Impacto da contaminação urbana no Rio Lontra: Avaliação de parâmetros fisico-químicos e ocorrência de enteropatógenos

Abstract

Despite their significance, aquatic ecosystems stand out as the most impacted by anthropogenic contamination. The deficiency in basic sanitation systems contributes to the emergence of waterborne diseases, whose agents include enteropathogens, causing considerable harm to public health. Brazilian regulations aimed at mitigating contamination in these environments often fall short. In this context, this study seeks to assess the physicochemical, microbiological parameters, and the presence of enteropathogens in the waters of the Lontra River, located in the urban perimeter of Araguaína, Tocantins, situated southwest of the Legal Amazon. Surface water samples were collected at 7 sampling points over 16 months. Molecular analyses for the detection of Salmonella spp. and Escherichia coli were conducted through conventional PCR. The data obtained were subjected to statistical analyses using SPSS 26 software. The results revealed that the waters of the Lontra River exhibit a slightly acidic pH, below legal parameters, with a significant decrease (p ≤ 0.05) in the transitional months between seasons compared to the rainy season (pH 0.33) and dry season (pH 0.66). Dissolved oxygen values were below the permitted limits, and the thermotolerant coliform index exceeded the standards, indicating fecal contamination. Out of 56 surface water samples obtained, a positivity rate of 32.14% (18) was observed for E. coli DEC, distributed among EAEC (21.42%), EPEC (19.64%), ETEC, and STEC (7.14%). For Salmonella spp., the positivity rate was 67.85% (38). Electrical conductivity and total solids parameters showed a significant correlation (ρ = 0.98; p ≤ 0.05), both exhibiting negative correlations (ρ = -0.74 and ρ = -0.73; p ≤ 0.05), associated with the transition from lentic to lotic environments due to damming at points 5 to 7. A relevant correlation of turbidity with the seasons (ρ = 0.72, p ≤ 0.05), as well as turbidity and precipitation (ρ = 0.64, p ≤ 0.05), was verified, potentially related to soil erosion along the riverbanks. Additionally, sampling points exhibited a moderate negative correlation with E. coli (-0.42; p ≤ 0.05) and a weak correlation with Salmonella spp (-0.21; p ≤ 0.05), indicating an increase in positivity along the course of the river through the urban perimeter of Araguaína, Tocantins. The results point to compliance with physicochemical parameters, contrasting with microbiological contamination evidenced by the presence of enteropathogens, representing a threat to local public health preservation. The analyzed correlations delineate the failure of the basic sanitation system as the origin of this contamination, along with damming and human intervention on the riverbanks, influencing the dynamics of this water body. Thus, the conducted analyses have proven crucial for evaluating the reality of water contamination in the Legal Amazon, highlighting the Lontra River in the northern state of Tocantins, Brazil.