BOSTON—Less is better. That much is clear about arsenic, the naturally occurring metal in soil and rock that sneaks into well water and infiltrates food crops. High levels in drinking water are linked to multiple cancers, lung and cardiovascular disease, and neurodevelopmental delays in children. But it’s not so clear exactly what levels are acceptable in food, and how best to limit our exposure. And concern is growing—particularly when it comes to rice, which is known to accumulate arsenic more readily than many other plants. At a session yesterday here at the annual meeting of AAAS, which publishes Science, researchers described efforts to keep the toxin out of our crops and off our plates.
Arsenic gets into plants through a “case of mistaken identity,” plant biologist David Salt of the University of Nottingham in the United Kingdom explained yesterday. It offers no benefit to a plant, but enters its roots thanks to mechanisms meant to bring in nutrients such as silicon. Several labs are working to describe the mechanisms of these cellular transporters, and eventually to render them more selective. That could happen through genetic engineering with a system such as CRISPR, he says. But it might also be possible through traditional breeding of plant varieties with a natural tendency to keep arsenic out. Salt and others are now testing the arsenic uptake in hundreds of rice varieties to identify relevant regions of their genome. “We’re closing in on genes,” he says, but “we don’t have genes yet.”
In parts of Asia, dangerous arsenic levels can arise when rice and other crops are irrigated with well water drawn from deep within arsenic-rich rock. And growing rice in flooded fields has been shown to increase its levels in the grain 10-fold by converting arsenic to a form that the roots take up more readily. Some researchers are exploring the effect of water-conserving strategies that allow fields to dry partially before reflooding. But plant biologist Mary Lou Guerinot of Dartmouth College, who organized the session, notes that those strategies will have to balance arsenic risk against another risk—higher uptake of the toxin cadmium in unflooded fields.
For U.S. policymakers, even the scale of the arsenic problem is hard to estimate, explained panelist Keeve Nachman, an environmental health scientist with the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland. Since 2013, the U.S. Food and Drug Administration has proposed limits on allowable arsenic levels in apple juice and infant rice cereal. But there’s still heated debate about what levels of exposure actually increase risk of cancer or other illnesses. Nachman, who is part of a 2-year effort known as the Collaborative on Food with Arsenic and Associated Risk and Regulation, aims to inventory the foods that can contain arsenic and prioritize those that may contribute most to our overall intake. Pressure on regulators and farmers to keep levels low will likely come from consumers, he says. “They’re the ones that drive change in the first place.”
Check out our full coverage of AAAS 2017.