Reducing Variability in Pollution Data: The Use of Lipid Classes for Normalization of Pollution Data in Marine Biota

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Abstract
Organochlorine residues (PCBs and pesticides) are usually normalized on lipid content, gravimetrically quantified after extraction in organic solvents. In this study, the lipid content of different biotic groups (e.g. phytoplankton, shrimp, bivalves, fish), obtained through different types of extraction (total extraction versus specific extraction of apolar lipids) and quantification techniques (total gravimetric determinations versus specific determinations of lipid classes (latroscan)) were compared. The different lipid quantification methods were interrelated. An overestimation of lipid content due to non-lipid co-extracts was shown to interfere with gravimetric lipid quantifications. The relative contribution of these co-extracts depended on the type of sample studied. Differences in pollution levels (individual PCB congeners) between different biotic groups (phytoplankton, shrimp, cockles, fish) and between different fish tissues are discussed in relation to lipid content, determined by the different methods. An important reduction in the variability of pollution levels was noted when data were normalized on total neutral lipid content (latroscan). Highly significant linear regression parameters were obtained between the pollutant and the total neutral lipid content of marine biotic samples from the same water mass. Water mass specific bio-lipid contamination levels, characteristic for the whole biotic community (excluding seabirds and sea mammals), were determined for the different PCB congeners, normalized on total neutral lipid content. These bio-lipid contamination levels were related to the Kow of the congeners. This functional relationship could be described by a second order polynomial regression.