HEAVY METALS CONTAMINATION, POLLUTION INDICES AND HEALTH RISK ASSESSMENT OF SOILS IN DUMPSITES WITHIN THE VICINITY OF UNIVERSITY OF PORT HARCOURT, NIGERIA.docx

This study investigated the levels of Lead(Pb), Zinc (Zn), Cadmium (Cd), Manganese (Mn), Chromium (Cr), Nickel (Ni), Arsenic (As) and Copper (Cu) in soils from four selected dumpsites in the vicinity of the University of Port Harcourt, East-west Road, Choba, Rivers State, Nigeria. Analysis of metals was done by wet digestion and atomic absorption spectroscopy, and the concentrations were found to fall within the following range; Zn (74.54–122.42mg/kg), Cr (28.76-42.17mg/kg), Ni (15.71-24.95mg/kg), Cu (13.62-23.17mg/kg), Mn (6.15-10.74mg/kg), Pb (4.87-10.32mg/kg), Cd (2.79-5.15mg/kg) and As (0.35-0.85mg/kg) for the four samples respectively, showing their occurrence to be in the order Zn&gt;Cr&gt;Ni&gt;Cu&gt;Mn&gt;Pb&gt;Cd&gt;As. The results were further evaluated with some pollution indices (Geo-accumulation Index (Igeo), Contamination factor (CF), Pollution Load Index (PLI), Ecological Risk factor (Erⁱ), and The Potential Ecological Risk Index (R_i)). The average daily intakes (ADI) of metals were below the reference dose (RfD) recommended by World Health Organisation (WHO) showing little or no risk from heavy metals is associated with the routes of exposure. Estimation of pollution indices showed soils from dumpsites were extremely polluted with cadmium. Specifically, Igeo results graded soil samples as unpolluted to moderately polluted (Ni and Cr in sites B and C), with Cd being observed to be highly polluted in all the sample areas studied. The same trend was also observed for the CF, which ranged from very slightly contaminated to moderately polluted in the following order Mni values were below 40, showing a low ecological risk posed by the other metals save Cd which had a moderate (sites B and C) to high ecological risk (sites A and D). R_i values (113- 200) is a presentation of a low to moderate potential ecological risk posed by the metals in all sample locations, with cadmium contributing 96.38–96.47% of the entire potential ecological risk. Measured concentrations of these metals used to calculate the health risk for adult and children population, showed that the average daily intakes (ADI) of metals were below the reference dose recommended by World Health Organisation (WHO) showing that little or no risk from heavy metals in these sites is associated with the routes of exposure. However, the ADI of Cu in control site was greater than the RfD by WHO standards thus calls for concern for non-carcinogenic health complications. The Hazard index (HI) value for adult and child population, via exposure was &lt; 1, indicating low non-carcinogenic effects to the population. However, the Hazard Index value for the population in the control site was &gt;1, indicating a high non-carcinogenic risk to adult and children exposed in the area. The carcinogenic risk for all metals in this study was within the cancer safe limits, and poses no potential to cause carcinogenic health risk.<br><br>

本研究针对尼日利亚河流州乔巴市东西大道哈科特港大学周边的4个选定垃圾场的土壤，检测了其中铅（Lead, Pb）、锌（Zinc, Zn）、镉（Cadmium, Cd）、锰（Manganese, Mn）、铬（Chromium, Cr）、镍（Nickel, Ni）、砷（Arsenic, As）与铜（Copper, Cu）的含量。采用湿法消解与原子吸收光谱法（atomic absorption spectroscopy）开展金属元素分析，4份土壤样品的各金属浓度范围依次为：Zn（74.54~122.42mg/kg）、Cr（28.76~42.17mg/kg）、Ni（15.71~24.95mg/kg）、Cu（13.62~23.17mg/kg）、Mn（6.15~10.74mg/kg）、Pb（4.87~10.32mg/kg）、Cd（2.79~5.15mg/kg）以及As（0.35~0.85mg/kg），各金属的含量排序为Zn>Cr>Ni>Cu>Mn>Pb>Cd>As。随后通过多项污染指数对检测结果进行评估，包括地质累积指数（Geo-accumulation Index, Igeo）、污染因子（Contamination Factor, CF）、污染负荷指数（Pollution Load Index, PLI）、生态风险因子（Ecological Risk Factor, Erⁱ）以及潜在生态风险指数（Potential Ecological Risk Index, Rᵢ）。金属的日均摄入量（Average Daily Intakes, ADI）均低于世界卫生组织（World Health Organisation, WHO）推荐的参考剂量（Reference Dose, RfD），表明经暴露途径摄入重金属带来的健康风险极低或几乎不存在。

污染指数评估结果显示，垃圾场土壤受到镉的重度污染。具体而言，地质累积指数结果将部分样品评定为无污染至中度污染（B、C点位的Ni与Cr），而所有采样区域的Cd均表现为重度污染。污染因子也呈现相同趋势，其污染等级从轻微污染至中度污染；其余金属的生态风险因子Erⁱ值均低于40，表明除Cd外，其余金属仅带来低生态风险，Cd在B、C点位表现为中度生态风险，在A、D点位则为高生态风险。潜在生态风险指数Rᵢ介于113~200之间，表明所有采样点位的金属污染均带来低至中度的潜在生态风险，其中Cd对总潜在生态风险的贡献率达96.38%~96.47%。基于实测金属浓度计算成人与儿童群体的健康风险，结果显示金属的日均摄入量均低于WHO推荐的参考剂量，表明上述采样点的重金属经暴露途径引发的健康风险极低或几乎不存在。但对照点位的Cu日均摄入量超出了WHO推荐的参考剂量，需警惕由此引发的非致癌性健康并发症。成人与儿童经暴露途径的危害指数（Hazard Index, HI）均小于1，表明人群面临的非致癌效应较低。但对照点位的危害指数大于1，表明该区域暴露的成人与儿童面临较高的非致癌健康风险。本研究中所有金属的致癌风险均处于癌症安全限值范围内，未带来潜在致癌健康风险。