Validation of a job-exposure matrix for assessment of utility worker exposure to magnetic fields

The aim of this study was to evaluate a 50-Hz electromagnetic field job-exposure matrix used in epidemiological studies of a nationwide cohort of utility workers in Denmark. We compared a job-exposure matrix that distinguished four categories of exposure to 50-Hz time-weighted average (TWA) magnetic fields: low (< 0.1 microT), medium (0.1-0.29 microT), high (0.3-0.99 microT) and very high (> 1.0 microT) of utility company employees with 196 measurements of 8-h exposure for 129 workers in this industry. The 129 workers were selected from the following five main work environments: generation facilities, transmission lines, distribution lines, substations, and other electrically and non-electrically relates jobs. This study shows that the job-exposure matrix can be expected to introduce misclassification mainly between adjacent categories of exposure. Thus, the distribution of measurements of exposure to 50-Hz magnetic fields was similar for workers in the medium and the high exposure matrix categories. But the two extreme categories satisfactorily separate low and very highly exposed workers. The study shows that epidemiological use of this job-exposure matrix might combine the two intermediate categories of exposure. If the sample size in extreme categories provides enough power, a study in which this job-exposure matrix is used should allow detection of a true association between exposure to 50-Hz magnetic field and disease.     

Occupational exposure to 50 Hz magnetic fields in workers employed in various jobs

BACKGROUND: Information on occupational exposure to ELF magnetic fields (MF) in workers is largely insufficient, and is mostly based on results obtained in Scandinavian countries and North America. Accordingly, the collection of further data is needed, especially in workers exposed in other countries, including in Italy. METHODS: One hundred and fifty workers (84 males and 66 females) employed in 28 different jobs in the Emilia-Romagna Region of Italy were examined. Individual exposure was measured using personal monitors worn on the hip in a belted pouch during three whole work-shifts (8 hours each) of a normal working week. A sampling interval of 10 seconds was adopted, resulting in the collection of more than 8600 measurements for each worker. The individual Time-Weighted Average (TWA) occupational exposure of workers was calculated as the arithmetic mean of all measurements during each work-shift. Environmental non-occupational exposure was also measured. RESULTS: The 50 degrees percentile of individual TWA in the whole group was 0.15 microT, and the 5 degrees - 95 degrees percentile was respectively 0.02-1.45 microT. Job-related exposure (expressed as the mean of the TWA measured in all workers engaged in that job) was highest in substation electric power plant workers (1.12 microT) and in sewing machine workers (0.84 microT), but was lower than 0.2 microT in more than the 70% of the examined jobs. Considering the geometric mean of individual TWA are 27 out of 28 the jobs inducing an exposure lower than 0.2 microT. The lowest exposure was observed in infant school teachers. A high variability was observed among different workers engaged in the same occupation, mainly in substation electric power plant workers, machine testers and grinders in the engineering industry and in sewing machine workers and quality control in garment production. A marked variability of the pattern of exposure during the work-shift was also observed The overall environmental (non-occupational) exposure was 0.044 microT, and individual exposure was lower than 0.2 microT in about 97% of the examined subjects. Occupational exposure was usually higher and was not correlated with environmental exposure. CONCLUSIONS: The results show that the occupational component of overall exposure must be considered in studies on the biological effects of ELF-MF in populations. The high variability observed among workers engaged in the same occupation and the variability of the pattern of exposure certainly constitute major problems and could be a cause of the scarce coherence of the results of epidemiological studies on biological effects of ELF-MF to date. An improvement in protocols for the evaluation of exposure in workers, including the use of personal monitoring, is certainly needed.     

Exposures of children in Canada to 60-Hz magnetic and electric fields.

OBJECTIVES: This study sought to characterize personal exposures of Canadian children to 60-Hz magnetic and electric fields and explain the variability. METHODS: Altogether 382 Canadian children up to 15 years of age wore meters recording 60-Hz electric and magnetic fields over 2 days. Meter location was noted. Thereafter, meters measured fields in the center of the children's bedrooms for 24 hours. Personal exposures were calculated for home, school or day care, outside the home, bedroom at night, and all categories combined (total). RESULTS: The arithmetic mean (AM) was 0.121 microT [geometric mean (GM): 0.085 microT), range 0.01-0.8 microT] for total magnetic fields. Fifteen percent of the total exposures exceeded 0.2 microT. The AM of the total electric fields was 14.4 (GM 12.3, range 0.82-64.7) V/m. By location category, the highest and lowest magnetic fields occurred at home during the day (0.142 microT) and during the night (0.112 microT), respectively. Measurements during sleep provided the highest correlation with total magnetic field exposure. Province of measurement explained 14.7% of the variation in the logarithms of total magnetic fields, and season accounted for an additional 1.5%. CONCLUSIONS: This study has identified differences in children's magnetic field exposures between provinces. Measurements at night provided the best surrogate for predicting total magnetic field exposure, followed by at-home exposure and 24-hour bedroom measurements. Electrical heating and air conditioning, wiring type, and type of housing appear to be promising indicators of magnetic field levels.     

Exposure to extremely low frequency magnetic fields among working women and homemakers.

Given concerns with potential health effects of exposure to magnetic fields, the goal of this study was to examine the magnitude and sources of occupational and residential exposure to extremely low frequency (primarily 60 Hz) magnetic fields among women. Exposure to 60 Hz magnetic fields was surveyed among cases and controls recruited for a study of breast cancer in 25 counties in North Carolina. The 273 women who participated wore an integrating personal magnetic-field exposure meter (AMEX 3-D) that measured their time-weighted average (TWA) exposure. A questionnaire was administered to determine the duration and frequency of electric appliance and machinery use. The geometric mean (GM) of the TWA exposure for employed women was 0.138 microT (range 0.022-3.636 microT) and for homemakers 0.113 microT (range 0.022-0.403 microT). Women working in manufacturing and industrial facilities had the highest exposure (GM 0.265 microT, range 0.054-3.436 microT), while nurses and health technicians (GM 0.134 microT, range 0.032-0.285 microT) and teachers and school administrators (GM 0.099 microT, range 0.035-0.673 microT) had the lowest exposures. Job titles, unless very limited in scope and/or environment, self-reported information about equipment use, potential exposure sources, time, and distance were not good predictors of magnetic-field exposure. Furthermore, the results show that occupations previously observed to have increased risk of breast cancer, such as teachers, nurses, administrative support, and housewives, did not have elevated average magnetic field exposures. Therefore, it is questionable whether exposure to power frequency magnetic fields is the cause of the increased breast cancer risk seen in these occupations.     

Assessment of occupational exposure patterns by frequency-domain analysis of time series data

Laboratory evidence increasingly points to exposure pattern characteristics, including the duration, frequency, and timing of the exposure during the day, as important factors influencing the biological response to extremely low-frequency magnetic fields. An exploratory analysis of exposure patterns was conducted in 113 electric utility workers employed as electricians, cable splicers, line workers, and power plant operators. The purpose of the study was to describe extremely low-frequency magnetic field exposure pattern characteristics of electric utility workers and evaluate grouping strategies for classifying occupational exposures based on their exposure pattern characteristics. Exposure patterns describe the cyclic fluctuation in exposures over time, and were evaluated by partitioning the variation of the time series into frequency components using frequency-domain analysis of the transformed and processed time series. The study samples were classified using traditional grouping strategies based on occupation and time-weighted average (TWA), and non-traditional grouping strategies based on cluster analysis of the standardized, low-frequency exposure pattern components. Rules for classifying samples into each group were developed using linear discriminant analysis, with the performance of each grouping strategy evaluated using a crossvalidation study design to estimate the rate of misclassification. Exposure patterns appeared unrelated to grouping strategies based on quartiles of the workday TWA, but were related to pattern clusters and occupation. The linear discriminant function produced very low misclassification error rates for the cluster grouping strategy (10%) compared to occupation (50%) and TWA quartile (69%) grouping strategies. Significant differences in the exposure patterns occurring between clusters and between occupational groups were observed, indicating that at least one of the spectral estimates in two of the groups were significantly different. However, patterns clusters produced the greatest contrast in exposure patterns of all grouping strategies, explaining 99 percent of the total variation compared to 58 percent of the total variation by occupation.     

Within-shift variability of short-term exposure to organic solvent in indoor workplaces

This study examined the degree of within-shift variability of short-term exposure concentrations for workers exposed to organic solvents in indoor workplaces. For this purpose, 117 exposure data sets of 15-minute time-weighted average (15-min TWA) and those of 60-min TWA were collected from 53 workers employed in the offset printing, gravure printing, screen printing, machine control board production, fiber-reinforced plastic production, hard metal production, electrical parts production, and chemical synthesizing industries. Data analysis showed that the tenth, fiftieth, and ninetieth percentiles of the geometric standard deviations of 15-min TWA values [GSD(15m)] were 1.4, 2.3, and 4.5, respectively; and those of GSD(60m) were 1.2, 1.7, and 3.4, respectively. Based on an assumption of lognormal exposure distribution, the maximum values of 15-min TWA (the 98.4th percentile) were estimated to be 4.3, 36, and 650 times as high as the minimum one (the 1.6th percentile) for the low, middle, and high exposure variabilities, respectively; and to be 2.0, 4.3, and 8.2 times the 8-hour TWA value, respectively. Consequently, when the 8-hour TWA exceeds 0.23 times (1/4.3) the short-term exposure limit value, the high short-term exposure condition should be evaluated. The maximum values of 60-min TWA (the 93.8th percentile) were estimated to be 1.8, 5.1 and 43 times as high as the minimum one, respectively; and to be 1.3, 2.0, and 3.1 times the 8-hour TWA value, respectively. The relationship between production factors and within-shift exposure variability was also examined. The intermittent solvent use group had significantly higher median values of GSD(15m) and GSD(60m) than the continuous group. The mobile pollutant source group had a significantly higher median value of GSD(60m) than the stationary group.     

Measurements of ELF electromagnetic exposure of the general public from Belgian power distribution substations

In this paper, the exposure of the general public due to distribution substations of 11/0.22-0.4 kV is investigated. The substations are categorized according to their location (substations in buildings, detached substations, substations between two houses, and underground substations in the pavement), and eight relevant substations are selected to perform measurements of the electromagnetic fields. The purpose of this paper is to determine the "minimum distances" for the general public--defined as the distances outside which the field levels do not exceed a certain field value--of these substations. In total, 637 field measurements were performed: 358 measurements of the magnetic field and 279 measurements of the electric field in different locations. Measured momentary magnetic field values are within the range of 0.025 to 47.39 microT. Electric fields are within the range 0.1 to 536 V m(-1). Also, magnetic field measurements as a function of the height above the ground were performed. The maximal magnetic (values over one day) and electric fields for all the investigated substations were below 100 microT and 5 kV m(-1), respectively. For exposure over a year, all substations except one delivered values below 100 microT. For the substation producing a magnetic field above 100 microT, a minimum distance of about 0.5 m was obtained. When comparing the average exposure with the value of 0.4 microT, minimum distances of maximally 5.4 m (average day) and 7.2 m (average year) were obtained.     

Accuracy of short-term residential measurement in the prediction of 72-h exposure to power frequency magnetic field in households very close to high-tension transmission lines

Between February and April 2003, a total of 80 single-dwelling households close (< 70 m) to high-tension (161 or 345 kV) power lines in a northern community of Taiwan received measurements of indoor extremely low-frequency (ELF) magnetic field for 72 h. Measurements were performed with EMDEX II meter at a sampling rate of every 300 s, yielding some 860 readings of ELF magnetic field for each household. In addition to the 72-h mean ELF magnetic field, we also calculated arithmetic means of the first 2, 6, 12, and 288 readings taken in each household to represent the information on spot, 30-min, 60-min, and 24-h exposures, respectively. The mean 72-h exposure to ELF magnetic field for the 80 study households was estimated at 0.80 micro-Tesla (microT) with a standard deviation (SD) of 1.13 microT. The mean for pot, 30-min, 60-min, and 24-h exposure was 0.88 (SD 1.38), 0.90 (SD 1.40), 0.9 (SD 1.17), and 0.83 (SD 1.17) microT, respectively. There were high agreements, indicated by a nearly perfect intra-class correlation coefficient, between 72-h mean exposure and those short-term exposure measures. Additionally, the sensitivity and specificity of various short-term exposures in the prediction of 72-h exposure greater than 0.4 microT were similar at values of 0.82-0.87 and 0.93-0.95, respectively. This study indicates that short-term measurements of indoor ELF magnetic field seem adequate to represent the mean 72-h exposure, but tended to overpredict 72-h exposure greater than 0.4 microT. Further investigation is needed to assess whether these findings can be replicated in households far away from high-tension power lines.     

Effects of electric and magnetic fields from high-power lines on female urinary excretion of 6-sulfatoxymelatonin

In 1998, the authors studied the effect of residential exposure to electric and magnetic fields from high-power lines on female urinary excretion of 6-sulfatoxymelatonin (6-OHMS) in the Quebec city, Canada, metropolitan area. A sample of 221 women living near a 735-kV line was compared with 195 women the same age living away from any power lines. Participants provided morning urine samples on 2 consecutive days and wore a magnetic dosimeter for 36 consecutive hours to measure personal magnetic exposure. The indoor electric field was assessed by spot measurements. After adjustment for other factors associated with low melatonin secretion, such as medication use or light exposure, nighttime concentration of 6-OHMS was similar in the two groups. When either 24-hour or sleep-time exposure to magnetic field or electric field measurements was used, no exposure-effect relation was evident. However, the trend of decreasing 6-OHMS concentration with age was more pronounced for women living near the lines, as was a lower 6-OHMS concentration in women with high body mass index. Chronic residential exposure to magnetic fields from high-power lines may accentuate the decrease in melatonin secretion observed in some vulnerable subgroups of the population.     

Occupational and residential 60-Hz electromagnetic fields and high-frequency electric transients: exposure assessment using a new dosimeter

One problem that has limited past epidemiologic studies of cancer and exposure to extremely low-frequency (0-100 Hz) electric and magnetic fields has been the lack of adequate methods for assessing personal exposure to these fields. A new 60-Hz electromagnetic field dosimeter was tested to assess occupational and residential exposures of a group of electrical utility workers and a comparison background group over a 7-day period. Comparing work periods only, utility workers' exposures were significantly higher than background levels by a factor of about 10 for electric (E) and magnetic (B) fields and by a factor of 171 for high-frequency transient electric (HFTE) fields. When overall weekly time-weighted averages combining work and nonwork exposures were compared, ratios of the exposed to background groups were lower. B and HFTE exposure ratios remained statistically significant, with values of 3.5 and 58, respectively, whereas the electric field exposure ratio was no longer significant, with a value of 1.7. E-field exposures of the background group were the highest during the nonwork period, probably reflecting the use of electrical appliances at home. Residential E- and B-field exposures were in the same range as published results from other surveys, whereas occupational E-field exposures tended to be lower than exposures reported in other studies. The high variability associated with occupational exposures probably accounts for the latter discrepancy. Worker acceptance of wearing the dosimeter was good: 95% of participants found it to be of little or no inconvenience while at work. At home, 37% found the device to be inconvenient in its present form but would not object to wearing a slightly smaller and lighter dosimeter.     

Sister chromatid exchange (SCE)and high-frequency cells in workers professionally exposed to extremely low-frequency magnetic fields (ELF)

BACKGROUND: Up now no firm conclusions can be drawn on the genotoxicity of Extremely Low Frequency (ELF) Magnetic Fields (MF) in exposed workers: both an increase in chromosomal aberrations (CA) and micronuclei (MN) or no effects were observed in substation workers, while a slight increase in CA, but not in sister chromatid exchanges (SCE) or MN was reported in linesman; an increase in CA was observed in cable splicers and, more recently, in train engine drivers, but results have not been replicated. OBJECTIVES: Objective of the study was an evaluation of possible genotoxicity of occupational exposure to ELF-MF. METHODS: SCE, high-frequency cells (HFC) and SCE in HFC were measured in peripheral blood lymphocytes from 70 workers exposed to various levels of ELF-MF in different occupations, not involving exposure to known mutagens or carcinogens. In all participants, individual ELF-MF exposure was measured throughout the whole work-shift for 3 consecutive days by personal monitoring. RESULTS: Time Weighted Average (TWA) values of ELF-MF in the whole group ranged from 0.01 to 3.48 microT; the geometric mean was 0.19 mT, and only 3 subjects exceeded 2 microT. According to the individual TWA exposure, subjects were divided into two groups: low exposed (< or = 0.2 microT) and highly exposed (> 0.2 microT). The mean values of SCE, HFC and SCE in HFC were compared between low and highly exposed: no significant differences were observed. The result was further tested by selection and comparison of workers exposed up to 0.1 microT vs. exposed > 0.4 microT only, i.e. excluding intermediate exposures: again no difference in genotoxicity indices was observed. Also multivariate analysis did not show any correlation between individual ELF-MF exposure and genotoxicity indices. CONCLUSIONS: The results of our study do not give any support to the hypothesis that occupational exposure to ELF-MF up to about 2 microT, i.e. at the levels currently found in most workplaces, can exert a genotoxic effect in workers.     

Magnetic fields of video display terminals and spontaneous abortion.

The aim of this study was to examine whether work with a video display terminal and exposure to the magnetic fields of video display terminals are related to spontaneous abortion. The study was conducted among women employed as bank clerks and clerical workers in three companies in Finland. The cases (191 spontaneous abortions) and controls (394 births) were identified from Finnish medical registers for the years 1975-1985. Use of video display terminals was defined using the workers' own reports and information provided by the companies. The assessment of exposure to the magnetic fields was based on measurements of the fields of video display terminals. The odds ratio for spontaneous abortion for working with video display terminals was not increased (odds ratio = 1.1, 95% confidence interval 0.7-1.6). However, the odds ratio for workers who had used a video display terminal with a high level of extremely low frequency magnetic fields (> 0.9 microT) was 3.4 (95% confidence interval 1.4-8.6) compared with workers using a terminal with a low level of these magnetic fields (< 0.4 microT). Adjustment for ergonomic factors and mental work load factors changed the odds ratio for magnetic field exposure only very slightly. The findings suggest the need for future studies with assessment of exposure to the magnetic fields in the actual working environment to confirm the possible risk.     

Hazard surveillance for industrial magnetic fields: II. Field characteristics from waveform measurements

Magnetic field characteristics have been surveyed systematically in six factories with the Multiwave(R) II waveform capture instrument. These six facilities manufactured plastics, pharmaceuticals, cement, liquid air products, aluminum parts, and aluminum-framed filters. The study goals were to survey the physical characteristics of magnetic fields that may be related to biological effects under various interaction mechanisms and to relate those characteristics to the field's sources. From 59 waveform measurements at worker locations near sources, we calculated the extremely low frequency (ELF) and static field magnitudes, their frequency characteristics, and spatial characteristics of the 60Hz component. The RMS vector magnitude of the ELF magnetic field (the usual exposure metric in most studies) had medians ranging from 0.53 to 12.83 microT in the six factories. The static magnetic field magnitudes had medians of 24.2-46.2 microT, which is well below the geomagnetic reference field of 55.0 microT because of shielding from steel structures. The maximum static field was 128.6 microT near a DC motor. The frequency spectra of the most common fields is dominated by 60Hz, and has a median total harmonic distortion equal to 14.8%. The most common higher frequencies are the third, fifth, and second harmonics of 60Hz. However, magnetic fields in these workplaces had many other 60Hz harmonics and non-harmonic frequencies due particularly to electric motors and computer monitors. The 60Hz component magnetic fields have elliptical polarization with median axial ratio of 25.4%. The average proportion of the 60Hz component parallel to the static field vector was 51.5+/-3.0%, which indicates a significant trend towards perpendicular orientation between these two field components. In this survey of only six factories, the Multiwave(R) II measurements documented a wide diversity of complex magnetic field characteristics and non-sinusoidal waveforms. Although these characteristics are important to the various mechanisms postulated to explain biological effects, they are overlooked by the popular exposure assessment methods which only measure the ELF magnitude. Therefore, spot measurements with the Multiwave(R) II or similar waveform capture instruments are necessary for a complete magnetic field exposure assessment.     

Occupational magnetic field exposure and myocardial infarction incidence

BACKGROUND: Studies on healthy volunteers have seen reduced heart rate variability after exposure to extremely low-frequency electric and magnetic fields (EMF). Because reduced heart rate variability has been linked to cardiovascular disease risk, it has been hypothesized that exposure to EMF might increase the risk of cardiovascular disease. One epidemiologic study has shown increased mortality from cardiovascular conditions in utility workers with elevated exposure to magnetic fields, but several other epidemiologic studies have failed to confirm this result. We tested the hypothesis that occupational EMF exposure increases the risk of myocardial infarction in a large population-based case-control study of myocardial infarction, with detailed information on potential confounders. METHODS: We used data from the SHEEP study, which is a population-based case-control study of acute myocardial infarction in Stockholm. Occupational EMF exposure was based on job titles 1, 5, and 10 years before diagnosis. We used 2 approaches to classify exposure: first, specific individual job titles with presumed elevated EMF exposure, and second, classification of subjects according to a job-exposure matrix. RESULTS: We found no increased risk of myocardial infarction in subjects classified as having elevated EMF exposure. For the highest exposure category of > or = 0.3 microT according to the job-exposure matrix, the adjusted relative risk was = 0.57 (95% confidence interval = 0.36-0.89). CONCLUSIONS: The results of this study do not support the hypothesis that occupational EMF exposure increases the risk of myocardial infarction.     

Correlation of year-to-year magnetic field exposure metrics among children in a leukemia survival study

The Childhood Leukemia Survival Study is examining the possible association between magnetic field exposure and survival of children with newly diagnosed acute lymphocytic leukemia (ALL). We report the results of serial 24-h personal magnetic field monitoring for 412 US and Canadian children and present the correlations between annual values. The mean time-weighted average (TWA) and geometric mean (GM) were similar for first, second, and third year measurements [TWA: 0.11 microT (n = 412), 0.13 microT (n = 304), and 0.12 microT (n = 134), respectively]. There were no consistent differences in mean TWA or GM based on age or gender. Significantly lower mean TWA and GM were found for children living in rural areas. Higher exposures were noted among children living in urban areas, among apartments dwellers, and those living in rental homes. Measurements taken during summer months and among children residing in the northeast and Canada also tended to be higher. Correlations for most metrics were increased among children who had annual measurements performed during the same season. The metric with the highest year-to-year correlation was the GM. The lowest correlations were found for metrics estimating field intermittency and temporal stability. First to second year GMs were well correlated when taken in the same home (Spearman rank correlation = 0.70), but a lower correlation (0.44) was noted among residentially mobile children. Our findings suggest that summarizing exposure using a single measurement of GM can estimate exposures for residentially stable children, but is not a good predictor of personal exposures among children who change residence during the study interval.     

Occupational exposures of pharmacists and pharmaceutical assistants to 60 Hz magnetic fields

We carried out the study to assess, using field surveys and personal dosimetry, the potential exposure of pharmacists and pharmaceutical assistants to 60 Hz magnetic fields in a medical center of Taiwan. Field surveys were conducted twice in the pharmacy where two workers were randomly selected and solicited to wear personal dosimetry instruments for a full-shift assessment of personal exposure. We used an EMDEX II for on site measurements and did not consider any specific instrument or equipment for health care services as potential sources of magnetic field. The results showed that the average magnetic flux densities for the selected areas were between 0.63 mill-Gauss (mG) and 2.23 mG, while the full-shift time-weighted-average exposure for the two selected workers was 4.98 mG and 6.54 mG, respectively. Both inadequate consideration for the field survey of the temporal variability in magnetic flux densities over the workday and that the monitored workers spent almost half of the full-shift working in places outside of the study areas may have contributed to such discrepancy in results between field survey and personal dosimetry. This study suggests that the potential for elevated exposure to 60 Hz magnetic fields in health care settings does exist, and that using job title as a surrogate for magnetic fields exposure classification might entail certain degrees of misclassification. Although limited in its scope and sample size, the study presented here seems to demonstrate the inadequacy of using stationary workplace measurements for the assessment of personal occupational exposure to 60 Hz magnetic fields.     

Task-based assessment of occupational vibration and noise exposures in forestry workers

Forty-two noise exposures and 164 whole-body (WBV) and hand-arm (HAV) vibration exposures were collected from 43 forestry workers in six trades employed by two forestry companies. Data were collected on 10 days over 8 weeks during various felling, logging, and log handling operations. Up to 5 volunteers were monitored for noise and vibration daily using datalogging noise dosimeters, which provided daily time-weighted averages (TWAs) and 1-min averages; and a precision sound level meter equipped to measure human vibration, which provided triaxial HAV and WBV event-weighted averages (AEQS). Workers completed a short questionnaire throughout the workday detailing the timing and number of tasks performed and equipment used. Substantial overexposures to noise and vibration were seen; for example, 60% of Occupational Safety and Health Administration (OSHA) TWAs and 83% of National Institute for Occupational Safety and Health (NIOSH) noise TWAs exceeded 85 dBA, 33-53% of the axis-specific HAV AEQS exceeded the 8-hour American Conference of Governmental Industrial Hygienists' HAV threshold limit value, and 34% of all summary weighted WBV AEQS exceeded the Commission of the European Communities' 8-hour exposure limit. The mean for 99 WBV summary weighted AEQ was 3.53 +/- 7.12 m/sec2, whereas the mean for 65 HAV summary weighted AEQ was 5.45 +/- 5.25 m/sec2. The mean OSHA TWA was 86.1 +/- 6.2 dBA, whereas the mean NIOSH TWA was 90.2 +/- 5.1 dBA. The task and tool with the highest exposure levels were unbelling chokers on landings and chain saws (noise), log processing and frontend loaders (WBV), and notching stumps and chain saws (HAV). An internal validation substudy indicated excellent agreement between worker-reported and researcher-documented tasks and tools.     

Assessment of occupational exposures to industrial hazardous substances. III. On the frequency distribution of daily exposure averages (8-h TWA)

A method based on interday fluctuation of contaminant concentrations for evaluating employee's exposure averages (8-h TWAs) was proposed in our previous report. The method was established on the assumption that daily exposure averages of the workers are lognormally distributed in actual workplaces. The study was conducted to elucidate whether the distribution of daily exposure averages is statistically lognormal or not and to examine the relationship between sample geometric standard deviation (sg) of worker's daily exposure averages and its estimate (sg2) calculated by measurements for two consecutive days. These are critical for our proposed method. The data on daily exposure concentrations over five to six weeks were collected from workers exposed to cobalt, acetone, n-hexane, toluene, xylene, ethylbenzene and ethylacetate. The data on organic lead, inorganic lead and mercury exposures reported by Cope et al. and Lindstedt et al. were also used for the study. The result can be summarized as follows: 1. Lognormal distribution of daily exposure averages was confirmed by plotting on normal probability paper and chi 2-test. 2. Median of sg2 on daily exposure averages obtained from individual worker was smaller than sg. 3. sg calculated by a set of measurements for two consecutive days in every worker can be corrected by the equation: (sg2) 1.48 in obtaining a better estimate of sigma g. 4. Statistical analysis on daily exposure averages of all workers showed that median of sg2 was smaller than that of sg, and 88% upper limit of sg2 was equal to that of sg. 5. Therefore, in evaluating TWA obtained by only single day's measurement using the proposed method, median of sg representative of industrial hazardous substance exposure workplaces could be also corrected by the equation described above. However, correction of 90% upper limit of sg2 is not necessary.     

Occupational and environmental exposure to extremely low frequency-magnetic fields: a personal monitoring study in a large group of workers in Italy

An inaccurate evaluation of exposure is considered a possible cause for the inadequate conclusiveness of epidemiological research on adverse effects of extremely low frequency-magnetic fields (ELF-MF). The objective of this study is to provide an evaluation of current ELF-MF exposure in workers, the specific contribution of occupational exposure to overall 24-h exposure, and the representativeness of a job exposure matrix (JEM). ELF-MF exposure was monitored in 543 workers for 2 days using personal meters. Time-weighted average (TWA) levels at work, at home and outside the home were calculated. A JEM based on the 1988 International Standard Classification of Occupations (ISCO 88) was created. Median exposure at work, at home and outside the home were 0.14, 0.03 and 0.05 μT, respectively. Occupational exposure accounted for about 60% of 24-h exposure. In the JEM, about 50% of the classified occupations included significantly different individual TWAs. Occupational exposure to ELF-MF appeared low. Median exposure levels at home and outside were 20-28% of the occupational level, giving a minor contribution to overall day-to-day exposure. The frequent occurrence of workers with different TWA included under the same job title highlights the risk of misclassification in epidemiological studies on ELF-MF effects based on JEM.