Mercury is a chemical element that exists in several forms in the water, air, and soil. It is found as elemental mercury in the earth's crust, as inorganic mercury compounds such as mercury salts, and as organic mercury compounds such as methylmercury.
Out of all potential sources, you're most likely to have exposure to methylmercury in your diet. Methylmercury forms when airborne inorganic mercury combines with an organic molecule like carbon, attaches to water droplets, and enters soil, lakes, rivers, or oceans, contaminating food sources.
If it enters the soil, it can contaminate crops in the area. If it enters the water, it can accumulate in the marine food chain, with larger species containing highest amounts of mercury.
Why You Should Avoid Mercury
Mercury is a toxic metal that can cause varying health effects if the amount you're exposed to surpasses threshold levels. These variations depend on the type of mercury, whether you're considered highly sensitive to the effects, and how long you're exposed to this heavy metal.
Exposure to methylmercury in food could cause neurological and behavioral issues, such as the following:
- Mood swings
- Memory issues
- Numbness or feeling of pins and needles
- Loss of motor skills
- Troubles breathing
- Vision and speech impairment
- Muscle weakness
- Trouble with walking
If exposed to high amounts of mercury —from food or other sources—you could then develop severe or even fatal effects in your kidney, lungs, digestive tract, or cardiovascular system.
Safe Limits for Food Containing Mercury
Eating foods like fish and seafood is important because they give you plenty of omega-3s, vitamins D and B12, and other nutrients. While you don't want to eat foods high in mercury, you should still eat seafood to enjoy the health benefits.
The safe level for consuming seafood is 1 part per million (ppm) of mercury per week. To stay below this threshold, choose seafood low in mercury and keep your consumption to one or two meals per week.
Foods With Mercury
Most food sources high in mercury come from saltwater species like fish and other sea animals, but freshwater fish contain mercury, too. While you could ingest small amounts of mercury from food crops, your highest exposure comes from some types of fish.
Here are eight foods you should avoid to reduce your exposure to dietary mercury.
A predatory fish that inhabits several ocean zones, swordfish is one of the highest sources of mercury. It has an average mercury load measuring 0.995 ppm and highest loads measuring 3.22 ppm.
The shark has a similarly high mercury load to that of swordfish. As predatory species, sharks generally have an average mercury measurement of 0.979 ppm, with higher measurements reaching 4.54 ppm.
Tilefish typically live in two main zones: the Atlantic ocean and the Gulf of Mexico. Gulf of Mexico tilefish are very high in mercury, with average load measuring 1.123 ppm and a highest reading of 3.73 ppm. While the Atlantic coast tilefish has lower averages of 0.144 ppm, it can reach 0.533 ppm.
Next up is king mackerel, which averages 0.73 ppm of mercury. This species can reach 1.67 ppm in some cases.
The second-largest species of tuna after bluefin, bigeye tuna can hold an average mercury load of 0.689 ppm and a high load of 1.816 ppm.
This fast-swimming species can accumulate an average mercury reading of 0.485 ppm and higher readings of 0.92 ppm.
The orange roughy is a deep-sea species that can live for 100 years or more. This lengthy lifespan can lead to high amounts of mercury, with average loads measuring 0.571 ppm and highest measurements of 1.12 ppm.
Chilean Sea Bass
Another slow-growing species, the chilean sea bass lives in the deep waters and can reach 50 years of age. While it has average mercury loads of 0.354, it can reach up to 2.18 ppm of mercury.
Here are four types of seafood that contain less mercury.
This seafood is a good source of astaxanthin, a carotenoid that can support your nervous and musculoskeletal systems. Shrimp is also a good source of selenium, vitamin B12, copper, and omega-3 fatty acids. The average mercury load is just 0.009 ppm, with higher measurements of 0.05 ppm.
Farmed salmon has omega-3s, but wild-caught salmon is a richer source of these heart-healthy and brain-healthy fatty acids. Salmon has an average mercury load of 0.014 ppm and can reach measurements up to 0.086 ppm.
Oysters are rich in several key nutrients, especially vitamin D, selenium, copper, iron, zinc, omega-3s, and vitamin B12. In terms of mercury, they have an average amount of just 0.012 ppm, with the highest measurement of 0.25 ppm.
Scallops are another type of seafood rich in nutrients like vitamin B12, omega-3 fatty acids, and selenium. They're also a good source of iodine, phosphorus, and protein. Scallops are one of the species with the lowest amount of mercury, with average amounts of 0.003 ppm and higher amounts at 0.033 ppm.