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Assessing Dietary Exposure to Pyrethroid Insecticides by LCIMS/MS of Food Composites
MACMILLAN, D. K., D. Zehri, A. E. SWANK, AND M. K. MORGAN. Assessing Dietary Exposure to Pyrethroid Insecticides by LCIMS/MS of Food Composites. Presented at American Society for Mass Spectrometry Conference on Mass Spectrometry and Allied Topics, Denver, CO, June 05 - 09, 2011.
Environmental chemical biomonitoring guides risk assessment by providing a link between chemical exposure and internal dose. Multiple sources can contribute to exposure. Biomonitoring does not provide their quantitative contributions. Pyrethroid insecticides have been found in food, dust, and on household surfaces, and also in human urine. The US Environmental Protection Agency initiated a study to reconstruct dietary and environmental pyrethroid exposure pathways and correlate results to biomonitoring. We will use LCIMS/MS to estimate the contribution of dietary exposure to pyrethroids in the normal diet of adult volunteers to observed body burden. This work describes optimization of analysis for seven pyrethroids, metabolites, and bisphenol A in control diets. Elsewhere, complementary measurements will be made for environmental and urine samples.
Method Commercially-obtained vegetables, chips, cereal, meat, and other solid food products were homogenized together to create composited control matrices at 1%, 5%, and 100/0 fat content. Lyophilized homogenates were spiked with 7 pyrethroids, 6 degradation products, bisphenol A, and internal standards, then subjected to multistep preparation protocols. Protocols included accelerated solvent extraction (ASE), partitioning, and solid phase extraction (SPE). Electrospray LC/MS/MS and selected reaction monitoring in positive and negative ion modes was performed on a Thermo TSQ Quantum Ultra AM triple quadrupole mass spectrometer. Isocratic elution (8% 5mM N~OH : 92% 5mM N~OH in methanol) from a Zorbax Eclipse XDB-C 18 column was used for positive ion analytes; a gradient was used for negative ion analytes. Preliminary Data Estimation of pyrethroid body burden from diet requires quantitation of the insecticides and their environmental degradation products in food. Quantitation methods for pyrethroids in food are available, but co-determination of degradation products has not been reported. Our method development approach focused on minimization of co-extracted interferences that caused ion suppression and optimization of analyte recoveries. The method starts with an ASE protocol performed on lyophilized food composites blended with a dispersant. Parent pyrethroids were extracted with hexane or acetonitrile; methanol extraction of the degradation products followed on a separate aliquot. Co-extracted contaminants were evaluated by gravimetry of residues obtained from small volumes of extract. Depending on the fat level of the control food, residues of -0.6 -0.8 g were obtained from the parent pyrethroid extraction; residues from methanol extracts were -0.5 g, independent of the fat level of the food. Three absorbents were evaluated for contaminant retention in the ASE cell: Hydromatrix, alumina, and florisil. A combination of alumina and florisil was most effective for contaminant retention in the pyrethroid extraction. Due to volume limitations, alumina alone was used in the cell; the extract was passed subsequently through florisil SPE. Approximately 50% of co-extracted interferences eluted in non-polar fractions from the florisil column; the analytes eluted in slightly polar fractions, providing improved clean-up. Use of a C18 SPE further reduced contamination and permitted LC/MS/MS detection. Fat and polar constituents (-30% of composite mass) were co-extracted with the degradation products. The absorbents did not significantly alter interference retention in the methanol fraction. Incorporation of a hexane wash reduced fat contamination; partitioning into ethyl acetate diminished more polar interferences. A final SPE step improved LC/MS/MS detection. These results suggest on-line SPE could be effective for sample cleanup, reduce preparation costs, and speed throughput. This abstract does not necessarily reflect EPA policy.