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

Impact of Variability in Job Coding on Reliability in Exposure Estimates Obtained via a Job-Exposure Matrix

OBJECTIVES

The use of a job-exposure matrix (JEM) to assess exposure to potential health hazards in occupational epidemiological studies requires coding each participant's job history to a standard occupation and/or industry classification system recognized by the JEM. The objectives of this study were to assess the impact of inter-coder variability in job coding on reliability in exposure estimates derived from linking the job codes to the Canadian job-exposure matrix (CANJEM) and to identify influent parameters.

METHOD

Two trained coders independently coded 1000 jobs sampled from a population-based case-control study to the ISCO-1968 occupation classification at the five-digit resolution level, of which 859 could be linked to CANJEM using both assigned codes. Each of the two sets of codes was separately linked to CANJEM and thereby generated, for each of the 258 occupational agents available in CANJEM, two exposure estimates: exposure status (yes/no) and intensity of exposure (low, medium, and high) for exposed jobs only. Then, inter-rater reliability (IRR) was computed (i) after stratifying agents in 4 classes depending, for each, on the proportion of occupation codes in CANJEM defined as 'exposed' and (ii) for two additional scenarios restricted to jobs coded differently: the first one using experts' codes, the other one using codes randomly selected. IRR was computed using Cohen's kappa, PABAK and Gwet's AC1 index for exposure status, and weighted kappa and Gwet's AC2 for exposure intensity.

RESULTS

Across all agents and based on all jobs, median (Q1, Q3; Nagents) values were 0.68 (0.59, 0.75; 220) for kappa, 0.99 (0.95, 1.00; 258) for PABAK, and 0.99 (0.97, 1.00; 258) for AC1. For the additional scenarios, median kappa was 0.28 (0.00, 0.45; 209) and -0.01 (-0.02, 00; 233) restricted to jobs coded differently using experts' and random codes, respectively. A similar decreasing pattern was observed for PABAK and AC1 albeit with higher absolute values. Median kappa remained stable across exposure prevalence classes but was more variable for low prevalent agents. PABAK and AC1 decreased with increasing prevalence. Considering exposure intensity and all exposed jobs, median values were 0.79 (0.68, 0.91; 96) for weighted kappa, and 0.95 (0.89, 0.99; 102) for AC2. For the additional scenarios, median kappa was, respectively, 0.28 (-0.04, 0.42) and -0.05 (-0.18, 0.09) restricted to jobs coded differently using experts' and random codes, with a similar though attenuated pattern for AC2.

CONCLUSION

Despite reassuring overall reliability results, our study clearly demonstrated the loss of information associated with jobs coded differently. Especially, in cases of low exposure prevalence, efforts should be made to reliably code potentially exposed jobs.

Development of a Coding and Crosswalk Tool for Occupations and Industries

Introduction

Job coding into a standard occupation or industry classification is commonly performed in occupational epidemiology and occupational health. Sometimes, it is necessary to code jobs into multiple classifications or to convert job codes from one classification to another. We developed a generic tool, called CAPS-Canada (http://www.caps-canada.ca/), that combines a computer-assisted coding tool covering seven International, Canadian and US occupation and industry classifications and an assistant facilitating crosswalks from one classification to another. The objectives of this paper are to present the different functions of the CAPS-Canada tool and to assess their contribution through an inter-rater reliability study.

Method

The crosswalk assistant was built based on a database of >30,000 jobs coded during a previous project. We evaluated to what extent it would allow automatic translation between pairs of classifications. The influence of CAPS-Canada on agreement between coders was assessed through an inter-rater reliability study comparing three approaches: manual coding, coding with CAPS-Canada without the crosswalk assistant, and coding with the complete tool. The material for this trial consisted of a random sample of 1000 jobs extracted from a case-control study and divided into three subgroups of equivalent size.

Results

Across the classification systems, the crosswalk assistant would provide useful information for 83-99% of jobs (median 95%) in a population similar to ours. Eighteen to eighty-one percent of jobs (median 56%) could be entirely automatically recoded. Based on our sample of 1000 jobs, inter-rater reliability in occupation coding ranged from 35.7 to 66.5% (median 53.7%) depending on the combination of classification/resolution. Compared with manual coding, the use of CAPS-Canada substantially improved inter-rater reliability.

Conclusion

CAPS-Canada is an attractive alternative to manual coding and is particularly relevant for coding a job into multiple classifications or for recoding jobs into other classifications.

Work and Female Breast Cancer: The State of the Evidence, 2002-2017

The authors undertook a scoping review to assess the literature from 2002 to 2017 on the relationship between occupation and female breast cancer. Case-control, cohort, and meta-analytic studies suggest that women working as flight attendants, in medical professions, some production positions, sales and retail, and scientific technical staff are likely to have elevated risk of breast cancer. In addition, occupational exposures to night-shift work, ionizing radiation, some chemicals, job stress, and sedentary work may increase risk of breast cancer. Occupational physical activity appears to decrease risk. Workplace exposures to passive smoke and occupational exposure to nonionizing radiation do not appear to affect breast cancer risk. Some studies of occupational categories and workplace exposures indicate that risk may be modified by duration of exposure, timing of exposure, dose, hormone-receptor subtypes, and menopausal status at diagnosis. The compelling data from this review reveal a substantial need for further research on occupation and breast cancer.

Exposure to Benzene and Risk of Breast Cancer among Shoe Factory Workers in Italy

Aims and background

Evidence of the association between leukemia and benzene exposure has been provided by several epidemiological studies. An increased risk of breast cancer among women exposed to benzene has also been suggested. The aim of this study was to analyze breast cancer risk in a cohort of 1,002 women exposed to benzene in a shoe factory in Florence, Italy, where an excess of leukemia in men was reported.

Methods

The cohort of women at work on January 1st, 1950, was followed from 1950 to 2003 for mortality and from 1985 to 2000 for incidence of breast cancer. For a sub-cohort of 797 women, cumulative exposure to benzene was available.

Results

Standardized mortality ratios were obtained for the 797 women for whom information on cumulative exposure was available. For those with <30 years of latency the standardized mortality ratio was 58.5 (95% CI, 18.9–181.2, based on 3 deaths) and 151.1 (95% CI, 78.6–290.3, based on 9 deaths) for ≥30 years of latency. In the >40 ppm-year and ≥30 year latency period category, the standardized mortality ratio was 166.0 (95% CI, 62.3–442.2, based on 4 deaths). The standardized incidence ratio for women with a latency period <30 years was 140.9 (95% CI, 75.8–261.9, based on 10 cases) and 108.2 (95% CI, 64.1–182.7) for a latency period ≥30 years. For cumulative exposure >40 ppm-years and a latency period <30 years, the standardized incidence ratio was 211.9 (95% CI, 29.9–1504.1, based on 1 case).

Conclusions

The study moderately supports the hypothesis that benzene represents a risk factor for breast cancer.

Chemical Exposures in the Workplace

Occupational health nurses need to be aware of the current science on breast cancer risks in the workplace because they are risk communicators for employees and their families. Occupational health nurses can serve as advocates for necessary research ultimately leading to risk reduction and prevention strategies in the workplace. Current research suggests exposure to organic solvents, metals, acid mists, sterilizing agents (ethylene oxide), some pesticides, light at night (shift work), and tobacco smoke increases breast cancer risk among women in occupational settings. Animal cancer bioassays conducted by the National Toxicology Program indicate more than 40 chemicals can induce mammary tumors, and most of these are still in production. A variety of occupations worldwide, including health care providers and metal, textile, dye, rubber, and plastic manufacturing workers, have been identified as having some evidence of higher breast cancer risk. Although some chemical exposures are suspected to affect breast cancer risk, estimates of or actual exposures to these chemicals in the workplace often have not been determined. Research needed to better identify breast cancer risks in occupational settings includes monitoring breast cancer incidence in occupations with exposures to suspected carcinogens, characterizing chemical exposures by job type and task, determining whether potential gender differences affect chemical exposures, and using molecular approaches to identify gene-environment interactions.

Meta-analysis of extremely low frequency electromagnetic fields and cancer risk: a pooled analysis of epidemiologic studies

Studies have suggested that extremely low frequency electromagnetic fields (ELF-EMF) may affect physiological functions in animal models. However, epidemiologic studies investigating the association of ELF-EMF with the susceptibility to cancer yield contradictory results. In this comprehensive analysis, we conducted a search for case-control surveys regarding the associations of ELF-EMF and cancer susceptibility in electronic databases. A total of 42 studies involving 13,259 cases and 100,882 controls were retrieved. Overall, increased susceptibility to cancer was identified in the ELF-EMF exposed population (OR=1.08, 95% CI: 1.01, 1.15, P=0.02). In the stratified analyses, increased risk was found in North America (OR=1.10; 95% CI: 1.02, 1.20, P=0.02), especially the United States (OR=1.10; 95% CI: 1.01, 1.20, P=0.03). However, studies from Europe contradict these results. Moreover, a higher risk was found to be statistically significantly associated with the residential exposed population (OR=1.18; 95% CI: 1.02, 1.37, P=0.03). Furthermore, an increased cancer risk was found in interview-based surveys (OR=1.16; 95% CI: 1.00, 1.35, P=0.04). In device measurement-based studies, a slight increased risk was found only in premenopausal breast cancer (OR=1.23; 95% CI: 1.01, 1.49, P=0.04). Our meta-analysis suggests that ELF-EMFs are associated with cancer risk, mainly in the United States and in residential exposed populations. Methodological challenges might explain the differences among studies.

Occupational exposure to magnetic fields and breast cancer among Canadian men

Occupational magnetic field (MF) exposure has been suggested as a risk factor for breast cancer in both men and women. Due to the rarity of this disease in men, most epidemiologic studies investigating this relationship have been limited by small sample sizes. Herein, associations of several measures of occupational MF exposure with breast cancer in men were investigated using data from the population-based case-control component of the Canadian National Enhanced Cancer Surveillance System. Lifetime job histories were provided by 115 cases and 570 controls. Average MF exposure of individual jobs was classified into three categories (<0.3, 0.3 to <0.6, or ≥0.6 μT) through expert blinded review of participant's lifetime occupational histories. The impact of highest average and cumulative MF exposure, as well as exposure duration and specific exposure-time windows, on cancer risk was examined using logistic regression. The proportion of cases (25%) with a highest average exposure of ≥0.3 μT was higher than among controls (22%). We found an elevated risk of breast cancer in men who were exposed to ≥0.6 μT (odds ratio [OR] = 1.80, 95% CI = 0.82-3.95) when compared to those with exposures <0.3 μT. Those exposed to occupational MF fields for at least 30 years had a nearly threefold increase in risk of breast cancer (OR = 2.77, 95% CI = 0.98-7.82) when compared to those with background levels of exposure. Findings for the other time-related MF variables were inconsistent. Our analysis, in one of the largest case-control studies of breast cancer in men conducted to date, provides limited support for the hypothesis that exposure to MF increases the risk breast cancer in men.

Invited commentary: extremely low-frequency magnetic fields and breast cancer--now it is enough!

Research on an association between extremely low frequency (ELF) magnetic fields and breast cancer has been conducted since the 1980s, based on the hypothesis that ELF fields suppress melatonin production and melatonin protects against breast cancer development. In this issue of the Journal, Li et al. (Am J Epidemiol. 2013;178(7):1038-1045) present a well-designed study on occupational exposure to ELF fields and breast cancer that adds to the already large pool of data that has not supported the hypothesis. Over time, the quality and statistical power of studies within this research area have increased considerably, and advances in exposure assessment have reduced exposure misclassification. The evidence is consistently negative. A World Health Organization health risk assessment concluded in 2005 that the evidence from experimental and epidemiologic studies is sufficient to give confidence that ELF magnetic fields do not cause breast cancer. The new study adds even more confidence to this conclusion. We should now focus our time and research resources on more promising hypotheses, the results of which could make a difference for public health and advance science. Further epidemiologic studies on ELF fields and breast cancer are likely to have little new knowledge to add.

A meta-analysis on the relationship between exposure to ELF-EMFs and the risk of female breast cancer

Objective

To comprehensively analyze the relationship between exposure to extremely low frequency electromagnetic fields (ELF-EMFs) and the development of female breast cancer.

Methods

Reports of case-control studies published from 1990 to 2010 were analyzed. The quality effect model was chosen to calculate total odds ratio (OR) depending on the data in studies and quality scores. Subgroup analyses were also performed by the situation of menopause, estrogenic receptor and exposure assessment respectively.

Results

For all 23 studies the OR was 1.07, 95% CI = 1.02–1.13, for estrogen receptor positive subgroup,OR = 1.11, 95% CI = 1.03–1.20; for premenopausal subgroup, OR = 1.11, 95% CI = 1.00–1.23. The results of other subgroups showed no significant association between ELF-EMF and female breast cancer.

Conclusion

ELF-EMFs might be related to an increased risk for female breast cancer, especially for premenopausal and ER+ females. However, it's necessary to undertake better epidemiologic researches to verify the association between ELF-EMF and female breast cancer due to the limits of current study, especially the one on exposure assessment.

Postmenopausal breast cancer is associated with exposure to traffic-related air pollution in Montreal, Canada: a case-control study

BACKGROUND

Only about 30% of cases of breast cancer can be explained by accepted risk factors. Occupational studies have shown associations between the incidence of breast cancer and exposure to contaminants that are found in ambient air.

OBJECTIVES

We sought to determine whether the incidence of postmenopausal breast cancer is associated with exposure to urban air pollution.

METHODS

We used data from a case-control study conducted in Montreal, Quebec, in 1996-1997. Cases were 383 women with incident invasive breast cancer, and controls were 416 women with other incident, malignant cancers, excluding those potentially associated with selected occupational exposures. Concentrations of nitrogen dioxide (NO2) were measured across Montreal in 2005-2006. We developed a land-use regression model to predict concentrations of NO2 across Montreal for 2006, and developed two methods to extrapolate the estimates to 1985 and 1996. We linked these estimates to addresses of residences of subjects at time of interview. We used unconditional logistic regression to adjust for accepted and suspected risk factors and occupational exposures.

RESULTS

For each increase of 5 ppb NO2 estimated in 1996, the adjusted odds ratio was 1.31 (95% confidence interval, 1.00-1.71). Although the size of effect varied somewhat across periods, we found an increased risk of approximately 25% for every increase of 5 ppb in exposure.

CONCLUSIONS

We found evidence of an association between the incidence of postmenopausal breast cancer and exposure to ambient concentrations of NO2. Further studies are needed to confirm whether NO2 or other components of traffic-related pollution are indeed associated with increased risks.

Campos magnéticos de frequência extremamente baixa e efeitos na saúde: revisão da literatura

A partir da publicação, em 1979, dos resultados de um estudo que apontava para o aumento do risco de leucemia em crianças associado à exposição a campos magnéticos, o interesse pelo tema vem aumentando, e diversos estudos foram publicados. O objetivo desta revisão é apresentar os diferentes métodos utilizados na avaliação da exposição aos campos magnéticos de frequência extremamente baixa, bem como as dificuldades enfrentadas na quantificação dessa exposição, além de relatar os resultados de estudos epidemiológicos publicados nos últimos 10 anos. A falta de um modelo fisiopatológico que explique uma possível influência dos campos magnéticos na saúde e a dificuldade para quantificar a exposição têm sido os maiores obstáculos da pesquisa na área. Leucemia e tumores do sistema nervoso central têm sido os efeitos mais estudados. Leucemia em crianças é o desfecho mais consistentemente associado à exposição a campos magnéticos. Estudos mais recentes apontam a associação entre esclerose lateral amiotrófica e campos magnéticos.

Exposure of mcf-7 breast cancer cells to electromagnetic fields up-regulates the plasminogen activator system

Effects of electromagnetic fields (EMFs) on the incidence of breast cancer (BC) have been proposed by a number of epidemiological studies. The molecular mechanism of the impact of EMFs on cells is not yet clear, although changes in gene expression have been reported in various cellular systems. In this investigation, the interference of low-frequency EMFs with the plasminogen activator system was examined in BC cells.MCF-7 BC cells from 2 different sources were exposed to highly homogeneous 50-Hz EMFs. Changes in gene expression were analyzed by reverse transcriptase-polymerase chain reaction.In MCF-7 cells exposed to 1.2 microT EMF expression of the urokinase plasminogen activator gene and of plasminogen-activator inhibitor-1 was markedly increased. The expression of the receptor for urokinase plasminogen activator was only marginally increased in 1 of the 2 tested cell lines and expression of the tissue plasminogen activator was at least slightly down-regulated in BC cells exposed to EMFs.EMFs may be able to increase the metastatic potential of breast tumors. The use of our newly established exposure system for EMFs may allow us to study the signaling processes involved in the induction of a metastatic phenotype of breast cancer cells.

Effects of long-term exposure of extremely low frequency magnetic field on oxidative/nitrosative stress in rat liver

Thirty-two adult Wistar-Albino female and male rats were used to investigate the long-term (45 days) effects of extremely low frequency magnetic field (ELF-MF; 50Hz, 1mT, 4h/day) exposure on oxidative/nitrosative stress in liver tissues of rats. The rats were divided randomly into four groups: female control (FC; n = 8) and MF-exposed female rats (F-MF; n = 8); male control (MC; n = 8) and MF-exposed male rats (M-MF; n = 8). Liver tissue from each animal was harvested and utilized for malondialdehyde (MDA) and 3-nitrotyrosine (3-NT) detection. MDA levels were measured by MDA-TBA method, while the 3-NT levels were determined by the HPLC-UV system. There were no significant differences between the MDA levels of the control (FC; MC) and MF-exposed (F-MF; M-MF) rats (P > 0.05). In the F-MF rats, 3-NT levels were significantly increased when compared to those of the FC rats (P < 0.05). There were no significant differences between the 3-NT levels of the MC and M-MF rats. In conclusion, our study suggests that the long-term ELF-MF exposure may enhance the oxidative/nitrosative stress in liver tissue of the female rats and could have a deteriorative effect on cellular proteins rather than lipids by enhancing 3-NT formation.

Occupation and breast cancer risk among Shanghai women in a population-based cohort study

INTRODUCTION

A total of 74,942 female subjects were recruited in a population-based cohort study in Shanghai, China between 1997 and 2000. We examined the relationship between occupation and breast cancer risk.

METHODS

Cases were 586 women previously diagnosed with breast cancer at baseline and 438 women newly diagnosed with breast cancer during follow-up through December 2004. Eight controls were randomly selected for each case from cancer-free cohort members and frequency-matched to the cases by year of birth and age at diagnosis. Logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) of breast cancer risk associated with occupations, adjusting for established breast cancer risk factors.

RESULTS

In the prevalent breast cancer data analysis, increased risks of breast cancer were associated with technicians in engineering/agriculture/forestry (OR = 1.6, CI: 1.0-2.4), teaching personnel (OR = 1.5, CI:1.1-2.0), tailoring/sewing workers (OR = 1.6, CI:1.0-2.7), and examiners/measurers/testers (OR = 1.5, CI:1.1-2.1) among those who started the jobs at least 20 years ago. Among incident breast cancer cases, significantly increased risks were associated with medical/health care workers (OR = 1.4, CI:1.0-2.0), administrative clerical workers (OR = 1.5, CI:1.0-2.4), postal/telecommunication workers (OR = 2.2, CI:1.0-5.5), and odd-job workers (OR = 1.7, CI:1.1-2.8) among those who started the jobs at least 20 years ago. The excess risks were found in both prevalent and incident cases for postal/telecommunication workers and purchasing/marketing personnel, although ORs reached only marginal significance.

CONCLUSIONS

This study suggests that white-collar professionals and several production occupations may be associated with an increased risk of breast cancer.

Occupational exposure to electromagnetic field and breast cancer risk in a large, population-based, case-control study in the United States

OBJECTIVE

Our objective was to evaluate women who were occupationally exposed to electromagnetic fields (EMF) and breast cancer risk.

METHODS

Women diagnosed with breast cancer (n=6213) and randomly selected age-matched control subjects (n=7390) provided breast cancer risk factor information and occupational history. A qualified industrial hygienist classified each job for EMF exposure as background, low, medium, or high.

RESULTS

When compared with the referent of background exposure, the odds ratio adjusted for age and state of residence was 1.06 (95% CI=0.99-1.14) for low exposure, 1.09 (95% CI=0.96-1.23) for medium exposure, and 1.16 (95% CI=0.90-1.50) for high exposure.

CONCLUSION

Our findings, taken together with previous epidemiological studies, suggest that exposure to EMF in the workplace may be associated with a slight elevation in breast cancer risk.

Risk for leukaemia and brain and breast cancer among Danish utility workers: a second follow-up

OBJECTIVE

To update a study of risks for leukaemia, brain cancer and breast cancer in a Danish nationwide, population-based cohort of utility employees.

METHODS

A multivariate statistical model including information on age, duration of employment, date of first employment and level of occupational exposure to electromagnetic fields was applied.

RESULTS

No increased risk for these cancers was seen among 28,224 subjects with more than 3 months of employment in whom cancer had not been diagnosed before first employment.

CONCLUSION

The results do not support the hypothesis of an association between occupational exposure to magnetic fields in the electric utility industry and risks for leukaemia, brain cancer and breast cancer.

Occupational Exposures and Breast Cancer Among Women Textile Workers in Shanghai

BACKGROUND

Breast cancer incidence rates have been increasing in China over the past 2 decades. Most studies have focused on reproductive, dietary, and genetic risk factors. Little is known about the contribution of occupational exposures.

METHODS

We conducted a case-cohort study within a cohort of female textile workers who had participated in a randomized trial of breast self-examination in Shanghai, China. We compared 1709 incident breast cancer cases with an age-stratified reference subcohort (n = 3155 noncases). Cox proportional hazards modeling, adapted for the case-cohort design, was used to estimate hazard ratios for breast cancer in relation to duration of employment in various job processes and duration of exposure to several agents. We also evaluated the associations of cotton dust and endotoxin with breast cancer.

RESULTS

Cumulative exposures to cotton dust and endotoxin demonstrated strong inverse gradients with breast cancer risk when exposures were lagged by 20 years (trend P-values <0.001). We did not observe consistent associations with exposures to electromagnetic fields, solvents, or other chemicals.

CONCLUSION

Endotoxin or other components of cotton dust exposures may have reduced risks for breast cancer in this cohort, perhaps acting at early stages of carcinogenesis. Replication of these findings in other occupational settings with similar exposures will be needed to confirm or refute any hypothesis regarding protection against breast cancer.

Occupation and breast cancer risk in Polish women: a population-based case-control study

BACKGROUND

The etiology of breast cancer is not well understood and the role of occupational exposures in breast carcinogenesis is still uncertain.

METHODS

The population-based case-control study included 2,386 incident breast cancer cases diagnosed in 2000-2003, and 2,502 controls. Lifetime occupational histories and information on other potential breast cancer risk factors were obtained through personal interviews. Conditional logistic regression analyses calculated odds ratios (ORs) associated with various occupations and industries after control for potential confounders.

RESULTS

We found statistically significant excesses of breast cancer among engineers (OR=2.0; 95% CI: 1.0-3.8), economists (2.1; 1.1-3.8), sales occupations-retail (1.2; 1.0-1.5), and other sales occupations (1.2; 1.0-1.5). Industries showing significantly elevated risks included special trade contractors (2.2; 1.2-4.3), electronic and electric equipment manufacturers (1.7; 1.1-2.7); and public administration/general government n.e.c. (2.7; 1.3-5.7). Each of these findings was supported by a statistically significant positive trend for duration of employment (P<0.05). A decreased breast cancer risk was observed in janitors and cleaners (0.7; 0.5-0.8).

CONCLUSIONS

In this study, we found few associations for breast cancer and occupations or industries. The suggestive findings for the electronic and electric equipment manufacturing industry and for the occupations with potential exposure to magnetic fields deserve further evaluation.

Electromagnetic fields and female breast cancer

The possibility that long term exposure to relatively weak power frequency electromagnetic fields (EMF) could increase the risk of breast cancer has been investigated during the past decade. The hypothesis is based on the assumption that magnetic field exposures suppress melatonin production and that melatonin is protective against breast cancer. Most epidemiological studies have indicated little or no overall effect of EMF exposure, but some early studies suggested effects among premenopausal women, particularly for estrogen receptor positive breast tumors. The early studies were often limited by small numbers, crude exposure information and lack of information on confounding factors. In more recent occupational studies, again no overall risk increases were reported, but some studies found increased risks in certain subgroups, although with no consistent pattern across studies. A recent very large occupational study with improved exposure assessment and enough statistical power also for subgroup analyses found no indications of increased risks in any subgroups. Most of the recent well-designed residential studies report no increased risks, and similar findings are reported in the majority of studies of bed heating devices. Overall, the weight of the evidence available today does not suggest an increased risk of breast cancer related to EMF exposure.

Proteomic response ofSchizosaccharomyces pombe to static and oscillating extremely low-frequency electromagnetic fields

There is considerable public concern regarding the health effects of exposure to low-frequency electromagnetic fields. In addition, the association between exposure and disease incidence or the possible biological effects of exposure are unclear. Using 2D-DIGE and MS in a blind study, we have investigated the effects of static and oscillating extremely low-frequency electromagnetic fields (ELF EMFs) on the proteomes of wild type Schizosaccharomyces pombe and a Sty1p deletion mutant which displays increased sensitivity to a variety of cellular stresses. Whilst this study identifies a number of protein isoforms that display significant differential expression across experimental conditions, there was no correlation between their patterns of expression and the ELF EMF exposure regimen. We conclude that there are no significant effects of either static or oscillating EMF on the yeast proteome at the sensitivity afforded by 2D-DIGE. We hypothesise that the proteins identified must be sensitive to subtle changes in culture and/or handling conditions, and that the identification of these proteins in other proteomic studies should be treated with some caution when the results of such studies are interpreted in a biological context.

Power Frequency Magnetic Fields Increase Cell Proliferation in the Mammary Gland of Female Fischer 344 Rats but Not Various Other Rat Strains or Substrains

Epidemiological data have raised concerns about the relationship between exposure to power frequency magnetic fields (MFs) and breast cancer. We have shown previously that 50-Hz MFs at microtesla flux densities enhance mammary gland tumor development and growth in the 7,12-dimethylbenz[a]anthracene (DMBA) model of breast cancer in female Sprague-Dawley (SD) rats. We also demonstrated that MF exposure results in an enhanced proliferative activity of the mammary epithelium of SD rats, which is a likely explanation for the cocarcinogenic or tumor-promoting effects of MF exposure in the DMBA model. Comparison of different SD substrains indicated that the genetic background plays a pivotal role in these effects of MF exposure. This prompted us to compare the effects of MF exposure (100 microT, 2 weeks) on cell proliferation in the mammary gland in eight different strains and substrains of outbred and inbred rats. Proliferation of epithelial cells in the mammary tissue and adjacent skin was examined by labeling proliferating cells with bromodeoxyuridine (BrdU). In addition to the MF-sensitive SD substrain (SD1) previously used in our experiments, Fischer 344 rats were the only strain in which MF exposure significantly enhanced BrdU labeling in the mammary epithelium, indicating a marked increase in cell proliferation. The MF-induced increase in BrdU labeling in Fischer 344 rats was similar to that seen after DMBA application. Furthermore, whole mount analysis of mammary tissue from Fischer 344 rats demonstrated that MF exposure increased the number of terminal end buds, i.e. the site of origin of mammary carcinomas. By comparison with MF-insensitive inbred rat strains, Fischer 344 rats may serve to evaluate the genetic factors underlying sensitivity to cocarcinogenic or tumor-promoting effects of MF exposure.

Effects of extremely low-frequency magnetic field in the brain of rats

An extremely low-frequency magnetic field (50 Hz, 0.5 mT) was used to investigate its possible effect on the brain of adult male Wistar rats following a 7-day exposure. The control rats were sham-exposed. Superoxide dismutase activities and production of superoxide radicals, lipid peroxidation, and nitric oxide were examined in the frontal cortex, striatum, basal forebrain, hippocampus, brainstem, and cerebellum. Significantly increased superoxide radical contents were registered in all the structures examined. Production of nitric oxide, which can oppose superoxide radical activities, was significantly increased in some structures: the frontal cortex, basal forebrain, hippocampus, and brainstem. Augmentation of lipid peroxydation was also observed, with significance only in the basal forebrain and frontal cortex, in spite of the significantly increased superoxide dismutase activities and nitric oxide production in the basal forebrain, and increased production of nitric oxide in the frontal cortex. The results obtained indicate that a 7-day exposure to extremely low-frequency magnetic field can be harmful to the brain, especially to the basal forebrain and frontal cortex due to development of lipid peroxidation. Also, high production of superoxide anion in all regions may compromise nitric oxide signaling processes, due to nitric oxide consumption in the reaction with the superoxide radical.

Risk of breast cancer among enlisted Army women occupationally exposed to volatile organic compounds

BACKGROUND

The military presents a unique opportunity to study the incidence of disease in a population with complete knowledge of person-time and occupation. Women in the Army are employed more frequently in non-traditional, industrial jobs such as auto mechanic and motor transport operators than in the general US population, increasing the probability of exposure to industrial chemicals. A cohort to investigate the risk of breast cancer among active duty Army women occupationally exposed to volatile organic chemicals (VOCs) was constructed.

METHODS

Age-adjusted incidence rates for breast cancer were calculated for more than 270,000 enlisted women who served between 1980-1996. Twenty-one VOCs, described in previously published literature as having a potential risk of breast cancer, were identified in an Army industrial hygiene survey database. Job title histories were linked to workplace chemical evaluations conducted by Army industrial hygienists, which included a subjective exposure potential rating (high, medium, low, and none) for each VOC. Poisson regression analysis was used to evaluate the association between the exposure rating by job title and breast cancer.

RESULTS

The incidence of breast cancer in the cohort was significantly elevated in women younger than 35 years of age, especially among black women, when compared to the age-specific rates in the general population. Women who worked in occupations with a moderate to high exposure potential to at least one VOC had a 48% increased risk (P < 0.05) of breast cancer while on active duty between 1980-1996 when compared to those women with low to no exposure potential.

CONCLUSIONS

This study provides preliminary evidence that exposure to one or more of the study VOCs is associated with an increased risk of breast cancer. Further substance-specific, quantitative analyses are warranted.