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RISK DUE TO AIR POLLUTANTS

This text provides an overview of risk assessment for air pollutants, including the process, purpose, and calculation methods. It also discusses the EPA IRIS database and evaluation of non-cancer health effects.

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RISK DUE TO AIR POLLUTANTS

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  1. RISK DUE TO AIR POLLUTANTS

  2. What is Risk Assessment? • The characterization of the potential adverse health effects of human exposures to environmental hazards • In a risk assessment, the extent to which a group of people has been or may be exposed to a certain chemical is determined • The extent of exposure is then considered in relation to the kind and degree of hazard posed by the chemical, thereby permitting an estimate to be made of the present or potential health risk to the group of people involved • Risk assessment provides information on the health risk, and risk management is the action taken based on that information

  3. Purpose of Risk Assessment • To provide a characterization of the types of health effects expected • To provide an estimate of the probability (risk) of occurrence of these health effects • To provide an estimate of the number of cases with these health effects • To provide a suitable acceptable concentration of a toxicant in air, water, or food • To cover cancerous as well as non cancerous chemicals

  4. Process of Risk Assessment • Hazard identification : A determination is made as to whether human exposure to the agent in question has the potential to increase the incidence of cancer • Dose-response assessment: A quantitative relationship is derived between the dose, or more generally the human exposure, and the probability of induction of a carcinogenic effect • Exposure assessment: An evaluation is made of the human exposure to the agent. Exposure assessments identify the exposed population, describe its composition and size, and present the type, magnitude, frequency, and duration of exposure • Risk characterization: The exposure and dose-response assessments are combined to produce a quantitative risk estimate and in which the strengths and weaknesses, major assumptions, judgments, and estimates of uncertainties are discussed

  5. Technical Hazard Characterization Hazard Assessment Population Technical Dose Response Characterization Risk Characterization Summary Data Response Assessment Integrative Analysis Technical Exposure Characterization Exposure Assessment CHARACTERIZATION OF RISK ASSESSMENT

  6. EPA IRIS Database • http://www.epa.gov/iris/index.html

  7. What is Risk? • Hazard is the potential of an entity (or activity) to cause harm to nature, property, or people • Risk from an hazard :- risk (harm/unit time) = frequency (event [exposure]/ unit time) * Consequence (harm/event [exposure])

  8. What is Total Risk? • Total risk :- R = i =n1∑ R i= 1,2,3,…,n where, i is hazard • For low value of C , R = f x Ch • For high value of C, R = f x Chn where n is some known number that reflects the roles of disruptions by severe accidents, as well as the public perception

  9. How to calculate frequency (f)? • Frequency (f) = Exposure / Unit time = Daily amount of air pollutant inhaled over a life time / person’s weight = (Breathing rate ( m3 / day) x indoor concentration ( µg/ m3) ) ( Weight of an individual in kg) = (B x C) / W where, B is breathing rate C is concentration W is weight of an individual • Units of frequency is ( µg / kg-day)

  10. How to calculate Consequence (C) ? • Consequence (c) = Life time excess cancer risk / Daily exposure to 1 µg of the pollutant / weight of an individual = βa x K ah x I where, βa = “potency” of the pollutant for inhalation in (µg/kg-day) -1 K ah = a conversion factor expressing the ratio of the risk to a human to the corresponding risk to an animal based on inhalation toxicity data (potency) I = a factor relating inhalation data to risk if other pathways were also available

  11. What is lifetime excess cancer risk ? • It is expressed as follows: R = (B x d). (βa x K ah x I ) W

  12. Calculation of Cancer Risk • Cancer Risk is a function of the lifetime average daily dose and the chemical specific potency slope. • For inhalation: cancer risk is calculated using unit risk factor and ground level concentration. • Risk (non-inhalation pathways ) = Dose * Potency slope • Risk (inhalation) = Cg * Unit Risk Where: Dose = Dose or the sum of doses from all routes of exposure ( mg/kg/day ) • Potency Slope = Pollutant specific potency (1/mg/kg/day ) • Cg = Ground level concentration ( 10-6 g/m3 ) • Unit Risk = Pollutant specific unit risk • Assumptions : • Exposure is for 70 years

  13. Range of Air Unit Risk Factor for Benzene • 2.2x10-6 per ug/m3 (Low-dose linearity utilizing maximum likelihood estimates) • 7.8x10-6 per ug/m3 (Low-dose linearity utilizing maximum likelihood estimates) Source: IRIS (USEPA)

  14. EVALUATION OF NON CANCER HEALTH EFFECTS • The chronic hazard index for each substance is calculated by dividing the estimated annual average exposure level by the REL (reference exposure limit). This ratio is called the hazard index. • The potential for acute health effects should be evaluated by comparing the estimated one- hour maximum concentrations with the acute RELs.

  15. Example of lifetime excess cancer risk • Risk to an adult from the exposure to tetrachloroethylene is calculated as follows by using the given information B = 20 , W = 70 , d = 3.5 , βa = 9.2 x 10-6 , K ah = 1 , I = 1 By using the above formula and substituting the above given values in the formula we get the lifetime excess cancer risk to an individual is R = 9.2 x 10 -6. • The above value of risk implies that an individual has a 9.2 chance in a million of getting cancer over his or her lifetime because of the daily exposure to tetracholoroethylene at a concentration level of 3.5 µg/m3 of air. If an individual has a life span of 70 years, then chance of getting cancer in any one year is 9.2/70 = 0.13 in a million

  16. Why are risk studies conducted on Animals? • While carrying out experiments there are risks from a spectral of real, suspected or conjured hazards related to chemical and biological substances. • The effect from a single substance on humans under controlled conditions cannot be studied . • Therefore, studies are conducted on test animals that are subjected to massive doses of a substance on a relatively short time scale. • These test conditions carried out on animals like rats and monkeys are atypical of human exposures. • The results of these animal studies are extrapolated for applications to human conditions by the use of mathematical models. • The mathematical models are actually equations which are formulated and solved for applications to animal test conditions

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