青银高速(吴子靖段)沿线不同地貌单元土壤重金属污染特征、风险评估及源解析

Soil heavy metal pollution characteristics, risk assessment and source analysis of heavy metal pollution in soils of different geomorphic units along the Qingyin Expressway (Wuzijing section)

关键词:  青银高速公路  地貌单元  土壤重金属  分布特征  风险评价

Key words:  Qingyin Expressway  geomorphic unit  heavy metals in soil  distribution characteristics  risk assessment

摘要:

生态脆弱地区交通运输导致的土壤重金属污染问题日益严重。文章以青银高速（吴子靖段）为研究对象，采集了路域黄土区、过渡区和沙漠区共34个土壤样品（0—20 cm），测定了Cd、Cr、Cu、Mn、 Ni、Pb、Zn和As共8种重金属含量。综合运用污染负荷指数法（PLI）、地累积指数法（I_geo）、主成分分析（PCA）和绝对主成分得分-多元线性回归（APCS-MLR）模型进行污染评价与源解析。结果显示：不同地貌单元土壤中Pb、Cr、Ni含量存在超标现象；PLI显示Pb（PLI为1.98—4.12）和Cr（PLI为0.68—1.96） 为主要污染物；I_geo评价表明，黄土区 Pb 污染达中度水平 （I_geo=1.16），过渡区和沙漠区 Pb 呈轻度污染 （I_geo分别为 0.92、0.91）。源解析结果揭示，黄土区 Mn、Pb、Ni 污染主要源于交通排放 （方差贡献率 42.788%）；过渡区As、Mn、Pb、Ni主要受交通与农业复合源影响（方差贡献率70.430%）；沙漠区重金属污染呈现自然地质背景与气候条件主导、叠加人类活动的复合特征。研究阐明了研究区不同地貌单元高速公路路域土壤重金属污染特征及主要来源，为精准制定污染防控策略提供了科学依据。

Abstract:

Background, aim, and scope Soil heavy metal pollution caused by transportation activities in ecologically fragile regions has become a growing environmental concern. The total length of the Wuzijing section of the Qingyin Expressway (G20) is 188.88 km and it in Shaanxi Province traverses five counties (Wubu,Suide, Zizhou, Hengshan, and Jingbian) and 19 towns in Yulin City. This section crosses three typical geomorphological units with the loess zone, the transitional zone, and the desert zone, characterized by high ecological sensitivity. However, the specific characteristics and potential ecological risks of heavy metal pollution resulting from traffic activities in this region remain unclear. To investigate the extent, risk, and sources of heavy metal contamination induced by traffic activities, and to provide a scientific basis for regional soil pollution control, this study collected 34 surface soil samples (0—20 cm) from the road corridor across the three geomorphic units. The concentrations of eight heavy metals (Cd, Cr, Cu, Mn, Ni, Pb, Zn, and As) were determined. Materials and methods The pollution load index (PLI), the geo-accumulation index (I_geo), principal component analysis (PCA), and the absolute principal component scores-multilinear regression (APCS-MLR) model were employed to assess pollution levels and identify potential sources. Results The results showed that the concentrations of Pb, Cr, and Ni in soils exceeded their respective background values across all geomorphic units. PLI identified Pb (PLI: 1.98—4.12) and Cr (PLI: 0.68—1.96) as the primary pollutants; and the I_geo assessment showed that Pb pollution reached a moderate level in the loess zone (I_geo=1.16), while Pb was at a slight pollution level in the transitional and desert zone (I_geo for 0.92 and 0.91, respectively). Source apportionment revealed that Mn, Pb, and Ni contamination in the loess zone was mainly attributable to traffic emissions with a variance contribution of 42.788%; in the transitional zone, As, Mn, Pb, and Ni were primarily influenced by a combined source of traffic and agricultural activities with a variance contribution of 70.430%. Discussion The enrichment of Pb was closely associated with traffic emissions, which aligns with the high contribution of traffic sources to Pb in the loess zone (65.25%) and the Pb concentration exceeding the background value by 2.98 times. This also explains the moderate Pb pollution level (I_geo>1) observed in the loess zone. In the transitional zone, Pb was influenced by both traffic and agricultural sources (70.430% contribution from mixed sources). The presence of As-commonly regarded as an indicator of agricultural activity-alongside Mn, Pb, and Ni in the same source further supports the contribution of agricultural practices to heavy metal accumulation in this zone. Conclusions In summary, anthropogenic activities, particularly traffic emissions and agricultural production, are the primary drivers of heavy metal pollution in the loess and transitional zone. In contrast, heavy metal contamination in the desert zone reflects a more complex pattern, predominantly governed by natural geological background and climatic conditions, with superimposed effects from localized human activities. These spatial differences are closely linked to variations in geomorphic characteristics and the intensity of human disturbances across the three regions. Recommendations and perspectives This study elucidates the pollution characteristics and dominant sources of heavy metals in soils from distinct geomorphic units along an expressway in an ecologically fragile region. The findings provide critical insights for developing targeted pollution control strategies. Specifically, the loess zone needs to strengthen traffic pollution control, the transition zone needs to balance traffic emission reduction and clean agricultural production, and the desert zone needs to pay attention to the superimposed risks of human activities under natural background conditions.