United States
[Environmental Protection
Agency
Environmental Research
Laboratory
Athens, GA 30613-7799
Research and Development
EPA/600/S3-91/019 April 1991
iSrEPA Project Summary
Preliminary Testing, Evaluation
and Sensitivity Analysis for the
Terrestrial Ecosystem Exposure
Assessment Model (TEEAM)
Sandra L. Bird, J. Mark Cheplick, and David S. Brown
This report documents an Initial test-
ing and sensitivity analysis of the Ter-
restrial Ecosystem Exposure Assess-
ment Model (TEEAM). TEEAM calcu-
lates the exposure concentrations of
plants and animals to contaminants in
terrestrial ecosystems.
This project was performed in two
phases. First, a sensitivity analysis
was performed using a simple system-
-an American robin inhabiting a typical
peanut field in Georgia that had been
treated with diazinon. The primary food
source for the robin was the earth-
worms living in the pesticide-contami-
nated soil. Second, an intensive model
testing and evaluation effort was un-
dertaken to examine each major model
component. Results of the testing
suggest that continued model develop-
ment should focus on better simula-
tion of surface ponding, plant trans-
port, and uptake by soil dweller and
aboveground insect populations.
This Project 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 of the same title (see Project
Report ordering information at back).
Introduction
Understanding the impacts of pesticides
and other toxic substances on wildlife is a
significant environmental concern. The
Terrestrial Ecosystem Exposure Assess-
ment Model (TEEAM) was developed to
allow the environmental analyst to com-
pute the level of wildlife exposure in
evaluating the registration or regulation of
specific pesticides. TEEAM is a logical
extension of the Pesticide Root Zone
Model (PRZM), which estimates pesticide
leaching and runoff from agricultural wa-
tersheds. TEEAM couples the physical
transport processes represented in PRZM
with transport into plants, soil-dwelling or-
ganisms, and wildlife. It is a short-term
exposure model with a weekly to sea-
sonal time frame with particular emphasis
on 30-day exposure scenarios.
This report documents the initial test-
ing, debugging, and sensitivity analysis
for the TEEAM model. The analysis was
performed in two phases. First, under
contract to USEPA's Woodward-Clyde, the
developer of the original model, performed
a sensitivity analysis on the model for a
simple ecosystem, i.e., an American robin
inhabiting a typical commerical peanut
production field in Georgia that had been
treated with diazinon. The primary food
source for the robin was earthworms living
in the treated soil. Second, an intensive
model testing and evaluation effort was
undertaken by the Assessment Branch,
Environmental Research Laboratory, Ath-
ens, GA.
Model Overview
The TEEAM model simulates (1) toxi-
cant application/deposition; (2) soil and
atmospheric transport and transformation;
(3) plant growth, uptake, translocation, and
fate; and (4) terrestrial food chain
bioaccumulation and biomagnification
processes. Calculations are made in a
time-variable mode and temporal resolu-
tion is on a daily basis. A schematic of
j Printed on Recycled Paper
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Rainfall
\ ',' i% t ; \ Spray Application
'
i'Hl
Evapotranspiration^
Foliar
Application
Inhalation
Animal Pesticide
Degradation
Granular/Ground Spray/Soil
Application
Volatilization
Evaporation
Evapotranspiration
A
Volatilization
Soil Pesticide
Degradation
*- water movement
pesticide movement
Figure 1. Processes represented in TEEAM.
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processes represented in the model is
shown in Figure 1.
Simulation of the principal model pro-
cesses are handled by five computational
subprograms. A toxicant application/
deposition submodel calculates a spatial
distribution of a pesticide based on me-
teorological factors and application tech-
niques. This submodel contains FSCBG,
a model developed by the USDA's Forest
Service to compute spray drift from aerial
applications, that includes options for
simulating the direct application of chemi-
cal to foliage, soil surfaces or subsurfaces,
and for evaluating a time release granular
formulation.
A terrestrial fate subprogram (TFAT)
calculates the system water balance;
movement of contaminant in the soil root
zone; and loss of contaminant from the
soil through degradation, volatilization,
plant uptake, runoff and erosion. TFAT is
based on the PRZM model with enhance-
ments to calculate volatilization and losses
through surface pond formation.
Plant growth is simulated to predict the
deposition of contaminant on the canopy
and soil and the uptake and translocation
of contaminants from the soil into the plant
either to estimate animal exposure, to
predict direct effects on plants themselves,
or to adjust the total mass balance. The
plant growth model in TEEAM was adapted
from the USDA's Erosion Productivity
Calculator (EPIC).
The plant contaminant transport module
calculates the amount of contaminant that
enters the plant and the concentration of
contaminant within and on the plant bio-
mass. Plant transport is simulated as a
two-compartment model, i.e., above-
ground plant parts and below-ground roots.
No distinction is made at present between
different above-ground plant parts.
The animal pesticide uptake module
calculates dosage to, and concentration
of, pesticides in soil-dwelling organisms
and above-ground habitat-mobile organ-
isms. Calculations made in previous
modules provide concentrations of toxi-
cant in the medium that the animal in-
gests. In addition, food chains may be
specified, and animal exposure may occur
by ingestion of prey animals. Above-
ground animals may move between habi-
tats, and media concentrations are calcu-
lated in each of these habitats as de-
scribed above.
Ftesults of Sensitivity Study
A sensitivity analysis for a robin living in
a single habitat eating earthworms in a
diazinon-treated field was performed al-
lowing variation of 19 input variables with
500 Monte Carlo simulations. Parameters
that were allowed to vary include: soil
bulk density, adsorption partition coeffi-
cient, wilting point water content, field ca-
pacity water content, soil hydraulic con-
ductivity, decay rate in soil, decay rate on
foliage, Henry's Law constant, pesticide
application rate, root reflection coefficient,
decay rate in plants, octanol water parti-
tion coefficient, runoff curve number,
bioconcentration factor for earthworms,
metabolic degradation rate in target spe-
cies, total feeding rate, soil preference
factor, pond water ingestion rate, and air
inhalation rate.
For this simple example, the most im-
portant parameters controlling dosage to
and concentration within the robin was
total application mass, bioconcentration
factor for earthworms, total feeding rate,
soil bulk density, decay rate in soil, soil
preference factor, and soil pesticide parti-
tion coefficient. However, these results
are for a very simple system and are
specific to the particular system. Chemi-
cal properties and specifics of the organ-
isms would greatly alter the parameters to
which the system is sensitive.
Module Testing
Response of each transport function in
TEEAM was tested and evaluated sepa-
rately. First, the TFAT portion of TEEAM
was compared to PRZM results for a
nonvolatile pesticide under conditions
where ponding did not occur, i.e., condi-
tions where TEEAM results should repli-
cate PRZM results. TEEAM performance
was satisfactory in this basic comparison
to PRZM.
Next, TFAT performance for the two
major modifications to PRZM, i.e., pond
formation and chemical volatilization were
evaluated by (1) examining the response
of pond formation with respect to soil
characteristics and meteorological condi-
tions and (2) examining the response of
volatilization flux to Henry's Law constant
for the chemical and meteorological con-
ditions.
The ponding formulation in TEEAM must
be parameterized in a counterintuitive way
in order for ponds to form; i.e., ponding
occurs only when SCS curve number val-
ues are set at values for a soil with a
large infiltration capacity. This approach
is not satisfactory for development of a
model with a prior predictive capability.
Volatilization fluxes increased proportion-
ally to an increase in Henry's Law con-
stant as expected. Volatilization fluxes
decreased during rainfall events. For some
chemicals, volatilization losses from soil
have been shown to be lowest under
drought conditions indicating that TEEAM's
volatilization algorithm may need some
modification.
Total uptake of pesticide by plants was
somewhat different for PRZM and TEEAM.
PRZM does not allow uptake of pesticide
by the plant from the surface layer whereas
TEEAM does. The presence of roots near
the soil surface is dependent on the spe-
cies of plant and seasonal moisture pat-
terns. TEEAM calculates the concentration
of pesticide within the plant in addition to
uptake of pesticide by the plant. Response
of concentration in the plant as a function
of soil Kd, chemical K^, and plant type was
evaluated. Two limitations were identified
in the plant transport module. First, the
formulation does not allow for calculation
of differential above-ground plant part, e.g.,
stems and leaves, concentrations. Sec-
ond, the formulation does not calculate
loss from the leaf surface as a function of
a chemical characteristic, i.e., Henry's Law
constant, reducing the potential predictive
capability of the approach.
Response of concentrations in soil-
dwelling organisms and above-ground
habitat-mobile organisms to biocon-
centration factors, metabolic degradation
rates, Henry's Law constant, and assimi-
lation efficiency were evaluated. Im-
provements to the animal uptake module
that should be performed fall into three
categories. First, uptake of pesticide for
all organisms should be based on formu-
lations using chemical properties and bio-
logical characteristics of the organism.
Currently, assimilation of contaminant by
the animals is an empirical factor specific
for a given chemical, organism, and
chemical concentration. Second, soil
dwelling organism uptake should be for-
mulated based on soil ingestion rates. Fi-
nally, formulations specifically for above-
ground insects, ingestion of which can be
a major exposure route for birds, should
be included in the model.
.S. GOVERNMENT PRINTING OFFICE: 199 ! /548-028/2020 I
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Sandra L Bird (the EPA Project Officer, see below) and David S. Brown are with
the Environmental Research Laboratory, Athens, GA 30613-7799; J. Mark
Cheplick is with Computer Sciences Corporation, Athens, GA 30613,
The complete report, entitled "Preliminary Testing, Evaluation and Sensitivity
Analysis for the Terrestrial Exposure Assessment Model (TEEAM)," (Order No.
PB91-161 711/AS; Cost: $23.00 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
U.S. Environmental Protection Agency
Athens, GA 30613-77999
United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
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EPA/600/S3-91/019
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