health effects of chronic arsenic exposure, was not involved in the current research.

For the average person, that means “you may be receiving an additional daily dose through rice. It adds to the cumulative burden of inorganic arsenic exposure,” he said.

Researchers calculated that women who ate just a half-cup of cooked rice each day — the average amount eaten in the study — would be getting just as much arsenic as if they drank a liter of tap water at the EPA's maximum allowable limit for arsenic.

Each gram of rice the women ate was associated with a 1% increase in their arsenic levels. A gram of rice is about 48 grains.

Previous studies have linked high arsenic levels in pregnant women to an increased risk of miscarriage. Exposure to arsenic in the womb has also been associated with lower birth weights in children and an increased risk of infant mortality. Most of those studies were in developing countries, however, where women had arsenic levels that were 50 to 200 times higher than those seen in this study.

“Obviously, people don't eat rice and drop dead the next day. You're looking at probably a chronic effect on health,” said researcher Tracy Punshon, PhD, a research assistant professor in the department of biological sciences at Dartmouth College.

Studies have shown, for example, that people with long-term exposure to arsenic have higher rates of skin, lung, and bladder cancers. Arsenic has also been linked to higher rates of cardiovascular disease.

The researchers say their study highlights the need to regulate arsenic in food and in rice.

Punshon said people should be choosy about the kinds of rice they eat and make sure it's not the only grain in their diet. Rice grown in the United States, for example, has been shown to have higher arsenic levels than jasmine or basmati rice grown in Thailand or India. Also, her studies have found that brown rice contains higher levels of arsenic than white rice, because arsenic concentrates in the outer layer of rice bran.

“What really worries me is that the gluten-free movement is using a lot of rice, specifically brown rice,” Punshon says. Brown rice turns up in a lot of products like cereal, rice syrup, baking mixes and crackers. (It's also a staple of macrobiotic diets.)

“If you replace all the grains in your diet with brown rice, you're putting yourself in a very unique exposure window,” for arsenic, she says, but adds, “We don't want to scare people off rice. It's still a healthy food.”

Follow Samantha Bonar @samanthabonar.

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