陕西潼关金矿区土壤Pb和Cd生物有效性的影响因素及其意义

Factors affecting bioavailability of heavy metal elements Pb and Cdinsoil o fthe Tongguan gold ore district and their significance

土壤中重金属形态与其赋存条件之间的关系是评估土壤重金属风险的关键问题。以受金矿开发影响的土壤中Pb、Cd为研究对象,采用动力学方程分析了土壤有机质、粘粒、pH、Eh等对Pb、Cd生物有效性的影响。结果表明,研究区影响Pb、Cd生物有效性的主要因素有土壤有机质、pH及Eh;有机质与土壤中的Pb、Cd总量呈现正相关性;但当有机质含量增加时,Pb、Cd的水溶态和离子交换态含量反而降低;土壤粘粒对Pb、Cd生物有效性的影响不甚明显;虽然较低的土壤pH值会加剧重金属离子的活性,增强其生物有效性,但过高的pH值又会提高Cd碳酸盐态、铁锰氧化态的含量;Pb、Cd生物有效性随着土壤氧化—还原电位的降低而减弱。研究发现,对于Pb、Cd污染的土壤,通过增施有机肥可提高农产品的安全性;保持土壤处于弱酸—弱碱有利于降低农产品风险;在农作物成熟期实施淹水灌溉,降低土壤氧化—还原电位,可抑制Pb、Cd在籽粒中的累积。

The relationship between morphology and occurrence conditions of heavy metals is key to assessing the risk of heavy metals in soil. In this paper, the authors studied Pb and Cd soil related to gold mining, analyzed the impact of such factors as organic matter, clay, pH and Eh in soil on bioavailability by means of the kinetic equation. The results show that the main factors affecting bioavailabil-ity are soil organic matter, pH and Eh. The content of organic matter has a distinct relationship with Pb or Cd in soil.Also, the in-crease in clay content in soil may slightly increase the proportion of the content of Cd and Pb in the ionic exchangeable form to the total content of Pb and Cd. The soil acidification may increase the content of cadmium in the ionic exchangeable form, which has a distinct relationship with the pH in soil. Bioavailability is weakened with decreasing soil Eh. It is obvious that the increase in organic matter in soil may obviously reduce the content of Cd and Pb in the ionic and exchangeable form. When the effective state is consid- ered, the maintenance of soil weak acidification or weak alkalinity is a good way to avoid active bioavailability. When the crops ma-ture, the implementation of flood irrigation can inhibit the accumulation of heavy metals in grain.