Monitoring program for pharmaceuticals, illegal substances and contaminants in farmed fish

1.1 - Background

Official control rules enable the enforcement of EU regulations and standards governing food safety and animal health. This ensures that businesses and operators comply with legal requirements, preventing fraudulent practices, and maintaining the integrity of food products. Moreover, the rules are designed to uphold standards of food safety and quality throughout the agri-food chain. By conducting official controls, authorities can identify, and address risks associated with food production, processing, and distribution, thereby increasing consumer safety and confidence in food products marketed in EU and EEA countries.

To introduce a more harmonized and coherent approach to official controls and to simplify the existing framework, the official control rules to verify compliance with food and feed law, animal health and welfare, plant health, and animal-by-products rules were integrated into a single regulation. With effect from 14 December 2017, the Official Controls Regulation (EU) 2017/625¹ (OCR) repealed Council Directive 96/23/EC. The OCR also included relevant transitional measures, which provided that, until 14 December 2022, competent authorities were obliged to continue the performance of necessary official controls in accordance with Directive 96/23/EC. In Norway, legislation on official controls (“kontrollforordningen”) was updated and aligned with the OCR, entering into force as of April 2020².

In 2022, supplementing regulations were adopted, laying down the specific requirements for the performance of official controls of pharmacologically active substances authorised as veterinary medicinal products or as feed additives and of prohibited or unauthorised pharmacologically active substances and residues thereof (Commission Delegated Regulation (EU) 2022/1644³ and Commission Implementing Regulation (EU) 2022/1646⁴), and contaminants in food (Commission Delegated Regulation (EU) 2022/931⁵ and Commission Implementing Regulation (EU) 2022/932⁶).

The requirements for the national risk-based control plan on illegal or authorized pharmacologically active substances and contaminants, in accordance with these specifications, were implemented in the monitoring program for farmed fish in 2023.

Considering relevance in aquaculture production, the following residues and substance groups were included into the national risk-based control plan for pharmacologically active substances in Norwegian farmed fish in line with Annexes I and II of Commission Delegated Regulation (EU) 2022/1644:

Group A – Prohibited or unauthorized pharmacologically active substances in food-producing animals

A1a Stilbenes;

A1c Steroids;

A1d Resorcylic acid lactones, including zeranol;

A1e Beta-agonists;

A2a Chloramphenicol;

A2b Nitrofurans;

A2c Metronidazole;

A2d Other substances;

A3a Dyes

Group B – Pharmacologically active substances authorized for use in food-producing animals

B1a Antimicrobial substances;

B1b Insecticides, fungicides, anthelmintics and other antiparasitic agents;

B1c Sedatives

Contaminant groups included in the national risk-based control plan according to Annex I of Commission Delegated Regulation (EU) 2022/931:

(1) Halogenated persistent organic pollutants;

(2) Metals;

(3) Other contaminants

1.2 - Group A, Prohibited or unauthorized pharmacologically active substances in food-producing animals

Fish tested for illegal compounds (Commission Regulation (EU) 37/2010⁷) were collected at the farm by official inspectors from the Norwegian Food Safety Authority (NSFA), without prior notification to the farmers. Samples were taken at all stages of farming in order to represent farmed fish during production. Substances monitored in Group A include growth promoters like steroids, stilbenes and beta-agonists, unauthorized pharmacologically active feed additives, such as resorcylic acid lactones and unauthorized drugs. Unauthorized drugs considered most relevant for aquaculture are chloramphenicol, nitrofurans, metronidazole and dyes.

To ensure harmonized levels for the control of unauthorized substances, the analytical methods should meet a minimum method performance requirements (MMPRs) set by the European Union⁸, and European reference laboratories (EU-RLs)⁹.

1.3 - Group B, Pharmacologically active substances authorized for use in food-producing animals

In order to protect public health, current EU legislation⁷ provisions the assignment of Maximum Residue Limits (MRLs), where required, for all legally applied pharmacologically active substances in products intended for human consumption. An MRL denotes the highest permitted residual concentration of a legally applied veterinary drug and is evaluated individually for each substance and food product. Consumption of food with drug residues below the MRL should not pose a health risk to the consumer. For fish, the MRLs are set for muscle and skin in natural proportions. Samples examined for veterinary drugs were collected from fish at processing plants and the samples are representative of fish ready to be placed on the market for human consumption.

1.4 - Contaminants

Samples examined for contaminants were collected from fish at processing plants and are representative of fish ready for human consumption. In the EU, maximum levels (MLs) have been established for certain contaminants in food¹⁰. For fish MLs are established for dioxins, dioxins and dioxin-like PCBs, PCB-6, per- and polyfluoroalkyl substances (PFAS) within the compound group of halogenated persistent organic pollutants, as well as the heavy metals mercury, cadmium, and lead, which are therefore mandated within the official control plan for contaminants. In addition, although no MLs have been established for fish, the levels of polybrominated diphenyl esters (PBDEs), chlorinated and organophosphorus pesticides, and other chemical elements were included in the monitoring in 2023.

2.1 - Sampling

Samples were taken on fish farms or slaughterhouses by official inspectors from the NFSA in all fish-producing regions in Norway. The sampling plan was randomized according to season and region. In 2023, the monitoring program included a total of 988 samples of Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss), turbot (Scophthalmus maximus), Atlantic halibut (Hippoglossus hippoglossus), Atlantic cod (Gadus morhua) and spotted wolffish (Anarhichas minor ).

Samples were transported to the Institute of Marine Research (IMR) in a frozen state. Analyses of substances with anabolic effects or unauthorized substances were performed on individual fish samples, whereas authorized pharmacologically active substances and contaminants were analyzed as pooled samples comprising three fish from the same cage/farm. For most analyses, the Norwegian quality cut (NQC) was used^11,12. However, both NQC and individual liver samples were collected for analysis of antibiotics. Samples to be used for analyses of substances with anabolic effects or unauthorized substances also included small fish from early life stages. In these cases, the whole fish except head, tail and gut were used.

2.2 - Pre-treatment

Upon arrival at the IMR the sample identification was anonymised for the analysts. A backup sample was stored for all samples. The muscle samples were homogenized before analyses. For analyses of group B substances and contaminants, pooled samples of muscle from three fish from the same cage/farm were homogenized. Samples of liver were excised from the fish to be screened for residues of antimicrobial agents by the microbiological inhibition zone assay. Liver samples were examined individually and if residues were detected, the backup sample of muscle was analyzed by chemical methods. The maximum residue limits for veterinary drugs are set for muscle and skin in natural proportions⁷. Therefore, according to the analytical protocol, any detection of drug residues in the muscle or liver was followed by a duplicate re-analysis of the backup sample, consisting of muscle and skin in natural proportions.

2.3 - Analytical methods

The laboratory routines and most of the analytical methods are accredited in accordance with the standard ISO 17025. A summary of the analytical methods and their limit of detection (LOD) or limit of quantification (LOQ) is shown in Table 1. The LOD is the lowest level at which the method is able to detect the substance, while the LOQ is the lowest level for a reliable quantitative measurement. For all methods, a sample blank and a quality control sample (QC) with a known composition and concentration of target analyte are included in each series. The methods are regularly verified by participation in inter laboratory proficiency tests, and by analysing certified reference material (CRM), where such exist.

3.1 - Substances with anabolic effects and unauthorized substances

In 2023, a total of 384 individual fillet samples were tested for residues of illegal substances, including stilbenes (191 samples), steroids (95 samples), resorcylic acid lactones (Zeranol & beta-Zearalanol; 191 samples), beta agonists (98 samples), and unauthorized veterinary drugs including Chloramphenicol (96 samples), Nitrofurans (98 samples), Metronidazole (95 samples), Dapsone (95 samples) and Dyes (191 samples). The samples were mainly taken from Atlantic salmon, but also samples from rainbow trout, Atlantic cod, spotted wolffish and Atlantic halibut were analysed. The evaluation criterion for samples for official controls of illegal substances is presence.

In 2023, testosterone was detected (3.7 ug/kg) in one sample rainbow trout. The confirmed (re-analysis) laboratory-analysed finding was reported to the Norwegian Food Safety Authority (Mattilsynet). The subsequent investigation concluded with compliance for the sample, identifying a source of cross-contamination at the sampling site as the cause for the positive result. The analysis result, handling, processing and conclusion on the positive sample were further reported to the European Authorities through the annual data reporting.

No residues of any other unauthorized compounds were detected in any of the samples. The individual substances included in the monitoring of these substance groups, analytical methods, and reference limits are listed in Table 1, Materials and Methods.

3.2 - Residues of authorized veterinary drugs

Samples analyzed for veterinary drugs were collected from fish at processing plants, representing fish ready for human consumption. The maximum residue limit (MRL) for veterinary drugs is defined for muscle and skin in natural proportions⁷. Therefore, according to the analytical protocol, any detection of drug residues in a sample of muscle or liver would be followed by a re-analysis of the backup sample, consisting of muscle and skin in natural proportions, in duplicate.

3.2.1 - Group B1a, Antimicrobial substances

Antibacterial agents were monitored through a combination of a three-plate bioassay and chemical methods. The broad groups a) quinolones, b) amphenicols and tetracyclines and c) sulfonamides were screened in 127 pooled liver samples, representing livers from 381 fish (Table 3). In addition, a total of 108 pooled fillet samples, representing 324 fish taken at processing sites (Group B samples), were tested for residues of antibacterial substances using chemical analysis methods (Table 4). No residues were detected in any of the samples analyzed. Furthermore, sulfonamides, ormethoprim and trimethoprim were measured in muscle samples of 95 individual fish samples taken at the farm (Group A samples), using a chemical analysis method (Table 4). None of the substances included in the measurement were detected above LOQ.

3.2.2 - Group B1b, Insecticides, fungicides, anthelmintics and other antiparasitic agents

3.2.2.1 - Carbamates and pyrethroids

In 2023, carbamates and pyrethroid substances were monitored in 111 samples (Table 5). Cypermethrin was detected in 22 out of 99 pooled fillet samples of Atlantic salmon and one out of seven samples of rainbow trout. Residues of deltamethrin were found in one samples of salmon.

Both cypermethrin and deltamethrin are synthetic pyrethroid substances used as pharmaceutical delousing agents applied as bath treatment in aquaculture farm cages, but also as insecticides in large-scale commercial agricultural applications. Residues of cypermethrin and deltamethrin in fish may therefore also originate from transfer via plant-based ingredients in fish feed. 

There are no pesticide MRLs established for cypermethrin or deltamethrin in fish muscle^13,14. The maximum values of cypermethrin measured were 2.9 µg/kg in salmon, and 1.2 µg/kg in rainbow trout, which are both below the MRL of 50 µg/kg⁷ established for cypermethrin residues from use as veterinary drugs. The MRL for deltamethrin used as veterinary drug is established at 10 µg/kg for fin fish⁷. The maximum value of deltamethrin detected (1.6 µg/kg in Atlantic salmon) was found below this MRL.

None of the other carbamate or pyrethroid substances included in the monitoring, were detected in any of the samples.

3.2.2.2 - Anthelmintics

The residues of anthelmintics, such as anti-sea-lice agents (Table 6) and agents for treatment of endoparasites (Table 7), were monitored in a total of 490 pooled fillet samples, representing 1470 fish.

Residues of the anti-sea lice agent emamectin (6.2 µg/kg) were detected in one out of 142 analyzed samples; the level was below the MRL of 100 µg/kg⁷. Residues of imidacloprid (5.6 µg/kg) were detected in one sample of Atlantic salmon and were below the MRL established at 600 µg imidacloprid/kg for fish fillet⁷. No residues of other anti-sea lice agents or antiparasitic agents were detected in any of the samples in 2023.

3.2.3 - Group B1c, Sedatives

No residues of isoeugenol or eugenol were found in any of the 113 samples analyzed (Table 8).

3.3 - Contaminants

3.3.1 - Halogenated persistent organic pollutants

3.3.1.1 - Dioxin, dl-PCBs and PCB-6

The levels of dioxin (PCDD+PCDF), dl-PCBs and PCB-6 in farmed fish are shown in Table 9. Most of the samples were taken from Atlantic salmon, but also samples from rainbow trout, Atlantic cod, turbot and Atlantic halibut were examined. The sums of dioxins, dioxins + dl-PCBs and PCB-6 are calculated as upper bound¹⁰. Accordingly, the numerical LOQ values were used for congeners with levels below LOQ.

The levels of dioxins and dl-PCBs are reported as ng toxic equivalents 2005 (TEQ05)/kg and represent the sum of 17 different PCDD/F and 12 dl-PCBs where each congener was multiplied by a Toxic Equivalency Factor (TEF). TEF values are determined by the World Health Organization (WHO), and the toxicity of each congener is expressed relative to the most toxic form of dioxin, which has a TEF value of 1^10,15. TEF values have recently been reevaluated and updated¹⁶. However, the new values have not yet been incorporated into the legal framework, and the 2005 TEF is still applied for the calculation of the TEQ.

Dioxin levels measured in different farmed fish species in 2023 were similar to those found in the previous year. For salmon, the median of the sum of dioxins was 0.11 ng TEQ/kg w.w. The maximum value found in salmon (0.28 ng TEQ/kg w.w.) was below the EU maximum level of 3.5 ng TEQ/kg w.w.¹⁰ The median of the sum of all 29 PCDD/F and dl-PCBs was 0.32 ng TEQ/kg w.w for salmon (same as in 2022) and 0.50 ng TEQ/kg w.w for rainbow trout. The highest result for sum dioxin and dl-like PCBs was 0.76 ng TEQ/kg w.w., measured in tubot. All measured values were below the EU maximum level of 6.5 ng TEQ/kg w.w.¹⁰. The median of PCB-6 for salmon was 2.7 μg/kg w.w and 3.9 μg/kg in rainbow trout, with maximum concentrations of 5.7 and 4.7 μg/kg w.w, respectively. For PCB-6, a maximum level is set at 75 μg/kg w.w. in the EU¹⁰.

3.3.1.2 - Organochlorine pesticides

For several of the pesticides, the amount present is calculated as a sum, including metabolites or transformation products¹⁷. The results for these groups of pesticides are presented in Table 10. To calculate the sum of the components, conversion factors (Table A1, Appendix) are used to adjust for different molecular weights¹⁷. The sums in Table 10 were calculated according to the upper bound (UB) formula. DDT and Chlordane levels were calculated as both the sum of all measured metabolites, as well as the sums of metabolites according to the legal residue definitions established through Regulation (EC) No 149/2008¹⁸. When using UB calculations, the numerical value of LOQ is used as a concentration value for each non-quantified analyte. UB thus represents a “worst-case scenario”. As an example, all measurements of endosulfan are below LOQ, however, a sum is generated based on the LOQ-values. The results for the organochlorine pesticides are summarised in Table 11.

There are currently no MRLs established in fish fillet for any of the listed pesticides¹⁹.

3.3.1.3 - Perfluorinated compounds

Per- and polyfluoroalkyl substances (PFAS) are a large class of synthetic chemicals. They have a wide range of physical and chemical properties and have been used in various applications for over 50 years. PFAS are increasingly detected as environmental pollutants, and some of the substances have been linked to negative health effects. From the 1^st January 2023, MLs have been established for fish fillet for four PFAS (PFOS, PFOA, PFNA, PFHxS) individually and their sum (PFAS-4). PFAS are thus included into the control plan for farmed fish and have been analyzed in a total of 296 fillet samples in 2023. To survey the potential presence of additional PFAS compounds, 40 samples (36 samples of Atlantic salmon, two samples of rainbow trout, one sample of cod, and one sample of turbot) were sent for analysis with an extended method covering an additional 29 compounds (listed in Table A2, Appendix). The combined results of the PFAS measurements are presented in Table 12.

While most of the analyzed PFAS compounds were not found at levels above the respective LOQs, perfluorbutansulfonamid, FOSA, and PFOS were detected in samples of (almost) all species analyzed.

In addition, PFDA, PFNA, PFUnDA and PFHxSA were detected in individual samples of mainly turbot, but also cod and salmon. However, the measured levels did not exceed the MLs established for PFOS and PFNA individually, nor their sum (Sum PFAS-4).

In 2023, two turbot samples were included in the control plan. These samples consistently showed the highest levels, albeit not always significantly higher than the other species.

3.3.1.4 - Brominated flame retardants

PBDEs were measured in 109 pooled fillet samples (Table 13). The EU currently has no maximum limit for BFRs in food.

3.3.2 - Metals and chemical elements

In 2023, monitoring of the levels of chemical elements, such as arsenic, total mercury, cadmium, and lead, included 341 samples of Atlantic salmon, 22 samples of rainbow trout, 10 samples of Atlantic cod, two samples of turbot and two samples of Atlantic halibut (Table 14).

The concentrations for total mercury were below the EU MLs for fish fillet, for all samples. The highest concentrations of total mercury were 0.06 mg/kg w.w. in salmon and rainbow trout (ML: 0.3 mg/kg), and 0.07 mg/kg w.w. in Atlantic cod (ML: 0.3 mg/kg), turbot (ML: 0.5 mg/kg) and halibut (ML: 1 mg/kg; Table 13).

Cadmium was found in one sample of Atlantic salmon (0.001 mg/kg w.w.) and one sample of Atlantic halibut (0.001 mg/kg w.w.), and both samples of turbot. The maximum concentration was 0.003 mg/kg w.w. in turbot, and was below the EUs maximum level of 0.05 mg/kg w.w.¹⁰. None of the samples of rainbow trout and Atlantic cod contained cadmium above the LOQ.

Lead was found in two samples of Atlantic salmon (0.01 mg/kg w.w.). In all remaining samples of Atlantic salmon, and all samples of rainbow trout, Atlantic cod, turbot and Atlantic halibut the concentration of lead was below the LOQ. The EU maximum level is currently set at 0.30 mg/kg w.w. in muscle meat of fish¹⁰.

Arsenic is determined as “total arsenic”, comprising the sum of all arsenic species. The highest concentration measured was 1.9 mg/kg w.w. in cod and turbot (Table 14). The median and maximum concentrations of total arsenic in Atlantic salmon were 0.51 and 1.5 mg/kg w.w., respectively. The median and maximum concentrations of Arsenic in rainbow trout samples were 0.8 and 1.7 mg/kg w.w., respectively. There is currently no EU upper limit for arsenic in fish fillets.

Eleven additional chemical elements were analyzed in 2023. There is currently no EU limit established for any of these elements. Molybdenum, nickel and silver were not detected in any of the analyzed samples. Cobalt and vanadium were only found in salmon (one and 44 samples, respectively), with maximum concentrations of 0.022 and 0.018 mg/kg w.w., respectively. Chromium was found in all fish species, with maximum concentrations ranging from 0.011 mg/kg w.w. in turbot to 0.17 mg/kg w.w. in Atlantic salmon.

Iron, manganese, selenium and zinc are essential nutrients for humans. The levels of iron, manganese and selenium were found to be similar to the previous years. Moreover, zinc and copper concentrations in fish fillet were found at similar levels to previous years²⁰.

3.3.3 - Others

The compound group “others” is a group not required for finfish products by Regulation (EU) 2017/625 but includes substances deemed relevant for analyses in Norwegian aquaculture fish by the NFSA and IMR, because these undesirable compounds are present in the environment and may affect food safety. In 2023, organophosphorous pesticides were included in this group.

3.3.3.1 - Organophosphorous compounds

Organophosphorus pesticide residues, chlorpyriphos, chlorpyriphos-methyl, and pirimiphos-methyl, were determined in 111 pooled fillet samples, representing fillet of 333 fish (Table 15). No residues of chlorpyriphos or chlorpyriphos-methyl were detected in any of the samples. Pirimiphos-methyl was detected in seven of 99 samples of Atlantic salmon. The maximum concentration was 0.31 µg pirimiphos-methyl/kg fillet w.w.. There is currently no MRL established for pirimiphos-methyl in fish fillet¹⁹. No residues were detected in samples of rainbow trout, Atlantic cod or spotted wolffish.

In 2023, presence of steroids (testosterone) was confirmed in one sample of rainbow trout. However, the sample was found compliant following investigation by the NFSA. Apart from that, no residues of substances with anabolic effect or unauthorized substances were detected in any of the samples analysed.

Residues of the authorized anti-sea-lice agents emamectin and imidacloprid were detected in one sample of salmon each. In addition, cypermethrin and deltamethrin, which can be used both as anti-sealice agents and plant protection agents, was found. However, the concentrations for all of the residues were well below the respective MRLs for the compounds.

As for the previous years, no residues of antibiotics, endoparasitic agents or sedatives were detected in any of the samples.

For contaminants, none of the samples exceeded the EUs maximum levels, where such levels have been established.

1. Regulation (EU) 2017/625 of the European Parliament and of the Council of 15 March 2017 on official controls and other official activities performed to ensure the application of food and feed law, rules on animal health and welfare, plant health and plant protection products, amending Regulations (EC) No 999/2001, (EC) No 396/2005, (EC) No 1069/2009, (EC) No 1107/2009, (EU) No 1151/2012, (EU) No 652/2014, (EU) 2016/429 and (EU) 2016/2031 of the European Parliament and of the Council, Council Regulations (EC) No 1/2005 and (EC) No 1099/2009 and Council Directives 98/58/EC, 1999/74/EC, 2007/43/EC, 2008/119/EC and 2008/120/EC, and repealing Regulations (EC) No 854/2004 and (EC) No 882/2004 of the European Parliament and of the Council, Council Directives 89/608/EEC, 89/662/EEC, 90/425/EEC, 91/496/EEC, 96/23/EC, 96/93/EC and 97/78/EC and Council Decision 92/438/EEC (Official Controls Regulation). Text with EEA relevance. (OJ L 095 7.4.2017, p. 1).

2. Forskrift om offentlig kontroll for å sikre etterlevelse av regelverket for mat, fôr, plantevernmidler, dyrehelse og dyrevelferd (Forskrift om offentlig kontroll på matområdet). Kunngjort 07.04.2020. Helse- og omsorgsdepartementet, Landbruks- og matdepartementet, Nærings- og fiskeridepartementet. (lovdata.no; https://lovdata.no/dokument/SF/forskrift/2020-03-03-704 ).

3. Commission Delegated Regulation (EU) 2022/1644 of 7 July 2022 supplementing Regulation (EU) 2017/625 of the European Parliament and of the Council with specific requirements for the performance of official controls on the use of pharmacologically active substances authorised as veterinary medicinal products or as feed additives and of prohibited or unauthorised pharmacologically active substances and residues thereof (Text with EEA relevance). (C/2022/4400).

4. Commission Implementing Regulation (EU) 2022/1646 of 23 September 2022 on uniform practical arrangements for the performance of official controls as regards the use of pharmacologically active substances authorised as veterinary medicinal products or as feed additives and of prohibited or unauthorised pharmacologically active substances and residues thereof, on specific content of multi-annual national control plans and specific arrangements for their preparation (Text with EEA relevance). (OJ L 248, 26.9.2022, p. 32–45).

5. Commission Delegated Regulation (EU) 2022/931 of 23 March 2022 supplementing Regulation (EU) 2017/625 of the European Parliament and of the Council by laying down rules for the performance of official controls as regards contaminants in food (Text with EEA relevance). (OJ L 162, 17.6.2022, p. 7–12).

6. Commission Implementing Regulation (EU) 2022/932 of 9 June 2022 on uniform practical arrangements for the performance of official controls as regards contaminants in food, on specific additional content of multi-annual national control plans and specific additional arrangements for their preparation (Text with EEA relevance). (OJ L 162, 17.6.2022, p. 13–22).

7. Commission Regulation (EU) No 37/2010 of 22 December 2009 on pharmacologically active substances and their classification regarding maximum residue limits in foodstuffs of animal origin (Text with EEA relevance). (OJ L 15, 20.1.2010, p. 1–72).

8. Commission Implementing Regulation (EU) 2021/808 of 22 March 2021 on the performance of analytical methods for residues of pharmacologically active substances used in food-producing animals and on the interpretation of results as well as on the methods to be used for sampling and repealing Decisions 2002/657/EC and 98/179/EC (Text with EEA relevance). (OJ L 180, 21/05/2021, p. 84–109).

9. European Reference Laboratories (EURL). EURL Guidance on Minimum Method Performance Requirements (MMPRs) for specific pharmacologically active substances in specific animal matrices. (2022).

10. Commission Regulation (EU) 2023/915 of 25 April 2023 on maximum levels for certain contaminants in food and repealing Regulation (EC) No 1881/2006 (Text with EEA relevance). (OJ L 119, 05/05/2023, p. 103–157).

11. Nøstbakken, O.J., Moxness Reksten, A., Hannisdal, R., Dahl, L. & Duinker, A. Sampling of Atlantic salmon using the Norwegian Quality cut (NQC) vs. Whole fillet; differences in contaminant and nutrient contents. Food Chem 418, 136056 (2023).

12. NS-9401 (1994). Atlantic salmon - Reference sampling for quality measurements. Norges standardiseringsforbund. Oslo.

13. EFSA. Review of the existing maximum residue levels for deltamethrin according to Article 12 of Regulation (EC) No 396/2005. EFSA Journal 13, 4309 (2015).

14. EFSA. Review of the existing maximum residue levels for cypermethrins according to Article 12 of Regulation (EC) No 396/2005. EFSA Journal 21, e07800 (2023).

15. Van den Berg, M. et al. The 2005 World Health Organization reevaluation of human and Mammalian toxic equivalency factors for dioxins and dioxin-like compounds. Toxicological sciences : an official journal of the Society of Toxicology 93, 223-241 (2006).

16. DeVito, M. et al. The 2022 world health organization reevaluation of human and mammalian toxic equivalency factors for polychlorinated dioxins, dibenzofurans and biphenyls. Regulatory Toxicology and Pharmacology 146, 105525 (2024).

17. EU DG SANTE (2022). Analytical Quality Control and Method Validation Procedures for Pesticide Residues Analysis in Food and Feed. SANTE 11312/2021.

18. Commission Regulation (EC) No 149/2008 of 29 January 2008 amending Regulation (EC) No 396/2005 of the European Parliament and of the Council by establishing Annexes II, III and IV setting maximum residue levels for products covered by Annex I thereto (Text with EEA relevance). ( https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A02008R0149-20080901 ).

19. EU Pesticides Database - European Commission. https://ec.europa.eu/food/plant/pesticides/eu-pesticides-database/start/screen/mrls Accessed: 15.05.2024.

20. Seafood Data: Concentrations of Zn and Cu in fillet of different farmed fish species 2006-2023. https://sjomatdata.hi.no/#compare/9182,9183/11300,11305,11304,11301 . Database hosted by the Institute of Marine Research. Accessed 15.05.2024.

¹ Legal residue definition according to Reg. (EC) No 149/2008.

² Legal residue definition according to Reg. (EU) No 310/2011.

³ Legal residue definition according to Reg. (EC) No 839/2008.

⁴ Legal residue definition according to Reg. (EU) 2015/868; Campechlor (Toxaphene).