Mercury in Fish
Mercury levels in fish and seafood vary by species, size, and location. This chart ranks fish by mercury concentration in parts per million, as monitored by the FDA across varying fish populations and sample sizes. Most of these fish are available in grocery stores as either fresh, frozen or canned. While some of the data is many years—and even a few decades—old, the overall mercury levels have not changed in these species. Recent FDA and EPA analyses indicate no statistically significant trends (increases or decreases) in mercury concentrations across fish categories since the data was collected.
Consuming contaminated fish is the primary source of mercury exposure in the US. Mercury, emitted by coal power plants and factories, pollutes air and settles into water bodies, where it is absorbed or ingested by small organisms and then starts working its way up the food chain, its concentration rising with each step.
Generally speaking, the larger the fish, the higher the mercury level. Large predatory fish often have the highest levels and are best to avoid eating. The safest seafood are clams, scallops and shrimp which have barely detectable levels.
The fish with the highest level of mercury is the Gulf of Mexico tilefish. Note that this chart highlights two types of tilefish: Atlantic and Gulf of Mexico. Tilefish are deep-water bottom-dwellers, living 30–40 years and growing to 80 pounds. Like all fish, they accumulate mercury from smaller contaminated prey. Gulf tilefish live in warmer, shallower waters (300–1,000 feet) and face higher mercury from industrial runoff and trapped pollutants. Atlantic tilefish have lower levels because they live in deeper, cooler waters with better circulation (up to 1,500 feet).
There is also a difference between fresh or frozen fish and fish sold in cans. Canned “chunk light” tuna, typically skipjack or yellowfin, is lower in mercury due to smaller fish size. Canned salmon, which is mostly pink or chum, has less mercury because these smaller and shorter-lived species accumulate less. Also, the canning process may trim away mercury-rich parts.
Based on these mercury levels, the NRDC established health guidelines for consumption.
