[NAIROBI] Climate change, combined with rising carbon dioxide levels, may significantly impact arsenic levels in paddy rice, potentially raising lifetime health risks for consumers, according to a new study.
Long-term exposure to inorganic arsenic can lead to cancers of the lung, bladder, and skin, as well as heart disease and diabetes, according to the study published in the journal The Lancet Planetary Health.
Inorganic arsenic is formed when arsenic combines with non-carbon-containing elements, such as oxygen or sulphur. It is far more toxic than organic arsenic compounds, such as those found in seafood.
The study by Columbia University’s Mailman School of Public Health, in New York, and the Chinese Academy of Sciences shows that increased temperatures above two degrees, coupled with rising carbon dioxide levels, lead to higher concentrations of inorganic arsenic in rice.
As rice is a dietary staple in many parts of the world, these changes could lead to a substantial rise in the global burden of cancer, cardiovascular diseases, and other arsenic-related health issues especially for populations in Asia by 2050, according to the researchers.
“Ingesting rice in regions like southern China and Southeast and South Asia is already a significant source of dietary arsenic and cancer risk,” said Lewis Ziska, an associate professor in environmental health sciences at the Mailman School of Public Health and lead researcher of the study.
Ziska explained that the higher arsenic levels are likely due to climate-related changes in soil chemistry that make it more easily absorbed into rice grain.
Climate experts predict an increase in global temperatures of 2.7 degrees above pre-industrial levels by 2100, if current policies remain unchanged. This is significantly higher than the 1.5 degrees limit outlined in the Paris Agreement, which would help mitigate the worst impacts of climate change.
According to the World Meteorological Organization, carbon dioxide in the atmosphere reached record levels of 420 parts per million in 2023 – 1.5 times pre-industrial levels and the highest in 800,000 years.
In their study, the researchers measured the effects of rising temperatures and carbon dioxide on 28 rice strains over ten years in the field. They used a method called Free-Air CO2 Enrichment, which involves elevating levels of CO2 in a specified area, and advanced modelling techniques.
This helped them estimate inorganic arsenic doses and health risks, including for cancer, in seven Asian countries: Bangladesh, China, India, Indonesia, Myanmar, the Philippines and Vietnam.
A farmer walking through a paddy rice field. Researchers warn that increases in arsenic in rice could lead to a rise in the global burden of cancer. Photo Copyright: chiến nguyễn bá from Pixabay
Country estimates of rice availability in 2021, as reported by the Food and Agriculture Organization were used as the starting point for estimating rice ingestion. The standard deviation of rice ingestion per kilogram bodyweight from US Environmental Protection Agency data was used to create a normal distribution for each country.
“We found that concurrent increases in temperature and CO2 can act synergistically to increase inorganic arsenic in multiple rice lines that are grown throughout Southeast Asia and that this increase will alter the health consequences…for rice consuming populations,” Ziska told SciDev.Net.
He noted that until now, the combined effects of rising carbon dioxide and temperatures on arsenic accumulation in rice have not been studied in detail.
“We have known that paddy rice can also absorb inorganic arsenic – the facilities in China were a unique opportunity to do both CO2 and temperature under field conditions,” he told SciDev.Net.
Limiting harm
The researchers suggest several actions that could help reduce arsenic exposure in the future.
“These include efforts in plant breeding to minimise arsenic uptake, improved soil management in rice paddies, and better processing practices,” Ziska said.
“Along with public health initiatives focused on consumer education and exposure monitoring, [these] could play a critical role in mitigating the health impacts of climate change on rice consumption.”
Geoffrey Onaga, associate research scientist at the Africa Research Center in, Côte D’Ivoire, who was not involved in the study, says the link between arsenic in rice and climate change is credible.
He noted that multiple approaches can be employed to reduce arsenic levels in rice grains including strategies during rice cooking.
“Research shows that the proportion of rice grains used for cooking, the volume of water employed for washing, the types of cooking vessels, and the length of the cooking process can reduce the arsenic levels in cooked rice,” he said.
Onaga says adding mineral nutrient elements such as silicon, phosphorus and iron when growing rice can significantly reduce the accumulation of arsenic in the grain by minimising its uptake in crops.
“Phosphorus and silicon exhibit complementary characteristics to arsenic in their competition for uptake,” he told SciDev.Net.
“Consequently, the external application of these mineral nutrients reduces the likelihood of arsenic absorption from the soil.”
Jauhar Ali, a principal scientist at the International Rice Research Institute, says researchers are developing rice varieties with better arsenic tolerance.
“We have advanced breeding lines that has reduced arsenic in rice grain. [However,] breeding new arsenic safe rice lines and mainstreaming requires funding,” Ali said.
This piece was produced by SciDev.Net’s Asia & Pacific desk.
