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

<p>Abstract</p> <p>Background</p> <p>From 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.</p> <p>Methods</p> <p>Once 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.</p> <p>Results</p> <p>The 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.</p> <p>Conclusion</p> <p>PCE 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.</p

Assessment of metal levels and pollution indices of the Songor Wetland, Ghana

Sediment, soil and fish samples collected from the Songor Wetland were assessed for the spatial distributions of metal (Al, Fe, Zn, Cr, Ni, Cu, Pb, As, Cd and Hg) levels and contamination loads, using pollution indices and multivariate analysis. The samples were processed through microwave digestions (Soil and Sediment: [HNO3, HCl, HF, H2O2]; Fish: [HNO3, H2O2]), followed by the analysis of extracts using ICP-MS. The results displayed patchiness of metal levels in the sediment and soil samples, and in some cases, defying the established trend that levels of metals in sediments are generally higher than in soils. The differences in the results were ascribed to geological dominance and anthropogenic impacts. The finfish species displayed relatively higher bioaccumulation patterns of the metal levels than crustaceans. Aluminium (Al) and Zn levels were moderately enriched in sediment and soil samples. Overall enrichment factors ([EF {Al} and EF {Fe}]) suggested low to minimal enrichment except in a few cases. Pollution Load Index (PLI) based on Contamination Factor (CF) suggested that metal loads were less than baseline levels. On the other hand, Pearson Correlation Coefficient demonstrated that the metals present in the wetland were more lithogenic with remarkable inputs of biogenic and anthropogenic components. Principal Component Analysis revealed an association of Zn to the western section of the wetland, Cd, and Hg to the eastern part while the remaining metals were concentrated at the mid-section of the wetland. Lead (Pb) levels (1.10 ± 0.70 mg/kg) in finfishes exceeded the EU Regulation 1881/2006/EU (0.05 mg/kg) for fish tissues and could pose public health concerns