In vitro Evaluation of Environmental Polycyclic Aromatic Hydrocarbon Compound (PAC) Mixtures#
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Recently, multiple states have explored treatment and monitoring procedures for water reuse. Advisory panels from states such as California and Texas have recommended using effects-based bioassays to screen for emerging contaminants. Due to the presence of polycyclic aromatic hydrocarbon compound (PAC) mixtures in environmental matrices, and the activation of the Aryl hydrocarbon Receptor (AhR) by PACs, effects-based bioassays for quantifying AhR activation has been identified as a useful tool to screen for emerging contaminants and mixtures with potential biological activity. We aim to understand potential discrepancies between PAC carcinogen reports and in vitro responses from PAC mixtures with different chemical concentration ratios, as well as compare relative potency and efficacy in vitro and in vivo. We used a commercially available effects-based tool; INDIGO Biosciences™ human AhR reporter assay, to determine relative potency (EC50 values) and efficacy (percent maximal response of positive control) of 13 individual PACs (Benzo[a]pyrene, Benzo[k]fluoranthene, Dibenz[a,h]anthracene, Chrysene, Benz[j]aceanthrylene, Benzo[b]fluoranthene, Indeno[1,2,3-cd]pyrene, Phenanthrene, Pyrene, Dibenzo[a,l]pyrene, and Dibenzothiophene), 2 equipotent PAC mixtures and 1 equimolar PAC mixture. Cells were plated in a 96 well plate and measured for luminescence and cytotoxicity. Individual PAC EC50 values ranged from 4.44x10-12M to 1.65x10-8M with Acenaphthenequinone having the highest relative potency. Phenanthrene, Pyrene, Dibenzo[a,l]pyrene, and Dibenzothiophene did not activate the AhR in vitro. Benzo[b]fluoranthene had the highest efficacy (111.6% response). The two equipotent mixtures’ 95% confidence intervals overlapped (EC50 = 1.97x10-6M – 3.90x 10-6M) which demonstrates all PACs contributed equally to the mixture response. Differences between potency and efficacy values of the individual compounds from in vitro and in vivo experimental responses gives a future aim to address discrepancy (compound degradation, metabolite production, or adherence to in vitro wells). The views expressed in this abstract are those of the author(s) and do not necessarily represent the view or policies of the U.S. Environmental Protection Agency.