Assessment of Trace Element Contents in Soils and Water from Cerrado Wetlands, Triângulo Mineiro Region

ABSTRACT In the Brazilian Cerrado biome, there are wetlands locally known as “Veredas”, which are swampy plains between hills and rivers. Since the 1970’s, the Cerrado biome has been gradually converted to livestock, crop, or forestry production. Until now, very few studies were conducted to evaluate the baseline contents of trace elements in Cerrado wetland soils. Due to their position in the landscape (bottom lands), the wetlands are potentially susceptible to contamination by runoff and/or leaching from surrounding areas at higher altitudes. This work evaluated the As, Cd, Pb, Ni, Zn, Cu, Mn, and Fe contents in soils from six wetlands (undisturbed and disturbed) in the Minas Gerais Triangle region, Brazil. In each wetland, we collected topsoil samples (0.00-0.20 m layer) and subsurface samples (0.40-0.70 m layer) at different landscape positions in the wetlands (upper, middle, and bottom positions). The soil samples were air-dried, ground, and sieved through 2-mm mesh. Afterwards, the soil digestion was performed according to the USEPA 3051A protocol, and the trace elements were determined by atomic absorption spectrometry (flame or graphite furnace atomization). Water samples were also collected monthly from September 2014 to September 2015 to determine the elemental composition by inductively coupled plasma optical emission spectrometry. The contents of all soil trace elements studied were below the threshold values established by Brazilian guidelines. The soil trace element (cations and/or oxyanions) distributions varied according to soil depth and organic matter content. Our findings contribute to the sparse inventory of Brazilian Cerrado wetlands regarding trace-element contents.

摘要：在巴西塞拉多生物群区（Brazilian Cerrado biome）中，存在当地俗称“Veredas”的湿地，这类湿地为坐落于丘陵与河流之间的沼泽化平原。自20世纪70年代以来，塞拉多生物群区已逐渐被开发为畜牧、农作物种植或林业生产用地。迄今为止，针对塞拉多湿地土壤微量元素基线含量的相关研究仍极为匮乏。由于这类湿地处于景观中的低洼地带，它们存在受到高海拔周边区域径流及/或淋溶作用带来的污染的潜在风险。本研究针对巴西米纳斯吉拉斯三角区的6处湿地（包含未受干扰与受干扰两种类型），测定了其土壤中砷（As）、镉（Cd）、铅（Pb）、镍（Ni）、锌（Zn）、铜（Cu）、锰（Mn）及铁（Fe）的含量。在每处湿地中，我们分别于湿地内的上部、中部及下部景观位置采集了表层土壤样品（0.00~0.20米土层）与亚表层土壤样品（0.40~0.70米土层）。土壤样品经风干、研磨后过2mm孔径筛。随后，参照美国环境保护署（USEPA）3051A标准方法完成土壤消解，采用原子吸收光谱法（火焰原子化或石墨炉原子化）测定其中的微量元素含量。此外，本研究于2014年9月至2015年9月期间按月采集水样，通过电感耦合等离子体光发射光谱法测定其元素组成。本次研究涉及的所有土壤微量元素含量均低于巴西相关导则所规定的阈值标准。土壤微量元素（阳离子及/或含氧阴离子）的分布随土壤深度与有机质含量的变化而存在差异。本研究结果可为现有巴西塞拉多湿地微量元素含量的稀缺数据集补充相关数据。