Harvard scientists say climate change is making fish toxic, and warn that eating tainted fish can cause brain damage.
Published On 7 Aug 20197 Aug 2019
Climate change and overfishing are increasing levels of toxic mercury in cod and tuna – and this can cause neurological disorders in children and babies whose mothers eat fish while pregnant, a study by Harvard scientists said on Wednesday.
The concentration of methylmercury – an organic compound which can cause severe damage to the brain and nervous system – rose by 23 percent in cod and by 27 percent in bluefin tuna in the Atlantic Ocean’s Gulf of Maine over about three decades, the study said.
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“Methylmercury is … particularly harmful during the third trimester of pregnancy when the brain is developing most rapidly and for young children,” said Elsie Sunderland, co-author of the paper, which was published in the journal Nature.
Pregnant women have long been advised to avoid swordfish and shark due to high mercury levels, but cod is one fish variety that the United States government recommends as a nutritious and protein-rich food that can help children’s development.
“It’s not that everyone should be terrified after reading our paper and stop eating seafood, which is very healthy, nutritious food,” said Sunderland, a professor of environmental chemistry at Harvard University’s School of Public Health.
“We wanted to show people that [climate change] can have a direct impact on what you’re eating today, that these things can affect your health … not just things like severe weather and flooding and sea-level rise.”
Warmer seas have increased the energy needs of small fish, so they ingest more prey containing methylmercury, Sunderland said. These small fish are in turn eaten by tuna, increasing their methylmercury levels as well, she said.
Overfishing of small herring and sardines has also changed the diet of Atlantic cod, forcing them to consume larger herring and lobster, which have higher levels of methylmercury, the paper said.
Global fish consumption has more than doubled since the 1960s to a record 20.2kg (44.5 pounds) per person, with a third of the world’s oceans suffering from overfishing, according to the United NationsFood and Agriculture Organization.
Sunderland said the situation could worsen in the US if President Donald Trump weakens limits on mercury emissions from coal-fired power plants – strictures that were enacted under his predecessor, PresidentBarack Obamaand that Trump has said are too costly.
A 2018 Harvard study found coal-fired power plants are the top source of mercury emissions in the US, as burning coal releases pollution into the air, which then falls into soil and water where it is eaten by aquatic organisms and fish.
“We need to reduce human emissions (of mercury) and the largest source in the United States presently, accounting for about 40 percent of emissions, is coal-fired utilities,” Sunderland told the Thomson Reuters Foundation.
FAQs
Climate change and overfishing are increasing levels of toxic mercury in cod and tuna – and this can cause neurological disorders in children and babies whose mothers eat fish while pregnant, a study by Harvard scientists said on Wednesday.
How polluted is cod fish? ›
On average, the levels of cadmium and lead contamination in cod were up to 22 and 3–4 times, respectively, higher than today's recommended limits in soft tissue. The corresponding figures for seal were 15 and 3–4 times, respectively.
How are fish affected by climate change? ›
Sudden rises in temperature and acidification can lead to the loss of marine habitats and species. Shifting ocean currents and warming waters are changing the distribution of fish stocks and altering the structure of ecosystems.
Is Atlantic cod bad for you? ›
Consuming cod in moderate amounts is safe and generally without adverse effects. Cod, like most types of fish, contains mercury. Excessive mercury consumption can be toxic and may cause neurological and behavioral disorders. It may be particularly problematic in children.
Does fish contain toxins? ›
At certain times of the year, various species of fish and shellfish contain poisonous biotoxins, even if well cooked. According to the CDC, it is considered an under-recognized risk for travelers, specifically in the tropics and subtropics.
Is cod a safe fish to eat? ›
The Bottom Line
Cod is both a nutritious and flavorful fish loaded with lean protein, vitamins, and minerals. Although lower in omega-3s than fatty fish, cod can still be part of a healthy diet. Cod contains less mercury than some seafood, including popular fish like tuna, and can be prepared in multiple ways.
Is cod fish in danger? ›
Causes for concern. Atlantic cod are overfished in U.S. waters and seriously depleted in Canadian waters. Despite strict management in the U.S. and Canada, cod stocks in these waters remain overfished and some Canadian populations are listed as endangered.
Is eating fish bad for climate change? ›
Seafood has a much lower impact on space and freshwater than land-based food. In addition to being one of the most carbon-efficient foods on the planet, wild-caught fish require no land, no freshwater, and has a much lower impact on wildlife—no marine fish has ever gone extinct due to fishing.
How does environment affect fish? ›
Changes in the extent and depth of water bodies determine not only space availability for the fish community, but the accessibility to other resources of the environment (Baber et al., 2002; Ruetz et al., 2005).
How are fish migrating due to climate change? ›
Marine fish species are rapidly migrating toward the poles in response to the challenges of global warming. This concerning trend was unveiled in a study led by Tel Aviv University.
Cod is a low-fat source of protein, making it an excellent choice for people who would like to reduce their fat intake and improve their heart health. Cod also contains a significant amount of iodine, which is an important mineral for thyroid function.
What is the most unhealthy fish to eat? ›
Worst: Fish High in Mercury
- Imported swordfish.
- Imported marlin.
- Shark.
- Tilefish.
Cod is leaner and contains healthier fats than tilapia.
Although both fish are nutritious, low-calorie options with similar protein content, cod contains higher levels of heart-healthy Omega-3 fatty acids and less fat overall than tilapia.
Does cooking fish remove toxins? ›
It depends on the type of contaminant. Contaminants such as PCBs and DDT concentrate in the fat of fish. These contaminants can be reduced by up to 50% by preparing and cooking fish properly.
What is the least contaminated fish? ›
Choose fish and shellfish that are lower in mercury such as salmon, trout, tilapia, cod, sole, sardines, shrimp, oysters, and other shellfish. For the most health benefits, choose fatty fish such as salmon, trout, herring, chub mackerel, and sardines. o These fish have healthy omega-3 fatty acids.
What is the most common fish toxin? ›
Scombroid. Scombroid (SKOM-broyd) poisoning is caused by eating fish that has not been properly refrigerated after being caught. Scombroid occurs worldwide and is one of most common fish poisonings.
What fish is most contaminated? ›
The most contaminated fish that you should never eat
- Tilefish.
- Bluefin/Bigeye/Ahi tuna (worst), slightly better Albacore and Yellowfin tuna however still highly contaminated.
- Swordfish.
- Shark.
- King mackerel and Spanish Mackerel.
- Orange roughly.
- Chilean sea bass.
- Grouper.
Smaller fish—sardines, anchovies, farmed trout, fresh tilapia, arctic char—and bivalves such as scallops, clams, and oysters don't build up as many contaminants as do the large carnivores. Small fish also reproduce quickly, so their populations can recover from overfishing much more easily than the long-lived giants.
Why is cod bad for the environment? ›
A high level of COD means that the wastewater contains too much organic material, which can reduce the level of dissolved oxygen (DO) in the water course if the effluent is discharged, thereby harming the local environment.
Is cod a measure of water pollution? ›
COD is a water quality measure used not only to determine the amount of biologically active substances such as bacteria but also biologically inactive organic matter in water [8]. It is an important and rapidly measured variable for characterizing water bodies, sewage, industrial wastes, and treatment plant effluents.
