Heavy metal contamination along the Duhok-Zakho highway soils: spatial analysis, risks, and ecological implications

This study investigates heavy metal contamination in soils of the Duhok-Zakho Highway of Iraq, where 20 samples were collected along a 50-km-long highway to assess Cu, Pb, Fe, Mg, Co, Ni, and Mn concentrations. Results revealed significant spatial variations in metal concentration, where the ranking of the metals followed: Fe > Mn > Mg > Ni > Co > Pb > Cu. The enrichment factor analysis indicated moderate to very high levels, while the geoaccumulation index exhibited a high level of metal enrichment, surpassing the standard background value. The ecological risk was assessed as moderate. Non-carcinogenic risk analysis revealed that Fe and Mn posed extreme non-cancer risk, with ingestion accounting for 99.95% of exposure. Children showed 10 times more vulnerability than adults to non-cancer risks. Carcinogenic risk derived from Ni and Pb exceeded the USEPA guideline threshold (1 × 10−6), with the children facing 25 times greater risks than the adults. The toxicity leaching test revealed substantial metals leaching (64–79%), suggesting a high potential for heavy metals to transport downstream the agricultural farmland and probable groundwater contamination. The findings highlight the impact of vehicle-induced metal pollution and industrial operations on heavy metal distribution in highway soils.本研究针对伊拉克杜胡克-扎霍公路沿线的土壤重金属污染展开调查，沿50公里长的公路共采集20份土壤样本，以测定铜（Cu）、铅（Pb）、铁（Fe）、镁（Mg）、钴（Co）、镍（Ni）及锰（Mn）的含量。研究结果显示，各重金属含量存在显著的空间变异性，元素含量排序为：Fe > Mn > Mg > Ni > Co > Pb > Cu。富集因子（enrichment factor）分析表明，重金属富集程度处于中等至极高水平；而地质累积指数（geoaccumulation index）则显示重金属富集程度较高，超出标准背景值。生态风险评估结果为中等水平。非致癌风险分析表明，Fe和Mn会带来极强的非致癌健康风险，其中经口摄入途径占总暴露量的99.95%；儿童相较于成人，非致癌风险的易感性高出10倍。由Ni和Pb引发的致癌风险超过了美国环境保护署（USEPA）的阈值标准（1 × 10⁻⁶），且儿童的致癌风险是成人的25倍。毒性浸出试验（toxicity leaching test）结果显示，64%~79%的重金属可被浸出，表明该区域重金属具有较高的向下游农田迁移并可能污染地下水的风险。本研究结果凸显了机动车引发的重金属污染及工业活动对公路沿线土壤重金属分布的影响。