Mercury in Fish: A Stubborn Pollutant’s Harmful Legacy

by | Mar 6, 2024 | Diet & Nutrition, Mercury / Dental Amalgam

Even though more dentists have moved away from filling teeth with mercury amalgam, the dental industry still uses up to 322 metric tons of dental mercury every year. And every year, as much as 35 tons of it gets released into the environment, much of it in dental office waste water. Other pathways include dental waste incineration, dental clinic emissions, cremation, and burial.

This pollution is compounded by mercury emissions from coal burning, mining, and other sources, much of which winds up in our oceans. When this mercury settles in the water, bacteria convert it to methylmercury, which builds up in the tissues of fish and other marine life as they feed. Larger predatory fish that eat many smaller contaminated fish end up with higher levels of mercury in their bodies.

This is how mercury makes its way up the food chain, leading to contamination in fish that could potentially be consumed by humans.

Now, you’d think with the concerted efforts that have been made to reduce mercury pollution, we’d be seeing at least somewhat lower levels of mercury in fish. New research in Environmental Science & Technology Letters, however, shows that this isn’t the case at all.

As the New York Times recently reported,

In an extensive effort that began more than a decade ago, scientists collected and combined previously published findings with their own data on mercury levels from nearly 3,000 samples from tuna caught in the Pacific, Atlantic and Indian Oceans between 1971 and 2022. They specifically looked at tropical tuna — skipjack, bigeye and yellowfin — which make up 94 percent of the global tuna catch.

They found that, in contrast to a global decrease in mercury emissions since the 1970s, mercury levels in tuna remained virtually unchanged. In skipjack caught in some parts of the Pacific, mercury levels rose, mirroring an increase in mercury emissions from Asia, they said.

The stubbornly high levels of mercury in tuna had to do with ocean mixing, which is churning up mercury that’s lurked for decades in the ocean’s depths.

Other fish that typically contain high levels of mercury include King mackerel, swordfish, marlin, orange roughy, and tilefish. Those with the lowest levels include sardines, salmon, cod, catfish, and tilapia.

Yet the answer isn’t necessarily to avoid all fish. After all, fish is a great source of omega-3 fatty acids which, among other things, support healthy gums. The key is to focus on fish that tend to be lowest in mercury while limiting consumption of those that are highest in mercury.

The National Resources Defense Council (NRDC) has a free, downloadable guide to mercury in fish which you can tuck away in your wallet as a handy reference while shopping or when dining out. In addition to categorizing fish by their mercury content, it also provides guidance on how frequently to eat from each group.

You can download a copy here.

But before we go, let’s go back to one more passage from that New York Times report: its description of some of the harms that can come from mercury exposure:

Even in small amounts, [mercury] can harm the brains of unborn children and have toxic effects on the human nervous, digestive and immune systems. The Environmental Protection Agency estimates that more than 75,000 newborns in the United States may have increased risk of learning disabilities linked to mercury exposure in the womb.

True, true, all true – except you don’t even need to eat fish to be exposed to this neurotoxic element if you’re one of the millions who have “silver” amalgam fillings in their mouths, which off-gas mercury with every bite and swallow. In fact, that mercury is a constant source of exposure.

It’s why we have not placed amalgam fillings for decades – and why, when a patient chooses to have their old amalgams removed and replaced with nontoxic, biocompatible restorations, we follow the strict precautions of the Safe Mercury Amalgam Removal Technique (SMART).

Our patients’ health, as well as ours and that of our planet depend on it.

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