If you eat a lot of fish and rice (and I know a lot of you do) you may want to cut back a bit on both. Fish has been the food most associated with high mercury levels and rice has been recently garnering negative attention due to dangerous levels of arsenic. Rice also contains mercury, albeit at officially “safe” levels. But things are not that simple.

Sushi isn't always as healthy as you might think. Pic: Rebecca Chai (Flickr CC)

From Rice Today, a publication of the International Rice Research Institute:

A potential problem is that, although mercury in rice is lower than in fish, a large amount of rice consumed from some contaminated areas may be enough to raise the overall consumption of mercury to a worrisome level. Since moderate mercury contamination is widespread from coal-burning exhaust, some scientists have been investigating how mercury contamination affects rice. One of the more toxic forms, methylmercury, is formed in flooded or intermittently flooded soils and is sometimes present in rice grains. Some rice varieties are better than others at excluding mercury from the grains, but we don’t know yet how they do this so we cannot recommend which varieties are the safest.

Increased industrialization has resulted in rising mercury levels from the countries where much of the rice and fish of the world are both produced and consumed. Mercury from recent emissions piles on top of old. In other words: it sticks around. New findings from Harvard University stress the importance of reducing mercury emissions precisely due to this tendency to accumulate [in] the air, soil and bodies of water.

One of the authors of the Harvard report is quoted by the Environmental News Network:

Today, more than half of mercury emissions come from Asia, but historically the U.S. and Europe were major emitters. We find that half of mercury pollution in the present surface ocean comes from emissions prior to 1950, and as a result the contribution from the U.S. and Europe is comparable to that from Asia.

–Daniel J. Jacob, Vasco McCoy Family Professor of Atmospheric Chemistry and Environmental Engineering at Harvard SEAS

So some serious reductions in mercury emissions need to take place only to stabilize current levels in the environment.

Yangtze River, China. Most mercury emissions come from coal plants. Pic: ishmatt (Flickr CC)

Yangtze River, China. Most mercury emissions come from coal plants. Pic: ishmatt (Flickr CC)

These days most mercury emissions are the result of coal fired power plants and artisanal gold mining. It first enters the atmosphere, rains down into bodies of water, gets absorbed by soil and is carried into the sea by rivers. Once it enters the oceans, microscopic organisms convert mercury into methylmercury, which accumulates in fish. Humans who consume a lot of fish are at risk for mercury poisoning; even more so are the few Japanese who eat whale and dolphin meat. 

Symptoms of mercury poisoning include neurological problems such as peripheral vision impairment, muscle weakness and loss of coordination, speech and hearing impairment and itching or pins and needles in the extremities and mouth. Fetuses are particularly sensitive to methylmercury poisoning.