Total and Bioaccesible Metal Concentrations in Surficial Sediment Affected by a Mining Spill: Case of Sonora River, Northwest of Mexico

Abstract

ABSTRACT Metals and metalloids are persistent contaminants that are associated with many anthropogenic activities and mining in particular. On August 6, 2014, approximately 40,000 m3 of toxic acid mining waste was spilled from the Buena Vista del Cobre Copper Mine. The spill affected 220 km of the Sonora River Basin (SRB) over a surface area of ~ 30,000 km2. This study evaluated the total and bioaccessible concentrations of six metals and their enrichment in surficial sediments in spill and no-spill sites in the SRB. All metal concentrations showed significant seasonal and spatial variation (p < .05) in surficial sediments, with a general distribution of Al > Fe > Mn > Zn > Cu > Pb. The total and bioaccessible concentrations of the elements in this study were similar between spill and no-spill sites. Variations in element levels were associated with re-suspension and advection related with rain run-off, and the element concentrations were associated with the high natural concentrations in surficial sediments found throughout the SRB (considering the predominant soil types). The enrichment factor (EF) indicated minor to moderate-severe enrichment of Fe and Mn, minor to severe enrichment of Pb and Zn, and moderate-severe to very severe enrichment of Cu. The bioaccessible percentages of metals with respect to the total concentrations varied from 0.23 to 69.9%. The Sediment Quality Guidelines criteria indicated that adverse effects on biota that are mainly due to Cu levels are potentially present. Chronic exposure to metals may produce intermediate and long-term effects on the metabolic responses of biota.