基于5种重金属元素全量及化学形态评价陕南某矿集区周边土壤生态风险

Ecological Risk Assessment Based on Total Amount and Chemical Species of 5 Heavy Metal Elements in Soil Around Mining Area in Southern Shaanxi

为了研究陕南某矿集区周边土壤中5种重金属元素(铜、铅、锌、镉、砷)的化学形态及其生态风险,采用网格法采集样品529件,用改进BCR(欧共体标准物质局)提取法提取其中30件样品中5种重金属元素的化学形态,采用电感耦合等离子体质谱法测定其全量和各化学形态含量。通过对检测数据进行描述性统计、正态分布检验、皮尔逊(Pearson)相关性检验、主成分分析等进行目标元素富集程度以及同源性分析,采用潜在生态危害指数法进行生态风险评价,采用风险评价编码法(RAC)进行目标元素活性评价,采用次生相/原生相分布比值法(RSP)进行目标元素来源区分。结果显示:研究区土壤样品中5种目标元素测定值的最大值分别为陕西省土壤背景值(2006年调查数据)的3.88~30.53倍,铜以外的4种目标元素测定值超出GB 15618-2018规定筛选值的样品数占总样品数比例为8.0%~27.0%,5种目标元素测定值的变异系数为42.5%~228.6%,说明矿集区周边土壤存在这5种目标元素不同程度的富集,且各目标元素在土壤中分布不均;其中铜、铅、锌可能同源,镉、砷分别为单独来源。5种目标元素的总潜在生态危害指数平均值和最大值分别为29.42和406.22,说明采样土壤生态风险属于安全级别,但是部分区域土壤受镉、砷污染非常严重。5种目标元素残渣态含量占比为47.3%~70.7%,水溶态与弱酸提取态占比为12.5%~34.8%,说明5种目标元素的化学形态主要为稳定的残渣态,但是存在迁移转化到土壤的风险。RAC评价指数显示,5种目标元素均达到中度生态风险(基于平均值),其中锌和镉达到重度生态风险(基于最大值),铜达到极严重生态风险(基于最大值);RSP评价指数显示,铅属于无污染水平(基于最大值),砷、锌和镉达到轻度污染水平(基于最大值),铜达到重度污染水平(基于最大值),说明人为因素对铜影响较大,其他4种目标元素污染主要源于自然形成。

In order to investigate chemical species and ecological risk of the 5 heavy metal elements(Cu, Pb, Zn, Cd and As) in the soil around mining area in southern Shaanxi, 529 samples were collected by grid sampling method, in which, chemical species of the 5 heavy metal elements in 30 samples were extracted by improved BCR extraction method. Total amount and each chemical specie amount were analyzed by inductively coupled plasma atomic emission spectrometry. Analysis of enrichment degree and homology of target elements was carried out on detection data by descriptive statistics, normal distribution test. Pearson correlation test and pricipal component analysis. Ecological risk was evaluated by potential ecological hazard index method. Activity and source of target elements were analyzed by RAC and RSP methods, respectively. It was shown that the maximum determination values of the 5 target elements were 3.88-30.53 times than background values(survey data in 2006) of Shaanxi province, and the proportion of samples with determination values of the other 4 target elements exceeded screening values of GB 15618-2018 were 8.0%-27.0% except for Cu. The variation coefficients of determination values of the 5 target elements ranged from 42.5% to 228.6%, indicating that the 5 target elements were accumulated to varying degrees in the soil around the mining area and the distribution was uneven. Cu, Pb and Zn might come from the same sources, and Cd and As might come from the independent source. The average and maximum values of total potential ecological hazard index were 29.42, 406.22, which revealed that the ecological risk of soil was in safe degree, whereas the soils were polluted seriously by Cd, As in some areas. The residual specie proportion of the 5 target elements ranged from 47.3% to 70.7%, and the sum proportion of water-soluble and weak acid-soluble species ranged from 12.5% to 34.8%, indicating that the main chemical specie of these 5 target elements was the stable residual specie, but there existed the risk that elements in the 2 chemical species might migrate and convert into soils. As found by RAC evaluation indexes, the 5 target elements reached moderate ecological risk level based on average values. Among which, Zn and Cd were belonged to severe ecological risk level based on maximum values, and Cu was belonged to extremely severe level based on maximum values. As found by RSP evaluation indexes, Pb was belonged to non-pollution level based on maximum values, As, Zn and Cd were belonged to moderate pollution level based on maximum values, and Cu was belonged to severe pollution level based on maximum values, indicating that human activity was the main factor that affected Cu and the other 4 target elements pollution might come from nature formation.