Salmon farming and heavy metal pollution: the facts

We are often (once again, wrongly) on the receiving end of claims that salmon is full of chemical and environmental contaminants. If that were so, why would we submit our salmon and trout for routine testing by the Federal Government?

Since we began reporting to the National Residue Survey in 2000 there has been no detection of any additives, anthelmintics, contaminants, hormones or insecticides in Huon Aquaculture products. The most recent survey results (2019) demonstrate that the presence of heavy metals in our fish is exceedingly low. Lead and mercury have a mandated limit of 0.5 to 1 mg/kg. Huon fish came in at 0.01mg/kg; some 50 to 100 times lower than the mandated level. For more information on the National Residue Survey, visit: https://www.agriculture.gov.au/ag-farm-food/food/nrs.

We also publish the survey results on our website.

Unfortunately, some people ignore rational and balanced science-based discussion and instead make unsubstantiated claims on social media.  Recent comments made by Dr Lisa-ann Gershwin, a Tasmanian biologist with expertise in jellyfish, are wrong and should be challenged.

Firstly, despite her claims, salmon farming is not a source of heavy metal pollution.

In Macquarie Harbour, the source of heavy metals is river outflows from adjacent catchments containing high levels of heavy metals accumulated from historical mining activity. In the Derwent River, the main sources of heavy metals are the zinc smelter at Lutana and urban stormwater run-off (as identified by the Derwent Estuary Program).

Heavy metals are not a health risk in Tasmanian farmed salmon. Huon has sampled our fish for heavy metals, primarily targeting gill, liver and kidney which are scientifically recognised as the organs most likely to show up any elevated levels of heavy metals in fish. All results, including in Macquarie Harbour, have been well below the levels reported by the Food Standards Code of Australian and New Zealand (FSANZ) as safe.

There is no scientific evidence to indicate that aquaculture derived nutrients are likely to enter the Derwent Estuary system at high enough loads and for long enough to then cause the required sustained hypoxia to cause heavy metal release. Those interested in the facts around this topic should contact the internationally recognised experts at the Institute of Marine and Antarctic studies (IMAS).

Nonetheless there is an extensive monitoring program in the Derwent Estuary and Storm Bay, including scientists from CSIRO and IMAS to monitor factors like oxygen concentration in the water and heavy metal levels in fish and shellfish.

The Tasmanian Department of Health website provides public health alerts in regard to consumption of shellfish and certain fish species (e.g. flathead) which is based on a long-term monitoring program.

Dr Gershwin’s comments go further to suggest that eating farmed salmon from Macquarie Harbour and Storm Bay may somehow lead to a human health event similar to that which occurred in Japan at Minamata in 1956 (sometimes referred to as Minamata disease).  Minamata disease in the local Japanese human population was caused by the toxic effect of methylmercury which had accumulated to high levels in the local fish and shellfish. The source of the methylmercury was wastewater released from a chemical factory, with methylmercury reported to be around 5% of the wastewater. This bears no relevance to farmed salmon in Tasmanian conditions.

Not only is this exaggerated and misleading comparison not based in science, its posting on the Environment Tasmania Facebook page has the potential flow-on to recklessly damage the whole Tasmanian brand and associated industries, rather than just the salmon industry which Dr Gershwin seems determined to malign.

 

 

 

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