USDA-Agricultural Research Service, Cropping Systems and Water Quality Research Unit, 1406 Rollins St., Rm 265, Columbia, MO 65211, USA.
Department of Crop, Soil, and Environmental Sciences, University of Arkansas, 1366 W. Altheimer Dr., Fayetteville, AR 72701, USA.
Sci Total Environ. 2019 Dec 20;697:133931. doi: 10.1016/j.scitotenv.2019.133931. Epub 2019 Aug 18.
Streams in the Salt River Basin (SRB) of northeastern Missouri, USA, have been chronically contaminated by atrazine and metabolites, with peak annual transport occurring from spring to early summer. Since 2005, increased fall-applied simazine has introduced a second chloro-triazine herbicide that degrades to deisopropylatrazine (DIA), creating the need for a method to partition DIA between its two parent sources - i.e., DIA derived from atrazine (DIA) and that from simazine (DIA). Distinguishing DIA parent sources would extend current understanding of chloro-triazine transport, leading to more accurate risk assessments and improved watershed-scale load estimates. The objectives of this study were to evaluate proposed methods for DIA partitioning, and to apply the most effective method to estimate DIA and DIA concentrations and loads. Three DIA partition methods were developed and statistically evaluated: 1) edge-of-field (EOF) based on DIA and deethylatrazine (DEA) concentrations in runoff from atrazine treated fields; 2) DIA:DEA concentration ratios (DR) in runoff from atrazine treated fields; and 3) concentration ratios of simazine:atrazine (SAR) in streams. Stream samples were collected year-round at 7 SRB stream sites from 2005 to 2010 and daily, quarterly, and annual concentrations and loads of atrazine, DEA, DIA, and simazine computed. The SAR method was superior to EOF and DR in its ability to estimate concentrations and loads of DIA and DIA that were more accurate and highly correlated to observed transport of simazine, atrazine, and DIA. The SAR method results demonstrated the differences in DIA and DIA transport timing, with peak DIA transport occurring from mid-Nov to Apr and peak DIA transport from May to Jun. Dual season triazine applications within a watershed substantially increased the period of high chloro-triazine concentrations in streams from ~3 to ~8 months/yr, potentially increasing the risk of toxicity to aquatic ecosystems.
美国密苏里州东北部盐河流域（SRB）的溪流长期受到莠去津及其代谢物的污染，每年的峰值运输发生在春季到初夏。自 2005 年以来，秋季施用的西玛津增加了第二种氯三嗪除草剂，它会降解为去异丙基莠去津（DIA），因此需要一种方法将 DIA 分配到其两个母体来源之间——即来自莠去津（DIA）和西玛津（DIA）的 DIA。区分 DIA 的母体来源将扩展对氯三嗪运输的现有认识，从而导致更准确的风险评估和改进流域尺度的负荷估计。本研究的目的是评估 DIA 分配的拟议方法，并应用最有效的方法来估计 DIA 和 DIA 的浓度和负荷。开发并统计评估了三种 DIA 分配方法：1）基于莠去津处理场径流中 DIA 和去乙基莠去津（DEA）浓度的田间边缘（EOF）；2）莠去津处理场径流中 DIA：DEA 浓度比（DR）；3）溪流中西玛津：莠去津（SAR）浓度比。2005 年至 2010 年，在 SRB 的 7 个溪流站点全年采集溪流样本，并计算了莠去津、DEA、DIA 和西玛津的日、季和年浓度和负荷。SAR 方法在估计 DIA 和 DIA 的浓度和负荷方面优于 EOF 和 DR，其结果更准确且与西玛津、莠去津和 DIA 的实际运输高度相关。SAR 方法的结果表明了 DIA 和 DIA 运输时间的差异，DIA 的峰值运输发生在 11 月中旬至 4 月，而 DIA 的峰值运输发生在 5 月至 6 月。流域内双季三嗪的施用大大增加了溪流中高氯三嗪浓度的时间，从大约 3 个月/年增加到大约 8 个月/年，这可能增加了对水生生态系统毒性的风险。
