Use of Nasal Pathology in the Derivation of Inhalation Toxicity Values for Hydrogen Sulfide.

Nasal pathology can play an important role in the risk assessment process. For example, olfactory neuron loss (ONL) is one of the most sensitive end points seen in subchronic rodent hydrogen sulfide (H2S) studies and has been used by several agencies to derive health-protective toxicity values. Alternative methods that rely on computational fluid dynamics (CFD) models to account for the influence of airflow on H2S-induced ONL have been proposed. The use of CFD models result in toxicity values that are less conservative than those obtained using more traditional methods. These alternative approaches rely on anatomy-based CFD models. Model predictions of H2S delivery (flux) to the olfactory mucosal wall are highly correlated with ONL in rodents. Three major areas of focus for this review include a brief description of nasal anatomy, H2S-induced ONL in rodents, derivation of a chronic inhalation reference concentration for H2S, and the use of CFD models to derive alternative toxicity values for this gas.