Arsenic in Drinking Water in Taiwan*

1
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
19978545-550.
2
Drinking Water Turbidity in PhiladelphiaMeasurem
ent Surrogates for Exposure

• Ecologic study Childrens 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
19978615-620.
3
Proximity to Hazardous Waste SitesGeographic
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
19978347-354.
4
Exposure Assessment Methods Protective (versus
Predictive) Assessments

• 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

Applications of exposure assessment
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Conservative Assumptions
Hazardous waste site remediation
Lifetime air pollution exposure
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Predictive Assessments

• 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

A major difference exists between predictive and
protective assessments
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Components of Environmental Exposure Assessment

• 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

Transport and transformation
Human contact exposure
Contaminant source emissions
Accumulation in environment
Potential dose to body
Internal dose
Early expression of disease
Health Effect
Biologically effective dose
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Uncertainty analysis variability versus
uncertainty

• 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

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Evaluation of significance of estimated exposures
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
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Chemical And Biological Contaminants In Workplace
Air
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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.

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

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The IOM Personal Inhalable Aerosol Sampler
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The Photoionization Real-time Detector For
Organic Vapors
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Ionizing Radiation Concept Of Radiation Dose

• 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

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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)

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Monitors For Exposure / Dose

• Activity ratemeters-
• ionization chambers.
• Geiger-Mueller counters, etc.
• scintillation counters.
• Personal dosimeters-
• film badge (amount of darkening dose).
• pocket dosimeter.

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Thermal Stress

• PHYSICAL ENVIRONMENT
• temperature
• humidity
• ambient wind
• work rate

• HUMAN ENVIRONMENT
• work rate
• heart rate
• oral temperature
• level of hydration

20
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.

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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

22
Vibration

• PROPERTIES
• displacement
• velocity
• acceleration
• resonance

• MEASUREMENT
• accelerometers (piezoelectric) to measure
  acceleration in both magnitude and direction

23
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.

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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

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Other Exposures . . . .

• SPECIAL PROBLEMS IN ASSESSING EXPOSURES
  THROUGH THE DERMAL AND INGESTION ROUTES

• WHAT ARE RELEVANT INDICES OF EXPOSURE?

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Retrospective Exposure Assessment

• . . . . . LOOKING BACKWARDS SO WE CAN PREDICT
  FORWARDS

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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).