What Contaminants Are in Farmed Salmon? Understanding the Risks

January 4, 2026 •

4 min read

According to a 2004 study published in the journal Science, researchers found that farmed salmon contained significantly higher levels of certain toxic contaminants, including PCBs, than wild salmon. This discovery brought into focus the critical question: what contaminants are in farmed salmon and how can they affect human health?

Quick Summary

Farmed salmon can contain higher levels of certain toxic substances like persistent organic pollutants (POPs) and antibiotics, largely influenced by feed and farming methods. Concerns also exist around pesticides and microplastics.

Key Points

PCBs and Dioxins: Farmed salmon often contain higher levels of persistent organic pollutants (POPs), including PCBs and dioxins, largely due to contaminants in their feed.
Antibiotics and Pesticides: Overcrowding in farms necessitates the use of antibiotics and pesticides, which can lead to bacterial resistance and environmental pollution.
Microplastics: Farmed salmon are exposed to and can ingest microplastics from both their environment and feed, which may carry other pollutants.
High-Fat Diet: Because POPs accumulate in fat, and farmed salmon are fed a high-fat diet, they can be more efficient collectors of these toxins compared to leaner wild salmon.
Informed Choices: Consumers can reduce their exposure by choosing wild-caught or certified sustainably farmed salmon and varying their fish intake.
Not All Farmed Salmon is Equal: Contaminant levels can vary significantly depending on the farming region and practices. For example, some studies suggest European farmed salmon historically had higher POPs.

The Primary Contaminants in Farmed Salmon

Modern aquaculture, while an important source of protein, presents specific challenges regarding contaminants. The confined, high-density environment of many open-net fish farms, combined with the composition of fish feed, contributes to the accumulation of various pollutants in farmed salmon that are less common in their wild counterparts. The following sections detail the most significant contaminants associated with farmed salmon production.

Persistent Organic Pollutants (POPs)

POPs are a group of toxic chemicals that includes polychlorinated biphenyls (PCBs), dioxins, and certain pesticides like DDT. These substances are known to persist in the environment and bioaccumulate in fatty tissues. Studies have consistently shown that farmed salmon often have higher levels of POPs than wild salmon, primarily because the concentrated fishmeal and fish oil used in their feed is a source of these contaminants. PCBs, in particular, are a major concern. The Environmental Protection Agency (EPA) has classified PCBs as probable human carcinogens, and exposure is linked to issues with the immune and nervous systems.

Antibiotics and Pesticides

The crowded conditions within many open-net salmon farms create a perfect breeding ground for disease and parasites, most notably sea lice. To combat these outbreaks, farms may use antibiotics and pesticides. While some countries, like Norway, have significantly reduced their reliance on antibiotics, they are still heavily used in other regions, such as Chile. The overuse of antibiotics contributes to the rise of antibiotic-resistant bacteria, which poses a serious public health risk. Pesticides used to treat sea lice can also leach into the surrounding water, harming other marine life, such as crustaceans.

Microplastics

As plastic pollution becomes more widespread, microplastics are now a known contaminant in marine food webs. Farmed salmon can ingest these tiny plastic particles from both the surrounding marine environment and their commercial feed. While the full extent of the health effects of consuming microplastics is still under investigation, these particles are known to absorb and concentrate other pollutants, potentially transferring them into the fish's tissues and, subsequently, to consumers. Some studies have confirmed the presence of microplastics in farmed salmon's gastrointestinal tracts and gills.

Heavy Metals

Heavy metals like mercury and arsenic can also be present in salmon. Unlike POPs, some studies have shown wild salmon can have slightly higher levels of certain metals compared to farmed salmon, depending on the region and the metal in question. However, overall levels in salmon are generally considered low compared to larger, predatory fish like swordfish or tuna. Nevertheless, chronic exposure to heavy metals is a legitimate concern for any regular fish consumer.

Farmed vs. Wild Salmon: A Contaminant Comparison

This table highlights the differences in contaminant profiles between farmed and wild salmon, informed by extensive research.


Feature	Farmed Salmon (Atlantic)	Wild Salmon (Pacific)
Persistent Pollutants (PCBs/Dioxins)	Significantly higher levels on average due to feed composition.	Lower levels, reflecting their natural, less contaminated diet.
Antibiotics	Used to prevent disease in crowded pens, leading to potential residue issues.	Not exposed to antibiotics.
Pesticides	Used to control sea lice infestations; residues may be present.	Natural environment, no pesticide exposure.
Microplastics	Can ingest microplastics from feed and farm environments.	Can ingest microplastics from the wider ocean ecosystem.
Heavy Metals (e.g., Mercury)	Generally low levels, though can vary by source. Some studies suggest slightly lower than wild.	Typically low, but can accumulate based on diet and longevity.
Fat Content	Higher total fat content from managed diet.	Leaner due to a more active lifestyle and varied diet.

The Role of Farming Practices in Contamination

The environment and methods of salmon farming are directly tied to the presence of contaminants. The high-density pens in coastal waters are essentially floating feedlots, which lead to significant waste output. This includes uneaten feed and fish feces, which can concentrate nutrients and create waste build-up on the seafloor. Additionally, the feed itself plays a crucial role. Fishmeal and fish oil, particularly from industrially polluted areas, are the main vectors for POPs entering the food chain.

Sustainable Aquaculture and Consumer Awareness

To address these issues, the aquaculture industry is undergoing changes. Some farmers are shifting to land-based, closed-containment systems that prevent the release of waste and the spread of disease. Changes in feed formulations, including the use of less contaminated or alternative protein sources, are also helping to reduce POP levels.

Consumers can take several actions to make more informed choices:

Prioritize wild-caught salmon: Especially wild Alaskan salmon, which typically boasts a cleaner contaminant profile.
Choose certified farmed salmon: Look for reputable certifications like the Aquaculture Stewardship Council (ASC), which enforce stricter standards on feed, water quality, and antibiotic use.
Vary your fish intake: Diversify your seafood consumption to avoid a high, consistent exposure to contaminants from a single source.
Limit consumption of fattier farmed salmon: Since POPs accumulate in fat, reducing intake or trimming fat and removing the skin can be a strategy, particularly with highly contaminated farmed salmon.

For more information on the risks associated with farmed salmon, the Environmental Working Group provides detailed reports on PCB contamination.(https://www.ewg.org/research/pcbs-farmed-salmon)

Conclusion

While farmed salmon remains a popular source of protein, consumers should be aware of the potential contaminants that can be present, including PCBs, dioxins, antibiotics, pesticides, and microplastics. The presence and levels of these substances are heavily influenced by specific farming practices and feed composition. By opting for wild-caught varieties, choosing certified farmed options, and diversifying seafood intake, consumers can mitigate potential risks while still enjoying the nutritional benefits of fish. The choice between wild and farmed salmon depends on a consumer's willingness to balance these nutritional benefits against the specific risks associated with modern aquaculture methods.

Frequently Asked Questions

Yes, regulatory bodies generally consider farmed salmon safe to eat. However, studies have identified higher levels of some contaminants, such as PCBs, compared to wild salmon. Consumers should weigh these potential risks against the nutritional benefits and consider consumption frequency.

Farmed salmon accumulate PCBs through their feed, which is often made from concentrated fishmeal and fish oil derived from smaller fish. Wild salmon consume a more varied diet in a broader ocean environment, leading to lower contaminant levels.

Antibiotic use varies significantly by region. While some countries like Norway have reduced usage substantially, others, such as Chile, still rely heavily on them due to high fish densities and disease outbreaks. Look for certifications that limit antibiotic use.

Pesticides are used to combat sea lice on farms. While regulations aim to minimize residues, the main concern is their environmental impact, as they can harm other marine life when released into the surrounding waters. The potential for residue transfer to human tissue is a secondary concern.

While microplastics have been found in the gills and digestive tracts of farmed salmon, some studies, including research by the major salmon farmer Mowi, have found no microplastics in the salmon fillets themselves. More research is needed on potential contaminant transfer from plastics to muscle tissue.

No. All marine fish can be exposed to environmental contaminants, including heavy metals like mercury and microplastics. However, wild salmon generally have lower levels of persistent organic pollutants (POPs) compared to conventionally farmed salmon.

Exposure to high levels of contaminants like PCBs and dioxins over time can potentially increase the risk of certain health issues, including cancer, immune system damage, and neurological problems. Regulatory limits are set to minimize this risk, but some studies have exceeded health-based guidelines.