Qualidade físico-química e microbiológica da água e avaliação residual dos praguicidas na criação de trutas arco-íris Oncorhynchus mykiss em sistema de raceway nas estações chuvosa e seca

Abstract

The objective of the present study was to evaluate the water quality of rainbow trout farm (Oncorhyncus mykiss) in a raceway system and to verify by chromatographic analysis coupled to mass spectrometry the presence of pesticide residues in water, trout, soil and feed. The physical-chemical variables of the water were evaluated between rainfall and dry seasons in trout farms A and B, and the two truecultures presented significant differences (p <0.05) for electrical conductivity (EC), biochemical oxygen demand (BOD), ammoniacal nitrogen (NH3+NH4+), phosphate (PO43-), total dissolved solids (STD), temperature and turbidity. Only the trout farm A presented significant differences for ammoniacal nitrogen (NH3+ NH4+), and trout farm B, chloride and pH levels showed significant differences (p <0.05). With respect to the collection points, the trout farm A showed significant difference (p<0.05) for BOD and the trout farm B, presented significant differences (p<0.05) for alkalinity and EC, and the two trout farms presented differences for STD. In the microbiological evaluations of the water for the thermotolerant coliform group (trout farm A), differences between rainy and dry seasons were observed, but there were no differences between the collection points. In trout farm B there was no difference between rainy and dry seasons. As for the presence of the Escherichia coli bacterium, a difference was verified only in trout farm B. For the toxicological evaluations in relation to the water matrix of the two trout farms, the organophosphorus insecticides (chlorpyrifos and dichlorvos) were quantified. In the trout farm A was detected and quantified chlorpyrifos in 0,019 mg/L point A1 and dichlorvos in the concentrations of 0.136 mg/L point A1 and 0,0465 mg/L point A6. In trunculture B, dichlorvos were quantified at 0.0209 mg/L point B1 and 0.0578 mg/L point B9. All concentrations of pesticides described above were above the Maximum Residue Limit (MRL) recommended by the European Union. For soil and feed matrices there was no detection of pesticide residues for the two trout farms. For the fish matrix there was no detection of waste in trout farm A, but there was detection (within the limit of the equipment) in trout farm B in the tissues: gills, liver and kidney. It was demonstrated in this study that the physico-chemical and microbiological alterations evaluated, are within the comfort standards for the cultivated species and in accordance with the effluent release standard of the Brazilian legislation, showing minimal impact to the receiving water bodies. The physicochemical variables evaluated may have provided the hydrolysis of the pesticides and the rainy season may have influenced the greater amount of waste in the water, but within the detection limit of the equipment. However, the dry period may have influenced the concentration of chlorpyrifos and dichlorvos. The identification of residues in the tissues of rainbow trout in trout farm B is not considered to be a risk to humans.