Tier I Exposure Refinements

&

Tier II Tools for Assessing Exposure of Bees 

to Pesticides

U.S. Environmental Protection Agency 1

Reuben Baris, M.S.

Environmental Fate and Effects Division

Office of Pesticide Programs
Outline

• Options for refining Tier I exposure estimates when 

the screen identifies chemicals that need additional 

evaluation

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• Tier II exposure study descriptions
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Potential Tier I Exposure Refinements 

• Purpose: provide an additional level of realism for conservative 

Tier I estimates.

• Empirical data that are routinely submitted as part of 

registration package that could be use to refine Tier I exposure 

estimates

Refinement options are based on available data already 

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• Refinement options are based on available data already 

submitted to fulfill data requirements under FIFRA

• Refinements for dietary exposure only

• Refinements are based on studies conducted on food commodities

• No guideline studies are currently available to provide additional 

information for contact exposure

• If Dietary AND Contact exposure exceed the LOC, a higher tier 

analysis is needed.
Potential Tier I Exposure Refinements 

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Study Type Foliar Applications Soil Applications

Cropped Terrestrial Field 

Dissipation 

(TFD; OCSPP 835.6100)

X X

Crop Field Trial 

(Magnitude of Residue Studies; X X

OCSPP 860.1500)

X X

Accumulation in Rotational 

Crops (OCSPP 860.1850) -- X

Nature of Residue 

(Plant Metabolism Studies; 

OCSPP 860.1300)

-- X

Plant Uptake and Translocation 

Test 

(OCSPP 850.4800)

X X
Tier II Exposure Studies

Purpose: obtain chemical specific, empirically-based exposure 

data relevant to bees in the field.

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Tier II Exposure Studies: Objectives

• Reducing uncertainty by using empirical data

• Addressing Tier I assumptions (e.g., concentrations in tall grass = nectar 

and pollen, consumption rates)

• Exposure on intended use sites, methods, and patterns

• Exposures are quantified through direct spray and diet

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• Exposures are quantified through direct spray and diet

• Shift focus from individual bee to whole colony

• Residues may be measured in pollen, nectar, on bees, and/or hive 

products

• Goal is to complete Tier II studies in a manageable way to 

obtain desired information on bee exposure

• Balancing certainty and uncertainty
Tier II Exposure Studies: Limitations

• Goal is to gather important information on chemical specific 

bee exposure in the field

• Uncertainties/Considerations

• In-hive residues may be different than those encountered by bees in the 

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• In-hive residues may be different than those encountered by bees in the 

field

• Addressing Tier I uncertainties – unprocessed food sources

• Time and resource allocation

• Unknown if residues in leaves and flowers are a conservative measure of 

residues in pollen and nectar
Tier II Exposure Studies: Study Design

Targeted Field Study (Field Residue Trial)

• Akin to a monitoring study

• Objective is to sample food sources relevant to bee exposures 

(i.e., pollen and nectar) by quantifying pesticide residues in 

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(i.e., pollen and nectar) by quantifying pesticide residues in 

matrices relevant to bees

• Option to adapt study design of existing study requirement for 

pesticides in pollen and nectar (e.g., Cropped TFD study)

• Sample timing is paramount (e.g., sampling during bloom when 

bees should be foraging)

• Applicable scenarios include seed treatments, soil applications, 

and foliar sprays
Tier II Exposure Studies: Study Design

Semi-Field Tunnel Study

• Treated crop is kept under an enclosure (Tunnel) along with a 

nucleus hive of bees

Pesticide concentrations can be quantified from the stomach 

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• Pesticide concentrations can be quantified from the stomach 

contents, pollen sacs, pollen traps, and from hive matrices.

• Pollen and nectar could be sampled directly from the plant

• Applicable scenarios include seed treatments, soil applications, 

and foliar sprays
Tier II Exposure Studies: 

Design Considerations

• Application methods are variable

• Target high-end exposure (maximum application)

• Crop selection must be relevant and attractive for bees

• Systemic transport is chemical and crop dependent

Plants may have different matrices that represent food sources for bees 

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• Plants may have different matrices that represent food sources for bees 

(e.g., corn vs. canola)

• Sampling design is paramount

• Target maximum concentrations found in pollen and nectar

• Sample pollen and nectar at different time points during bloom

• Sampling to target crop and application method (e.g., foliar applications 

sampled on day-0; soil applications and delayed transport)

• Climatic and regional variability
Questions?

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