Human Health Risk Assessment of Mineral Dust Exposure, Nellis Dunes Recreation Area, NV, USA.

An increased risk of asthma, cardiovascular and respiratory morbidity, lung cancer, and increased mortality is associated with exposure to particulate matter. In southern NV, the Nellis Dunes Recreation Area (NDRA) has been used for over 40 years for off-highway vehicle (OHV) recreation with an estimated 300,000+ drivers per year. The area is composed of 4 major groups of surfaces: dunes and sandy surfaces, rock-covered surfaces (e.g. desert pavements), silty surfaces including badlands, and dry drainages. Naturally occurring arsenic concentrations in soils vary between 3 and 346 ppm. Arsenic concentrations are controlled by geological processes with the highest concentrations of arsenic primarily associated with faults and in highly permeable units. Dust emissions from OHV recreation and from natural wind erosion were measured. Airborne arsenic concentrations are greatest in the dune areas during windy days, or on specific highly emissive surfaces when driving OHVs. Simulated lung and gastric fluids measured arsenic and other element solubility. In vivo experiments using B6C3F1 mice were performed to determine dose-responsive subacute exposure to oropharyngeal aspiration of PM4 dust from 7 surface types. Mice were exposed once a week for 28 days. These experiments examined the immunotoxicity, neurotoxicity, general toxicity, and lung pathology of the mice. Additionally, a human exposure study was performed to characterize blood chemistry before and after a defined OHV ride. Pharmacokinetic experiments in the rodent model were used to bridge internal dose exposures between toxicology studies and human exposure data. These data are used to produce a probabilistic model to identify human health risk to cancer and non-cancer endpoints.