Food & Climate
A new study found that arsenic in rice increased as carbon dioxide (CO2) levels in the atmosphere and temperatures rise.
Then epidemiologists modelled how, at current rice consumption levels, these arsenic levels could affect people’s health.
They estimated that the corresponding increases in arsenic levels in rice could contribute approximately 19.3 million more cancer cases in China alone.
The researchers grew 28 different strains of paddy rice at four different locations in China in experimental conditions over a 10-year period, according to a report seen by “Food & Climate” platform.
Arsenic can cause health impacts
“Inorganic arsenic has been shown in more studies than I can throw a stick at to be a carcinogen, to have adverse effects with respect to pulmonary health, with respect to cardiovascular health – it’s a long laundry list,” says Lewis Ziska, associate professor of environmental health science at Columbia University in New York, who co-authored the study. “And two metrics of climate change – the increase in CO2 and the increase in temperatures – are resulting in greater amounts.”
The most dire predictions assume temperatures rise by 2C, and CO2 levels increase by an additional 200 parts per million between 2025 and 2050.
While the researchers focused on locations in China for their experiments, they say such impacts are likely to be seen in rice grown in regions including Europe and the US too, as inorganic arsenic is common in rice grown around the world.
Of course, the study has limitations, aside from the metrics chosen for the 2050 scenario. For one, it assumed that people will continue to consume the same amount of rice per person in 2050 that they were eating in 2021, even though, as countries get wealthier, their rice consumption tends to drop.
On the other hand, it also assumed that people would continue to eat far more white rice than brown rice, like they do now. Because of how it is processed, white rice contains less inorganic arsenic than brown rice – so a shift in the other direction could make numbers even worse.
Over the last few decades scientists have discovered that even lower amounts of arsenic can cause health impacts when exposure happens chronically over a lifetime.
This is particularly true of inorganic arsenic, which is more readily able to attach to biomolecules in the human body where it can cause harm.
Lowering the arsenic in rice
If you want to lower your arsenic in rice, there are a few things you can do.
First, some types of rice have more inorganic arsenic than others. White rice has a lower inorganic arsenic content than brown rice but has less nutritional value. Basmati rice has less inorganic arsenic than other varieties. And rice from certain areas, including east Africa, has less arsenic than rice from other areas, including parts of the US, Europe, and south-east Asia.
Researchers at the University of Sheffield in the UK also recently discovered a way of cooking rice that can remove 50% of the arsenic in brown rice and 74% from white rice. They recommend first parboiling the rice in pre-boiled water for five minutes before draining. Then add fresh water and cook it on a lower heat to absorb all the water.
The UK’s Food Standard’s Agency recommends rinsing your rice before cooking and then boiling it in six parts water to one part rice before draining and rinsing again.
The problem comes down to how around 75% of the world’s supply of rice is grown, says Ziska – in irrigated paddy fields.
Rice tends to be choked out by weeds. But rice can grow in water, while weeds cannot. “That gives rice a big advantage over weeds, and you don’t have to spray, you don’t have to hoe,” Ziska says. “But there’s a downside. The downside is, because it’s flooded, there’s no oxygen in the soil.” In these conditions, anaerobic bacteria in the soil then turn to arsenic as an alternative to oxygen to accept electrons as they respire. These bacteria then facilitate reactions with other minerals in the soil that make the arsenic more bioavailable and easier for the rice plants to absorb through their root systems.
“When you shift the soil by making it less having less oxygen, arsenic comes into its own,” Ziska says. It changes the microbiome of the soil in such a way that arsenic-loving bacteria become more prolific.
And this is what he and his fellow researchers predict will get worse as temperature and carbon dioxide levels in the atmosphere rise. “This bacteria in the soil is getting more carbon. It’s getting warmer. And it’s being more active,” Ziska says. “It really is a synergistic effect. You’re making the little bacteria happier with warm, warmer temperatures, but you’re also giving them more carbon, and they just go crazy.”
Ziska and his team found that this effect played out for about 90% of the 28 different types of rice that they grew over their 10-year study, according to “BBC“.