ARB Recommended Interim Risk Management Policy for Inhalation-Based Residential Cancer Risk - Frequently Asked Questions

This last reviewed on July 29, 2008

Frequently Asked Questions

Q1) Why are we recommending this approach?

A)

ARB is recommending this interim policy to address two issues. The first issue is the evolving nature of risk assessment and the potential for changes to the HRA Guidance Manual in the near future. OEHHA is evaluating further refinements to exposure assessment methods that may result in significant changes to exposure estimates for the breathing (inhalation) pathway for residential receptors. OEHHA anticipates that the new exposure information will be released over the next few years. Since all risk assessments include the breathing pathway, the ARB believes that this interim guidance is timely and prudent.

The second issue is the ongoing need to use a single cancer risk value to address some risk management situations. Current district programs often rely on a single cancer risk value to trigger specific actions (e.g., notification, risk reduction audit and plans, installation of toxics best available control technology, and project permitting). Because of this ongoing need, ARB believes that interim guidance is appropriate and necessary.
   
Q2) When are we recommending this policy be used?

A)

We recommend that this interim policy be used to augment the OEHHA Air Toxic Hot Spots Program Guidance Manual for Preparation of Health Risk Assessment where a single cancer risk value (rather than a range of risk) is needed or prudent for characterizing risk or where a single risk value is used for (cancer) risk management decision-making for residential receptors.
   
Q3) Why are we recommending the 80th percentile as a minimum exposure value for risk management purposes?

A)

Based on existing exposure information, the ARB, with concurrence from OEHHA, is recommending the interim use of the 80th percentile value (breathing pathway) as the minimum value for risk management decisions at residential receptors. This will continue to give health protective estimates that are consistent with previous risk assessment methods and provides continuity for the regulated community during the period of forthcoming changes to the risk assessment exposure methodology. The use of any single risk assessment result that is based on exposures less than the 80th percentile is not considered to be health protective nor prudent public health policy.

The ARB will reconsider this interim risk management policy in its entirety as new scientific data (e.g. exposure information) are released by the ARB or OEHHA. At that time, all data, full exposure distributions, and methods that are published by the ARB or OEHHA will be used to determine future policies that are protective of public health.
   
Q4) To which type of risk assessment analysis and receptor does this interim policy apply?

A)

The policy applies only to a carcinogenic risk assessment for adult residents. Noncancer chronic and acute analyses should be conducted according to the OEHHA Air Toxic Hot Spots Program Guidance Manual for Preparation of Health Risk Assessment (August 2003).
   
Q5) What breathing rate should be used when calculating residential cancer risk for the 80th percentile?

A)

The 80th percentile corresponds to a breathing rate of 302 Liters/Kilogram-day (302 L/Kg-day).
   
Q6) What breathing rates are used for children and workers?

A)

Risk assessments that address workers or children should use the breathing rates listed in the OEHHA Air Toxic Hot Spots Program Guidance Manual for Preparation of Health Risk Assessment (August 2003).
   
Q7) Is the 80th percentile the only breathing rate that should be included in a risk assessment?

A)

No. The ARB, in consultation with OEHHA, is recommending the interim policy utilize the OEHHA HRA Guidance Manual's range of exposure for determining potential cancer risk at the mean (65th percentile for the breathing pathway) and high-end (95th percentile) values. For the breathing pathway, this policy further recommends the use of the midpoint value of the percentile range (i.e., the 80th percentile) between the mean and high-end as the minimum exposure level for risk management decisions where a single cancer risk value must be used for a residential receptor.
   
Q8) Where can I learn more about the Tiered-approach to risk assessment (Tier 1 to Tier 4) that is referred to in the interim policy?

A)

See the OEHHA Air Toxic Hot Spots Program Guidance Manual for Preparation of Health Risk Assessment (August 2003).
   
Q9) What is the definition of a dominant exposure pathway in a multipathway cancer risk assessment?

A)

Dominant exposure pathways are defined as the two exposure pathways that have the largest contribution to the cancer risk estimate when using high-end point-estimates for all applicable exposure pathways. The determination of dominant pathways is substance-specific.
   
Q10) How does the Derived (OEHHA) Cancer Risk method work?

A)

This method applies to multipathway risk assessments and is described in detail in the OEHHA Air Toxic Hot Spots Program Guidance Manual for Preparation of Health Risk Assessment (August 2003). In brief, for a multipathway cancer risk assessment, the two dominant (driving) exposure pathways use the high-end point-estimates of exposure, while the remaining exposure pathways use average point estimates listed in the OEHHA HRA Guidance Manual.
   
Q11) How does the Derived (Adjusted) Cancer Risk method work?

A)

This method is identical to the method used for the Derived (OEHHA) Cancer Risk with one exception. The Derived (Adjusted) method uses the breathing rate at the 80th percentile of exposure rather than the high-end point-estimate when the inhalation pathway is one of the dominant exposure pathways. The Derived (Adjusted) method is used to meet the recommendations of this policy when the inhalation pathway is determined to be a dominant exposure route in a multipathway assessment. The Derived (Adjusted) results should be presented in a risk assessment in addition to the results from the Derived (OEHHA) method.
   
Q12) When do the Derived (OEHHA) and the Derived (Adjusted) methods yield the same result?

A)

When the inhalation exposure pathway is not a dominant exposure pathway, the Derived (OEHHA) and the Derived (Adjusted) methods will yield the same result. The results will only differ when the inhalation pathway is a dominant exposure pathway (see question directly above).

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