Risk Characterization

U.S. Environmental Protection Agency 1

Thomas Steeger, Ph.D. 

Environmental Fate and Effects Division

Office of Pesticide Programs
Risk Characterization

• Overview

• Role within the risk assessment process

• Integration of multiple lines of evidence

• Articulation of risk assessment assumptions, limitations, and 

uncertainties

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uncertainties
Risk Characterization

• The risk characterization process and results should 

be:

• Transparent --assessment process is explicit

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• Clear -- assessment itself is free from obscure language and 

is easy to understand.

• Consistent -- assessment followed appropriate Agency 

guidelines.

• Reasonable -- assessment is based on sound judgment.
Risk Characterization

• Two Major Components

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Risk Estimation

• Compare exposure and effects data

• Point estimate-based risk quotient (RQ) method

• Distribution-based probabilistic assessment

• Consideration of integrated exposure and effects data 

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• Consideration of integrated exposure and effects data 

in context of LOC’s

• State potential for risk
Risk Estimation

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•Deriving Acute and Chronic Risk Quotient (RQ) Values

•Consistent with process used for other taxa.

•Risk as a function of e as a function of exposure and t e and toxicity

•RQ= Estimate Exposure Concentration/Toxicity Endpoint
Risk Estimation

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Risk Estimation

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Risk Estimation

• Point estimate-based RQs are compared to Levels of Concern 

(LOCs)

• Levels of Concern (LOCs) based on:

• Historic default probit dose-response slope for other taxa of 4.5

• Analysis of honey bee adult acute contact and acute oral toxicity probit

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• Analysis of honey bee adult acute contact and acute oral toxicity probit

dose-response

• Contact slope: mean=3.93

• Oral slope: mean= 3.40

• Individual Effect Chance Model (IEC)
Risk Estimation

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•Levels of Concern (LOCs) based on:

•Assuming median slope of 3.2 and 10% mortality

•LOC for acute risk set to 0.4.

•LOC for chronic risk set to 1.0

•Based on comparison of peak EEC to NOAEC
Risk Estimation

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Risk Description

• Interpretation of risks based on assessment endpoints

• Evaluate lines of evidence supporting or refuting risk 

estimates

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• Interpret relevance of lines of evidence to assessment 

endpoints
Risk Description

• Screening-level (Tier I) RQ values

• Possible refinements in Tier I RQ values

Tier II Semi-field studies (whole colony)

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• Tier II Semi-field studies (whole colony)

• Tier III Full-field studies (whole colony)

• Other scientifically relevant information
Risk Description

• Established through the process of integrating available 

information and its relevancy to assessment endpoints.

• More than simply a comparison of risk quotients to levels of 

concern.

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• Both quantitative and qualitative information supporting or 

refuting risk finding.

• As additional lines of evidence become clear, the problem 

formulation, including the conceptual model, are refined.
Risk Description

•Evaluation of lines of evidence

•ADEQUACY AND QUALITY OF DATA

Degree and type of variability and uncertainty 

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•Degree and type of variability and uncertainty 

•Relationship of evidence to risk assessment questions
Adequacy and Quality of Data

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• Were data quality objectives (and guidelines) 

adhered to?

• What assumptions were made in light of data gaps?

• What limitations does the use of supplemental data put 

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• What limitations does the use of supplemental data put 

on the ability to assess risk from this pesticide?

• Were experimental designs appropriate to answer 

questions posed in problem formulation?
Risk Description

• Evaluation of lines of evidence

• Adequacy and quality of data

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• DEGREE AND TYPE OF VARIABILITY/UNCERTAINTY

• Relationship of evidence to risk assessment questions
Degree and Type of Uncertainty- Variability

• Variability exists in characteristics such as ecological effects and 

environmental fate

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• Assessments should account for variability in dose-response 

relationships
Risk Description

• Evaluation of lines of evidence

• Adequacy and quality of data

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• Degree and type of variability and uncertainty

• RELATIONSHIP OF EVIDENCE TO RISK ASSESSMENT
Risk Description

• Relationship of Evidence to Risk Assessment

• Put the risk in the context of:

• Previous OPP decisions on similar pesticides

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• Previous OPP decisions on similar pesticides

• Previous Agency decisions, if applicable

• Risk assessments performed by other organizations

• Existing program policies and decisions
Risk Description

• Relationship of Evidence to Risk Assessment

• Significance of surrogate species to others in class

• Discussion of open literature-derived from ECOTOX

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•

• Consideration of sensitive ecosystems and organisms

• Consideration of effects not reflected in data (e.g., sublethal 

effects or inhalation exposure)
Risk Description

• Relationship of Evidence to Risk Assessment

• Adversity

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• Nature and intensity of effects

• Temporal and spatial scale

• Recovery potential
Risk Characterization

Questions?

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