Horckmans L, Swennen R, Deckers J
Geologie, K.U.Leuven, Celestijnenlaan 200E, B-3001 Heverlee, Belgium.
Sci Total Environ. 2007 Apr 15;376(1-3):86-99. doi: 10.1016/j.scitotenv.2007.01.077. Epub 2007 Feb 20.
In the northern Campine in Belgium, large areas are contaminated by heavy metals such as Zn and Cd due to the (former) non-ferro metal industry. In the sandy soils, the heavy metal adsorption/attenuation in the spodic horizon represents the main retention mechanism of leached pollutants from the contaminated topsoils. In this study, the pH-dependent behaviour of the elements in these spodic horizons was tested by pH(stat) experiments and compared to sandy loam soils. Extractions with CaCl(2) 0.01 M and EDTA 0.05 M provided a further insight into the binding mechanisms. The results indicate that organic matter is the main factor responsible for the mobility of Cd, Zn and Ca in the spodic horizons. The binding of elements is not very strong, however, and highly dependent on pH. A slight decrease in pH can cause a significant release of metals from the spodic horizons, with up to 60% of Cd and 90% of Zn being released within a 1.5 unit change in pH (starting from the naturally occurring pH). This pH change can happen rapidly in these soils, due to the low buffering capacity, and is realistic given the acidification in Flanders. For the sandy loam soils, a pH decrease of 3 units is needed to release 40% of Cd and 20% of Zn, and the acid neutralization capacity is exhausted more gradually, suggesting that slower buffering mechanisms take place. For the sandy loam soils, Cd retention is mainly governed by organic matter, while for Zn other factors such as the clay minerals also play an important role. Despite the high potential mobility and pH dependence of the heavy metal retention in the spodic horizons, the actual risk for groundwater pollution is limited. For the diffusely contaminated areas, where traditional remediation is not an option, spodic horizons may therefore contribute to a natural attenuation of the soil contamination.
在比利时北部的坎皮讷地区，由于（以前的）有色金属工业，大片区域被锌和镉等重金属污染。在沙质土壤中，灰化淀积层中重金属的吸附/衰减是受污染表土中淋溶污染物的主要滞留机制。在本研究中，通过pH（恒）实验测试了这些灰化淀积层中元素的pH依赖性行为，并与砂壤土进行了比较。用0.01 M氯化钙和0.05 M乙二胺四乙酸进行萃取，进一步深入了解了结合机制。结果表明，有机质是导致镉、锌和钙在灰化淀积层中迁移的主要因素。然而，元素的结合不是很强，并且高度依赖于pH值。pH值略有下降会导致大量金属从灰化淀积层中释放出来，在pH值变化1.5个单位（从自然发生的pH值开始）范围内，高达60%的镉和90%的锌会被释放出来。由于缓冲能力低，这种pH值变化在这些土壤中可能会迅速发生，考虑到佛兰德地区的酸化情况，这是现实的。对于砂壤土，需要将pH值降低3个单位才能释放40%的镉和20%的锌，并且酸中和能力的耗尽更为缓慢，这表明存在较慢的缓冲机制。对于砂壤土，镉的滞留主要受有机质控制，而对于锌，其他因素如粘土矿物也起着重要作用。尽管灰化淀积层中重金属滞留具有高潜在迁移性和pH依赖性，但对地下水污染的实际风险是有限的。因此，对于传统修复不可行的扩散污染区域，灰化淀积层可能有助于土壤污染的自然衰减。
