The Houston Ship Channel (HSC) and upper Galveston Bay (GB), Texas, are known to be contaminated with dioxins (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans), the majority of which are associated with sediments. Since 1914, dredging operations to establish, sporadically expand, and consistently maintain a navigable channel for large ships has been and remains continuous here. The objectives of this research focus on determining if dredging activities have any significant impact on the quantities of dioxins associated with surface sediments in the HSC and GB. Four transects were sampled, located on the dredged and undredged sides of two dredge-spoil islands. Sediment samples were characterized in terms of their organic carbon contents, grain size fractions, indicator dioxin concentrations (2,3,7,8-tetrachlorinated dibenzo-p-dioxin [TCDD], 2,3,7,8-tetrachlorodibenzofuran [TCDF], and toxic equivalents), and fallout radionuclide activities. The physical and geochemical data were examined using a combination of principal components analysis and one-way analysis of variance. Results of the statistical tests show that (1) sedimentary dioxin concentrations are significantly higher adjacent to the northernmost dredge-spoil island, which is located closer to a recently identified dioxin point source (San Jacinto waste pits); and (2) while mean sedimentary dioxin concentrations were slightly higher for undredged as compared to dredged transect samples as a whole, these differences were not significant (p > 0.05). Mean fallout isotope ratio values (7Be/137Cs, 7Be/210Pbxs) were greater for the dredged sample population, indicating that dredged sediments contain more of the shorter-lived radionuclides (i.e., 7Be), as their buildup is more rapid after dredging than those isotopes with longer half-lives (210Pb) or those for which a longer time has passed since introduction into the environment (137Cs).
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Vol. 2010 • No. 264