Michael G. Yost

Time-varying and static magnetic fields act in combination to alter calcium signal transduction in the lymphocyte

We have tested the hypothesis that extremely low frequency (ELF) time‐varying magnetic fields act in combination with static magnetic fields to alter calcium signalling in the lymphocyte. Results indicate that a 60‐min exposure of thymic lymphocytes at 37 ± 0.05°C to a 16 Hz, 421 mG (42.1 μT) magnetic field simultaneously with a colinear static magnetic field of 234 mG (23.4 μT) (a.c./d.c. field intensity ratio = 1.8) inhibits calcium influx triggered by the mitogen Concanavalin A. Significantly, resting lymphocytes do not respond to the fields, thus, only mitogen‐activated cells undergoing calcium signalling exhibit a field response. These results indicate that signal transduction involving calcium is an important biological constraint which operates to mediate this field interaction. Additional split field exposures show that the presence of the a.c. field or the d.c. field alone does not produce an effect. This is consistent with a proposed parametric resonance theory of interaction of low intensity magnetic fields with biological systems (L.L. Lednev (1991) Bioelectromagnetics 12, 71–75), which predicts the occurrance or biological effects at specific values for the frequency and field intensity of the ELF and static magnetic fields.

Geomagnetic disturbances are associated with reduced nocturnal excretion of a melatonin metabolite in humans

The effects of geomagnetic disturbances on urinary excretion of the melatonin metabolite, 6-hydroxymelatonin sulfate (6-OHMS), were studied in conjunction with 60 Hz magnetic field (MF) and ambient light exposure in 132 electric utility workers. Geomagnetic activity was assessed using a local (equivalent amplitude or A(K), Boulder, CO) and global (average antipodal or aa) index. Personal exposures to 60 Hz MFs and light were obtained using data-logging meters. The relationship between geomagnetic activity and 6-OHMS was assessed with adjustment for age, light exposure, and month of participation. Mean overnight 6-OHMS excretion was lower on days when the 36-h A(K) or aa values exceeded 30 nT. A greater reduction in 6-OHMS excretion was observed when increased geomagnetic activity was combined with elevated 60 Hz MF or reduced ambient light exposures.

Environmental risk factors for primary malignant brain tumors: A review

ConclusionsThis review suggests that existing theories of carcinogenesis provide much of the necessary framework for understanding the etiologies of malignant gliomas. Most of the environmental risk factors associated with brain tumors involve exposures to infectious, chemical, or physical agents capable of inflicting genetic damage. It is equally important to recognize that some potential risk factors for brain tumors, if their association proves causal, suggest as yet unknown or undefined mechanisms of carcinogenesis. For example, the mechanisms through which extremely-low-frequency electromagnetic fields might induce cancer are unknown, but interest in this area is intensifying [165].Large population based studies currently being conducted throughout the world will help to estimate the relative importance of some suspected factors. Several of the most serious limitations of previous studies can be overcome by careful study design including sample size planning to ensure adequate power for important hypotheses and subgroup analyses, systematic pathology review to enable analyses by histologie type, collecting sufficiently detailed exposure data to minimize recall problems and permit flexibility in classifications, and using rapid case ascertainment systems to minimize the need for interviews with proxies and concomitant reporting bias. Furthermore, as important genes for brain tumors are identified, they can be used to further refine subtype classifications and to improve sensitivity in the search for environmental culprits.

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 ≤1 compared to those with ratios >1. Conclusions: This ratio may help identify workers at increased risk for accidents or injuries.

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 childs 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 (κ=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.

A nested case-control study of residential and personal magnetic field measures and miscarriages.

We conducted a nested case-control study (177 cases, 550 controls) to assess the relation between retrospective magnetic field measures and clinical miscarriage among members of the northern California Kaiser Permanente medical care system. We also conducted a prospective substudy of 219 participants of the same parent cohort to determine whether 12-week and 30-week exposure assessments were similar. We evaluated wire codes, area measures, and three personal meter metrics: (1) the average difference between consecutive levels (a rate-of-change metric), (2) the maximum level, and (3) the time-weighted average. For wire codes and area measures we found little association. For the personal metrics (30 weeks after last menstrual period), we found positive associations. Each exposure was divided into quartiles, with the lowest quartile as referent. Starting with the highest quartile, adjusted odds ratios and 95% confidence intervals were 3.1 (95% CI = 1.6–6.0), 2.3 (95% CI = 1.2–4.4), and 1.5 (95% CI = 0.8–3.1) for the rate-of-change metric; 2.3 (95% CI = 1.2–4.4), 1.9 (95% CI = 1.0–3.5), and 1.4 (95% CI = 0.7–2.8) for the maximum value; and 1.7 (95% CI = 0.9–3.3), 1.7 (95% CI = 0.9–3.3), and 1.7 (95% CI = 0.9–3.3) for the time-weighted average. The odds ratio conveyed by being above a 24-hour time-weighted average of 2 milligauss was 1.0 (95% CI = 0.5–2.1). Exposure assessment measurements at 12 weeks were poorly correlated with those taken at 30 weeks. Nonetheless, the prospective substudy results regarding miscarriage risk were consistent with the nested study results.

Melatonin metabolite excretion among cellular telephone users

Purpose : The relationship between cellular telephone use and excretion of the melatonin metabolite 6-hydroxymelatonin sulfate (6-OHMS) was evaluated in two populations of male electric utility workers (Study 1, n =149; Study 2, n =77). Materials and methods : Participants collected urine samples and recorded cellular telephone use over 3 consecutive workdays. Personal 60-Hz magnetic field (MF) and ambient light exposures were characterized on the same days using EMDEX II meters. A repeated measures analysis was used to assess the effects of cellular telephone use, alone and combined with MF exposures, after adjustment for age, participation month and light exposure. Results : No change in 6-OHMS excretion was observed among those with daily cellular telephone use >25 min in Study 1 (5 worker-days). Study 2 workers with >25 min cellular telephone use per day (13 worker-days) had lower creatinine-adjusted mean nocturnal 6-OHMS concentrations (p =0.05) and overnight 6-OHMS excretion (p =0.03) compared with those without cellular telephone use. There was also a linear trend of decreasing mean nocturnal 6-OHMS/creatinine concentrations (p =0.02) and overnight 6-OHMS excretion (p =0.08) across categories of increasing cellular telephone use. A combined effect of cellular telephone use and occupational 60-Hz MF exposure in reducing 6-OHMS excretion was also observed in Study 2. Conclusions : Exposure-related reductions in 6-OHMS excretion were observed in Study 2, where daily cellular telephone use of >25min was more prevalent. Prolonged use of cellular telephones may lead to reduced melatonin production, and elevated 60-Hz MF exposures may potentiate the effect.

An assessment of occupational noise exposures in four construction trades.

Three hundred thirty-eight noise exposure samples were collected from 133 construction workers employed in 4 construction trades: carpenters, laborers, ironworkers, and operating engineers. Four sites using a variety of construction techniques were sampled at least 12 times on a randomly chosen date over a 22-week period. Up to 10 volunteer workers were sampled for an entire work shift on each sampling day using datalogging noise dosimeters, which recorded both daily time-weighted averages (TWAs) and 1-min averages. Workers also completed a questionnaire throughout the workday detailing the tasks performed and tools used throughout the day. Regression models identified work characteristics associated with elevated exposure levels. Comparisons were made between exposures measured using the Occupational Safety and Health Administration (OSHA) exposure metric and the 1996 draft National Institute for Occupational Safety and Health/International Organization for Standardization (NIOSH/ISO) metric to examine the effects of differing exchange rates and instrument response times on construction noise exposures. The mean OSHA TWA for 338 samples was 82.8 dBA +/- 6.8 dBA, whereas the mean NIOSH/ISO TWA for 174 samples was 89.7 dBA +/- 6.0 dBA. Forty percent of OSHA TWAs exceeded 85 dBA, and 13% exceeded 90 dBA, the OSHA permissible exposure limit. The tasks and tools associated with the highest exposure levels were those involving pneumatically operated tools and heavy equipment. Trade was a poor predictor of noise exposure; construction method, stage of construction, and work tasks and tools used were found to be better exposure predictors. An internal validation substudy indicated excellent agreement between worker self-reporting and researcher observation. These data provide substantial documentation that construction workers in several key trades are frequently exposed to noise levels that have been associated with hearing loss, and demonstrate the need for targeted noise reduction efforts and comprehensive hearing conservation programs in the industry.

Melatonin metabolite levels in workers exposed to 60-Hz magnetic fields : Work in substations and with 3-phase conductors

Melatonin suppression by 50/60-Hz magnetic fields represents a plausible biological mechanism for explaining increased health risks in workers. Personal exposure to magnetic fields and ambient light, and excretion of the melatonin metabolite 6-hydroxymelatonin sulfate (6-OHMS), were measured over 3 consecutive workdays in electric utility workers. There was a magnetic field-dependent reduction in adjusted mean nocturnal and post-work 6-OHMS levels among men working more than 2 hours per day in substation and 3-phase environments and no effect among those working 2 hours or less. No changes were observed among men working in 1-phase environments. The results suggest that circular or elliptical magnetic field polarization, or another factor linked to substations and 3-phase electricity, is associated with magnetic field induced melatonin suppression in humans.

Imaging Indoor Tracer-Gas Concentrations with Computed Tomography: Experimental Results with a Remote Sensing FTIR System

This work demonstrates for the first time the feasibility of computed tomography (CT) reconstructions of pollutant concentrations in a real room setting. A remote sensing Fourier transform infrared spectrometer was mounted on a moving base in a controlled ventilation chamber. A passive tracer was released from a point source into the room under constant ventilation conditions. A series of experiments gathered multiple path-averaged measurements in a two-dimensional plane for CT reconstruction. Simultaneous readings were gathered with a multiple-point sampling array for later comparison to the CT reconstructed concentrations. Good qualitative agreement between the reconstruction and point sample data was obtained. Limitations encountered due to the temporal resolution, size, and geometry of the experimental apparatus are clearly surmountable with better instrumentation.