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Whether it's the legacy of toxic arsenic-based pesticides used on apple orchards and cotton fields or the naturally occurring arsenic in irrigation water and soil, this heavy metal has become pervasive in our diets. And a new study from Dartmouth University researchers has concluded that foods that contain arsenic could easily be your primary exposure sources for this harmful metal.

After comparing arsenic levels found in about 850 people's toenails (over time, arsenic concentrates in the keratin your body uses to create nails) with food questionnaires, Dartmouth researchers concluded that "diet can be an important contributor to total arsenic exposure in U.S. populations, regardless of arsenic concentrations in drinking water." Although the Environmental Protection Agency has set limits for arsenic in municipal water supplies, the metal isn't regulated in private wells used for drinking and irrigation. and its presence has always been an issue for people who survive off well water.

"After we accounted for exposures via water, we still saw high levels of exposure from food," says lead author Kathryn Cottingham, PhD, professor of biological sciences at Dartmouth. However, she adds, "We can't say much about the potential for harm because we don't know the health risks yet for the levels we found."

Although it's fatal at high doses, the low levels of arsenic in food don't cause immediate health problems for the average person, but with chronic exposures, their dangers can be serious. Long-term exposure to the metal is known to cause lung, kidney, skin, and bladder cancers, and it interferes with estrogen and testosterone, as well as with the hormones that regulate your metabolism and immune system. The Food and Drug Administration (FDA) has been trying to decide how to cope with foods that contain arsenic ever since independent tests by Consumer Reports magazine and others revealed high levels of arsenic in rice, apple juice, and other processed foods. The agency has never set a limit on how much of the metal can be allowed in food.

"My advice," says Cottingham, "if there are foods that are high in arsenic, just don't eat them all the time."

Based on the Dartmouth study results, here are 5 foods that shouldn't make regular appearances in your daily diet:

1. Brussels sprouts

Despite the fact that these vegetables are among the healthiest you can eat, Cottingham's research, along with others studies, note that inorganic arsenic that exists in soil is highly attracted to sulfur compounds in brussels sprouts, along with other "super-veggies" in the cruciferous family, including kale, broccoli, and cauliflower. The arsenic could also come from contaminated irrigation water, or even your own cooking water if you happen to draw your water from a private well. Arsenic levels in regular sprout eaters were 10.4 percent higher than in people who never ate them or ate them less than once a month.

2. Dark-meat fish

Arsenic exists naturally in seawater and, as a result, it exists naturally in fish. However, the forms of arsenic usually detected in seafood are organic, which are presumed to be relatively harmless. They usually clear your body a few days after they're consumed. But this study found inorganic forms of arsenic were 7.4 percent higher in people eating dark-meat fish (tuna, mackerel, salmon, sardines, bluefish, and swordfish) once a week, compared to people who ate them less than once a month. And that's concerning, Cottingham says. It suggests that the body can metabolize organic arsenic into the inorganic forms that cause cancer and other health problems, or that the organic forms of arsenic are as harmful as the inorganic forms. "That's part of the reason the FDA has had such a hard time acting on arsenic in rice," she says. "It's not just inorganic arsenic that we need to be concerned about. Some forms of organic arsenic are toxic, too." The problem, she adds, is that scientists don't know enough about the various organic forms to determine which are harmful and which aren't. Since all seafood tends to be high in arsenic, Cottingham says, make it an occasional meal.

3. Rice

Cottingham's study didn't show a significant association between rice consumption and arsenic levels, but that's likely due to the fact that her study participants weren't big rice eaters. They reported eating one to three cups of white rice a month, whereas arsenic is found in much higher levels in brown rice. Other studies, though, are "pretty compelling," she says, showing that people who eat rice closer to the amount the average American does (about half a cup per day) have consistently high arsenic levels. Consumer Reports suggests restricting your rice intake to two servings per week.

4. Chicken and other poultry

Like rice, chicken and other poultry weren't a big hit with this population, but Cottingham says these meats are still concerning. Poultry birds are regularly given feed containing with arsenic-based drugs, which studies have shown, lead to an elevated level of arsenic in their meat. Thankfully, the FDA recently revoked approvals for three out of four of these toxic feed additives, but industry experts estimate that it'll be at least a year before producers run through the remaining supplies of their arsenic-laced feed. Continue to opt for organic poultry, which is raised without the use of arsenic feed additives.

5. Beer and Wine.

Call it the contaminant that killed your happy hour: In the Dartmouth study, men who had 2.5 beers per day had arsenic levels over 30 percent higher than nonconsumers, and women who drank five to six glasses of wine per week had levels 20 percent higher than nonconsumers. The arsenic may be coming from the water used to brew these beverages, but beer and wine producers also use a filtration material, diatomaceous earth, that's know to harbor arsenic; it's made up of ground fossils collected from ocean and lake floors. The good news is that some producers are moving away from using diatomaceous earth since it can pose inhalation problems for workers, but there's really no way to know whether your favorite producer uses it unless you ask.

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