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GENEEC User's Manual

(GEN)ERIC (E)STIMATED (E)NVIRONMENTAL (C)ONCENTRATION MODEL

Environmental Fate and Effects Division
Office of Pesticide Programs
U.S. Environmental Protection Agency

Tier One Screening Model for Pesticide Aquatic Ecological Exposure Assessment

Version 2.0

August 1, 2001

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Introduction to GENEEC Version 2.0

August 1, 2001

GENEEC Version 2.0 is an update of GENEEC Version 1.2 (Parker et. al., 1995) which was issued by the USEPA Office of Pesticide Programs (OPP) Environmental Fate and Effects Division (EFED) in May 1995 for use in tier 1, screening level pesticide aquatic ecological risk assessments. Version 2 was developed in response to suggestions by users for improvements, by the desire to stay current with the newer versions of the PRZM (Carsel, 1997) and EXAMS (Burns, 2000) programs upon which GENEEC is based and by availability of much improved data on spray drift and quantitative methods of estimation of offsite spray drift developed by the Spray Drift Task Force (SDTF). The main differences between versions 1.2 and 2.0 include:

  1. an entirely new binding curve to represent dissolved concentration as a function of Kd

  2. the use of the binding parameter, Kd in preference to Koc to represent pesticide attachment to soil, to organic matter or to water-body bottom sediments

  3. changes in the recommendation for depth of incorporation

  4. a change in the timing of the single event rainstorm for chemicals which receive multiple applications

  5. addition of a subroutine from the SDTF to estimate spray drift

  6. a change in the time durations of the output values to better match the durations of relevant toxicity tests.

For additional details see, "Development and Use of GENEEC Version 2.0 for Pesticide Aquatic Ecological Exposure Assessment".

EFED uses a tiered system of pesticide exposure modeling to assess risk of a pesticidal product to the environment. This tiered system is designed to minimize the amount of analysis which is required to register any given chemical. Each of the tiers is designed to screen out pesticides by requiring higher, more complex levels of investigation only for those that have not passed the next lower tier. Each tier screens out a percentage of pesticides from having to undergo a more rigorous review prior to registration or reregistration.

The GENEEC (GENeric Estimated Environmental Concentration) model, the tier one computer program, uses the soil/water partition coefficient and degradation kinetic data to estimate runoff from a ten hectare field into a one hectare by two meter deep "standard" pond. This first tier is designed as a coarse screen and estimates conservative pesticide concentrations in surface water from a few basic chemical parameters and pesticide label use and application information. Tier 1 is used to screen chemicals to determine which ones potentially pose sufficient risk to warrant higher level modeling. Chemicals failing to pass this program, move on to the tier two modeling. As a matter of policy, OPP does not take significant adverse regulatory action based upon the results of tier 1 screening models.

GENEEC is a program to calculate acute as well as longer-term estimated environmental concentration (EEC) values. It considers reduction in dissolved pesticide concentration due to adsorption of pesticide to soil or sediment, incorporation, degradation in soil before washoff to a water body, direct deposition of spray drift into the water body, and degradation of the pesticide within the water body. It is designed to mimic a PRZM-EXAMS simulation.

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Running GENEEC Version 2.0

The following description provides the screen images which the GENEEC program produces, with a " ---> " at each point where the user needs to provide input. The bold text incorporated throughout is instructions on selecting and entering data and running the program.

Begin by creating a subdirectory called "GENEEC2" on your hard drive and copy the program "GENEEC2.EXE" to that subdirectory. Then, while in DOS, go to that subdirectory (C:\>cd GENEEC2) to run the program.

Type "GENEEC2" and press "Enter" to get the following screen:

GENEEC

ENVIRONMENTAL FATE AND EFFECTS DIVISION
OFFICE OF PESTICIDE PROGRAMS
U.S. ENVIRONMENTAL PROTECTION AGENCY

TIER ONE SCREENING MODEL
FOR PESTICIDE AQUATIC ECOLOGICAL
EXPOSURE ASSESSMENT

VERSION 2.0

AUG 1, 2001

THIS PROGRAM IS DESIGNED TO CALCULATE A SET OF SCREENING LEVEL
GENERIC ESTIMATED ENVIRONMENTAL CONCENTRATION (EEC) VALUES
RESULTING FROM RUNOFF FROM A TEN HECTARE TREATED AGRICULTURAL
FIELD INTO A ONE HECTARE BY TWO METER DEEP STATIC WATER BODY

GENEEC IS USED TO ESTIMATE CONSERVATIVE PESTICIDE CONCENTRATION
VALUES FOR AQUATIC ECOLOGICAL EXPOSURE ASSESSMENT

PLEASE ENTER A RUN NUMBER TO CONTINUE --->

The run number is a book-keeping aid to allow the user to keep track of multiple consecutive runs; any integer may be entered. This number will appear on the output screen and in the output file to identify each run of the program.

PLEASE SELECT AN OUTPUT FILE NAME --->

The choice of a name for the output file is up to the user, but must be in standard DOS format with eight (8) or fewer alphanumeric characters, followed by a dot "." and then three (3) alphameric characters. Examples of output file names might be: CAPTAN1.OUT or CAPTAN2.OUT. If the same output file name is used in successive runs, the new output file will write over the old file and the old one will be lost. To save an older output file, give each new file a new, different name.

The output file will be stored in the GENEEC2 subdirectory. If the subdirectory and program are on the C:\ drive, the output file will be C:\GENEEC2 \CAPTAN1.OUT. If you run the program again, and use the same output file name, it will write directly over the old file, and any previous results will be lost unless they have been retrieved and stored elsewhere. See below for retrieving output files with WordPerfect®. Once retrieved and saved as a WordPerfect® file to another subdirectory, the "output" file in GENEEC2 can be safely overwritten.

PLEASE ENTER THE CHEMICAL NAME --->

Use either the common or chemical name. The structure is optional; use whatever is the most easily understood. This name will appear on the output screen and in the output file to identify the chemical and will be printed when the output file is printed out (using either a DOS printer, or WordPerfect®).

PLEASE ENTER THE CROP NAME --->

Enter the name of the crop being modeled. This name will appear on the output screen and in the output file to identify the crop on which the pesticide is applied and will be printed when the output file is printed out (using either a DOS printer, or WordPerfect®).

The "standard farm pond" simulated in this program is assumed to be static in that inflow to the pond is equally balanced by evaporation from the pond so that the pond volume remains constant.

THE PROGRAM ASSUMES THAT RAINFALL AND RESULTING RUNOFF ARE
SUFFICIENT TO REMOVE UP TO TEN PERCENT OF THE PESTICIDE
FROM THE TEN HECTARE TREATED AGRICULTURAL FIELD

THE PORTION OF THE CHEMICAL WHICH IS REMOVED FROM THE FIELD
IN THIS WAY, FLOWS INTO THE POND AND IS DISSOLVED IN THE POND WATER

THE CHEMICAL CONCENTRATION IN THE POND REPRESENTS THE PART
WHICH IS DISSOLVED AND NOT BOUND TO FIELD SOIL OR TO POND BOTTOM SEDIMENTS

THE FOLLOWING INFORMATION SHOULD BE TAKEN FROM THE MOST
CURRENT, ACCEPTED LABEL FOR THE USE SITE IN QUESTION

PLEASE ENTER APPLICATION RATE (IN POUNDS a.i./ ACRE)--->

In most cases, this will be the maximum rate permitted by the label. Situations may also arise when it is desirable to use an average or typical application rate or some other rate less than the maximum rate. To use a rate in units of kilograms per hectare, enter a value of "zero" (0) at the prompt.

ENTER MAXIMUM NUMBER OF APPLICATIONS PERMITTED PER YEAR--->

The maximum number of applications or maximum pounds of pesticide is included in most labels. If the maximum annual mass is given on the label, divide this by the application rate to find the number of applications. A situation may also arise when it is desirable to use an average or typical number of applications. If the number of applications entered is greater than one, the following will be requested:

PLEASE ENTER INTERVAL BETWEEN APPLICATIONS (DAYS)--->

Use the minimum interval permitted by the label or the typical interval in practice in the area of use, whichever is most appropriate. If not specified on the label, the interval is available directly from the registrant or from county extension agents in use areas.

The program assumes the pesticide degrades in the field by the aerobic soil metabolism rate between multiple applications and for two days following the final application. The actual amount of pesticide that is available in the field to be washed into the pond is the amount remaining in the treated field two days after the final application. (The period after the final application is set to zero days for pesticides for which the label specifies application just prior to rainfall or irrigation).

THE DISSOLVED PESTICIDE CONCENTRATION IN THE POND IS
CALCULATED BY SUBTRACTION OF THE PORTION OF THE CHEMICAL
WHICH IS BOUND TO FIELD SOIL, TO FIELD ORGANIC MATTER OR
TO POND BOTTOM OR SUSPENDED SEDIMENT

THIS BOUND FRACTION IS ESTIMATED BY USE OF THE SOIL/WATER
EQUILIBRIUM PARTITION COEFFICIENT (Kd) OR THE ORGANIC
CARBON NORMALIZED SOIL/WATER EQUILIBRIUM PARTITION
COEFFICIENT (Koc)

SEE THE GENEEC PROGRAM USERS MANUAL FOR THE APPROPRIATE Kd
OR Koc VALUE TO USE

TO USE A Kd VALUE, PLEASE ENTER IT HERE - TO USE A Koc
VALUE PLEASE ENTER ZERO (0) --->

Adsorption and desorption (pesticide binding to soil) tests are performed on soils of different textural classes, pH's and organic matter contents. Either the soil/water partition coefficient (Kd) or the organic carbon normalized soil/water equilibrium partition coefficient (Koc) can be used to estimate the dissolved and the adsorbed fraction for any chemical. To use a Kd value, choose the lowest of the Kd values which was measured on a non-sand texture soil (not sand, coarse sand, fine sand, loamy sand). This will result in a realistic yet conservative water column exposure value. If an appropriate value for Kd is available, enter it here. If not, enter a value of zero (0) at the prompt and you will be asked for a Koc value:

PLEASE ENTER THE APPROPRIATE Koc VALUE --->

The organic carbon normalized, soil/water equilibrium partition coefficient (Koc) may also be used in lieu of the Kd value. The Koc of choice, when two or more are available, is the lowest Koc value measured on a non-sand texture soil (see above). When in question, the actual number to be used should be decided in discussion with EFED scientists. The Kd / Koc conversion is based on an organic matter content of 2 percent and an organic carbon content of 1.16 percent. If neither the Kd nor the Koc is available, use 0.35 times the Kow value.

THE DISSOLVED PESTICIDE CONCENTRATION IS ALSO REDUCED BY
DEGRADATION IN THE FIELD PRIOR TO A RAINFALL / RUNOFF EVENT

THE PROGRAM ASSUMES DEGRADATION BY AEROBIC METABOLISM
BETWEEN AND FOR TWO DAYS AFTER THE FINAL APPLICATION

(IF STABLE TO AEROBIC METABOLISM OR IF DATA IS
UNAVAILABLE, PLEASE ENTER ZERO (0))

PLEASE ENTER SOIL AEROBIC METABOLIC HALFLIFE (IN DAYS) --->

There are often multiple half-life values from tests performed on a variety of soil types. In order not to underestimate the actual value, EFED policy is to use an upper 90% confidence limit on the mean value. The appropriate aerobic metabolic halflife value to use in GENEEC is calculated by the following formula:

if n=1: model input value = laboratory value × 3, where
n = number of laboratory half-life values

if n ≥ 2: model input value = µ + t90 × s /√n, where
µ = mean of the n laboratory half-life values
t90 single tail student's t, α = 0.1 (Table 1 below, n-1 d.o.f.)
s = sample standard deviation of the n laboratory half-life values, and

Table 1. t90 Single Tail Student's "t" Values
Number of Half-life Values (n) t90 Single Tail Student's "t"
(n-1 degrees of freedom)
23.078
31.886
41.638
51.533
61.476
71.440

SOME PESTICIDE LABELS REQUIRE THAT THE PESTICIDE BE
WETTED-IN EITHER THROUGH RAINFALL OR IRRIGATION:

IN THIS CASE, RUNOFF TO THE POND IS ASSUMED TO
OCCUR IMMEDIATELY RATHER THAN AFTER TWO DAYS

IS THIS PESTICIDE TO BE WETTED-IN ? (Y or N) --->

Choose the appropriate response based on the label. Some pesticides must be activated by water. If so, this will be specified on the label. In this case, the pesticide enters the pond on the day of the final application rather than two days after the final application.

In the next section of the model, spray drift is added to the pond.

THE DISSOLVED PESTICIDE CONCENTRATION MAY BE INCREASED
BY DIRECT DEPOSITION OF SPRAY DRIFT INTO THE POND

THE PROGRAM ASSUMES A TWO HUNDRED AND EIGHT FOOT WIDE POND
LOCATED DIRECTLY DOWN WIND FROM THE SPRAY APPLICATION

THE SPRAY DRIFT PERCENTAGE IS BASED UPON THE WIDTH OF THE NO-
SPRAY ZONE AND ON THE SPRAY QUALITY (DROPLET SIZE DISTRIBUTION)

PLEASE ENTER A, B, C or D TO SELECT METHOD OF APPLICATION:
A: AERIAL SPRAY
B: GROUND SPRAY
C: AIRBLAST SPRAY (ORCHARD & VINEYARD)
D: GRANULAR (NON-SPRAY) --->

Type of application is found on the label instructions. The spraydrift enters the pond at the time of each application, even when runoff happens only after two days. Depending on how this question is answered, you will be prompted for additional information. If the method = A: AERIAL SPRAY:

THE DISTRIBUTION OF DROPLET SIZES IN PESTICIDE SPRAY
(SPRAY QUALITY) IMPACTS THE DISTANCE OF TRAVEL AND
THE QUANTITY OF PESTICIDE WHICH WILL DRIFT OFF-SITE
WITH THE WIND.

PLEASE CHOOSE AN AERIAL DROPLET SIZE DISTRIBUTION:
A: VERY FINE TO FINE
B: FINE TO MEDIUM (EFED DEFAULT)
C: MEDIUM TO COARSE
D: COARSE TO VERY COARSE --->

Spray quality is the droplet size distribution as defined by American Society of Agricultural Engineers (ASAE) Standard 572 for all types of applications.

If the method = B: Ground Spray:

THE AMOUNT OF OFF-SITE SPRAY DRIFT FROM GROUND APPLICATION
DEPENDS ON THE SPRAYER CONFIGURATION AND THE SPRAY QUALITY
(DROPLET SIZE DISTRIBUTION)

PLEASE ENTER THE NOZZLE HEIGHT ABOVE THE CROP OR GROUND:
A: LOW BOOM GROUND SPRAYER (20 INCHES OR LESS), or
B: HIGH BOOM GROUND SPRAYER (20 TO 50 INCHES: EFED DEFAULT) --->

The selection of the sprayer configuration depends on the mandatory requirements of the pesticide label. If the label does not specify boom height or spray quality with mandatory language, use default values. After choosing the sprayer type, the spray droplet size designation must be chosen.

PLEASE CHOOSE SPRAY QUALITY (DROPLET SIZE DISTRIBUTION):

A: FINE (EFED DEFAULT)
B: MEDIUM-COARSE --->

The "FINE" droplet size designation is the EFED default. This will lead to the most conservative drift assumption and EEC values. Note: Code for application in output file:

GRHIFI - Ground Spray - High Boom - Fine Spray Quality

GRHIME - Ground Spray - High Boom - Medium/Coarse Spray Quality

GRLOFI - Ground Spray - Low Boom - Fine Spray Quality

GRLOME - Ground Spray - Low Boom - Medium/Coarse Spray Quality

If the method = C: (Airblast Spray):

PLEASE ENTER AIRBLAST TYPE:
A: ORCHARDS AND DORMANT VINEYARDS
B: FOLIATED VINEYARDS --->

For citrus, pome fruits and nuts, choose the "ORCHARD" option. For any application, choose "B: VINEYARD". For applications to dormant vineyards choose "A: ORCHARD". For airblast application only, a safety factor of 3.0 is applied to the SDTF drift estimate.

The next section of the program allows the model user to simulate the impact of a no-spray zone (buffer zone) between the pesticide treated agricultural field and the standard pond. The actual amount of drift is higher on the side of the pond nearer to the field and lower on the opposite side. The program, however, integrates this varying amount over the width of this 208 foot wide water body. A no-spray zone is only simulated if specified with mandatory language on the pesticide label. Otherwise the no-spray zone width is specified as zero.

If the method = A: AERIAL SPRAY, or B: GROUND SPRAY, or C: AIRBLAST SPRAY:

SPRAY DRIFT TO THE POND MAY BE REDUCED BY A NO-SPRAY ZONE
LOCATED BETWEEN THE TREATED FIELD AND THE WATER BODY

THE EFED DEFAULT NO-SPRAY ZONE WIDTH IS ZERO (0) UNLESS
REQUIRED BY THE PESTICIDE LABEL

PLEASE ENTER THE WIDTH OF THE NO-SPRAY ZONE (FEET)
(IF THE LABEL DOES NOT REQUIRE A NO-SPRAY ZONE, ENTER ZERO) --->

Enter the width of the no-spray zone required on the label or enter "zero" if a no-spray zone is not required.

Pesticide applied as a granular product or as a ground spray may be incorporated into the soil by various types of equipment driven or pulled through the field. The following section allows the model user to simulate the impact of physical incorporation on the amount of pesticide which runs off of the field and is dissolved in the water-body:

If the Method = B: Ground spray or D: Granular (Non-spray), then the following will be asked:

THE DISSOLVED PESTICIDE CONCENTRATION MAY ALSO BE
REDUCED BY INCORPORATION OF THE PESTICIDE AT THE TIME
OF APPLICATION - THE FOLLOWING DEPTHS ARE SUGGESTED:

METHOD OF APPLICATION INCORPORATION DEPTH (IN)
BROADCAST0.0
DISKED IN AFTER BROADCAST4.0
CHISEL PLOWED AFTER BROADCAST6.0
SURFACE BANDED0.0
BANDED - INCORPORATED1.2
T - BANDED1.5
IN FURROW2.0
AERIAL or AIRBLAST SPRAY0.0
GROUND SPRAYDEPENDS ON METHOD

PLEASE ENTER DEPTH OF INCORPORATION (IN INCHES) --->

The method of application will be specified on the label. Enter one of the suggested depths based on label instructions. If more than one application method is possible use the one which calls for the shallowest depth of incorporation.

THE DISSOLVED PESTICIDE CONCENTRATION IN A WATER
BODY CANNOT EXCEED THE SOLUBILITY OF THE CHEMICAL

PLEASE ENTER THE SOLUBILITY (IN PPM) -->

This number does not actually affect the exposure estimate unless for some reason the estimated exposure concentration is greater than this value. If so, the EEC will be automatically reduced to the maximum solubility.

CHRONIC (MULTIPLE DAY) EEC VALUES ARE CALCULATED BY
SUMMING THE AQUATIC DEGRADATION PATHWAYS

ENTER ANY OR ALL OF THE FOLLOWING WHICH ARE AVAILABLE:
(ENTER ZERO FOR ANY WHICH ARE UNAVAILABLE)

ENTER AEROBIC AQUATIC METABOLIC HALFLIFE - DAYS (IF UNAVAILABLE,
RECOMMENDED EFED DEFAULT IS 2x AEROBIC SOIL INPUT VALUE) --->

If there is range of half-life values, enter the longest of them. This will result in a more conservative exposure estimate. However, if the choice is unclear the actual value used should be decided in discussion with the EFED scientists.

PLEASE ENTER pH 7 HYDROLYSIS HALFLIFE (DAYS) --->

The program requests the hydrolysis halflife value only if the aerobic aquatic halflife value entered is zero. Otherwise the program assumes the aerobic aquatic value includes the hydrolysis value. If there is range of values, enter the longest halflife value. If this value is not available or if the test was performed in a water/sediment system rather than a water-only system, the appropriate value is twice the aerobic soil half-life. If the value to use is unclear, it should be decided in discussion with EFED scientists.

PLEASE ENTER PHOTOLYSIS HALFLIFE (DAYS) --->

The half-life entered here is usually the longest one, which would result in the highest exposure. However, the actual number used should be decided in discussion with the EFED scientists. The effective photolysis halflife will be 124 times longer than the one entered in the program due to light attenuation in the pond.

Check over the output on the screen to ensure that all the values are those that you wished to enter. The "output" will be saved to the designated output file name as it appears on the screen.

At the bottom of the output screen is the following question:

DO YOU WANT TO DO ANOTHER RUN (Y OR N) --->

You may run another scenario with the same chemical, or run a scenario on a new chemical and have the results reported in the same output file which was named above. If you say "Y"es, you will be asked for a new run number as below. If you say "N"o the program stops and you are returned to the DOS prompt.

PLEASE ENTER A NEW RUN NUMBER --->

After entering a new run number, the program will start over asking for the chemical name, etc. These results will be added to the bottom of the existing output file. None of the inputs from the previous run are saved and therefore must be entered again for subsequent runs.

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Retrieving Output Files

Once you have finished running GENEEC and have exited the program, the output is automatically saved under the file name you specified in your GENEEC subdirectory. This file may be retrieved and printed with any text editor or word processing program. To inset the GENEEC output file into a WordPerfect® report, set the font to Courier to maintain the needed spacing between alphabetic- and numeric characters. Once retrieved with WordPerfect®, it may be inserted directly into reviews and science chapters or printed and included as an attachment.

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Bibliography

  1. Burns, L.A. 2000. Exposure Analysis Modeling System (EXAMS), Environmental Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Athens, GA.

  2. Carsel R.F., J.C.Imhoff, P.R.Hummel, J.M.Cheplick and J.S.Donigian, Jr. 1997. PRZM-3, A Model for Predicting Pesticide and Nitrogen Fate in Crop Root and Unsaturated Soil Zones: Users Manual for Release 3.0; Environmental Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Athens, GA.

  3. Parker, R.D., R.D.Jones, and H.P. Nelson , 1995. GENEEC: A Screening Model for Pesticide Environmental Exposure Assessment.,in Proceedings of the International Exposure Symposium on Water Quality Modeling; American Society of Agricultural Engineers, pp. 485-490; Orlando, Florida.

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