Rate Andrew W, Lee Karen M, French Peter A
School of Earth and Geographical Sciences, M087, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
Bioresour Technol. 2004 Feb;91(3):223-31. doi: 10.1016/s0960-8524(03)00206-2.
Mineral sands mining involves stripping topsoil to access heavy-mineral bearing deposits, which are then rehabilitated to their original state, commonly pasture in south-west Western Australia. Organic amendments such as biosolids (digested sewage sludge) can contribute organic carbon to the rehabilitating system and improve soil chemical fertility and physical conditions. Use of biosolids also introduces the risk of contamination of the soil-plant system with heavy metals, but may be a useful source of trace elements to plants if the concentrations of these elements are low in unamended soil. We expected that biosolids amendment of areas mined for mineral sands would result in increased concentrations of metals in soils and plants, and that metal uptake would be decreased by adding stockpiled topsoil or by liming. A glasshouse experiment growing a mixed annual ryegrass (Lolium rigidum)-subterranean clover (Trifolium subterraneum) sward was conducted using two soil materials (residue sand/clay and conserved topsoil) from a mineral sands mine amended with different rates of biosolids (0, 10, 20, 50 dry t/ha), and including a liming treatment (2 t/ha). Total concentrations of metals (As, Cd, Co, Cr, Cu, Ni, Pb and Zn) in soil increased with increasing rate of biosolids application. Metal uptake was generally lower where topsoil was present and was decreased by liming. With increasing biosolids application, plant metal concentrations increased for Cd, Ni and Zn but decreased or were erratic for other elements. In clover, biosolids application removed the Zn deficiency observed where biosolids were not applied. Plant uptake of all elements increased with increasing biosolids application, suggesting dilution by increased plant biomass was responsible for erratic metal concentration results. Despite the observed increases in uptake of metals by plants, metal concentrations in both species were low and below food standard thresholds. It is unlikely that a single application of biosolids in this system posed a threat from heavy metal contamination of soils or plants, and was beneficial in terms of Zn nutrition of T. subterraneum.
矿砂开采涉及剥离表土以获取含重矿物的矿床，之后再将其恢复至原始状态，在西澳大利亚西南部通常恢复为牧场。诸如生物固体（消化后的污水污泥）等有机改良剂可为恢复系统贡献有机碳，并改善土壤化学肥力和物理状况。使用生物固体还会带来土壤 - 植物系统被重金属污染的风险，但如果未改良土壤中这些元素的浓度较低，生物固体可能是植物微量元素的有用来源。我们预计，对矿砂开采区域施用生物固体改良剂会导致土壤和植物中金属浓度增加，并且通过添加堆存的表土或施用石灰会减少金属吸收。利用来自一个矿砂矿的两种土壤材料（残留砂/黏土和留存表土）进行了一项温室试验，种植一年生黑麦草（多花黑麦草）和地下三叶草的混合草皮，施用不同比例的生物固体（0、10、20、50干吨/公顷），并设置了一个石灰处理（2吨/公顷）。土壤中金属（砷、镉、钴、铬、铜、镍、铅和锌）的总浓度随着生物固体施用量的增加而增加。在有表土的地方，金属吸收量通常较低，并且施用石灰会降低金属吸收量。随着生物固体施用量的增加，镉、镍和锌的植物金属浓度增加，而其他元素的浓度则降低或不稳定。在三叶草中，施用生物固体消除了未施用生物固体时观察到的锌缺乏现象。所有元素的植物吸收量都随着生物固体施用量的增加而增加，这表明植物生物量增加导致的稀释作用是金属浓度结果不稳定的原因。尽管观察到植物对金属的吸收增加，但两种植物中的金属浓度都很低，低于食品标准阈值。在该系统中单次施用生物固体不太可能对土壤或植物造成重金属污染威胁，并且对地下三叶草的锌营养有益。
