Rice is the largest global staple crop, consumed by more than half the world's population -- but new experiments from Stanford University suggest that with climate change, production in major rice-growing regions with endemic soil arsenic will undergo a dramatic decline and jeopardize critical food supplies.
Arsenic is a chemical that is found naturally in the soil, and is not generally transmitted to plants, but according to the new study, climate changes can transfer it, especially to rice.
The experiments' findings, which are published in the Nature Communication journal, show that rice production in future climate conditions could drop about 40 percent by 2100, and that changes to soil processes due to increased temperatures will cause rice to contain a high level of arsenic.
The researchers specifically looked at rice because it is grown in flooded paddies that help loosen the arsenic from the soil and make it especially sensitive to arsenic uptake.
While many food crops today contain small amounts of arsenic, future changes in soil due to higher temperatures combined with flooded conditions cause arsenic to be taken up by rice plants at higher levels, and using irrigation water with naturally occurring high arsenic exacerbates the problem.
While these factors will not affect all global commodities in the same way, they do extend to other flood-grown crops.
The researchers created future climate conditions in greenhouses based on estimates of a possible 5 degree Celsius temperature increase and twice as much atmospheric carbon dioxide by 2100, as projected by the Intergovernmental Panel on Climate Change.
While previous research examined the impacts of increasing temperature in the context of the global food crisis, this study was the first to account for soil conditions in combination with shifts in climate.
For the experiments, the group grew medium-grain rice. The greenhouses were controlled for temperature, carbon dioxide concentrations and soil arsenic levels, which will be higher in the future due to its buildup in soils from irrigating crops with arsenic-contaminated water, a problem that is worsened by over-pumping groundwater.
The researchers found that with increased temperatures, microorganisms destabilized more of the soil's inherent arsenic, leading to greater amounts of the toxin in the soil water that is available for uptake by the rice. Once taken up, arsenic inhibits nutrient absorption and decreases plant growth and development, factors that contributed to the 40 percent decrease in yield the scientists observed.
Scott Fendorf, co-author and professor at the University of Stanford said "The findings highlight a 'dangerous issue' that would lead to negative consequences on the global food security".
In a report published on the university's website, Fendorf said: "By the time we get to 2100, we're estimated to have approximately 10 billion people, so that would mean we have 5 billion people dependent on rice, and 2 billion who would not have access to the calories they would normally need. We have to be aware of these challenges that are coming so we can be ready to adapt."
Dr. Khaled Abdel Sattar, nutrition expert at the Egyptian Ministry of Health, sees that along the crop failure challenge, the high levels of arsenic highlighted in the study is concerning, not only because of rice's global significance, but also because it is a low-allergen food often introduced early to infants.
"Because infants are a lot smaller than we are, if they eat rice, that means that they take up more arsenic relative to their body weight," he added. Chronic exposure to arsenic leads to skin lesions, cancers, aggravation of lung diseases and ultimately death.