Using artificial burrows to evaluate inhalation risks to burrowing mammals

Since the onset of plutonium production at the U.S. Department of Energy's Hanford Site, several hundred cubic meters of carbon tetrachloride (CCl4) has been discharged to the soil column, resulting in a dispersed CCI4 vapor plume in the subsurface. Inhalation of volatile organic chemicals could be an important exposure pathway for burrowing animals there. Historical levels of CCl4 in soil pore gas exceeded the inhalation ecological screening level for CCl4. Thus, the inhalation exposure pathway was evaluated with the use of artificial burrows deployed at locations that had elevated levels of CCl4 in soil gas. Artificial burrows were designed on the basis of information available for Hanford Site fossorial wildlife. After installation, the artificial burrow atmosphere was sampled and analyzed for CCl4 and its degradation products: chloroform, methylene chloride, and chloromethane. Sampling was repeated on 3 occasions to capture varying atmospheric conditions affecting exposure concentrations. CCl4 was detected in the artificial burrows, and maximum exposures were observed during relatively low barometric conditions. The highest CCl4 detections were still well below the inhalation-based ecological screening level and CCl4 degradation products were never detected. This study shows that artificial burrows are an efficient method for obtaining relevant exposure data and illustrates the utility of directly measuring the medium for exposure under ecologically realistic conditions.