Rice is a staple crop around the world—but it’s becoming increasingly toxic

Rice, the world’s most consumed grain, will become increasingly toxic as the atmosphere heats and as carbon dioxide emissions rise, potentially putting billions of people at risk of cancers and other diseases, according to new research published Wednesday in The Lancet. 

Eaten every day by billions of people and grown across the globe, rice is arguably the planet’s most important staple crop, with half the world’s population relying on it for the majority of its food needs, especially in developing countries.

But the way rice is grown—mostly submerged in paddies—and its highly porous texture means it can absorb unusually high levels of arsenic, a potent carcinogenic toxin that is especially dangerous for babies.

Lewis Ziska, a plant physiologist and associate professor at Columbia University, has studied rice for three decades and has more recently focused his research on how climate change reduces nutrient levels across many staple crops, including rice. He teamed up with researchers from China and the U.S. to conduct a first-of-its-kind study, looking at how a range of rice species reacted to increases in temperature and carbon dioxide, both of which are projected to occur as more greenhouse gas emissions are released into the atmosphere as a result of human activities. The new study was published in The Lancet Planetary Health.

“Previous work has focused on individual responses—some on CO2 and some on temperature, but not both, and not on a wide range of rice genetics,” Ziska said. “We knew that temperature by itself could increase levels, and carbon dioxide by a little bit. But when we put both of them together, then wow, that was really something we were not expecting. You’re looking at a crop staple that’s consumed by a billion people every day, and any effect on toxicity is going to have a pretty damn large effect.”

For six years, Ziska and a large team of research colleagues in China and the U.S. grew rice in controlled fields, subjecting it to varying levels of carbon dioxide and temperature. They found that when both increased, in line with projections by climate scientists, the amount of arsenic and inorganic arsenic in rice grains also went up.  

Arsenic is found naturally in some foods, including fish and shellfish, and in waters and soils.

Inorganic arsenic is found in industrial materials and gets into water—including water used to submerge rice paddies.  

Rice is easily inundated with weeds and other crops, but it has one advantage: It grows well in water. So farmers germinate the seeds, and when the seedlings are ready, plant them in wet soil. They then flood their fields, which suppresses weeds, but allows the rice to flourish. Rice readily absorbs the water and everything in it—including arsenic, either naturally occurring or not. Most of the world’s rice is grown this way.

The new research demonstrates that climate change will ramp up those levels. 

“What happens in rice, because of complex biogeochemical processes in the soil, when temperatures and CO2 go up, inorganic arsenic also does,” Ziska said. “And it’s this inorganic arsenic that poses the greatest health risk.”

Exposure to inorganic arsenic has been linked to cancers of the skin, bladder and lung, heart disease and neurological problems in infants. Research has found that in parts of the world with high consumption of rice, inorganic arsenic increases cancer risk.

Ziska and his colleagues took the data from their field trials and then, based on per capita consumption data in seven of the top rice-consuming countries in Asia, projected how disease risk could also increase. They found that in those seven countries—Vietnam, Indonesia, China, Bangladesh, the Philippines, Myanmar, and India—disease risk rose across the board.  

“There is a toxicological effect of climate change relative to one of the most consumed staples in the world,” Ziska said, “and the consumption is one of the hallmarks of whether you’re going to be vulnerable to that effect.”

Researchers have known that rice can contain high levels of arsenic and regulators have suggested exposure limits, especially for infants who are particularly vulnerable and tend to eat a lot of rice. This new research should put extra pressure on regulators to set more stringent thresholds, the authors say. The U.S. Food and Drug Administration has never set limits for arsenic in foods.

The researchers also point to the potential of various interventions that could limit exposure to inorganic arsenic from rice, including developing strains of rice that are less absorbent and educating consumers about alternatives to rice.

“Rice has always been a food where arsenic is an issue, and climate change is making it worse,” said Keeve Nachman, one of the report’s authors, a professor at Johns Hopkins University and a longtime researcher of health risks related to food production and consumption. “This is one more reason to intervene—to control people’s exposure. The number one thing we can do is everything in our power to slow climate change.”

—Georgina Gustin, Inside Climate News

This article originally appeared on Inside Climate News. It is republished with permission. Sign up for their newsletter here.

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