Abstract

The evaluation of water resources quality is an important tool for controlling and monitoring water bodies, among which, the evaluation of toxic metal levels in benthic macroinvertebrates has been highlighted. This study aimed to evaluate the biological quality of the Alvorada and Mandaguari rivers and to evaluate the metal bioaccumulation by means of the metal concentrations in surface waters, bottom sediments and benthic macroinvertebrates. Samples of water, biological material and sediments were conducted at six sampling points, 3 points in each river during 12 months. Macroinvertebrates were sorted, identified and analysed from the biological metrics, BMWP′ index and statistical analyses. The samples of benthic macroinvertebrates and sediments were submitted to nitroperchloric digestion for further determination of the metal content. The metal concentrations in sediment had become high in both rivers, reaching values of up to 1752.50 mg kg−1 of Pb in point M1 and 53.80 mg kg−1 of Cd in point M3. Macroinvertebrate tissues exhibited high levels of toxic metals, reaching values of 146.11 mg kg−1 of Cr in point M1, 144.28 mg kg−1 of Pb and 3.11 mg kg−1 of Cd in point M3, which indicates the occurrence of bioaccumulation and insertion in the food chain. The results from the evaluation using the BMWP′ index do not present the real conditions of the watersheds, which suggests a review of the evaluation method. In addition, the environmental evaluation using macroinvertebrates is a good tool to verify the impacts in a river.