An alternative approach to assess ecotoxicological effects of agrochemical combinations used in Brazilian aquaculture farms.

Agrochemicals used for treating and preventing aquaculture diseases are usually present in combination with other compounds, and the toxicity resulting from their chemical interactions presents an important reason to assess the ecotoxicity of compound mixtures in view to better understanding the joint action of chemicals and avoiding their environmental impacts. In this study, we evaluated the acute aquatic ecotoxicity of several compounds used in Brazilian fish farming (Oxytetracycline [OXT], Trichlorfon [TRC], and BioFish® [BIO]), both individually and in binary and ternary mixtures. Initial test concentrations were prepared according to the recommended concentrations for aquaculture application, and from these, a geometric dilution series was tested on two important fresh water quality indicator species, the microcrustacean Daphnia magna and the bacterium Aliivibrio fischeri. At the recommended pond application rate, TRC and BIO applied individually showed toxicity to the tested organisms in terms of the lowest-observed-effect concentration (LOEC), and D. magna was always more sensitive than A. fischeri. For the two test organisms, the results obtained with the binary mixtures showed that the TRC and BIO mixture was more toxic than TRC and OXT, which in turn was more toxic than OXT and BIO. The toxicity from all agrochemicals in the ternary mixture was more than that of the agrochemical combinations in the binary mixtures. Given the results presented in this study, it is evident that the mode of action and availability of the tested compounds undergo changes that increase toxicity when they are present in combination, and therefore, aquaculture wastewater treatment should be adopted to ensure decontamination of agrochemical residues.

Assessment of phytotoxicity and impact on the enzymatic activity of soil microorganisms caused by veterinary antibiotics used in Brazilian farms.

This work aimed to evaluate the impact of veterinary antibiotics on biomass phytoproductivity and soil enzyme activity. The soil was sampled in the city of Camboriú (state of SC, Brazil). The soil enzyme activity was assessed through hydrolysis of fluorescein diacetate (FDA), while phytotoxicity was tested using Lactuca sativa (lettuce). Results showed that the most appropriate exposure time to assess the impact of antibiotics on soil microbiology was 24 h, while the incubation time of 3 h was the most appropriate for FDA hydrolysis. Ampicillin and Amoxicillin at the tested concentrations did not interfere with the enzyme activity of the soil microbiota, while Oxytetracycline and Neomycin showed a significant reduction in soil enzyme activity. For the dry and wet biomass of lettuce, 2% Colistin and 1% Ampicillin were the treatments that reduced lettuce biomass. Hence, the use of excessive antibiotics in animal production may lead to environmental impacts and, in the future, to public health problems.