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Introduction to Risk Assessment

Introduction to Risk Assessment. EH202 April 26, 2009. Origin of risk assessment. Early days of EPA (1970s) Visible and demonstrable environmental hazards Federal standards and enforcement provisions seen as solution

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Introduction to Risk Assessment

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  1. Introduction to Risk Assessment EH202 April 26, 2009

  2. Origin of risk assessment • Early days of EPA (1970s) • Visible and demonstrable environmental hazards • Federal standards and enforcement provisions seen as solution • Little focus on impact of pollution on environment and public health and intrinsic assumption that pollutants have thresholds

  3. Cayuga River Fire, New York (1965)

  4. Love Canal, New York 1942 Love Canal, New York 1978

  5. Valley of the Drums Louisville, Kentucky (1979)

  6. Superfund Site Nassau County, New York

  7. Location of National Priority List (NPL) Hazardous Waste Sites

  8. In ‘70s and ‘80s growing interest in toxic chemicals and their effect on cancer • Cancer rates associated with toxic exposures are unobservable in most circumstances • Acceptable level of risk generally 1-in-a-million • If any exposure to a substance causes some risk, how can standards be set? • When cleaning up a hazardous waste site, at what point is the project completed?

  9. What is risk assessment? • The process of identifying and evaluating adverse events that could occur in defined scenarios • A quantitative framework for evaluating and combining evidence from toxicology, epidemiology, and disciplines, with a goal of providing a basis for decision making

  10. “Risk assessment ... is a way of examining risks so that they may be better avoided, reduced, or otherwise managed ...” • “Risk assessments, except in the simplest of circumstances, are not designed for making judgments, but to illuminate them ...” Source: Wilson and Crouch, Science, 1987.

  11. Evaluate the risk, Then decide what to do… Risk assessment is the use of the factual base to define the health effects of exposure of individuals or populations to hazardous materials and situations Risk management is the process of weighing policy alternatives and selecting the most appropriate regulatory action ... integrating the results of risk assessment with social, economic, and political concerns to reach a decision National Research Council (1983)

  12. Four Steps of Risk Assessment • Hazard Identification – the process of determining a particular chemical is causally linked to particular health effects • Dose-Response Assessment – process of characterizing the relationship between the dose of an agent and the incidence of an adverse health effect • Exposure Assessment – involves determining the size and nature of the population that has been exposed to the toxicant under consideration • Risk Characterization – integration of the above three steps which produces an estimate of the magnitude of the public-health problem

  13. Hazard Identification • Examines the evidence that associates exposure to an agent with its toxicity or potential to cause harm • Collection of data • Various sources • Toxicological and epidemiological studies • Information should answer these questions • Does exposure to the substance produce any adverse effects? • If yes, what are the circumstances associated with the exposure? • Produces a qualitative judgment about the strength of that evidence

  14. Philippe Grandjean

  15. 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 The Dose-Response Obtain a mathematical relationship between the amount of a toxin an individual is exposed to and an adverse health responseFrequently only have animal test data LOAEL Proportion Responding NOAEL 0 0 2 4 6 8 10 Dose (mg/kg/day) Harvard Center for Risk Analysis

  16. Applying toxicology • The dose is an exposure averaged over a specific length of time • Usually assume a lifetime of exposure (70 yrs) • The response (risk) has no units • It is a probability of an adverse effect • Extrapolate from high to low dose • Assumes response in animals is comparable to humans Response Experimental Region Dose Human Exposure Region

  17. Exposure Assessment • Process of measuring or estimating the intensity, frequency, and duration of human exposure to an agent present in the environment, or estimating the exposures that might occur from the release of new chemicals Quantifying Exposures: • Direct personal exposure measurements • Build exposure model using concentration measurements • Fate and transport model to estimate/simulate exposures • Biomonitoring to capture dose measures

  18. Exposure Assessment – a few issues to consider • Exposure to whom? • Sensitive subpopulations • Exposure over what time period? • Lifetime exposure, peak exposure, etc. • Exposure through which pathway? • Inhalation, food consumption, drinking water, dermal exposure • Do important factors modify the concentration-exposure relationship? • What about the exposure-dose relationship?

  19. Risk CharacterizationCancer vs Non-Cancer • Cancer is treated as a stochastic response • Any dose carries a risk • Increasing dose of chemical doesn't increase the severity of the response, only the likelihood that it will occur • Potency – slope of the dose response curve Incremental lifetime cancer risk = CDI * potency factor Where, CDI = Average daily dose (mg/day) Body weight (kg)

  20. Example: Benzene emissions Suppose an industrial facility that emits benzene is being proposed for a site near a residential neighborhood. Air quality models predict that 6-% of the time, prevailing winds will blow benzene away from the neighborhood but 40% of the time, the benzene concentrations will be 0.01 mg/m3. Should this plant be allowed to be built? What information do you need to calculate the chronic daily intake?

  21. Ex. An occupational exposure What is the incremental cancer risk for a 60- kilogram worker exposed to a carcinogen that has a potency factor of 0.02 mg/kg/day 5 days per week, 50 weeks per year, over 25 year period?

  22. Non-Cancer Risk Assessment • Non-cancer responses are considered deterministic • Thresholds exist • Exposure below the threshold poses no risk • Reference Dose– obtained by dividing the NOEL by uncertainty factors and is expressed in mg/kg/day Hazard Quotient = Average daily dose during exposure period (mg/kg/day) RfD U.S. EPA Guidelines for Development of RfD* ExtrapolationUncertainty Factor Animal to Human (H) 10 Average to Sensitive Human (S) 10 LOAEL to NOAEL (L) 10 Less than Chronic to Chronic (C) 10 Data Quality (MF) 1-10

  23. Ex. Drinking water contaminants Suppose drinking water contains 1.0 mg/L of toluene and has a RfD of 0.200 mg/kg-day based on changes to the liver and kidneys. A 70 kg adult drinks 2-L per day of this water for 10 years. Is this a safe exposure?

  24. Ex. Tuna • How could you estimate exposure? • How could you estimate dose?

  25. Back to tuna … What is the exposure? What is the dose? FDA maximum permissible level of 1 ppm Data from FDA

  26. NEJM 2002; 347:1735

  27. US EPA Exposure Factors Handbook http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=12464

  28. What is average mercury dose?

  29. Got Mercury ? http://gotmercury.org/article.php?id=1034

  30. Perception of Risk Source: Based on Slovic (1987) and Slovic et al (1980)

  31. Activities that increase mortality risk by one in a million Source: Wilson 1979

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