Laboratoire Génie Environnement Ecotechnologie, Ecole Nationale d'Ingénieurs de Sfax, Université de Sfax, 3038 Sfax, Tunisia.
Departamento de Ingeniería Geológica y Minera, Instituto de Geología Aplicada, Universidad de Castilla-La Mancha, 13400 Almadén, Spain.
Int J Environ Res Public Health. 2020 Jul 8;17(14):4912. doi: 10.3390/ijerph17144912.
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 Zn can form smithsonite (ZnCO) or hydrozincite (Zn(CO)(OH)), 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).
如果采矿提取物中的元素被纳入土壤、沉积物或生物群中，它们可能具有潜在毒性。已经使用了许多方法来评估这个问题，包括顺序提取和选择性提取。这两种方法都有其局限性和优点，它们的结合使用通常可以粗略估计潜在有毒元素的可用性或（生物）可用性，因此可以评估它们在食物链中作为毒物的实际潜力。这些间接形态数据在绝对值上是有趣的，但在本文中，通过评估与从排放源到土壤和沉积物的运输过程有关的可用性相关形态的演变，进一步发展了这一方面，这些运输过程主要是由河流和风驱动的。这一目标是通过对尾矿样本进行特征描述来实现的，这些尾矿样本是土壤和沉积物中元素的来源，距离排放源越来越远，以研究某些元素的演变情况。采用的标准程序包括五步骤顺序提取和乙酸铵选择性提取。结果表明，尾矿、土壤和沉积物样品中 Zn 和 Pb 的最高百分比与水合氢氧化物有关，同时存在大量抗性矿物形态。对于 Cd，其与有机质的结合是该地区第二重要的捕集机制。沿剖面的传输物理化学机制并没有改变主要的矿物结合（水合氢氧化物和抗性矿物形态），但它们使 Zn 的其他次要基质结合产生了混乱的演化模式，使土壤中可交换和碳酸盐结合的 Pb 形式减少。有趣的是，在沉积物中，这些可移动形式的 Zn 减少，Pb 呈现混乱的演化。造成这种观察结果的最可能原因是 Zn 可以形成菱锌矿（ZnCO）或羟锌矿（Zn(CO)(OH)），这解释了土壤剖面中 Zn 存在碳酸盐结合形式的原因。相比之下，Pb 和 Cd 可以呈现不同的矿物相。尾矿中 Zn 的（生物）可利用性顺序为 Pb>Zn>Cd，但土壤中 Cd> Pb> Zn。从尾矿到土壤的传输过程中涉及的物理化学过程会增加 Cd 的（生物）可利用性。从源（尾矿）向外移动的趋势是生物利用度降低，在靠近源区（200-400 m）的 Cd 处获得最大值。
