Abstract
Lipids generally represent the major matrix contributing to the absorptive capacity for hydrophobic organic contaminants in aquatic ecosystems. The aim of the present study was to determine whether contaminants partition to a different degree to the different storage lipid classes: wax ester (WE) and triacylglycerol (TAG). This was undertaken by studying experimentally the partitioning of organochlorine compounds between lipids (WE or TAG) and silicone rubber phase. Our results indicate that hydrophobic compounds have a slightly higher affinity for WE than for TAG. The findings thus corroborate earlier suggestions that contaminants accumulate to a greater extent in food webs with a higher reliance of on WE, such as in the Arctic. This knowledge is of interest since it implies that possible changes in planktonic community species composition, and thereby possible changes in the lipid composition, may have consequences for accumulation of hydrophobic contaminants in apex predators. However, the magnitude of these consequences remains unknown, and there may well be other factors of importance for previously observed higher accumulation of contaminants in Arctic systems. Thus, we have here identified aspects regarding partitioning of contaminants to lipids that need further scrutiny, and there is a need for further quantitative estimates of the suggested difference in absorptive capacities for hydrophobic contaminants between WE and TAG.
Highlights
The aim of the present study was to determine experimentally whether there is a difference in the partitioning of HCB, polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) to two storage lipid classes, namely wax ester (WE) and triacylglycerol (TAG)
Of the compounds added to the experimental units, 88%e110% of the organochlorine compounds (HCB and PCBs), and 91%e136% of the PBDEs were recovered (136% for BDE-183 in triacyl glycerols (TAG), otherwise recoveries were 91 %e115%; Table 1)
This increase was larger for those that equilibrated with wax esters (WE) (~2.8%) than for those that equilibrated with TAG (~0.4%; significantly different; ANOVA; Fig. S2; Table S3, Supplemental data)
Summary
Contaminant concentrations in biological matrices are often reported normalized to the lipid content (total extractable lipids). This allows for comparison between organisms, e.g. to quantify biomagnification in a food web (Ruus et al, 2002). High lipid content represents a high storage capacity for hydrophobic contaminants such as hexachlorobenzene (HCB), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs; with octanol-water partition coefficients, KOW >105). If changes in food availability and metabolism affect the energy allocation and lipid storage in organisms, subsequent alterations in hydrophobic contaminant bioaccumulation and lipid class distribution is likely. The probability of toxicological effects may increase, as increased lipid turnover results in increased contaminant mobilization to the blood stream that can transport them to target organs (Bustnes et al, 2010)
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