A Quantitative Risk Assessment for Stachybotrys chartarumToxic Mold

The inhalation exposure to Stachybotrys chartarum (SC) has been playing a critical role in public health domain due to its ability to produce toxins (trichothecene and other mycotoxins), that are implicated in the cases of acute idiopathic pulmonary hemorrhages (AIPH) in infants. Despite multiple studies reporting an association of exposure to airborne mold with negative human health effects such as respiratory, immunological, and hematological diseases, there currently are no regulatory guidelines for quantifying the airborne exposure threat associated with SC spores/toxins in indoor environments. The primary goal for this study was to use risk assessment framework as a mechanism to quantify the potential risk of death associated with known concentrations of S. chartarum spores and toxins. Additionally, an attempt was made to provide a benchmark dose level above which an adverse effect may occur in human infants. To this end, best-fit dose-response models were generated by using published animal studies, followed by stochastic risk assessment to predict the likelihood of death in infants from AIPH. By using 10% as the benchmark response level, permissible exposure limits were obtained as 413 SC-spores/m3 or 2.66 x 10 -04 mg-toxin/m3. The predicted risk of death in infants for acute 24-hour exposure to toxins ranged from 1.0 x 10-11 to 3.0 x 10-06. Sensitivity analysis was conducted using Monte Carlo simulations to identify factors that are highly correlated with risk estimates. This study suggests that S. chartarum exposure via inhalation in residential conditions may pose a risk for AIPH resulting in mortality in human infants, but a conclusive epidemiological study is needed to validate risk estimates.