The question of whether mackerel contains a lot of mercury is common, as this popular oily fish is well-known for its nutritional benefits, including high levels of omega-3 fatty acids. The answer depends entirely on the specific species of mackerel being considered. Distinguishing between the different types is necessary because mercury contamination varies significantly due to biological factors like size and lifespan, which influence how much of the neurotoxin they accumulate.
Differentiating Mackerel Species and Mercury Levels
The mercury content in mackerel is not uniform, varying significantly between large, long-lived species and smaller, shorter-lived ones. The most important distinction for consumers is King Mackerel versus all other commonly eaten varieties. King Mackerel (often found in the Gulf of Mexico and South Atlantic) is identified as a high-mercury fish. Its average concentration is around 0.730 parts per million (ppm), which is significantly higher than most other fish.
In contrast, smaller species like Atlantic Mackerel (or Boston Mackerel) and Pacific Mackerel (or Chub Mackerel) are consistently categorized as very low in mercury. Atlantic Mackerel has an average concentration of approximately 0.050 ppm, placing it among the safest choices for regular consumption. Spanish Mackerel generally falls in the middle, though the Gulf of Mexico variety has a higher average concentration of about 0.454 ppm. Consumers can confidently choose the smaller, lower-mercury varieties, while King Mackerel should be treated with caution due to its significantly higher levels.
Understanding Methylmercury Bioaccumulation
The reason for these differences in mercury levels lies in the process of bioaccumulation and biomagnification within the marine food web. The primary form of mercury found in fish tissue is methylmercury, a potent neurotoxin. Methylmercury is created when bacteria in aquatic sediments convert inorganic mercury into an organic compound. Aquatic organisms absorb this methylmercury from the water and food, and its high bioavailability means it is efficiently absorbed and slowly excreted.
Methylmercury concentrations increase as it moves up the food chain, a process called biomagnification. Organisms at lower trophic levels accumulate methylmercury, and when they are eaten by larger fish, the mercury is passed on and concentrated. Larger, predatory fish that live longer, like King Mackerel, consume many smaller fish, resulting in a much higher accumulation in their tissues. Smaller, shorter-lived fish like Atlantic Mackerel occupy a lower position in the food web and do not accumulate similarly high concentrations. High levels in humans are of particular concern because methylmercury readily crosses the placenta, potentially causing neurological damage in developing fetuses and young children.
Official Consumption Guidelines for Mackerel
Official guidelines from organizations like the U.S. Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) help consumers navigate the varying mercury levels in fish. These advisories categorize fish into three groups based on mercury content to provide clear advice on safe consumption. King Mackerel is explicitly placed in the “Choices to Avoid” category due to its high mercury content, alongside shark, swordfish, and Gulf of Mexico Tilefish.
Conversely, Atlantic Mackerel is listed in the “Best Choices” category, which includes fish with the lowest mercury levels, such as salmon, shrimp, and canned light tuna. This designation means it is safe for women who are pregnant or breastfeeding, and for young children, to consume two to three servings per week. A standard serving size is four ounces for adults.
For vulnerable populations, the FDA and EPA recommend consuming between 8 and 12 ounces per week of a variety of seafood from the “Best Choices” list. This recommendation emphasizes that the nutritional benefits of low-mercury fish, such as omega-3 fatty acids that support brain development, outweigh any minimal risk. Following these specific guidelines allows individuals to enjoy the health benefits of fish while minimizing their exposure to methylmercury.