Oxytetracycline accumulation in the macroalgae Ulva: Potential risks for IMTA systems

Financial support was given by FEDER through the project ReNATURE - Valorization of the Natural Endogenous Resources of the Centro Region (Centro 2020, Centro-01-0145-FEDER-000007) and SmarBioR - Smart Valorization of Endogenous Marine Biological Resources Under a Changing Climate (Centro 2020, Centro-01- 0145-FEDER-000018), co-funded by Centro (2020) Program, Portugal 2020, European Union, through the European Regional Development Fund. Authors also acknowledge FCT for the grant attributed to Joao Rosa (grant SFRH/BD/102008/2014) and to Sara ~ Leston (grant SFRH/BPD/91828/2012). The funding source did not interfere with the study design, or in the collection, analysis or interpretation of the data. It also had no involvement in the writing of the report and in the decision to submit the present manuscript for publication.

Oxytetracycline (OTC) is one of the most used antibiotics in aquaculture. With the development of Integrated Multitrophic Aquaculture (IMTA) systems in order to mitigate some aquacultures' adverse effects, attention needs to be shifted to other co-cultured species that can also accumulate such pharmaceuticals and pose a risk to human consumption. Therefore, the present work evaluated the exposure of the seaweed Ulva to OTC at two realistic concentrations (0.040 and 0.120 mg L1 ). Oxytetracycline degradation rates in seawater were dependent on the initial concentration but were not influenced by the presence of Ulva. The macroalgae presented good assimilation rates of OTC, with internal concentrations reaching 40.9934 ng g1 WW for the lowest concentration tested and 108.6787 ng g1 WW for the highest, with a steep decrease after 48 and 24 h, respectively. Nonetheless, concentrations were still half of the Maximum Residue Limit set for fish (100 mg kg1) 48 h after C2 treatment. The highest dosage tested stimulated growth 96 h after the beginning of the trial, although some signs of decay could also be found in Ulva's fronds.

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