Incidence of cancer among workers in Norwegian hydroelectric power companies

Occupational exposures and cancer: a review of agents and relative risk estimates

OBJECTIVES

The contribution of occupational exposures to the cancer burden can be estimated using population-attributable fractions, which is of great importance for policy making. This paper reviews occupational carcinogens, and presents the most relevant risk relations to cancer in high-income countries using France as an example, to provide a framework for national estimation of cancer burden attributable to occupational exposure.

METHODS

Occupational exposures that should be included in cancer burden studies were evaluated using multiple criteria: classified as carcinogenic or probably carcinogenic by the International Agency for Research on Cancer (IARC) Monographs volumes 1-114, being a primary occupational exposure, historical and current presence of the exposure in France and the availability of exposure and risk relation data. Relative risk estimates were obtained from published systematic reviews and from the IARC Monographs.

RESULTS

Of the 118 group 1 and 75 group 2A carcinogens, 37 exposures and 73 exposure-cancer site pairs were relevant. Lung cancer was associated with the most occupational carcinogenic exposures (namely, 18), followed by bladder cancer and non-Hodgkin's lymphoma. Ionising radiation was associated with the highest number of cancer sites (namely, 20), followed by asbestos and working in the rubber manufacturing industry. Asbestos, bis(chloromethyl)ether, nickel and wood dust had the strongest effect on cancer, with relative risks above 5.

CONCLUSIONS

A large number of occupational exposures continues to impact the burden of cancer in high-income countries such as France. Information on types of exposures, affected jobs, industries and cancer sites affected is key for prioritising policy and prevention initiatives.

Do polychlorinated biphenyls cause cancer? A systematic review and meta-analysis of epidemiological studies on risk of cutaneous melanoma and non-Hodgkin lymphoma

In 2015 a IARC Working Group upgraded the classification of PCBs to Group 1 "Carcinogenic to humans", also on the basis of evidence from epidemiological studies showing an excess risk for melanoma. Increased risks for non-Hodgkin lymphoma (NHL) and breast cancer were also reported though the evidence was limited. However, some recent reviews of studies on PCB exposure and risk of cancer provided discrepant findings. Therefore, we re-evaluated the association between exposure to PCBs and risk of melanoma and NHL by a systematic review and meta-analysis. We retrieved 11 independent cohort studies on occupationally exposed workers. About half of them showed increased standardized mortality or incidence ratios (SMRs or SIRs) for melanoma and none for NHL. The pooled SMRs were 1.32 (95% CI: 1.05-1.64) for melanoma and 0.94 (0.73-1.23) for NHL. Among population-based cohort and case-control studies with individual measures of PCB exposure, one only study was carried out on PCB exposure and melanoma, showing an odds ratio (OR) of 6.0 (2.0-18.2) for the highest compared to lowest quartile of PCB distribution. 13 cohort and case-control studies evaluated the association between NHL and PCB concentration in blood or subcutaneous fat, with summary OR = 1.5 (1.1-1.7) for the highest vs lowest quantile of PCB distribution. However, two cohort studies on people intoxicated by rice oil containing PCBs found no excess of deaths for skin cancer and inconsistent results for NHL. In conclusion, these findings do not provide a strong evidence that PCB exposure can increase the risk of melanoma and NHL in humans.

Occupational Exposures and Non-Hodgkin's Lymphoma in Southern Sweden

In a case-control study based on 859 consecutive non-Hodgkin's lymphoma (NHL) cases identified through a tumor registry between 1990 and 1998, the authors collected demographic, occupational, exposure, and education information. Exposures were identified through self-report, reported occupational history, and the use of a job-exposure matrix. Conditional logistic regression analyses of the 859 cases and 1,310 controls showed increased risks in workers exposed to gasoline (odds ratio [OR] 1.46; 95% confidence interval [CI] 1.04, 2.05), aliphatic or alicyclic hydrocarbons (OR 1.75; CI 1.03, 2.99), aromatic hydrocarbons (OR 1.45; (CI 1.13, 1.86), and solvents for mole than five years (OR 1.59: CI 1.11, 2.28), as well as automobile mechanics (OR 1.82; CI 1.18, 2.81) and painters (OR 1.77; CI 1.13, 2.76). Exposures to pesticides and farming were not associated with increased risk. Prior radiotherapy was associated with increased risk (OR 2.84; (CI 1.85, 4.37). Concordance between analyses based on self-reported exposures, occupations, and the job-exposure matrix supported the links between organic solvents and prior radiotherapy and NHL but did not support associations between farming or pesticides and NHL.

Polychlorinated biphenyls and cancer: an epidemiological assessment

Polychlorinated biphenyls (PCBs) are toxic and persistent chemicals produced between 1930s and 1980s primarily for insulating fluids in heavy-duty electrical equipment in power plants, industries, and large buildings. They persist in the environment and accumulate in plants and animals, and have been classified as probable carcinogens to humans. We performed a systematic review and meta-analysis of scientific literature on the relationship between PCB exposure and human cancer. Two cohorts of people highly exposed to PCBs through ingestion of contaminated rice oil and some cohorts of occupationally exposed workers failed to show a definite increase in total cancer mortality and provided inconsistent results regarding single cancers. Several cohort and case-control studies investigated the association between PCBs and specific cancers, showing an association between PCB serum levels and non-Hodgkin lymphomas (NHL), with a summary odds ratio of 1.5 (95% confidence interval: 1.1-1.7), but no consistent results for the other cancer sites and types. In conclusion, this review provides some evidence for the role of PCBs in the development of NHL, although the inconsistent results of studies performed on highly polluted people and occupationally exposed workers do not allow a firm conclusion to be drawn.

Extremely low frequency electric fields and cancer: assessing the evidence

Much of the research and reviews on extremely low frequency (ELF) electric and magnetic fields (EMFs) have focused on magnetic rather than electric fields. Some have considered such focus to be inappropriate and have argued that electric fields should be part of both epidemiologic and laboratory work. This paper fills the gap by systematically and critically reviewing electric-fields literature and by comparing overall strength of evidence for electric versus magnetic fields. The review of possible mechanisms does not provide any specific basis for focusing on electric fields. While laboratory studies of electric fields are few, they do not indicate that electric fields should be the exposure of interest. The existing epidemiology on residential electric-field exposures and appliance use does not support the conclusion of adverse health effects from electric-field exposure. Workers in close proximity to high-voltage transmission lines or substation equipment can be exposed to high electric fields. While there are sporadic reports of increase in cancer in some occupational studies, these are inconsistent and fraught with methodologic problems. Overall, there seems little basis to suppose there might be a risk for electric fields, and, in contrast to magnetic fields, and with a possible exception of occupational epidemiology, there seems little basis for continued research into electric fields.

Occupation and malignant lymphoma: a population based case control study in Germany

AIMS

To identify occupations suspected to be associated with malignant lymphoma and to generate new hypotheses about occupational risks in a multicentre, population based case control study.

METHODS

Male and female patients with malignant lymphoma (n = 710) aged 18-80 years of age were prospectively recruited in six study regions in Germany. For each newly recruited lymphoma case, a sex, region, and age matched control was drawn from the population registers. Odds ratios and 95% confidence intervals for major occupations and industries were calculated using conditional logistic regression analysis, adjusted for smoking (in pack-years) and alcohol consumption. Patients with specific lymphoma subentities were additionally compared with the entire control group using unconditional logistic regression analysis.

RESULTS

The following economic/industrial sectors were positively associated with lymphoma: food products, beverages, tobacco; paper products, publishing and printing; and metals. Chemicals; real estate, renting, and business activities were negatively associated with lymphoma diagnosis. The authors observed an increased overall lymphoma risk among architects; maids; farmers; glass formers; and construction workers. Shoemaking and leather goods making was negatively associated with the lymphoma diagnosis (although based on small numbers). In the occupational group analysis of lymphoma subentities, Hodgkin's lymphoma was significantly associated only with rubber and plastic products making; diffuse large B cell lymphoma risk was considerably increased among metal processors; follicular lymphoma showed highly significant risk increases for several occupational groups (medical, dental, and veterinary workers; sales workers; machinery fitters; and electrical fitters); and multiple myeloma showed a particularly pronounced risk increase for farmers as well as for agriculture and animal husbandry workers.

CONCLUSIONS

The results partly confirm previously defined occupational risks. Occupational risk factors for follicular lymphomas might differ from the overall risk factors for malignant lymphoma.

Mortality among workers exposed to polychlorinated biphenyls (PCBs) in an electrical capacitor manufacturing plant in Indiana: an update

An Indiana capacitor-manufacturing cohort (n=3,569) was exposed to polychlorinated biphenyls (PCBs) from 1957 to 1977. The original study of mortality through 1984 found excess melanoma and brain cancer; other studies of PCB-exposed individuals have found excess non-Hodgkin lymphoma and rectal, liver, biliary tract, and gallbladder cancer. Mortality was updated through 1998. Analyses have included standardized mortality ratios (SMRs) and 95% confidence intervals (CIs) using rates for Indiana and the United States, standardized rate ratios (SRRs), and Poisson regression rate ratios (RRs). Estimated cumulative exposure calculations used a new job-exposure matrix. Mortality overall was reduced (547 deaths; SMR, 0.81; 95% CI, 0.7-0.9). Non-Hodgkin lymphoma mortality was elevated (9 deaths; SMR, 1.23; 95% CI, 0.6-2.3). Melanoma remained in excess (9 deaths; SMR, 2.43; 95% CI, 1.1-4.6), especially in the lowest tertile of estimated cumulative exposure (5 deaths; SMR, 3.72; 95% CI, 1.2-8.7). Seven of the 12 brain cancer deaths (SMR, 1.91; 95% CI, 1.0-3.3) occurred after the original study. Brain cancer mortality increased with exposure (in the highest tertile, 5 deaths; SMR, 2.71; 95% CI, 0.9-6.3); the SRR dose-response trend was significant (p=0.016). Among those working >or= 90 days, both melanoma (8 deaths; SMR, 2.66; 95% CI, 1.1-5.2) and brain cancer (11 deaths; SMR, 2.12; 95% CI, 1.1-3.8) were elevated, especially for women: melanoma, 3 deaths (SMR, 5.99; 95% CI, 1.2-17.5); brain cancer, 3 deaths (SMR, 2.87; 95% CI, 0.6-8.4). These findings of excess melanoma and brain cancer mortality confirm results of the original study. Melanoma mortality was not associated with estimated cumulative exposure. Brain cancer mortality did not demonstrate a clear dose-response relationship with estimated cumulative exposure.

Risk of non-Hodgkin lymphoma associated with occupational exposure to solvents, metals, organic dusts and PCBs (Australia)

OBJECTIVE

Several studies have suggested that there is an occupational component to the causation of non-Hodgkin lymphoma (NHL). We aimed to use accurate means to assess occupational exposures to solvents, metals, organic dusts and polychlorinated biphenyls (PCBs) in a case-control study.

METHODS

Cases were incident NHLs during 2000 and 2001 in two regions of Australia. Controls were randomly selected from the electoral roll and frequency matched to cases by age, sex and region. A detailed occupational history was taken from each subject. For jobs with likely exposure to the chemicals of interest, additional questions were asked by telephone interview using modified job specific modules. An expert allocated exposures using the information in the job histories and the interviews. Odds ratios were calculated for each exposure adjusting for age, sex, region and ethnic origin.

RESULTS

694 cases and 694 controls (70 and 45 respectively of those potentially eligible) participated. The risk of NHL was increased by about 30 for exposure to any solvent with a dose response relationship, subgroup analysis showed the finding was restricted to solvents other than benzene. Exposure to wood dust also increased the risk of NHL slightly. Exposures to other organic dusts, metals, and PCBs were not strongly related to NHL.

CONCLUSIONS

The risk of NHL appears to be increased by exposure to solvents other than benzene and possibly to wood dust.

Occupational exposure to electromagnetic fields and acute leukaemia: analysis of a case-control study

AIMS

To investigate whether the risk of acute leukaemia among adults is associated with occupational exposure to electromagnetic fields.

METHODS

Probable occupational exposure to electromagnetic fields at higher than typical residential levels was investigated among 764 patients diagnosed with acute leukaemia during 1991-96 and 1510 sex and age matched controls. A job exposure matrix was applied to the self reported employment histories to determine whether or not a subject was exposed to electromagnetic fields. Risks were assessed using conditional logistic regression for a matched analysis.

RESULTS

Study subjects considered probably ever exposed to electromagnetic fields at work were not at increased risk of acute leukaemia compared to those considered never exposed. Generally, no associations were observed on stratification by sex, leukaemia subtype, number of years since exposure stopped, or occupation; there was no evidence of a dose-response effect using increasing number of years exposed. However, relative to women considered never exposed, a significant excess of acute lymphoblastic leukaemia was observed among women probably exposed to electromagnetic fields at work that remained increased irrespective of time prior to diagnosis or job ever held.

CONCLUSION

This large population based case-control study found little evidence to support an association between occupational exposure to electromagnetic fields and acute leukaemia. While an excess of acute lymphoblastic leukaemia among women was observed, it is unlikely that occupational exposure to electromagnetic fields was responsible, given that increased risks remained during periods when exposure above background levels was improbable.

Residential and occupational exposure to 50 Hz magnetic fields and malignant melanoma: a population based study

AIMS

To test the hypothesis that exposure to electromagnetic fields from high voltage power lines increases the incidence of cutaneous malignant melanoma in adults aged 16 and above.

METHODS

Nested case-control study. The study population comprised subjects aged 16 and above who had lived in a residence situated in a broad corridor around a high voltage power line in 1980, or one of the years from 1986 to 1996. The cases were incident cases that were diagnosed in 1980-96 and reported to the Cancer Registry of Norway. Two controls were matched to each case by year of birth, sex, municipality, and first year entering the cohort. Time weighted average exposure to residential magnetic fields generated by the power lines was calculated for the exposure follow up from 1 January 1967 until diagnosis by means of a computer program, in which distance from residency to the line, line configuration, and current load were taken into account. Exposure was analysed using cut off points at 0.05 and 0.2 microtesla ( microT). Exposure to magnetic fields at work was classified by an expert panel who assessed magnetic field exposure by combining branch and occupation into one of three levels: <4 hours, 4-24 hours, and >24 hours per week above background (0.1 micro T). The categories were cumulated over the occupationally active years for the exposure follow up from 1 January 1955 until diagnosis, and cut off points at 18 and 31 category-years were evaluated.

RESULTS

Analysis of the two upper residential magnetic field categories showed an odds ratio of 2.01 (95% CI 1.09 to 3.69) and 2.68 (95% CI 1.43 to 5.04) for women, and an odds ratio of 1.70 (95% CI 0.96 to 3.01) and 1.37 (95% CI 0.77 to 2.44) for men, respectively. Occupational exposure showed no significant association with cutaneous malignant melanoma, and analysis of both residential and occupational exposure simultaneously, showed no additional effect.

CONCLUSION

The present study provides some support for an association between exposure to calculated residential magnetic fields and cutaneous malignant melanoma, but because of the lack of a biological hypothesis and the known strong association between solar radiation and melanoma, no firm conclusions can be drawn and further studies would be of interest.

Brain cancer and occupational exposure to magnetic fields among men: results from a Canadian population-based case-control study

BACKGROUND

The relationship between occupational exposure to magnetic fields and brain cancer in men was investigated using population-based case-control data collected in eight Canadian provinces. Emphasis was placed on examining the variations in risk across different histological types.

METHODS

A list of occupations was compiled for 543 cases and 543 controls that were individually matched by age. Occupations were categorized according to their average magnetic field exposure through blinded expert review (<0.3, 0.3-<0.6, and > or = 0.6 microT). In total, 133 cases (14%) and 123 controls (12%) were estimated to have at least one occupation whereby magnetic field exposures exceeded 0.3 microT. Odds ratios (OR) were generated using conditional logistic regression, and were adjusted for suspected occupational risk factors for brain cancer.

RESULTS

A non-significantly increased risk of brain cancer was observed among men who had ever held a job with an average magnetic field exposure >0.6 microT relative to those with exposures <0.3 microT (OR = 1.33, 95% CI : 0.75-2.36). A more pronounced risk was observed among men diagnosed with glioblastoma multiforme (OR = 5.36, 95% CI : 1.16-24.78). Moreover, a cumulative time weighted index score of magnetic field exposure was significantly related to glioblastoma multiforme (P = 0.02). In contrast, magnetic field exposures were not associated with astrocytoma or other brain cancers.

CONCLUSIONS

Our findings support the hypothesis that occupational magnetic field exposure increases the risk of glioblastoma multiforme.

Long-term exposure of male and female mice to 50 Hz magnetic field: effects on fertility

The effect of an extremely low frequency (ELF) magnetic field on the fertility of adult male and female Swiss mice was investigated. Adult male and female mice were exposed to a 50 Hz sinusoidal magnetic field at approximately 25 microT (rms) for 90 days before they were mated with unexposed counterparts. There were no exposure related effects on the fertility of male or female mice. The number of implantation sites, viable fetuses, and the total number of resorptions were not significantly affected in females impregnated by males exposed to the 50 Hz magnetic field as compared with the control group. The number of implantation sites, viable fetuses and the total number of resorptions in exposed females were also not statistically different from the control group. There were no significant effects on the weights of the testes, seminal vesicles, preputial gland or body weights of males exposed to 50 Hz magnetic field. Furthermore, body and uterine weights were not affected in females exposed to 50 Hz field; however, ovarian weight was significantly increased in females exposed to the same field. These results suggest that exposure of male and female mice to low frequency magnetic field had no adverse effects on fertility and reproduction in mice.

Case-cohort analysis of brain cancer and leukemia in electric utility workers using a refined magnetic field job-exposure matrix

BACKGROUND

The potential association between occupational electric and magnetic field exposure and cancer is well documented in the literature, but there is uncertainty regarding a causal relation.

METHODS

Using data from a completed cohort study, we sought to refine the job-exposure matrix in a case-cohort analysis by regrouping jobs into more homogeneous groups, but without making additional measurements. From the original cohort, we selected the 164 men who died of leukemia, 145 men who died of brain cancer, and a random subcohort of 800 men (0.6% of the cohort). Erroneous job assignments were corrected and job groups were subdivided based on differences in work environments or tasks performed.

RESULTS

Magnetic field exposure remained unrelated to leukemia mortality and positively associated with brain cancer mortality based on both cumulative and average magnetic field indices. Although not monotonic across the middle intervals, increased risk of brain cancer was found in relation to career exposure, with risk ratios of 1.8 (95% CI = 0.7-4.7) and 2.5 (95% CI = 1.0-6.3) in the uppermost categories for cumulative and average exposure, stronger for exposure 2-10 years past.

CONCLUSIONS

Improvements in exposure assignment based only on reassignment of job titles to occupational categories had little impact on the measured associations of magnetic fields with leukemia or brain cancer.

Comparative analyses of the studies of magnetic fields and cancer in electric utility workers: studies from France, Canada, and the United States

OBJECTIVES

To summarise and to facilitate comparison of three major studies of electric utility workers that examined the relation between quantitative measurements of occupational exposure to magnetic fields and risk of brain cancer and leukaemia. These studies have been interpreted as providing conflicting evidence.

METHODS

A common analytical approach was applied to data from the five cohorts included in the three studies based on original data from four of the cohorts, and published data from one additional cohort. A nested case-control design with conditional logistic regression was used to estimate the relative risk/10 microtesla-years (microT-years) for each of the contributing cohorts and for the combined data. The homogeneity of these estimates among the studies was also evaluated.

RESULTS

Apparent inconsistencies in the findings of these studies can be explained by statistical variation. Overall, the studies suggest a small increase in risk of both brain cancer and leukaemia. Different methodological choices had little impact on the results. Based on a combined analysis of data from all five studies, the relative risk/10 microT-years was 1.12 (95% confidence interval (95% CI) 0.98 to 1.28) for brain cancer, and 1.09 (95% CI 0.98 to 1.21) for leukaemia.

CONCLUSIONS

The combined estimates seem to provide the best summary measures of the data from all studies. However, fluctuations in risks among studies may reflect real differences, and the exposure measurements in different studies may not be entirely comparable.

The relationship between electromagnetic field and light exposures to melatonin and breast cancer risk: a review of the relevant literature

Worldwide, breast cancer is the most common malignancy accounting for 20-32% of all female cancers. This review summarizes the peer-reviewed, published data pertinent to the hypothesis that increased breast cancer in industrialized countries is related to the increased use of electricity [Stevens, R.G., S. Davis 1996]. That hypothesis specifically proposes that increased exposure to light at night and electromagnetic fields (EMF) reduce melatonin production. Because some studies have shown that melatonin suppresses mammary tumorigenesis in rats and blocks estrogen-induced proliferation of human breast cancer cells in vitro, it is reasoned that decreased melatonin production leads to increased risk of breast cancer. To evaluate this hypothesis, the paper reviews epidemiological data on associations between electricity and breast cancer, and assesses the data on the effects of EMF exposure on melatonin physiology in both laboratory animals and humans. In addition, the results on the effects of melatonin on in vivo carcinogenesis in animals are detailed along with the controlled in vitro studies on melatonin's effects on human breast cancer cell lines. The literature is evaluated for strength of evidence, inter-relationships between various lines of evidence, and gaps in our knowledge. Based on the published data, it is currently unclear if EMF and electric light exposure are significant risk factors for breast cancer, but further study appears warranted. Given the ubiquitous nature of EMF and artificial light exposure along with the high incidence of breast cancer, even a small risk would have a substantial public health impact.

Occupational electric and magnetic field exposure and leukemia. A meta-analysis

We conducted a meta-analysis to acquire an understanding of the association between leukemia and occupational exposure to electric and magnetic fields. To explore sources of heterogeneity, study characteristics were scored and examined using regression analysis. While most studies present a small elevation in risk, the apparent lack of a clear pattern of exposure to EMF and risk of leukemia substantially detracts from the hypothesis that measured magnetic fields in the work environment are responsible for the observed excess risk of leukemia. Findings were not sensitive to assumptions, influence of individual studies, weighting schemes, and modeling. Some evidence of publication bias is noted.

Occupational exposure to magnetic fields in relation to mortality from brain cancer among electricity generation and transmission workers

OBJECTIVE

To investigate whether the risks of mortality from brain cancer are related to occupational exposure to magnetic fields.

METHODS

A total of 112 cases of primary brain cancer (1972-91) were identified from a cohort of 84,018 male and female employees of the (then) Central Electricity Generating Board and its privatised successor companies. Individual cumulative occupational exposures to magnetic fields were estimated by linking available computerised job history data with magnetic field measurements collected over 675 person-workshifts. Estimated exposure histories of the case workers were compared with those of 654 control workers drawn from the cohort (nested case-control study), by means of conditional logistic regression.

RESULTS

For exposure assessments based on arithmetic means, the risk of mortality from brain cancer for subjects with an estimated cumulative exposure to magnetic fields of 5.4-13.4 microT.y v subjects with lower exposures (0.0-5.3 microT.y) was 1.04 (95% confidence interval (95% CI) 0.60 to 1.80). The corresponding relative risk in subjects with higher exposures (> or = 13.5 microT.y) was 0.95 (95% CI 0.54 to 1.69). There was no indication of a positive trend for cumulative exposure and risk of mortality from brain cancer either when the analysis used exposure assessments based on geometric means or when the analysis was restricted to exposures received within five years of the case diagnosis (or corresponding period for controls).

CONCLUSIONS

Although the exposure categorisation was based solely on recent observations, the study findings do not support the hypothesis that the risk of brain cancer is associated with occupational exposure to magnetic fields.

Magnetic fields of high voltage power lines and risk of cancer in Finnish adults: nationwide cohort study

OBJECTIVE

To investigate the risk of cancer in association with magnetic fields in Finnish adults living close to high voltage power lines.

DESIGN

Nationwide cohort study.

SUBJECTS

383,700 people who lived during 1970-89 within 500 metres of overhead power lines of 110-400 kV in a magnetic field calculated to be > or = 0.01 microT. Study subjects were identified by record linkages of nationwide registers.

MAIN OUTCOME MEASURES

Numbers of observed and expected cases of cancer, standardised incidence ratios, and incidence rate ratios adjusted for sex, age, calendar year, and social class--for example, by continuous cumulative exposure per 1 microT year with 95% confidence intervals from multiplicative models for all cancers combined and 21 selected types.

RESULTS

Altogether 8415 cases of cancer were observed (standardised incidence ratio 0.98; 95% confidence interval 0.96 to 1.00) in adults. All incidence rate ratios for both sexes combined were non-significant and between 0.91 and 1.11. Significant excesses were observed in multiple myeloma in men (incidence rate ratio 1.22) and in colon cancer in women (1.16).

CONCLUSIONS

Typical residential magnetic fields generated by high voltage power lines do not seem to be related to the risk of overall cancer in adults. The previously suggested associations between extremely low frequency magnetic fields and tumours of the nervous system, lymphoma, and leukaemia in adults and breast cancer in women were not confirmed.