Blue cod slightly contaminated with imported salmon feed

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New Zealand farmed salmon.  Their diet contains traces of organic contaminants.

KIRK HARGREAVES / Stuff

New Zealand farmed salmon. Their diet contains traces of organic contaminants.

Salmon farms in New Zealand import organic contaminants in their fish feed, but levels are low by global standards, a new study has found.

PCB levels in blue cod were found to be “significantly higher” at some sites, although below guidelines. Blue cod may be a species of interest in future contaminant monitoring.

Dr Rebecca McMullin and her colleagues from the University of Otago and Utah State University led a complex experience over several years who were looking for organic contaminants in five wild marine species that lived near salmon farms in the Marlborough Sounds.

They also tested salmon feed imported into New Zealand for these same contaminants and sought to track contaminants and their ‘breakdown products’ in marine environments.

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“We found that salmon farms in the Marlborough Sounds were operating favorably globally with levels of contaminants in food and organisms observed well below limits set by the European Union,” they wrote.

Additionally, “it is not surprising that the pollutant concentrations we measured differ from those previously reported given the improvements in aquaculture feeds over the past two decades and the decrease in concentrations of banned persistent organic pollutants. in the world”.

“The main objective of our research was to test new methods of identifying and tracing organic waste (food and faeces) from salmon farms in the surrounding marine environment, so that we know more about where it ends up. and how they affect soft sediments and reef communities,” McMullin said in an email.

Salmon feed comes to New Zealand from Norway, Brazil and Chile. The tests showed traces of eight PCBs, one PBDE (a flame retardant) and seven pesticides that have been used in the past or currently.

Researchers searched for many other contaminants that had previously been found in animal feeds and did not find them. Organic contaminants are found at low background levels in all environments.

They then looked for identified contaminants, or their degraded products, in blue cod, humphead wrasse, Australasian sea cucumbers, blue mussels and horse mussels.

Meanwhile, these same species and Chinook salmon were kept for two years in a “mesocosm” – two covered, outdoor, concrete ponds located at sea level in Otago Harbour. Salmon food has been added to the ponds from time to time.

Mesocosms lie somewhere between highly artificial laboratory conditions and the wild sea.

“If salmon farming were the source of contaminants…entering the system, we would expect to see clear and consistent changes in concentrations in both mesocosm work and field surveys,” McMullin said. by e-mail.

“This appears to be the case for some PCBs (but not for other contaminants), but the levels detected in the samples indicated very low levels of environmental risk.”

PCBs have accumulated in blue cod, although at modest levels.

Provided

PCBs have accumulated in blue cod, although at modest levels.

Blue cod are long-lived and travel little, which may explain why they accumulate PCBs. A previous study of blue cod in the Marlborough Sounds showed that around 90% were found within 100 meters of where they were previously tagged.

PCBs are serious environmental pollutants and have been banned in New Zealand and around the world for decades. But they persist for long periods. It should be noted that PCBs may have entered the Marlborough Sounds from land-based sources.

Contaminants associated with New Zealand salmon feed do not represent a level of risk of concern to the marine environment, McMullin wrote.

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