Toxicity of functionalized fullerene and fullerene synthesis chemicals.

Fullerene is one of the most studied carbon-based nanoparticles due to its unique structure and potential for diverse applications. This study focuses on toxicological effects of two fullerene nanomaterials, contributing to ecological as well as human risk assessment strategies. The biological responses from two basic fullerene materials, aqueous-nanoC60 and alkaline-synthesized fullerenol, were examined using four model organisms. Bioassays were conducted on bacteria (Pseudomonas aeruginosa and Staphylococcus aureus) to determine population impacts and to assess mechanisms of cellular effects for both Gram-negative and Gram-positive species. LC50 of aqu-nC60 stirred for 28 days for P. aeruginosa was estimated to be 1336 mg/L; however, toxicity of the same aqu-nC60 preparation for S. aureus was insignificant. Freshwater green algae Raphidocelus subcapitata and invertebrate Ceriodaphnia dubia were exposed to 28-day stirred aqu-nC60 with no significant toxicological impact. Aqu-nC60 stirred for 14 days bore no toxicity within two orders of magnitude greater than the highest concentration administered. LC50 for organisms exposed to alkaline-synthesized fullerenol prepared in the laboratory was 2409 mg/L for P. aeruginosa with no determinable toxicity to S. aureus, and 1462 mg/L and 45.2 mg/L for R. subcapitata and C. dubia, respectively. Toxicity thresholds for commercially-prepared fullerenol were lower for all species, an impact attributed to the presence of impurities. Mechanistic analysis of membrane damage on bacteria by laboratory-prepared fullerenol indicated necrotic and apoptotic responses with and without photoactivation. Toxicological responses from fullerenol synthesis by-products were only determinable for C. dubia with effects attributable to impurities.

Field data and numerical modeling: A multiple lines of evidence approach for assessing vapor intrusion exposure risks.

USEPA recommends a multiple lines of evidence approach to make informed decisions at vapor intrusion sites because the vapor intrusion pathway is notoriously difficult to characterize. Our study uses this approach by incorporating groundwater, soil gas, indoor air field measurements and numerical models to evaluate vapor intrusion exposure risks in a Metro-Boston neighborhood known to exhibit lower than anticipated indoor air concentrations based on groundwater concentrations. We collected and evaluated five rounds of field sampling data over the period of one year. Field data results show a steep gradient in soil gas concentrations near the groundwater surface; however as the depth decreases, soil gas concentration gradients also decrease. Together, the field data and the numerical model results suggest that a subsurface feature is limiting vapor transport into indoor air spaces at the study site and that groundwater concentrations are not appropriate indicators of vapor intrusion exposure risks in this neighborhood. This research also reveals the importance of including relevant physical models when evaluating vapor intrusion exposure risks using the multiple lines of evidence approach. Overall, the findings provide insight about how the multiple lines of evidence approach can be used to inform decisions by using field data collected using regulatory-relevant sampling techniques, and a well-established 3-D vapor intrusion model.

Sewer Gas: An Indoor Air Source of PCE to Consider During Vapor Intrusion Investigations.

The United States Environmental Protection Agency (USEPA) is finalizing its vapor intrusion guidelines. One of the important issues related to vapor intrusion is background concentrations of volatile organic chemicals (VOCs) in indoor air, typically attributed to consumer products and building materials. Background concentrations can exist even in the absence of vapor intrusion and are an important consideration when conducting site assessments. In addition, the development of accurate conceptual models that depict pathways for vapor entry into buildings is important during vapor intrusion site assessments. Sewer gas, either as a contributor to background concentrations or as part of the site conceptual model, is not routinely evaluated during vapor intrusion site assessments. The research described herein identifies an instance where vapors emanating directly from a sanitary sewer pipe within a residence were determined to be a source of tetrachloroethylene (PCE) detected in indoor air. Concentrations of PCE in the bathroom range from 2.1 to 190 ug/m3 and exceed typical indoor air concentrations by orders of magnitude resulting in human health risk classified as an "Imminent Hazard" condition. The results suggest that infiltration of sewer gas resulted in PCE concentrations in indoor air that were nearly two-orders of magnitude higher as compared to when infiltration of sewer gas was not known to be occurring. This previously understudied pathway whereby sewers serve as sources of PCE (and potentially other VOC) vapors is highlighted. Implications for vapor intrusion investigations are also discussed.