Investigation into River Sediments Toxicity as a Result of Inappropriate Waste Disposal

Sediments of the São Francisco River basin (Brazil) were investigated to determine the environmental consequences of incorrect disposal of wastes generated by a zinc industry. Surface sediments were characterized by X-ray diffraction (XRD) and chemically analyzed by X-ray fluorescence (XRF). Total organic carbon (TOC), acid volatile sulfides (AVSs), and simultaneously extracted metals (SEMs) were also determined. AVS/SEM procedure was employed to assess the bioavailability of the metals in sediments. XRD analyses indicated that the main phases in the sediments were kaolinite and quartz. The total concentration of Zn and Pb, near the old industrial discharge point, indicated high levels of contamination according to the sediment quality guidelines (SQGs). According to the AVS/SEM criteria, despite the high levels of zinc and lead in the sediments, the toxicity resulting from these metals is unlikely in most of the samples. However, in one of the samples, collected near the old industrial discharge point, the toxicity is uncertain—according to the USEPA criteria