Impact of shrimp farming effluents on estuarine areas: a study in the Guaraíras Lagoon region, Rio Grande Do Norte – Brazilian Northeast

As indicated by research conducted in the state of Rio Grande do Norte, located in northeastern Brazil, the region ranks as the second-largest shrimp producer in the country. However, the environmental impacts associated with shrimp production by micro and small-scale enterprises remain insufficiently explored. The aim of this study was to assess the physical, chemical, microbiological, and phytoplanktonic parameters of water quality in both the intake and effluent water from shrimp farms situated around the Guaraíras Lagoon. Results demonstrated that all analyzed physical and chemical parameters adhered to Brazilian environmental regulations (CONAMA 357/2005 and 430/2011). Nevertheless, statistically significant differences (p < 0.05) were observed between sample types for parameters such as pH (8.36 ± 0.22 vs. 8.41 ± 0.24), suspended solids (0.010 mg/L ± 0.015 vs. 1.16 mg/L ± 1.30), and settleable solids. With respect to phytoplankton composition, the predominant classes identified were Bacillariophyceae (44%), followed by Mediophyceae (25%) and Cyanophyceae (17%). A statistically significant difference in phytoplankton composition was observed in intake water during the dry season, where the average concentration exceeded that of the rainy season by more than fourfold, and by over tenfold when compared to effluent samples (p < 0.001). Additionally, species known to potentially produce cyanotoxins were found at concentrations five times higher in effluent samples compared to intake water (p < 0.001). From the standpoint of Brazilian environmental legislation, the results indicate that small-scale shrimp farming exerts a low environmental impact. However, these findings emphasize the importance of further studies focused on cyanotoxin monitoring, with the goal of enhancing our understanding of the potential environmental and public health implications of shrimp farming in the region.