Mercury in fish is a severe concern for seafood lovers, but don’t let it hook you into giving up your love for seafood.
Let’s learn more about mercury so you can make informed choices about the seafood you eat. Let’s discover the natural and human sources of mercury, mercury levels in wild and farm-raised fish, safe consumption levels, and alternative omega-3 fatty acids.
So, come along for the ride, and let’s make sure you enjoy the health benefits of eating fish while reducing the risks.
What is Mercury? A Natural Element in the Environment
Mercury, also known as quicksilver, is a naturally occurring chemical element found in rocks, coal, and soil. In chemistry, it has the symbol Hg and atomic number 80. Pure mercury looks silvery and is the only liquid metal at normal room temperature, as its melting point is -38.83°C or -37.894°F. The chemical is released into the air through volcanic eruptions, weathering of rocks, burning coal, and mining. Mercury in the air falls back to earth with rain or snow, and since it is liquid, it quickly runs into rivers, lakes, and seas, where it can accumulate in plants, animals, fish, and shellfish.
Where Does Mercury in Fish Come From? How Fish and Seafood Get Contaminated
Fish are exposed to mercury through plants and other animals in the sea, and the contamination continues to accumulate upwards in the food chain. When large fish consume smaller fish, they slowly get a higher level of mercury over time, which is why bigger and older fish often have higher mercury levels than smaller and younger fish. The apex predators, like sharks and swordfish at the top of the food chain, tend to have more mercury.
The Health Effects and Risks of High Mercury Exposure and Consumption
If we overeat mercury, we can suffer from adverse health effects, and fish and seafood is the primary way that mercury enters our bodies. We can limit our exposure to mercury by carefully choosing which fish we eat and how often, picking fish low in mercury, and following guidelines for safe consumption, such as those given by the FDA and EPA. Pregnant or breastfeeding women and children younger than 18 are more vulnerable to the effects of mercury. They should be more aware and careful of how much they consume, as high levels of mercury are linked to brain development issues.
Which Fish Has the Least Mercury? Fish Lower in Mercury: Best Choices
Consider low mercury fish to be the good boys of the sea. Small amounts of mercury are less likely to give you any health problems in the long term.
When it comes to mercury, we can classify fish into three categories: low, medium, and high mercury. The risk of mercury poisoning increases the more fish you eat and the higher its mercury levels are.
FDA/EPA’s best choices for fish (2-3 servings per week):
- Atlantic croaker
- Atlantic mackerel
- Black sea bass
- Lobster (American and spiny)
- Pacific chub mackerel
- Perch (freshwater and ocean)
- Trout (freshwater)
- Tuna (canned light, skipjack)
Fish With Medium Level of Mercury: Good Choices
FDA/EPA’s good choices for fish (1 serving per week):
- Chilean sea bass (Patagonian toothfish)
- Mahi Mahi (dolphinfish)
- Spanish mackerel
- Striped bass (ocean)
- Tilefish (Atlantic ocean)
- Tuna (albacore/white tuna, canned, fresh, frozen)
- Yellowfin tuna
- Weakfish (Seatrout)
- White croaker (Pacific croaker)
Fish Contain Higher Levels of Mercury: Bad Choices (Avoid)
FDA/EPA’s fish choices to avoid (high mercury levels):
- King mackerel
- Orange roughy
- Tilefish (Gulf of Mexico)
- Bigeye Tuna
A serving is 4 ounces for adults and 2 ounces for children ages 4 to 7. The information listed above is from the FDA and EPA as of January 2017, and you can read more at FDA and EPA about fish advice.
Identifying Fish with High Mercury Levels
Scientists believe that eating fish is healthy overall, as it is an excellent source of protein and omega-3 fatty acids, vital for proper health, brain function, and development. Being deficient in omega-3 can cause many adverse symptoms, such as heart problems, depression, dry skin, fatigue, memory loss, and poor blood flow.
We want to enjoy the health benefits of eating fish but should balance it with minimizing our mercury exposure. We can do this by eating low-mercury fish and avoiding high-mercury fish. Some fish typically low in mercury include salmon, tilapia, cod, sole, sardines, shrimp, oysters, and other shellfish. Avoid fish high in mercury, such as shark, swordfish, king mackerel, and tilefish.
How Much Fish is Too Much Mercury?
The amount of fish that people consider “too much mercury” varies depending on fish species, serving size, mercury levels and the person’s age, body weight, and gender, and which government or agency guidelines to follow.
Anything more than the recommended amount of fish servings is too much mercury.
If we’re talking about specific fish and serving sizes, let’s use the list above and the FDA’s guidelines as an example, as their serving sizes are different across all age ranges. For children aged 1-3, a serving size is 1 ounce; for 4-7 is 2 ounces; for 8 to 10 is 3 ounces; and for ages 11+ is 4 ounces. They can eat no more than 2 servings per week from the “best choices” or 1 serving from the “good choices” lists.
If we’re talking about specific amounts of mercury, the safe weekly limit of mercury consumption is 0.7 micrograms per kilogram of body weight per week. Anything more than this safe limit is too much.
For example, a person with a body weight of 60 kg can eat 42 micrograms of mercury per week as a safe limit (0.7 µg/kg/week * 60 kg = 42 µg/week).
A person with a body weight of 100 kg can eat 70 micrograms of mercury per week as a safe limit (0.7 µg/kg/week * 100 kg = 70 µg/week).
Let’s consider a serving of canned albacore tuna containing 0.350 ppm of mercury, or 39.67 micrograms per 4 ounces (113 grams). A person weighing 60 kg will have reached 94.4% of their safe weekly limit of 42 micrograms by this one serving. A person weighing 100 kg will have eaten 56.67% of their weekly safe limit of 70 micrograms from this one serving.
To illustrate the difference between low-mercury fish and high-mercury fish, let’s look at another example. Let’s consider anchovies of a mercury concentration of 0.016 ppm or roughly 1.8 micrograms per 4 ounces (113 grams). People weighing 60 and 100 kg can eat 23 and 38 servings to reach their safe weekly limits if they don’t consume any other source of mercury. These are just estimations and thought examples, not recommendations for how much tuna or anchovies you should eat.
Health Consequences of Consuming High-Mercury Fish for Pregnant Women and Children
While fish is an excellent nutrient-dense food source, the experts recommend limiting our consumption of specific fish types that are often high in mercury. The U.S. Environmental Protection Agency (EPA) and U.S. Food and Drug Administration (FDA) recommend that pregnant women, breastfeeding mothers, and younger children avoid eating shark, swordfish, king mackerel, tilefish, and other fish that may contain high mercury levels.
Balancing the Benefits and Risks of Fish Consumption
What can we do to reduce our mercury exposure? Since mercury levels vary by location and species, we can choose to eat a variety of fish species from various sources instead of from a single source, giving you a more balanced intake of nutrients. Remove fish organs such as kidneys and livers as they are often higher in chemicals than the meat or flesh of the fish.
Safe Eating Guidelines for Fish from California Lakes and Reservoirs
If you live in California, here are some guidelines for eating fish from specific sources, reservoirs, and lakes. For example, the California Office of Environmental Health Hazard Assessment (OEHHA) advises that women aged 18 to 49 years old, and children 1 to 17 years old, should not eat:
- many bass species
- large brown trout
- some rockfish species
- white sturgeon
The age range for women is set to their child-bearing age as mercury can build up in their body long before they are pregnant, and they should, therefore, only eat low-mercury fish. Women aged 50+ and men 18+ can safely eat more than women 18-49 and children 1-17. You can read more on OEHHA’s website.
Do Farm-Raised Fish Have Mercury?
Some people believe that farm-raised fish have less mercury, but you can find mercury in both wild and farm-raised fish. Some mercury contamination is due to industrial pollution from rivers, lakes, and seas, so farm-raised fish can have higher or lower levels depending on where it is raised and kept. Another significant factor is the fish’s diet. Mercury tends to accumulate upwards in the food chain, so if the fish eat mercury-contaminated food sources, they will also get mercury.
Additional Advice for Reducing Mercury Exposure in Fish and Seafood
You can find mercury in most fish from any source. Still, some fish contain higher levels of mercury than others, so we should be aware of mercury levels in fish and pick fish with lower mercury to minimize exposure. There are many health benefits from eating fish, and following the guidelines from the EPA and FDA, we can do it safely and reduce the risk of adverse health effects.