Avaliação dos Índices de Qualidade da Água e Concentrações de Metais no Igarapé do Mindu em Período de Cheia e Seca

Abstract

The economic growth that the capital of Amazonas experienced, either during the rubber cycle or following the implementation of the Manaus free zone, promoted a rapid increase in population density, generating an expansion of the urbanized region. Such socioeconomic growth entailed an overload on the local environment, in addition to the lack of adequate environmental policies for the municipality on the part of the public power, which resulted in a gradual process of degradation of urban water bodies. The degradation of the urban basins of the municipality causes damage to the population and the environment. Among the urban basins, the largest hydrographic basin, São Raimundo, whose main stream is the Mindu, stands out. To assess the contamination of the Mindu stream, the Water Quality Index - WQI was used, which includes 9 parameters: dissolved oxygen, thermotolerant coliforms, hydrogenion potential (pH), biochemical oxygen demand (BOD), total nitrogen, phosphorus total, temperature, turbidity and total solids. Water samples were collected at 5 points, in the rainy season (Feb/2020) and dry season (Oct/2020). In addition, analyzes were carried out to verify and quantify the presence of 61 metallic elements in a soluble and/or suspended form at five collection points, during 6 months: December/2019, January/2020 and February/2020 (rainy period) and June/2020, July/2020 and August/2020 (dry period). Thus, the results, for the rainy season (Feb/2020), classified point 1 as GOOD, points 2, 3 and 4 as POOR and point 5 as GOOD, and in general the Mindu stream was classified as ACCEPTABLE. In turn, for the dry period (Oct/2020), point 1 was classified as GOOD, point 2 POOR, point 3 VERY POOR, point 4 POOR, point 5 ACCEPTABLE, and in general the Mindu stream classified as BAD. Through the analysis of metallic elements, it was possible to identify and quantify 10 elements: Aluminum, Barium, Calcium, Magnesium, Iron, Manganese, Potassium, Rubidium, Silicon and Sodium. Of these, the legislation establishes values only for Aluminum, Barium, Iron and Manganese, and of these, only Barium and Manganese did not exceed the borderline values of the resolution. In addition, the enrichment factor was calculated for the quantified elements, based on the values obtained for the Iron element. These data showed that the elements Barium, Calcium, Potassium and Rubidium show concentrations that show enrichment with anthropic sources.