Another problem with China’s coal: Mercury in rice

Mercury pollution is a problem usually associated with fish consumption.

Pregnant women and children in many parts of the world are advised to eat fish low in mercury to protect against the adverse health impacts, including neurological damages, posed by a particularly toxic form of mercury, methylmercury.

But some people in China, the world’s largest mercury emitter, are exposed to more methylmercury from rice than they are from fish. In a recent study, we explored the extent of this problem and which direction it could go in the future.

We found that China’s future emissions trajectory can have a measurable influence on the country’s rice methylmercury. This has important implications not only in China but across Asia, where coal use is increasing and rice is a staple food. It is also relevant as countries across the world implement the Minamata Convention, a global treaty to protect human health and the environment from mercury.

Why is mercury a problem in rice?

Measurements of methylmercury in rice in China from the early 2000s were in areas where mercury mining and other industrial activities led to high mercury levels in soil that was then taken up by rice plants. More recent research, however, has shown that methylmercury in rice is also elevated in other areas of China. This suggests that airborne mercury – emitted by sources such as coal-fired power plants and subsequently settling onto the land – might also be a factor.

To better understand the process of methylmercury accumulation in rice through deposition – that is, mercury originating from the air that rains out or settles to the land – we constructed a computer model to analyze the relative importance of soil and atmospheric sources of rice methylmercury. Then we projected how future methylmercury concentrations could change under different emissions scenarios.