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Assessing Dose and Potency of Chemicals

Assessing Dose and Potency of Chemicals. Robert Blaisdell, Ph.D, Chief Exposure Modeling Section Office of Environmental Health Hazard Assessment. Air Programs Using Risk Assessment Information in California.

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Assessing Dose and Potency of Chemicals

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  1. Assessing Dose and Potency of Chemicals Robert Blaisdell, Ph.D, Chief Exposure Modeling Section Office of Environmental Health Hazard Assessment

  2. Air Programs Using Risk Assessment Information in California • Toxic Air Contaminant Program. Chemical specific risk assessments (developed by OEHHA) and emission data, exposure assessment (ARB) are to used to inform Air Toxics Control Measures (ATCMs) (180 chemicals). • ATCMs are industry-wide requirements for air pollution control (ARB). • Chemical specific risk assessment (dose-response assessment) allows prioritization so that high risk industries are addressed (e.g diesel emitters, dry cleaners and metal platers).

  3. Air Programs Using Risk Assessment Information in California • The Hot Spots Program uses both chemical-specific risk assessment and exposure assessment to address air pollution from stationary sources (~400 chemicals). • Facilities must report emissions every four years. • Facilities that may pose a threat to public health are required to do a risk assessment. • Facilities are required to notify the exposed public if the risks are above a certain level. • Info is used in the Risk Reduction and Audits program to require additional pollution control devices on high risk facilities.

  4. How is Chemical Risk Assessment Done? • Hazard Identification—Do the chemicals in question pose a potential risk? • Exposure assessment—How much of the chemical are people exposed to? • Dose-Response Evaluation—What is the relationship between the dose of the chemical and the health effect? • Risk Characterization—What is the risk from the facility?

  5. Noncancer Health Effects Dose-Response • It is generally accepted that there is a threshold or level of exposure at or below which noncancer health effects will not occur. • Noncancer health values are designed to be “safe” levels where health impacts are not expected even in sensitive members of the general population. • Limited number of chemicals have been considered due to lack of resources and data.

  6. Non Cancer Health Effects Dose-Response • Multiple noncancer health effects on different organ systems can occur with one chemical at different doses. • Human and animal toxicology studies are reviewed and the health effect occurring at the lowest dose is selected as the basis for the REL. • A No Observed Adverse Effect Level (NOAEL) or Lowest Observed Adverse Effect Level (LOAEL) is determined from the study. • Benchmark dose applies a statistical approach to estimate REL.

  7. Reference Exposure Level • Chronic inhalation REL—a “safe” air concentration (µg/m3) for continuous inhalation exposure (80 chemicals). • Acute inhalation REL—a “safe” air concentration (µg/m3) for 1 hour infrequent exposures (52 chemicals). • Oral Chronic REL—a “safe” level of exposure through the oral route (mg/kg body weight/day) [7 chemicals].

  8. Reference Exposure Level • Uncertainty factors are used to ensure that the noncancer health value will be below the threshold. Typical uncertainty factors include: • 10 X for animal to human. • 10X if short term study is used for a chronic REL. • 10X currently for variability in the human population. • 10 X if a LOAEL is used instead of a NOAEL.U • Uncertainty factors are multiplied together and are not usually higher than 3000. • Exceeding the REL means the likelihood of health effects is increased but does not necessarily mean that they will occur.

  9. Cancer Potency Factors • Cancer-causing Chemicals (carcinogens) are not considered to have a threshold below which there is no risk. • Animal studies or human epidemiological studies (usually workers) are used to estimate the relationship between dose and excess cancer risk. • The cancer potency factor is the slope of that dose-response relationship (121 chemcals). • The dose (mg/kg-day) is multiplied X the cancer potency factor [1/(mg/kg-day)] to give cancer risk.

  10. Cancer Risk Estimation • Cancer risk can be defined as the excess risk of getting cancer with a 24 hour/day exposure to a given daily dose of a chemical for 70 years. • 1 X 10-6 (1 in a million) cancer risk means that if a million people are exposed, one additional cancer case would be expected. • The level of cancer risk considered acceptable or de minimus is politically determined. It varies in different programs from 1 X 10-6 to 1 X 10-4 (1 per million to 100 per million).

  11. Cancer Risk • The background lifetime risk of getting all types of cancer is around 1 in 3 to 1 in 4. • The inhalation cancer risk from breathing the general air pollution in the South Coast is somewhere around 700 in a million. • The acceptable cancer risk from stationary facilities, as determined by the local Air Pollution Control District is generally 10 in a million for lifetime exposures.

  12. Exposure Assessment of Airborne Chemicals • The amount of chemical emitted from a stationary facility, freeway or rail yard can be estimated. • The dispersion of the chemical can be estimated using local meteorological data and a computer air model.

  13. Exposure Assessment of Airborne Chemicals • Air modeling techniques have been validated with air monitoring and are generally considered to be accurate within about a factor of 2. • Accuracy in a given situation is dependent on terrain, applicability of the meteorological data to the site and other factors. • Modeling of multiple facilities, complex facilities, freeways, etc within a small region is currently feasible with high end desktop computers.

  14. Exposure Assessment of Airborne Chemicals • Many airborne chemicals are gases and exposure only occurs by inhalation. • The ground level air concentrations as well as the deposition of metals and semivolatile organic chemicals onto to soil or plants can be modeled.

  15. Exposure Assessment of Airborne Chemicals • Inhalation exposure can be estimated by using a daily breathing rate and the air concentration. • Estimation of noninhalation routes of exposure to metals and semivolatile organic chemicals deposited into soil is more complex (and less certain). • Exposure to these chemicals may occur by inadvertent soil ingestion, consumption of home grown produce, meat, contaminated surface water (as a drinking water source), mother’s milk, or from skin contact with contaminated soil or surfaces.

  16. Site-Specific Exposure Assessment • Estimates of the dose that an individual is exposed from all the pathways that occur at particular site can be made. • The procedures in the Hot Spots risk assessment guidelines will tend to overestimate rather than underestimate exposure (and thus dose) in order to protect public health.

  17. Risk Characterization for the Hot Spots program--Cancer Risk • The dose of the emitted carcinogens are estimated using standardized exposure parameters. • The estimated doses are multiplied times the cancer potency factors to give cancer risk for each chemical. • Cancer risks from all emitted carcinogens are summed. • Carcinogens without sufficient data for cancer potency slopes cannot be evaluated.

  18. Risk Characterization for Hot Spots Program-Noncancer Health Effects • A noncancer hazard quotient is determined by dividing the modeled air concentration by the REL. • The hazard index is the sum of all hazard quotients for all chemicals emitted that impact a particular organ system.

  19. Risk Characterization-Hot Spots • A chemical may be a carcinogen and/or cause noncancer health effects. • The cancer and noncancer risks are determined for the following receptors: • The Residential Maximally Exposed Individual—the existing residence with the highest noncancer and cancer risk (could be different locations for noncancer and cancer risk). • The Maximally Exposed Individual Worker—this is for offsite workers. • The Maximally Exposed Individual—the point with highest risk offsite.

  20. Public Comment and Peer Review • OEHHA’s chemical specific risk assessment and exposure assessment documents are released for public comment. • There is a formal response to public comment and revision of the document. • The State’s Scientific Review Panel on Toxic Air Contaminants then reviews and endorses the documents. • This process, although lengthy, helps ensure the scientific validity of risk assessment procedures.

  21. Concerns about Risk Assessment • The first administrator of USEPA compared risk assessment to a captured spy. If you torture it long enough it would tell you anything. • Comment: “Gaming” can be minimized with standardized procedures for emissions estimation, air modeling, dose response and exposure assessment, and oversight, such as we have in California’s Hot Spots program.

  22. Concerns About Risk Assessment • Communities often do not have the expertise to use the tools or verify the results, or the resources to hire experts to evaluate the results. • Risk assessment has been used to look at one facility at a time and does not consider the entire burden of multiple facilities. This can a particular problem in environmental justice communities with mixed residential-industrial zoning and bad historical land use decisions. • Comment: Risk assessment now has the capability of modeling multiple sources, unlike a few years ago.

  23. Concerns About Risk Assessment • The current toxicological scientific body of literature is inadequate. Basic toxicological Information is lacking on many chemicals in current use. • Comment: Yes a serious problem for those chemicals lacking data.

  24. Concerns About Risk Assessment • Asthma induction and asthma exacerbation are not well characterized in terms of dose-response. • Comment: Work in progress--may be possible in the future for some chemicals.

  25. Advantages of Risk Assessment • Risk assessment provides a useful tool that incorporates scientific information and serves as a yardstick for comparison. • Risk assessment can be used to compare the risks between chemicals as well as between different facilities and to inform risk management decisions.

  26. Advantages of Risk Assessment • Risk assessment incorporates health conservative assumptions. • It is much more defensible than not considering issues of chemical toxicity and exposure in decision-making.

  27. For More InformationAir Toxics "Hot Spots" Program Risk Assessment Guidelines • Parts I, II, III & IV Technical Support Documents • And the overview: Air Toxics Hot Spots Program Guidance Manual for Preparation of Health Risk Assessments. • All at: http://www.oehha.ca.gov/air/hot_spots/index.html

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