Development of an inhalation reference concentration for diethanolamine

An inhalation reference concentration (RfC) was developed for diethanolamine (DEA), based principally on evaluation of three animal studies (Gamer et al., 1993, 1996, 2008). The RfC (25 μg/m³) was based on statistically significantly increased relative liver weight in female rats in Gamer et al. (2008) as the critical effect. The lower confidence limit on the benchmark dose (BMDL₁₀ of 5.5 mg/m³) was adjusted to a human equivalent concentration and to continuous exposure before dividing the final point of departure (2.3 mg/m³) by a total factor of 90 that considered standard key areas of uncertainty (intrahuman variability, potential interspecies toxicodynamic differences, database limitations). While laryngeal effects observed in Gamer et al. (2008) were also considered as candidate critical effects, evaluation of the adversity and human relevance of rat laryngeal squamous metaplasia and concomitant effects at the various exposure levels resulted in identifying a LOAEL for laryngeal squamous hyperplasia and chronic inflammation that was much higher than the liver weight LOAEL identified. The RfC of 25 μg/m³ is considered health protective for the general population and can be used to evaluate the potential health effects of long-term environmental exposure of the general public (i.e., long-term, ambient air dispersion modelling or monitoring data).