Principal components analysis of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in sediments from Lake Champlain and Lake George, New York, USA

Abstract

Principal-components analysis (PCA) was used to compare concentrations of polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) compounds in sediments collected from two interconnected lakes, Lake Champlain and Lake George, New York, USA. Two different PCDD/PCDF congener profiles were present in surface sediment samples from Lake George. Samples collected near residential areas and power-boat marinas had elevated hepta- and octa-CDDs (1±0.3 ng/g) and tetra-octa-CDFs compared with samples collected in other areas of the lake. The PCDD/PCDF pattern in the high-level samples was similar to the PCDD/PCDF pattern in sediments from Green Lake, NY, a small lake in which atmospheric deposition is the only route for PCDD/PCDF contamination, either from local sources or from long range transportation from multiple sources in the midwest. The samples containing the higher PCDD/PCDF concentrations also contained higher lead concentrations (173±33 μg/g) compared to the low-level PCDD/PCDF samples (52±25 μg/g). However, the increase in lead concentrations was accompanied by increased concentrations of other trace metals. Consequently, it can be concluded that emissions from power boats are not responsible for the PCDD/PCDF contamination in Lake George. Concentrations of PCDDs/PCDFs in the low-level samples were similar to PCDD/PCDF concentrations in sediments from remote midwestern lakes where long range atmospheric deposition was the only plausible route of entry for the PCDD/PCDF compounds. However, other studies have shown that offshore sediments in Lake George have lower concentrations of organic carbon than inshore samples and, therefore, the low-level PCDD/PCDF pattern may be an artifact related to a reduced PCDD/PCDF concentration in sediments with a low organic carbon content. Surface and core sediments from Lake Champlain also partitioned into two groups, which both had PCDD/PCDF patterns differing from the high-level surface sediments collected from Lake George. The largest group of samples was characterized by the presence of high octa-CDD concentrations (3.5–18 ng/g). The second group of samples was four sections from a single core sample collected near a bleached kraft pulp and paper mill, which closed in 1970. These samples had high concentrations of tetra-CDFs (0.5–1.4 ng/g), primarily 2,3,7,8-tetra-CDF, accompanied by comparable concentrations of octa-CDD (0.9–4.4 ng/g). The presence of 2,3,7,8-tetra-CDF is consistent with results from several studies where PCDDs/PCDFs were analyzed in samples taken from various stages of the bleached kraft process. These samples were grouped in the same quadrant on a PCA plot as coal soot and pulp and paper mill sludge. However, the grouping was not close, and the PCDD/PCDF contamination in these sediments cannot be associated with either source. Five sections of a core collected near a currently operating bleached kraft pulp and paper mill also had elevated 2,3,7,8-tetra-CDF concentrations (0.3±0.05 ng/g), but these 2,3,7,8-tetra-CDF concentrations were accompanied by considerably higher octa-CDD concentrations (7.5±0.5 ng/g). Therefore, they could not be distinguished by PCA from the majority of the Lake Champlain samples.