Summary:

1. Human Activities • Water Uses QL Cin QG CGin z VG CG QG CG • Location • Within the home • Away from home Pollutant Emissions • Exposure Factors • Breathing Rate QL Cout QG Cin Remediation VG CG QG CG • Fate and Transport • Indoor air quality • model QL Cin VL CL QL CL • Ambient Concentrations • Croom Human Health Effects Exposure Calculation QG Qg Co Cg VG CG VL CL Estimated Exposure and Risk to a Community Resulting from Use of A TCE Contaminated Water Supply N J Giardino Brooks AFB, Texas, USA, and C R Wilkes Wilkes Technologies, Bethesda, Maryland, USA A community's groundwater supply was contaminated with trichloroethylene (TCE) at a concentration of 25 ppb. This case study addresses the community's concerns about excess lifetime cancer risk due to exposure to TCE resulting from normal household water uses. Through modeling, the population based exposure and excess cancer risk is estimated for the inhalation, dermal, and ingestion exposure routes. The Total Exposure Model (TEM), used in this study, stochastically represents input parameters, such as activity patterns, building characteristics, and water-use behavior. TEM samples activity patterns from a representative database, and uses information from other sources to simulate water-use behavior within the sampled activity pattern. TEM then deterministically models the emission, fate, and transport of the contaminant, resulting in air and water concentrations. Combining these concentrations with occupant location results in an estimate of the resultant exposures. These exposures are subsequently provided as input for pharmacokinetic calculations, predicting the absorbed dose by each exposure route. Numerous simulations are executed to estimate the distribution of exposures, absorbed dose, and excess cancer risk for the studied population group. This study examines the exposures and risks posed to the community by each of 3 scenarios: (1) using the contaminated water supply, (2) using a bathroom fan to reduce air concentrations, and (3) treating the water at a typical municipal treatment facility. The third option assumes the Maximum Contaminant Level (MCL) for trihalomethanes (MCL = 100 ppb) in the form of chloroform and bromoform at 50 ppb each. Summary: Use of household appliances results in emissions of VOCs into indoor air from contaminated drinking water Problem: Methods: Finite difference modeling used to predict air and water concentrations as a result of water use Uptake models used to calculate internal dose from exposure to contaminants Approach Emission Models Idealized Building • Inhalation • Lung model assumes equilibrium between lung air and lung blood • Plug Flow Models • Showers, Faucets • Dermal • Membrane Model (Bunge and McDougal, 1998) -- Combination steady-state and non-steady-state diffusion • CMFM • (Completely Mixed Flow Models) • (Bathtubs, Clothes Washers, • Toilets) • Ingestion • Assumes 100% uptake • Other • Equilibrium Model • (Dishwashers) Exposure/Dose Results Results: Results Cumulative Risk from exposure to contaminants Population Based Results Individual Results (Note the difference in x-axis scaling between Figures 1,2, and 3) 1,100 Iterations Contaminated Groundwater Supply Trichloroethylene (25 µg/L) Municipal Water Supply, DBPs (50 µg/L Chloroform; 50 µg/L Bromoform) Chloroform Combined with activity/location patterns, uptake models, etc. to calculate exposure and dose Chloroform Bromoform Without Fan during shower With Fan during shower • • • Percentile of the Population Discussion: We have demonstrated the comparatively higher risk due to the DBP chloroform as compared to the TCE contaminated drinking water, as well as the dramatic reduction in risk when a bathroom fan was run during the showering period. The cost to remove these chemicals from a contaminated groundwater supply, for this hypothetical population of 1,100 residences (2,200 individuals), is approximately $318,000,000 over a 20-year period (5). The cost for this 20-year project was adjusted to 1999 dollars assuming 3% inflation per year using Equation 1. Present Cost = Past Cost(1 + i)n (1) where Present Cost is the cost in 1999 dollars, Past Cost is the cost in 1985 dollars ($210,000,000), i is the inflation rate taken as 3% per year, and n is the number of years (in this case 14). Point-of-use remediation of the contaminated groundwater by use of a bathroom fan may be a feasible alternative to a large-scale remediation project or switching to a municipal water supply. This conclusion is based both on a comparative risk analysis, as well as a cost benefit tradeoff.