Distribution of heavy metals in sediments and their bioaccumulation on benthic macroinvertebrates in a tropical Brazilian watershed

Abstract

The objectives of this study were (i) to evaluate the quality of the Ouro River, a tropical Brazilian river, assessing the concentration of the metals in surface waters, sediments, and benthic macroinvertebrates; (ii) to investigate the possible sources of pollution in Ouro River basin through field research and spatial analysis (G.I.S.); (iii) to evaluate the possible occurrence of metals bioaccumulation in the trophic chain, by comparing the concentration of the metals in water, sediments (total and bioavailable) and in benthic macroinvertebrates; and (iv), to assess the biological metrics of benthic macroinvertebrates that inhabit the Ouro River, and the possible relation regarding its distribution (richness, abundance, dominance) with the human occupancy. Water, sediment, and macroinvertebrates samples were assessed in five sample sites for 9 months. The macroinvertebrates were arranged, identified, and analyzed taxonomically. The concentrations of Cu, Zn, Fe, Mn, Cd, Pb, and Cr in waters and sediments (total and Mehlich-1) were determined, the obtained results were compared to Brazilian and international standards indexes (Igeo and E.F.). According to our findings, the quality of Ouro River is directly affected by the human activities carried out in the watershed, and despite that the vast majority of the assessed metals in water was found below the legislation maximum levels, these accumulate in sediments, with extremely high enrichment of Cd, and moderately to heavily contamination of Cd, Mn, and Cu. Also, Zn and Pb high bioaccumulation in macroinvertebrates was observed, in which concentrations were 172% and 92% higher than the mean total concentration in sediment. The fit's goodness indicates that Mehlich-1 could be used as an extractant solution for the correlation of Pb in sediments and B.M.I. On average, Pb levels in the benthic are 14.94× higher than the bioavailable fraction in sediments (Mehlich-1). Mainly for Decapoda, Bivalve, and Gastropoda, results indicate high adsorption rates of Pb and Zn. The probable metal contamination in the Ouro River basin is from diffuse sources such as agriculture erosion (fertilizers and fertilizers with heavy and toxic heavy metals).