Are Environmental Toxins Lower in Wild-Caught or Farmed Fish?

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The adverse effects of industrial pollutants in seafood may counteract the benefits of nutrients in fish.

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Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Although the levels of industrial pollutants, like dioxins and PCBs, continue to decline in the food supply, there is one dietary source that still remains a major threat: fish. Everything eventually flows into the sea. Yes, we can get some dioxins from eating horses, but most of our exposure comes from eating fish.

The U.S. Environmental Protection Agency puts the tolerable upper limit of dioxin intake per kilogram of body weight at 0.7 picograms—less than one trillionth of a gram—per day. So, we should get less than this in our diet every day. As you can see, we’re already skirting the max by just consuming dairy, and fish takes us right over the top, even at low levels of consumption.

So, the adverse effects of chemical contaminants in seafood may counteract the benefits of any nutrients in fish. So much so that many dietary guidelines recommend no more than one serving a week of fish and seafood to cut down on exposure to toxic pollutants. But which is worse? Wild-caught or farmed?

Take salmon, for example. Salmon had the highest toxic equivalents of PCBs, followed by canned tuna, as well as the highest neurotoxic equivalents of PCBs. If you compare the levels of PCBs in salmon farmed in Maine and Canada, versus salmon wild-caught in Alaska, versus organically farmed salmon from Norway, compared to the wild-caught salmon, the farmed salmon, organic or otherwise, had significantly higher PCB levels.

This appears to extend to other contaminants too. Based on the testing of literally tons of salmon samples from around the world, for every toxin the researchers tested, the samples of farmed salmon had higher levels than did the wild-caught salmon—higher levels of DDT and these other banned pesticides. Over 10 times more PCBs in farmed salmon; over 10 times more dioxins. In order to not exceed EPA safety levels, we wouldn’t want to eat supermarket salmon more than once every two weeks in Denver or New Orleans, more than once a month in LA, Vancouver, DC, Seattle, Chicago, or New York, just once every two months in Edinburgh, Paris, London, Oslo, Boston, San Francisco, or Toronto, and just a few times a year in Frankfurt, Germany.

We can track pollutants from the ocean to the table, and it’s through the fish oil. The fish oil used in the feed for farmed fish transfers pollutants to the fish themselves, and then the fish carries the pollutants to human consumers. So yes, salmon have the healthy omega-3 fatty acids, but they also contain high levels of toxic chemicals, and not just the PBCs, dioxins, and pesticides. Farmed salmon test positive for antibiotic residues, higher levels of forever chemicals, flame retardants, and also test positive for endocrine disrupting compounds—hormone disruptors like BPA. Something you don’t see in samples of sea vegetables like seaweed, presumably because of their low-fat content.

Farmed salmon may also have higher levels of mercury than wild-caught, though the opposite may be the case for farmed tuna. Arsenic also goes both ways, with more arsenic in wild sea bream compared to farmed, but less in wild sea bass. However, all the arsenic levels were bad, exceeding cancer benchmark values indicating a moderate risk of cancer due to fish consumption.

Some analyses have found dioxin and PCB levels similar across the board, but in general, you can think of aquaculture fish as “farmed and dangerous” compared to wild-caught in terms of higher levels of most pollutants. So that’s why researchers emphasize the importance of labeling as a means to help consumers avoid unnecessary exposure to highly contaminated fish. Unfortunately mislabeling is rampant.

So, the farmed versus wild-caught question may be largely academic, given the extent of seafood fraud and mislabeling. An investigation by the New York Attorney General found that consumers who bought what was advertised as “wild” salmon actually often received farm-raised salmon instead. Up to 43 percent of salmon tested across the United States, for example, were mislabeled, most commonly passing off farmed salmon as wild-caught.

Please consider volunteering to help out on the site.

Motion graphics by Avo Media

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Although the levels of industrial pollutants, like dioxins and PCBs, continue to decline in the food supply, there is one dietary source that still remains a major threat: fish. Everything eventually flows into the sea. Yes, we can get some dioxins from eating horses, but most of our exposure comes from eating fish.

The U.S. Environmental Protection Agency puts the tolerable upper limit of dioxin intake per kilogram of body weight at 0.7 picograms—less than one trillionth of a gram—per day. So, we should get less than this in our diet every day. As you can see, we’re already skirting the max by just consuming dairy, and fish takes us right over the top, even at low levels of consumption.

So, the adverse effects of chemical contaminants in seafood may counteract the benefits of any nutrients in fish. So much so that many dietary guidelines recommend no more than one serving a week of fish and seafood to cut down on exposure to toxic pollutants. But which is worse? Wild-caught or farmed?

Take salmon, for example. Salmon had the highest toxic equivalents of PCBs, followed by canned tuna, as well as the highest neurotoxic equivalents of PCBs. If you compare the levels of PCBs in salmon farmed in Maine and Canada, versus salmon wild-caught in Alaska, versus organically farmed salmon from Norway, compared to the wild-caught salmon, the farmed salmon, organic or otherwise, had significantly higher PCB levels.

This appears to extend to other contaminants too. Based on the testing of literally tons of salmon samples from around the world, for every toxin the researchers tested, the samples of farmed salmon had higher levels than did the wild-caught salmon—higher levels of DDT and these other banned pesticides. Over 10 times more PCBs in farmed salmon; over 10 times more dioxins. In order to not exceed EPA safety levels, we wouldn’t want to eat supermarket salmon more than once every two weeks in Denver or New Orleans, more than once a month in LA, Vancouver, DC, Seattle, Chicago, or New York, just once every two months in Edinburgh, Paris, London, Oslo, Boston, San Francisco, or Toronto, and just a few times a year in Frankfurt, Germany.

We can track pollutants from the ocean to the table, and it’s through the fish oil. The fish oil used in the feed for farmed fish transfers pollutants to the fish themselves, and then the fish carries the pollutants to human consumers. So yes, salmon have the healthy omega-3 fatty acids, but they also contain high levels of toxic chemicals, and not just the PBCs, dioxins, and pesticides. Farmed salmon test positive for antibiotic residues, higher levels of forever chemicals, flame retardants, and also test positive for endocrine disrupting compounds—hormone disruptors like BPA. Something you don’t see in samples of sea vegetables like seaweed, presumably because of their low-fat content.

Farmed salmon may also have higher levels of mercury than wild-caught, though the opposite may be the case for farmed tuna. Arsenic also goes both ways, with more arsenic in wild sea bream compared to farmed, but less in wild sea bass. However, all the arsenic levels were bad, exceeding cancer benchmark values indicating a moderate risk of cancer due to fish consumption.

Some analyses have found dioxin and PCB levels similar across the board, but in general, you can think of aquaculture fish as “farmed and dangerous” compared to wild-caught in terms of higher levels of most pollutants. So that’s why researchers emphasize the importance of labeling as a means to help consumers avoid unnecessary exposure to highly contaminated fish. Unfortunately mislabeling is rampant.

So, the farmed versus wild-caught question may be largely academic, given the extent of seafood fraud and mislabeling. An investigation by the New York Attorney General found that consumers who bought what was advertised as “wild” salmon actually often received farm-raised salmon instead. Up to 43 percent of salmon tested across the United States, for example, were mislabeled, most commonly passing off farmed salmon as wild-caught.

Please consider volunteering to help out on the site.

Motion graphics by Avo Media

Doctor's Note

For more on what you might ingest when eating fish, see:

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