Ecological risk assessment of heavy metals in rainfall runoff of different land use types in Suzhou of Taihu Basin

Abstract

随着城市化进程的不断加快，不同用地类型上产生的降雨径流中重金属含量高且差异较大，而目前仍缺乏对降雨径流所携带的重金属风险评价的研究.以苏州城区为研究对象，选取商业区、居住区、历史文化保护区和文教区，监测降雨径流中铜（Cu）、锌（Zn）和铅（Pb）3种常见重金属浓度，通过物种敏感性分布（SSD）曲线获取预测无效应浓度（PNEC），基于重金属的生态有效性，应用风险商（RQ）法对重金属的生态风险进行评价.结果表明：以6场有效降雨事件的事件平均浓度（EMC）统计结果的平均值为分析依据，对照《地表水环境质量标准》（GB 3838—2002），苏州城区径流中的Zn、Cu浓度满足Ⅱ类水质标准，Pb浓度则劣于Ⅴ类水质标准；主要受地面交通活动和屋面材料的影响；在不同用地类型内Cu、Pb和Zn浓度的分布存在一定差异，商业区受重金属污染程度最为严重，其余3种用地类型均不同程度受到不同重金属的污染，对应的3种重金属的生态风险在不同用地类型内也显示相同规律；不同的重金属产生不同的环境行为，导致对水生生物的毒性差异较大，降雨径流中的重金属浓度在水环境中产生的有效生态风险程度为Pb > Cu > Zn.研究认为Cu、Zn和Pb对淡水生物的生态风险均达到高风险程度，而我国目前的《地表水环境质量标准》未充分考虑生态影响，低估了部分重金属的生态风险.;With the rapid development of urbanization, heavy metal pollution resulting from runoff increase and vary greatly in different land use. However, there is still a lack of research on the risk assessment of heavy metal carried by the runoff. In Suzhou urban area, four land use types including commercial area, residential area, historical and cultural protection area, and cultural and educational area were selected to monitor the content of Cu, Zn and Pb in rainfall runoff. Further, the ecological risk of these three heavy metals was evaluated by risk quotient (RQ), which was on the basis of predicted no-effect concentration (PNEC) obtained by species sensitivity distribution (SSD) curve. Based on the event mean concentration (EMC) of six effective rainfall events, compared with the Environmental Quality Standard for Surface Water (GB 3838-2002), statistical results show that Zn and Cu in the rainfall runoff meet grade Ⅱ water quality standard, while Pb is inferior to grade V water quality standard, which are mainly affected by the traffic activities and roofing materials in different land use types. Correspondingly, commercial area is polluted by all these three heavy metals worst, the other areas are polluted in different degrees by different heavy metals, resulting in a large difference in toxicity to aquatic organisms. Generally, the ecological risks by heavy metals in rainfall runoff are in high-risk degree, and in the order of Pb > Cu > Zn. Therefore, the current environmental quality standard for surface water in China does not fully consider the ecological impact and underestimates the ecological risks of heavy metals.