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Assessing Dietary Exposure to Pyrethroid Insecticides by LC/MS/MS of Food Composites
Citation:
MacMillian, D., R. ZEHR, A. E. SWANK, AND M. K. MORGAN. Assessing Dietary Exposure to Pyrethroid Insecticides by LC/MS/MS of Food Composites. Presented at American Society for Mass Spectrometry Conference, Salt Lake City, UT, May 23 - 27, 2010.
Impact/Purpose:
A PILOT STUDY TO ESTIMATE HUMAN EXPOSURES TO PYRETHROIDS USING AN EXPOSURE RECONSTRUCTION APPROACH (Ex-R Study)
Description:
Introduction Pyrethroid insecticides are widely used to control household pests such as cockroaches, for public works control of mosquitoes, and on crops and livestock. Though more toxic to insects than to mammals, some pyrethroids are highly toxic to fish, bees, and cats. Permethrin, a widely used pyrethroid, and esfenvalerate are potential carcinogens. Pyrethroids have been found in low levels in food, dust, and on residential surfaces, suggesting ingestion may be a primary exposure route. Dietary exposure can be assessed by determination of pyrethroids in food by LC/MS/MS. This work describes optimization of an analytical method for 6 pyrethroids and their degradation products by using homogenized control diets prior to analysis of meal composites provided by participants of an exposure reconstruction study. Method Commercially-obtained vegetables, chips, cereal, meat, and other solid food products were homogenized together to create composited control matrices at 1%, 5%, and 10% fat content. Homogenates were spiked with 6 pyrethroids, 5 degradation products, and internal standards. Samples were lyophilized and underwent a multistep preparation protocol which included accelerated solvent extraction (ASE), partitioning, solvent exchange, and solid phase extraction (SPE). LC/MS/MS using electrospray 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 (pH 6.8) : 92% 5mM N~OH in methanol) from a Zorbax Eclipse XDB-CI8 column was used for positive ion analytes; a gradient was used for negative ion analytes. Preliminary Data Determination of pyrethroid body burden due to diet requires quantitation of pyrethroids and their degradation products in food. Methods for quantitation of pyrethroids in food are available, but concomitant determination of the degradation products has not been reported. Our initial approach began with an ASE protocol performed on lyophilized food composites blended with a dispersant. Parent pyrethroids were eluted with acetone:hexane (75:25). The polar degradation products were removed with methanol. The methanol extracts were acidified and partitioned into ethyl acetate, then combined with the acetone:hexane extracts. The combined extracts were partitioned into acetonitrile and passed over C18 SPE cartridges to remove any remaining interferences. High levels of fat co-extracted in the acetone:hexane fraction were not eliminated by the clean-up steps, however, and led to ion suppression during the analysis. By adding alumina to the ASE cell (10:1 alumina:lyophilized food) and extracting with hexane alone, fat content was reduced by more than 90% to sufficiently low levels for the subsequent clean-up to remove residual interferences and preserve analyte signal during LC/MS/MS. Fat and polar food constituents such as polysaccharides, representing approximately 35% by mass of the lyophilized food composite, were co-extracted with the degradation products. Post-extraction addition of the analytes to the methanol extract, followed by acidification and partitioning, gave <5% recovery for three parent compounds and recoveries ranging from -50-200% for the others. Signal for the polar analytes was enhanced ~ 2-to 8-fold by matrix interferences. The preliminary results suggested that improved method performance could be achieved by analyzing the two extracts separately, improving the clean-up of the polar fraction with increased solvent volume during partitioning, and use of the divert valve before and after analyte elution during LCIMSIMS. Method validation results will be presented. This abstract does not necessarily reflect EPA policy. Novel aspect Simultaneous determination of pyrethroids and degradation products Complex food matrices LCIMSIMS Sample preparation