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.     

Within-day variability of magnetic fields among electric utility workers: consequences for measurement strategies

Occupational exposure to 50-Hz magnetic fields was surveyed among electric utility workers to investigate (1) components of exposure variability, (2) patterns of autocorrelation between short-term measurements, and (3) imprecision and misclassification due to short-term measurements. Spot measurements every 10 seconds during 81 working days were analyzed for 42 electric utility workers from 10 occupational subgroups and during 8 working days for 4 office workers from the same company. For the 8-hour time-weighted average (TWA) magnetic fields, the variability was partitioned into its components: within workers, between workers, and between groups. For spot measurements of magnetic fields, the within-day variance component also was examined. Autocorrelation functions were determined and numbers of short-term measurements necessary for reliable estimates of 8-hour TWA magnetic fields were assessed. Spot measurements of magnetic fields, as well as 8-hour TWA magnetic fields, were approximately log normally distributed among workers. The mean exposure to magnetic fields was 0.47 microT (n = 81 days) in electric utility workers and 0.12 microT (n = 8 days) in office workers. A large fraction, 76% of the spot measurements total variance, could be attributed to variability within days. For the 8-hour TWA magnetic fields, between-group variability was small and of the same magnitude as between-worker variability. Significant autocorrelations between short-term averages of 7.5, 15, and 30 minutes were present, when taken within periods of 30 minutes. One-hour averages showed no autocorrelation. Simulations showed that, due to high within-day variability and autocorrelation, a limited number of short-term measurements of magnetic fields in electric utility workers are likely to result in imprecise estimates of 8-hour TWA magnetic fields. Measurement strategies relying on short-term (spot) measurements are therefore likely to result in misclassification of exposure and consequently absent or spurious exposure-response relations.     

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.     

Individual estimation of exposures to extremely low frequency magnetic fields in jobs commonly held by women

Exposures to extremely low frequency (ELF) magnetic fields have not been documented extensively in occupations besides the work environments of electric or telephone utilities. A 1980-1993 study of childhood acute lymphoblastic leukemia (ALL) in Québec, Canada, gathered detailed information about the occupations of 491 mothers of ALL cases and mothers of a similar number of healthy controls. This information was combined with published data on the intensities of ELF magnetic fields associated with sources or work environments to estimate ELF magnetic field exposures for a wide range of jobs commonly held by women. Estimated exposures for 61 job categories ranged from 0.03 to 0.68 microT; the 25th, 50th, and 75th percentiles were 0.135, 0.17, and 0.23 microT, respectively. By job category, the most highly exposed jobs (>0.23 microT) included bakery worker, cashier, cook and kitchen worker, electronics worker, residential and industrial sewing machine operator, and textile machine operator. By work environment, the most highly exposed job categories were electronics worker in an assembly plant (0.70 microT) and sewing machine operators in a textile factory (0.68 microT) and shoe factory (0.66 microT). These results provide new information on expected levels of exposure in a wide range of jobs commonly held by women.     

Occupational exposures to extremely low frequency magnetic fields and postmenopausal breast cancer

BACKGROUND: The association between occupational exposure to extremely low frequency magnetic fields (ELF-MF) and risk of postmenopausal breast cancer was assessed in a case-control study. METHODS: Breast cancer cases were compared to cancer controls. Interviewers elicited information on risk factors and on lifetime work history. Industrial hygienists assigned to each job average duration of exposure to ELF-MF at four levels of intensities ("none," <0.2 microT; "low," 0.2-<0.5microT; "medium," 0.5-<1microT; "high," > or =1-10microT). Unconditional logistic regression was used to estimate adjusted odds ratios (OR) and 95% confidence intervals (95% CI). RESULTS: A total number of 608 cases and 667 controls participated. Adjusting for accepted breast cancer risk factors, we found an OR of 1.13 for lifetime occupational exposure to ELF-MF at medium or high intensities. Risks were larger for exposures before age 35 (OR = 1.40), and statistically significant for exposures before 35 among cases with progesterone receptor positive tumors (OR = 1.56, 95% CI=1.02-2.39). CONCLUSIONS: There appears to be a small increased risk for breast cancer among postmenopausal women exposed occupationally to ELF-MF.     

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.     

Exposure of school employees to extremely low frequency magnetic fields

This study was initiated to determine and compare daily occupational exposure (OE) and non-occupational exposure (NOE) of three employee groups of teachers, maintenance workers and secretarial staff in a Canadian school district. The time-weighted average (TWA) individual OE for subjects ranged from 0.4-3.8 milligauss (mG), and the TWA NOE ranged from 0.2-7.1 mG. TWA OE and NOE were 1.2 mG and 1.5 mG for teachers, 1.8 mG and 1.2 mG for maintenance workers, and 2.9 mG and 2.1 mG for secretarial staff. The differences between TWA OE and NOE of each group and also among the three groups were not statistically significant. OE and NOE of secretarial staff exceeded 10 mG 9.0% and 6.4% of the time--significantly (p < 0.001) higher rates than those of OE and NOE of teachers (1.0% and 1.4%) and maintenance workers (2.8% and 0.1%). Exposures were well below recommended criteria.     

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.     

Assessment of exposure to magnetic fields in occupational settings

OBJECTIVE: It is important to have data about occupational magnetic field intensity to consider the contribution of occupational magnetic field exposure on the human body. We conducted research on exposure to occupational magnetic fields and tried to qualify data on the distribution of magnetic field' intensity in certain general working environments with individual measurements. SUBJECTS AND METHODS: We performed sample research on the exposure to low-frequency magnetic fields of workers in certain occupations and in the working environment. We also assessed the relationship between working environmental magnetic field distribution and individual exposure. RESULTS: Some occupations were found to be exposed to high magnetic fields. We observed that some workspaces, such as the transformer substation, generally had a uniform and high magnetic field measurement but employees were exposed to a lower intensity. We also found that welders were exposed to high magnetic fields at about 600 microT in a very short time but with a geometrical value of 0.08 microT. CONCLUSION: The determination of administrative levels and control levels, not only of the time weighted average of threshold limits or short term exposure limits, but also ceiling limits should be considered. More systematic research is necessary to determine variables such as operating conditions, measuring position, and frequency bands. Also, further studies will be needed to make a job-exposure matrix for the magnetic fields for each occupation type and to combine it with exposure in non-occupational settings such as commuting and ordinary life situations to explore the causal relationship between exposure to magnetic fields and disease.     

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.     

The Joint Effect of Industrial Noise Exposure and Job Complexity on All-Cause Mortality - The CORDIS Study

In a previous follow-up study of industrial workers (the CORDIS study, Melamed et al., 1999a) we demonstrated a dose-response relationship between occupational noise exposure levels and all-cause mortality. In that study the type of jobs that workers were engaged in was not taken into account. However, in further analyses of CORDIS data we have found that noise exposure is particularly detrimental to health for workers engaged in complex jobs. Therefore in this 12-year study we attempted to determine the combined effect of job complexity and noise exposure on all-cause mortality in 2606 industrial workers. We divided the workers into four groups based on a combination of either high or low noise exposure, and whether they performed simple or complex jobs. There was an increased risk for all-cause mortality (OR = 1.86, 95% CI = 1.04-3.32), in workers who performed complex jobs under high noise exposure levels compared to those who performed simple jobs under low noise exposure. This remained significant even after adjusting for possible confounding variables. There was a trend for a more pronounced effect among less educated workers, among blue-collar workers, and in those with higher tenure. We conclude that occupational noise exposure is associated with excess mortality risk among workers performing complex jobs.     

Occupational exposure to electromagnetic fields and risk of Alzheimer's disease

BACKGROUND: Extremely-low-frequency magnetic field (ELF-MF) exposure is suspected to increase the risk of Alzheimer's disease. Such fields are present in the vicinity of electrical motors and other electric appliances containing coils. METHODS: We investigated lifetime occupational ELF-MF exposure in relation to Alzheimer's disease and dementia among a community dementia-free cohort (n = 931) age 75 years and older in Stockholm, Sweden. This cohort was followed from 1987-1989 until 1994-1996 to detect dementia cases (Diagnostic and Statistical Manual of Mental Disorders, revised 3rd edition criteria). Information on lifetime job history was obtained by interview, usually of next of kin. ELF-MF exposure was assessed using a job-exposure matrix, measurement on historical equipment, and expert estimation. We analyzed the data with Cox models controlling for potential confounders. RESULTS: Dementia was diagnosed in 265 subjects, including 202 with Alzheimer's disease. Among men, ELF-MF exposure > or=0.2 microT in lifetime principal job was related to multivariate-adjusted relative risks of 2.3 (95% CI = 1.0-5.1) for Alzheimer's disease and 2.0 (1.1-3.7) for dementia. We found no association among women. A similar sex-specific pattern was seen for the associations with average ELF-MF exposure throughout the work life. A dose-response relation was suggested in men, with multivariate-adjusted relative risks of 2.4 (0.8-6.8) for Alzheimer's disease and 2.5 (1.1-5.6) for dementia for the upper tertile of lifetime average exposure. CONCLUSIONS: Long-term occupational exposure to a higher ELF-MF level may increase the risk of Alzheimer's disease and dementia in men. Similar patterns were not seen in women, which may in part be the result of a greater exposure misclassification in women than in men.     

Genotoxic hazard evaluation in welders occupationally exposed to extremely low-frequency magnetic fields (ELF-MF)

Electric arc welding is known to involve considerable exposure to extremely low-frequency magnetic fields (ELF-MF). A cytogenetic monitoring study was carried out in a group of welders to investigate the genotoxic risk of occupational exposure to ELF-MF. This study assessed individual occupational exposure to ELF-MF using a personal magnetic-field dosimeter, and the cytogenetic effects were examined by comparing micronuclei (MN) and sister chromatid exchange (SCE) frequencies in the lymphocytes of the exposed workers with those of non-exposed control subjects (blood donors) matched for age and smoking habit. Cytogenetic analyses were carried out on 21 workers enrolled from two different welding companies in Central Italy and compared to 21 controls. Some differences between the groups were observed on analysis of SCE and MN, whereas replication indices in the exposed were found not to differ from the controls. In particular, the exposed group showed a significantly higher frequency of MN (group mean ± SEM: 6.10 ± 0.39) compared to the control group (4.45 ± 0.30). Moreover, the increase in MN is associated with a proportional increase in ELF-MF exposure levels with a dose-response relationship. A significant decrease in SCE frequency was observed in exposed subjects (3.73 ± 0.21) compared to controls (4.89 ± 0.12). The hypothesis of a correlation between genotoxic assays and ELF-MF exposure value was partially supported, especially as regards MN assay. Since these results are derived from a small-scale pilot study, a larger scale study should be undertaken.     

An assessment of the exposure of water reclamation workers to hydrogen sulphide

The paper describes a 4-month study of water reclamation workers in a rural area. Workers were chosen randomly from each of three groups: permanent site workers, mobile workers and tanker drivers. The exposure to H2S of each of these workers was monitored with pumped long-term colorimetric tubes over 4 days. The reclamation sites were visited over the period of the study and monitored with a hand-held H2S-measuring instrument to identify sources of possible exposure. Data on the weather conditions were also collected. Routine exposure to H2S was found to be low; only 14% of exposures were above the minimum detection limit of 0.1 ppm 8-h time-weighted average (TWA). None of the 190 valid samples were above the 8-h TWA occupational exposure standard (OES) of 10 ppm. If all the exposure had occurred in a 10 min period, 6% of exposures would have been above the 10 min TWA limit. The hand-held readings and knowledge of the work pattern suggest that this was unlikely to have been the case. Most of the positive personal exposure measurements were associated with tanker drivers who were not dealing with treated sludge only. There was a statistically significant difference between the likelihood of exposure to H2S occurring in warmer, drier weather and in cooler, wetter weather. Sites and jobs which can result in transient exposure to H2S are identified.     

Biological monitoring of low level occupational xylene exposure and the role of recent exposure

The correlation between low level time-weighted average (TWA) atmospheric xylene exposure (p.p.m.) and urinary methylhippuric acid (MHA) expressed per gram of creatinine was examined. Subjects were recruited from workplaces that utilized xylene. Ambient monitoring of o-, m- and p-xylene isomers was carried out using passive diffusion vapour monitors. Adjusted (post-shift minus pre-shift) and post-shift urinary levels of xylene metabolites (2-, 3- and 4-MHA) were determined by GC-MS. Twenty subjects were recruited into the study. Total xylene TWA exposures were 3.36 +/- 3.63 p.p.m. (mean +/- SD) with a range of 0.03-14.44 p.p.m. The r(2) values for the regression equations between xylene exposure and individual and total adjusted MHA isomers were 0.390, 0.709, 0.677 and 0.631 for o-, m-, p- and total xylenes, respectively, which was greater than the respective correlations between non-adjusted samples. In conclusion, biological monitoring of occupational xylene exposure at levels <15 p.p.m. using urinary MHA showed a good correlation with atmospheric levels and is a valid complement to ambient monitoring. Even though occupational xylene exposure in the workplaces studied was generally low, MHA was found in the pre-shift urine of all workers and the use of adjusted values showed modest improvements in correlations. Recent exposure prior to sampling, either from occupational or non-occupational sources, should be considered when biological monitoring of xylene is undertaken. Extrapolation of data from this study predicted a MHA concentration in post-shift urine of 1.3 g/g creatinine after exposure to a TWA of 100 p.p.m. xylene.     

Evaluation of the dose of mercury in exposed and control subjects

OBJECTIVES: The aim of this paper was to analyse the concentrations of HgU and HgB in three different groups: 122 workers exposed, 18 workers formerly exposed and 196 subjects not occupationally or environmentally exposed to mercury. METHODS: All the subjects filled out a questionnaire concerning personal data, lifestyle, occupational or non-occupational exposure to Hg and medical history. The amalgam fillings area was measured by a standardised method. RESULTS: Urinary mercury excretion was significantly greater in the group of the exposed workers respect to the group of subjects not occupationally exposed (Median value of 8.3 micrograms/g creatinine and the 5 degrees and 95 degrees percentile respectively of 2.66 e 23.50 micrograms/g creatinine against Median value of 1.2 micrograms/g creatinine and the 5 degrees and 95 degrees percentile respectively of 0.18 and 5.42 micrograms/g creatinine). U-Hg in formerly exposed workers were comparable to U-Hg in non-occupationally exposed subjects, with a median value of 1.6 micrograms/g creatinine. B-Hg values were similar in the three groups: the median value was 3.1 micrograms/l in the non-occupationally exposed, 4.0 micrograms/l in the exposed workers and 3.9 micrograms/l in the past exposed. These value were not significantly different. Among the considered variables (amalgam fillings, fish consumption, age, sex, alcohol intake, chewing-gum and smoking) dental amalgam and fish consumption were significantly related with the Hg urinary excretion and the B-Hg levels. This is particularly true considering the subjects altogether: for the exposed workers, indeed, the occupational exposure was the most relevant variable. CONCLUSIONS: The results of the present research confirmed that the U-Hg excretion in non-occupationally exposed subjects is influenced by amalgam dental fillings. Furthermore, in our study Hg urinary excretion was significantly related with fish consumption. This fact can be explained, according to several recent experimental human and animal trials, considering that methylmercury contained in fish is partially converted, through breakage of the carbon-Hg bond, into Hg inorganic forms, which accumulate in the kidney and have a urinary excretion pathway.     

Maternal occupational exposure to electromagnetic fields before, during, and after pregnancy in relation to risks of childhood cancers: findings from the Oxford Survey of Childhood Cancers, 1953-1981 deaths

BACKGROUND: The concern that maternal exposure to electromagnetic fields (EMF) might be related to childhood cancer risks, particularly leukemia risks. METHODS: Maternal occupational data already collected as part of the Oxford Survey of Childhood Cancers have been reviewed. Information on occupations held before, during, and after the pregnancy was sought for 15,041 children dying of cancer in Great Britain in the period 1953-1981, and for an equal number of matched controls. Each period of working was classified under one of five headings: (1) sewing machinist; (2) textile industry workers (other than sewing machinists) with likely exposures to EMF; (3) other machinists and other jobs with likely "higher" EMF exposure; (4) other jobs with likely exposure to some EMF, and (5) jobs with little potential for EMF exposure. RESULTS: Relative to risks in the children of mothers who held occupations with little potential for EMF exposure during pregnancy (a category that included housewives), risks of all childhood cancers were close to unity both for the children of sewing machinists (22 case and 31 control mothers, RR 0.72, 95% CI 0.42 to 1.25) and for the children of other machinists with likely "higher" EMF exposures (44 case and 47 control mothers, RR 0.93, 95% CI 0.61 to 1.41). Corresponding risks for all childhood leukemias and for all childhood brain cancers were similarly unexceptional. Simultaneous adjustment for social class, maternal age at birth of child, and sibship position had little effect. CONCLUSIONS: The study findings did not indicate that maternal occupational exposure to EMF during pregnancy is a risk factor for childhood leukemias, childhood brain cancers, or the generality of all childhood cancers.     

A model for assessing occupational exposure to extremely low-frequency magnetic fields in fabrication rooms in the semiconductor health study

A model was created to assess occupational exposure to extremely low-frequency MAgnetic fields (ELF-MF) among semiconductor fabrication-room (fab) workers. This model was based on the assumption that each subject's exposure arose from being near identifiable ELF-MF sources or being in areas with high ELF-MF levels. To assess ELF-MF exposures, the model superimposed subjects' time-activity patterns (patterns of how and where they spent their time) with measurements of MAgnetic-field levels from devices and work areas. This model, which was validated by personal dosimetry on 192 persons in three fabs, predicted actual time-weighted average exposures with a correlation coefficient of 0.62. The inability of the model to predict individual exposures more accurately was attributed to unforeseen sources of elevated ELF-MF (transformers, distribution panels, sources in adjacent rooms) or to errors in subjects' judgments of time spent near devices. These unpredictable errors are intrinsic to the method used to Estimate exposure.     

Neurodegenerative diseases in welders and other workers exposed to high levels of magnetic fields

BACKGROUND: Previous work has suggested an increase in risk of amyotrophic lateral sclerosis (ALS) and Alzheimer's disease among workers exposed to extremely low-frequency magnetic fields (ELF-MF). We evaluated the relation between ELF-MF from occupational exposures and mortality from neurodegenerative diseases. METHODS: The study was based on a cohort of Swedish engineering industry workers, comprising 537,692 men and 180,529 women. The cohort was matched against the 3 most recent censuses and The Causes of Death Registry. Levels of ELF-MF exposure were obtained by linking occupation according to the censuses to a job exposure matrix. We used 4 levels of exposure and considered both the primary and contributing causes of death, 1985-96. RESULTS: The risk of Alzheimer's disease as primary or contributing cause of death increased with increasing exposure to ELF-MF among both men and women, with a relative risk (RR) of 4.0 and a 95% confidence interval (95% CI) of 1.4-11.7 in the highest exposure group for both sexes combined. There was a RR of 2.2 (95% CI: 1.0-4.7) for ALS in the highest exposure group with the suggestion of an exposure-response relationship. No evidence of increased risk was seen for Parkinson's disease or multiple sclerosis. CONCLUSIONS: The findings support previous observations of an increased risk of Alzheimer's disease and ALS among employees occupationally exposed to ELF-MF. Further studies based on morbidity data are warranted.     

Occupational exposures to noise resulting from the workplace use of personal media players at a manufacturing facility

This study examined the contribution of noise exposures from personal media player (PMP) use in the workplace to overall employee noise exposures at a Colorado manufacturing facility. A total of 24 workers' PMP and background noise exposures were measured. Twelve PMP users worked in high-background-noise exposure (HBNE) areas, and 12 worked in low-background-noise exposure (LBNE) areas. The self-selected PMP listening level of each worker was measured using an ear simulator, and the background noise of each employee workstation was measured using a sound level meter. Workers' self-reported PMP duration of use, PMP listening exposure levels, and background noise levels were used to estimate the daily occupational noise exposures. Measured background noise levels averaged 81 dBA for HBNE workers and 59 dBA for LBNE workers. Measured, free-field equivalent listening exposure levels were significantly greater for HBNE workers (85 dBA) compared with LBNE workers (75 dBA) (p = 0.0006). Estimated mean daily noise exposures for both groups were below the ACGIH threshold limit value for noise of 85 dBA8-hr time weighted average (TWA), specifically 84 dBA TWA for HBNE workers and 72 dBA TWA for LBNE workers. Three of 12 (25%) HBNE workers had estimated exposures greater than 85 dBA TWA when only background noise was considered, yet when PMP use was also considered, 6 of 12 (50%) had estimated exposures greater than 85 dBA TWA, suggesting that PMP use doubled the number of overexposed workers. None of the LBNE workers had estimated exposures greater than 85 dBA TWA. The contribution of PMP use to overall noise exposures was substantially less among HBNE workers than LBNE workers due to the disproportionate selection of noise-attenuating headsets among HBNE workers compared with LBNE workers. It is recommended that the facility management either restrict workplace PMP use among HBNE workers or require output-limiting technology to prevent occupational noise-induced hearing loss.