Submitted to: American Chemical Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 6/23/2012
Publication Date: 8/10/2012
Citation: Rice, C., Bialek Kalinski, K.M., Mccarty, G.W. 2012. Chiral separation of metolachlor ethane sulfonic acid as a groundwater dating tool. American Chemical Society Abstracts. 2:891.
Technical Abstract: We have studied the hydrologic fate of metolachlor and its two predominant metabolites, metolachlor ethane sulfonic acid (MESA) and metolachlor oxanilic acid, in groundwater and base flows of streams for several years. These two metabolites are excellent markers for groundwater processes related to agriculture, and they appear to have extended retention in aquifers. Chiral separations were carried out on selected archived samples from these sites extending from 2000 to 2005. Enantiomeric excess values for the S and R racemic forms show a clear signal for increasing levels of the S-enriched form of MESA over this time interval. This shift in chiral abundance agrees with the change in usage patterns for metolachlor, where the S-enriched form was introduced in 1997 replacing the less effective racemic product used prior to that date. Hydrologic dating with this very specific agricultural marker appears to be a promising application for this information.