Análise da influencia dos sólidos suspensos na Daphnia similis em ensaios de ecotoxicidade aquática

Abstract

Recognition of problems caused by suspended solids in aquatic ecosystems shows that not only chemical contaminants can cause negative effects on aquatic organisms. These suspended solids that are found in the composition of the water body, added to those generated by the anthropogenic action, influence the life cycle of aquatic organisms. And also factors like size, size and quantity of suspended solids are determinants for the responses of aquatic organisms. Organisms such as microcrustaceans and fish respond to particles or suspended solids with death, reduction of reproduction rates, frequency of feeding and decrease in the efficiency of spawning, attacking their prey and escaping from predators. These suspended solids can be measured by turbidity. Thus, using 12 previously treated samples of lubricants industry effluent with physical-chemical parameters within the legislation for the disposal of industrial effluents, and nine synthetic solutions prepared with clay of 44 micrometers inert material, that cause turbidity, the ecotoxicity assays with the organisms Daphnia similis NBR 12713 of 2016. In these tests carried out without and with filtration, all the samples were submitted to process of removal of solids in effluents by filtration with membrane of 0.45 µm and in both cases was compared the immobility Of microcrustacean. Assays performed caused immobility of organisms using suspended clay particles of size 44 μm or 0.044 mm. Thus, a relation of lower turbidity in NTU (Turbidity Nephelometric Units), lower RNFT (Total Non-Filterable Residues) and lower number of immobile organisms was evidenced. There was also a reduction in the number of immobile organisms due to suspended solids causing turbidity. This result suggests the presence of a deleterious turbidity range for the microcrustacean Daphnia similis. Due to the importance of the organism Daphnia similis in the food chain and the results obtained, which evidences a value range between 50.9 and 725 NTU as causing immobility in the organisms, this work suggests CONAMA Resolution 357 be revised in the turbidity parameter.