9. Bioaccumulation and Trophic Transfer of Organic Contaminants
211
Some experiments have examined this issue more directly. One such study
extracted lipids from phospholipid-rich organisms and from triglyceride-rich organisms. The extracted lipids were coated onto filters, and the relative partitioning
onto the filters was determined. The data indicated that the filters coated with
triglyceride-rich lipids accumulated nearly twice the amount of tetrachlorobiphenyl compared with filters containing lipids with 20% or more phospholipids
(Ewald and Larsen, 1994). From this more direct study, the bioaccumulation by
biota was deduced to vary with triglyceride composition of the species.
In another study, the two lipid types, buoyant nonpolar and polar membraneassociated lipids, were separated by physical means, and the corresponding accumulation of contaminant in each phase along with the corresponding lipid composition of each phase were examined. On a lipid-normalized basis, both phases
contained essentially the same concentration of the nonmetabolized contaminants,
suggesting that the polarity of the lipid when it exists in the organism does not
dramatically affect the accumulation of nonpolar contaminants (Gardner et aI.,
1990).
The ability to accurately determine the influence of differing lipid compositions
contaminant bioavailability is not completely resolved, and new approaches to
study the issue are required. An additional interesting finding of the Gardner et aI.
(1990) study was a dynamic imbalance (differences in normalized lipid concentrations) among the lipid pools that continued for a relatively long time period
(>24 h) in mysids. Thus, before comparing among lipid pools, it is critical that
adequate exposure time be allowed to ensure that the pools are dynamically in
balance (i.e., have equal chemical activities [lipid-normalized contaminant concentrations] among the lipid pools). If this is not the case, the analyses may
artificially indicate that there are differences in the contaminant distribution relative to lipid content when, in fact, the organism is out of steady state relative to the
distribution among the various pools. The absence of balance among the lipid
pools is more likely to occur for larger animals in which the distribution processes
require longer times before pools attain equal chemical activity.
9.4. Mimicking Bioconcentration with Semipermeable
Membrane Devices
With the recognition that the lipid content of organisms drives the bioaccumulation of nonpolar contaminants, attempts have been made to develop nonbiological
surrogates. These surrogates would directly sample the chemical activity of systems without the difficulty of maintaining live organisms or accounting for processes such as biotransformation that complicate the interpretation. Early efforts
used solvent-filled dialysis membranes or hexane "droplets" as surrogates for
accumulation of contaminants (Sodergren and Okla, 1988; Sodergren, 1987). This
early work produced encouraging comparisons between the accumulation by
nonbiological surrogates and organisms. However, there were difficulties with the
211
Some experiments have examined this issue more directly. One such study
extracted lipids from phospholipid-rich organisms and from triglyceride-rich organisms. The extracted lipids were coated onto filters, and the relative partitioning
onto the filters was determined. The data indicated that the filters coated with
triglyceride-rich lipids accumulated nearly twice the amount of tetrachlorobiphenyl compared with filters containing lipids with 20% or more phospholipids
(Ewald and Larsen, 1994). From this more direct study, the bioaccumulation by
biota was deduced to vary with triglyceride composition of the species.
In another study, the two lipid types, buoyant nonpolar and polar membraneassociated lipids, were separated by physical means, and the corresponding accumulation of contaminant in each phase along with the corresponding lipid composition of each phase were examined. On a lipid-normalized basis, both phases
contained essentially the same concentration of the nonmetabolized contaminants,
suggesting that the polarity of the lipid when it exists in the organism does not
dramatically affect the accumulation of nonpolar contaminants (Gardner et aI.,
1990).
The ability to accurately determine the influence of differing lipid compositions
contaminant bioavailability is not completely resolved, and new approaches to
study the issue are required. An additional interesting finding of the Gardner et aI.
(1990) study was a dynamic imbalance (differences in normalized lipid concentrations) among the lipid pools that continued for a relatively long time period
(>24 h) in mysids. Thus, before comparing among lipid pools, it is critical that
adequate exposure time be allowed to ensure that the pools are dynamically in
balance (i.e., have equal chemical activities [lipid-normalized contaminant concentrations] among the lipid pools). If this is not the case, the analyses may
artificially indicate that there are differences in the contaminant distribution relative to lipid content when, in fact, the organism is out of steady state relative to the
distribution among the various pools. The absence of balance among the lipid
pools is more likely to occur for larger animals in which the distribution processes
require longer times before pools attain equal chemical activity.
9.4. Mimicking Bioconcentration with Semipermeable
Membrane Devices
With the recognition that the lipid content of organisms drives the bioaccumulation of nonpolar contaminants, attempts have been made to develop nonbiological
surrogates. These surrogates would directly sample the chemical activity of systems without the difficulty of maintaining live organisms or accounting for processes such as biotransformation that complicate the interpretation. Early efforts
used solvent-filled dialysis membranes or hexane "droplets" as surrogates for
accumulation of contaminants (Sodergren and Okla, 1988; Sodergren, 1987). This
early work produced encouraging comparisons between the accumulation by
nonbiological surrogates and organisms. However, there were difficulties with the