Differential Accumulation of Polychlorinated Biphenyl Congeners in the Terrestrial Food Web of the Kalamazoo River Superfund Site, Michigan

A series of field studies was conducted to determine the
bioaccumulation of polychlorinated biphenyl (PCB)
congeners in the terrestrial food web of the Kalamazoo
River flood plain. Samples included colocated soils, native
plants likely to be consumed by wildlife, several taxa of
terrestrial invertebrates, small mammals, passerine bird eggs,
nestlings, and adults, and great horned owl plasma and
eggs. Mean concentrations of total PCBs in samples from
the former Trowbridge impoundment were 6.5 mg/kg dry
weight for soils and 0.023, 0.13, 1.3, 1.3, 1.6, and 8.2 mg/kg
wet weight for plants, small herbivorous mammals,
depurated earthworms, shrews, great horned owl eggs,
and house wren eggs, respectively. Historical data from the
Kalamazoo River have reported Aroclor-equivalent total
PCB concentrations in the terrestrial food web; however,
the degree of environmental weathering of the parent PCB
mixtures was unknown. In this study, earthworms and
composite samples of coleoptera exhibited PCB congener
patterns that were similar to patterns in colocated soils.
However, in plants, less chlorinated PCBs (e.g., mono-, di-,
tri-, and tetrachlorinated biphenyls) were predominant,
and in small mammals, there was a notable enrichment of
PCBs 153, 180, 138, 118, and 99. In general, concentrations
of PCBs were lower in most biota than in soil from the
Kalamazoo River Area of Concern (KRAOC) although there
was a modest biomagnification of PCBs from lower
trophic level biota to higher trophic levels. As a consequence
of environmental weathering of PCBs in the terrestrial
food web of the KRAOC, the relative potency of the PCBs
(expressed as mg TEQs/kg PCBs) decreased from soil
to most biota. While there was a general trend, as expected,
in which concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs) increased with total PCBs, this
relationship was rather poor (R2 = 0.13). Taken together,
these data suggest that the differential accumulation of PCB
congeners in the terrestrial food web can be explained
by congener-specific differences in bioavailability from soil,
exposure pathways, and metabolic potential of each of
the food web components.