期刊
JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY
卷 68, 期 8, 页码 2297-2305出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.jafc.9b06187
关键词
groundwater mean residence time; groundwater lag time; POCIS; metolachlor ethanesulfonic acid (MESA); metolachlor
资金
- USDA-ARS intramural project in the National Program 211: Water Availability and Watershed Management
- USDA-ARS intramural project in the National Program 212: Soil and Air
- USDA-ARS intramural project in the National Program 216: Sustainable Agricultural Systems Research
- USDA-Natural Resources Conservation Service
We previously discovered a method to estimate the groundwater mean residence time using the changes in the enantiomeric ratio of metolachlor ethanesulfonic acid (MESA), (2-[(2-ethyl-6-methylphenyl)(2-methoxy-1-methylethyl)amino]-2-oxoethanesulfonic acid), a metabolite of the herbicide metolachlor. However, many grab samples would be needed for each watershed over an extended period, and this is not practical. Thus, we examined the use of a polar organic chemical integrative sampler (POCIS) deployed for 28 days combined with a modified liquid chromatography-mass spectrometry LC-MS/MS method to provide a time-weighted average of the MESA enantiomeric ratio. POCISs equipped with hydrophilic-lipophilic-balanced (HLB) discs were deployed at five sites across the United States where metolachlor was used before and after 1999 and compared the effectiveness of the POCIS to capture MESA versus grab samples. In addition, an in situ POCIS sampling rate (R-s) for MESA was calculated (0.15 L/day), the precision of MESA extraction from stored POCIS discs was determined, and the effectiveness of HLB to extract MESA was examined. Finally, using molecular modeling, the influence of the asymmetric carbon of metolachlor degradation on the MESA enantiomeric ratio was predicted to be negligible. Results of this work will be used in projects to discern the groundwater mean residence times, to evaluate the delivery of nitrate-N from groundwater to surface waters under various soil, agronomic, and land use conditions, and to examine the effectiveness of conservation practices.
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