Bases for secondary standards for residual radionuclides in soil and some recommendations for cost-effective operational implementation.

The future use of land contaminated with radionuclides depends upon scientifically defensible bases for setting limits for radionuclides in soil. The purpose of this work is to develop such bases for establishing "posting criteria" to protect nonradiological workers at the Nevada Test Site and to provide a rationale for cost-effective measurements to readily determine the boundary conditions. The analysis begins with a mandated limit on total effective dose equivalent (1 mSv y(-1)) via all pathways. The possible pathways of exposure are external gamma exposure, inhalation of resuspended material, and incidental soil ingestion. These pathways are evaluated for each radionuclide of interest on the Nevada Test Site, and the results are used to define for each radionuclide the deposition-density limits for each pathway of exposure. The minimum deposition-density limits are noted to occur via the external gamma-exposure pathway for most radionuclides; exceptions are incidental soil ingestion for 90Sr/90Y and inhalation for 238Pu, 239,240Pu, and 241Am. The limiting values of deposition density or average concentration in soil are then determined appropriately by combining all pathways. Procedures are developed for dealing with mixtures of many radionuclides and to apply the principles developed so that even a simple measurement of external gamma-exposure rate may be used to define the boundary conditions in the field, provided that the relative abundance of the radionuclide mixture is known and that the defining level of exposure rate is sufficiently above background.

Estimating human exposure through multiple pathways from air, water, and soil.

This paper describes a set of multipathway, multimedia models for estimating potential human exposure to environmental contaminants. The models link concentrations of an environmental contaminant in air, water, and soil to human exposure through inhalation, ingestion, and dermal-contact routes. The relationship between concentration of a contaminant in an environmental medium and human exposure is determined with pathway exposure factors (PEFs). A PEF is an algebraic expression that incorporates information on human physiology and lifestyle together with models of environmental partitioning and translates a concentration (i.e., mg/m3 in air, mg/liter in water, or mg/kg in soil) into a lifetime-equivalent chronic daily intake (CDI) in mg/kg-day. Human, animal, and environmental data used in calculating PEFs are presented and discussed. Generalized PEFs are derived for air----inhalation, air----ingestion, water----inhalation, water----ingestion, water----dermal uptake, soil----inhalation, soil----ingestion, and soil----dermal uptake pathways. To illustrate the application of the PEF expressions, we apply them to soil-based contamination of multiple environmental media by arsenic, tetrachloroethylene (PCE), and trinitrotoluene (TNT).

Uncertainties in the link between global climate change and predicted health risks from pollution: hexachlorobenzene (HCB) case study using a fugacity model.

Industrial societies have altered the earth's environment in ways that could have important, longterm ecological, economic, and health implications. In this paper, we examine the extent to which uncertainty about global climate change could impact the precision of predictions of secondary outcomes such as health impacts of pollution. Using a model that links global climate change with predictions of chemical exposure and human health risk in the Western region of the United States of America (U.S.), we define parameter variabilities and uncertainties and we characterize the resulting outcome variance. As a case study, we consider the public health consequences from releases of hexachlorobenzene (HCB), a ubiquitous multimedia pollutant. By constructing a matrix that links global environmental change both directly and indirectly to potential human-health effects attributable to HCB released into air, soil, and water, we define critical parameter variances in the health risk estimation process. We employ a combined uncertainty/sensitivity analysis to investigate how HCB releases are affected by increasing atmospheric temperature and the accompanying climate alterations that are anticipated. We examine how such uncertainty impacts both the expected magnitude and calculational precision of potential human exposures and health effects. This assessment reveals that uncertain temperature increases of up to 5 degrees C have little impact on either the magnitude or precision of the public-health consequences estimated under existing climate variations for HCB released into air and water in the Western region of the U.S.