Organochlorines in Lake Superior's Food Web

Abstract

Lake Superior's food web was analyzed in 1994 for hydrophobic organochlorine contaminants (OCs) including toxaphene, chlordane and metabolites, hexachlorocyclohexanes, hexachlorobenzene, dieldrin, and polychlorinated biphenyl congeners. Toxaphene was the dominant organochlorine contaminant in the Lake Superior food web, with concentrations 2-15 times higher than total PCBs. Among the biota studied, wet weight toxaphene levels were highest in bloaters (Coregonus hoyi) at 1100 ( 270 ng/g (mean ( 1 standard deviation) and lowest in Mysis relicta (32 ( 804 ng/g). Total PCB concentrations ranged more than a factor of 20 on a wet weight basis but less than a factor of 6 on a lipid weight basis. The lipid content of the organisms explains 81% of the variability in wet weight t-PCB, with trophic position exerting a smaller influence. Using path analysis and regression techniques, the main influence of trophic position on t-PCBs was shown to be due to the concurrent increase in lipid content with trophic position. The relative distributions of organochlorines among trophic levels were very similar, despite the 3 orders of magnitude range in OC hydrophobicity. Unlike our work in Lake Baikal, the accumulation of OCs in the Lake Superior food web was not significantly (p < 0.05) related to the log octanol/water (K ow ) partition coefficient, suggesting either that organochlorines in this food web equilibrate with surrounding dissolved OCs rapidly relative to dietary uptake or that the OC assimilation efficiency of predators does not vary with log K ow . Based on OC concentrations in benthic amphipods, we conclude that settling particles are an important source of OCs to deep water organisms in Lake Superior.

Bioaccumulation and differential partitioning of polychlorinated biphenyls in freshwater, planktonic food webs

“…Increasing concentrations of OCs with trophic level may instead be attributed to differences in lipid content (Bentzen et al 1996;Kucklick and Baker 1998), depuration rates (LeBlanc 1995;Sijm and Van der Linde 1995), size (Bergner 1985), and exposure duration (Harding et al 1997). LeBlanc (1995) argued that the apparent increase in lipid content with trophic levels would cause an increase in lipophilic OCs by bioconcentration alone, driven by passive diffusion over a fugacity gradient.…”

The effect of protozoan grazers on the cycling of polychlorinated biphenyls (PCBs) in marine systems

“…In this process, PCBs associate with outer membranes and rapidly diffuse into the phospholipid bilayer surrounding the cytoplasm (Dulfer et al, 1996;Dulfer et al, 1998). For large organisms such as fish and marine mammals, PCBs accumulate through ingestion (Connolly, 1991;Campfens and Mackay, 1997;Kucklick and Baker, 1998). PCBs pass through the walls of the digestive system, enter the bloodstream and are subsequently carried to lipid-rich tissues.…”

O legado das bifenilas policloradas (PCBs)

“…Apresenta-se na Figura 2 uma proposição para as possíveis rotas de acumulação de compostos xenobióticos, pelos peixes através da água ou por seus hábitos alimentares. Entretanto, o padrão de absorção pode ser alterado devido a mudanças comportamentais ou mesmo devido a mudanças climáticas da região onde a espécie habita 31 .…”