What are Toxic Air Contaminants "All substances are poisons; there is none which is not a poison. The right dose differentiates a poison from remedy." Theophrastus Bombastus von Hohenheim (Paracelsus, 1493- 1541)
What is Toxic New Source Review? By rule or policy most districts review new sources of toxic emissions Districts may have different approaches on: Risk Characterization –Cancer and Non-Cancer risks How populations are exposed
Overview of Health Risk Assessment (HRA) Components of Risk Assessment Guidance Documents for HRA Risk Characterization –Cancer and Non-Cancer risks Exposure Routes Health Effects Databases
What is Health Risk Assessment? Health risk assessment involves a comprehensive analysis of the dispersion of emitted chemicals in the air and the extent of human exposure via relevant pathways (exposure assessment), the toxicology of those chemicals (dose- response assessment), and the estimation of cancer risk and non-cancer health impacts to the exposed community (risk characterization)
Toxic NSR Process Identify Toxic Air Contaminants (TACs) that are emitted Model Emissions from the Source Characterize Risk –Cancer and Non-Cancer risks Compare to Established Standards
Guidelines for Health Risk Assessment The Office of Environmental Health Hazard Assessment (OEHHA) is required to develop guidelines for conducting health risk assessments under the Air Toxics Hot Spots Program (Health and Safety Code Section 44360 (b) (2)). OEHHA was also required to develop a stochastic or probabilistic approach to exposure assessment This lead to the development of the Air Toxics Hot Spot Program Guidance Manual for Preparation of Health Risk Assessments (OEHHA 2003). Available on www.oehha.ca.govwww.oehha.ca.gov OEHHA developed four Technical Support Documents (TSDs) in response to this statutory requirement which provided the scientific basis for values used in assessing risk from exposure to facility emissions.
Guidelines for Health Risk Assessment (cont’d) The four TSDs describe acute Reference Exposure Levels (RELs), chronic RELs, cancer potency factors, and the general exposure assessment methodology. This Guidance Manual supercedes the risk assessment methods presented in CAPCOA’s Risk Assessment Guidelines, 1992,93. The new Guidance Manual updates health effects values, exposure pathway variates (e.g breathing rates), and presents a tiered approach in conducting a HRA.
Risk Characterization Cancer –Based on a exposure of breathing the TAC for 70 years (health protective) Non-Cancer –Acute- short term high level exposure – generally one hour may be 4,6, or 7 hours –Chronic – long term low level-annualized averaged over a year
Measurements for Risk Cancer – cancer risk not exceed of “x” in a million typically 1 x 10 -6, 10x 10 -6 with TBACT Cancer burden not to exceed normally 0.5 Non-cancer – Hazard Index (HI) not to exceed normally 1 –HI acute = ratio of modeled concentration to Acute REL –HI chronic = ratio of modeled concentration to chronic REL
Risk Characterization-Cancer risk Estimate Added lifetime risk of contracting cancer as a result of a given exposure Risk of one in a million(1x10 -6 ) means that the individual chance of contracting cancer has increased by one chance in a million over and above background and the chance of contracting cancer from other factors (e.g. diet, smoking, heredity,etc)
Risk Characterization-Cancer risk(cont’d) Carcinogenic inhalation potency factor (unit risk factor) or oral cancer potency factor URF is the estimated probability that an individual will contract cancer as a result of inhalation of a concentration of 1 ug/m3 of the TAC continuously over a period of 70 years and expressed in units of inverse concentration as micrograms per cubic meter (ug/m3) -1 Cancer potency factor is an upper bound probability of developing cancer assuming continuous lifetime exposure to a substance at a dose of one milligram per kilogram of body weight and expressed in units of inverse dose as a potency slope, (mg/kg/day) -1 Breathing rates expressed in units of liters per kilogram of body weight-day (L/kg#BW-day) can be coupled with air concentrations to estimate dose in mg/kg-day
Risk Characterization-Cancer risk(cont’d Cancer burden- increased number of cancer cases as a result of exposure to the TACs Excess cancer burden for a population unit (city, census tract, subarea or grid) is the product of the exposed population and the estimated individual risk from ambient air.
Reference Exposure Level (REL) The concentration level at or below which no adverse health effects are anticipated Based on most sensitive, relevant, adverse health effect reported in the medical and toxicological literature. Designed to protect the most sensitive individuals in the populations by the inclusion of margins of safety.
Risk Characterization for Non- Cancer Risk Hazard Index = Estimate Exposure Level/ Reference Exposure Levels A HI of 1 or less indicates that no adverse health effect are expected HI > 1 indicates that adverse impacts can be expected Simultaneous exposure to two or more TACs at subthreshold levels may result in a toxic response. In this case, the Total HI is estimated for the individual target organs.
Risk Characterization for Non- Cancer Risk (cont’d) –Central or peripheral nervous system –Cardiovascular or blood system –Immune System –Kidney –Respiratory system –Reproductive system –Skin –Eye –Gastrointestinal system and liver Toxicological Endpoints Considered Total Hazard Index Summation of HI for each target organ for exposure to a mixture of TACs
Health Effects Databases ARB –(TAC documents, the "Hot Spots" emissions inventory, ARB's ambient air toxics monitoring network) U.S. EPA –Hazardous Substances Data Bank (HSDB), –Integrated Risk Information System (IRIS), –Toxic Release Inventory (TRI)], World Health Organization –International Agency for Research on Cancer (IARC) Monographs On the Evaluation of Carcinogenic Risks to Humans OEHHA –Safe Drinking Water and Toxic Enforcement Act of 1986 (Proposition 65) Others –Handbook of Chemistry and Physics and the Merck Index
District Rules South Coast Rule 212 Bay Area Regulation 2, Rule 5 San Joaquin Valley Integrated Air Toxics Program Monterey Bay Rule 1000