Document R2Bdmz09BX5e16BJKywVezLDk

Issues Motivating the Collection of Occupational Exposure Data S. M. Rappaport, Ph.D. University of California, Berkeley srappaport@berekeley.edu Topics Why measure airborne chemicals? - Hazard control v. health surveillance (epidemiology) - Air measurements v. exposures Evolution of air and exposure measurements Exposure variability and its sources How many measurements? If you build it will they come? Biomarkers of exposure 2 Health Surveillance v. Hazard Control Health surveillance (epidemiology) - Primarily focus upon long-term effects (years-decades) Investigate exposure-response relationships Best with extensive long-term quantitative exposure data Hazard control - Focus upon both short-term and long-term hazards Short-term: (seconds-hours, e.g., H2S, CO, NO2, NH3) Require air (not exposure) measurements in some cases Long-term: (years-decades, e.g., benzene, PAHs, asbestos, heavy metals) Require extensive long-term exposure data 4 Evolution of Air and Exposure Measurements Type Air /Exposure Time frame Area Breathing zone Personal Direct-reading (hand-held or personal) Air Exposure Exposure Air or exposure 1920 - present 1940 - present 1960 - present 1980 - present Weight (g) >1000 100 - 1000 10 -1000 1 -1000 Assay Lab Lab or direct Lab or direct Direct 5 Area Sampling: 1920s-Present (Air measurements not exposures) A: Collection of benzene by adsorption on charcoal about 1926 (Greenburg, 1926). B: Greenburg-Smith impinger used for dust sampling about 1930 (Drinker and Hatch, 1936). C: Collection of benzene by aspiration and absorption in acid about 1928 (Smyth and Smyth, 1928). D: Collection of asbestos with a highvolume sampler and a cascade impactor about 1953 (Photograph courtesy of R. Herrick). Rappaport and Kupper (2008) 6 Quantitative Exposure Assessment Breathing-zone Sampling: 1940s - Present (Moving from air measurements to exposures) Two examples of breathing-zone sampling. Left: sampling with a midget impinger of explosive vapors (probably nitroglycerine) at an ordinance plant - USA (1943). US PHS . (Photograph courtesy of R. Herrick). Right: Benzene sampling with an explosimeter and silica gel tubes during manufacture of mechanical seals - UK (1950). (Photograph courtesy of R.J. Sherwood). Rappaport and Kupper (2008) 7 Quantitative Exposure Assessment Personal Sampling: 1960s-Present (Exposure measurements) Personal samplers to measure styrene, styrene oxide and MEKP in the reinforced-plastics industry- USA (1986). Left: active sampling with sorbent tubes and micro-impinger; Right: passive sampling with activated carbon (styrene and styrene oxide only). Rappaport and Kupper (2008) Quantitative Exposure Assessment 8 Direct Measurements: 1980s - Present (Air measurements or exposures) Hand-held devices (air measurements) Direct-reading personal monitors (exposures) 9 Exposure Variability Styrene levels in a boat factory (162 personal measurements - 1986-87) Data from: Rappaport, et al. Cancer Res, 56: 5410-5416 (1996) Air Sample Assay error (0.2-fold) Exposure Variability Welding-fume exposures among construction workers (198 measurements from 62 workers in 4 trades - 1996-97) Data from: Rappaport etal. Ann. Occup. Hyg. 43:457-469, 1999 1000-Fold range 12 Exposure Variability Welding-fume exposures among construction workers (198 measurements from 62 workers in 4 jobs) Group variability (4-fold) Data from: Rappaport etal. Ann. Occup. Hyg. 43:457-469, 1999 13 Determinants of Exposure to Welding Fumes (From fixed effect in mixed models) 56 40 - 10 30 20 10 CD 0 8 6 Cj a 4- CD 2 - I0 1,0 Activity 1,1 7 1,0 Activity 8 1,1 10 5 &8 6 CJoc 4 - Q) 2 " !0 4 3 2 0 Afe # Activity 1,1 1,0 Activity 1,1 Fig. 7.6 Predicted mean exposures to welding fumes for Groups 5 - 8 (5=BM; 6=IW; 7=PF; 8=WF), based upon the model shown in Table 7.5. Activity (IO, TW): (0,0)=outdoor brazing/cutting; (0,1)=outdoor welding; (1,0)=indoor brazing/cutting; (1,1)=indoor welding. Controls consisted of local-exhaust or mechanical ventilation (VE = 1) and reduction of hot work to less than 50% (CI = 1). (Note that magnitudes of the y-axes differ across groups). Rappaport and Kupper (2008) Quantitative Exposure Assessment Why so variable? Multiplicative effects of several variables - Jobs (fixed) - Time (fixed) - Locations (fixed or random) - Sources of contamination (fixed or random) - Activities and equipment (fixed or random) - Worker/source mobility (mostly random) - Environmental conditions (mostly random) Implications of Exposure Variability Health surveillance (focus upon chronic health effects) - Many personal measurements needed to characterize long-term exposures - Longitudinal studies, evaluate variation within and between persons and across groups Cannot assume all workers in a group are equally exposed - Advanced statistical models (mixed-effects models) Hazard control - Long-term hazards: same issues as above for health surveillance (repeated personal measurements, mixed modeling, etc.) - Short-term hazards: focus shifts to air levels/warnings of immediate dangers (high air concentrations not exposures) Only most acutely toxic substances Area sampling sufficient (e.g., confined spaces or at point of release) 19 Sample Sizes for Air Measurements (1920s -1950s) Focus upon health effects (exposure-response) Few professionals (mostly governmental) Cumbersome equipment No OELs Few studies but relatively large sample sizes (hundreds of measurements) Variability recognized Desired accurate estimates of average levels for each location or factory Classic study of Oldham and Roach (1952) 779 Breathing zone measurements (3-min) randomly collected repeatedly from Welsh coal miners 20 Repeated Random Measurements APPENDIX JtiSUVrs OF " RANDOM COLLEEFL5 " aUllVSV Total T:tHC .Spent on Coal' 1 Him. i Duration of M]d- shift Hreak (mio.) Thermal PrcCipLtator Sample* lNo_ pE particles pet ml. bci^cem D\5 and S-Om I 315 430 2-- i 350 365 4 345 5_ 25 l,0 S00 M00 920 1.500 l(?70 gj ] ,430 1,540 15 950 *100-- Cottier no huger working ?t pit 20 <100 1,320 650 <100 <100 3*0 [<J00| + < [00 21Q ISO 20 SOU Mtt pu 8B0 430 430 390 3b0 460 440 20 1,750 1,690 2,030 2,730 1,980 940 1,360 2,070 2.190 330 2,650 1" Collier tfbseiu on both occasiona 6 270 335 7 325 3*5 & JOG 3*5 20 570 <100 <100 {HQ) 310 740 2,000 j:o 25 240 170 450 56U 320 2W (<L0Q) 320 520 820 520 510 40 390 700 920 1,240 1,580 1,330 910 530 35 U10 730 (<100>(<100) 750 1,090 720 1.130 580 770 25 JB0 770 470 (<KXJ) 25 350 ],460 800 1,230 1,150 1,010 i,<100} 460 920 7W 840 A portion of an appendix originally published by Oldham and Roach (Oldham and Roach, 1952). Each entry represents the dust level for a random 3-min sample obtained from a coal worker. Note that several such measurements were obtained from each subject on a given day. Rappaport and Kupper (2008) 21 Quantitative Exposure Assessment First Application of Lognormal Distribution to Occupational Data 200 r Histogram of logged deviations of 779 breathingzone measurements of dust in British coal mines [from Oldham (1953)]. Provides basis for advanced statistical modeling of data Deviation of log concentration from shift mean log (particles/ml.) Fig. 2.--Distribution of deviations of 779 cranslormcd samples from their shift means, with the Normal curve ot equal area and standard deviation 0*2203 Rappaport and Kupper (2008) Quantitative Exposure Assessm 22t Exposure Data in Modern Epidemiological Studies Only 13% of studies used quantitative measurements From: B.K. Armstrong et al. Principles of Exposure Measurement in Epidemiology, Oxford Med. Pubs., 1992 Sample Sizes for Workplace Measurements after OSH Act of 1970 Many professionals (mostly employer-based) Advanced personal samplers and direct-reading monitors Focus upon hazard control rather than health surveillance - Only 16 new OSHA PELs since 1971 Almost all air monitoring for acute hazards ('safety'), e.g., confined spaces, LEL, O2 deficiency, substances IHTL Few measurements for chronic health effects - Median = 4 meas. from 696 published studies reviewed by Symanski et al. (1967-1996) What about industrial surveys? 24 Sample Sizes for Industrial Surveys Numbers of measurements obtained in 4864 annual surveys of occupational groups of workers in the nickel producing industry 1970 - 1990. [From (TorneroVelez et a/., 1997)]. 25 Better Equipment & More Professionals but Fewer Measurements - Why? Current trends - From government inspectors to employer-based inspectors (vested interests) - Increasing reliance on measurement-free methods ('exposure models', 'control-banding', etc.) - From exposure-response (long time frame) to compliance with OELs (short time frame) OELs have existed since the 1950s - Prior to 1970 OELs were guides - After OSH Act they became legal limits 26 Compliance Testing Rarely performed by OSHA inspectors - Fewer than 10,000 health inspections per year in 2.5 million US workplaces (P{health inspection} < 0.004/year) Vast majority performed by employers who must provide workplaces "...free from recognized hazards." - Company representatives (e.g., IH) can measure personal levels of persons in all groups with potential for excessive exposures One-to-one comparison of observed air levels with PEL - Compliance: All measurements < PEL No additional measurements needed 27 Probability of Compliance Let yh represent the probability that a person in Group h would be exposed on one day above the OEL (exceedance of Group h) - Yh = PXj > OEL} Then the probability of compliance for Group h is P{Q = (1 -Yh)Nh Rappaport and Kupper (2008) Quantitative Exposure Assessment 28 Noncompliance and Sample Size Rappaport and Kupper (2008) Quantitative Exposure Assessment 29 Noncompliance and Sample Size Since P(Ch} depends greatly on Nh, employers have incentive to maximize P(Ch} by making very few measurements (Compliance testing can only be applied with small sample sizes) Rappaport and Kupper (2008) Quantitative Exposure Assessment 30 The Advantage of Air Monitoring OSHA standards mandate air monitoring for conditions IHTL (safety standards) Employers have incentives to avoid situations IHTL (confined spaces, trigger alarms, etc.) Acute hazards easily assessed (reduces employer liability) Hundreds of direct-reading air monitors commercially available Employers prefer to measure air levels of chronic toxicants because they are not clearly tied to exposures Use of area rather than personal measurements Evaluating air levels for tasks rather than workers Can ignore between-worker differences in exposure 31 The Problem with Exposure Monitoring Under the OSH Act the burden of proof is upon the government to prove noncompliance with PELs - But there are essentially no government inspections (the OSH Act is based upon voluntary compliance!) - The use of compliance testing implicitly discourages exposure monitoring But - chronic health effects are slow to develop and difficult to relate to exposures without extensive exposure monitoring - Many employers don't want extensive exposure data in their files The situation is unlikely to change without a paradigm shift, such as REACH (Registration, Evaluation, Authorization and Restriction of Chemical Hazards) which places the burden of proof on the manufacturer to prove the safety of its products 32 If you build it will they come? (You've got a DREAM ...) Nanosensors of the future: Ultra-small personal monitors Multiple analytes Data logging Measure all workers' exposures - to everything - all the time! I. Simon et al. / Sensors and Actuators B 73 (2001) 126 Air monitoring 1920 1970 2008 Trends for measurements None of the Ik workers Half the workers All the workers Ever Half the time All the time 1920 2008 Exposure monitoring 33 What about biomarkers of exposure? Described in: Yager, et al. (1993) Mut. Res. 319:155-165. 34 Styrene in Air and Breath Reinforced-plastics workers (3 - 7 meas./subj.) Data from: Rappaport, et al. Cancer Res, 56: 5410-5416 (1996) 35 Styrene in Air and Breath Reinforced-plastics workers (3 - 7 meas./subj.) Data from: Rappaport, et al. Cancer Res, 56: 5410-5416 (1996) 1 10 100 1000 GM Air Styrene (mg/m3) 36 DREAM Biomarkers of Exposure Good idea - Highly relevant to exposure and health effects - When used with exposure measurements can illuminate important human kinetic processes - Adaptable to nanosensing and LOC systems (high throughput, multiple analytes) But U.S. employers don't like biomarkers (even less than personal exposure measurements) - Few OSHA standards require biomonitoring (Pb, Cd) - More demand in Europe, Asia, and for non-occupational exposures in the U.S. Self-Assessment of Exposure Before Passive monitor Rappaport and Kupper (2008) Quantitative Exposure Assessment 10000 1000 o 100 7 Oflo' 10000 1000 CT) 100 \ Cl) 10 20 Worker o o S , 8 o 20 30 Worker Fig. 3.2 Exposures to terpenes in sawmills (top) and to styrene in reinforced plastics factories (bottom). Open circles represent self-measurements made by workers and closed circles represent measurements made by an occupational hygienist on different days. Numbers represent different workplaces of a particular type. [Data from Liljelind et al. (2001)]. Take Home Messages Historically, exposure measurements were the holy grail that motivated breathing zone and personal sampling for studies of health effects - Early studies recognized exposure variability and included many measurements as a result 39 Take Home Messages Hazard control trumps health surveillance for contaminant measurements in U.S. workplaces - Regulatory focus is upon acute (safety) hazards not health hazards - Only 16 new OSHA standards in 37 years - Emphasis upon compliance with PELs discourages employers from monitoring exposures - Reinvigorating exposure monitoring will require a paradigm shift (e.g., REACH-type system) Take Home Messages Exposure levels vary tremendously across groups, between workers (within groups), and within workers over time - Puts a premium on repeated exposure measurements over the long term - Sophisticated statistical models needed to characterize exposures and their determinants 41 Take Home Messages Applications of DREAM technology for air (rather than personal) measurements are straightforward - Satisfy needs for control of acute hazards Extending DREAM to collect large numbers of measurements of personal exposure or biomarkers will require a shift in regulatory focus and/or enforcement 42 30 Years of thinking - in 183 pages The vagaries of exposure limits Measurement-based exposure assessment Statistical tools for exploring exposure variability Within- and between-worker sources of variability Determinants of exposure Implications for hazard control and epidemiology Choosing between environmental measurements and biomarkers Available from Lulu Press http://www.lulu.com/content/1341905 43