煤矿区农田土壤多环芳烃生态风险评估方法比较

A method for assessing the ecological risks due to the polycyclic aromatic hydrocarbons in the farming soil near coal mine area

调查了迁安煤矿区农田土壤中优先控制的16种多环芳烃（PAHs）质量比,通过同一尺度对生态效应低中值、风险商值法（RQ）、有机碳归一化法及苯并（a）芘毒性等效当量4种常用评估方法的评估结果进行了比较,并尝试将商值法（RQ）与苯并（a）芘毒性等效当量（TEQBa P）相结合对该矿区土壤进行风险评估。结果表明,煤矿区农田土壤中16种PAHs总量为118.10~1 042.31μg/kg,并以2~4环为主。4种生态风险方法评估结果与衡量尺度比较表明,生态效应低中值、RQ两种方法对PAHs处于低水平的地区适用性欠佳;有机碳归一化法及苯并（a）芘毒性等效当量两种方法能较好地表征该地区PAHs的生态风险水平,但不能对不同污染水平下的生态风险程度予以分级。RQ-TEQ复合法评估结果显示,11%土壤样品存在重度生态风险,11%处于中度风险,45%存在轻度生态风险,22%处于警戒线范畴,11%不存在生态风险。与单一方法相比,复合方法评估结果分级明确,与衡量尺度吻合较好,较适用于该煤矿区PAHs的生态风险评估。

The present paper is aimed at introducing a new method of ecological risk evaluation we have developed to determinate the con-centrations of polycyclic aromatic hydrocarbons （PAHs） in the nine surface soil samples we have collected from the farm-land soil in the coal-mlne area in Qianan, Hebei, in July, 2012. In our evaluation, we have extracted the concentrations of PAHs with four kinds of dif- ferent separate methods（i, e. the low median interval of ecological ef- fect; the risk quotients（RQ）; the organic carbon normalization and the toxic equivalency quantity（TEQ） and then made an assessment of the said ecological risk by using a new method, that is, the method known as RQ - TEQ developed by us. The results of our investigation have shown that the concentration rate of PAHs is ranging between 118.10 - 1 042.31 /~g/kg（dry weight）, with the dominant PAHs be- ing 2 - 4 rings. What is more, we have detected all the sixteen kinds of most important PAHs in all the samples and put necessary marks as points prone to ecological risks in all the sampling points in the said farmland area. The points have also been shown by the low median interval of the ecological effects and RQ methods. In addition, the method of the organic carbon normalization has also helped us to find that No. 1, 2, 5, 7 and 9 sampling points are all potentially prone to the ecological risks. At the same time, the TEQ method indicates that No. 1, 2, 5 and 9 sampling points also belong to such areas with ecological risks. Furthermore, joining all the results of the evaluation gained by using the four methods with measurement data, we have made a conclusion that the low median interval of the ecological effect and RQ methods tends to be more suitable for the ecological risk as- sessment in the severely polluted soil here under study. The results of the organic carbon normalization and TEQ evaluation may account for the characterization of the ecological risks of PAHs in this area, but it may not be suitable for the effective identification of the ecological risks at the different pollution levels. The result of RQ - TEQ method tends to prove that the 11% of the sampling points tends to be subject to the severe ecological risk： Another 11% of the sampling points may belong to the area of moderate ecological risk. And, still another ll % of sampling points can be categorized into the area slightly prone to the ecological risks. In the same way, the 22 % of the sam- pling points may belong to the alert range, whereas the rest 11% of sampling points can be said totally safe from such risks. Thus, it can be seen that, as compared with the results of the single method, the RQ- TEQ method we have developed can be classified as one more consistent with the actual situation of the land actuality in-situ. Therefore, the method proves to be more advantageous in assessing the ecological risks of PAHs in such kinds of mining areas.