Chèvre Nathalie, Loepfe Christian, Singer Heinz, Stamm Christian, Fenner Kathrin, Escher Beate I
Swiss Federal Institute for Aquatic Science and Technology (Eawag), Duebendorf, Switzerland.
Environ Sci Technol. 2006 Jan 15;40(2):426-35. doi: 10.1021/es050239l.
Monitoring programs throughout America and Europe have demonstrated the common occurrence of herbicides in surface water. Nevertheless, mixtures are rarely taken into account in water quality regulation. Taking mixtures into account is only feasible if the water quality criteria (WQC) of the single compounds are derived by a common and consistent methodology, which overcomes differences in data quality without settling on the lowest common denominator but making best use of all available data. In this paper, we present a method of defining a risk quotient for mixtures of herbicides with a similar mode of action (RQm). Consistent and comparable WQC are defined for single herbicides as a basis for the calculation of the RQm. Derived from the concentration addition model, the RQm can be expressed as the sum of the ratios of the measured environmental concentration and the WQC for each herbicide. The RQm should be less than one to ensure an acceptable risk to aquatic life. This approach has the advantage of being easy to calculate and communicate, and is proposed as a replacement for the current limit of 0.1 microg/L for herbicides in Switzerland. We illustrate the proposed approach on the example of five commonly applied herbicides (atrazine, simazine, terbuthylazine, isoproturon, and diuron). Their risk profile, i.e., the RQm as a function of time for one exemplary river, clearly shows that the single compounds rarely exceeded their individual WQC. However, the contribution of peaks of different seasonally applied herbicides, whose application periods partially overlap, together with the continuously emitted herbicides from nonagricultural use, results in the exceedance of the RQm threshold value of one upon several occasions.
美国和欧洲各地的监测项目已表明，地表水中普遍存在除草剂。然而，水质监管中很少考虑混合物的情况。只有当单一化合物的水质标准（WQC）通过通用且一致的方法得出时，考虑混合物才可行，这种方法能克服数据质量的差异，不是采用最低公分母，而是充分利用所有可用数据。在本文中，我们提出了一种为具有相似作用模式的除草剂混合物定义风险商（RQm）的方法。为单一除草剂定义一致且可比的WQC，作为计算RQm的基础。从浓度相加模型推导得出，RQm可表示为每种除草剂的实测环境浓度与WQC之比的总和。RQm应小于1，以确保对水生生物的风险可接受。这种方法具有易于计算和传达的优点，并被提议作为瑞士目前除草剂0.1微克/升限值的替代方法。我们以五种常用除草剂（莠去津、西玛津、特丁津、异丙隆和敌草隆）为例说明了所提议的方法。它们的风险概况，即一条典型河流的RQm随时间的变化情况，清楚地表明单一化合物很少超过其各自的WQC。然而，不同季节施用的除草剂（其施用期部分重叠）的峰值贡献，以及来自非农业用途持续排放的除草剂，导致RQm阈值多次超过1。
