A study conducted by the U.S. Geological Survey (USGS) in 2009 revealed mercury contamination in every fish analyzed. The mercury levels exceeded the Environmental Protection Agency’s (EPA) safety criteria for average fish consumption in approximately 25% of the samples, a clear sign that contamination was already widespread.

Fast forward to today, and not much has changed.

Recent assessments, including a comprehensive 2023 study from the EPA, show persistent mercury contamination across U.S. water systems. Mercury was detected in 100% of the fish samples taken from rivers stretching over 79,000 kilometers in 2013-2014 and 66,000 kilometers in 2018-2019. In both periods, mercury concentrations surpassed the EPA’s recommended safe levels, specifically in predator fish species consumed by humans, such as bass and catfish.

This is a fossil fuel problem

Mercury pollution originates primarily from atmospheric emissions, largely from coal-fired power plants and mining activities, with a minority of it coming from forest fires and volcanoes. When mercury is released into the atmosphere, it eventually settles into bodies of water, where bacteria transform it into methylmercury.

Mercury is a powerful neurotoxin, particularly dangerous to pregnant women and young children. Methylmercury is significantly more toxic and builds up in fish and animals that consume them. Oftentimes, the higher you go up the food chain, the more mercury pollutants tend to accumulate.

“Mercury is a highly toxic element; there is no known safe level of exposure,” the authors of a recent study noted. “Ideally, neither children nor adults should have any mercury in their bodies.”

According to the EPA’s 2023 study, approximately 26% of the analyzed fish exceeded the mercury threshold deemed safe for human consumption, marking a slight increase from the 23.5% recorded in 2013-2014. These percentages reflect significant public health concerns, particularly for communities that depend heavily on freshwater fish as a primary protein source.

The U.S. has taken steps to limit mercury emissions, particularly from industrial sources, yet legacy pollution and continued emissions from less-regulated sources mean mercury persists in many ecosystems. To make matters even worse, because of mercury’s persistent nature, even if we reduce emissions, contamination will remain a hazard for years to come. However, if we continue producing and using fossil fuels, the problem will only get worse.

A global problem

While the problem is acute in the U.S., Europe also grapples with mercury in its seafood. A recent report by the non-governmental organization BLOOM highlights troubling findings about mercury in tuna, one of the most consumed fish in Europe.

In an extensive study of 148 cans of tuna from five European countries, BLOOM found mercury in every single sample. Over half of these exceeded Europe’s strictest mercury limits for fish. This revelation raises questions about the safety standards applied to fish consumed globally, as regulations often favor industry interests over public health.

Europe’s maximum permissible mercury level for tuna is set higher than for other fish, ostensibly to protect economic interests rather than consumer health. The NGO report highlights the need for regulatory bodies to reconsider these thresholds and adopt more protective standards.

Tuna, a predator species at the top of the food chain, accumulates more mercury than smaller fish, a process known as biomagnification. This process, along with lax regulatory standards in certain regions, allows contaminated fish to reach consumers’ plates. In many countries, routine testing of seafood for mercury content is minimal, leaving consumers uninformed about the risks associated with fish consumption.

Can we fix this problem?

Tackling mercury contamination in fish is a complex, but not impossible, task. Reducing mercury in the environment requires a multi-pronged approach, targeting both emissions and the contamination already present in rivers and streams.

The most straightforward way to curb mercury contamination is to prevent it from entering the environment in the first place. Emissions from coal-fired power plants are among the largest contributors to mercury pollution, both in the U.S. and globally. The U.S. has made strides with policies like the Mercury and Air Toxics Standards, which set strict limits on emissions from power plants.

However, while these standards have reduced emissions domestically, it’s not enough. Additionally, the U.S. remains affected by mercury pollution originating abroad, highlighting the need for robust global agreements. Essentially, one country by itself can’t fix the problem. While international agreements do exist (most significantly the Minamata Convention on Mercury), action has been relatively slow and mercury pollution is still widespread.

Addressing mercury that has already settled into ecosystems is considerably more challenging. In many cases, mercury binds to sediments at the bottoms of rivers and lakes, where it can linger for decades and continue to make its way up the food chain. Some remediation projects have seen success with sediment dredging, removing contaminated layers from riverbeds. However, this method is costly and disruptive, often stirring up more contamination in the process.

What can we do as consumers

Realistically, the way things are going, we’re not going to clean up mercury from our fish anytime soon. This means the first thing we need to do is be aware of the issue and make informed decisions.

Not all fish are equally contaminated with mercury. Predator species, such as tuna, swordfish, and king mackerel, are more likely to contain higher levels of mercury. By contrast, smaller, short-lived fish like sardines, herring, and anchovies tend to have lower mercury levels. Salmon, trout, and tilapia are also considered safer choices, as they generally contain less mercury than large ocean predators.

For those who enjoy tuna or other high-mercury fish, moderation is key. The FDA recommends that adults eat no more than one serving per week of high-mercury fish, while pregnant women and children should avoid them altogether. When consuming canned tuna, opt for light tuna over albacore, as it generally contains less mercury. Tracking and balancing weekly fish intake with these guidelines can help consumers manage their mercury exposure while still incorporating fish into a healthy diet.

Fish caught in local, regulated waters may be subject to stricter environmental standards, reducing the likelihood of high mercury levels. Additionally, buying from local sources often supports sustainable fishing practices that aim to minimize the impact on fish populations and ecosystems.

Improved labeling on fish products—detailing mercury levels and safe consumption limits—could help consumers make informed choices and reduce their exposure risk. Health agencies and advocacy groups also continue to push for clearer, more accessible advisories, helping vulnerable communities, such as subsistence fishers, navigate the risks of mercury contamination more effectively.

Ultimately, it’s pretty damning for our society that we can’t truly fix something as problematic as mercury in fish.