Avaliação da qualidade do sedimento de tanque escavado para a produção de alevinos de tilápia do nilo no semiárido pernambucano

Abstract

The success of the fish farming activity requires a demand for fry production that supports the development of the sector. However, production methods can cause damage to the environment by making waste available. The increase of the aquaculture activity in the reservoirs has contributed to the increase of the nutrient supply, among them nitrogen and phosphorus. In addition to the addition of nutrients, the crops also release into the body water rejects drugs, such as antibiotics, antifungals and hormones. Sediment is one of the most important compartments when assessing the degree of contamination in aquatic ecosystems, considering their ability to accumulate organic and inorganic compounds over time, as well as, under certain conditions, to make such contaminants available again medium. The environmental impacts and toxicity generated by aquaculture activities in the São Francisco sub-region, especially in excavated tanks, are little known. In this way, the present work generated knowledge about the impacts of this production system, subsidizing information for the improvement of the environmental management of the fish farming activity. The study area consists of three tuna production tanks and the body of the Itaparica reservoir, located in Itacuruba, semi-arid region of Pernambuco. The toxicity of the sediment of the nile tilapia fingerlings (Oreochromis nilotic) and of the receiving body and of two compounds of higher use in the production of fingerlings, the masculine hormone 17α-methyltestosterone, and the antibiotic oxytetracycline were evaluated. Sediment and water nutrients as well as sediment granulometry were quantified. As test organisms, the amphipod Hyalella azteca (Saussure, 1858) and the crustacean Daphnia similis (Richard, 1894) were used. The nutrients present in the sediment, showed values within the recommended by the legislation Conama 454/12. The granulometric fractions exhibited a higher percentage of sand at most sampling points. The ecotoxicological tests with the integral sediment of the culture tanks and the Itaparica reservoir, using the test organism Hyalella azteca, did not show an acute effect in the organisms, however a chronic effect was observed in the exposure of the organisms for 240 hours at points T1, T2 and reservoir. Ecotoxicological tests on sediment elutriate using Daphnia similis exhibited acute toxicity for two sample points T2 and T3 on organisms exposure for 48 hours. The hormone 17α-methyltestosterone, caused toxicity to Daphnia similis (EC50; 48h = 7.62 μg L-1,) and Hyalella azteca (EC50; 240h = 0.03 μg L-1). The antibiotic oxytetracycline showed no toxicity at the concentrations tested for the two test organisms. The results demonstrate that the activity causes significant disturbances to the environment and that they must be monitored to avoid that environmental impacts on water quality may represent a barrier to the growth of the sector in the region.