The data comes from a new study by the U.S. Geologic Survey.
About 40 percent of all U.S. exposure to mercury comes from eating contaminated tuna from the Pacific. Roughly 75 percent of all human exposure to mercury in general comes from eating fish. Mercury poisoning early in life, even in very small amounts, can lead to permanent developmental effects.
Mercury becomes toxic when it is converted by bacteria into a form called methylmercury. Scientists have long known how this conversion takes place in freshwater lakes, reservoirs and rivers, but this study is the first to document how that conversion takes place in the ocean. It shows that methylmercury is produced in mid-depth ocean waters by bacteria decomposing settling algae.
Many of you are likely now aware that most fish, whether from streams, lakes, oceans or farm-raised, is contaminated with mercury and other toxins. What may be a surprise is just how much mercury contamination has increased in recent years -- 30 percent since 1990, with another 50 percent increase expected by 2050.Why is So Much Mercury Contaminating Our Oceans?
Further, a full 75 percent of all human exposure to mercury comes from eating fish, U.S. officials say, with 40 percent of that from contaminated Pacific tuna alone.
According to this latest research, the large increases are due to rapid industrialization in China, where they are constructing as many as one new coal-fired power plant a week.Mercury is Toxic for You and Your Family
Mercury is released from the smokestacks of coal-fired power plants, cement kilns and certain types of mining activities. Once in the air, the toxic mercury rains down into bodies of water. From there it is converted by bacteria into a particularly dangerous form called methylmercury, where it finds its way into fish, accumulating especially in fish that are higher up the food chain.
Fish like tuna, sea bass, marlin, and halibut show some of the worst contamination, but dozens of species and thousands of water bodies have been seriously polluted.
Asia is a growing part of the pollution problem, as winds carry the airborne toxins over the ocean, where it rains down. Ocean currents also carry the pollution throughout the basin. The United States is also a major contributor; 40 tons of mercury are released into the United States alone every year due to burning coal to generate electricity.
People who regularly eat fish have higher levels of methylmercury than those who don’t, which is concerning, considering that methylmercury toxicity can result in paraesthesia (a tingling sensation on your skin), depression, and blurred vision.Should All Tuna be Avoided?
In fetuses and developing infants it can also have negative effects on attention span, language, visual-spatial skills, memory and coordination. It is estimated that nearly 60,000 children each year are born at risk for neurological problems due to methylmercury exposure in the womb.
Even in low doses mercury can interfere with a child’s development, leading to shortened attention span and learning disabilities. These risks are incredibly prevalent, as a 2005 report from the Centers for Disease Control and Prevention found that one in 17 women of childbearing age have mercury levels (above 5.8 micrograms per liter) that could harm a developing fetus.
Mercury is especially damaging to your central nervous system (CNS), and studies show that mercury in the CNS causes psychological, neurological, and immunological problems including:• Arrhythmias and cardiomyopathiesTo make matters worse, mercury bonds very firmly to structures in your CNS. Unless actively removed, mercury has an extremely long half-life of somewhere between 15 and 30 years in the CNS!
• Personality changes and irritability
• Blurred vision
• Slowed mental response
• Unsteady gait
Tuna is a popular fish in the United States, both in canned form and at sushi restaurants. In 2007, canned tuna was the second most eaten seafood, with the average American eating nearly three pounds of it that year.How to Get the Health Benefits of Fish Without All the Risk
However, tuna can grow to be extremely large. Bluefin tuna, for instance, can weigh up to 550 pounds, and because they eat many, many small fish to grow that large, tuna may be among the most mercury-contaminated seafood out there.
In fact, laboratory tests in New York released in 2007 found so much mercury in tuna sushi that two or three pieces a week at some restaurants could be a health hazard. Plus, 10 percent of the tuna samples were unsafe for all consumers, because they contained mercury levels above 1.0 ppm, which is the legal action limit for fish sold in the U.S.
Even canned light tuna, which is touted as a safer, lower mercury seafood choice, can be unsafe. Six percent of cans tested contained more than 0.35 ppm, and as much as 0.85 ppm. White or albacore canned tuna had an average of 0.35 ppm.
If you eat a lot of fish during pregnancy, or even as little as a single serving of a highly contaminated fish, you can expose your developing child to excessive levels of mercury. The toxic metal can cross through your placenta to harm your child’s rapidly developing nervous system, including your baby’s brain.
So if you are pregnant or nursing, or planning to become pregnant, you should be very careful about eating fish. Some fish are more problematic than others. These are some of the ones you should definitely avoid if you are pregnant or nursing:• Tuna steaksIn a perfect world, fish would be a near-perfect food -- high in protein and full of essential nutrients and fats. But our world is not perfect, and, sadly, neither is our fish supply. Therefore, I do not recommend eating tuna or any fish -- unless you have lab results in your hand that can attest to its purity.
• Canned tuna
• Sea bass
• Oysters (Gulf of Mexico)
• White croaker
• Largemouth bass
Just because fish in the 21st century are nearly universally contaminated, that does not erase your genetic requirement for omega-3 fats. Just get them by taking a high-quality krill oil or fish oil, instead of risking your health by eating contaminated fish.
Eating smaller fish, like anchovies and sardines, is also an option, as their small size makes them far less likely to be contaminated.