Evaluation of the Webler-Brown model for estimating tetrachloroethylene exposure from vinyl-lined asbestos-cement pipesReport as inadecuate




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Environmental Health

, 7:24

First Online: 02 June 2008Received: 22 October 2007Accepted: 02 June 2008DOI: 10.1186-1476-069X-7-24

Cite this article as: Spence, L.A., Aschengrau, A., Gallagher, L.E. et al. Environ Health 2008 7: 24. doi:10.1186-1476-069X-7-24

Abstract

BackgroundFrom May 1968 through March 1980, vinyl-lined asbestos-cement VL-AC water distribution pipes were installed in New England to avoid taste and odor problems associated with asbestos-cement pipes. The vinyl resin was applied to the inner pipe surface in a solution of tetrachloroethylene perchloroethylene, PCE. Substantial amounts of PCE remained in the liner and subsequently leached into public drinking water supplies.

MethodsOnce aware of the leaching problem and prior to remediation April-November 1980, Massachusetts regulators collected drinking water samples from VL-AC pipes to determine the extent and severity of the PCE contamination. This study compares newly obtained historical records of PCE concentrations in water samples n = 88 with concentrations estimated using an exposure model employed in epidemiologic studies on the cancer risk associated with PCE-contaminated drinking water. The exposure model was developed by Webler and Brown to estimate the mass of PCE delivered to subjects- residences.

ResultsThe mean and median measured PCE concentrations in the water samples were 66 and 0.5 μg-L, respectively, and the range extended from non-detectable to 2432 μg-L. The model-generated concentration estimates and water sample concentrations were moderately correlated Spearman rank correlation coefficient = 0.48, p < 0.0001. Correlations were higher in samples taken at taps and spigots vs. hydrants ρ = 0.84 vs. 0.34, in areas with simple vs. complex geometry ρ = 0.51 vs. 0.38, and near pipes installed in 1973–1976 vs. other years ρ = 0.56 vs. 0.42 for 1968–1972 and 0.37 for 1977–1980. Overall, 24% of the variance in measured PCE concentrations was explained by the model-generated concentration estimates p < 0.0001. Almost half of the water samples had undetectable concentrations of PCE. Undetectable levels were more common in areas with the earliest installed VL-AC pipes, at the beginning and middle of VL-AC pipes, at hydrants, and in complex pipe configurations.

ConclusionPCE concentration estimates generated using the Webler-Brown model were moderately correlated with measured water concentrations. The present analysis suggests that the exposure assessment process used in prior epidemiological studies could be improved with more accurate characterization of water flow. This study illustrates one method of validating an exposure model in an epidemiological study when historical measurements are not available.

List of AbbreviationsDEPMassachusetts Department of Environmental Protection

EPAUnited States Environmental Protection Agency

LnNatural logarithm

NDNot detected

OROdds ratio

PCPoint concentration

PCEPerchloroethylene or tetrachloroethylene

Qs-1Magnitude of pipe water flow in pipe segments

RDDRelative Delivered Dose

SAGSuggested No Adverse Response Level

tTime of sampling

tsTime of pipe installation for pipe segments

VL-ACVinyl-lined asbestos-cement.

Electronic supplementary materialThe online version of this article doi:10.1186-1476-069X-7-24 contains supplementary material, which is available to authorized users.

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Author: Lisa A Spence - Ann Aschengrau - Lisa E Gallagher - Thomas F Webster - Timothy C Heeren - David M Ozonoff

Source: https://link.springer.com/







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