| Autor: |
Plummer RE; Beltsville Agricultural Research Center (BARC) , US Department of Agriculture (USDA), Agricultural Research Service (ARS) , 10300 Baltimore Avenue , Beltsville , Maryland 20705 , United States., Hapeman CJ; Beltsville Agricultural Research Center (BARC) , US Department of Agriculture (USDA), Agricultural Research Service (ARS) , 10300 Baltimore Avenue , Beltsville , Maryland 20705 , United States., Rice CP; Beltsville Agricultural Research Center (BARC) , US Department of Agriculture (USDA), Agricultural Research Service (ARS) , 10300 Baltimore Avenue , Beltsville , Maryland 20705 , United States., McCarty GW; Beltsville Agricultural Research Center (BARC) , US Department of Agriculture (USDA), Agricultural Research Service (ARS) , 10300 Baltimore Avenue , Beltsville , Maryland 20705 , United States., Schmidt WF; Beltsville Agricultural Research Center (BARC) , US Department of Agriculture (USDA), Agricultural Research Service (ARS) , 10300 Baltimore Avenue , Beltsville , Maryland 20705 , United States., Downey PM; Beltsville Agricultural Research Center (BARC) , US Department of Agriculture (USDA), Agricultural Research Service (ARS) , 10300 Baltimore Avenue , Beltsville , Maryland 20705 , United States., Moorman TB; National Laboratory for Agriculture and the Environment , US Department of Agriculture (USDA), Agricultural Research Service (ARS) , 1015 N. University Blvd. , Ames , Iowa 50011 , United States., Douglas EA; National Laboratory for Agriculture and the Environment , US Department of Agriculture (USDA), Agricultural Research Service (ARS) , 1015 N. University Blvd. , Ames , Iowa 50011 , United States., Strickland TC; Southeast Watershed Research Laboratory , US Department of Agriculture (USDA), Agricultural Research Service (ARS) , 2316 Rainwater Road , Tifton , Georgia 31793 , United States., Pisani O; Southeast Watershed Research Laboratory , US Department of Agriculture (USDA), Agricultural Research Service (ARS) , 2316 Rainwater Road , Tifton , Georgia 31793 , United States., Bosch DD; Southeast Watershed Research Laboratory , US Department of Agriculture (USDA), Agricultural Research Service (ARS) , 2316 Rainwater Road , Tifton , Georgia 31793 , United States., Elkin KR; Pasture Systems & Watershed Management Research , US Department of Agriculture (USDA), Agricultural Research Service (ARS) , Curtin Road, Building 3702 , University Park , Pennsylvania 16802 , United States., Buda AR; Pasture Systems & Watershed Management Research , US Department of Agriculture (USDA), Agricultural Research Service (ARS) , Curtin Road, Building 3702 , University Park , Pennsylvania 16802 , United States. |
| Abstrakt: |
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. |
