arsenic in drinking water in taiwan* ecologic study of 243 townships (11.4 million residents)...

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 1976.– 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;8:545-550.

Drinking Water Turbidity in Philadelphia*Measurement Surrogates for Exposure

• Ecologic study: Children’s hospital visits for Gastrointestinal Illness in Philadelphia

• Turbidity for 5 years (1989-1993)– 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;8:615-620.

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;8:347-354.

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

Environmental and Occupational

Epidemiology

Risk Assessment

Risk Management

Disease Diagnosis and Treatment

Current & Historical

Prospective

Assessment of regulatory compliance

Eval. of interventions to reduce exposure

Estimate exposure status & trends

A P P L I C A T I O N S

Applications of exposure assessment

Hazardous waste site remediation Lifetime 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

Applications of Exposure Assessment

Environmental and Occupational

Epidemiology

Risk Assessment

Risk Management

Disease Diagnosis and Treatment

Current & Historical

Prospective

Assessment of regulatory compliance

Eval. of interventions to reduce exposure

Estimate exposure status & trends

A P P L I C A T I O N S

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 PELsNIOSH RELs, IDLH

Community standardsEPA 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 ExposureFR

EQ

UEN

CY

TWA EXPOSURE INTENSITYFOR 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 . . . .

SPECIAL PROBLEMS IN ASSESSING EXPOSURES THROUGH THE DERMALDERMAL AND INGESTION 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).