• The fate of oxytetracycline in the marine environment of a salmon cage farm

      Coyne, R; Smith, P; Moriarty, C (Marine Institute, 2001)
      This paper gives a summary of previously published results of studies on the dispersal of oxytetracycline from the vicinity of a typical salmon farm. These studies showed the environmental impact of occasional treatments to be negligible. Concentrations of oxytetracycline (OTC) were measured in the benthic sediments and in mussel Mytilus edulis sampled in the vicinity of an inshore salmon farm on the west coast of Ireland. Concentrations between 1.0 μg/g and 14.7 μg/g were observed in sediments within 120 m from the farm. Concentrations declined exponentially with time, reaching low levels after 32 days and reduced to traces at 66 days. The highest concentrations were observed in the top 2 cm of sediment, falling to trace levels at a depth of 10 cm. The half-life of OTC persistence in mussels was found to be approximately 2 days. Residues in unpolluted sediment beneath the cages were never present in high concentrations and were flushed out rapidly. In the presence of excessive quantities of unconsumed food pellets on the seabed and in anoxic sediment, the persistence of OTC was significantly prolonged. Monitoring the quality of the sediment could therefore provide adequate indication of any risk of accumulation of antibiotic, without the need for elaborate chemical analyses. Residues in sediment, invertebrates and salmon could account for not more than 1.3% of total input of OTC. It was concluded that the antibiotic was very rapidly dispersed in the environment and its use in salmon therapy posed no material risk to human or environmental health.