Fingerprinting Arsenic Contamination in the Sediments of the Hylebos Waterway, Commencement Bay Superfund Site, Tacoma, Washington

Abstract

Two of the potential sources of arsenic in Hylebos waterway sediments are an arsenic-rich copper smelter slag and sodium arsenite (NaAsO 2 ), an arsenic pesticide. The slag9s high Pb, Cu, and Zn concentrations (>1000 mg/kg) and distinct Pb, Cu, Zn, and As concentration ratios, in comparison to those of sodium arsenite-contaminated sediments, are used to distinguish which of these two potential sources is most likely the predominant source of arsenic in Hylebos sediments. Correlation analyses indicate that among the 42 Hylebos sediment samples collected in this study and 241 sediment samples collected by the Hylebos Cleanup Committee, Pb, Zn, and Cu log concentrations are highly correlated with As log concentrations (R values range from 0.69 to 0.79 with significance levels below 0.00005). These high correlations are consistent with slag not sodium arsenite contamination. To illustrate this point, sediment contamination by slag and sodium arsenite was numerically simulated to produce Pb, Cu, and Zn versus As contaminant titration curves. The results show that sediment data plot along the simulated slag contamination curves, not the sodium arsenite contamination curves, suggesting that slag is the predominant source of As in contaminated sediments. Two multivariate statistical analyses, a cluster analysis and discriminant analysis, strongly support these conclusions.