Measurement / residue studyindependent cross-checkabstract checked★ key study I-FSH-111 in-depth review
Norwegian wild salmon carried more pollutants than farmed salmon
An Update on the Content of Fatty Acids, Dioxins, PCBs and Heavy Metals in Farmed, Escaped and Wild Atlantic Salmon (Salmo salar L.) in Norway.
Overview
Jensen IJ et al.. Foods 2020 · PMID 33352671 · DOI 10.3390/foods9121901
Dioxins, PCBs and mercury were about three times higher in wild than in farmed salmon, all below EU limits; farmed salmon had a lower omega-3:omega-6 ratio but more EPA+DHA per portion.
Does the study support the specific claim? No · Methodological quality: moderate
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Update salmon composition data.
- How was the study done?
Analysis of 60 fillets.
- How many people, animals or samples were studied?
Farmed, escaped and wild salmon.
- What was actually found?
Wild more contaminated; farmed has more omega-6.
- How large was the observed effect?
About 3-fold contaminant difference.
- What do the results mean in everyday life?
Farmed salmon is not more polluted today.
- What are the study's limitations?
One farm, small n.
- What does it say about Elawady's specific claim?
Contradicts 'farmed = more toxic'; supports the ratio direction.
- Do the results apply to Germany and Europe?
High.
- What can explicitly not be concluded from this study?
Other farms or countries.
Scientific in-depth review
1. Full reference
- Authors
- Jensen IJ et al.
- Journal
- Foods
- Year
- 2020
- Identifier
- PMID 33352671 DOI 10.3390/foods9121901
- Verification
- verified – PubMed efetch 2026-10-26; Crossref checked; full text PMC7766777: methods, results and discussion excerpts and funding read
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
Publication fund of UiT The Arctic University of Norway; no conflicts declared; farmed fish obtained from a producer
2. Research question
How do farmed, escaped and wild Atlantic salmon in Norway compare in nutrients and contaminants?
3. Study design and population
- Study design
- Measurement / residue study – Cross-sectional composition and contaminant analysis
- Population
Atlantic salmon fillets (farmed from one producer, July 2017; wild from Finnmark, 2017-2018; origin checked by scale analysis)
- Country
Norway
- Period
2017-2018
- Sample size
Farmed 20, escaped 17, wild 23
4. Methods and endpoints
- Exposure / intervention
Farmed versus wild origin
- Comparator
Wild Atlantic salmon
- Endpoints
Fatty acids, dioxins, dl-PCBs, PCB-6, Hg, As, Pb, Cd
- Statistical methods
Group comparisons
5. Actual results
- Results
Dioxins, dl-PCBs, mercury and arsenic were 'three times higher in wild compared to farmed salmon, but all well below EU-uniform maximum levels'. PCB-6: wild 5.09 versus farmed 3.34 ng/g. Fat: farmed 18%, about three times wild. Marine long-chain n-3 share 8.9% (farmed) versus 24.1% (wild). n-6:n-3 ratio 0.7 (farmed) versus 0.05 (wild). One 150 g portion a week gives 2.1 g (farmed) and 1.8 g (wild) EPA+DHA. Mercury in wild salmon nine-fold below the EU maximum level.
- Absolute risks
not applicable
- Authors' conclusion
Both farmed and wild Atlantic salmon are valuable sources of EPA and DHA.
6. Strengths
- Same-species comparison
- Origin of 'wild' fish verified (43% were farmed escapees)
7. Weaknesses
- Single farm, small n
- Single region
8. Risk of bias
- Orienting tool
- none applicable
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- some concerns
- Rationale
Small convenience samples.
9. Assessment of the statistical interpretation
n-6:n-3 0.7 corresponds to n-3:n-6 about 1.4; 0.05 corresponds to 20 (stats/C-FSH-04_ratios.py).
10. Relevance to the specific claim
Replicates I-FSH-02: farmed Atlantic salmon now has lower POPs and mercury than wild Atlantic salmon; the n-3:n-6 ratio is lower in farmed salmon.
11. Independent contrary findings
12. Transferability to Germany and Europe
High.
13. Overall methodological judgement
Independent replication of the reversal of the 2002 pattern.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | moderate |
| Risk of bias | some concerns |
| Precision of results | moderate |
| Directness | direct |
| Reproducibility | replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
15. Linked fact checks
- Farmed salmon contain significantly higher concentrations of organochlorine contaminants (PCBs, dioxins, chlorinated pesticides) and PBDE flame retardants than wild salmon, and European-farmed salmon carry the highest loads (based on samples analysed by Hites et al. around 2002). – Studies contradicting or limiting the claim
- Farmed fish today accumulate PCBs, dioxins and PBDEs at concentrations significantly higher than in their wild counterparts (present-tense generalisation in the archive summary). – Studies contradicting or limiting the claim
- The omega-3 to omega-6 ratio is about 10 in wild salmon but only 3-4 in farmed salmon. – Studies supporting the claim
- Because of the lower omega-3:omega-6 ratio, farmed salmon is converted from an anti-inflammatory into a pro-inflammatory meal, and the expected nutritional benefit disappears. – Studies contradicting or limiting the claim
- All salmon is farmed and salmon should not be eaten; sea bass, sea bream and similar fish should be eaten instead. – Studies contradicting or limiting the claim