Due to overfishing and climate change, the mercury content of marine fish may increase further.

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Editor’s note: In 2013, in the Tsukiji market in Tokyo, Japan, a major 222 kilograms of tuna was finally auctioned for $1.76 million, equivalent to $7,200 per kilogram. However, many marine fish, such as tuna, are now facing even more severe problems of increasing levels of mercury. Behind this, even with measures to reduce mercury emissions and introduce more stringent laws and regulations, this problem is still becoming more and more severe due to factors such as overfishing, especially climate change. The original title of this article is Some Fish Are Still Full of Mercury, for a Worrying Reason, author ED YONG introduced the findings behind this serious problem.

The mercury content of the world's marine fish exceeds the standard, and the cause is worrying

The level of mercury in the body may be further increased by the influence of tuna predators. Image source: KIM KYUNG HOON, REUTERS

In recent years, there seems to be less and less stories about significant progress in environmental protection. However, it is worth mentioning that the phenomenon of mercury pollution has improved. Mercury, commonly known as mercury, is a toxic metal that is mainly derived from emissions from coal-fired factories and other related industries. It can circulate in the atmosphere, enter the ocean, and cause damage to marine life. In the end, because humans ingested seafood, these toxins entered the human body.

For decades, the mercury content of marine fish products has been a huge hazard to human health. It can cause long-term harm to the human brain and may also increase the risk of heart disease. In addition, it has a greater impact on the fetus. Therefore, pregnant women have been told not to use seafood with excessive mercury levels, such as tuna and swordfish.

However, from 1995 to 2010, mercury levels in the Northern Hemisphere fell by 30% due to stricter laws and regulations, reduced use of coal, and mercury in many commodities. In 2017, the world’s first contract to reduce mercury emissions also came into force.

You will definitely think that in this departmentUnder the influence of the factors, the mercury content in marine fish products has certainly decreased, and it will also show a downward trend. However, two professors at Harvard University, Amina Schartup and Elsie Sunderland, found through a study that the mercury content of the future seafood is not only It will not decrease, but will increase further.

There are mainly two unusual factors behind this: overfishing and climate change. These two factors may cause fish to prey on more polluted food. Although the amount of mercury in the atmosphere has decreased, our human behavior has led to a higher level of mercury in the body of fish such as tuna. In addition, the carbon we emit into the atmosphere will eventually affect the toxin content of our table foods.

Climate change, “It’s not just about what the climate will look like after 10 years,” said Shatap. “It’s also related to your daily diet after 5 years.”

Once mercury enters the ocean, it is converted to a neurotoxin-containing environmental pollutant, methylmercury, by the action of marine microbes, although it enters the food chain. All marine animals contain methylmercury in their food, and these captured foods are also produced by other foods containing methylmercury, and so on.

Therefore, predatory fish such as tuna, swordfish and Atlantic salmon often have the highest levels of mercury and the largest toxins. But in the end, after humans eat these fish foods, the toxins also enter the human body.

In the United States, 80% of methylmercury exposure is associated with seafood products. Of these, 40% are from tuna.

The mercury content of the world's marine fish exceeds the standard, and the cause is worrying

Image source: unsplash @rresenden

However, behind these simple data, there are hidden more complex issues.

The researchers found that among different types of fish, even fish living in similar marine environments, the trend of changes in mercury levels is significantly different.

“When we look further at the trends in mercury levels in these fish, we will see some upward trends, some showing a downward trend, and others maintaining a steady trend.” Shatap said, “They Living in the same sea environmentWhy is this difference?

This problem has also caused great confusion to industry regulators. In their eyes, they hope that through the implementation of various emission reduction tasks, they can also really bring about continuous improvement.

To further explore this issue, Shatap and her colleagues collated the fish resources and mercury content data for the past 30 years in Maine Bay (a semi-enclosed sea between the United States and Canada under the Atlantic Ocean).

With this data, they also created a model and simulated the food chain in the area. In this food chain, virtual fish grow in virtual seas and feed on virtual plankton, while still ingesting virtual mercury levels.

By adjusting the model to simulate environmental changes in the waters over the past half century, they show how the corresponding levels of mercury enter different species of fish under the influence of human activities.

In the 1970s, humans overfished and killed squid, and the salmon population in Maine Bay declined sharply. The squid was originally a predator for fish such as Atlantic salmon and white-spotted sharks. In this context, these predatory fish also had to capture other hunting targets.

Atlantic squid turns to live on a variety of small fish species, such as sardines and sardines, which also contain relatively little mercury. However, the grouper shark began to live on salmon. The squid mainly lives on the lower body of the animal in the food chain, so its mercury content is relatively high.

The mercury content of the world's marine fish exceeds the standard, and the cause is worrying

Image source: unsplash @gkumar2175

And after the salmon population has recovered, they have become the predators of Atlantic salmon and white-spotted sharks. As a result, Atlantic salmon returned to hunting with higher levels of methylmercury, while grouper sharks returned to predation with lower levels of methylmercury.

“All those who saw these trends changed to me, ‘you are not crazy.’” said Shatap.

Of course, temperature is another factor. Since the 1960s, the water temperature in the Gulf of Maine has continued to rise, making it one of the fastest warming waters in the world. Since most fish are cold-blooded animals, they will certainly feel uncomfortable due to the rising temperature of sea water.

And as sea temperatures get higher, they have to swim faster and be more active, and these activities consume more calories. Therefore, they will hunt againEat more fish food and also consume more mercury (although tuna can control its body temperature to some extent, it will still be affected by increased mercury content. After all, they are eating other Food, more toxins have accumulated in the body).

If the future mercury emissions have been at a low level, but the temperature continues to rise, and humans are again overkilling the squid, what changes will happen? For this problem, the main factor is still fish.

Through the models built by Shatap and Sunderland, we can see that the level of mercury in Atlantic salmon can continue to decrease, but the level of mercury in the white sharks will continue to increase.

For the Atlantic bluefin tuna, because they are the most exposed fish populations with the highest mercury exposure, future developments are not optimistic. Although the level of mercury has indeed declined due to emission reductions, as the water temperature continues to rise, by 2030, these reduced levels of mercury will “return”.

According to the latest tuna facts, the two professors’ models are not wrong, and the level of mercury in the “returning” has begun to show a certain trend.

“Even if we keep mercury emissions at a certain level, we will see an increase in the level of mercury in tuna due to the increase in seawater temperature,” said Shatap.

“For regulators, they must be aware that the rate of reduction in the level of mercury in food does not reach its expected rate. Of course, this does not mean that their regulation is problematic,” Shatap added. “If they don’t control emissions reductions, the situation may be even worse.”

Compared to most studies of mercury levels in predatory fish, the special study of the two professors is that they incorporate research into the entire ecosystem from a more macro perspective.

“This study is extremely important. It shows us the close relationship between the quality of marine life and the entire ocean. It also tells us that human behavior related factors such as overkill and climate change can also Directly affects toxin contamination in marine organisms,” said Anela Choy of the Scripps Institution of Oceanography.

The mercury content of the world's marine fish exceeds the standard, and the cause is worrying

Image source: unsplash @jAkobowens1

Of course, anything is toxic, but whether it really constitutes a poison depends on its dosage.

Whether it is now or in the future, will the mercury content of fish be related to human health? Sunderland’s answer to this question is affirmative, and it will always be affirmative.

According to relevant epidemiological studies, exposure to mercury can cause impaired brain development and can lead to cognitive impairment, especially when the fetus is not yet born (mercury can pass through the mother’s blood circulation) And affect the fetus).

“It seems that there is no actual solution at the moment,” Sunderland said. “Everyone does not want mercury in the sea. It is not good for human health.”

Of course, reducing the intake of fish food seems like a solution. But on a global scale, there are a large number of people who make a living from seafood.

“We are not advocating the refusal to consume fish food. After all, fish food is still rich in many nutrients.” Sunderland said, “What we want to express is how to make these foods healthier and safer.” Of course, this is also inseparable from the actions we have taken in climate change.”

Today, from a government perspective, protection against mercury pollution appears to be waning. Under the leadership of the Trump administration, the National Environmental Protection Agency seems to be further relaxing regulations related to reducing pollution of mercury to the environment during the Obama administration.

According to the US Environmental Protection Agency’s statement, these regulations have led to a sharp increase in the cost of the coal industry. They even submitted a bill and hope to pass the bill to change the way regulators work in assessing the benefits and costs of mercury control.

This bill is obviously proposed to patronize the coal industry, but the price behind it is the deterioration of the environment and health.

“This will inevitably weaken the influence of existing regulations, while also actively opening a back door, and there may be more regulatory omissions in the future.” Sunderland said, “There will be no such practices.” Benefits.”

Regression in existing regulations will also result in huge waste. Previously, the implementation of this regulation has already cost $18 million. In addition, this kind of failure is also counterproductive. As Shatap and Sunderland have studied, regulations on mercury emissions need to be further strengthened rather than continuously weakened.

Translator: Ishii Junichi