212
P.E Landrum and S.w. Fisher
hexane-filled bags and with the dialysis tubing. The hexane tended to dialyze out
of the bags, and the dialysis membranes degraded over time. More recent approaches have used thin polymeric film membrane bags with a lipid material for
filler (Huckins et aI., 1990a) and an improved method for contaminant recovery
from these samplers (Huckins et aI., 1990b). Because these semipermeable membrane devices (SPMDs) are filled with lipid materials, they should more accurately reflect the contaminant capacity of lipids in organisms. Further, unlike
solvents, the large molecular size of the lipids precludes their diffusion out of the
sampler into the water.
The properties of these samplers have been well characterized by deploying
them alongside caged organisms including both fish and bivalves (Ellis et aI.,
1995; Prestet aI., 1992). In both cases, the SPMDs performed well in sampling the
environment for nonpolar organic contaminants. In one study, the results of the
SPMDs were compared with another method that measured concentrations in
ultrafilter permeates (Ellis et aI., 1995). The SPMDs gave equivalent results with
the ultrafilter permeates in indicating the amount of contaminants bioavailable for
aqueous exposures. However, caged (channel catfish) and feral fish (carp and
sauger) residues exhibited fewer contaminants. The differences between caged
and feral fish may be due to mobility of the feral population reflecting differing
sources, differences in species, and enhanced metabolism in the feral organisms.
In general, the SPMDs had higher concentrations of contaminants compared with
the fish. This may reflect more rapid accumulation, the absence of biotransformation, and/or rapid elimination of the contaminants from fish (Ellis et aI., 1995).
When contaminant concentrations in the samplers were compared with caged
bivalves (Corbiculafluminea), there were again differences between the mussels
and the SPMDs. In general, the SPMDs sequestered a wider range of contaminants, and there were differences in the distribution between the clams and the
SPMDs. Further, the clams sequestered greater concentrations than the SPMDs,
which may be the result of greater uptake rates and additional pathways such as
accumulation from food (Prest et aI., 1992). It is clear that SPMDs can take a long
time to come to true equilibrium, and this can be further modified by biofouling in
aquatic systems. However, these devices hold the potential to provide a good
baseline for aqueous exposures. Because they are passive storage devices, they
will never reflect the active processes that govern the uptake and loss of contaminants by aquatic organisms. This also serves to suggest that although bioconcentration and bioaccumulation, even when evaluated at steady state, may be
proportional to the storage capacity (lipid content) of the organism, neither may
reflect the chemical activity of a given contaminant in the system. Both bioconcentration and bioaccumulation depend on the toxicokinetics that are dictated by
chemical and biological processes affecting contaminant exposure and loss and
the available contaminant sources.
P.E Landrum and S.w. Fisher
hexane-filled bags and with the dialysis tubing. The hexane tended to dialyze out
of the bags, and the dialysis membranes degraded over time. More recent approaches have used thin polymeric film membrane bags with a lipid material for
filler (Huckins et aI., 1990a) and an improved method for contaminant recovery
from these samplers (Huckins et aI., 1990b). Because these semipermeable membrane devices (SPMDs) are filled with lipid materials, they should more accurately reflect the contaminant capacity of lipids in organisms. Further, unlike
solvents, the large molecular size of the lipids precludes their diffusion out of the
sampler into the water.
The properties of these samplers have been well characterized by deploying
them alongside caged organisms including both fish and bivalves (Ellis et aI.,
1995; Prestet aI., 1992). In both cases, the SPMDs performed well in sampling the
environment for nonpolar organic contaminants. In one study, the results of the
SPMDs were compared with another method that measured concentrations in
ultrafilter permeates (Ellis et aI., 1995). The SPMDs gave equivalent results with
the ultrafilter permeates in indicating the amount of contaminants bioavailable for
aqueous exposures. However, caged (channel catfish) and feral fish (carp and
sauger) residues exhibited fewer contaminants. The differences between caged
and feral fish may be due to mobility of the feral population reflecting differing
sources, differences in species, and enhanced metabolism in the feral organisms.
In general, the SPMDs had higher concentrations of contaminants compared with
the fish. This may reflect more rapid accumulation, the absence of biotransformation, and/or rapid elimination of the contaminants from fish (Ellis et aI., 1995).
When contaminant concentrations in the samplers were compared with caged
bivalves (Corbiculafluminea), there were again differences between the mussels
and the SPMDs. In general, the SPMDs sequestered a wider range of contaminants, and there were differences in the distribution between the clams and the
SPMDs. Further, the clams sequestered greater concentrations than the SPMDs,
which may be the result of greater uptake rates and additional pathways such as
accumulation from food (Prest et aI., 1992). It is clear that SPMDs can take a long
time to come to true equilibrium, and this can be further modified by biofouling in
aquatic systems. However, these devices hold the potential to provide a good
baseline for aqueous exposures. Because they are passive storage devices, they
will never reflect the active processes that govern the uptake and loss of contaminants by aquatic organisms. This also serves to suggest that although bioconcentration and bioaccumulation, even when evaluated at steady state, may be
proportional to the storage capacity (lipid content) of the organism, neither may
reflect the chemical activity of a given contaminant in the system. Both bioconcentration and bioaccumulation depend on the toxicokinetics that are dictated by
chemical and biological processes affecting contaminant exposure and loss and
the available contaminant sources.