9. Bioaccumulation and Trophic Transfer of Organic Contaminants
215
More often, however, exposure to contaminants results in a reduction in lipids.
For instance, when rainbow trout were exposed to PCP, the surviving organisms at
the high dose showed significant reductions in total lipids (van den Huevel et aI.,
1991). Other similar examples exist for exposures to both organic and inorganic
contaminants. For example, the accumulation of lead in fish yielded reductions in
total lipids, phospholipids, and cholesterol. This was accompanied by an increase
in lipase and free fatty acids (Tulasi et aI., 1992). Both of these effects were
observed during the preparation for reproduction. Organic pesticides, y-BHC and
malathion, were observed to affect lipid metabolism during the vitellogenic phase
of the annual reproductive cycle in the catfish Clarias batrachus (Lal and Singh,
1987). These contaminants affected both nonpolar lipid and phospholipid metabolism. In particular, these pesticides inhibited the esterification of free fatty acids to
acyl glycerides and also affected their mobilization from liver to gonads (Lal and
Singh, 1987). Thus, the impact of contaminants on lipid metabolism, particularly
in preparation for reproduction, provides some insight into mechanisms for reproductive impairment offish and presumably to other aquatic organisms exposed
to environmental contaminants.
9,6. Relevance of Food Chain Transfer to Bioaccumulation
9.6.1. Relevance of Trophic Transfer to Bioaccumulation
Previous sections have dealt primarily with the uptake of contaminants directly
from water and the role of lipids in determining bioconcentration. However, Ii ving
organisms can also accumulate contaminants via consumption of contaminated
food. Dietary transfer of contaminants has been a controversial subject for several
decades. A large number of investigators have argued that uptake of contaminants
from dissolved form in water eclipses accumulation from any other source and,
thus, can be considered the primary source of contaminant exposure in the aquatic
environment (Shaw and Connell, 1986; Bruggerman et aI., 1981; Chiou et aI.,
1977; Moriarty, 1975). Because there are tremendous political and policy ramifications that stem from resolution of this issue and because the role of lipids in
bioaccumulation takes on several added dimensions if accumulation from food is
significant, the major points of argument are presented here.
Identification of bioconcentration as the most relevant route of contaminant
exposure stems largely from the observation that uptake of contaminants from
water is very rapid and can quickly generate significant body burdens (Fisher et
aI., 1993; Reynoldson, 1987). Because bioconcentration is a partitioning phenomenon between an aqueous phase and a lipid phase, movement of the contaminant
from water into the organism is driven by the lipid content of the organism and is
usually predictable from log Kow as described above. Short-term laboratory assays
are effective in measuring bioconcentration. However, in aquatic systems, most of
the contaminant load is retained in sediment (DiPinto et aI., 1993). Thus, it is
highly likely that slower transfer processes such as accumulation from sediment
215
More often, however, exposure to contaminants results in a reduction in lipids.
For instance, when rainbow trout were exposed to PCP, the surviving organisms at
the high dose showed significant reductions in total lipids (van den Huevel et aI.,
1991). Other similar examples exist for exposures to both organic and inorganic
contaminants. For example, the accumulation of lead in fish yielded reductions in
total lipids, phospholipids, and cholesterol. This was accompanied by an increase
in lipase and free fatty acids (Tulasi et aI., 1992). Both of these effects were
observed during the preparation for reproduction. Organic pesticides, y-BHC and
malathion, were observed to affect lipid metabolism during the vitellogenic phase
of the annual reproductive cycle in the catfish Clarias batrachus (Lal and Singh,
1987). These contaminants affected both nonpolar lipid and phospholipid metabolism. In particular, these pesticides inhibited the esterification of free fatty acids to
acyl glycerides and also affected their mobilization from liver to gonads (Lal and
Singh, 1987). Thus, the impact of contaminants on lipid metabolism, particularly
in preparation for reproduction, provides some insight into mechanisms for reproductive impairment offish and presumably to other aquatic organisms exposed
to environmental contaminants.
9,6. Relevance of Food Chain Transfer to Bioaccumulation
9.6.1. Relevance of Trophic Transfer to Bioaccumulation
Previous sections have dealt primarily with the uptake of contaminants directly
from water and the role of lipids in determining bioconcentration. However, Ii ving
organisms can also accumulate contaminants via consumption of contaminated
food. Dietary transfer of contaminants has been a controversial subject for several
decades. A large number of investigators have argued that uptake of contaminants
from dissolved form in water eclipses accumulation from any other source and,
thus, can be considered the primary source of contaminant exposure in the aquatic
environment (Shaw and Connell, 1986; Bruggerman et aI., 1981; Chiou et aI.,
1977; Moriarty, 1975). Because there are tremendous political and policy ramifications that stem from resolution of this issue and because the role of lipids in
bioaccumulation takes on several added dimensions if accumulation from food is
significant, the major points of argument are presented here.
Identification of bioconcentration as the most relevant route of contaminant
exposure stems largely from the observation that uptake of contaminants from
water is very rapid and can quickly generate significant body burdens (Fisher et
aI., 1993; Reynoldson, 1987). Because bioconcentration is a partitioning phenomenon between an aqueous phase and a lipid phase, movement of the contaminant
from water into the organism is driven by the lipid content of the organism and is
usually predictable from log Kow as described above. Short-term laboratory assays
are effective in measuring bioconcentration. However, in aquatic systems, most of
the contaminant load is retained in sediment (DiPinto et aI., 1993). Thus, it is
highly likely that slower transfer processes such as accumulation from sediment