Quantitative assessments of long-term, national-scale responses of groundwater quality to pesticide applications are essential to evaluate the effectiveness of pesticide regulations. Retardation time in the unsaturated zone (R_u) was estimated for selected herbicides (atrazine, simazine, and bentazon) and degradation products (desethylatrazine (DEA), desisopropylatrazine (DIA), desethyldesisopropylatrazine (DEIA), and BAM) using a multidecadal time series of groundwater solute chemistry (∼30 years) and herbicide sales (∼60 years). The sampling year was converted to recharge year using groundwater age. Then, R_u was estimated using a cross-correlation analysis of the sales and the frequencies of detection and exceedance of the drinking water standard (0.1 μg/L) of each selected compound. The results showed no retardation of the highly polar, thus mobile, parent compounds (i.e., bentazon), while R_u of the moderately polar compounds (i.e., simazine) was about a decade, and their degradation products showed even longer R_u. The temporal trends of the degradation products did not mirror those of the sale data, which were attributed to the various sale periods of the parent compounds, sorption of the parent compounds, and complex degradation pathways. The longer R_u in clayey/organic sediments than in sandy sediments further confirmed the role of soil-specific retardation as an important factor to consider in groundwater protection.

中文翻译：

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全国地下水对农药监管的长期响应评估

对地下水质量对农药应用的长期、全国性响应的定量评估对于评估农药法规的有效性至关重要。使用多年代际时间序列估计选定除草剂（阿特拉津、西玛津和苯达松）和降解产物（去乙基莠去津 (DEA)、去异丙基莠去津 (DIA)、去乙基去异丙基莠去津 (DEIA) 和 BAM）的延迟时间 ( R _u )地下水溶质化学（~30 年）和除草剂销售（~60 年）。使用地下水年龄将采样年份转换为补给年份。那么_，鲁使用对每种选定化合物的销售额以及检测和超过饮用水标准 (0.1 μg/L) 的频率进行互相关分析来估计。结果表明，高极性、因此可移动的母体化合物（即苯达松）没有延迟，而中等极性化合物（即西马津）的R _u约为十年，它们的降解产物显示出更长的R _u。降解产物的时间趋势并未反映销售数据的趋势，这归因于母体化合物的不同销售期、母体化合物的吸附以及复杂的降解途径。R越_长与沙质沉积物相比，粘土/有机沉积物进一步证实了土壤特异性阻滞作为地下水保护中需要考虑的重要因素的作用。