Risk Assessment 101

Scott D. Dwyer, PhD, DABTPractice LeaderRisk Analysis and ToxicologyKleinfelder14710 NE 87th Street, Suite 100Redmond WA 98074425-636-7910sdwyer@kleinfelder.com

The Risk Assessment/Risk Management Process

What is risk assessment?The process of evaluating environmental information about a site to estimate the likelihood that adverse health effects will occur in humans or animals.Goal - to develop the information necessary to make sound and reasonable decisions about how to manage risks associated with a contaminated site.

Value of Risk Assessment

Sound scientific basis for deciding whether remediation is necessarySound scientific basis for deciding how much remediation is necessary

Value of a Risk AssessmentRisk = Hazard x Outrage

--Peter Sandman

When to do a risk assessment…

Negotiate closurePermittingTerminate remediationReal estate transactionsLegal/Litigation supportAir quality – industrial emissionsConsumer productsNew markets

What is risk management?

Approaches or methods to prevent or reduce exposure to chemicals (in the environment).A risk management plan is based on a risk assessment.

Basic Risk Assessment Concepts

“The dose makes the poison”- Paracelsus

Question: Is the consumption of 500 aspirin lethal?

Basic Risk Assessment Concepts

“The dose makes the poison”- Paracelsus

Question: Is the consumption of 500 aspirin lethal?

Answer: Not if you take only one per day.

Basic Risk Assessment Concepts

No Exposure = No Risk

Risk Assessment Approach

Screening-level risk assessment (Tier 1)is there a problem?

Baseline Risk Assessment (Tier 2, Tier 3)how serious is the problem?

Risk Managementwhat are we going to do about the problem?

Screening Level Risk Assessment

Screening-level Risk Assessment

Compare maximum concentrations of contaminants to risk-based concentrations.

EPA Regional Screening Levels (formerly PRGs)Texas Risk-Based Exposure Limits (RBELs)Texas Protective Concentration Levels (PCLs)California CHHSLs

Decisionif concentration < screening level = no further action (NFA)if concentration > screening level = risk assessment or remediation

Baseline Risk AssessmentIdentify chemicals of concern

Which chemicals are we worried about?Exposure Assessment

How will people be exposed and to how much?

Toxicity AssessmentWhat effects at what doses?

Risk CharacterizationQuantify risk or hazard

Identification of Chemicals of Concern

Purpose - to select chemicals that will be evaluated in the risk assessmentApproach

Eliminate lab contaminantsFrequency of detectionCompare inorganics to natural background

Exposure Assessment

Identify exposed populationsIdentify exposure pathwaysEstimate exposure point concentrationsEstimate chemical intake (dose)

Estimate Exposure Point Concentrations

Calculate mean concentration in each medium (soil, water, air)

this is the average (central tendency) exposure

Calculate 95th percentile UCLthis is the reasonable maximum exposure (RME)

Estimate Intake (Dose)

Use default assumptionsUse site-specific assumptionsNeed estimates of:

intake rate (soil, water, air)concentrationhow frequent (exposure frequency)how long (exposure duration)

Generic Intake (Dose) Equation

Where:C = exposure point concentrationIR = intake rate (soil or water ingestion, etc.)EF = exposure frequency (days per year)ED = exposure duration (years)BW = estimated body weightAT = averaging time

Toxicity Assessment

Toxicity AssessmentCollect toxicity values

Noncancer Reference Doses (RfDs)Cancer Slope Factors (SFs)

Sources – IRIS, PPRTVs, HEAST, ATSDRDescribe toxicology of chemicals of concern

Risk Characterization

Quantifying Risk and Hazard

Exposure Assessment:estimate of intake

Toxicity Assessment:slope factor or RfD

Risk Characterization:cancer risk or noncancer hazard

Risk Characterization

Integrate exposure and toxicity assessmentsQuantify risk and hazard from individual chemicalsSum risk and hazard from multiple chemicalsSum risk and hazard across exposure pathwaysDiscuss uncertainty

Quantifying Risk and Hazard (Carcinogens)

1. From Exposure Assessment - Estimate Intake (dose)

Intake = (C x IR x EF x ED)/(BW x AT)

Intake = (100 mg/kg x 100 mg/d x 350 d/yr x 30 y)/(70 kg x 25,550 d)

Intake = 0.0000587 mg/kg-day

2. From Toxicity Assessment - Find Cancer Slope FactorExample: Benzene, 0.029 (mg/kg-day)-1

3. Risk Characterization (Calculate Cancer Risk)

Cancer Risk = Intake x SF = 0.0000587 x 0.029 = 2 x 10-6

Quantifying Risk and Hazard (Noncarcinogens)

1. Intake = 0.0137 mg/kg-day

2. From Toxicity Assessment - Find RfD

Example: Toluene, 0.2 mg/kg-day

3. Risk Characterization(Calculate Noncancer Hazard Quotient)

HQ = (0.0137 mg/kg-day)/(0.2 mg/kg-day) = 0.069

Results of Risk Assessment

If cancer risk < 1 x 10-6, no further actionIf cancer risk > 1 x 10-6, further investigation or risk management

If hazard quotient < 1.0, no further actionIf hazard quotient > 1.0, further investigation or risk management

Risk Management

Risk Management Options

No Further ActionSource ControlDeed Restrictions, Institutional ControlsRemediation

Calculating Remediation GoalsProvides a screening level for evaluation of a site during the investigationEstablishes a soil or water concentration for a given hazard or risk levelProvides a target for remediation

Calculating Remediation Goals

Information Needed:

Target hazard or risk level (e.g., hazard quotient = 1 or cancer risk = 1 x 10-6)RfD for noncancer hazard, or SF for cancer riskExposure assumptions

Calculating Remediation Goals (Noncancer)

C = (THQ x BW x AT x RfD)/(EF x ED x IR)

C = remediation goal in soil (mg/kg) or water (mg/L)THQ = target hazard quotientBW = body weight (kg)AT = averaging time (days)RfD = reference dose (mg/kg-day)EF = exposure frequency (days/year)ED = exposure duration (years)IR = intake rate (mg/day, soil; L/day, water)

Calculating Remediation Goals (Cancer)

C = (TR x BW x AT)/(EF x ED x IR x SF)

C = remediation goal in soil (mg/kg) or water (mg/L)TR = target cancer riskBW = body weight (kg)AT = averaging time (years)EF = exposure frequency (days/year)ED = exposure duration (years)IR = intake rate (mg/day, soil; L/day, water)SF = slope factor (1/mg/kg-day)

Final Thoughts…