In November 2025, an antibiotic called florfenicol was approved for emergency use to treat a serious bacterial disease affecting farmed salmon in south-east Tasmania.
Because this antibiotic is used in marine waters, the Environment Protection Authority (EPA) carried out a detailed assessment to understand whether it could harm the environment.
What the EPA did
The EPA took four key steps:
Reviewed existing science to understand how florfenicol behaves in seawater, how it breaks down, and how it may affect marine life
Collected environmental data from salmon farms using the antibiotic, including testing water and seabed (sediment) samples
Set a safe guideline level for florfenicol based on national water quality methods
Assessed environmental risk by combining all available evidence
Guideline for safety
The EPA set a precautionary interim guideline value of 50 micrograms per litre (µg/L). This level is appropriate for local waterways, which are considered modified (not pristine) ecosystems and is therefore designed to protect 95% of marine species.
What the monitoring showed
Between November 2025 and March 2026, a large monitoring program was carried out. This is the most comprehensive dataset in the world for florfenicol in marine environments.
There are 4,240 laboratory results from collection of samples of water and sediment. Samples were taken at different depths, locations, and distances from fish farms, including reference sites.
Key results:
- 88% of samples had no reportable antibiotic
- 12% of samples had reportable levels
In water:
- No samples exceeded the guideline value of 50 µg/L
- The highest level recorded was 5.2 µg/L (10 times lower than the guideline value)
For the breakdown product (florfenicol amine):
- All measurements were also below 50 µg/L
- The highest level recorded was 4.2 µg/L
What was found in sediments:
Florfenicol in sediments was limited to areas close to fish farms. It broke down quickly, with levels returning to below reportable levels within 7 days after treatment stopped.
Overall findings
Based on all the evidence, the EPA found the use of florfenicol during the 2025–2026 treatment period posed a low risk of unacceptable harm to marine ecosystems. This result applies to marine plants and animals but does not include bacteria.
What is still being studied
The EPA recognises that antibiotics in the environment are complex and can affect bacterial communities in different ways.
This assessment did not examine:
- impacts on bacteria
- the potential for antimicrobial resistance
To address this, the University of Tasmania is currently conducting further research. Results will be used to improve future assessments.
Looking ahead
The EPA will continue to update this assessment as new science becomes available and will continue to require salmon companies to carry out ongoing environmental monitoring. This will help ensure that any future use of florfenicol in Tasmania’s marine environment is carefully managed and environmentally responsible.
Risk Assessment
Environmental Risk Assessment of Florfenicol Use in Marine Salmonid Aquaculture in SE Tasmania 2025 - 2026 (PDF 3Mb)