Key points for Mercury in Rice:
Mercury from air pollution accumulates in rice
Mercury in rice may be high enough to harm brain development
Relying on rice as a staple food may be bad idea.
We know mercury is bad for you. It harms brain development and increases risk of heart disease. There is also evidence that it may increase risk of diabetes (Jeppesen et al. 2015). It is especially bad for pregnant women, young infants and women who may become pregnant because of the harm it may do to their future children. Women and children (as well as men) are advised to limit the amount of mercury they eat by limiting intake of some kinds of fish. Older, larger predators (swordfish, tuna) that eat high on the food chain are likely to have the most mercury. Younger, smaller fish have less time to build up mercury in their tissues. They are thus less likely to pass it on to human consumers. Fish, especially oily fish, has a lot of health benefits though. Fish, or oil from fish, has been associated with reduced cardiovascular disease, less depression, and higher IQ. Regulators have tried to balance risk from mercury against some of the health benefits of fish. That’s a tough one. The best strategy seems to be to limit high-risk fish, and enjoy lower risk fish.
Mercury in Rice: how it gets there
Mercury in rice starts with burning of coal, trash, and forest fires. Mercury is released to air. Mercury can travel the globe and is widely distributed. The most dangerous form of mercury is methyl-mercury. This is mercury that has entered the environment and been transformed from elemental mercury to mercury with a methyl group on it. The methyl group lets mercury lodge in fatty tissue, including the brain and other nervous tissue. Methylation is done by bacteria in low-oxygen conditions. The bacteria transform the mercury, small mud-dwellers pick it up. The mud-dwellers get eaten by fish. Which get eaten by larger fish. Which get eaten by us . . . where the mercury stays. The bacteria that transform mercury are found on lake, river and ocean bottoms. But these same bacteria are also found in rice paddies. This mercury starts with air pollution, which settles in agricultural areas. Sometimes far-away agricultural areas, but ends up in rice. Scientists at the University of South Carolina and in China have been studying mercury in rice and its effects on children who do not eat fish (Rothenberg et al. 2016). These are important studies because they show how mercury impacts children without the beneficial effects of fish confusing the picture. A strategy to reduce mercury exposure may be to reduce the amount of rice you eat.
Babies, Children and Mercury in Rice
So far the effects observed have been small, but measureable, declines in cognition. Or IQ to simplify things. It is important to note that the people studied live in China, and eat more rice than most Americans. I asked the lead researcher, Susan Rothenberg, if American rice had less mercury than rice in China. “unfortunately, American rice has similar levels of Mercury.” So . . . it looks like buying local, or American rice, will not help. Something that may be important is that rice is a staple food for babies. It is often the first solid food we feed our children. One of the reasons we are advised to eat a varied diet is so that we will get a wide range of nutrients. It can also be important to eat a varied diet so that you do not get too much of a particular contaminant like mercury. I would not know what to suggest to parents, other than to talk to your baby’s pediatrician or dietary specialist for questions about child nutrition. Varying a young child’s diet can be challenging. Sorry there. More research is coming out and we may reinvestigate mercury exposures in children. Till then, less rice, perhaps. Oh. And clean air is important.
Genchi G, Sinicropi MS, Carocci A, Lauria G, Catalano A. 2017. Mercury exposure and heart diseases. Int. J Environ Res Public Health. 14(1): pii: E74. doi: 10.3390/ijerph14010074
Jeppesen C, Valera B, Nielsen NO, Bjerregaard P, Jorgensen ME. 2015. Association between whole blood mercury and glucose tolerance among adult Inuit in Greenland. Environ Res. 142(PtA): 192-7.
Rothenberg SE, Yu X, Liu J, Biasini FJ, Hong C, Jiang X, Nong Y, Cheng Y, Korrick SA. 2016. Maternal methylmercury exposure through rice ingestion and offspring neurodevelopment: a prospective cohort study. Internaional Journal of Hygiene and Environmental Health. (In Press).