Global Assessment of Organic Contaminants in Farmed Salmon

The Original Study

According to Spinning Farmed Salmon:

The study on which the Science paper was based was undertaken at the Institute for Health and the Environment at the State University of New York, Albany, funded by the Pew Charitable Trust. The study, entitled ‘Global Assessment of Organic Contaminants in Farmed Salmon’ tested for levels of ‘organochlorine contaminants in Farmed Atlantic salmon from eight major producing regions in the Northern and Southern hemispheres’. For comparison, ‘samples of five wild species of Pacific salmon were obtained from different geographic regions. The analysis examined fourteen contaminants, focusing ‘additional analysis’ on ‘PCBs, dioxins, toxaphene, and dieldrin’ which ‘were consistently and significantly more concentrated in the farmed salmon as a group than in the wild salmon’.

Poly Chlorinated Biphenyls (PCBs) are components popularly used in electrical manufacturing until 1977 when the US Congress prohibited their use due to high levels of toxicity.

Dioxins are produced as a waste product of the production of some chemicals and on incineration of organic waste in the presence of chlorine. Toxaphene and Dieldrin are pesticides banned in the US in 1986 and 1990 respectively. PCBs (as a result of disposal methods) and dioxins and the pesticides (for obvious reasons) have found their way into the food chain. Along with other organochlorine contaminants, they accumulate progressively in organisms over time meaning that those at the top of the food chain, humans, are exposed to the highest levels.

The authors stated clearly that ‘Individual contaminant concentrations in farmed and wild salmon do not exceed U.S. Food and Drug Administration (FDA) action or tolerance levels for PCBs and dieldrin. However, FDA action and tolerance levels are not strictly health-based, do not address the health risks of concurrent exposure to more than one contaminant, and do not provide guidance for acceptable levels of toxaphene and dioxins in fish tissue.’ A key reason the authors used the EPA guidelines were that they were developed to understand multiple contaminant intake rather than intake of a single contaminant.

The results showed that farmed salmon contained levels of PCBs significantly higher than that of wild salmon with Scottish farmed salmon displaying the highest levels in the sample. The authors recommended: ‘The combined concentrations of PCBs, toxaphene, and dieldrin trigger stringent consumption advice for farmed salmon purchased from wholesalers and for store-bought farmed fillets. This advice is much more restrictive than consumption advice triggered by contaminants in the tissues of wild salmon.’ With reference to the EPA’s standards, they argued that safe consumption of the most toxic salmon (purchased in Frankfurt and farmed in the Faroe Islands and Scotland) should not exceed more than one half-portion of salmon per month.

The risks of other non-cancer ill effects (such as ‘adverse neurobehavioral and immune effects and endocrine disruption’) were not factored into the advice because there are no recognised risk levels adopted by official agencies. This is a crucial point in relation to the most important finding of the researchers. Although they examined the concentrations of 14 contaminants they undertook additional analysis on four (including dioxins). But the researchers only provided consumption advice based on risk levels for three of the contaminants (PCBs, dieldrin, toxaphene excluding dioxins). The key reason for this was, as the researchers told us, ‘because of the international disagreement around dioxin risk assessment’. In particular, there is a disagreement on risk assessment between the EPA and other bodies such as the FDA and WHO. This became a key point on which the study was (wrongly) attacked.

Spinning the story

Within a week of publication, the study was effectively neutralised as a threat to the industry. To illustrate this we can examine coverage in The Scotsman, one of the two main ‘quality’ papers in Scotland. On the 9th of January the headline was: ‘Eating farm salmon "raises risk of cancer"‘. The following day the story was already being questioned: ‘Chemicals in fish are well known’. Subsequent headlines became increasingly sceptical: ‘Salmon is safe says US food expert’, ‘Green campaigners fund salmon study’, ‘Salmon scare report was flawed and biased’ and finally, ‘Claims of unsafe fish run contrary to the facts, say scientists’.