Relationship between stream size, watershed land use, and pesticide concentrations in headwater streams.

A quantitative multiresidue study of current-use pesticides in multiple matrices was undertaken with field sampling at 32 headwater streams near Lac Saint-Pierre in Québec, Canada. A total of 232 samples were collected in five campaigns of stream waters and streambed sediments from streams varying in size and watershed land use. Novel multiresidue analytical methods from previous work were successfully applied for the extraction of pesticide residues from sediments via pressurized liquid extraction (PLE) and quantitative analysis using ultra high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) with online sample preparation on a hydrophilic-lipophilic balance (HLB) column. Of the 31 target compounds, including 29 pesticides and two degradation products of atrazine, 29 compounds were detected at least once. Consistent with other studies, atrazine and metolachlor were the most widely-detected herbicides. Detections were generally higher in water than sediment samples and the influence of land use on pesticide concentrations was only detectable in water samples. Small streams with a high proportion of agricultural land use in their watershed were generally found to have the highest pesticide concentrations. Corn and soybean monoculture crops, specifically, were found to cause the greatest impact on pesticide concentration in headwater streams and correlated strongly with many of the most frequently detected pesticides. This study highlights the importance of performing multiresidue pesticide monitoring programs in headwater streams in order to capture the impacts of agricultural intensification on freshwater ecosystems.

Fast and simplified quantitative multiresidue analytical method for pesticides in surface waters by UHPLC-MS/MS with online sample preparation.

A quantitative multiresidue analytical method for the simultaneous analysis of current-use agricultural pesticides in surface waters is reported. The method involves minimal sample manipulation and small sample collection volumes (for 1 mL and 5 mL injections) with online sample clean-up and analyte preconcentration on a hydrophilic-lipophilic balance (HLB) column. To our knowledge, this online approach with the use of an HLB column has not yet been reported for multiresidue pesticide analysis in surface waters. Chromatographic separations of isomeric pesticides were achieved through the sequential coupling of C8 and polar endcapped C18 analytical columns. High resolution accurate mass (HRAM) quadrupole Orbitrap spectrometry was performed in full scan mode followed by data-dependent MS/MS fragmentation (FS-ddMS2) with concurrent electrospray ionization in both positive and negative modes. The method was validated for thirty-one (31) diverse current-use pesticides and demonstrated strong linearity (R2 > 0.9912) and precision (% RSD <8.4%) with low quantitation limits (average LOQ of 41 ng L-1). The majority of target analytes experienced minimal matrix effects (<±20%) in fortified environmental water samples. When applied to surface water samples, the method detected fourteen of the target analytes, including twelve herbicides, one insecticide, and one fungicide. This method offers a fast, simple, and reliable approach for the quantitative analysis of diverse current-use pesticides in surface water samples within hours of sample collection in the field. The robust nature of the method may allow for potential application to other types of water and the targeted or untargeted screening of other emerging contaminants.