United States
Environmental Protection
Agency
Environmental Research
Laboratory
Athens, GA 30613
V
Research and Development
EPA/600/S3-87/038 Apr. 1988
ve/EPA Project Summary
FGETS (Food and Gill
Exchange of Toxic Substances):
A Simulation Model for
Predicting Bioaccumulationof
Nonpolar Organic Pollutants by
Fish
M. Craig Barber, Luis A. Suarez, and Ray R. Lassiter
A FORTRAN program that
simulates the kinetic exchange of a
nonpolar, nonmetabolized organic
chemical across fish gills and from
contaminant food is described. The
program is based on a set of
diffusion and forced convection
differential equations. Gill
morphometric and physiological
parameters are estimated by the
program via two internal databases.
The database of gill morphometry
spans approximately 30 species,
whereas the physiological database
presently is complete only for
salmonid fishes and rainbow trout
(Sa/mo gairdneri).
This Projedt Summary was
developed by EPA's Environmental
Research Laboratory, Athens, GA, to
announce key findings of the
research project that is fully
documented in a separate report (see
Project Report ordering information
at back).
Introduction
When aquatic ecosystems are
polluted with organic chemicals, fish in
those systems will bioaccumulate such
substances both directly from the water
and from their prey, which have likewise
become contaminated with the
chemicals. For benthic species,
chemicals also may be accumulated by
dermal contact with contaminated
sediments. If these chemicals are not
metabolized, then their ultimate
concentrations in fish should be
predictable based on principles of
thermodynamic partitioning. The purpose
of this work is to present a dynamic
model, FGETS (Food and Gill Exchange
of Toxic Substances), that describes
thermodynamically driven bio-
accumulation of nonmetabolized organic
toxicants by fish. This work is an
extension of a previously published
model, GETS, which describes the
uptake and depuration of organic
toxicants across fish gills.
Development of the FGETS model is
part of a four-laboratory ecological risk
assessment research program.
Contributing to the research program are
scientists at EPA's Environmental
Research Laboratories in Athens, GA,
Corvallis, OR, Duluth, MN, and Gulf
Breeze, FL.
FGETS itself is a FORTRAN
simulation model that predicts temporal
dynamics of a fish's whole body
concentration, Cf (ppm = pg chemical/g
live weight fish), of a nonmetabolized,
organic chemical. The chemical is
bioaccumulated either from water only,
which is, perhaps, the predominant route
of exchange during acute exposures.or
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from water and food jointly, which is the
more characteristic route for chronic
exposures. These dynamics are
calculated algebraically as the ratio of the
fish's predicted total body burden, Bf =
ng chemical/fish, to its live weight, W =
g live/fish. The dynamics are simulated
by a system of coupled differential
equations.
In particular, fish growth is modeled
using the mass balance equation,
dW/dt = F-E-R-SDA
d)
where:
F = fish's feeding fluxes (g/day)
E = fish's egestive fluxes (g/day)
R = fish's respiratory fluxes
(g/day)
SDA = fish's specific dynamic
action (g/day)
The total body burden of a fish is
modeled by
dBf/dt = S J. + J,
(2)
where:
Se = the fish's total gill area
(cm2)
Jg = the net diffusive flux across
the gills (ng/cm2/day)
J, = the net mass exchange
across the fish's intestine
from food (ng/day)
kw = the chemical's mass
conductance through the
interlamellar water of the
gills (cm/day)
Cw = the chemical's concen-
tration in the
environmental water
(ppm)
Ca = the chemical's concen-
tration in the fish's
aqueous blood (ppm)
The gill exchange portion of equation
2 is simply a direct application of Pick's
first law of diffusion FGETS allows a
user to select one of three possible
model formulations to represent chemical
exchange from food. In particular, J, can
be modeled assuming either a constant
toxicant assimilation efficiency, in which
the fish's feces and whole body are
thermodynamically equilibrated, or a
kinetic expression of Pick's first law of
diffusion.
To use equation 2, a functional
relationship between a chemical's
concentration in whole fish and its
aqueous fraction must be specified. To
this end, fish are treated conceptually as
a three-phase solvent consisting of
water, lipid, and structural organic matter.
It is further assumed that equilibration
between these phases is rapid in
comparison to exchange across the fish's
gills and intestine. Consequently, the
fish's whole body concentration of the
chemical can be written as
Cf = Bf/W =
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kthe difference between a fish's
Dhysiological and anatomical surface
areas.
Any initial whole body concentration,
Cf, of the chemical in the fish may be
specified by the user. The chemical's
aqueous environmental concentration,
Cw, can be input as either an arbitrary
time series or as a constant, sinusoidal
or exponential function of exposure time.
Chemical concentrations in the prey (Cp)
are assumed to be a fixed proportion of
that predicted by thermodynamic
equilibrium. This proportion can be either
less than or greater than unity (i.e.,
biomagnification of prey can be
specified). Consequently, the user can
analyze a myriad of possible exposure
scenarios.
Prospectus
FGETS has been preliminarily
validated and appears capable of
predicting dynamic internal body
concentrations of organic chemicals in
fish. This capability is important when
chemical exchange between fish and
their environment becomes kinetically
limiting either by the physicochemical
properties of the chemical (e.g., high
logP or low water solubility) or by
allometric propertie of the fish (e.g.,
, dynamic surface to volume ratios)
because it is actually the chemical's
concentration within the fish at specific or
nonspecific sites of action that elicit
acute or chronic ecological/physiological
effects.
Additionally, the ability of FGETS to
predict dynamics of bioaccumulation of
organic chemicals in fish offers a
powerful tool to assess potential food
chain exposure for terrestrial fish-eating
organisms. For example, if the use of a
particular chlorinated organic pesticide
was banned within a river basin, one
could determine when the pesticide's
concentration might no longer pose a
health risk to man or an environmental
threat to bald eagles or other piscivorous
birds in the region.
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The EPA authors, M. Craig Barber (also the EPA Project Officer, see below),
Luis A. Suarez, and Ray R. Lassiter, are with Environmental Research
Laboratory, Athens, GA 30613.
The complete report, entitled "FGETS (Food and Gill Exchange of Toxic
Substances): A Simulation Model for Predicting Bioaccumulation of Nonpolar
Organic Pollutants by Fish," (Order No. PB 88-133 558/AS; Cost: $14.95,
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
U.S. Environmental Protection Agency
Athens, GA 30613
United States
Environmental Protection
Agency
U.S. OFFICIAL MA
Center for Environmental Research
Information
Cincinnati OH 45268
V PERMIT jfo (5-5&=ll -2 5
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Official Business
Penalty for Private Use $300
EPA/600/S3-87/038
0000329 PS
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•ft- U.S. GOVERNMENT PRINTING OFFICE- 1988—548-013/87038
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