Pollutants in Norwegian farmed salmon 1999-2011

Overview

Nøstbakken OJ et al.. Environ Int 2015 · PMID 25454244 · DOI 10.1016/j.envint.2014.10.008

Pollutant levels fell from 1999 to 2011 and no sample exceeded EU limits; the authors calculated up to 1.3 kg per week to reach the safety limit then in force, which EFSA has since made much stricter.

Does the study support the specific claim? No · Methodological quality: high

Original publication

Plain-language summary

Scientific in-depth review

1. Full reference

Authors

Nøstbakken OJ, Hove HT, Duinker A, Lundebye AK, Berntssen MH, Hannisdal R, Lunestad BT, Maage A, Madsen L, Torstensen BE, Julshamn K

Journal

Environ Int

Year

2015

Identifier

PMID 25454244 DOI 10.1016/j.envint.2014.10.008

Verification

verified – PubMed E-utilities efetch, 2026-10-25

Retracted

no

Corrections

none

Extent checked

full text

Conflicts of interest and funding

No funding or competing-interest statement in the available full text; authors from NIFES (Norwegian state institute) using Norwegian Food Safety Authority surveillance data; acknowledgement to NFSA.

2. Research question

Trends in contaminants in Norwegian farmed salmon 1999-2011 relative to tolerable intakes

3. Study design and population

Study design

Measurement / residue study – Analysis of 13 years of official surveillance data (EU Council Directive 96/23/EC programme run by the Norwegian Food Safety Authority; analyses at NIFES) on contaminants in farmed salmon fillets, with time-trend regression and TWI-based consumption limits

Population

Market-size (3-5 kg) Norwegian farmed Atlantic salmon collected from processing plants in all coastal regions with aquaculture

Country

Norway

Period

1999-2011

Sample size

>2300 samples (individual fish 1999-2003; pools of 5 fish 2004-2011; >10,000 fish in total). Per analyte: metals 1,025 samples (2005-2011); dioxins/dl-PCBs 432 (1999-2011); PCB6 475 (2002-2011); pesticides 324 (2006-2011)

Inclusion and exclusion criteria

Sampling randomised by season and region; regions covering >=10% of farm sites each year; analysts blinded to sample identity; skin removed (subcutaneous fat added back)

4. Methods and endpoints

Exposure / intervention

Sampling year

Comparator

Earlier years; SCF PTWI 14 pg WHO-TEQ/kg bw/week for dioxins + dl-PCBs (2001) and EFSA TWI 1.3 ug/kg bw/week for methylmercury (2012); EU maximum levels

Endpoints

Fillet mass fractions of Hg, As, Cd, Pb, dioxins and dl-PCBs (TEQ), PCB6, DDT and other organochlorine pesticides; maximum weekly salmon intake for a 70 kg person to reach the TWI

Statistical methods

Medians with IQR (non-normal data, many <LOQ); linear regression and Kruskal-Wallis for trends; upper-bound LOQ for TEQ sums; conversion of older TEQ values (WHO-1998 to 2005) by published regression; no regression when >50% <1.5x LOQ

5. Actual results

Results

Hg median 0.029 and As 1.07 mg/kg ww (2005-2011), both declining (As slope -0.72, r2 0.52; Hg slope -0.48, r2 0.23; p<0.0001). Cd (933/1,025) and Pb (994/1,025) mostly <LOQ. Dioxins + dl-PCBs declined 1999-2011 (slope -0.66, r2 0.43, p<0.0001); median all years 0.9, 2011 0.6 pg TEQ-WHO05/g. PCB6 median 5.94 ug/kg ww, no clear trend. Sum DDT declined, median 9.40 ug/kg ww; other pesticides near LOQ. No sample exceeded EU maximum levels. Maximum weekly intake to reach the TWI (salmon as only source) rose from 370 g in 1999 to >1.3 kg in 2011; dioxins + dl-PCBs were the limiting contaminants; 660 g/week would contribute 50% of the TWI (2011 data).

Absolute risks

not reported (exposure/TWI comparison only)

Authors' conclusion

Contaminant levels in Norwegian farmed salmon generally decreased 1999-2011; dioxins and dl-PCBs were limiting; safe consumption rose from 370 g/week (1999) to >1.3 kg/week (2011), not including other dietary sources.

6. Strengths

• Large official surveillance dataset with randomised sampling and blinded analysis
• Accredited methods with certified reference materials
• Upper-bound LOQ handling (conservative)
• Explicit comparison with earlier critical studies (Hites 2004)

7. Weaknesses

• Uses SCF 2001 TWI (14 pg TEQ/kg bw/week); EFSA lowered the TWI to 2 pg TEQ/kg bw/week in 2018 (I-FSH-17), so the 1.3 kg figure is outdated
• Other dietary sources excluded from consumption limits
• Ends 2011; feed composition has changed since
• Change in sampling unit (individual to pooled) and in methods over time; older TEQ data converted by regression
• No wild-salmon comparison in the same programme
• Authors from state institute linked to seafood sector (no COI statement)

8. Risk of bias

Orienting tool

No standard tool fits (contaminant surveillance/exposure measurement); structured validity judgement

Type of assessment

structured assessment based on the full text by a single reviewer (no formal double review)

Full formal assessment

no

Overall risk of bias

low

Rationale

Single-reviewer structured judgement based on the full text; not formal (needs two independent reviewers). Measurement validity is high; the main concern is interpretation against an outdated TWI.

Full-text review (25 October 2026): Added per-analyte sample sizes, medians and regression slopes, randomised/blinded sampling, no EU maximum-level exceedance, 370 g (1999) to >1.3 kg (2011), TWI used (SCF 14 pg TEQ/kg bw/week) and outdated relative to EFSA 2018; no COI/funding statement; structured validity domains (overall unchanged: low).

9. Assessment of the statistical interpretation

Trend estimates robust (p<0.0001) but r2 moderate (0.23-0.52). The 1.3 kg/week figure uses the SCF 2001 PTWI of 14 pg TEQ/kg bw/week; EFSA's 2018 TWI of 2 pg TEQ/kg bw/week (I-FSH-17) is 7-fold lower, so by simple proportional recalculation (reviewer arithmetic, not in the paper, ignoring WHO-1998 vs WHO-2005 TEF differences) the same 2011 levels would correspond to roughly 190 g/week from salmon alone.

10. Relevance to the specific claim

Contradicts C-FSH-01/02/03/13.

11. Independent contrary findings

12. Transferability to Germany and Europe

High (Norwegian salmon dominates EU market).

13. Overall methodological judgement

Key EU-relevant surveillance evidence that contaminant levels in Norwegian farmed salmon fell 1999-2011 and stayed below EU maximum levels; the consumption limit (1.3 kg/week) is based on a TWI that EFSA has since lowered substantially, so it overstates the current margin of safety. Contradicts claims of rising or present-day extreme contamination, but not the point that farmed salmon contributes to dioxin/PCB intake.

14. Open questions

Levels after 2011 and against the 2018 EFSA TWI; direct comparison with wild salmon under the same programme.

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
• Farmed Atlantic salmon from northern Europe should be eaten no more than once every five months to stay below an acceptable cancer-risk threshold (and, per the archive's card for Foran 2005, dioxin-contaminated farmed salmon less than once a month). – 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

Use by the Tayebat archive

Note: according to the archive, the studies were compiled by the archive operators. Whether Dr. Elawady himself cited this study is not established.

What the archive says about the study

Bibliography only.

A. What was actually studied?

Contaminant trends.

B. What did the authors find?

Hg, As, dioxins, dl-PCBs and DDT declined 1999-2011; no EU maximum-level exceedances; tolerable intake rose from 370 g to >1.3 kg salmon/week (SCF 2001 TWI, salmon as sole source).

C. What conclusions do the authors themselves draw?

Levels decreased.

D. What does the archive derive from it?

Not discussed; listed among farmed-fish studies.

E. Is this derivation scientifically justified?

Not discussed by the archive; its findings contradict the narrative of current high contamination.

Adequacy of the interpretation (by the archive)

not applicable