You might be surprised to learn how much mercury is actually in your seafood. Let’s find out together!
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The Facts About Mercury
You may know that mercury is a neurotoxin and a powerful toxin to our environment. It is present in the atmosphere and it is easily absorbed by fish, reptiles, and mammals. Therefore, the larger the animal gets, the more mercury it will have stored in its body. When mercury is released into the environment due to natural disasters or accidental spills, it tends to accumulate in the food web. This is why it is called a “toxic” element because it is extremely harmful to living creatures!
Mercury does not break down easily, which means that it can stay in the environment for a long time – even decades! Due to its long half-life, it is considered one of the most environmentally persistent chemicals. That being said, the symptoms of mercury exposure are usually very similar to the ones caused by other compounds, such as lead and arsenic. If you suffer from any of these symptoms, you should not hesitate to consult a doctor:
- Frequent headaches
- Nervousness or depression
- Irritability
- Impaired motor skills or coordination
- Cognitive impairment or memory loss
- Sickness or debility
- Nausea or vomiting
- Diarrhea or constipation
- Weakness
- Skin disorders
- Speech impediments
- Hair loss
- Changes in appetite or weight
- Kidney damage
- Fertility issues
- Infections
- Miscarriage
- Stillbirth
- DNA damage
- Allergies
Due to mercury’s harmful effects, many countries have restricted or banned its use in small manufactured goods. However, its use continues to exist in large scale industry, such as:
- Manufacturing of electrical and electronic equipment
- Oil and gas extraction
- Construction
- Pulp and paper production
- Pharmaceutical industry
- Mineral processing
- Fishing industry
So, how much mercury is there in fish, anyway?
How Much Mercury Is In Fish?
The amount of mercury that you should consider to be safe to eat varies by species and gender. The general recommendation is as follows:
- For fish labeled “mature”, the dose is 0.15 mg/kg of body weight. (This is the provisional tolerable weekly intake (PTWI) for mercury set by the WHO and the EPA.)
- For fish labeled “baby”, the dose is 0.3 mg/kg of body weight.
- For women, the recommended dose is 0.15 mg/kg of body weight. For men, it is 0.3 mg/kg of body weight.
- These recommendations apply only to fresh or frozen fish; cooked fish is considered to be hazardous because of the high levels of mercury that are released during the cooking process. (The mercury levels increase as the temperature increases.)
To find out how much mercury is in the fish you eat, you must first figure out what kind of fish you have. There are five basic categories of fish that you should know about:
- Marine species ((bony fishes)): These are fish that live in salt water. Marine fish are usually farmed and they are usually the target of recreational fishing. Examples of marine species include: anchovies, Arctic salmon, Atlantic mackerel, Chilean sea bass, cod, corvina (sea bass), dab, flounder, green tide, gulf shrimp, haddock, herring, horse mackerel, ocean perch, ong, patagonia cilantro, orange roughy, petralexis, pompano, salmon, sardine, sea bass, shad, silver pomatum, and swordfish.
- (Freshwater species) ((bony fishes)): These are fish that live in fresh water. They are usually small in size and they are omnivorous, which means that they will eat both plant and animal matter. Popular freshwater fish include: carp, grayling, and trout. (Note: some trout are farmed and they are sometimes called “rainbow trout” due to the colors they can range from. These farmed trout are usually fed corn, which makes them extra-vulnerable to mercury poisoning.)
- (Coastal species) ((bony fishes): These are fish that live near or in shore. They are usually a mix of marine and freshwater species. Popular coastal fish include: bluefish, flounder, grouper, monkfish, mullet, orange roughy, perch, pompano, and salmon. (Note: the above fish are all considered to be fairly high in mercury content.)
- (Tropical species) ((bony fishes)): These are fish that live in warm climates and they are usually smaller in size than the ones mentioned above. Some tropical fish are eaten in their entirety, while others are only used for human consumption after being cooked. Popular tropical fish include: angelfish, barracuda, giant grouper, horse mackerel, king mackerel, tuna, and wahoo. (Note: mackerel are very high in mercury and many people are sensitive to their mercury content; mackerel are also some of the most popular fish in canned and frozen form, so if you are eating any of these products, you are certainly getting your share of mercury!)
- (Oceanic species) ((bony fishes)): These are fish that live in the ocean and some of them can grow large in size. They are usually very bony and they have thick skins. Popular oceanic fish include: bluefish, California blackfish, clownfish, green sea turtle, grouper, herring, mackerel, and salmon. (Note: all of these fish are known to be high in mercury content but, again, it depends on the brand and style of fish you are eating. Some types of salmon are farmed and their mercury levels can be lowered by undergoing a “depuration” process before being made into food. If you are consuming any kind of salmon, it’s important to know that you are increasing your intake of mercury.)
- (Inland species) ((freshwater fishes)): These are fish that live in large lakes and streams. They are usually native to North America, where they were originally found in clean, unpolluted lakes and streams. Popular freshwater fish include: black bass, brown trout, and rainbow trout. (Note: all of these fish are fairly high in mercury content.)
Once you know what kind of fish you have, you can easily figure out how much mercury is in it by using a safe conversion rate. To do this, simply take your weight (in kg) and multiply it by 0.15 for marine species or 0.3 for freshwater species. This is the amount of mercury that you should consider to be safe to eat in one serving:
- For marine species: multiply your weight by 0.15
- For freshwater species: multiply your weight by 0.3
The Safe Way To Eat Fish
If you want to protect yourself from mercury poisoning, it is recommended that you choose fish that are low in mercury. Checking the mercury levels in fish is simple and quick as you will see on most store’s websites. To do this: