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