Equilibrium Lipid Partitioning Concentrations as a Multi-Media Synoptic Indicator of Contaminant Levels and Trends in Aquatic Ecosystems

Abstract

Large quantities of monitoring data have been gathered over many years for the Great Lakes basin in the form of contaminant concentrations in a variety of media including air, water, suspended and bottom sediments, wildlife (especially fish, birds, and birds’ eggs), soils, vegetation, foodstuffs, and human tissues. The quantity of data and the diversity of units used to report the concentrations are such that it is difficult to gain a comprehensive, ecosystem-wide, interpretation of contaminant levels and trends. It is suggested that the problems arising from the use of a diversity of units can be addressed, at least for an organic contaminant, by expressing all concentrations on a common equilibrium partitioning basis. The equilibrium lipid partitioning (ELP) concentration is suggested as being most appropriate for this purpose. It is shown that expressing monitoring data as ELP concentrations permits a more reliable determination of time trends in contaminant levels in multi-media systems, facilitates comparison between ecosystems, and contributes to an improved understanding of contaminant sources and fate. An “adjusted” ELP concentration may be deduced to compensate for differences in equilibrium status between media, thus consolidating all multi-media contaminant levels in a single, ecosystem-wide, synoptic indicator of trends in contaminant status. The approach is illustrated for polychlorinated biphenyls (PCBs) in the Lake Ontario and Lake Superior ecosystems showing a definite decrease in concentrations over the period 1977 to 1993 with estimated decay half-lives of 8.1 and 11.4 years, respectively.