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Ecological Committee on FIFRA Risk Assessment Methods (ECOFRAM)
Terrestrial Workgroup Report: II. Exposure Assessment for Dietary Route

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Avian Exposure Pathways

Animals are exposed to pesticides through a variety of pathways. This poster focuses on exposure via contaminated food, but ECOFRAM is developing similar approaches for other pathways.

flow diagram with final target of total exposure in mg/kg/unit time from 3 sources: (1) inhalation that is also the target of source air, (2) dermal that is also the target of sources: direct contact, surface water, soil, and vegetation and (3) total oral which is also the target of two sources: (1) dietary(food) which is itself a target of sources: vertebrate prey, invertebrate prey, seeds and fruits, and vegetation, (2) other oral (non food) which is also the target of sources: granules/baits, preening, soil, and surface water.

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Estimating exposure via contaminated food

Exposure via contaminated food is estimated using the dietary dose equation, adapted from Pastorok et al. (1996).

DD = ∑ FIR · AVCi · PDi · PTi · Ci · FDRi /W


DD = dietary dose (mg pesticide/kg body weight/unit time)

FIR = Food ingestion rate

AVCi = Avoidance factor at concentration Ci

PDi = Proportion of food type i in the diet

PTi = Proportion of food type i obtained in treated area

Ci = Concentration of pesticide in food type i

FDRi = Fresh to dry weight ratio for food type i

W = Body weight

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Short-term and Long-term exposures

Exposure is estimated on two time scales:

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Levels of Refinement

Each input to the dietary dose equation may be estimated at up to 4 different levels of refinement, as shown in the following Tables. Exposure by other pathways may be treated in similar ways.

Level I is intended as a simple Screening Level Assessment. It produces a point estimate and is based on "reasonable worst case" assumptions for each input parameter. Its purpose is to assist the assessor in deciding whether the dietary route is significant enough to warrant more detailed analysis at Levels II-IV.

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Levels of Refinement in Dietary Exposure Analysis

Level 1Level 2Level 3Level 4
  • Produce point estimate of reasonable worst case dietary exposure for generic species

  • Short- and long-term exposure estimated separately

  • Estimate distribution of exposures for focal species

  • Use simple estimates of distributions for input variables, based on existing data or expert judgement

  • Separate short- and long-term estimates

  • As Level 2 but use more refined estimates of input distributions

  • Also, take account of exposure due to spray drift

More refined assessment which may include:
  • field studies to estimate input distributions in relevant conditions

  • distributions based on explicit landscape models

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