Posted on Sun, 19 Sep 10
Rice, a staple food for more than half the world population, may be a significant source of toxic mercury. This discovery raises new concerns about the health risks associated with mercury exposure.
A study in China has found that in areas where heavy pollution from mining and coal has released mercury into the environment contaminated rice is raising mercury intakes above acceptable limits (1).
Once released into the environment mercury is metabolised by aquatic bacteria into more toxic methylmercury which concentrates up the food chain in predatory species such as fish. This process occurs in the world’s oceans and rivers but may also occur in the water rich environment of rice paddies.
Mercury is particularly toxic and low-level exposure may affect mood and cognitive function, increase heart disease risk and impair child brain development (2). Until this report the major source of exposure was thought to be fish.
A press release in Environmental Health Perspectives commented that “it is unknown whether methylmercury limits, which are based on fish consumption, provide adequate protection for a population with rice-based exposure because rice lacks the micronutrients found in fish that might partly offset neurotoxicity. Given that heavy inorganic mercury pollution exists in other rice-growing regions of Asia, further investigation is critical to assess exposure and correlate it with human biomonitoring (especially for pregnant women) and potential health effects (3).”
1. Zhang H, et al. In inland China, rice, rather than fish, is the major pathway for methylmercury exposure. Environ Health Perspect. 2010 Sep;118(9):1183-8.
2. Holmes P, James KA, Levy LS. Is low-level environmental mercury exposure of concern to human health? Sci Total Environ. 2009 Dec 20;408(2):171-82
3. Barrett JR. Rice is a significant source of methylmercury: research in china assesses exposures. Environ Health Perspect. 2010 Sep;118(9):a398.