Establishing a point of departure for risk assessment using acute inhalation toxicology data

A simple method is presented for estimating a non-lethal level for inhalation toxicity studies. By reviewing 209 LC(50) studies representing 96 chemicals that also reported a non-lethal level, it has been shown that taking 1/3 of the LC(50) is a conservative estimate for a non-lethal exposure level. This approach was also compared to studies with LC(01) and BMCL(05) calculations. In the 38 studies that reported either of these values, again taking 1/3 of the LC(50) provided a more conservation estimate for the non-lethal threshold. The studies included time intervals from 5min out to 8h and utilized multiple species such as the rat, mouse, hamster, guinea pig and dog. In all but 13 cases, taking 1/3 of the LC(50) provided a more conservative estimate for a non-lethal exposure level compared to the experimentally observed value. In all but one of the 13 cases, the higher values were consequences of the selection of the exposure levels.