Summary
The EPA issued antibiotic residue monitoring schedules for the first three Florfenicol treatments in the D'Entrecasteaux Channel and Huon River Marine Farming Development Plan Area. These schedules required a total 488 sediment, 101 water, and 190 pooled wild fish samples to be collected and analysed.
The EPA has received the laboratory results for 286 sediment, 104 water, and 119 pooled wild fish samples collected up to seven (7) days post-treatment of Florfenicol and analysed these results. This number of data points provides sufficient replicates to enable the EPA to complete a preliminary analysis of results.
Florfenicol and Florfenicol-amine have not been measured above the limit of reporting in any of the sediments analysed.
Florfenicol and Florfenicol-amine have not been measured above the limit of reporting in water samples after day-1 post-treatment at locations exceeding 35 m from the lease boundary.
Two (2) water samples have measured above the limit of reporting for Florfenicol and Florfenicol-amine after day-7 of post-treatment.
Two (2) pooled fish samples contained Florfenicol-amine above the limit of reporting. These fish were both sampled day-1 post-treatment within 1,000 m of the lease boundary and were Australian salmon.
Introduction
The EPA has developed and issued Antibiotic Residue Monitoring Schedules to Environmental Licence holders, in response to notifications of the intended use of Florfenicol to treat the disease
Piscirickettsia salmonis at multiple leases in the D'Entrecasteaux Channel and Huon River Marine Farming Development Plan Area.
These monitoring schedules have been developed based on a review of scientific literature and with support from Public Health Services. They have been designed to address the intended use of Florfenicol on individual leases, the shorter half-life of Florfenicol and its potential fate in the marine environment.
These monitoring schedules aim to collect data on the presence and breakdown of antibiotic residues in sediments, water, and wild fish. To ensure the environmental impacts from the application of Florfenicol can be assessed, baseline sampling has been included as a requirement of these monitoring schedules.
Results from these monitoring schedules will inform future environmental risk assessments and public health advice relating to the use of Florfenicol in Tasmania. A final report for each antibiotic treatment event will be published on the EPA website when residue monitoring has been completed.
Report scope and context
The EPA issued antibiotic residue monitoring programs for the first three Florfenicol treatments for three (3) leases (Meads Creek – MF077, Stringers Cove – MF 209, and South of Zuidpool Rock – MF141) in the D'Entrecasteaux Channel and Huon River Marine Farming Development Plan Area that required a total of 488 sediment, 101 water, and 190 pooled wild fish samples to be taken.
This preliminary EPA report aims to provide an initial assessment of the results that have been reported to the EPA for the data collected at baseline, mid-treatment, day-1 and day-7 post-treatment, providing an overview of the findings to date.
This report summarises the analysis of laboratory results for 286 sediment, 104 water, and 119 pooled wild fish samples up to seven (7) days post-treatment of Florfenicol at these sites. Additional water samples were collected above what was required.
These results do not present a full environmental risk assessment of the use of Florfenicol in the Tasmanian marine environment, but provide sufficient data to complete a preliminary assessment.
The EPA anticipates that a full environmental risk assessment will be finished early in 2026 once all laboratory results are received. The risk assessment will include establishing guideline values for Florfenicol in the Tasmanian marine environment.
The Limit of Reporting that is referred to throughout this preliminary report is the lowest concentration of a substance that a laboratory can reliably and consistently measure (Table 1). Further information regarding the analytical methods for detecting Florfenicol can be found on Analytical Services Tasmania's website: AST rapidly develops Florfenicol antibiotic residue testing | Analytical Services Tasmania.
Day-1 post-treatment is considered the day when the highest amounts of antibiotics should be present in samples collected, as the full dosage amount has been applied to the environment within the treatment sites.
The report also refers to the measurement of two compounds, Florfenicol and Florfenicol-amine. Florfenicol is the antibiotic used to treat
Piscirickettsia salmonis. Florfenicol-amine is the sum of metabolites that Florfenicol breaks down to within the fish and the environment. When measuring Florfenicol in fish, the fish samples are reported as the sum of Florfenicol and its metabolites measured as Florfenicol-amine, this is due to the method required to extract Florfenicol from the fish tissues.
Table 1: Required limit of reporting (Therapeutant Residue Monitoring Schedule)
| |
Sample Matrix
|
|---|
|
Analyte |
Water
(µg/L) |
Sediment
mg/Kg) |
Fish Tissue
(mg/Kg) |
| Florfenicol | 0.1
| 0.005
| -
|
| Florfenicol-amine | 0.1
| 0.01
| -
|
| Sum of Florfenicol and its metabolites measured as Florfenicol-amine | -
| -
| 0.01
|
* µg – is one million (1,000,000) times smaller than a gram.
* mg – is one thousand (1,000) times smaller than a gram
Results/Discussion
This section summarises the data collected at baseline, mid-treatment, day 1, and day 7 post-treatment for Florfenicol residue monitoring associated with marine farming leases Meads Creek (MF077) and Stringers Cove (MF209). Treatment at the sites commenced on 7 November 2025 and day-7 post-treatment was 23 November 2025.
Sediment sampling
Florfenicol and Florfenicol-amine have not been measured above the limit of reporting (see Table 1) in any of the 156 sediment samples collected and analysed up to day-7 post-treatment.
Sediment samples were collected from pen bays within the two treated leases (Meads Creek - MF077 and Stringers Cove - MF209) and at multiple distances up to 7,150 m from the boundary of the leases (see Map 1).
Sediment samples were analysed from the surface (top 2.5 cm) of the sediments and an integrated sample between 2.5 cm deep to 7.5 cm deep.
MAP 1: Sediment sampling for residues of Florfenicol and Florfenicol-amine in response to Florfenicol treatment at marine farming leases Meads Creek - MF077 and Stringers Cove - MF209.
Water sampling
Sixty (60) water samples have been analysed for Florfenicol and Florfenicol-amine. A total of 27 water samples detected either Florfenicol or Florfenicol-amine above the limit of reporting at low concentrations. The majority (18) of the water samples that detected Florfenicol or Florfenicol-amine were collected on day-1 post-treatment. The maximum concentration of Florfenicol (0.5
µg/L) was measured at sites CP1.4 and CP2.3 (Map 2). The maximum concentration of Florfenicol-amine (1.9 µg/L) was measured at sites CP1.4 and CP2.3 (Map 2). Both sites are situated 35 m from the boundary of the lease and both samples were taken during day-1 post-treatment sampling.
Florfenicol was detected (0.1 µg/L) at reference site B12 during mid-treatment sampling. Florfenicol (0.2 µg/L) and Florfenicol-amine (0.2-0.3 µg/L) were detected in water samples collected from two reference sites B12 and S7 up to 700 m from the lease boundary during day-1 post-treatment (Map 2). All concentrations detected are considered low.
Florfenicol and Florfenicol-amine were not detected above the limit of reporting for all water samples collected at day-7 post-treatment.
MAP 2: Water sampling for residues of Florfenicol and Florfenicol-amine in response to Florfenicol treatment at marine farming leases Meads Creek - MF077 and Stringers Cove - MF209.
Wild Fish sampling
Fifty-six (56) pooled samples of wild fish, consisting of three (3) individual fish per pooled sample, were caught across three zones (500, 1,000 and 3,000 m) from the lease boundary. In total, 168 wild fish were sampled, including a mix of Australian salmon, flathead, and wrasse.
Of these wild fish pooled samples, two (2) pooled samples comprising of Australian salmon, contained Florfenicol-amine on day-1 post-treatment. These were collected within the 500 metre (0.02 mg/Kg) and the 1,000 m (0.66 mg/Kg) zones from the lease boundary (Map 3), representing 3.5 % of all wild fish sampled up to day 7 post-treatment for the Meads Creek (MF077) and Stringers Cove (MF209) leases.
Florfenicol and its metabolites were not detected above the limit of reporting for any wild fish pooled samples at day-7 post-treatment.
MAP 3: Wild Fish sampling for residues of Florfenicol-amine in response to Florfenicol treatment at marine farming leases Meads Creek - MF077 and Stringers Cove - MF209.
This section summarises the data collected at baseline mid-treatment, day-1 and day-7 post-treatment for Florfenicol residue monitoring associated with marine farming lease South of Zuidpool Rock (MF141).
Sediment sampling
Florfenicol and Florfenicol-amine have not been measured above the limit of reporting (see Table 1) in any of the 130 sediment samples analysed up to day-7 post-treatment.
Sediment samples were collected from pen bays within the treated lease (South of Zuidpool Rock - MF141) and at multiple reference sites up to 9,000 m from the boundary of the lease (Map 4).
Sediment samples were analysed from the surface (top 2.5 cm) of the sediments and an integrated sample between 2.5 cm deep to 7.5 cm deep.
MAP 4: Sediment sampling for residues of Florfenicol and Florfenicol-amine in response to Florfenicol treatment at marine farming lease South of Zuidpool Rock MF141.
Water sampling Forty-four (44) water samples have been analysed for Florfenicol and Florfenicol-amine. A total of thirteen water samples contained Florfenicol or Florfenicol-amine above the limit of reporting at low concentrations. A total of ten (10) samples that contained Florfenicol or Florfenicol-amine were collected during mid-treatment. The maximum concentration of Florfenicol measured in water samples beyond the boundary of the lease was 0.2 µg/L at CP2.2 during mid-treatment. The maximum concentration of Florfenicol-amine measured in water samples beyond the boundary of the lease was 0.2 µg/L at CP1.2, CP2.2 and C11.2 during mid-treatment and CP 6.2 during day-1 post-treatment (Map 5).
One (1) of the water samples collected outside the boundary of the lease (site C1.2) contained Florfenicol above the limit of reporting (0.1 µg/L) during day-7 post-treatment sampling (Map 5). The presence of Florfenicol in this water sample may be explained by the start of the second application of Florfenicol occurring on the same day as the day-7 post-treatment sampling took place for the first Florfenicol treatment on this lease.
MAP 5: Water sampling for residues of Florfenicol and Florfenicol-amine in response to Florfenicol treatment at marine farming leases South of Zuidpool Rock MF141.
Wild Fish sampling
Sixty-three (63) pooled samples of wild fish were caught across three zones (500, 1,000 and 3,000 m) and at multiple reference sites up to approximately 9,000 m from the lease boundary (Map 6). In total, 176 wild fish were sampled, including a mix of Australian salmon, flathead, wrasse, dog fish, jackass morwong, barracuda, and school shark.
Florfenicol and its metabolites were not measured above the limit of reporting (see Table 1) in any of the wild fish pooled samples analysed up to day-7 post-treatment.
MAP 6: Wild Fish sampling for residues of Florfenicol-amine in response to Florfenicol treatment at marine farming leases South of Zuidpool Rock MF141.
Conclusions
A total of 286 sediment samples, 104 water samples and 119 pooled samples of wild fish have been analysed for samples collected up to day-7 post-treatment across three leases treated with Florfenicol in the D'Entrecasteaux Channel and Huon River Marine Farming Development Plan Area.
The preliminary results presented in this report indicate that for the first three treatment events Florfenicol and Florfenicol-amine:
are not present in sediments within or external to treatment sites during or after treatment events. This is in contrast to historical treatment events administering Oxytetracycline;
are not present in water samples at a distance greater than 35 metres from the lease boundary after day-1 post-treatment;
was present in two water samples collected within 35 m of the lease boundaries at day-7 of treatment;
was detected above the limit of reporting in two fish samples collected day-1 after treatment, representing less than two (2) percent of all pooled wild fish sampled up to day-7 post-treatment.
These preliminary results agree with the literature on Florfenicol, which suggests:
the chemical properties of Florfenicol indicate that it is unlikely to bioaccumulate in the Tasmanian marine environment.
Florfenicol has a significantly shorter half-life in the environment compared to Oxytetracycline;
based on this information, it would be expected that the detection of Florfenicol residues in the water column would be limited, as reported here for samples collected and analysed up to day-7 post-treatment;
and that concentrations of residual antibiotic measured during the initial three (3) treatments are unlikely to present a risk to the Tasmanian marine environment.