New survey indicates elevated Mercury levels in Derwent estuary bream and trout

The Director of Public Health, Dr Roscoe Taylor, today (6/3/2008) advised people to avoid eating bream caught in the Derwent estuary and to limit consumption of other Derwent fin fish species. 

Dr Taylor said his advice was a precautionary measure based on the preliminary results from a pilot survey of fish caught in the estuary which found mercury levels in bream, and sea-run brown trout, are in excess of recommended food safety standards.

Derwent Estuary Program Director Christine Coughanowr said the pilot survey was part of a University of Tasmania Honours project and the fish samples were collected with assistance from recreational fishers, community groups and Nyrstar Hobart smelter.

As part of the survey, 28 black bream and 25 sea run trout were collected mainly in the area between Bridgewater and New Norfolk.

Twenty five mullet samples were collected from the Rose Bay area and 30 flathead were collected from the Derwent above the Tasman Bridge.

Ms Coughanowr said the survey found the average mercury levels in bream were about three times the maximum permitted levels for commercial sale.

It confirmed findings in previous years of slightly elevated levels of mercury in flathead, and found similar slightly elevated levels in sea-run trout, but lower levels - well below the national guidelines - in mullet.

Ms Coughanowr said further investigations are being planned to confirm the pilot study findings and to extend the survey within the Derwent estuary.

Dr Taylor said pending further surveys and detailed examination of the data; he believed it prudent to advise the public to avoid consumption of Derwent caught bream.

“Pregnant women and young children should limit consumption of all other Derwent caught fin fish to one meal per week, and avoid eating other fish in the same week.

“Other adults should limit their consumption of other Derwent caught fin fish to 2-3 meals per week.

“This advice is precautionary and it is possible that it will be lifted for various fish species as more results become available.

“It is important to note that the above advice only applies to fish in the Derwent Estuary and not similar species caught elsewhere.”

The health advice about limiting consumption is particularly directed towards fishermen catching larger amounts and keeping the fish for regular family consumption.   Smaller ethnic groups and migrants who may have particular cultural and dietary practices relating to high fish consumption also need to be aware of the advice.

Dr Taylor said he wanted to emphasise the health benefits of eating fish, which includes limited amounts of Derwent sourced fish.

”Fish are a valuable source of protein, minerals, vitamin B12, and iodine and are low in saturated fat and contain omega-3 fatty acids,” he said.

Dr Taylor said the public health advice will be reviewed when the recent survey work is completed and published, and also when further studies are done.

Ms Coughanowr said the source of the mercury in Derwent estuary fish is thought to be linked to sediment contamination associated with historical wastewater discharges from industries.

Current discharges from these sources are monitored and are low.

Heavy metal levels have been monitored in Derwent flathead, oysters and mussels for more than a decade.

Flathead have been considered to be a good indicator of mercury levels in Derwent seafood as they live in the estuary year-round and are bottom feeders.

Surveys of a wide range of seafood in the mid 1970s found that flathead had higher mercury levels than many other fish and they were selected for long time monitoring because they are most commonly caught fish by recreational fishers.

Bream and sea run trout were targeted in the pilot survey because, as the condition of the Derwent has improved, these recreational fisheries are becoming increasingly popular.

More information on mercury in fish can be found at:

http://www.foodstandards.gov.au/newsroom/mediareleases/mediareleases2004/fsanzupdatesadviceon2393.cfm

Further details on environmental sampling in the Derwent can be found at http://www.derwentestuary.org.au/