Warmer water temperatures increase mercury risk

Warmer water temperatures increase mercury risk
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(NaturalHealth365) If the current trend towards warmer surface temperatures in our oceans and lakes continues, we can expect to see higher mercury concentrations in fish and shellfish – along with increased health risks for humans. In a new study published in the scientific journal PLoS One, researchers at Dartmouth College examined killifish – small fish common in saltwater marshes – to determine the effect of warmer water temperatures on mercury concentrations in fish. Killifish are an important food source for larger, predatory fish, which in turn are consumed by humans.

Researchers exposed the fish to three different temperatures; the highest was 27 degrees Celsius, or 80.6 degrees Fahrenheit – consistent with what scientists are predicting in the trend towards warmer ocean water. Water temperatures have been rising steadily at a rate of 1 to 2 degrees Celsius every year; further increases are expected to range between 1.5 and 4.5 degrees Celsius per year.

They found that the elevated temperature raised the metabolism of the fish, leading to increased uptake of methyl mercury and significantly higher concentrations in tissues.

Study finding is a cause for concern

As anyone who ever owned a fish tank knows: fish eat more in warmer water. Researchers had originally thought it possible that the higher feeding rates in the warmer water could lead to greater growth – which would actually decrease concentrations of toxic mercury.

However, this wasn’t the case. Although the fishes’ consumption increased, their respiration increased even more, causing low growth efficiency. In other words, the killifish ate more, but grew less.

The result: a troubling rise in mercury levels.

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Making the situation even more alarming is the fact that methylation rates are thought to be more rapid in warm water. More methyl mercury being created, and higher mercury concentrations in tissue: the two unwelcome “bonuses” that accompany warmer ocean water, and twin ingredients in a recipe for environmental disaster.

What is methyl mercury, and how does it get into the water?

Mercury, a naturally-occurring metal, is released into the atmosphere from industrial pollution. It eventually settles into waterways, where sulfate-reducing bacteria in the water transform it into methyl mercury – a more toxic form of the pollutant.

Coastal waters are particularly prone to methylation – a reason the researchers choose to study fish in tidal marshes. Methyl mercury accumulates in fish, as well as other marine life, presenting a concern for those who eat the fish. Methyl mercury is a neurotoxin that can cause heart disease and nervous system dysfunction; early exposure can cause cognitive deficits and lowered IQ.

Mercury levels are currently rising in fish in heartland lakes

The picture is especially grim when you consider that – after decades of falling mercury levels – two commonly-consumed game fish in the Great Lakes are manifesting growing mercury levels.

In 2010, an article in Environmental Science and Technology reported that mercury levels are increasing in brown trout and walleye pike in Lake Erie. Scientists believe this could be because of the advent of invasive zebra mussels, which absorb high levels of mercury from the water and then pass it up the food chain.

Although government regulations have helped to substantially reduce mercury pollution in the Great Lakes – since 1985, there has been a 48 percent decline in mercury emissions from industries in the area – a 2011 report published in Ecotoxicology states that mercury concentrations in the local fish remains above the EPA-designated human health criterion.

Fish, with their abundance of lean protein, essential minerals and beneficial omega-3 fatty acids, are a near-perfect food – a nutritional gift. Yet, due to the presence of toxic methyl mercury, the gift now comes with a warning: eat at your own risk.

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