Presentation on theme: "Introduction to Risk Assessment"— Presentation transcript:
1 Introduction to Risk Assessment EH202April 26, 2009
2 Origin of risk assessment Early days of EPA (1970s)Visible and demonstrable environmental hazardsFederal standards and enforcement provisions seen as solutionLittle focus on impact of pollution on environment and public health and intrinsic assumption that pollutants have thresholds
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 circumstancesAcceptable level of risk generally 1-in-a-millionIf 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 scenariosA 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 situationsRisk 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 decisionNational Research Council (1983)
12 Four Steps of Risk Assessment Hazard Identification – the process of determining a particular chemical is causally linked to particular health effectsDose-Response Assessment – process of characterizing the relationship between the dose of an agent and the incidence of an adverse health effectExposure Assessment – involves determining the size and nature of the population that has been exposed to the toxicant under considerationRisk 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 harmCollection of dataVarious sourcesToxicological and epidemiological studiesInformation should answer these questionsDoes 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
15 The Dose-Response Obtain a mathematical relationship between the amount of a toxin an individual is exposed to and an adverse health response Frequently only have animal test data0.10.20.30.184.108.40.206.80.91LOAELProportion RespondingNOAEL246810Dose (mg/kg/day)Harvard Center for Risk Analysis
16 Applying toxicologyThe dose is an exposure averaged over a specific length of timeUsually assume a lifetime of exposure (70 yrs)The response (risk) has no unitsIt is a probability of an adverse effectExtrapolate from high to low doseAssumes response in animals is comparable to humansResponseExperimental RegionDoseHuman Exposure Region
17 Exposure AssessmentProcess 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 chemicalsQuantifying Exposures:Direct personal exposure measurementsBuild exposure model using concentration measurementsFate and transport model to estimate/simulate exposuresBiomonitoring to capture dose measures
18 Exposure Assessment – a few issues to consider Exposure to whom?Sensitive subpopulationsExposure over what time period?Lifetime exposure, peak exposure, etc.Exposure through which pathway?Inhalation, food consumption, drinking water, dermal exposureDo important factors modify the concentration- exposure relationship?What about the exposure-dose relationship?
19 Risk Characterization Cancer vs Non-Cancer Cancer is treated as a stochastic responseAny dose carries a riskIncreasing dose of chemical doesn't increase the severity of the response, only the likelihood that it will occurPotency – slope of the dose response curveIncremental lifetime cancer risk = CDI * potency factorWhere,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?
22 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?
23 Non-Cancer Risk Assessment Non-cancer responses are considered deterministicThresholds existExposure below the threshold poses no riskReference Dose– obtained by dividing the NOEL by uncertainty factors and is expressed in mg/kg/dayHazard Quotient = Average daily dose during exposure period (mg/kg/day)RfDU.S. EPA Guidelines for Development of RfD*Extrapolation Uncertainty FactorAnimal to Human (H) 10Average to Sensitive Human (S) 10LOAEL to NOAEL (L) 10Less than Chronic to Chronic (C) 10Data Quality (MF) 1-10
25 Ex. Drinking water contaminants Suppose drinking water contains 1.0 mg/L of toluene and has a RfD of 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?
26 Ex. Tuna How could you estimate exposure? How could you estimate dose? Measure the environment—the amt of mercury in the tuna. Do biological monitoring---blood or urine.
27 Back to tuna … What is the exposure? What is the dose? MethylmercuryRangeMercuryTUNA, fresh0.220-0.90.69TUNA, canned0.170-0.750.2TUNA, white albacore canned0.240-0.490.36TUNA, albacore canned--0.35TUNA, chunk light tongol0.08TUNA, canned chunk light0.190-0.180.120-0.72FDA maximum permissible level of 1 ppm in seafoodacceptable daily intake (ADI) for methylmercury (as mercury) of 30 µg and assumes a maximum fish ingestion rate of 30 g/day--the equivalent of one 7-8 oz serving per week--by a 70-kg adult. Higher ingestion rates, lower body weights, higher mercury levels in the fish, or a combination of these factors would result.17 ug/gram *3.491 gram/day = 0.6 ug/day … need to divide by BW (0.009 ug/kg)Provisional tolerable weekly intake (PTWI) of 1.6 µg/kg bw – WHO (0.22 ug/kg bw)FDA maximum permissible level of 1 ppmData from FDA
32 Perception of RiskAttributes that elevate perception of riskAttributes that lower perception of riskInvoluntaryVoluntaryExoticFamiliarUncontrollableControllableControlled by othersControlled by selfDreadAcceptCatastrophicChronicCaused by humansNaturalInequitableEquitablePermanent effectTemporary effectNo apparent benefitVisible benefitsUnknownKnownUncertaintyCertaintySource: Based on Slovic (1987) and Slovic et al (1980)
33 Activities that increase mortality risk by one in a million ActivityTypes of riskSmoking 1.4 cigarettesCancer, heart diseaseDrinking ½ liter of wineCirrhosis of the liverSpending 1 hour in a coal mineBlack lung diseaseLiving 2 days in New York or BostonAir pollutionTravelling 300 miles by carAccidentFlying 1000 miles by jetFlying 6000 miles by jetCancer by cosmic radiationTraveling 10 miles by bicycleLiving 2 months with a cigarette smokerEating 40 tablespoons of peanut butterLiver cancer caused by aflatoxinLiving 50 years within 5 miles of nuclear reactorAccident releasing radiationSource: Wilson 1979