Exposure pathway evaluation system

The Remedial Action Priority System (RAPS) and Multimedia Environmental Pollutant Assessment System (MEPAS) are different names for an objective exposure pathway evaluation system developed by Pacific Northwest Laboratory to rank chemical and radioactive releases according to their potential human health impacts. Constituent migration and impact are simulated using air, groundwater, overland, surface water, and exposure components based on standard assessment principles and techniques. A shell allows interactive description of the environmental problem to be evaluated, defines required data in the form of problem-specific worksheets, and allows data input. The assessment methodology uses an extensive constituent database as a consistent source of chemical, physical, and health-related parameters. 

System considers surface water and groundwater pathways of exposure in evaluating the potential for adverse effects. Air and soil pathways will be added as will numerous built-in error checking routines. 

A set of conditions or assumptions about sources, exposure pathways, amount, or concentrations of agent(s) involved, and exposed organism, system, or (sub)population (i.e., numbers, characteristics, habits) used to aid in the evaluation and quantification of exposure(s) in a given situation. 

KENNEDY, W.E., JR., PARKHURST, M.A., AABERG, R.L., RHOADS, K.C., HILL, R.L. and MARTIN, J.B. (1992). Evaluation of Exposure Pathways to Man from Disposal of Radioactive Materials into Sanitary Sewer Systems, U.S. Nuclear Regulatory Commission Report NUREG/CR-5814 (National Technical Information Service, Springfield, Virginia). 

Essentially, all organ systems must be evaluated. Thus laboratory tests, should include complete blood count, liver and renal functional tests, and blood, nail and urine arsenic levels. Other biomarkers of arsenic exposure include nonerythrocyte porphyrin enzyme activities and urine transforming growth factor TNF-a, accompanied by induction of heme oxygenase, mitogen-activated protein kinases, the ubiquitin-dependent proteolytic pathway, and protein kinase C in various tissues. These tests are still being investigated in laboratories and their clinical usefulness remains to be proven (Chapell et al, 2001). 

Calculation of Exposure. A great advantage of Risk Assistant is that it allows users to consider a wide range of factors that will influence quantitative exposure estimates (e.g., specific exposure factors for different populations, pathways, and scenarios) with a minimum of effort. Thus, a user can rapidly produce alternative exposure evaluations, including best estimates, reasonable worst-case exposure estimates, and worst case exposure estimates. Moreover, the system provides the user with information on the degree of uncertainty contributed by various assumptions used in the analysis, which can guide the user s future data collection efforts so that they result in maximum reduction of uncertainty. 

---