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

Sediments of the S？o 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. 1. Introduction The S？o Francisco River, one of the most important Brazilian rivers, runs through seven Brazilian States and its basin covers 7.5% of country’s territory. In the southern part of the S？o Francisco basin a zinc mining is the main responsible industry for the environmental impacts [1]. One of the main impacts occurred up to the 1980s and was caused mainly by incorrect disposal of solid wastes, which were disposed right on the soil. In fact, the wastes were disposed in piles along the river banks for over 30 years and ended up in river bed which aggravated the situation. In 1983, the zinc industry built its first tailings dam; however, it did not have protection layers to prevent seepage of the contaminants from the wastes into the ground or groundwater. More recently, corrective measures are being implemented by the industry in accordance to the requirements of the Brazilians environmental agencies [2–4]. Nevertheless, the environmental impact which occurred before 2002 still poses a threat to the water, sediments, and soil quality. The aforementioned area has been monitored extensively by the governmental agencies with assessment of the physical and chemical parameters of the water and sediments; however, the bioavailability of metals is still poorly investigated. For the assessment of potential bioavailability of metals in river sediments, a traditional method is the AVS/SEM which determines the acid volatile sulfide (AVS) and the metals that are solubilized during acidification