The United States Environmental Protection Agency Endocrine Disruptor Screening Program (EDSP) has endorsed certain high-throughput (HT) in vitro assays and computational approaches for regulatory use.  Determining the suitability of chemicals for HT testing based on physicochemical (PC) properties such as a Henry’s Law Constant (HLC) is necessary to have confidence in the results, for prioritization, and for incorporation of the data into computational models.

This investigation was conducted to determine if EPA could have confidence in negative HT results for certain substances with high HLCs, and if an in silico mass balance model, described by Armitage (2014), could be used to determine chemicals suitable for HT testing based on HLC.  Ten chemicals, with varying HLC values and published ToxCast ER bioactivity results, were selected from the EDSP Universe of Chemicals.  Each chemical was incubated in a modified ACEA-ER-80h HT assay in a 96-well plate format.  Chemical concentration in the incubation mixture was measured at selected time points via gas- or liquid- chromatography coupled with mass spectrometry and compared to chemical-specific model-predicted steady-state concentrations derived using an in silico mass balance model with PC- and assay-specific parameters as input values.  Experimental results demonstrated loss of the test articles from the wells for all high HLC substances.  Overall, this investigation demonstrated a properly parameterized in silico mass balance model can be used to establish PC parameter value cutoffs for determining chemicals suitable for testing in HT assays and eliminating false negative bioactivity findings.  This abstract does not necessarily reflect U.S. EPA policy.