| Popis: |
Principal components analysis (PCA) has been applied to a large data set of the concentrations of chlorinated dibenzo-p-dioxins and dibenzofurans in samples of crab hepatopancreas from British Columbia, Canada (B.C.). These samples have been collected since 1987 from locations in the vicinity of B.C. coastal mills and the principal B.C. harbors. PCA distinguishes harbor samples from mill samples, reveals differences between individual mill sites and reliably classifies the dioxin and furan congener patterns according to chlorine bleaching, digested polychlorinated phenol and pentachlorophenol wood preservative sources. PCA may also be used to assign sources to individual crab samples. Since 1987 both the proportion of toxic 2,3,7,8-chlorinated congeners and the overall dioxin and furan concentrations have generally decreased near B.C. mill sites. The mill-related tetrafurans have been removed faster than the hexadioxins, with the result that composition profiles and PCA projections have become more similar over time at the mill sites. Crab samples from B.C.’s harbors have lower proportions of the toxic 2,3,7,8-chlorinated congeners, but have shown less change over time. |
