Response General Approaches To Risk Assessment Where the Question of Health Risk is Raised Qualitative approach using scientific judgment Quantitative approach using safety factors Human EPI Data Animal Data Quantitative approach using mathematical models Log Dose Quantitative approach using linear extrapolation Paustenbach 1995 What Drives Most Types of Environmental Health Risk Assessment There are many types of risk assessment Cancer Developmental toxicity Neurotoxicity Cancer Risk Assessment Population risks for environmental carcinogens are usually set at one additional cancer per 100 000 or 1 000 000 individuals Occupational risks are frequently much higher with one additional cancer per 1 000 workers being not uncommon 1 Hazard Identification A qualitative risk assessment Does an agent have the potential to increase the incidence of cancer under any conditions Exposure Assessment EPA uses the cumulative dose received over a lifetime This is expressed as the average daily exposure Occupational exposures are usually based on exposure during the work week Dose Response Assessment The relationship between dose and response cancer incidence Two sets of data are usually available Data in the observable range Extrapolation to responses below the observable range Risk Characterization Provides an overall conclusion and confidence of risk for the risk manager Gives the assumptions made Explains the uncertainties Outlines the data gaps 2 Issues Related to Uncertainty in Risk Assessment Major Default Assumptions in Cancer Risk Assessment High to low dose extrapolation Chemicals that are carcinogenic in animals are expected to be carcinogenic in humans Species to species extrapolation Humans are assumed to be as sensitive as the most sensitive animal Mechanism of carcinogenesis The dose response is assumed to be linear Interindividual differences Emerging Issues in Biologically based Risk Assessment Potential of Molecular Dosimetry in Risk Assessment Incorporation of PBPK models Use of molecular dosimetry as a surrogate of exposure Role of cell proliferation Mode of action information Life stage differences in susceptibility High to low dose extrapolation Saturation of metabolic activation Saturation of detoxication Saturation of DNA repair Route to route differences Species to species differences 3 Bradford Hill Criteria for Cancer Causation How is Causality Determined IPCS EPA Framework for Evaluating Mechanistic Data Introduction Postulated mode of action Key events Dose response relationship Temporal association Strength consistency and specificity of association with key events Biological plausibility and coherence Other modes of action Assessment of mode of action Uncertainties inconsistencies and data gaps Consistency Strength Specificity Temporality Coherence Dose Response Biological Plausibility Experimental Support Analogy Chemical Exposure air water food etc k1 Internal Exposure k2 Metabolic Activation k 3 k Macromolecular Binding DNA RNA k5 4 Detoxication Protein Biomarker Biologically Effective Dose X Efficiency of Mispairing X k 6 Initiation Cell Proliferation 4 SOURCES OF MUTATIONS Increasing Adduct Concentration Sublinear a c ENDOGENOUS DNA DAMAGE EXOGENOUS DNA DAMAGE Free Polymerase Environmental Life Radicals Errors Depurination Agents Styles b DNA REPAIR Supralinear CELL REPLICATION Increasing External Exposure MUTATION Progression Initiating Event Cell Proliferation clonal expansion nt Eve ting a t Mu ond Sec Cell Proliferation ng tati Mu rd i h T nt Eve Cell Proliferation Malignancy 5 A Moolgavkar Representation of Multistage Carcinogenesis D D Role of Increased Cell Proliferation in Carcinogenesis Decreases time available for DNA repair 2 S 2 I I S Necessary for chromosomal aberrations insertions deletions and gene amplification I S S M First Event Clonally expands existing cell populations I Second Event Oxidative Stress Induced DNA Damage DNA Base Modification ROS Lipid Peroxidation Lipid Peroxide MDA 4 HNE DNA Base adduct M1G edG edA Control Rat Liver Tissues DNA Base adduct Sugar Damage Base Propenal Converts repairable DNA damage into nonrepairable mutations 8 oxo G FapyGua Glycosylase hOGG1 AP Sites Glycosylase MPG 6 0 8OHdG dG 10e 6 1 5 0 4 0 3 0 2 0 1 0 0 0 4 wk 12 wk 2 yr Rat Ages 6 Non smoker Lymphocytes Pentachlorophenol 9 00 Used as a Pesticide and Wood Preservatives Introduction to Humans Air Food and Drinking water Mutagen Rodent Carcinogen 8 00 OH 8OHdG dG 10e 6 7 00 Cl OH Cl Cl Cl Cl O Cl Cl Cl Cl Cl 6 00 Cl 5 00 Cl Cl OH OH O2 4 00 H2O2 3 00 O 2 00 Cl Cl O2 OH 1 00 Cl 0 00 1 2 3 4 5 6 7 8 9 Induced Oxidative Stress M1G formation from 1 4 TCBQ treatment Calf Thymus DNA Exposed to TCHQ 35 30 M1G in 108 Nt 50 40 8OHdG dG 10e 6 Cl O 10 30 25 20 15 10 20 5 10 0 0 0 1 1 10 TCHQ uM 100 1000 1 4 TCBQ M 0 1 10 0 1mM NADPH 0 1mM CuCl2 7 Aldehydic DNA lesions ADL in HeLa cells exposed to H2O2 0 06 20 mM for 15 min Efficiency of Low Doses of H2O2 50 Increased ADLs H 2O 2 concentration A D L 1 0 0 0 0 0 0 ntd 25 20 15 10 5 40 30 20 10 0 0 0 01 0 5 10 15 0 1 1 H2O 2 mM 20 10 100 H2O 2 mM 10000 40 N 7 Methylguanine N7Alkyl O6 Akyl O4 Alkyl O2 Alkyl Guanine Guanine Thymine Thymine MMS 85 0 3 MNU DMN ENU DEN 70 7 0 1 0 4 Alkylations 106 guanines 1000 6 O Methylguanine 30 100 10 20 1 0 1 10 A 0 01 14 7 2 7 0 001 0 001 Alkylations 106 guanines DNA Alkylation B 0 0 01 0 1 1 10 100 0 1 2 3 DMN mg kg 8 1 20E 05 O4 EtdThd 8 00E 06 6 00E 06 4 00E 06 2 00E 06 O6 EtdGuo 0 00E 00 0 10 20 30 40 50 60 70 80 Duration of DEN exposure days Vinyl Chloride Molecular Dosimetry of DEN 100 100 15 15 O2 ET ET pM dT M Molar ratio in DNA 1 00E 05 80 O4 ET 10 10 5 5 80 60 60 0 0 5 10 15 0 20 40 40 20 20 Vinyl chloride is a known human and animal carcinogen that induces hepatic angiosarcomas Carcinogenic response is associated with high exposure 50 ppm To date 178 VC workers have developed hepatic angiosarcomas All of them started work prior to lowering the occupational exposure 1 ppm Vinyl chloride is present in many Superfund sites and some public drinking water in ppb amounts 0 0 0 20 40 60 Dose ppm DEN 80 100 9 Vinyl Chloride Metabolism Exposure Response for Vinyl Chloride Metabolism and Carcinogenicity Cl O O 10000 g 6 hr Cl Cl DNA Adducts Epoxide Hydrolase Gehring et al 1978 Alcohol dehydrogenase Glutathione Detoxication O 5000 ASL Incidence P 450 0 2 0 1 Maltoni et al 1981 0 0 0 0 1000 2000 3000 4000 OH VC Exposure ppm 0 2000 4000 6000 VC Exposure ppm Cl HO Formation of 13C2 DNA