Fish: the other contaminated meat

Apr 26

Here’s a comparison of the pollution and contaminants commonly found in four of the most consumed types of fish: salmon, tuna, tilapia, and cod. These fish are among the most popular worldwide, both wild-caught and farmed, and vary in their risk profiles for pollutants like mercury, PCBs, microplastics, and dioxins.

Contaminants to know:

PCBs (Polychlorinated Biphenyls)

What they are:
PCBs are man-made chemicals that were once widely used in things like electrical equipment (transformers, capacitors), paints, coolants, and plastics because they are really good at resisting heat and chemical breakdown.

Why they matter:
Even though the U.S. banned PCBs in 1979, they linger in the environment — especially in waterways. Fish absorb PCBs from contaminated water and sediments.
PCBs build up in fat tissue, and when people eat contaminated fish, they can accumulate PCBs over time.

Health concerns:

Cancer risk (classified as a probable human carcinogen)
Immune system suppression
Reproductive and developmental problems
Endocrine (hormone) disruption

Dioxins

What they are:
Dioxins are a group of toxic chemical compounds that are byproducts of industrial processes like waste incineration, chemical manufacturing, and paper bleaching.
They aren’t intentionally made — they’re kind of an unwanted side effect.

Why they matter:
Like PCBs, dioxins accumulate in the food chain, especially in animal fat — which includes fish.

Health concerns:

Cancer (known human carcinogen)
Damage to the immune system
Disruption of hormones
Developmental problems in children
Skin conditions (like chloracne)

Mercury

is a naturally occurring metal found in the earth’s crust — but it becomes a serious pollutant because of human activities like coal burning, mining, and industrial processes.
Once released into the air, mercury falls into oceans, rivers, and lakes.

How it ends up in fish:
In water, certain bacteria convert mercury into a highly toxic form called methylmercury.
Fish absorb methylmercury from the water and from eating smaller contaminated organisms.

Bioaccumulation:
Mercury builds up over time in a fish’s body — and bigger, older, predatory fish (like tuna, shark, swordfish) have the highest levels because they eat lots of smaller contaminated fish.
→ (this process is called biomagnification)

Health concerns for humans:

Brain and nervous system damage, especially risky for pregnant women, babies, and young children (it can affect brain development)
Impaired memory, coordination, and fine motor skills
Heart and kidney problems at very high exposures

Microplastics

Microplastics are tiny pieces of plastic, usually smaller than 5 millimeters (about the size of a sesame seed — or even much smaller).

Where they come from:

Primary microplastics: Tiny plastics that were made small on purpose (like microbeads in face scrubs, glitter, or industrial pellets).
Secondary microplastics: Pieces that broke off from larger plastics — like water bottles, fishing nets, or plastic bags breaking down over time from sunlight, waves, or weather.

Where they are found:
Literally everywhere: oceans, rivers, lakes, soil, even in the air.
Fish, shellfish, and even drinking water can contain microplastics.

Why they matter:

Animals (including fish) mistake microplastics for food, which can block their digestive systems or cause other harm.
Microplastics can carry toxic chemicals (like pesticides, heavy metals, or PCBs) that stick to their surfaces.
Scientists are studying how eating microplastics could affect human health — there's concern about inflammation, toxicity, and exposure to harmful chemicals.

THE 4 MOST COMMONLY CONSUMED FISH

Salmon

Types: Wild-caught (e.g., Alaskan) vs. farmed (e.g., Atlantic)
Common Contaminants:
- PCBs (Polychlorinated Biphenyls): Higher in farmed salmon due to feed.
- Dioxins: Present in farmed varieties, linked to feed sources.
- Mercury: Generally low, especially in wild-caught salmon.
- Microplastics: Potential concern in both farmed and wild, depending on water source.
Notes: Wild Alaskan salmon tends to have lower contaminant levels compared to farmed Atlantic salmon.

Tuna

Types: Albacore, yellowfin, bluefin, skipjack (often used in canned tuna)
Common Contaminants:
- Mercury: High, especially in large species like albacore and bluefin.
- PCBs: Moderate levels possible, especially in older, larger fish.
- Microplastics: Present in ocean species due to widespread ocean plastic pollution.
Notes: Mercury content is a serious concern; pregnant women and children are advised to limit intake.

Tilapia

Types: Mostly farmed worldwide
Common Contaminants:
- PCBs & Dioxins: Can be high depending on farming conditions and feed quality.
- Antibiotic Residues: Risk in tilapia farmed in countries with poor regulations.
- Mercury: Low
Notes: When sourced from reputable farms, contaminant levels are low. Cheap imports (e.g., from poorly regulated farms) are riskier.

Cod

Types: Atlantic and Pacific
Common Contaminants:
- Mercury: Moderate, generally lower than in tuna but higher than salmon or tilapia.
- PCBs & Dioxins: Possible in older, wild fish or contaminated waters.
- Microplastics: A concern due to bottom-feeding and widespread ocean contamination.
Notes: Considered relatively safe, but sustainability and source are important (Atlantic cod stocks are overfished in some regions).

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References

U.S. Food and Drug Administration. (2023). Advice about eating fish. U.S. Department of Health and Human Services. https://www.fda.gov/food/consumers/advice-about-eating-fish

Environmental Defense Fund. (n.d.). Seafood Selector. https://seafood.edf.org/

World Health Organization. (2019). Microplastics in drinking-water. https://www.who.int/publications-detail-redirect/9789241516198

Consumer Reports. (2014, June). The trouble with tilapia. https://www.consumerreports.org/cro/magazine/2014/06/the-trouble-with-tilapia/index.htm

Peer-Reviewed Journal Articles:

Barboza, L. G. A., Vieira, L. R., Branco, V., Figueiredo, N., Carvalho, F., Guilhermino, L., & Loureiro, S. (2020). Microplastics cause neurotoxicity, oxidative damage, and energy-related changes in the brain of fish (Dicentrarchus labrax). Environmental Research, 188, 109734. https://doi.org/10.1016/j.envres.2020.109734

Burger, J., & Gochfeld, M. (2004). Mercury in canned tuna: White versus light and temporal variation. Environmental Research, 96(3), 239–249. https://doi.org/10.1016/j.envres.2004.01.002

Hites, R. A., Foran, J. A., Carpenter, D. O., Hamilton, M. C., Knuth, B. A., & Schwager, S. J. (2004). Global assessment of organic contaminants in farmed salmon. Science, 303(5655), 226–229. https://doi.org/10.1126/science.1091447

Zhang, D., Xu, D., Zhu, M., Li, L., & Luo, Y. (2020). Occurrence, fate, and ecological risk of antibiotics in mariculture areas: A review. Environmental Pollution, 267, 115629. https://doi.org/10.1016/j.envpol.2020.115629

Lauren Plunkett https://laurenplunkett.com