Federal University of Reconcavo of Bahia, Cruz das Almas, Brazil.
Federal University of Reconcavo of Bahia, Cruz das Almas, Brazil.
Sci Total Environ. 2017 Dec 1;601-602:1762-1774. doi: 10.1016/j.scitotenv.2017.06.035. Epub 2017 Jun 11.
Many countries and some Brazilian regions have defined the guideline values for metals in soils. However, the local geological features may be so heterogeneous that global or even regional guideline values cannot be applied. The Greenstone Belts are worldwide geological formations of vast extension, containing mineralization of various metals (e.g., Au, Cr, Ni, and Ag). Natural concentrations of soils must be known to correctly assess the impact of mining. We studied the soils of the Rio Itapicuru Greenstone Belt (RIGB), of Paleoproterozoic age, sampling at 24 sites (0-0.20m) in the areas not or minimally human impacted, equally distributed in the three units of the RIGB: Volcanic Mafic Unit (VMU), Volcanic Felsic Unit (VFU), and Volcano-clastic Sedimentary Unit (SU). The natural pseudo-total concentrations of Cr, Ni, Cu, Zn, Pb, Fe, and Mn were obtained by acid digestion (EPA3050b) both in the soil and the particle-size fractions (sand and clay+silt). The concentrations of metals in RIGB soils, especially Cr and Ni, are generally higher than those reported for other regions of Brazil or other countries. Even the sedimentary soils have relatively high metal values, naturally contaminated by the VMU of the RIGB; a potential impact on Mesozoic and Cenozoic sedimentary rocks located near the study region is highly expected. Metals are concentrated (80%) in the fine particle-size fraction, implying an easy availability through surface transport (wind and runoff). We introduced a new index, called the Fe-independent accumulation factor - AF, which reveals that 90-98% of the dynamics of the trace metals is associated with the iron geochemical cycle. We primarily conclude that determining the guideline values for different soil classes in variable geological/geochemical environment and under semiarid climate is meaningless: the concentration of metals in soils is clearly more related to the source material than to the pedogenesis processes.
许多国家和一些巴西地区已经为土壤中的金属定义了指导值。然而，当地的地质特征可能非常不均匀，以至于无法应用全球甚至区域的指导值。绿岩带是全球广泛延伸的地质构造，含有各种金属的矿化作用（例如 Au、Cr、Ni 和 Ag）。为了正确评估采矿的影响，必须了解土壤的自然浓度。我们研究了里奥伊塔皮库里绿岩带（RIGB）的土壤，该绿岩带为古元古代，在未受或最小程度受人类影响的地区，在 RIGB 的三个单元（火山镁铁质单元（VMU）、火山长英质单元（VFU）和火山碎屑沉积单元（SU））中，在 24 个采样点（0-0.20m）处进行采样。通过酸消解（EPA3050b）获得土壤和粒度级分（砂和粘土+粉砂）中 Cr、Ni、Cu、Zn、Pb、Fe 和 Mn 的天然总浓度。RIGB 土壤中的金属浓度，尤其是 Cr 和 Ni，通常高于巴西其他地区或其他国家报道的浓度。即使是沉积土壤也具有相对较高的金属值，这是由于 RIGB 的 VMU 自然污染所致；预计对研究区域附近的中生代和新生代沉积岩会产生潜在影响。金属主要集中在细颗粒级分中（80%），这意味着通过表面运输（风和径流水）很容易获得。我们引入了一个新的指数，称为 Fe 独立积累因子 - AF，它表明痕量金属的 90-98%的动力学与铁地球化学循环有关。我们主要得出的结论是，在不同的地质/地球化学环境和半干旱气候下，为不同土壤类型确定指导值是没有意义的：土壤中金属的浓度显然与源材料比与成土过程更相关。
