A Risk Assessment Comparison: Evaluation of Relevant Indoor Air Exposure Concentrations and Periods and Implications for Developing Indoor Air Sampling Plans

摘要

U.S. Environmental Protection Agency (USEPA) initially released risk assessment guidance in 1984 followed by the publication of the first Risk Assessment Guidance for Superfund document in 1989. Over time, USEPA has continued to refine and define the various aspects of risk assessment from data evaluation and exposure methods to toxicity and dose response methods, with each aspect being critical in ensuring that risk calculations provide reasonable, albeit conservative, estimates of potential risk to receptors. In reality, it is difficult to determine the true exposure and risk as there are many variables, both environmental and personal, that affect how individuals interact with their surroundings, and therefore, how much exposure may occur. Risk assessors are often faced with inadequate data and other uncertainties in both environmental concentrations and individual exposures. To address these uncertainties, risk assessments use conservative estimates of exposure concentrations, exposure parameters, and toxicity. In this paper, we examine how exposure concentrations (ECs) for indoor air exposures differ from other exposure pathways and how data for indoor air exposures can be used to develop more realistic estimates of risk. Using a large data set available from USEPA-sponsored testing of an Indianapolis duplex, we evaluate potential indoor inhalation risks based on daily and weekly indoor air concentration data. Taking advantage of the time series this data set offers, we evaluate how different statistics of concentration calculated through time would influence risk estimates in comparison to single measurements taken at different points in the time series. The potential variation and range in risk results are discussed, as well as how those risk results would change if only a subset of the data was available for analysis, simulating the amount of data typically available to practitioners for vapor intrusion (Ⅵ) sites. Although calculations and results focus on tetrachloroethylene (PCE) and chloroform, the relevance of the EC calculations and risk results to other chemicals including trichloroethylene (TCE) is also discussed, along with implications for risk-based decisions at Ⅵ sites.