Spatial-temporal Variation of Metallic Contamination in Sediments from Una Basin Macro-Drainage Project Area (Pará, Brazil)

Abstract

The objective of this study was to investigate the variation of levels of organic pollution and metal contamination (Al, Ca, Cd, Cu, Cr, Fe, K, Mg, Mn, Na, Pb and Zn) in the sediments of the drainage channels from Una basin in 2002 and 2015, after implementation of the Una Basin Macro-drainage Project (PMBU). The Una basin is located within the Metropolitan Region of Belém (MRB) in the state of Pará (Amazon), Brazil. 21 samples of superficial sediments (0-20 cm) were collected during the period of low precipitation (June and July) in 2002 and 2015. From the results, the positive and negative impacts generated were identifying, including environmental, socioeconomic and cultural aspects. The analytical procedures followed known protocols for sediment extraction and acid digestion. The results were converted into environmental indexes: Contamination Factor (CF), Enrichment Factor (EF), Potential Ecological Risk (ER) and Pollution Loading Index (PLI), and presented in isovalues categories and maps. The highest rates of reduction with the implementation of the macro-drainage project were observed for metals Mg (58%), Ca (49%) and Zn (38%). The total Fe had a reduction of 10%, and among the metals with high toxicity to the biota, the lowest reduction rates occurred for Cd (11%), Pb (25%) and Cr total (28%). Organic matter levels also had a small reduction, suggesting a recurrence of sources of pollution to the system. The analytical indices (CF) and (EF) indicated a very diversified quality of the sediments, with classification from low to high contamination, and from low to extremely high enrichment, respectively. The results suggest a state of attention and alert for sites of contamination in the basin. The lack of consciousness of the local population, coupled with the lack of public service in relation to sanitation and new irregular occupations in the region has led to the deterioration of the quality of sediments and possibly the waters of the channels.