Biodegradation of some aquaculture chemotherapeutants weathered in flocculent samples collected at hard-bottom sites in Newfoundland (Canada)

Abstract The impact of aquaculture chemotherapeutants (antibiotics, and anti-lice parasiticides) on non-target organisms is dependent on their dissipation and degradation in marine sediments. Abiotic and biotic weathering may change their composition and toxicity, and influence their fate. In this study, biodegradation of a few aquaculture chemotherapeutants was investigated over a 96 days period at 4 °C in a marine flocculent sample collected at an active site. The detected antibiotics ([sulfadiazine, amoxicillin], and one parasiticide [deltamethrin]) would have been bound to flocculent organic matter for periods exceeding a year while another anti-lice compound (emamectin benzoate) for approximately 3 months. Our results show that organic matter degradation was not accompanied by a decrease in concentrations of the antibiotics and parasiticides. This preliminary study suggests longer half-lives than documented in literature for two antibiotics and highlights the difficulty in using half-lives of chemicals determined in laboratory settings without taking into account weathering.