Variação Sazonal da Concentração de Metais na Microbacia do Educandos, Manaus-AM

Abstract

The rapid growth of the city of Manaus in recent decades did not promote the development of planned urban structures, which resulted in the construction of numerous precarious housing in areas close to the city's streams, which have suffered severe environmental degradation over the years. One of the affected water bodies is the Educandos watershed, located in the South Zone of the city of Manaus. It is densely inhabited, and surrounded by approximately 500 industries distributed throughout the region, being, therefore, the part of the city most exposed to pollution, being of paramount importance to monitor the quality of these waters. For this, analyzes were carried out to obtain the Water Quality Indexes (WQI) for 5 points of the Educandos watershed, which were carried out in two months: Feb/2020 (rainy period) and Oct/2020 (dry period). In addition, analyzes of soluble and suspended metals were carried out, being carried out for the 5 points during 6 months: Dec/2019, Jan/2020 and Feb/2020 covering the rainy season and Jun/2020, Jul/2020 and Aug/ 2020 covering the dry period. The average IQA for the 5 points of the Educandos watershed was 36 in the rainy season and 28 in the dry season (both classified as POOR). In detail, during the rainy season points 1, 3 and 4 were classified as POOR, point 2 as ACCEPTABLE and point 5 as GOOD. In the dry period, points 1, 4 and 5 were classified as POOR, point 2 remained as ACCEPTABLE and point 3 was classified as VERY POOR. It was noted that, in general, the quality was better in the rainy season. Analyzing the parameters individually, it was observed that the parameters dissolved oxygen, thermotolerant coliforms, biochemical oxygen demand and total phosphorus were outside the values established by CONAMA resolution 357/2005. Only the parameters of total nitrogen, total solids and turbidity were within the allowed range. Temperature there is no value established by legislation and the value established for pH does not reflect the reality of the region. Based on the above, the basin in question did not show class 2 characteristics but class 4 characteristics, and should only be used for navigation and landscape harmony. Regarding metals, the presence of 61 metals was investigated and 11 of these were detected and quantified, namely: aluminum, barium, boron, calcium, erbium, strontium, iron, lithium, magnesium, manganese and thorium. Of the 11, only aluminum (dissolved), barium, boron, iron (dissolved), lithium and manganese have limits established by CONAMA resolution 357/2005. The metals that were above the limits were aluminum and iron. The others, although they do not have values specified in the legislation, demonstrated through the enrichment factor values that most of them are being added to the water body studied, predominantly through anthropic sources. Only aluminum, magnesium and manganese pointed to come mainly from the soil.