The Environment Protection Authority (EPA) has released its Environmental Risk Assessment on the use of the antibiotic florfenicol to treat Piscirickettsia salmonis (P. salmonis) at nine salmon farm leases in southern Tasmania.
EPA Director, Catherine Murdoch, said the rigorous and contemporary risk assessment uses the largest and most complete set of data ever collected to examine how antibiotics affect the environment in marine aquaculture worldwide and continues to support the initial findings released by the EPA that indicates the majority of the antibiotic administered has been taken up by salmon, with measured concentrations in the environment remaining very low and consistent with the results previously reported.
“This risk assessment brings together extensive field work and a detailed review of florfenicol and its breakdown product florfenicol amine," said Ms Murdoch.
“It outlines how the EPA developed interim Default Guideline Values (DGVs) for florfenicol to help identify harmful impacts, looks at 4,240 results from water and sediment samples, and uses several types of evidence together to assess environmental risk."
Ms Murdoch said the EPA has followed national water quality guidelines for protecting aquatic ecosystems and set an interim guideline level of 7 µg/L for florfenicol in pristine Tasmanian marine ecosystems, and 50 µg/L for florfenicol in modified Tasmanian marine ecosystems, such as the D'Entrecasteaux Channel.
The risk assessment shows that florfenicol was found in water and sediment samples collected both inside and outside nine treated fish farm sites. The highest levels of florfenicol and its breakdown product were found in surface waters and surface sediment samples collected within the farm leases. Levels dropped quickly with distance from the farm leases, with depth from surface waters to the seabed, and with time after treatment finished.
Of the 4,240 results, less than 12 % had any measurable amount of florfenicol or its breakdown product. None of the 4,240 sample results showed florfenicol levels above the interim DGV.
Of the 171 water samples where florfenicol was detected, the highest level found was 5.2 µg/L (or 5.2 parts per billion). This sample was collected during florfenicol treatment, right next to a fish pen. The highest result was approximately 10 times lower than the EPA's interim DGV, and the average level (0.4 µg/L, or 0.4 parts per billion) was approximately 125 times lower.
Florfenicol amine was found in 297 water samples. The highest level measured was 4.2 µg/L (or 4.2 parts per billion), also collected during treatment next to a fish pen. While there is no guideline value set for the breakdown product florfenicol amine, EPA's risk assessment has considered that it may be as toxic as florfenicol. Both the highest and average levels (0.6 µg/L, or 0.6 parts per billion) are considerably lower than the interim DGV set for florfenicol.
The presence of florfenicol or florfenicol amine within sediments was highly localised to treated fish farm leases, with only 29 out of 1,680 sediment samples containing florfenicol or florfenicol amine. 24 of these samples were collected within the lease boundary. Florfenicol did not persist in the sediment beyond 14 days after treatment.
“The findings of this environmental risk assessment highlight that the use of florfenicol in Tasmania's marine waters between November 2025 and March 2026 posed a low risk of causing unacceptable environmental harm. Overall, the results indicate that impacts were limited and unlikely to affect the health of the marine environment," said Ms Murdoch.
The Environmental Risk Assessment can be viewed at: Environmental risk assessment of florfenicol use in marine salmonid aquaculture in SE Tasmania 2025 - 2026
Published on:
21/05/2026