The Newcastle Herald understands silver biddy in the Hunter River have tested positive for perfluorooctane sulfonate at levels exceeding the “screening value” of 9.1. 

Prawn trawlers have been locked out of the river since last November, when they agreed to a self-imposed ban because elevated levels of the same chemical had been detected in crustaceans. 

However the river was never included in a fishing ban spanning upper Tilligerry Creek and Fullerton Cove, imposed by authorities when news of the Williamtown RAAF base contamination scandal broke in September. 

A spokeswoman for the NSW Department of Primary Industries said the full closure of the Hunter River to fishing was contemplated after the silver biddy results were received. She admitted there was concern that “some fish species yet to be analysed may also exceed the screening value”. 

However it was ultimately decided there would be “precautionary messaging for high consumers of seafood” instead. 

She said a child would need to consume 260 grams of silver biddy every day and an adult 950 grams every day to pose a risk to their health. 

“Given silver biddy is not a commonly consumed species, it was thought that this is unlikely,” she said. 

However she said the results had been discussed directly with fishers, who were considered a risk group because of their own levels of consumption. 

Newcastle Commercial Fishermen’s Co-operative general manager Robert Gauta said it was not a popular fish and “most of the region haven’t even heard of a silver biddy, to be honest.” 

The DPI was still awaiting data on other species of fish in the river, which would be considered as part of the full human health risk assessment. 

The spokeswoman said that would allow decisions to be based on a “clear picture of the potential exposure” and would “ensure health human is protected while not impacting unnecessarily on the fishers’ livelihoods.”

A school of prawns from the Stockton Bight was sampled in December and showed up elevated levels of PFOS. The Bight has remained open to prawn trawling, however, because the levels were below the screening value established by authorities. 

Mr Gauta said fishermen believed the prawns that washed up in the Bight came from a range of sources, including Lake Macquarie, Tuggerah Lakes and even as far south as the Hawkesbury.

However Mr Gauta said that the fishermen were “absolutely” in favour of more testing on the prawns so as to give authorities a better picture of where prawns in the Stockton Bight were coming from and their levels of contamination.  

​The silver biddy results were originally considered at length by the Williamtown Contamination Expert Panel but it was unable to come to a decision on a “proportionate” response. 

According to minutes from a meeting on February 17, NSW Chief Scientist Mary O’Kane referred the matter to the Department of Primary Industries so it could bring “regulatory policy expertise to the issue”.