U.S. Geological Survey, Sacramento, CA, United States of America.
U.S. Geological Survey, Austin, TX, United States of America.
Sci Total Environ. 2020 May 1;715:136795. doi: 10.1016/j.scitotenv.2020.136795. Epub 2020 Jan 18.
Transient, acutely toxic concentrations of pesticides in streams can go undetected by fixed-interval sampling programs. Here we compare temporal patterns in occurrence of current-use pesticides in daily composite samples to those in weekly composite and weekly discrete samples of surface water from 14 small stream sites. Samples were collected over 10-14 weeks at 7 stream sites in each of the Midwestern and Southeastern United States. Samples were analyzed for over 200 pesticides and degradates by direct aqueous injection liquid chromatography with tandem mass spectrometry. Nearly 2 and 3 times as many unique pesticides were detected in daily samples as in weekly composite and weekly discrete samples, respectively. Based on exceedances of acute-invertebrate benchmarks (AIB) and(or) a Pesticide Toxicity Index (PTI) >1, potential acute-invertebrate toxicity was predicted at 11 of 14 sites from the results for daily composite samples, but was predicted for only 3 sites from weekly composites and for no sites from weekly discrete samples. Insecticides were responsible for most of the potential invertebrate toxicity, occurred transiently, and frequently were missed by the weekly discrete and composite samples. The number of days with benthic-invertebrate PTI ≥0.1 in daily composite samples was inversely related to Ephemeroptera, Plecoptera, and Trichoptera (EPT) richness at the sites. The results of the study indicate that short-term, potentially toxic peaks in pesticides frequently are missed by weekly discrete sampling, and that such peaks may contribute to degradation of invertebrate community condition in small streams. Weekly composite samples underestimated maximum concentrations and potential acute-invertebrate toxicity, but to a lesser degree than weekly discrete samples, and provided a reasonable approximation of the 90th percentile total concentrations of herbicides, insecticides, and fungicides, suggesting that weekly composite sampling may be a compromise between assessment needs and cost.
溪流中农药的瞬时、急性毒性浓度可能会被固定间隔采样计划所忽略。在这里，我们将当前使用的农药在每日综合样本中的出现时间模式与每周综合样本和每周离散样本进行了比较，这些样本来自美国中西部和东南部的 14 个小流域地点的地表水。在 7 个溪流地点收集了 10-14 周的样本，每个地点都在美国中西部和东南部。通过直接水样注入液相色谱串联质谱法对超过 200 种农药及其降解产物进行了分析。每日样本中检测到的独特农药种类几乎是每周综合样本和每周离散样本的 2 倍和 3 倍。基于急性无脊椎动物基准（AIB）和（或）农药毒性指数（PTI）>1 的超标情况，从每日综合样本的结果预测了 14 个地点中的 11 个地点存在潜在的急性无脊椎动物毒性，但仅从每周综合样本预测了 3 个地点，而从每周离散样本没有预测到任何地点。杀虫剂是造成大多数潜在无脊椎动物毒性的原因，它们具有瞬时性，并且经常被每周离散和综合样本所忽略。每日综合样本中底栖无脊椎动物 PTI≥0.1 的天数与地点的蜉蝣目、石蝇目和毛翅目（EPT）丰富度呈反比。该研究结果表明，每周离散采样经常会错过农药的短期、潜在毒性峰值，而这些峰值可能导致小流域中无脊椎动物群落状况的恶化。每周综合样本低估了最大浓度和潜在的急性无脊椎动物毒性，但程度低于每周离散样本，并且合理地近似了除草剂、杀虫剂和杀菌剂的第 90 百分位总浓度，这表明每周综合采样可能是评估需求和成本之间的折衷。
