洪水淹没对矿区下游农用地土壤重金属污染特征的影响

为评估洪水淹没对西南某有色金属矿区下游农用地土壤重金属污染状况及土壤质量的影响,采用单因子指数法、内梅罗指数法、潜在生态风险指数法,对矿区下游淹没区及非淹没区农用地进行评价.结果表明,研究区域内主要重金属污染物为Cd、Sb、Pb、As、Zn,淹没区6种重金属As、Cr、Pb、Zn、Cd、Sb的平均含量分别为36.66、63.48、82.54、128.21、0.61、39.46 mg·kg~(-1),非淹没区6种重金属As、Cr、Pb、Zn、Cd、Sb的平均含量分别为7.38、71.44、13.27、35.27、0.16、5.62 mg·kg~(-1),除重金属Cr外,淹没区与非淹没区重金属平均含量存在显著性差异(p0.05).淹没区As、Pb、Zn、Cd、Sb的超标率分别为52.23%、44.54%、48.14%、72.03%、88.25%,非淹没区As、Pb、Zn、Cd、Sb的超标率分别为4.12%、3.23%、2.16%、15.03%、22.00%,淹没区土壤环境质量类别为安全利用,综合潜在环境风险为很强生态风险(RI=600.3),非淹没区土壤环境质量呈现优先保护状态,综合潜在环境风险为轻微生态风险(RI=69.1).有色金属矿区下游农用地被洪水长期淹没导致As、Pb、Zn、Cd、Sb的污染加重,由于研究区域特殊的地质背景,土壤中大量存在的铁锰氧化物胶膜对重金属具有强吸附作用,当洪水中存在大量重金属,随着水位上升洪水浸没土壤,铁锰氧化物胶膜把大量重金属截留在中下层土壤中,从而导致污染更为严重.

Distribution characteristics of heavy metal pollution in agricultural land downstream of a non-ferrous metal mining area in Southwest China

Three index including single factor pollution index, Nemero index and potential ecological risk index were used to evaluate the effects of flooding on the heavy metal pollution and the soil quality of the flooded area and the non-flooded agricultural areas, which are along the downstream of a river nearby a non-ferrous metal mine in the southwest of China. The results showed that the main pollutants in the investigated area were Cd, Sb, Pb, As and Zn. The average concentrations of six heavy metals in the flooded area were 36.66, 63.48, 82.54, 128.21, 0.61 and 39.46 mg·kg^-1 for As, Cr, Pb, Zn, Cd and Sb, respectively, while the average values in non-flooded area were 7.38 (As), 71.44 (Cr), 13.27(Pb), 35.27(Zn), 0.16(Cd) and 5.62 (Sb) mg·kg^-1, respectively. The significant differences were observed between the heavy metals except Cr in the flooded and non-flooded areas (p<0.05). The over-proof ratios of the heavy metals in the flooded area were 52.23%,44.54%, 48.14%, 72.03% and 88.25% for As, Pb, Zn, Cd, and Sb, respectively, while the relative ratios in the non-floode area were only 4.12%, 3.23%, 2.16%, 15.03%, and 22.00%. The soil-quality class of the non-flooded area belonged to the safely utilizable land, and its comprehensive potential ecological risk was strong (RI=600.3). As for the non-flooded area, it was classified to the high-priority land, and its its comprehensive potential ecological risk was slight (RI=69.1). Long-term flooding caused the aggravation of the pollution of As, Pb, Zn, Cd and Sb in the investigated area., which was attributed to the special geological background. In the soil of the studied area, there is much iron-manganese oxide film which has a strong adsorption to heavy metals. When a lot of heavy metals is transferred by the river flood, the iron-manganese oxide film in the flooded soil traps a part of these metals into the middle and lower layers of the soil, and then results to a heavier pollution of heavy metals.