Parâmetros limnológicos e de pesticidas e a influência das vazões em três regiões do Baixo São Francisco

Abstract

The great advance of the agricultural frontier with the use of agrochemicals and the process of expansion without planning of the municipalities, which sometimes do not have effluent treatment systems, lead to problems of contamination in the water. The discharge of sanitary or industrial sewage constitutes punctual contamination and the presence of pesticides is characterized by diffuse contamination in the aquatic environment.In the present study, water samples were collected in the Lower São Francisco, more precisely in the municipalities of Piranhas (AL), São Brás (AL) and Penedo (AL). The samples were collected in three distinct periods (November 2021, March 2022 and July 2022) with the objective of analyzing the presence of pesticides, the quality of the physicochemical and microbiological parameters and the influence of the flows practiced in the period.Aiming to verify the impacts on the aquatic ecosystem and its effects on the biota, contributing to the correct management of water resources and normative instructions in the environmental area. Through the analysis of the physicochemical parameters, high levels of salinity, conductivity and ammonia were observed in periods of lower flows.And, high levels of total dissolved solids and iron that may be associated with the carryover of denuded soil particles in periods of high flows. Dissolved oxygen was above the minimum established by Conama 357/2005 in periods of higher flow rates (4000 m³ s⁻¹).Highlighting the influence of the flows of the São Francisco River on these parameters and on the dynamics of the river as a whole. Gas chromatography coupled to mass spectrometry (GC-qMS) was used to monitor pesticides. The presence of 6 pesticides was detected, among the 20 evaluated, and the lowest frequency of identification was observed in collection 2, where the flow rates are higher, and consequently, dilutes the compounds.Among the pesticides identified, Heptachlorepoxide Isomer B is classified as extremely toxic, ALPHA-BHC, BETABHC, Endosulfan II and Lindane are classified as highly toxic and Aldrin as moderately toxic.Due to the toxic capacity of these compounds, it was possible to observe through genotoxicity analysis in fish, how contaminants can affect aquatic organisms. Stressing the importance of implementing measures with the purpose of managing and reducing the genetic damage identified in fish, considering that such damage is associated with the presence of contaminants in the water, which in turn may have implications for human health.