Lasee Method

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In May 2023, the United States Environmental Protection Agency (EPA) announced the results of its analysis of ten different pesticide products sampled for the presence of per- and polyfluoroalkyl substances (PFAS). EPA’s sampling efforts were prompted by a highly publicized September 2022 third-party study that reported the presence of PFAS (in particular, perfluorooctanesulfonate (PFOS)) in six out of ten pesticide products sampled. The September 2022 study caused alarm as to the potential for unknown PFAS content or cross-contamination of certain pesticide products. However, EPA’s more recent sampling of ten pesticide products, using a new and purportedly more accurate sampling method, casts doubt on the prior sampling results since EPA did not detect PFAS in any of the ten pesticide products it sampled. EPA emphasized in its May 2023 announcement that it is confident in the results of its newer sampling method, which is specifically targeted to analyze for PFAS in pesticide products formulated with surfactants and non-volatile oils.

EPA obtained samples of the ten pesticide products from the third-party study author and from purchases of the same products on the open market. EPA evaluated the ten pesticide products using both EPA’s new method (the ACB Method) and the method used in the third-party’s earlier study (the Lasee Method). EPA did not detect any of the 29 additional PFAS for which EPA screened the pesticide products for (including PFOS), above the lab instrument’s detection limit of 0.2 parts per billion (ppb). Notably, EPA’s detection limit is 2,500 times more sensitive than the limit in the earlier third-party study. EPA requested additional information and raw data from the study author but did not receive anything other than the published results.

EPA has released a newly developed and validated analytical methodology for testing pesticide products for the presence of per- and polyfluoroalkyl substances (PFAS). Referred to as the ACB Method, this new PFAS-detection method was developed by EPA’s Analytical Chemistry Branch (ACB). The ACB Method primarily differs from an alternative PFAS-detection method (the Lasee Method) in its approach to sample preparation. As background, the Lasee Method was introduced by Steven Lasee in November 2022 in his co-authored study titled “Targeted Analysis and Total Oxidizable Precursor assay of several insecticides for PFAS” in the Journal of Hazardous Materials.

The Lasee Method prepares a sample through dilution in a solvent/water solution to dilute the matrix using a single instrument for analysis. The ACB Method requires a more intense extraction to isolate PFAS compounds from the sample matrix before instrumental analysis, thereby reducing matrix interference and increasing the accuracy of PFAS detection. In short, EPA’s ACB Method is designed to eliminate interference from non-volatile oils and surfactants present in pesticide formulations that can result in false positive detections of PFAS. EPA’s verification analysis contains additional scientific details on the difference between the two methods and the significance of using EPA’s ACB Method when testing specific formulations.