Rising CO2 and temperatures make rice more toxic – The Lancet

Rice, the most widely consumed grain in the world, is likely to become increasingly toxic as global temperatures and carbon dioxide levels rise, according to new research published in The Lancet on April 17.

The findings suggest that billions of people who depend on rice as a staple food could face heightened health risks from exposure to arsenic, a known carcinogen.

A team of researchers from the United States and China, led by Lewis Ziska, a plant physiologist and associate professor at Columbia University, found that higher concentrations of carbon dioxide and increased temperatures – both key consequences of climate change – cause rice to absorb greater amounts of arsenic. “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,” said Ziska.

The study involved growing various rice species in controlled agricultural settings over a six-year period. By manipulating the levels of CO₂ and temperature to reflect projections based on current emissions trajectories, the researchers discovered a significant rise in both total arsenic and the more harmful inorganic arsenic within the rice grains.

Arsenic, which can be found naturally in soil and water or introduced through industrial pollution, is easily absorbed by rice due to the way it is cultivated. Most rice is grown in flooded paddies, where submerged conditions suppress weeds but facilitate the uptake of minerals and contaminants through the water. “What happens in rice, because of complex biogeochemical processes in the soil, when temperatures and CO₂ go up, inorganic arsenic also does,” said Ziska. “And it’s this inorganic arsenic that poses the greatest health risk.”

Exposure to inorganic arsenic has been associated with cancers of the skin, bladder and lung, cardiovascular disease, and neurological damage, particularly in infants. Previous studies have already shown that populations with high rice consumption may face increased cancer risks due to arsenic content.

“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.”