Use of EpiAirwayTM and MucilAirTM in vitro models to Assign Acute Inhalation Categories to Ten Agrochemical Formulations

• First use of EpiAirway™ and MucilAir™ to determine inhalation toxicity of agrochemical formulations • EpiAirway™ and MucilAir™ consistently identified the agrochemical formulations containing a known respiratory irritant, with portal of entry effects, as toxic by inhalation • Evaluating EpiAirway™ and MucilAir™ results in conjunction with prior knowledge i.e. eye irritation and acute oral (systemic) toxicity of agrochemicals, supported assigning an appropriate category to all but one formulation Understanding acute inhalation toxicity potential from formulated agrochemical products is important to protect consumers and workers. Functional models of human airway epithelium are potentially good candidates to replace in vivo inhalation test methods. Five suspension and five emulsifiable concentrate agrochemical products were tested in two different models of human upper airway epithelium, MucilAir™ and EpiAirway™. Cell viability, barrier integrity, cytotoxicity and morphology after 24 h were evaluated following apical application at the air liquid interface (ALI), at six different concentrations (ranging from 0.03125 to 19.16 mg/cm 2 tissue surface area). The in vitro models consistently identified the formulation containing a known respiratory irritant that has portal of entry effects, as toxic by inhalation. Seven of nine formulations that did not contain a respiratory irritant had GHS categories of 4 or 5 for in vivo inhalation. Six and five were low toxicity by barrier integrity, and five and six with the (4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide assay (MTT) or resazurin reduction with EpiAirway™ and MucilAir™ respectively. Two formulations with no respiratory irritants, with GHS categories of 2 or 3, and an oral LD 50 less than 500 mg/kg were underpredicted as low toxicity with barrier integrity and MTT/resazurin reduction with both models. One of those formulations had a high toxicity score with histopathology with EpiAirway™. Both models were associated with better discrimination between toxicity categories with lower applied amounts of formulation. Evaluating the results in conjunction with prior knowledge, for example eye irritation and acute oral (systemic) toxicity, supported assigning an appropriate category to all but one formulation and could be used in a weight of evidence approach to support acute inhalation toxicity potential without in vivo testing.