\' I
United States
Environmental Protection
Agency
Environmental Research
Laboratory
Gulf Breeze FL 32561
Research and Development
EPA/600/S4-85/040 Aug. 1985
&ER& Project Summary
WASTOX, A Framework for
Modeling the Fate of
Toxic Chemicals in
Aquatic Environments:
Part 2. Food Chain
John P. Connolly and Robert V. Thomann
A food chain bioaccumulation mathe-
matical framework was developed as
part of a broader framework for model-
ing the fate of toxic chemicals in natural
water systems, entitled WASTOX. A
user's guide for WASTOX was pub-
lished in August 1984 as Part 1 of this
report (1).
The food chain component of WAS-
TOX described here is a generalized
model for estimating the uptake and
elimination of toxic chemicals by
aquatic organisms. Rates of uptake and
elimination are related to the bioen-
ergetic parameters of the species en-
compassed in either a linear food chain
or a food web. Concentrations are cal-
culated as a function of time and age for
each species included. Exposure to the
toxic chemical in food is based on a
consumption rate and predator-prey re-
lationships that are specified as a func-
tion of age. Exposure to the toxic chem-
ical in water is functionally related to
the respiration rate. Steady-state con-
centrations may also be calculated.
Food chain exposure to chemicals
may be specified by the user of the
model or may be taken directly from
the values calculated by the exposure
concentration component of WASTOX.
Migratory species, as well as nonmigra-
tory species, may be considered.
The model has been successfully
used to model Kepone in the James
River striped bass food chain and PCBs
in the Lake Michigan lake trout food
chain and Saginaw Bay, Lake Huron yel-
low perch food.
This Project Summary was devel-
oped by EPA's Environmental Research
Laboratory, Gulf Breeze, FL, to an-
nounce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
The hazard posed to a natural water
system by a toxic chemical is governed
by the uptake of the chemical by the
resident biota and subsequent acute
and chronic health effects. Evaluation of
the hazard involves three steps pro-
ceeding from the specification of the
rate of chemical discharge to the sys-
tem:
1) estimation of the chemical concen-
trations in the water and sediment
2) estimation of the rate of uptake of
chemical by segments of the resi-
dent biota
3) estimation of the toxicity resulting
from uptake of the chemical.
Execution of each step in this hazard
assessment requires consideration of
the transport, transfer, and reaction of
the chemical and the dependence of
these processes on properties of the af-
fected natural water system and its
biota. Based on experimentation and
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theoretical development, each process
has been, or can be, described mathe-
matically, specifying its functional de-
pendence on specific properties. These
expressions may be combined, using
the principle of conservation of mass, to
form a mathematical model that ad-
dresses one of the steps in the hazard
assessment.
Steps 1 and 2 of this hazard assess-
ment are addressed by the general
modeling framework entitled WASTOX,
an acronym for Water (Quality) Analysis
Simulation for TOXics. This modeling
framework is composed of two parts
which may be termed the exposure con-
centration and food chain components,
respectively.
The exposure concentration compo-
nent is the computational structure for
applying step 1 to a specific natural
water system, as described in Part 1 of
this report published in August, 1984
(1). The food chain component de-
scribed in this report is the computa-
tional structure for applying step 2 to a
specific natural water system. Both
components were developed to deter-
mine the fate of toxic chemicals in estu-
aries (CR807827) and the Great Lakes
(CR807853).
Model Framework
The concentration of a toxic sub-
stance that is observed in an aquatic or-
ganism is the result of several uptake
and loss processes that include: trans-
fer across the gills, surface sorption, in-
gestion of contaminated food, desorp-
tion, metabolism, excretion and growth.
These processes are controlled by the
bioenergetics of the organisms and the
chemical and physical characteristics of
the toxic substance. The equations used
to describe these processes were for-
mulated by Norstrom et al. (2) and
Weininger (3) and for food chain by
Thomann (4) and Thomann and Con-
nolly (5).
For phytoplankton and detrital or-
ganic material representative of the
base of the food chain, sorption-
desorption controls toxic substance ac-
cumulation. Instantaneous equilibrium
is assumed because the sorption rates
are generally much faster than the up-
take and excretion rates of higher levels
of the food chain and the transport and
transformation rates of the toxic sub-
stance. The concentration of chemical
in phytoplankton detritus is computed
as the product of a user specified parti-
tion coefficient and the dissolved chem-
ical concentration.
For species above the phytoplankton/
detritus level, uptake of toxicant due to
ingestion of contaminated food must be
considered. This uptake will depend on
a) toxicant concentration in the food,
b) rate of consumption of food, and
c) the degree to which the ingested tox-
icant in the food is actually assimilated
into the tissues.
The rate of consumption of food is
computed from user specified respira-
tion and growth rates and food assimi-
lation efficiency. The uptake of toxicant
from water by these species is deter-
mined by the rate of transfer of toxicant
across the gills. This rate of transfer is
calculated from the rate of transfer of
oxygen from water to the blood of the
fish.
The rate of loss of the toxicant from
an organism is the sum of the excretion
and detoxification or degradation rates
of the chemical. If the organism is ex-
posed to the toxicant in water only, this
rate is related to the uptake rate by the
bioconcentration factor.
In the model the excretion rate may
be internally calculated from a specified
bioconcentration factor or it may be
specified. If it is specified directly, the
equivalent bioconcentration factor will
decrease during an age class. The up-
take rate decreases as a function of
weight because the respiration is de-
pendent on weight. If the excretion rate
is constant for an age class, the result is
a decreasing bioconcentration factor.
The processes mentioned above are
defined by bioenergetic and chemical
related parameters. In addition, the vari-
ation of these parameters with age and
the feeding habits of each species mod-
eled must be specified.
Feeding habits are generally discon-
tinuous functions of age. The prey size
or prey species generally change as an
organism grows. Life span is separated
into age classes in which the predator-
prey relationships are assumed to be
constant.
Species at the lower end of the food
chain tend to exhibit a concentration of
chemical that does not vary with age.
Their relatively rapid uptake and excre-
tion rates, and the lack of a major diet
change with age, cause them to achieve
equilibrium with the chemical in a short
time relative to their life span. This fact
justifies the use of an equilibrium or
steady-state modeling approach for
these species. For each species in the
model, the user may choose to calcu late
either a steady-state concentration or
the concentration distribution with age.
The specific parameter requirements
for each species in the model are listed
in Table 1.
Table 1. Input requirements for each
species included in the food
chain model
Bioenergetic Related Parameters:
growth rate
respiration rate
assimilation efficiency of food
predator-prey relationships
Toxic Chemical Related Parameters:
assimilation efficiency of chemical in
food; molecular diffusivity of the toxic
chemical; bioconcentration factor or
whole body excretion rate
If migratory species are modeled,
then the spatial variability of the toxic
chemical and the seasonal movement
of the species must be considered. This
is accomplished through the use of
"spatial compartments." The water
body or system is separated into com-
partments in which the toxic chemical
concentration is assumed to be con-
stant. Nonmigratory food chains are
specified for each compartment reflect-
ing the predator-prey relationships in
that region of the system. The migratory
species is exposed sequentially to each
of these food chains in a pattern that
reflects its seasonal movement.
To facilitate interfacing the food chain
model with the exposure concentration
component of WASTOX, the toxic
chemical concentration in each spatial
compartment is computed as the arith-
metic average of the segments in the
exposure concentration component
that lie within the spatial compartment.
Water column and sediment segments
are averaged separately to provide con-
centrations for the pelagic and benthic
components of the food chain.
Model Application
The food chain component of WAS-
WASTOX has been applied to the fol-
lowing chemicals and food chains:
1) PCB—Lake Michigan lake trout
food chain
2) Kepone—James River, VA, striped
bass food chain
In the PCB-lake trout application, a
single spatial compartment was consid-
ered and the model was calibrated for a
single year, 1970. The model compared
favorably with concentration in each
level of the food chain and with the age
distribution of concentration in alewife
and lake trout.
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In the Kepone-striped bass applica-
tion two spatial compartments account
for migration of atlantic croaker and
striped bass. The model was calibrated
to a seven-year time-history of data. The
model reproduced the observed within-
year and year-to-year concentration
variations for all three fish species con-
sidered: white perch, atlantic croaker,
and striped bass. The calibrated model
was used to project the response of the
food chain to reductions in water
umn and sediment chemical concentra-
tions for both applications.
Conclusions
WASTOX is a framework for model-
ing toxic chemicals in natural water
system that is generally useful in devel-
opment of a model for a specific appli-
cation. The food chain component can
simulate any food web configuration.
The successful use of the food chain
component in modeling both lake and
estuarine food chains demonstrates its
validity and wide-range applicability.
References
1. Connolly, J. P., and R. P. Winfield.
1984. A User's Guide for WASTOX, A
Framework for Modelling the Fate of
Toxic Chemicals in Aquatic Environ-
ments, Part 1: Exposure Concentra-
tion. Manhattan College, Department
of Engineering and Science, Bronx,
NY, 10471.
2. Norstrom, R. J., A. E. McKinnon, and
A. S. W. DeFreitas, 1976. A bioen-
ergetics based model for pollutant
accumulation in fish: Simulation of
PCB and methyl mercury residue lev-
els in Ottawa River yellow perch
(Perca flavescens). J. Fish. Res. Bd.
Can. 33(3):280-296.
3. Weininger, D. 1978. Accumulation of
PCBs by lake trout in Lake Michigan.
Ph.D. Thesis, The University of
Wisconsin-Madison, 232 p.
4. Thomann, R. V. 1981. Equilibrium
model of the fate of microcontami-
nants in diverse aquatic food chains.
Can. J. Fish. Aquat. Sci., 3S(3):280-
296.
5. Thomann, R. V. and J. P. Connolly.
1983. A model of PCB in the Lake
Michigan lake trout food chain. Envi-
ron. Sci. Technol.
J. P. Connolly and Robert V. Thomann are with Manhattan College, Bronx, NY
10571.
P. H. Pritchard and W. L. Richardson are the EPA Project Officers (see below).
The complete report, entitled "WASTOX, A Framework for Modeling the Fate of
Toxic Chemicals in Aquatic Environments: Part 2. Food Chain," (Order No. PB
85-214 435/AS; Cost: $10.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road •
Springfield, VA 22161
Telephone: 703-487-4650
P. H. Pritchard can be contacted at:
Environmental Research Laboratory
U.S. Environmental Protection Agency
Gulf Breeze, FL 32561
W. L. Richardson can be contacted at:
Environmental Research Laboratory
U.S. Environmental Protection Agency
620 J Congdon Blvd.
Duluth, MN 55804
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United States Center for Environmental Research
Environmental Protection Information
Agency Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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