Arsenic in Drinking Water in Taiwan* Ecologic study of 243 townships (11.4 million residents) National survey of arsenic in 80,000 wells conducted between 1974 and –Arsenic levels for each well grouped into 6 categories to reflect precision of method –Percentage of wells in each category for each township used for analysis * Guo et al. Arsenic in Drinking Water and Incidence of Urinary Cancers. Epidemiology 1997;8:

Drinking Water Turbidity in Philadelphia* Measurement Surrogates for Exposure Ecologic study: Children’s hospital visits for Gastrointestinal Illness in Philadelphia Turbidity for 5 years ( ) –Collected to meet EPA requirements –A surrogate for microbial contamination and effectiveness of water treatment –Daily mean from 3 water treatment plants serving different areas Time series analysis adjusted for season, temperature & day-of-week with lagged exposure * Schwartz et al. Drinking Water Turbidity and Pediatric Hospital Use for Gastrointestinal Illness in Philadelphia, Epidemiology 1997;8:

Proximity to Hazardous Waste Sites* Geographic Surrogates for Exposure Population: mothers of birth defect cases and controls in California –Residential histories during “periconceptual” period Location of 764 hazardous waste sites identified –105 National Priority List sites identified & information on site-related contamination collected (media contaminated, chemicals, clean-up, etc) –Census tract, latitude/longitude & boundaries identified Analysis: census tract & residence within 1 mile *Croen et al. Maternal residential Proximity to Hazardous Waste Sites and Risk for Selected Congenital Malformations. Epidemiology 1997;8:

 Protective assessments are designed for initial investigations as a screening tool, and for risk- based corrective actions.  General criterion is conservatism, e.g., use of worst- case scenario for potential exposure and risk.  Often estimates exposure to most-exposed individual, MEI, a hypothetical individual.  Use of generic parameters  Often criticized as overly conservative  Protective exposure assumptions often used in prospective risk assessments Exposure Assessment Methods: Protective (versus Predictive) Assessments Applications of exposure assessment

Hazardous waste site remediationLifetime air pollution exposure Conservative Assumptions

Predictive assessments are designed to assess actual exposure (risk) to population for use in epidemiological, dose- response studies.  Uses reasonable case scenario, most likely scenarios  Requires demographic information  Requires site-specific parameters Predictive Assessments A major difference exists between predictive and protective assessments

 Determine and characterize source(s)  Identify exposure pathway(s) & environmental fate  Estimate concentration at human/environment boundary  Perform integrated exposure analysis  Identify exposed population  Uncertainty analysis (throughout)  Evaluate significance Components of Environmental Exposure Assessment Transport and transformation Contaminant source emissions Accumulation in environment Human contact exposure Potential dose to body Early expression of disease Health Effect Biologically effective dose Internal dose

 Uncertainty represents a lack of knowledge about factors affecting exposure or risk, whereas variability arises from true heterogeneity across people, places, or time  Uncertainty can lead to inaccurate or biased estimates, whereas variability can affect the precision of the estimates and the degree to which they can be generalized Uncertainty analysis: variability versus uncertainty

1. Comparison to Exposure Limits Consensus, regulatory, and/or guideline levels are available for many agents. Occupational standards (all for airborne contaminants) ACGIH TLVs OSHA PELs NIOSH RELs, IDLH Community standards EPA NAAQS(ambient air contaminants) FDA ADI (food contaminants) EPA MCLs(drinking water contaminants) WHO guidelines (various media) 2. Estimation of Individual and Population Risks = Risk Assessment Evaluation of significance of estimated exposures

Chemical And Biological Contaminants In Workplace Air

Similarly Exposed Group (SEG) Of Workers... A GROUP OF WORKERS DEFINED BY THE EXPECTATION THAT, ON AVERAGE, THEY WILL BE EXPOSED TO THE SAME CONTAMINANT COMING FROM THE SAME SOURCES.

Variability Of Exposure FREQUENCY TWA EXPOSURE INTENSITY FOR THE SEG STUDIED MEDIAN LOG-NORMAL DISTRIBUTION OEL

Technical Methods For Air Sampling In Workplaces FIXED POINT, STATIC or AREA SAMPLING: now mostly absent in developed countries (with notable exceptions). PERSONAL SAMPLING NOW CONSIDERED TO BE THE ‘NORM’: small personal sampling devices worn on the lapel or jacket in the breathing zone.

The ‘IOM’ Personal Inhalable Aerosol Sampler

The Photoionization Real-time Detector For Organic Vapors

DOSE: the quantity of radiation energy absorbed by a given mass. SIEVERT (Sv): the amount of absorbed radiation, weighted according to the biological effectiveness of the radiation Ionizing Radiation: Concept Of Radiation ‘Dose’

Typical Radiation Exposures Radiologists (X and  ): 0.7 mSv/year Flight crews (X and  ): 1.7 mSv/year Nuclear power plant workers (PWR) (  ): 4.9 mSv/year Dentists (X): 0.7 mSv/year Nuclear power plant workers (PWR) (neutron): 0.5 mSv/year Uranium mining (  ): 11 mSv/year (Note: OEL = 50 mSv/year)

Activity ratemeters:- –ionization chambers. –Geiger-Mueller counters, etc. –scintillation counters. Personal dosimeters:- –film badge (amount of darkening ~ dose). –pocket dosimeter. Monitors For Exposure / Dose

Thermal Stress PHYSICAL ENVIRONMENT –temperature –humidity –ambient wind –work rate HUMAN ENVIRONMENT –work rate –heart rate –oral temperature –level of hydration

Noise The physical intensity of sound or noise is expressed in units of sound pressure level. But the decibel (dB) scale is used to contract (logarithmically) the range of numbers we would have to measure.

Measurement of Noise Sound level meter (SLM) –instantaneous dBA (or dBC) levels Personal noise dosimeter –time-integrated dose Noise-intensity analyzer –magnitude and direction of noise Narrow-band analyzer –to investigate noise sources, to indicate frequency content

Vibration PROPERTIES displacement velocity acceleration resonance MEASUREMENT accelerometers (piezoelectric) to measure acceleration in both magnitude and direction

Injury: Exposure To Risk Of Accidents By Truck Drivers Technical factors (technical review) –type of vehicle –hours driven –seasonal –geographical, etc. Human factors (questionnaire) –education and training –personality –state of health –experience, etc.

Injury: Exposure To Risk Of Repetitive Strain Injury Technical factors (technical review) –exposure situation –hours exposed –exposure frequency Human factors (questionnaire):- –education and training –personality –state of health

Other Exposures.... DERMAL INGESTION SPECIAL PROBLEMS IN ASSESSING EXPOSURES THROUGH THE DERMAL AND INGESTION ROUTES WHAT ARE RELEVANT INDICES OF EXPOSURE?

Retrospective Exposure Assessment..... LOOKING BACKWARDS SO WE CAN PREDICT FORWARDS

Rationale To re-construct past exposures to provide more complete exposure histories in order to better perform epidemiologic studies for environment-related diseases that have very long time scales (e.g., some cancers).