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Office of Pesticide Programs Level 2
Refined Acute Lethal Risk Assessment Model for Birds

E.C. Fite, E.W. Odenkirchen, T.M. Barry, D.F. Young, T.A. Bargar, J.D. Felkel, F. Mastrota, G.T. Patrick, D.B. Farrar

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The U.S. Environmental Protection Agency, Office of Pesticide Programs continues to develop a model to estimate the magnitude and probability of acute effects to non-target avian species from pesticides. This effort is part of the initiative to revise the Agency's ecological assessments for pesticides.

As part of the continued improvement process the Agency consulted with the EPA Science Advisory Panel on elements of a pilot risk assessment model that utilised Monte Carlo sampling techniques to evaluate probability and magnitude of acute lethal response of selected bird species to dietary and drinking water exposures of chemical residues in a pesticide treated agroenvironment.

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SAP Recommendations to the Agency

Among the recommendations made by the SAP concerning improvement of the pilot model were:

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Updated Model Features

Over the past year the Agency has developed the following improvements to its Level 2 avian acute risk model:

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Typified Bird Species

Species grouped by:

Resident insectivoreBuffer Insectivore
Resident herbivoreBuffer herbivore
Resident granivoreBuffer granivore

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Bimodal Feeding Pattern

The Level 2 model integrates a bimodal daily feeding pattern model with a two-state, first-order Markov chain model of on-field/off-field behaviors. This integration permits improved simulation of individual behaviors and exposures. Key elements include:

bimodal feeding pattern tables and charts

Integrated Level 2 Model

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Behavioral Fidelity

image of transitional possibilities of avian behavioral fidelity

Transitional probabilities for the Level 2 two-state, first-order model of avian behavioral fidelity

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Field-Scale Puddle Model

Equilibrium based,mass accounting model of the runoff, infiltration, and dissipation of pesticide in an on-field puddle. Used as the basis for wildlife drinking water exposure. Allows for a temporally limited puddle, based on infiltration and evaporation.

graphic of puddle model:  precipitation, infiltration, depth of runoff interaction zone

Pesticide runoff:

Soil infiltration rate is dependant upon soil type.
Precipitation events are linked to site specific meteorological data
Runoff based on NRCS curve number method
Depth of runoff interaction zone (d) is based on literature

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Interception of Runoff

graphic representation of puddle interception of runoff

Puddle interception of runoff:
Puddle size and position on field are randomly varied

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Puddle Hydrology/Pesticide Concentration

graphic representation of puddle hydrology:  runoff input, evaporation, infiltration, overflow and puddle volume

Puddle hydrology:
Puddle volume is an important factor in determining the pesticide mass retained after a precipitation event

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Modeling the Inhalation Route

graphic of inhalation route:  directly applied spray, volatilization of residues on plant canopy and in soil residues, soil particulate residues

Modeling the Inhalation Route

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Inhalation of Directly Applied Spray

Inhalation dose = [(mass/area)(1/release height)(fraction respired)(inhalation volume)] / body weight

mass/area: application rate from label

release height: default spray drift assumption (ground or aerial)

fraction respired: volumetric droplet spectrum segregated by upper size limit of respired particles for birds (ca. 7 um)

inhalation volume: (inhalation rate)(exposure duration)

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Calculating Air Concentration

C air = (Mass pesticide mg/Ha) / (V air + (Mass plant*(B vol / Density plant)))

V air : Air volume based on crop canopy height

Mass plant : Mass of crop in a hectare of treated field

Density plant : Density of fresh crop material

B vol : Plant/air biotransfer factor (USEPA HWIR)

log B vol = (1.065(K ow) - log(HL / (UGC*K°)) -1.654

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Modeling the Dermal Route

graphic of dermal route: directly applied spray, bathing, foot contact in soil, dislodgeable residues on plant canopy

Modeling the Dermal Route

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Directly Applied Spray Dermal Exposure

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Dermal Contact with Foliar Residues

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Example Model Outputs

graph of PDF (probability of N deaths): y-axis of probability, x-axis of number dead

PDF (Probability of N Deaths)

graph of CCDF (probability of N or more deaths): y-axis of probability, x-axis of number dead

CCDF (Probability of N or More Deaths)

bar graph of Mean Dose by Pathway; dose fractions by pathway for:  food, puddle, dew, inhalation: vapor and spray, dermal: contact and spray

Mean Dose by Pathway

graph of Time to Death: y-axis of frequency, x-axis of hours

Time to Death

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