Risk Assessment and Environmental Policy

Transcription

1 Risk Assessment and Environmental Policy Gene Schroder, PhD Risk Assessment and Environmental Policy the dichotomy that exist between the perceptions of the public and the experts on which risks are important presents and enormous challenge to a pluralistic, democratic country. Learning Objectives Compare environmental health risks with other risks. Review the process of risk assessment. Present concepts of relative risk assessment. Relate environmental policy to environmental risks. 1

2 Nature of Risk What is risk? The possibility of loss or injury Risk assessment - "the characterization of the potential adverse health effects of human exposures to environmental hazards" (NRC, 1983) May be broadly based (risks of exposure to ozone or lead in air) or local (risks associated with living near a superfund site). May be retrospective or prospective (e.g. asbestos exposure; new pesticide) Risk Assessment A risk assessment for a toxic pollutant combines results of studies on the health effects of various animal and human exposures to the pollutant with results of studies that estimate the level of people's exposures at different distances from the source of the pollutant. We Deal With Risk Daily Personal Activities: motorcycling = 2,000 deaths/100,000 persons at risk/year (2%) fire fighting = 80 deaths/100,000/yr (0.08%) motor vehicle accidents = 24 deaths/100,000/yr (0.024%) personal activities that affect health (smoking, drinking, food, exercise etc.) Accidents of Nature: Lightning kills 0.05 people/yr/100,000 ( %) Risk from meteorite hits per 100,000 or ( %) 2

3 Estimating Risks from Toxic Substances Exposures to Toxic Substances - estimates based on animal studies not actual human deaths in most instances. Cancer risk from chlorinated drinking water 0.8/100,000/yr (0.0008%) How is this risk estimate different from the above? Previous data were based on observed incident rates Based on adverse effects from animal studies using various chlorinated compounds Result is a worst-case estimate (upper bound). Assumes there is no safe dosage This is an average attributed risk. (no particular high or low risk group is identified) Estimates of Common Risks Source: Should We Risk It? D. Kammenand D. Hassenzahl Princeton Univ. Press, 1999 Strength of Association Source: Risk Assessment for Toxic Air Pollutants: A Citizen's Guide -EPA 450/ ,March

4 Quality of Risk Estimates Dealing with uncertainty in complex systems Big Picture Based on Educated Guesses Direction and magnitude of process What data are missing? What assumptions must be made? Qualitative Analysis of Existing Data Make needed assumptions Arrive at detailed quantitative solution (model) Evaluate Robustness of Conclusions How sensitive to assumptions? Will new or better data improve the predictions? Intuitive Modeling Source: Should We Risk It? D. Kammenand D. Hassenzahl Princeton Univ. Press, 1999 Intuitive Modeling Source: Should We Risk It? D. Kammenand D. Hassenzahl Princeton Univ. Press,

5 Intuitive Modeling Source: Should We Risk It? D. Kammenand D. Hassenzahl Princeton Univ. Press, 1999 Intuitive Modeling Source: Should We Risk It? D. Kammenand D. Hassenzahl Princeton Univ. Press, 1999 Intuitive Modeling Which of the graphs best represent Linear Convex Concave Threshold the number the number of leaks accidents of of carcinomas space a sewer a shuttle driver a line surfer has, accidents as a is function a likely as a to function of get the of as total number a of of years cumulative function total it has number miles been of total driven? in of service lifetime missions without hours flown? in maintenance the sun? or replacement? Source: Should We Risk It? D. Kammenand D. Hassenzahl Princeton Univ. Press,

6 Non-cancer Health Risks Cancer not the only risk from environmental chemicals (immune, hormonal, developmental, reproductive) These endpoints are usually regulated by determining the no effect (NOEC or NOEL) level in animals and applying a safety margin (X100) (Reference dose). Unlike carcinogens, these regulations assume a safe level of exposure. Risks of 10-6 (one in a million / lifetime) are not worth regulating. Average lifetime risk of cancer is about 33%. Health Effects of Air Pollutants Source: Risk Assessment for Toxic Air Pollutants: A Citizen's Guide -EPA 450/ ,March 1991 The National Academy of Sciences Paradigm for Risk Assessment Hazard Identification Dose-Response Relationships Exposure Analysis Risk Characterization 6

7 Risk Assessment Process Source: Risk Assessment for Toxic Air Pollutants: A Citizen's Guide -EPA 450/ ,March 1991 Hazard Identification Hazard Identification - to determine whether the available scientific data describe a causal relationship between an environmental agent and demonstrated injury to human health or the environment. In humans observed injury (birth defects, cancer, etc.) In the environment ( fish kills, defoliation, etc.) Possible causal factors identified (workplace, food, water) Evidence that observed effects can result from exposure to causal factors Good environmental epidemiology Dose-Response Evaluation If there is reason to believe a causal relationship then the following steps are appropriate: Dose-Response Relationships - designed to establish the quantitative relationship between exposure and response. It is based on extrapolation (high level lab studies with animals to low dose human exposures). The number produced is an estimated toxicity, R (e.g /mg/kg/d) or NOEC. 7

8 Dose-response Relationship for Cancer Derivation of Slope Factor In the absence of clear evidence to the contrary, EPA assumes that there are no exposures that have "zero risk" -- even a very low exposure to a cancer-causing pollutant can increase the risk of cancer (albeit a small amount). EPA also assumes that the relationship between dose and response is a straight line -- for each unit of increase in exposure (dose), there is an increase in cancer response. Source: Risk Assessment for Toxic Air Pollutants: A Citizen's Guide -EPA 450/ ,March 1991 Dose-response Relationship for Non-cancer Effects Derivation of Reference Dose A dose may exist below the minimum health effect level for which no adverse effects occur. EPA typically assumes that at low doses the body's natural protective mechanisms repair any damage caused by the pollutant, so there is no ill effect at low doses. However, for some substances, noncancer effects may occur at low doses. The dose-response relationship (the response occurring with increasing dose) varies with pollutant, individual sensitivity, and type of health effect. Source: Risk Assessment for Toxic Air Pollutants: A Citizen's Guide - EPA 450/ ,March 1991 Dose-Response Curve 8

9 Dose-Response Curve Dose-Response Curve Dose-Response Curve Source: Risk Assessment for Toxic Air Pollutants: A Citizen's Guide -EPA 450/ ,March

10 Exposure Analysis & Risk Characterization Exposure Analysis - moves the assessment from known populations (lab studies, or epi studies) to other potentially exposed populations. Questions raised include: likely sources of the pollutant (incinerator, dump site, ground water) concentrations at the source, transport and transformation to target population actual levels of exposure Risk Characterization - to fully describe the expected risk by examining the exposure prediction for real-world conditions. Putting all the data together to estimate risk to population Exposure Analysis Source: Risk Assessment for Toxic Air Pollutants: A Citizen's Guide -EPA 450/ ,March 1991 Risk Characterization Source: Risk Assessment for Toxic Air Pollutants: A Citizen's Guide -EPA 450/ ,March

11 The basic equation for calculating excess lifetime cancer risk is: Risk = CDI x SF where: Estimating Cancer Risk Risk = a unitless probability of an individual developing cancer over a lifetime; CDI = chronic daily intake or dose [mg/kg-day; and risk/pci] SF = slope factor, expressed in [(mg/kg-day)-1; pci/risk] Slope Factor Slope factor is derived from bioassay results at lowest effective doses. Source: Estimating Cancer Risk Risk values for carcinogens are calculated by multiplying the lifetime average daily dose (LADD) from the exposed population times the potency or slope factor as defined in the dose-response assessment phase of the risk assessment. Let us assume an LADD of mg/kg body weight/day. We can use the potency of Aldrin at 17 cancers/mg/kg /d): = LADD x Slope factor = mg/kg/d x 17/mg/kg/d = excess cancers = one in 29 people exposed An unacceptably high risk of death. What to do? 11

12 Estimating Non-Cancer Risks The basic equation for calculating systemic toxicity (i.e., noncarcinogenic hazard) is: Noncancer Hazard Quotient = CDI/ RfD where: CDI = chronic daily intake for the toxicant expressed in mg/kg/day, and RfD = chronic reference dose for the toxicant expressed in mg/kg/day. Reference Dose Reference Dose (RfD): The RfDis a numerical estimate of a daily exposure (oral, inhalation) to the human population, including sensitive subgroups such as children, that is not likely to cause harmful effects during a lifetime. RfDs are generally used for health effects that are thought to have a threshold or low dose limit for producing effects. Estimating Reference Dose Reference dose (RfD) is estimated from either the highest dose showing no effect (NOEL) or lowest dose showing significant effect (LOEL). The dose for the most sensitive endpoint is used and divided by a safety/uncertainty factor (UF) of 10. RfD = NOEL / UF NOEL LOEL Source: 12

13 Regulatory Standards Derived from Permissible Concentrations Permissible concentration is equal to: RfD x Body weight Intake x Duration x Frequency These values are used to set regulatory standardsfor safe drinking water maximum contaminant levels, permissible exposure limits in the workplace, and pesticide residue limits in food and feed products. Note that for those with small body weights, such as children the permissible concentration levels within the environment will have to be lower. Source: Routes of Exposure and Other Complexities Routes of Exposure Oral Dermal Inhalation Others Duration of Exposure Acute Chronic Age of Exposed Population Complex Mixtures A Simple Example Assume: A job-related exposure to an airborne toxic chemical has been detected. (assume inhalation exposure) hazard assessment A review of literature shows that past studies of exposed workers showed excess cancers. hazard assessment & dose/response Based on estimated occupational exposures and inhalation studies with laboratory rats, the estimated toxicity of this chemical is 10-3 /(mg/kg/d). dose/response Monitoring of site showed average exposure was 10 years at 0.1 mg/m 3. exposure assessment 13

14 Standard Values Used in Risk Assessment Standard Inhalation Values A Simple Example Estimate dose (concentration x inhalation) m mg 1 mg kg = d 70 kg d m Adjust SF for period of exposure and breathing rate kg d 10yr 250d 10m d 3 mg 70yr 365d 10.8m d Thus risk to workers is kg d = mg 6 14

15 Quality of Risk Estimates Quality of Risk Estimates only as good as the data and assumptions. How extensive is the data base? Does it include human epidemiological data? Does the laboratory data base include test data on multiple species? Did all species respond the same? What are the scientific uncertainties? What working assumptions underlie the risk assessment? What is the overall confidence level in the risk assessment? Risk Assessment/Risk Management Uncertainties and Policy Choices Policy Choices - The outcome of a risk analysis is affected by the assumptions made during the process. Different experts may have different views about what is important or how factors should be weighted. Politics will affect what experts are heard and what assumptions are used. 15

16 Statutory Mandates on Risk EPA responsible for implementing about a dozen major environmental statutes. Many include specific risk management directives: Pure Risk Standards - also called zero-risk standards. Delaney clause of Federal Food, Drug and Cosmetic Act once prohibited the approval of any food additive that has been found to induce cancer in humans or animals. Very controversial. (repealed in 1998) Clean Air Act - calls for primary standards for 6 listed pollutants that protect the public health allowing an adequate margin of safety (assures protection of public health without regard to technology or cost factors). Statutory Mandates on Risk Technology-Based Standards - direct the Agency to focus on the effectiveness and cost of alternative control technologies rather than on how control actions could affect risks. Best examples are the Clean Water Act that require industries to control wastes using best available technology, best conventional technology or best demonstrated control technology. Which of these that are required consider total costs, age of equipment, processes involved, engineering and environmental factors. Statutory Mandates on Risk No Unreasonable Risk Standards - require balancing risk against benefits in making risk management decisions. The Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) requires EPA to approve and license pesticides that will cause no unreasonable adverse effects on the environment. These decisions take into account economic, social, and environmental costs and benefits. The Toxic Substances Control Act (TOSCA) requires EPA to take action if it finds a chemical substance presents or will present an unreasonable risk or injury to health or the environment. 16

17 Comparative Risk Analysis EPA must resort to some method of setting priorities. Ideally the most important problems should get the most attention. However, many forces play a critical role in directing policy: statutory mandates, considerations of costs and benefits, the state of technology, environmental equity, public values and concerns. Comparative risk analysis attempts to use objective, relevant, and fair means to set priorities. Comparative Risk Analysis Process - teams of experts put together a list of problems then sort the problems by types of risk (e.g. cancer, non-cancer health, materials damage, ecological effects ) they rank within each type by severity of effects, the likelihood of problem occurring, the number of people exposed, the result is a prioritized list of problems that are then modified by factors listed above. Comparative Risk Analysis Funding does not reflect the results of this priority setting process. Funds set up for construction of wastewater treatment plants and superfund accounted for over 70% of the 1990 EPA budget. Only 16% was allocated toward the high risk problems (indoor radon, indoor air, stratospheric ozone, global warming received 2% in 1992). Congress also adds unfunded projects which EPA must address. 17

18 Public s Risk Perception Public s perception of risk drives environmental budget often causing spending inefficiencies. Source: Environmental Science Systems and Solutions, M.L. McKinney, R.M. Schoch, West Publishing, Readings on Topic 18