Abstract
Elements in mining extracts can be potentially toxic if they are incorporated into soils, sediments or biota. Numerous approaches have been used to assess this problem, and these include sequential extractions and selective extractions. These two methods have limitations and advantages, and their combined use usually provides a rough estimate of the availability or (bio)availability of potentially toxic elements and, therefore, of their real potential as toxicants in food chains. These indirect speciation data are interesting in absolute terms, but in the work described here, this aspect was developed further by assessing the evolution of availability-related speciation in relation to the transport processes from the emission source, which are mainly fluvial- and wind-driven. This objective was achieved by characterizing tailings samples as the source of elements in soils and sediments at increasing distances to investigate the evolution of certain elements. The standard procedures employed included a sequential five-step extraction and a selective extraction with ammonium acetate. The results show that the highest percentages of Zn and Pb in tailings, soils and sediment samples are associated with oxyhydroxides, along with a significant presence of resistant mineralogical forms. In the case of Cd, its association with organic matter is the second-most important trapping mechanism in the area. The physicochemical mechanisms of transport did not transform the main mineralogical associations (oxyhydroxides and resistant mineralogical forms) along the transects, but they produced a chaotic evolution pattern for the other minor matrix associations for Zn and a decrease in exchangeable and carbonate-bound forms for Pb in soils. Interestingly, in sediments, these mobile forms showed a decrease in Zn and a chaotic evolution for Pb. The most probable reason for these observations is that Zn2+ can form smithsonite (ZnCO3) or hydrozincite (Zn5(CO3)2(OH)6), which explains the retention of a carbonate-bound form for Zn in the soil transect. In contrast, Pb and Cd can appear as different mineral phases. The order of (bio)availability was Pb > Zn > Cd in tailings but Cd > Pb > Zn in soils. The physicochemical processes involved in transport from tailings to soils produce an increase in Cd (bio)availability. The trend is a decrease in bioavailability on moving away from the source (tailings), with maximum values obtained for Cd near to the source area (200–400 m).
Highlights
Contamination with potentially toxic elements (PTEs) is a global concern due to their nonbiodegradable nature and persistence in different environmental compartments [1,2]
In the different environmental compartments, PTEs can exist in the form of different minerals but, as more labile compounds or species, the mobilities of which are dependent on the properties of each species and other environmental factors [12]
In the work described here, sequential and selective extractions were performed on soils, sediments and mine tailings from an area affected by mining-related contamination by potentially toxic elements [13]
Summary
Contamination with potentially toxic elements (PTEs) ( described as “heavy metals and metalloids”) is a global concern due to their nonbiodegradable nature and persistence in different environmental compartments [1,2]. A more realistic approach involves a determination of the proportion of the (bio) available fraction(s), which correspond to those that form compounds or species that are labile enough in the soil or sediments to be taken up by the organisms present [15] In this respect, a range of chemical extraction procedures have been proposed to estimate the metal (bio) availability, with some based on the so-called sequential extractions [16,17,18] and others based on “selective extractions” [19,20,21]. In the work described here, sequential and selective extractions were performed on soils, sediments and mine tailings from an area affected by mining-related contamination by potentially toxic elements [13]. Presence of the decommissioned mine upstream of a reservoir used for irrigation was considered
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
