Martínez C E, Motto H L
Department of Soil, Crop, and Atmospheric Sciences, Cornell University, Ithaca, NY 14853, USA.
Environ Pollut. 2000 Jan;107(1):153-8. doi: 10.1016/s0269-7491(99)00111-6.
Elevated levels of heavy metals in soils are a result of industrial activities, atmospheric deposition, and the land application of sewage sludges and industrial by-products. Their persistence in the soil environment has created interest in the possible changes in solubility. In this study, total dissolved concentrations of Pb, Zn, and Cu were monitored in seven metal-amended soils (a calcareous and six acid mineral soils). Single metal solutions were added to soils and equilibrated (aged) for 40 days. During the 40 days the soil was allowed to air-dry and was rewetted in cycles of about 5 days. At the end of this reaction period, metal solubility was measured (by atomic absorption spectrometry and direct current plasma spectrometry) at the initial soil pH and at decreased pH values which were induced by addition of small aliquots of acid. As expected, solubility of added Pb, Zn, and Cu increased with a decrease in pH. Furthermore, the results showed that the solubility relationship with pH was similar in all non-calcareous soils. This suggests that metal solubility may be controlled by similar soil components, presumably involving soil characteristics such as pH, organic matter content, and soil mineralogy. For each metal, an approximate pH value was found at which solubility deviated from the solubility of metals when they occur in soils at typical (natural) values. This pH was about (pH+/-0.2): 5.2 for Pb, 6.2 for Zn, and 5.5 for Cu. Thus, pH values below these thresholds may enhance metal mobility, biological availability and toxicity in soils. Metals dissolved at higher pH in the calcareous soil (18.8 g kg(-1) inorganic carbon, initial pH 8.2). In a calcareous soil, a significant fraction of these metals react with carbonates, and decreased pH results in much higher metal dissolution. Yet, metal solubility in soils is not determined by the formation and dissolution of single metal compounds.
土壤中重金属含量升高是工业活动、大气沉降以及污水污泥和工业副产品土地施用的结果。它们在土壤环境中的持久性引发了人们对其溶解度可能变化的兴趣。在本研究中，监测了七种添加金属的土壤（一种石灰性土壤和六种酸性矿质土壤）中铅、锌和铜的总溶解浓度。将单一金属溶液添加到土壤中并平衡（老化）40天。在这40天里，土壤被晾干，并以约5天的周期重新湿润。在这个反应期结束时，在初始土壤pH值以及通过添加少量酸诱导降低的pH值下测量金属溶解度（通过原子吸收光谱法和直流等离子体光谱法）。正如预期的那样，添加的铅、锌和铜的溶解度随着pH值的降低而增加。此外，结果表明，所有非石灰性土壤中溶解度与pH值的关系相似。这表明金属溶解度可能受相似的土壤成分控制，大概涉及土壤特性，如pH值、有机质含量和土壤矿物学。对于每种金属，都发现了一个近似的pH值，在该pH值下，溶解度偏离了金属在典型（自然）值土壤中时的溶解度。这个pH值约为（pH±0.2）：铅为5.2，锌为6.2，铜为5.5。因此，低于这些阈值的pH值可能会增强土壤中金属的迁移性、生物有效性和毒性。在石灰性土壤（无机碳含量为18.8 g kg⁻¹，初始pH值为8.2）中，较高pH值下金属会溶解。在石灰性土壤中，这些金属的很大一部分会与碳酸盐反应，pH值降低会导致更高的金属溶解量。然而，土壤中金属的溶解度并非由单一金属化合物的形成和溶解所决定。
