Binding and Orientation of Carbamate Pesticides on Silica Surfaces

Carbaryl (1-naphthyl-N-methyl carbamate) is one of the most abundantly used carbamate pesticides and a common ground and surface water contaminant. Despite this, there is a lack of understanding regarding the specific interactions between this pesticide and mineral particles with environmental impact, including soil and dust aerosol interfaces. Here, we examine the adsorption of carbaryl to hydrophilic silica surfaces by applying a combination of vibrational Sum Frequency Generation (vSFG) spectroscopy and atomistic simulations. We find that carbaryl molecules readily adsorb to silica/air interfaces by hydrogen-bonding interactions between the carbamate group (primarily the −NH terminus, secondarily the ester −C═O ester moiety) and the surface silanols and silenolates. On average, this results in the naphthyl aromatic ring being oriented roughly parallel to the surface. Our characterization of interactions of carbamate pesticides at silica surfaces is particularly valuable for understanding the transport, stabilization, and potential degradation mechanisms of carbamate pesticides by interfaces during downstream processes of environmental relevance.