Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: April 25, 2001
Publication Date: N/A
Technical Abstract: A pesticide can form a sequence of different localized interactions of varying strengths in different environments, while changing its orientation on the surface of the sorbent. The degree to which the different interactions contribute to the retention of an organic pollutant is a function of both the pesticide and the sorbent. By knowing the specific interactions and orientation of a sorbed pesticide at a molecular level, w will have a better understanding of its availability and susceptibility to degradation. The changes in 13C and 1H-NMR T1 relaxation times were measured at various molecular sites of metolachlor and the probe compound acetanilide to identify their specific interaction sites in organic matter (OM) surrogates. The T1 relaxation times were determined as a function of the dissolved and colloidal OM concentration. The specific interaction sites of metolachlor varied as a function of the properties of the OM. The echanges in T1 relaxation parameters together with NMR chemical shifts at specific molecular sites and molecular mechanics were used to predict the orientation of the pesticide on the organic matter surface. Thermodynamic parameters suggest that metolachlor formed weak hydrophobic interactions with some OM while more specific and relatively stronger interactions are formed with others.