Confined space ventilation by shipyard welders: observed use and effectiveness

Shipbuilding involves intensive welding activities within enclosed and confined spaces, and although ventilation is commonly used in the industry, its use and effectiveness has not been adequately documented. Workers engaged in welding in enclosed or confined spaces in two shipyards were observed for their use of ventilation and monitored for their exposure to particulate matter. The type of ventilation in use, its placement and face velocity, the movement of air within the space, and other ventilation-related parameters were recorded, along with task characteristics such as the type of welding, the welder's position, and the configuration of the space. Mechanical ventilation was present in about two-thirds of the 65 welding scenarios observed, with exhaust ventilation used predominantly in one shipyard and supply blowers predominantly in the other. Welders were observed working in apparent dead-spaces within the room in 53% of the cases, even where ventilation was in use. Respiratory protection was common in the two shipyards, observed in use in 77 and 100% of the cases. Welding method, the proximity of the welder's head to the fume, and air mixing were found to be significantly associated with the welder's exposure, while other characteristics of dilution ventilation did not produce appreciable differences in exposure level. These parameters associated with exposure reduction can be assessed subjectively and are thus good candidates for training on effective ventilation use during hot work in confined spaces. Ventilation used in confined space welding is often inadequate for controlling exposure to welding fume.

Measurement of spatial and temporal variation in volatile hazardous air pollutants in Tacoma, Washington, using a mobile membrane introduction mass spectrometry (MIMS) system

The objective of this study was to use membrane introduction mass spectrometry (MIMS), implemented on a mobile platform, in order to provide real-time, fine-scale, temporally and spatially resolved measurements of several hazardous air pollutants. This work is important because there is now substantial evidence that fine-scale spatial and temporal variations of air pollutant concentrations are important determinants of exposure to air pollution and adverse health outcomes. The study took place in Tacoma, WA during periods of impaired air quality in the winter and summer of 2008 and 2009. Levels of fine particles were higher in winter compared to summer, and were spatially uniform across the study area. Concentrations of vapor phase pollutants measured by membrane introduction mass spectrometry (MIMS), notably benzene and toluene, had relatively uniform spatial distributions at night, but exhibited substantial spatial variation during the day-daytime levels were up to 3-fold higher at traffic-impacted locations compared to a reference site. Although no direct side-by-side comparison was made between the MIMS system and traditional fixed site monitors, the MIMS system typically reported higher concentrations of specific VOCs, particularly benzene, ethylbenzene and naphthalene, compared to annual average concentrations obtained from SUMA canisters and gas chromatographic analysis at the fixed sites.

Development of a passive air sampler to measure airborne organophosphorus pesticides and oxygen analogs in an agricultural community

Organophosphorus pesticides are some of the most widely used insecticides in the US, and spray drift may result in human exposures. We investigate sampling methodologies using the polyurethane foam passive air sampling device to measure cumulative monthly airborne concentrations of OP pesticides chlorpyrifos, azinphos-methyl, and oxygen analogs. Passive sampling rates (m(3)d(-1)) were determined using calculations using chemical properties, loss of depuration compounds, and calibration with side-by-side active air sampling in a dynamic laboratory exposure chamber and in the field. The effects of temperature, relative humidity, and wind velocity on outdoor sampling rates were examined at 23 sites in Yakima Valley, Washington. Indoor sampling rates were significantly lower than outdoors. Outdoor rates significantly increased with average wind velocity, with high rates (>4m(3)d(-1)) observed above 8ms(-1). In exposure chamber studies, very little oxygen analog was observed on the PUF-PAS, yet substantial amounts chlorpyrifos-oxon and azinphos methyl oxon were measured in outdoor samples. PUF-PAS is a practical and useful alternative to AAS because it results in little artificial transformation to the oxygen analog during sampling, it provides cumulative exposure estimates, and the measured sampling rates were comparable to rates for other SVOCs. It is ideal for community based participatory research due to low subject burden and simple deployment in remote areas.

A sensitive LC-MS/MS method for measurement of organophosphorus pesticides and their oxygen analogs in air sampling matrices

A rapid liquid chromatography tandem mass spectrometry (LC-MS/MS) method has been developed for determination of levels of the organophosphorus (OP) pesticides chlorpyrifos (CPF), azinphos methyl (AZM), and their oxygen analogs chlorpyrifos-oxon (CPF-O) and azinphos methyl-oxon (AZM-O) on common active air sampling matrices. XAD-2 resin and polyurethane foam (PUF) matrices were extracted with acetonitrile containing stable-isotope labeled internal standards (ISTD). Analysis was accomplished in Multiple Reaction Monitoring (MRM) mode, and analytes in unknown samples were identified by retention time (±0.1 min) and qualifier ratio (±30% absolute) as compared to the mean of calibrants. For all compounds, calibration linearity correlation coefficients were ≥0.996. Limits of detection (LOD) ranged from 0.15-1.1 ng/sample for CPF, CPF-O, AZM, and AZM-O on active sampling matrices. Spiked fortification recoveries were 78-113% from XAD-2 active air sampling tubes and 71-108% from PUF active air sampling tubes. Storage stability tests also yielded recoveries ranging from 74-94% after time periods ranging from 2-10 months. The results demonstrate that LC-MS/MS is a sensitive method for determining these compounds from two different matrices at the low concentrations that can result from spray drift and long range transport in non-target areas following agricultural applications. In an inter-laboratory comparison, the limit of quantification (LOQ) for LC-MS/MS was 100 times lower than a typical gas chromatography-mass spectrometry (GC-MS) method.

Testing of glove efficacy against sprayed isocyanate coatings utilizing a reciprocating permeation panel

OBJECTIVES

Modify a permeation panel to evaluate dermal protective clothing for resistance to sprayed coatings with minimal variability in spray paint loading across the test panel. Determine isocyanate protection effectiveness of natural rubber latex (5 mil or 0.13mm), nitrile rubber (5 mil or 0.13mm), and butyl rubber (13 mil or 0.33mm) glove materials against a commonly used automotive clear coat formulation. The latex and nitrile gloves were the type used by the local autobody spray painters.

METHODS

Glove materials were tested by spraying paint onto an automated reciprocating permeation panel (permeation panel II). Temperature, relative humidity, and spray conditions were controlled to optimize paint loading homogeneity as evaluated by gravimetric analysis. Isocyanate permeation was measured using 1-(2-pyridyl)-piperazine-coated fiber-glass filters analyzed by a modified version of the OSHA 42/PV2034 methods.

RESULTS

Latex exhibited a higher permeation rate compared with nitrile for isocyanates (1,6-hexamethylene diisocyanate (HDI) and isophorone diisocyanate monomers) and both materials presented permeation at all of the time points suggesting a fast isocyanate breakthrough. Butyl material exhibited no permeation or breakthrough for isocyanates under the tested conditions. The spray application at 69±8°F was optimally homogeneous at 45±0.5mg weight of dry clear coat per 5cm(2).

CONCLUSIONS

The permeation panel II is a reliable method to assess dermal protective clothing performance against polymerizing coatings. Commonly used 5-mil (0.13-mm) latex and nitrile gloves were determined to be ineffective barriers against the isocyanates found in a commonly used clear-coat formulation while butyl gloves were protective.

Development of a unique multi-contaminant air sampling device for a childhood asthma cohort in an agricultural environment

This research describes the design, deployment, performance, and acceptability of a novel outdoor active air sampler to provide simultaneous measurements of multiple contaminants at timed intervals for the Aggravating Factors of Asthma in Rural Environment (AFARE) study-a longitudinal cohort of 50 children in Yakima Valley, Washington. The sampler was constructed of multiple sampling media connected to individual critical orifices and a rotary vane vacuum pump. It was connected to a timed control valve system to collect 24 hours samples every six days over 18 months. We describe a spatially representative approach with both quantitative and qualitative location criteria to deploy a network of 14 devices at participant residences in a rural region (20 × 60 km). Overall the sampler performed well, as the concurrent mean sample flow rates were within or above the ranges of recommended sampling rates for each exposure metric of interest. Acceptability was high among the study population of Hispanic farmworker participant households. The sampler design may prove useful for future urban and rural community-based studies with aims at collecting multiple contaminant data during specific time periods.

Comparison of polyurethane foam and XAD-2 sampling matrices to measure airborne organophosphorus pesticides and their oxygen analogs in an agricultural community

Side-by-side active air sampling for the organophosphorus (OP) pesticide, chlorpyrifos (CPF) and its oxygen analog, chlorpyrifos-oxon (CPF-O) was conducted with two recommended air sampling matrices: OSHA Versatile Sampling (OVS) tubes with XAD-2 resin, polyurethane foam (PUF) tubes, and passive PUF deposition disks. The study compared the proportion of artificially transformed CPF-O in the laboratory and in the field during a tree fruit application in Washington State. Lab results demonstrated that the NIOSH-recommended OVS tubes artificially transformed up to 32% of CPF to CPF-O during the sampling process, whereas PUF tubes had little to no artificial transformation (⩽0.1%). In the field, the proportion of CPF-O in the sample was significantly higher on OVS tubes than on PUF tubes (p<0.001), confirming that OVS tubes were converting a significant portion of CPF to CPF-O. In addition, PUF tubes reported measurable levels CPF-O in the field even when no artificial transformation was expected. We conclude that the PUF matrix is the superior sampling medium for OP oxygen analogs when compared to XAD-two resin. Community-located PUF tube samples 24h post-application had considerably higher levels CPF-O (16-21ngm(-3)) than near field samples during application (2-14ngm(-3)), suggesting that the oxygen analog is volatile and formed during atmospheric transport. It is recommended that worker and community risk assessments begin to take into consideration the presence of the more toxic oxygen analogs when measuring for OP pesticide mixtures.

Evaluation of urinary metabolites of 1-nitropyrene as biomarkers for exposure to diesel exhaust in taxi drivers of Shenyang, China

Diesel exhaust (DE) is a significant contributor to the toxicity associated with particulate matter (PM). 1-Nitropyrene (1-NP) has been used as a molecular marker for DE, and the urinary metabolites of 1-NP have been proposed as biomarkers for exposure to DE. In this study, several urinary 1-NP metabolites were evaluated for their utility as markers of short-term exposures to DE. The study population was a cohort of 24 taxi drivers from Shenyang, China, who submitted urine samples collected before, after, and the next morning following their workshifts. The urinary metabolites studied were isomers of hydroxy-1-nitropyrene (3-, 6-, 8- OHNPs) and hydroxy-N-acetyl-1-aminopyrene (3-,6-, 8-OHNAAPs). Exposure to DE was estimated based on exposure to 1-NP in air samples collected during and after the driver's workshift; 6- and 8-OHNP, and 8-OHNAAP were consistently detected in the drivers' urine. Concentrations of the metabolites in the taxi drivers' urine were greater than metabolite levels previously reported in non-occupationally exposed subjects; however no associations were observed between subject-specific exposures to 1-NP and urinary metabolites measured at the end of the workshift or in the next morning void. Significant autocorrelation was observed in metabolite levels in successive urine samples, from which half-lives for urinary elimination of ~10-12 h were estimated. These observations suggest that, in an occupational setting, urinary 1-NP metabolites may be more suitable as markers of ongoing exposure (timescales of several days) rather than indicators of acute exposure associated with single workshifts.

Presence of organophosphorus pesticide oxygen analogs in air samples

A number of recent toxicity studies have highlighted the increased potency of oxygen analogs (oxons) of several organophosphorus (OP) pesticides. These findings were a major concern after environmental oxons were identified in environmental samples from air and surfaces following agricultural spray applications in California and Washington State. This paper reports on the validity of oxygen analog measurements in air samples for the OP pesticide, chlorpyrifos. Controlled environmental and laboratory experiments were used to examine artificial formation of chlorpyrifos-oxon using OSHA Versatile Sampling (OVS) tubes as recommended by NIOSH method 5600. Additionally, we compared expected chlorpyrifos-oxon attributable to artificial transformation to observed chlorpyrifos-oxon in field samples from a 2008 Washington State Department of Health air monitoring study using non-parametric statistical methods. The amount of artificially transformed oxon was then modeled to determine the amount of oxon present in the environment. Toxicity equivalency factors (TEFs) for chlorpyrifos-oxon were used to calculate chlorpyrifos-equivalent air concentrations. The results demonstrate that the NIOSH-recommended sampling matrix (OVS tubes with XAD-2 resin) was found to artificially transform up to 30% of chlorpyrifos to chlorpyrifos-oxon, with higher percentages at lower concentrations (< 30 ng/m3) typical of ambient or residential levels. Overall, the 2008 study data had significantly greater oxon than expected by artificial transformation, but the exact amount of environmental oxon in air remains difficult to quantify with the current sampling method. Failure to conduct laboratory analysis for chlorpyrifos-oxon may result in underestimation of total pesticide concentration when using XAD-2 resin matrices for occupational or residential sampling. Alternative methods that can accurately measure both OP pesticides and their oxygen analogs should be used for air sampling, and a toxicity equivalent factor approach should be used to determine potential health risks from exposures.

Transport of a solvent mixture across two glove materials when applied in a paint matrix

The transport of mixed paint solvents through natural rubber latex (4 mil) and nitrile rubber (5 mil) gloves was evaluated after spray application of the paint formulation directly on the glove surface. Glove materials and thicknesses were those selected by the majority of spray painters in the local automobile repair industry. A flat panel containing glove specimens mounted in multiple permeation cells permitted evaporation of solvents from the applied paint and incorporated a solid sorbent receiving medium for measuring glove membrane transport. The panel was sprayed in a paint booth to simulate use conditions. Charcoal cloth under the glove adsorbed transported solvents, which were quantified by gas chromatography. For each solvent component, results were expressed as mass transported through the glove relative to the mass applied, per unit area, during 30 min after spray application. The paint formulation contained ketones, acetates, and aromatics. Natural rubber latex allowed 6-10 times the transport of solvents relative to nitrile rubber for all eight solvent components: methyl ethyl ketone, toluene, styrene, ethyl benzene, xylene isomers, and 2-heptanone. m-Xylene showed the largest difference in transport between the two glove materials. This solvent also had the highest transport for each material. The results indicate that nitrile rubber gloves offer somewhat greater chemical resistance to all eight solvents studied compared with natural rubber latex gloves, regardless of the chemical properties of the individual solvent components. However, it must be emphasized that neither of the glove materials, in the thicknesses used in this study, provide adequate protection when exposed by direct spray painting. Simulation of realistic spray conditions may offer a source of useful information on the performance of chemical protective gloves because it accounts for solvent evaporation and the effect of paint polymerization after application on glove transport.

Survey of dermal protection in Washington State collision repair industry

Substantial exposure to isocyanates may occur during spray painting in autobody shops, yet information is lacking on the efficacy of the protective clothing used during spray painting. We investigated the personal and workplace factors associated with painters' dermal protection use during a large-scale exposure assessment study. Survey data indicated that 69% of painters always used gloves, with latex gloves (47%) and nitrile gloves (34%) used most frequently. Among latex glove users, 53% used thin latex (0.05-0.13 mm), 6% used medium latex (0.15-0.20 mm), and 12% used thick latex (> 0.20 mm). Among nitrile glove users, 27% used thin nitrile and 45% used medium nitrile. Sixty-three percent of painters always used coveralls, 44% preferring one particular brand. Although overspray presents an opportunity for dermal exposure to the neck and face, only 19% of painters protected these areas with personal protective equipment. Painters who always used coveralls were more likely to use gloves (odds ratio = 7.9, p = 0.061). Painters who reported ever having smoked cigarettes used gloves (p = 0.05) and coveralls (p = 0.04) more frequently. Painters who sprayed more than 34 clear coat jobs per month used coveralls most frequently (p = 0.038). Exact logistic regressions along with random sample calculations indicated that the survey results were independent of the shops. Because of the small sample size in this study, future research is warranted to corroborate these results. Studying the effectiveness of gloves and coveralls against polyurethane paints and understanding the underlying motivators and preferences for painters and business owners is needed for the development of best practices for the selection and use of dermal protection.

Development of a permeation panel to test dermal protective clothing against sprayed coatings

OBJECTIVES

Design, construct, and characterize an apparatus to evaluate dermal protective clothing for resistance to polymerizing materials. Specifically, we evaluated the permeation of the most common glove material used in automotive collision repair (0.10-0.13 mm or 4-5 mil latex) with representative isocyanate-containing clear coats. Our ultimate goal is to make informed recommendations on dermal protective materials to prevent isocyanate exposures and reduce the likelihood of occupational illness in automotive collision repair and other industries.

METHODS

A novel permeation panel was developed to assess dermal protective clothing. With this apparatus, up to eight test materials may be evaluated under typical-spray application conditions. Solid collection media comprised of 1-(2-pyridyl)-piperazine (2-PP)-coated fiberglass filters or colorimetric SWYPE™ pads were placed behind test materials to capture permeants. The 2-PP-coated filters were subsequently analyzed using a modified OSHA42/PV2034 method. Color change in the SWYPEs provided an immediate field estimate of breakthrough time. In addition, Teflon filters were mounted proximal to the permeation cells to measure the mass of clear coat applied to the panel and to evaluate loading homogeneity. This study evaluated the permeation of isocyanates through 0.10-0.13 mm latex glove material at a fixed time (30 min post-spraying) and over a time course (6-91 min post-spraying).

RESULTS

Monomers 1,6-hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI) permeated through (0.10-0.13 mm) latex glove material under typical glove use conditions (30 min). The latex glove material exhibited immediate breakthrough, with a permeation rate of 2.9 ng min(-1) cm(-2). The oligomeric forms of HDI and IPDI did not permeate the latex glove material. The spray application at 71 ± 5 °F was fairly homogeneous (33.7 ± 8 mg weight of dry clear coat per 5 cm(2)).

CONCLUSIONS

The permeation panel is a viable method to assess dermal protective clothing performance against polymerizing materials. Thin (0.10-0.13 mm) latex gloves were determined to be ineffective barriers to the isocyanates commonly found in clear coats. Because this type of glove is used frequently in auto body shops, the potential for isocyanate exposure is of concern. Permeation tests with other dermal protective clothing materials and other clear coat formulations are needed to make recommendations about alternative materials.

Relation between index finger width and hand width anthropometric measures

Measures of hand and finger anthropometry are very important for designing many hand held devices as well as understanding anthropometric effects on the operation of such devices. Many historical datasets have measured and recorded gross hand dimensions but do not often record the finer dimensions of the hand such as finger anthropometry. Knowing the size and mass of fingers across genders can be critical to the design and operation of hand held devices. In this paper we compare two empirical linear models that predicts index finger width at the proximal interphalangeal (PIP) joint (a finger anthropometric measure) based on hand-width (hand anthropometric measure). This will be especially useful for deriving population measures of finger anthropometry from large historical data sets where only gross hand dimensions are available.

Objective color scale for the SWYPE surface sampling technique using computerized image analysis tools

Colorimetric SWYPE pads are useful tools for identifying unpolymerized aliphatic isocyanates on a variety of surfaces. This technique has been used in autobody shops to determine the presence of hexamethylene diisocyanate and other aliphatic isocyanates that are important constituents of many automotive coatings. SWYPEs have the advantage of being relatively inexpensive, rapid, and portable. The color change elicited by aliphatic isocyanates (from yellow to red) provides a visual indication of the extent of surface contamination. To quantify isocyanate contamination based on the colorimetric response, an objective color scale was developed for isocyanate loading. Sampled pads were digitized on a calibrated, portable flatbed scanner, and red-green-blue (RGB) histograms of SWYPE images were created. A calibration curve was created from a series of reference images derived from SWYPEs loaded with an isocyanate-containing product. The SWYPE RGB analysis allowed for quantification over a range of isocyanate loadings: from approximately 0.01 to 24.0 microg/cm(2), with reproducibility of >90%, accuracy >90%, and a surface extraction efficiency of >90%. RGB analysis exhibited a lower detection limit than visual scoring (approximately 3 microg versus approximately 10 microg). The colorimetric response was cross validated with a high-performance liquid chromatography quantitative assay. When combined with RGB analysis, SWYPE colorimetric wipes represent a rapid and inexpensive method to assess objectively surface contamination with aliphatic isocyanates.

Children's inhalation exposure to methamidophos from sprayed potato fields in Washington State: exploring the use of probabilistic modeling of meteorological data in exposure assessment

We examined the significance of meteorology and postspray volatilization of methamidophos (an organophosphorus insecticide) in assessing potential inhalation risk to children in an agricultural community. We combined fluxes from sources and dispersion modeling with a range of possible local meteorology to create output to study the variability in potential community exposure as a result of changing temperature, wind speeds and wind directions. This work is based on an aerial spray drift study where air sampling measurements of methamidophos were made before, during and after a spray event were used to examine acute inhalation risk for children living in an Eastern Washington State community in close proximity (between 15 and 200 m) to sprayed potato fields. We compared the measured average air concentrations of methamidophos in the community to a "no observed adverse effect level" for subchronic inhalation to characterize acute and subchronic inhalation risks. The baseline estimates of inhalation exposure were below Environment Protection Agency's (EPA) level of concern based on a target margin of exposure of 300. As meteorological conditions during and after spraying influence the amount of material moving into areas where children reside we used historical meteorological data to drive model simulations that predicted likely air residue concentrations under different wind and temperature conditions. We also added variability to the decay constant and initial emission fluxes to create a 2-D simulation of estimated air concentrations in the community near the fields. This work provides a methodological framework for the assessment of air concentrations of pesticides from agricultural sprays in the absence of extended measurements, although including variability from meteorological conditions. The deterministic as well as the probabilistic risk analyses in this study indicated that postspray volatilization in the specific spray situation analyzed (methamidophos applied on potato fields in Eastern Washington) did not pose acute or subchronic risks as defined by the EPA. However, this study did not consider any pathway of exposure other than inhalation (e.g. diet, dermal, etc.) and the risk assessment should be evaluated in that context.

A population-based cohort study of occupational exposure to magnetic fields and cardiovascular disease mortality

PURPOSE

This cohort study aims to examine cardiovascular disease (CVD) mortality risks among workers in occupations potentially exposed to magnetic fields (MF).

METHODS

Risks for major CVD mortality by potential job-related MF exposure were examined in a sample of U.S. workers from the National Longitudinal Mortality Study using multivariate proportional hazards models.

RESULTS

After adjustment for demographic factors, there were no significant excess risks between individuals with medium (0.15 to <0.20 microT), high (0.20 to < 0.30 microT), or very high (>/= 0.30 microT) exposure levels as compared with individuals with background exposure levels of MF (<0.15 microT) for the CVD mortality outcomes. Indirect adjustment for potential confounding by current smoking prevalence did not change the pattern of these results.

CONCLUSION

Our study does not provide evidence for an association between occupational MF exposure and CVD mortality risk.

Geomagnetic activity and human melatonin metabolite excretion

Elevated geomagnetic activity has been linked with human psychological, neurological and cardiovascular outcomes, and altered melatonin production has been implicated as an underlying mechanism to explain these effects. The relationship between geomagnetic activity and overnight excretion of the melatonin metabolite, 6-hydroxymelatonin sulfate (6-OHMS), was evaluated in a population of 153 male electric utility workers. The effect of geomagnetic activity combined with either 60Hz magnetic field or ambient light exposures was also evaluated. Elevated equivalent amplitudes (USGS, Boulder, CO) were associated with lower adjusted mean nocturnal 6-OHMS/cr concentrations and reduced total overnight 6-OHMS excretion, consistent with a previous study. Time intervals in which geomagnetic activity predicted the largest differences in mean 6-OHMS excretion generally occurred between 15- and 33-h prior to urine sample collection. These times coincide with key periods of melatonin regulation and production, respectively, suggesting that geomagnetic activity may play a role in the entrainment of human melatonin rhythms.

A population-based job exposure matrix for power-frequency magnetic fields

A population-based job exposure matrix (JEM) was developed to assess personal exposures to power-frequency magnetic fields (MF) for epidemiologic studies. The JEM compiled 2,317 MF measurements taken on or near workers by 10 studies in the United States, Sweden, New Zealand, Finland, and Italy. A database was assembled from the original data for six studies plus summary statistics grouped by occupation from four other published studies. The job descriptions were coded into the 1980 Standard Occupational Classification system (SOC) and then translated to the 1980 job categories of the U.S. Bureau of the Census (BOC). For each job category, the JEM database calculated the arithmetic mean, standard deviation, geometric mean, and geometric standard deviation of the workday-average MF magnitude from the combined data. Analysis of variance demonstrated that the combining of MF data from the different sources was justified, and that the homogeneity of MF exposures in the SOC occupations was comparable to JEMs for solvents and particulates. BOC occupation accounted for 30% of the MF variance (p << 10(-6)), and the contrast (ratio of the between-job variance to the total of within- and between-job variances) was 88%. Jobs lacking data had their exposures inferred from measurements on similar occupations. The JEM provided MF exposures for 97% of the person-months in a population-based case-control study and 95% of the jobs on death certificates in a registry study covering 22 states. Therefore, we expect this JEM to be useful in other population-based epidemiologic studies.

Comparison of global positioning system (GPS) tracking and parent-report diaries to characterize children's time-location patterns

Respondent error, low resolution, and study participant burden are known limitations of diary timelines used in exposure studies such as the National Human Exposure Assessment Survey (NHEXAS). Recent advances in global positioning system (GPS) technology have produced tracking devices sufficiently portable, functional and affordable to utilize in exposure assessment science. In this study, a differentially corrected GPS (dGPS) tracking device was compared to the NHEXAS diary timeline. The study also explored how GPS can be used to evaluate and improve such diary timelines by determining which location categories and which respondents are least likely to record "correct" time-location responses. A total of 31 children ages 3-5 years old wore a dGPS device for all waking hours on a weekend day while their parents completed the NHEXAS diary timeline to document the child's time-location pattern. Parents misclassified child time-location approximately 48% of the time using the NHEXAS timeline in comparison to dGPS. Overall concordance between methods was marginal (kappa=0.33-0.35). The dGPS device found that on average, children spent 76% of the 24-h study period in the home. The diary underestimated time the child spent in the home by 17%, while overestimating time spent inside other locations, outside at home, outside in other locations, and time spent in transit. Diary data for time spent outside at home and time in transit had the lowest response concordance with dGPS. The diaries of stay-at-home mothers and mothers working unskilled labor jobs had lower concordance with dGPS than did those of the other participants. The ability of dGPS tracking to collect continuous rather than categorical (ordinal) data was also demonstrated. It is concluded that automated GPS tracking measurements can improve the quality and collection efficiency of time-location data in exposure assessment studies, albeit for small cohorts.

The Washington aerial spray drift study: children's exposure to methamidophos in an agricultural community following fixed-wing aircraft applications

This study characterized exposures of eight children living in an agricultural community near potato fields that were treated by aerial application with the organophosphorus (OP) insecticide, methamidophos (O,S-dimethyl phosphoramidothioate). Exposure monitoring included air and deposition samples in the outdoor community environment, outdoor and indoor air samples at each residence, wipe samples of playground equipment, toys, indoor surfaces, and children's hands, and periodic urine samples. Monitoring occurred prior to, the day of, and 1 day following applications. Methamidophos deposition in the community was very low compared to deposition inside the boundaries of the treated fields. Community air concentrations increased from 0.05 microg/m3 (prespray) to 0.11 and 0.48 microg/m3 (spray day morning and afternoon, respectively), decreasing to 0.10 microg/m3 on the postspray day. Air concentrations outside residences followed a similar pattern; indoor levels did not exceed 0.03 pg/m3. Methamidophos residues were found on playground equipment following applications, but not on indoor residential surfaces. The median hand wipe levels increased from < 0.02 (prespray) to 0.08 microg/sample (spray day), decreasing to 0.05 microg/sample (postspray day). Median concentrations of the primary methamidophos urinary metabolite were 61 microg/l before 1100 hours on the spray day, 170 microg/l after 1100 hours on the spray day, and 114 microg/l on the postspray day. Spray day metabolite levels were correlated with time outside on the spray day (rs = 0.68), with spray day hand wipe levels (rs = 0.67), and with postspray day metabolite levels (rs = 0.64). Postspray day metabolites levels were also positively associated with postspray day hand wipe levels (rs = 0.66). The documentation of children's exposure in this study does not necessarily mean that risks for these children were significantly altered, since nearly all children in the United States are exposed to some level of OP pesticides through dietary intake and other pathways. The association of metabolite levels with time spent outside, and the absence of methamidophos in homes indicates that children's exposures occurred primarily outdoors.

Radio frequency nonionizing radiation in a community exposed to radio and television broadcasting

Exposure to radio frequency (RF) nonionizing radiation from telecommunications is pervasive in modern society. Elevated disease risks have been observed in some populations exposed to radio and television transmissions, although findings are inconsistent. This study quantified RF exposures among 280 residents living near the broadcasting transmitters for Denver, Colorado. RF power densities outside and inside each residence were obtained, and a global positioning system (GPS) identified geographic coordinates and elevations. A view-shed model within a geographic information system (GIS) characterized the average distance and percentage of transmitters visible from each residence. Data were collected at the beginning and end of a 2.5-day period, and some measurements were repeated 8-29 months later. RF levels logged at 1-min intervals for 2.5 days varied considerably among some homes and were quite similar among others. The greatest differences appeared among homes within 1 km of the transmitters. Overall, there were no differences in mean residential RF levels compared over 2.5 days. However, after a 1- to 2-year follow-up, only 25% of exterior and 38% of interior RF measurements were unchanged. Increasing proximity, elevation, and line-of-sight visibility were each associated with elevated RF exposures. At average distances from > 1-3 km, exterior RF measurements were 13-30 times greater among homes that had > 50% of the transmitters visible compared with homes with < or = 50% visibility at those distances. This study demonstrated that both spatial and temporal factors contribute to residential RF exposure and that GPS/GIS technologies can improve RF exposure assessment and reduce exposure misclassification.

Melatonin, sleep, and shift work adaptation

BACKGROUND

Night work is associated with disrupted circadian rhythms, fatigue, accidents, and chronic disease. Melatonin secretion helps regulate sleep and circadian rhythms.

OBJECTIVE

Melatonin, sleep disturbances, and symptoms (sleep, fatigue, mental) were compared among workers on permanent day, swing, and night shifts.

METHODS

Urinary 6-hydroxymelatonin sulfate (6-OHMS) was measured in postwork and postsleep samples. Disrupted circadian melatonin production was evaluated using the sleep:work 6-OHMS ratio. Wrist actigraphy characterized light exposures and sleep characteristics.

RESULTS

Night workers had altered melatonin, disrupted sleep, and elevated symptom prevalence. Subjects grouped by their sleep:work 6-OHMS ratio rather than shift had even greater symptom prevalence. Risks for two or more symptoms were 3.5 to 8 times greater among workers with sleep:work ratios < or =1 compared to those with ratios >1.

CONCLUSIONS

This ratio may help identify workers at increased risk for accidents or injuries.