Sardines are one of the lowest-mercury fish you can eat. With an average mercury concentration of just 0.013 parts per million (ppm), sardines contain roughly 25 times less mercury than albacore tuna and far less than nearly every other commonly sold seafood. The FDA places sardines in its “Best Choices” category, the safest tier for all populations including pregnant women and young children.
How Much Mercury Sardines Actually Contain
FDA testing of commercial sardines found a mean mercury level of 0.013 ppm, with individual samples ranging from non-detectable levels up to a maximum of 0.083 ppm. To put that in perspective, the FDA’s action level for mercury in fish is 1.0 ppm. Even the highest-mercury sardine ever tested came in at less than one-tenth of that threshold.
For comparison, here’s how sardines stack up against other popular fish:
- Sardines: 0.013 ppm (mean)
- Shrimp: 0.009 ppm
- Salmon: 0.022 ppm
- Canned light tuna: 0.126 ppm
- Albacore tuna: 0.350 ppm
- Swordfish: 0.995 ppm
Sardines sit near the very bottom of the mercury scale, alongside anchovies, shrimp, and scallops.
Why Sardines Stay So Low in Mercury
Mercury accumulates as it moves up the food chain, a process called biomagnification. A tiny plankton-eating fish absorbs a small amount. A medium fish eats hundreds of those small fish and concentrates the mercury further. A large predator like swordfish or shark eats hundreds of medium fish over a lifespan of 15 to 20 years, building up dramatically higher levels.
Sardines short-circuit this process in several ways. They feed near the bottom of the food chain, eating mostly plankton and tiny crustaceans. They’re small, typically under 20 centimeters. And they have short lifespans, usually only a few years, which gives mercury less time to build up in their tissue. Fish size, age, diet, and metabolic rate all influence how much mercury a species accumulates, and sardines get favorable marks on every count.
Sardines Are Safe During Pregnancy and for Children
Both the FDA and the Mayo Clinic specifically name sardines as a recommended fish for pregnant and breastfeeding women. The FDA advises eating two to three servings per week (8 to 12 ounces total) from its “Best Choices” list during pregnancy, and sardines qualify. For children ages 1 through 11, the recommendation is two servings per week from that same list.
The Dietary Guidelines for Americans goes a step further. When recommending that children eat even higher amounts of fish, the guidelines specifically limit those portions to the lowest-mercury options within the “Best Choices” category. Sardines made that shortlist alongside salmon, shrimp, pollock, tilapia, and a handful of others. In practical terms, sardines are about as safe as fish gets for the most vulnerable groups.
Selenium Adds a Layer of Protection
Sardines are rich in selenium, a mineral that binds to mercury in the body and reduces its harmful effects. Research on canned sardines found selenium concentrations between 310 and 1,370 micrograms per kilogram, far exceeding their mercury content. The ratio of selenium to mercury in sardines is high enough that the selenium effectively neutralizes whatever trace mercury is present. This means the already-tiny amount of mercury in sardines is even less of a concern than the raw number suggests.
What About Other Contaminants?
Mercury isn’t the only heavy metal found in seafood. A study of canned sardines sold in Brazil detected arsenic, lead, cadmium, and other elements across multiple brands. Arsenic was the most notable finding, with levels that raised health concern flags for chronic exposure in the Brazilian samples tested. Lead levels, by contrast, were extremely low across all brands and well below thresholds for concern.
Geography matters here. Arsenic levels in sardines sold in the United States were dramatically lower than those in the Brazilian samples, essentially negligible. The source of the fish, local water contamination, and canning processes all play a role. If you’re buying sardines from brands sold in North American or European markets, the available data suggests arsenic exposure is minimal. Still, eating a variety of low-mercury seafood rather than relying on a single species is a reasonable approach to limiting any one contaminant.
How Often You Can Eat Sardines
Given their extremely low mercury levels and their place in the FDA’s top safety tier, sardines are one of the few fish you can eat multiple times a week without concern. The general guidance of two to three servings per week from “Best Choices” fish is designed to cover all the fish in that category. For a species as low in mercury as sardines, staying within that range leaves an enormous safety margin.
Beyond safety, sardines pack a dense nutritional profile. They’re one of the richest sources of omega-3 fatty acids, and because you eat them bones and all, they deliver significant calcium. A single 3.75-ounce can provides roughly 1.4 grams of omega-3s. For people looking to get the cardiovascular and neurological benefits of seafood with the least possible mercury exposure, sardines are one of the best options available.