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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