Rice feeds billions. It thrives in warm, wet fields and stores energy in a way that fits busy lives and tight budgets. Those same flooded fields can also make arsenic more available to rice plants, and some of that arsenic can end up in the grain.
A growing body of field evidence points to a new twist: as the planet warms and CO₂ rises, flooded soils lose oxygen more often and for longer stretches. That chemical shift frees arsenic from soil particles, and rice roots take up more of it.
Climate, rice, and arsenic
After years of outdoor trials, researchers report that climate conditions expected by mid-century would increase the flow of inorganic arsenic – the harmful form – from soil to plant to grain.
The work appears in a leading medical journal and was conducted by teams at Columbia University’s Mailman School of Public Health, with collaborators in China and the United States.
“Our results suggest that this increase in arsenic levels could significantly elevate the incidence of heart disease, diabetes, and other non-cancer health effects,” explained Dr. Lewis Ziska, associate professor of Environmental Health Sciences at the Columbia Mailman School.
Why arsenic is in rice
Arsenic occurs naturally in many soils and waters. In paddies that stay flooded, oxygen dwindles. Iron minerals that normally bind arsenic dissolve, and arsenic becomes more mobile.
Warmer conditions paired with higher CO₂ push that chemistry along, especially in fields that remain waterlogged.
Under future settings – temperatures more than 2°C (about 3.6°F) above pre-industrial levels plus elevated CO₂ – the balance tilts toward more inorganic arsenic entering the plant.
That does not make every bowl risky. Local geology, irrigation sources, soil type, and farming practices all shape grain levels. It does mean that the odds can shift in places where paddies stay saturated for long periods.
Studying rice and arsenic
The scientists did not rely on short greenhouse trials. They grew 28 rice varieties outdoors for roughly a decade using a Free-Air CO₂ Enrichment (FACE) system.
This process releases extra CO₂ around crops in the open air so that sunlight, wind, microbes, and soil behave as they do in real life.
Those long-running field data then fed into models linking plant arsenic levels to typical rice intake and body size across major rice-eating countries in Asia.
The projections indicate a sizable shift in risk. Lifetime cancer risks, particularly for lung and bladder cancer, increased by 44% relative to ambient conditions. China alone may face 19.3 million excess cancer cases related to arsenic exposure through rice.
“From a health perspective, the toxicological effects of chronic iAs exposure are well established; and include cancers of the lung, bladder, and skin, as well as ischemic heart disease,” said Dr. Ziska.
Non-cancer outcomes also matter. The modeling points to increased risks for cardiovascular and metabolic diseases tied to long-term inorganic arsenic exposure in populations with high rice intake.
Where risks are the highest
Diet and water sources shape exposure. Regions where rice is a daily staple and paddies are often kept flooded will see the largest impacts under warmer, CO₂-richer conditions.
“Ingesting rice in regions like southern China and Southeast and South Asia is already a significant source of dietary arsenic and cancer risk,” said Dr. Ziska.
Within countries, irrigation that draws from arsenic-rich groundwater can raise grain levels. Varieties also differ in how strongly they transport arsenic from roots to grain, which creates room for practical solutions.
This is bad, what can be done?
Plant breeding can help: select and develop varieties that limit arsenic uptake even when soils push it toward the roots. Breeders already see large differences among rice lines in how much arsenic reaches the grain.
Water management is another lever. Continuous flooding increases arsenic mobility, while giving soils time to drain lets oxygen return, which can hold arsenic in less available forms.
Post-harvest steps matter too. Milling and cooking methods can reduce how much arsenic ends up on the plate.
No single fix works everywhere. Shifting water regimes, for example, can raise cadmium in some settings, so local testing and tailored management are essential to avoid trading one problem for another.
Limits and moving parts
Any mid-century projection carries uncertainty. Policies can bend emissions paths, and farmers adapt as technology and economics shift.
Diets change with income, urbanization, and migration. The underlying processes are well established. The decade of fieldwork done for this study adds weight because it includes real weather, pests, and microbial communities.
Rice, arsenic, and human health
Rice remains a staple food, and the findings from this research don’t claim that every bowl on every table becomes unsafe. Instead, the scientists point to smarter ways of managing risk and a need to act upstream.
Farmers can adjust irrigation where feasible. Breeders can favor varieties that move less arsenic to the grain. Public health agencies can track arsenic in grains and irrigation sources to guide choices in hotspots.
“Our study underscores the urgent need for action to reduce arsenic exposure in rice, especially as climate change continues to affect global food security,” said Dr. Ziska.
Keeping rice safe in a warming world is within reach: breed smarter, water smarter, process smarter—and cut emissions, because the air over our fields follows us to the table.
The full study was published in the journal The Lancet Planetary Health.
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