United States
Environmental Protection
Agency
Environmental Research
Laboratory
Duluth MN 55804
Research and Development
EPA-600/S3-84-026 Mar 1984
oEPA Project Summary
AMENDED
SEEPAGES 1 and 3
An Age-Dependent Model of
PCB in a Lake Michigan
Food Chain
Robert V. Thomann and John P. Connolly
An age-dependent food chain model
that considers species bioenergetics
and toxicant exposure through water
and food was developed. It was
successfully applied to PCB contamina-
tion of the Lake Michigan lake trout
food chain represented by phytoplank-
ton. My sis, alewife, and lake trout. The
model indicated that for the top
predator lake trout, PCB exposure
through the food chain can account for
greater than 99 percent of the observed
body burden. A simple steady-state
computation indicated that ratios of
chemical concentration in predators to
that in prey in feeding experiments may
be as low as 0.2 and still result in signifi-
cant food chain transfer.
It was estimated that a criterion spec-
ifying that PCB concentrations of all
ages of lake trout be at or below 5 fjg/g
(wet weight) in the edible portion would
require that dissolved PCB concentra-
. tions be reduced to between 0.5 and :
• 2.5 ng/L. The range reflects uncertainty;
in the PCB assimilation efficiency of the
species and the dissolved PCB concen-
tration.
This Project Summary was developed
by EPA's Environmental Research Lab-
oratory. Duluth, MN, to announce key
findings of the research project that is
fully documented in a separate report of
the same title (see Project Report order-
ing information at back).
Introduction
The PCB concentration in the fishes of
Lake Michigan has been a matter of study
and concern for a number of years.
Concentrations of PCB in adult lake trout
(Salvelinus namaycush) in 1971, for
example, averaged about 5-20 /yg/g(w),
substantially above the U S. Food and
Drug Administration (FDA) guidelines of
5 A/g/g(w) in the edible portion of fish.
In order to understand the mechanisms
that give rise to these levels, it is neces-
sary to analyze the data through use of a
model of the principal phenomena of
chemical uptake and transfer. These
mechanisms include two principal
routes'
1) uptake of PCB directly from water,
and
2) accumulation of PCB through
consumption of contaminated food
The significance of the food chain route,
i.e., the degree to which a chemical such
as PCB's may be accumulated in an
organism by predation, needs to be
placed in a mechanistic predictive
framework to be able to calculate
expected levels under field conditions
It has been suggested that the maxi-
mum environmental concentration in fish
can be estimated without recourse to a
food chain route. Such an approach
assumes that a first approximation to
expected levels of a chemical can be
obtained either from simple partitioning
concepts or from a simple model of direct
uptake from the water.
The issue of whether a simple calcula-
tion of uptake of a chemical directly from
the water is sufficient relates to the
degree to which such a calculation would
actually reproduce observed field data for
important species such as the lake trout.
If such a calculation does account for the
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observed data in thefield, thenthere is no
need for a model that includes a food
chain component If a simple partitioning
calculation fails to reproduce the
observed data, then the principal feature
of the food chain must be included
The principal objectives of this effort
therefore were to.
1 develop an age-dependent food
chain model of uptake and transfer
of potentially toxic chemicals,
2 determine the relative importance
of water uptake and food chain
routes of PCB in a Lake Michigan
food chain with specific emphasis
on lake trout,
3. test the utility of simple partitioning
approaches for PCB that do not
include the food chain route, and
4 provide a preliminary projection of
response in PCB concentration m
the lake trout following a reduction
m PCB water concentration.
Approach
The accumulation of PCBs in the Lake
Michigan food chain was modeled
assuming a four species food chain
consisting of phytoplankton, Mysisrelicta,
alewife (Alosa pseudoharengus), and
lake trout (Salvelinus namaycush) This
species linkage constitutes the major
energy transport route to the lake trout
Both Mysis and alewife were viewed as
representative species of the middle
levels of the food chain acknowledging
that other invertebrates and small fish
also contribute to the observed PCB levels
in lake trout The phytoplankton
component of the model was assumed to
represent nonliving paniculate organic
material as well as living plankton
Phytoplankton were represented by a
single compartment that was assumed to
be in dynamic equilibrium with water
column dissolved PCB. PCB concentra-
tions in the other species were calculated
m time using a framework that considers
uptake directly from water, uptake from
food, excretion and growth The uptake
and excretion rates were calculated from
the species bioenergetics Uptake from
water and excretion were related to
respiration rate Uptake from food was
related to consumption rate which was
calculated from the respiration and
growth rates
The species above phytoplankton were
separated into discrete age classes.
Predator-prey relationships were
specified for each age class based on
observed feeding habits.
Results
Data for 1971 were used in the
calibration of the model A constant
dissolved PCB concentration of 5 ng/L
was assumed The model successfully
reproduced the observed data for alewife
and lake trout with the exception of the
early age classes of lake trout No
combination of parameters was
successful at reproducing the high PCB
values m age class 2 and 3 lake trout
while maintaining consistency with
reported parameter values and
reproducing the observed concentrations
in the upper age classes. A possible
explanation of these high values is that
young trout may be exposed to higher
dissolved PCB concentrations because of
their tendency to stay in near shore areas.
The data and the model both indicate
that PCB concentrations in lake trout are
3 to 4 times those in alewife. The
computed increase results from the
higher PCB concentration in lake trout
prey (alewife) relative to alewife prey
(Mysis). The model calculated that
greater than 99% of the PCB in adult trout
is taken up in food.
Empirical evidence indicates that the
extent of accumulation of organic
chemicals by aquatic species in
laboratory studies is related to the
lipophilic nature of the chemicals.This
lipophilic nature is normally expressed
as the equilibrium concentration ratio of
the chemical partitioned between n-
octanol and water, i.e., the octanol-water
partition coefficient. Some evidence indi-
cates that field observed contaminant
concentrations may be directly estimated
from water concentrations using lipid
content and the octanol-water partition
coefficient of the contaminant. To test
this possibility, the highest reported
octanol-water partition coefficient avail-
able in the literature (10672for HCB) was
used with the lake trout lipid content to
predict lake trout PCB concentration. The
resulting PCB concentrations were 4 to 5
times lower than the data and food chain
model calculation for adult trout and
clearly an unsatisfactory estimation of
lake trout contamination. The poor fit
results from the failure to consider ex-
posure through food which, as shown
earlier, is the dominant contributor of
PCB to the top predator lake trout.
The model was used to assess the
effect of reduced dissolved PCB concen-
trations on PCB levels in the lake trout.
The results indicate that a period of abou
5 years would be required to "clear out'
the initial higher concentrations for th<
upper age class fish. The overal
relationship between age class and th<
required dissolved water concentration t<
maintain 5-10 /ug/g(w) on a whole fist
basis (estimated to result in approximate!'
5 /ug/g/w for the edible portion) wa;
determined. The older age classe:
require the lowest dissolved PCB wate
concentration to meet the 5-10yug/g(w
level. If a level of 2 ng/L were obtained
then whole fish 6 years and older wouli
have concentrations between 5 and 1(
/ug/g(w). Conversely, whole fish less thai
6 years old would have PCB concentra
tions less than 5//g/g(w). Inordertohavi
the PCB concentrations of all age classe
of lake trout at or below 5 //g/g(w) in trv
edible portion, it is estimated that th>
dissolved water concentrations woul<
have to be between 0.5-2.5 ng/L usm<
growth rates representative of stocke<
fish.
Conclusions
The contamination of Lake Michigai
alewife and lake trout by PCB can b
adequately modeled using an age
dependent computation that consider
species bioenergetics and uptake of PCI
from water and food. The mode
successfully reproduces the age
dependent trends and magnitude of PCI
contamination observed in 1971.
Both the model and the PCB dat
compiled for this study indicate that foo
chain transfer is a significant route c
contamination. Data from 13 species c
fish suggest an increase in PCI
concentration as one proceeds up th
food chain to the top predators. Transfe
of PCB through the food chain is th
major contributor to calculated PCB cor
centrations, accounting for greater tha
99% of the body burden in adult lak
trout. A simple steady-state computatio
indicates that ratios of chemical concer
tration in predators to that in prey i
feeding experiments may be as lowasO.
and still result in appreciable food chai
transfer.
An empirical relationship between lak
trout excretion rate and lipid conter
significantly improved the lake trout cal
bration, suggesting that lipid tissue is a
important factor in PCB dynamics.
A simple empirical correlation betwee
octanol/water partitioning of PCB an
partitioning between water and fish hpi
tissue failed to reproduce the observe
concentrations in alewife and lake trou
It is concluded that although this simpl
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partitioning approach may be useful in
assessing trends, it cannot estimate
actual concentrations, especially in higher
trophic level species, because it does not
consider food chain transfer
Projections of the response of the lake
trout food chain to reduced water concen-
trations indicate that a period of about 5
years is needed to reduce whole body
PCB concentrations in upper age class
lake trout. In order to have the PCB
concentrations of all age classes of lake
trout at or below 5 /ug/g(w) in the edible
portion, it is estimated that the dissolved
water concentrations would have to be.
; between 0.5-2.5 ng/L.The range results:j
from the uncertainty of the parameter'
values m the model. These water
concentrations represent a 75-95%
reduction of apparent 1961-1971 water
concentrations. Young age classes can
generally be exposed to higher water PCB
concentrations than older age classes
without exceeding the objective of 5
yug/g(w) As a result, if water quality pro-
jections indicate a lower bound in the
achievable PCB water concentrations, a
size-dependent fish consumption guide-
line can be developed
Recommendations
This analysis of the PCB contamination
of a Lake Michigan food chain has illus-
trated gaps of knowledge that add
uncertamtytothe estimation of the effect
of concentration reductions. These gaps
are most significant in regard to the
compound-related parameters needed by
the model, i.e..assimilation efficiency and
excretion rate It is therefore
recommended that experimental investi-
gations be conducted to more accurately
determine these parameters. Of signifi-
cant value would be relationships, both
within and across species, between these
parameters and characteristics of the
compound and species, e.g., octanol/
water partition coefficient and % lipid.
Additional significant gaps of
knowledge are the PCB concentrations of
the invertebrate and plankton compon-
ents of the food chain and accurate
estimates of the water concentration.
Differences were found between
growth rates of pre-stocked and stocked
lake trout. The model was shown to be
sensitive to these differences. It is
recommended that lake trout growth rate
be investigated to provide an accurate
estimate that will decrease uncertainty in
the model projections
An empirical relationship between lake
trout excretion rate and % lipid signifi-
cantly improved the model calibration
suggesting that lipid content is an
important factor in accumulation. It is
recommended that the model structure
be modified to include a more
fundamental description of lipid, possibly
separating the species into lipid and non-
lipid components.
The sediment of Lake Michigan
contains a substantial quantity of PCB
Because the sediment responds more
slowly to reductions in PCB loading than
does the water column, it will have signif-
icant PCB concentrations even when
water column concentrations decline to
some "acceptable" level A significant
question, then, is the extent to which
benthic fauna may transfer this
sediment PCB to the pelagic food chain,
thus mitigating the concentration
reduction in that food chain This
question should be addressed by
including a benthic component in the
food chain
The food chain model was calibrated to
data collected in 1971. Data are also
available through 1979. These data
indicate a decline of lake trout PCB
concentrations after 1975. A further
calibration of the model, using these data,
would increase confidence in its
prediction capability It is also
recommended that the model be applied
to other chemicals for which a sufficient
data base exists. This would test the
applicability of the model as a general
framework for assessing the response of
the food chain to toxic substances
exposure
R. V. ThomannandJ. P. Connolly are with Manhattan College. Bronx, NY 10471.
W. L. Richardson is the EPA Project Officer (see below).
The complete report, entitled "An Age~Dependent Model of PCB in a Lake
Michigan Food Chain," (Order No. PB 84-155 993; Cost: $13.00, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Research Laboratory—Du/uth (LLRS)
U.S. Environmental Protection Agency
9311 Groh Road
Grosselle, Ml 48138
*US GOVERNMENT PRINTING OFFICE. 1985 — 559-016/7895
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