Abstract

Background

The effects of magnetic field exposure on cancer risks remains unclear.

Aims

To examine cancer incidence among a cohort of UK electricity generation and transmission workers.

Methods

Cancer morbidity experienced by a cohort of 81 842 employees of the former Central Electricity Generating Board of England and Wales was investigated for the period 1973–2008. All employees had worked for at least 6 months with some employment between 1973 and 1982. Standardized registration ratios (SRRs) were calculated on the basis of national rates.

Results

Overall cancer morbidity was slightly below expectation in males and females. Significant excesses were found in male workers for mesothelioma (Observed [Obs] 504, SRR 331), skin cancer (non-melanoma) (Obs 3187, SRR 107) and prostate cancer (Obs 2684, SRR 107) and in female workers for cancer of the small intestine (Obs 10, SRR 306) and nasal cancer (Obs 9, SRR 474). Brain cancers were close to expectation in males and below expectation in females. Leukaemia incidence (all types) was slightly below expectation in males and females. More detailed analyses showed import ant contrasts for mesothelioma and leukaemia.

Conclusions

The clear occupational excess of mesothelioma was not matched by a corresponding excess of lung cancer, and the level of asbestos-induced lung cancer in this industry must be low. Leukaemia risks declined with period from hire; confident interpretation of this finding is not possible. The excesses of cancers of the nasal cavities and small intestine are probably not occupational, though the excess of skin cancer may be due to outdoor work.

Introduction

A cohort of UK electricity generation and transmission workers was established in the 1980s to investigate whether such workers have elevated mortality; original concerns related to non-malignant respiratory disease. More recently, concerns that electromagnetic field (EMF) exposure may cause leukaemia or brain cancer or have a role in cardiovascular or neurodegenerative diseases have been the focus of many epidemiological studies in this industry [1–8], and a number of reviews are available [9–12]. In recent years, cancer registration (incidence) data have been incorporated into the UK cohort, and an analysis of these data has now been carried out with the aims of providing a more complete assessment of cancer risks in this cohort, identifying any other types of cancer that merit further investigation and increasing the statistical power of any subsequent studies of specific occupational exposures.

Methods

The study population and computerized data have been described previously [5–8,13]. The cohort made available for analysis comprised 83 923 employees (72 889 males and 11 034 females) of the former Central Electricity Generating Board (CEGB) of England and Wales for whom computerized information were available. All employees were known to have a minimum of 6 month employment with some period of employment between 1973 and 1982. The total cohort was subdivided into three categories based on the work location of the first known job: power stations (n = 53 265), substation or transmission sites (n = 3223) and non-operational locations (n = 22 327). These numbers are a little different to those published previously [13], because 158 ‘linesmen’ based at non-operational locations have been re-classified as transmission/substation workers. There were a further 4019 employees for whom no job history was available and 1089 employees whose work history could not be classified.

The study received mortality follow-up particulars from the National Health Service Central Register (NHSCR). For those employees who had moved to Scotland, mortality data were supplied by the General Register Office for Scotland. By the closing date of the study (31 December 2008) 27 788 workers had died, 1102 workers had emigrated, 53 683 workers were traced alive and 1350 workers were untraced. In recent years, permission was obtained to receive cancer registration data. After excluding workers currently residing in Scotland (because Scottish registrations were not available at the time of analysis) and workers untraced at the NHSCR, a total of 81 842 employees were considered for the cancer incidence analysis.

Cancer incidence in the cohort was compared with expected values based on incidence rates for the general population of England and Wales, taking sex, age and calendar period into account; calculations were performed with the Person Years computer program [14]. Study subjects entered the person-years-at-risk (pyr) on completion of 6 month employment or the date of computerization for the region of their employment, whichever was later. Individuals left the pyr on the date of death, date of em barkation, the date they were last confirmed to be alive or the closing date of the study, whichever was the earlier. Study subjects made no contribution to observed or expected numbers after their 85th birthday, in case some subjects in later age groups had been incorrectly traced alive.

Standardized registration ratios (SRRs) were calculated as the ratio of observed to expected numbers of cancer cases expressed as a percentage. In calculating P-values and 95% confidence intervals (95% CIs), cancer was assumed to occur as a Poisson process. Any significance tests were two tailed. This study was established with the approval of the Central Ethical Committee of the British Medical Association, and the author is currently accredited by the Office for National Statistics as the ‘Approved Researcher’ of this cohort study. The study contained no information on ethnic origin, medical histories, smoking histories or other lifestyle factors.

Results

Table 1 shows observed and expected numbers of site-specific cancers for male and female study subjects. Compared with national rates, all cancers combined were slightly below expectation for males (observed [Obs] 13 651, SRR 96) and females (Obs 1452, SRR 98).

Table 1.

Cancer incidence in UK electricity generation and transmission workers, 1973–2008 (71 360 males, 10 482 females)

Site of cancer ICD9 Males Females 
Obs Exp SRR (95% CI) Obs Exp SRR (95% CI) 
Lip 140 24 25.4  95  (61–141) 0.8 – 
Tongue 141 46 73.3  63(***)   (46–84) 4.6 108 (35–253) 
Salivary gland 142 29 29.2  99  (67–143) 2.6 78 (9–280) 
Mouth 143–145 49 82.2  60(***)  (44–79) 5.2 77 (21–196) 
Pharynx 146–149 74 119.2  62(*** (49–78) 5.7 70 (19–179) 
Oesophagus 150 396 454.7  87(** (79–96) 19 23.3 82 (49–128) 
Stomach 151 734 740.0  99  (92–107) 31 30.9 100 (68–143) 
Small intestine 152 42 37.2 113  (81–153) 10 3.3 306** (147–562) 
Large intestine 153 1087 1112.4  98  (92–104) 105 100.8 104 (85–126) 
Rectum 154 798 845.8  94  (88–101) 50 54.1 92 (69–122) 
Liver 155.0, 155.1 112 141.6  79*  (65–95) 8.3 84 (34–174) 
Gallbladder 156 78 61.8 126 (100–158) 10 7.5 134 (64–246) 
Pancreas 157 323 395.3  82(*** (73–91) 40 33.7 119 (85–162) 
Peritoneum 158 17 16.0 106  (62–170) 2.9 103 (21–301) 
Other digestive 159 22 28.4  77  (48–117) 2.4 84 (10–304) 
Nose and sinuses 160 22 28.2  78  (49–118) 1.9 474*** (217–899) 
Larynx 161 146 224.3  65(*** (55–77) 4.9 41 (5–147) 
Lung and bronchus 162 2516 3083.6  82(*** (78–85) 150 159.5 94 (80–110) 
Pleura (mesothelioma)a 163 504 152.4 331*** (303–361) 3.1 96 (20–280) 
Bone 170 20 20.9  96  (58–148) 2.0 152 (31–443) 
Connective tissue 171 76 69.6 109  (86–137) 6.6 76 (25–178) 
Melanoma 172 280 261.9 107  (95–120) 36 44.3 81 (57–113) 
Skin, other 173 3187 2971.1 107*** (104–111) 269 244.1 110 (97–124) 
Breast 174–175 35 30.1 116  (81–162) 535 494.0 108 (99–118) 
Cervix 180 – –   35 53.9 65** (45–90) 
Uterus 182 – –   64 67.4 95 (73–121) 
Ovary 183 – –   78 80.9 96 (76–120) 
Other genital 184, 187 48 48.0 100  (74–133) 15 15.3 98 (55–161) 
Prostate 185 2684 2511.5 107*** (103–111) – –   
Testis 186 82 96.8  85  (67–105) – –   
Bladder 188 961 960.7 100  (94–107) 29 31.3 93 (62–133) 
Bladder (all)b  1258 1273.7  99  (93–104) 43 42.5 101 (73–136) 
Kidney 189.0 337 347.0  97  (87–108) 22 21.1 104 (65–158) 
Other urinary 189.1–189.9 65 62.0 105  (81–134) 3.3 92 (19–269) 
Eye 190 22 26.9  82  (51–124) 2.7 112 (23–326) 
Brain 191–192 264 256.9 103  (91–116) 14 22.1 63 (35–106) 
Brain (all)c  344 340.8 101  (91–112) 27 38.3 71 (47–103) 
Thyroid 193 36 34.2 105  (74–146) 10 10.9 91 (44 –168) 
Other endocrine glands 194 10 11.7  86  (41–158) 1.5 69 (2–384) 
Secondary and other cancers 195–199 612 700.8  87(*** (81–95) 56 65.2 86 (65–112) 
Hodgkin’s disease 201 62 67.4  92  (70–118) 6.5 107 (43–221) 
Non-Hodgkin’s lymphoma 200, 202 465 470.4  99  (90–108) 40 43.5 92 (66–125) 
Multiple myeloma 203 203 199.1 102  (88–117) 12 16.4 73 (38–128) 
Leukaemia 204–208 333 355.4  94  (84–104) 24 26.1 92 (59–137) 
Acute lymphoid leukaemia 204.0 10 13.2  76  (36–139) 1.4 145 (18–524) 
Chronic lymphoid leukaemia 204.1 151 145.1 104  (88–122) 8.4 84 (34–172) 
Acute myeloid leukaemia 205.0 86 106.4  81(* (65–100) 12 9.6 125 (64–218) 
Chronic myeloid leukaemia 205.1 43 39.3 110  (79–148) 3.2 31 (1–174) 
Other leukaemiad  43 51.4  84  (61–113) 3.5 57 (7–206) 
All malignant neoplasms 140–209e 13 651 14 220.7  96(*** (94–98) 1452 1475.2 98 (93–104) 
Site of cancer ICD9 Males Females 
Obs Exp SRR (95% CI) Obs Exp SRR (95% CI) 
Lip 140 24 25.4  95  (61–141) 0.8 – 
Tongue 141 46 73.3  63(***)   (46–84) 4.6 108 (35–253) 
Salivary gland 142 29 29.2  99  (67–143) 2.6 78 (9–280) 
Mouth 143–145 49 82.2  60(***)  (44–79) 5.2 77 (21–196) 
Pharynx 146–149 74 119.2  62(*** (49–78) 5.7 70 (19–179) 
Oesophagus 150 396 454.7  87(** (79–96) 19 23.3 82 (49–128) 
Stomach 151 734 740.0  99  (92–107) 31 30.9 100 (68–143) 
Small intestine 152 42 37.2 113  (81–153) 10 3.3 306** (147–562) 
Large intestine 153 1087 1112.4  98  (92–104) 105 100.8 104 (85–126) 
Rectum 154 798 845.8  94  (88–101) 50 54.1 92 (69–122) 
Liver 155.0, 155.1 112 141.6  79*  (65–95) 8.3 84 (34–174) 
Gallbladder 156 78 61.8 126 (100–158) 10 7.5 134 (64–246) 
Pancreas 157 323 395.3  82(*** (73–91) 40 33.7 119 (85–162) 
Peritoneum 158 17 16.0 106  (62–170) 2.9 103 (21–301) 
Other digestive 159 22 28.4  77  (48–117) 2.4 84 (10–304) 
Nose and sinuses 160 22 28.2  78  (49–118) 1.9 474*** (217–899) 
Larynx 161 146 224.3  65(*** (55–77) 4.9 41 (5–147) 
Lung and bronchus 162 2516 3083.6  82(*** (78–85) 150 159.5 94 (80–110) 
Pleura (mesothelioma)a 163 504 152.4 331*** (303–361) 3.1 96 (20–280) 
Bone 170 20 20.9  96  (58–148) 2.0 152 (31–443) 
Connective tissue 171 76 69.6 109  (86–137) 6.6 76 (25–178) 
Melanoma 172 280 261.9 107  (95–120) 36 44.3 81 (57–113) 
Skin, other 173 3187 2971.1 107*** (104–111) 269 244.1 110 (97–124) 
Breast 174–175 35 30.1 116  (81–162) 535 494.0 108 (99–118) 
Cervix 180 – –   35 53.9 65** (45–90) 
Uterus 182 – –   64 67.4 95 (73–121) 
Ovary 183 – –   78 80.9 96 (76–120) 
Other genital 184, 187 48 48.0 100  (74–133) 15 15.3 98 (55–161) 
Prostate 185 2684 2511.5 107*** (103–111) – –   
Testis 186 82 96.8  85  (67–105) – –   
Bladder 188 961 960.7 100  (94–107) 29 31.3 93 (62–133) 
Bladder (all)b  1258 1273.7  99  (93–104) 43 42.5 101 (73–136) 
Kidney 189.0 337 347.0  97  (87–108) 22 21.1 104 (65–158) 
Other urinary 189.1–189.9 65 62.0 105  (81–134) 3.3 92 (19–269) 
Eye 190 22 26.9  82  (51–124) 2.7 112 (23–326) 
Brain 191–192 264 256.9 103  (91–116) 14 22.1 63 (35–106) 
Brain (all)c  344 340.8 101  (91–112) 27 38.3 71 (47–103) 
Thyroid 193 36 34.2 105  (74–146) 10 10.9 91 (44 –168) 
Other endocrine glands 194 10 11.7  86  (41–158) 1.5 69 (2–384) 
Secondary and other cancers 195–199 612 700.8  87(*** (81–95) 56 65.2 86 (65–112) 
Hodgkin’s disease 201 62 67.4  92  (70–118) 6.5 107 (43–221) 
Non-Hodgkin’s lymphoma 200, 202 465 470.4  99  (90–108) 40 43.5 92 (66–125) 
Multiple myeloma 203 203 199.1 102  (88–117) 12 16.4 73 (38–128) 
Leukaemia 204–208 333 355.4  94  (84–104) 24 26.1 92 (59–137) 
Acute lymphoid leukaemia 204.0 10 13.2  76  (36–139) 1.4 145 (18–524) 
Chronic lymphoid leukaemia 204.1 151 145.1 104  (88–122) 8.4 84 (34–172) 
Acute myeloid leukaemia 205.0 86 106.4  81(* (65–100) 12 9.6 125 (64–218) 
Chronic myeloid leukaemia 205.1 43 39.3 110  (79–148) 3.2 31 (1–174) 
Other leukaemiad  43 51.4  84  (61–113) 3.5 57 (7–206) 
All malignant neoplasms 140–209e 13 651 14 220.7  96(*** (94–98) 1452 1475.2 98 (93–104) 

Obs, observed; Exp, expected; SRR, standardized registration ratios.

aIncludes observed and expected numbers for mesothelioma of other and unspecified sites for deaths in the period 2001–8 (ICD-10 C45).

bMalignant, benign, in situ, and neoplasms of uncertain or unspecified behaviour (ICD-9 188, 223.3, 233.7, 236.7, 239.4).

cMalignant, benign, and neoplasms of uncertain or unspecified behaviour (ICD-9 191, 192, 225, 237.5, 237.6, 239.6).

dRemainder of ICD-9 204–208.

eExcluding ‘skin, other’, ICD-9 173.

*P < 0.05, **P < 0.01, ***P < 0.001, () indicates deficit.

In males, statistically significant deficits were shown for a number of cancers including cancers of the oeso phagus (Obs 396, SRR 87), larynx (Obs 146, SRR 65), lung (Obs 2516, SRR 82) and acute myeloid leukaemia (Obs 86, SRR 81), and significant excesses were shown for cancer of the pleura (mesothelioma) (Obs 504, SRR 331), skin cancer (excluding melanoma) (Obs 3187, SRR 107) and cancer of the prostate (Obs 2684, SRR 107). In females, a statistically significant deficit was shown for cancer of the cervix (Obs 35, SRR 65), and significant excesses were shown for cancer of the small intestine (Obs 10, SRR 306) and nasal cancer (Obs 9, SRR 474). Findings for malignant brain cancer and all brain tumours (malignant and benign) were unexceptional as were findings for all leukaemias combined.

An examination of findings from Table 1 for smoking-related cancers other than lung cancer also indicated important deficits. For those other sites of cancer identified by a recent International Agency For Research On Cancer (IARC) Working Group [15] as capable of being caused by cigarette smoking (oral cavity, pharynx, nasal cavity and paranasal sinuses, larynx, oesophagus, stomach, pancreas, liver, kidney, ureter, urinary bladder, uterine cervix, myeloid leukaemia), the SRR (males and females combined) was significantly below expected (Obs 3585, SRR 91, 95% CI: 88–94). The SRR for all remaining cancer sites (excluding unspecified cancers and skin cancer other than melanoma) was significantly elevated (Obs 8184, SRR 106, 95% CI 104 to 108).

The findings from Table 1 were reviewed and the following topics were selected for further investigation: cancer of the small intestine and nasal cancer in female workers, mesothelioma and prostate cancer in male workers, and skin cancer (excluding melanoma) in the total cohort. To this list was added brain cancer and leukaemia in the total cohort, and breast cancers in male and female workers given that some positive findings have been reported for these cancer sites in workers exposed to magnetic fields [11].

Observed and expected numbers of cancer registrations for cancer of the small intestine in females are shown in Table 2 by year of hire, period from hire, period from leaving employment, industry sector and type of work. There were no significant trends with year of hire, period from hire, or period from leaving employment. There was a significant excess in administrative and clerical workers (Obs 7, SRR 321). There were five adenocarcinomas, two carcinoid tumours and three unspecified carcinomas (data not shown). Carcinoid tumours and adenocarcinomas both appear in the category ‘adenomas and adenocarcinomas’ in the International Classification of Diseases for Oncology (ICD-0 814–838). There were 70% (7/10) of cases in this category compared with an expected percentage of 63% based on the morphology distribution of the 6624 cancers of the small intestine registered in females in England and Wales for the period 1979–2006.

Table 2.

Incidence of cancer of the small intestine and nasal cancer in 10 482 female UK electricity generation and transmission workers, by year of commencing employment, period from hire, period from leaving employment, industry sector and type of work, 1973–2008

 Cancer of small intestine Nasal cancer 
Obs Exp SRR (95% CI) Obs Exp SRR (95% CI) 
Year of hire 
   1926–39    0 0.01     – 0.00 – 
   1940–49    0 0.05     – 0.03 – 
   1950–59    2* 0.23 870 (105–3141) 0.14 714    (18–3980) 
   1960–69    0 0.81     – 0.48 417    (50–1505) 
   1970–82    8* 2.18 367 (158–723) 6** 1.24 484 (178–1053) 
P-value for trend NS NS 
Period from first employment (years)  
   019    3 0.74 405    (84–1185) 0.62 161     (4–899) 
   20–29    3 1.31 229    (47–669) 4* 0.71 563 (154–1442) 
   30–39    4* 0.93 430 (117–1101) 0.44 455    (55–1642) 
   ≥40    0 0.29     – 2* 0.13 1538 (186–5557) 
P-value for trend NS NS 
Period from leaving employment (years) 
   <5    0 0.50     – 0.43 233     (6–1295) 
   5–14    5** 0.93 538 (175–1255) 0.61 328    (40–1184) 
   15–24    4 1.37 292    (80–748) 4** 0.66 606 (165–1552) 
   ≥25    1 0.47 213     (5–1185) 2* 0.20 1000 (121–3612) 
P-value for trend NS NS 
Industry sector 
   Power stations    6* 1.27 472 (173–1028) 4* 0.74 541 (147–1384) 
   Transmission    0 0.06     – 0.03 3333    (84–18 572) 
   Non-operational    4 1.69 237    (64–606) 4* 0.98 408 (111–1045) 
   Unclassifiablea    0 0.05     – 0.03     – 
   No work history    0 0.19     – 0.12     – 
Type of work 
   Managers    0 0.00     – 0.00     –  
   Engineers    1 0.05 2000    (51–11143) 0.03     – 
   Admin, clerical    7* 2.18 321 (129–662) 5* 1.25 400 (130–933) 
   Industrial    2 0.85 235    (28–850) 4** 0.49 816 (222–2090) 
   Building construction    0 0.01     – 0.01     – 
   Not known    0 0.19     – 0.12     – 
Total 10** 3.27 306 (147–562) 9** 1.90 474 (217–899) 
 Cancer of small intestine Nasal cancer 
Obs Exp SRR (95% CI) Obs Exp SRR (95% CI) 
Year of hire 
   1926–39    0 0.01     – 0.00 – 
   1940–49    0 0.05     – 0.03 – 
   1950–59    2* 0.23 870 (105–3141) 0.14 714    (18–3980) 
   1960–69    0 0.81     – 0.48 417    (50–1505) 
   1970–82    8* 2.18 367 (158–723) 6** 1.24 484 (178–1053) 
P-value for trend NS NS 
Period from first employment (years)  
   019    3 0.74 405    (84–1185) 0.62 161     (4–899) 
   20–29    3 1.31 229    (47–669) 4* 0.71 563 (154–1442) 
   30–39    4* 0.93 430 (117–1101) 0.44 455    (55–1642) 
   ≥40    0 0.29     – 2* 0.13 1538 (186–5557) 
P-value for trend NS NS 
Period from leaving employment (years) 
   <5    0 0.50     – 0.43 233     (6–1295) 
   5–14    5** 0.93 538 (175–1255) 0.61 328    (40–1184) 
   15–24    4 1.37 292    (80–748) 4** 0.66 606 (165–1552) 
   ≥25    1 0.47 213     (5–1185) 2* 0.20 1000 (121–3612) 
P-value for trend NS NS 
Industry sector 
   Power stations    6* 1.27 472 (173–1028) 4* 0.74 541 (147–1384) 
   Transmission    0 0.06     – 0.03 3333    (84–18 572) 
   Non-operational    4 1.69 237    (64–606) 4* 0.98 408 (111–1045) 
   Unclassifiablea    0 0.05     – 0.03     – 
   No work history    0 0.19     – 0.12     – 
Type of work 
   Managers    0 0.00     – 0.00     –  
   Engineers    1 0.05 2000    (51–11143) 0.03     – 
   Admin, clerical    7* 2.18 321 (129–662) 5* 1.25 400 (130–933) 
   Industrial    2 0.85 235    (28–850) 4** 0.49 816 (222–2090) 
   Building construction    0 0.01     – 0.01     – 
   Not known    0 0.19     – 0.12     – 
Total 10** 3.27 306 (147–562) 9** 1.90 474 (217–899) 

NS, not significant.

aUnclassifiable work history.

*P < 0.05, **P < 0.01.

Corresponding findings for nasal cancer are also shown in Table 2. There was a highly elevated SRR for female industrial workers (Obs 4, SRR 816). There were two adenoid cystic carcinomas, two squamous cell carcinomas, an amelanotic melanoma, a basal cell adenocarcinoma, a fibrous histiocytoma, a leiomyosarcoma and an unspecified carcinoma (data not shown). Adenoid cystic carcinoma and basal cell adenocarcinoma both appear in the category ‘adenomas and adenocarcinomas’ (ICD-0 814–838). There were 33% (3/9) of cases in this category compared with an expected percentage of 12% based on the morphology distribution of the 4409 nasal cancers registered in females in England and Wales for the period 1979–2006.

Corresponding findings for mesothelioma and prostate cancer in males are shown in Table 3. For mesothelioma, there was a highly significant negative trend with year of hire (P < 0.001) such that SRRs were higher with earlier decades of hire and a highly significant positive trend with period from hire (P < 0.001) such that SRRs were higher with later periods of follow-up. There were markedly elevated SRRs in power station workers (Obs 401, SRR 379) and in workers with no job history (Obs 24, SRR 470). Elevated SRRs were shown for all job types except administration and clerical workers (Obs 6, SRR 67). For prostate cancer, there was a significant positive trend (P < 0.05) with period from hire. Elevated SRRs were found in workers at non-operational sites (Obs 596, SRR 114) and in engineers (Obs 771, SRR 123).

Table 3.

Incidence of mesothelioma and prostate cancer in 71 360 male UK electricity generation and transmission workers, by year of commencing employment, period from hire, period from leaving employment, industry sector and type of work, 1973–2008

 Mesothelioma Prostate cancer 
 Obs Exp SRR (95% CI) Obs Exp SRR (95% CI) 
Year of hire 
   1926–39     6* 2.1 280 (103–610)     49 51.9 94    (70–125) 
   1940–49    74*** 14.1 527 (414–661)    306* 268.7 114 (101–127) 
   1950–59 145*** 30.6 474 (400–558)    578 533.0 108 (100–118) 
   1960–69 205*** 63.1 325 (282–373) 1111* 1034.7 107 (101–114) 
   1970–82    74*** 42.6 174 (137–218)    640 623.3 103    (95–111) 
P-value for trend *** NS 
Period from first employment (years) 
   0–19    29** 14.7 198 (132–284)    151 143.6 105    (89–123) 
   20–29    71*** 38.1 186 (146–235)    533 548.1 97    (89–106) 
   30–39 185*** 50.8 364 (313–420)    940* 869.8 108 (101–115) 
   ≥40 219*** 48.7 449 (392–513) 1060*** 950.0 112 (105–119) 
P-value for trend *** 
Period from leaving employment (years) 
   <5    61*** 22.2 275 (216–350)    179 191.3 94    (81–108) 
   5–14 189*** 56.1 337 (291–389)    970* 903.2 107 (101–114) 
   15–24 207*** 60.4 343 (298–393) 1270** 1169.4 109 (103–115) 
   ≥25    47*** 13.7 344 (253–457)    265 247.6 107    (95–121) 
P-value for trend NS NS 
Industry sector 
   Power stations 401*** 105.9 379 (342–418) 1816* 1731.6 105 (100–110) 
   Transmission    15* 7.8 193 (108–318)    130 126.7 103    (86–122) 
   Non-operational    62*** 32.4 192 (147–246)    596** 523.2 114 (105–123) 
   Unclassifiablea     2 1.2 169    (21–612)     23 20.9 110    (70–165) 
   No work history 24*** 5.1 470 (301–699)    119 109.1 109    (90–131) 
Type of work 
   Managers     9*** 2.0 450 (206–854)     36 37.2 97    (68–134) 
   Engineers 133*** 40.4 329 (276–390)    771*** 628.5 123 (114–132) 
   Administration, clerical     6 8.9 67    (25–146)    166 154.6 107    (92–125) 
   Industrial 318*** 94.0 338 (302–378) 1550 1547.5 100    (95–105) 
   Building, construction.    14*** 1.7 833 (456–1398)     33 29.2 113    (78–159) 
   Not known    24*** 5.4 444 (285–661)    128 114.5 112    (93–133) 
Total 504*** 152.4 331 (303–361) 2684*** 2511.5 107 (103–111) 
 Mesothelioma Prostate cancer 
 Obs Exp SRR (95% CI) Obs Exp SRR (95% CI) 
Year of hire 
   1926–39     6* 2.1 280 (103–610)     49 51.9 94    (70–125) 
   1940–49    74*** 14.1 527 (414–661)    306* 268.7 114 (101–127) 
   1950–59 145*** 30.6 474 (400–558)    578 533.0 108 (100–118) 
   1960–69 205*** 63.1 325 (282–373) 1111* 1034.7 107 (101–114) 
   1970–82    74*** 42.6 174 (137–218)    640 623.3 103    (95–111) 
P-value for trend *** NS 
Period from first employment (years) 
   0–19    29** 14.7 198 (132–284)    151 143.6 105    (89–123) 
   20–29    71*** 38.1 186 (146–235)    533 548.1 97    (89–106) 
   30–39 185*** 50.8 364 (313–420)    940* 869.8 108 (101–115) 
   ≥40 219*** 48.7 449 (392–513) 1060*** 950.0 112 (105–119) 
P-value for trend *** 
Period from leaving employment (years) 
   <5    61*** 22.2 275 (216–350)    179 191.3 94    (81–108) 
   5–14 189*** 56.1 337 (291–389)    970* 903.2 107 (101–114) 
   15–24 207*** 60.4 343 (298–393) 1270** 1169.4 109 (103–115) 
   ≥25    47*** 13.7 344 (253–457)    265 247.6 107    (95–121) 
P-value for trend NS NS 
Industry sector 
   Power stations 401*** 105.9 379 (342–418) 1816* 1731.6 105 (100–110) 
   Transmission    15* 7.8 193 (108–318)    130 126.7 103    (86–122) 
   Non-operational    62*** 32.4 192 (147–246)    596** 523.2 114 (105–123) 
   Unclassifiablea     2 1.2 169    (21–612)     23 20.9 110    (70–165) 
   No work history 24*** 5.1 470 (301–699)    119 109.1 109    (90–131) 
Type of work 
   Managers     9*** 2.0 450 (206–854)     36 37.2 97    (68–134) 
   Engineers 133*** 40.4 329 (276–390)    771*** 628.5 123 (114–132) 
   Administration, clerical     6 8.9 67    (25–146)    166 154.6 107    (92–125) 
   Industrial 318*** 94.0 338 (302–378) 1550 1547.5 100    (95–105) 
   Building, construction.    14*** 1.7 833 (456–1398)     33 29.2 113    (78–159) 
   Not known    24*** 5.4 444 (285–661)    128 114.5 112    (93–133) 
Total 504*** 152.4 331 (303–361) 2684*** 2511.5 107 (103–111) 

NS, not significant.

aUnclassifiable work history.

*P < 0.05, **P < 0.01, ***P < 0.001.

Corresponding findings for breast cancer are shown separately for males and females in Table 4. There were no significant trends with year of hire, period from hire or period from leaving employment. A significantly elevated SRR was found in female workers with no work history (Obs 39, SRR 143), and the elevated SRR in male engineers approached statistical significance (Obs 13, SRR 178).

Table 4.

Incidence of breast cancer in UK electricity generation and transmission workers (71 360 males and 10 482 females), by year of commencing employment, period from hire, period from leaving employment, industry sector, and type of work, 1973–2008

 Males Females 
Obs Exp SRR (95 CI) Obs Exp SRR (95% CI) 
Year of hire 
   1926–39 0.63 – 0.6 – 
   1940–49 3.09 32     (1–180) 5.4 129    (52–266) 
   1950–59 12* 6.10 197 (102–344) 33 25.4 130    (89–182) 
   1960–69 13 12.22 106    (57–182) 116 100.6 115    (95–138) 
   1970–82 8.09 111    (51–211) 379 362.0 105    (94–116) 
P-value for trend NS    NS 
Period from first employment (years) 
   0–19    6 4.72 127    (47–277) 166 153.4 108    (92–126) 
   20–29 11 8.02 137    (68–245) 216 202.6 107    (93–122) 
   30–39    8 9.19 87    (38–172) 126 112.6 112    (93–133) 
   ≥40 10 8.20 122    (58–224) 27 25.4 106    (70–155) 
P-value for trend NS NS 
Period from leaving employment (years) 
   <5    9 7.08 127    (58–242) 113 101.5 111    (93–134) 
   5–14 12 10.79 111    (57–195) 161 153.2 105    (90–123) 
   15–24 11 10.14 108    (54–194) 193 173.6 111    (97–128) 
   ≥25    3 2.12 142    (29–414) 68 65.7 104    (82–131) 
P-value for trend NS NS 
Industry sector 
   Power stations 25 20.84 120    (78–177) 204 186.8 109    (95–125) 
   Transmission    0 1.47 – 9.1 99    (45–188) 
   Non-operational    9 6.20 145    (66–276) 274 263.4 104    (92–117) 
   Unclassifiablea    1 0.25 400    (10–2229) 7.3 123    (56–233) 
   No work history    0 1.37 – 39* 27.3 143 (102–195) 
Type of work 
   Managers    0 0.41 – 0.1 1000    (25–5572) 
   Engineers 13 7.31 178    (95–304) 8.9 90    (39–177) 
   Admin, clerical    2 1.87 107    (13–386) 384 347.7 110 (100–122) 
   Industrial 20 18.76 107    (65–165) 102 109.0 94    (76–114) 
   Building, construction    0 0.35 – 1.0 102     (3–569) 
   Not known    0 1.43 – 39* 27.4 142 (101–195) 
Total 35 30.13 116    (81–162) 535 494.0 108    (99–118) 
 Males Females 
Obs Exp SRR (95 CI) Obs Exp SRR (95% CI) 
Year of hire 
   1926–39 0.63 – 0.6 – 
   1940–49 3.09 32     (1–180) 5.4 129    (52–266) 
   1950–59 12* 6.10 197 (102–344) 33 25.4 130    (89–182) 
   1960–69 13 12.22 106    (57–182) 116 100.6 115    (95–138) 
   1970–82 8.09 111    (51–211) 379 362.0 105    (94–116) 
P-value for trend NS    NS 
Period from first employment (years) 
   0–19    6 4.72 127    (47–277) 166 153.4 108    (92–126) 
   20–29 11 8.02 137    (68–245) 216 202.6 107    (93–122) 
   30–39    8 9.19 87    (38–172) 126 112.6 112    (93–133) 
   ≥40 10 8.20 122    (58–224) 27 25.4 106    (70–155) 
P-value for trend NS NS 
Period from leaving employment (years) 
   <5    9 7.08 127    (58–242) 113 101.5 111    (93–134) 
   5–14 12 10.79 111    (57–195) 161 153.2 105    (90–123) 
   15–24 11 10.14 108    (54–194) 193 173.6 111    (97–128) 
   ≥25    3 2.12 142    (29–414) 68 65.7 104    (82–131) 
P-value for trend NS NS 
Industry sector 
   Power stations 25 20.84 120    (78–177) 204 186.8 109    (95–125) 
   Transmission    0 1.47 – 9.1 99    (45–188) 
   Non-operational    9 6.20 145    (66–276) 274 263.4 104    (92–117) 
   Unclassifiablea    1 0.25 400    (10–2229) 7.3 123    (56–233) 
   No work history    0 1.37 – 39* 27.3 143 (102–195) 
Type of work 
   Managers    0 0.41 – 0.1 1000    (25–5572) 
   Engineers 13 7.31 178    (95–304) 8.9 90    (39–177) 
   Admin, clerical    2 1.87 107    (13–386) 384 347.7 110 (100–122) 
   Industrial 20 18.76 107    (65–165) 102 109.0 94    (76–114) 
   Building, construction    0 0.35 – 1.0 102     (3–569) 
   Not known    0 1.43 – 39* 27.4 142 (101–195) 
Total 35 30.13 116    (81–162) 535 494.0 108    (99–118) 

aUnclassifiable work history.

*P < 0.05.

Corresponding findings for skin cancer (excluding melanoma) and malignant brain tumours in males and females combined are shown in Table 5. For skin cancer, significant positive trends were shown with period from hire (P < 0.01) and period from leaving employment (P < 0.001). An elevated SRR was found in transmission workers (Obs 189, SRR 125). For malignant brain neoplasms, there were no significant trends with year of hire, period from hire, or period from leaving employment. Somewhat elevated SRRs were found in managers (Obs 5, SRR 179) and engineers (Obs 79, SRR 120).

Table 5.

Incidence of skin cancer (non-melanoma) and malignant brain tumours in UK electricity generation and transmission workers (71 360 males, 10 482 females), by year of commencing employment, period from hire, period from leaving employment, industry sector, and type of work, 1973–2008

 Skin cancer (non-melanoma) Malignant brain tumours 
 Obs Exp SRR (95% CI) Obs Exp SRR (95% CI) 
Year of hire         
   1926–39     64 56.0 114    (89–416) 3.6 139 (45–325) 
   1940–49    319 305.5 104    (94–117) 22 20.9 105 (66–159) 
   1950–59    674* 619.2 109 (101–117) 59 46.8 126 (98–163) 
   1960–69 1365** 1259.1 108 (103–114) 98 106.0 92 (76–113) 
   1970–82 1034 975.5 106 (100–113) 94 101.8 92 (75–113) 
P-value for trend NS NS 
Period from first employment (years) 
   0–19    351 376.0 93    (84–104) 70 69.4 101 (79–127) 
   20–29    911** 830.3 110 (103–117) 69 84.6 82 (63–103) 
   30–39 1039 1025.5 101    (95–108) 82 75.0 109 (87–136) 
   ≥40 1155*** 983.5 117 (111–124) 57 50.1 114 (86–147) 
P-value for trend ** NS 
Period from leaving employment (years) 
   <5    457 510.4 90    (82–98) 84 90.9 92 (75–114) 
   5–14 1153 1090.4 106 (100–112) 116 99.8 116 (97–139) 
   15–24 1468*** 1300.1 113 (107–119) 64 72.9 88 (69–112) 
   ≥25    378*** 314.3 120 (109–133) 14 15.4 91 (50–153) 
P-value for trend *** NS       
Industry sector         
   Power stations 2309*** 2146.3 108 (103–112) 183 186.4 98 (85–113) 
   Transmission    189** 151.8 125 (108–144) 10 12.8 78 (38–144) 
   Non-operational    812* 751.8 108 (101–116) 73 66.7 109 (87–138) 
   Unclassifiablea     30 28.9 104    (70–148) 2.6 154 (42–392) 
   No work history    116 136.4 85    (71–102) 10.6 75 (33–149) 
Type of work         
   Managers     35 41.5 85    (61–119) 2.8 179 (58–418) 
   Engineers    862*** 747.7 115 (108–123) 79 65.7 120 (96–150) 
   Admin, clerical    384* 347.4 111 (100–122) 30 31.1 96 (65–138) 
   Industrial 2018** 1902.0 106 (102–111) 155 165.7 94 (80–109) 
   Building construction     37 34.2 108    (78–149) 2.8 36    (1–199) 
   Not known    120 142.5 84    (70–101) 11.0 73 (31–144) 
Total 3456*** 3215.2 107 (104–111) 278 279.0 100 (88–112) 
 Skin cancer (non-melanoma) Malignant brain tumours 
 Obs Exp SRR (95% CI) Obs Exp SRR (95% CI) 
Year of hire         
   1926–39     64 56.0 114    (89–416) 3.6 139 (45–325) 
   1940–49    319 305.5 104    (94–117) 22 20.9 105 (66–159) 
   1950–59    674* 619.2 109 (101–117) 59 46.8 126 (98–163) 
   1960–69 1365** 1259.1 108 (103–114) 98 106.0 92 (76–113) 
   1970–82 1034 975.5 106 (100–113) 94 101.8 92 (75–113) 
P-value for trend NS NS 
Period from first employment (years) 
   0–19    351 376.0 93    (84–104) 70 69.4 101 (79–127) 
   20–29    911** 830.3 110 (103–117) 69 84.6 82 (63–103) 
   30–39 1039 1025.5 101    (95–108) 82 75.0 109 (87–136) 
   ≥40 1155*** 983.5 117 (111–124) 57 50.1 114 (86–147) 
P-value for trend ** NS 
Period from leaving employment (years) 
   <5    457 510.4 90    (82–98) 84 90.9 92 (75–114) 
   5–14 1153 1090.4 106 (100–112) 116 99.8 116 (97–139) 
   15–24 1468*** 1300.1 113 (107–119) 64 72.9 88 (69–112) 
   ≥25    378*** 314.3 120 (109–133) 14 15.4 91 (50–153) 
P-value for trend *** NS       
Industry sector         
   Power stations 2309*** 2146.3 108 (103–112) 183 186.4 98 (85–113) 
   Transmission    189** 151.8 125 (108–144) 10 12.8 78 (38–144) 
   Non-operational    812* 751.8 108 (101–116) 73 66.7 109 (87–138) 
   Unclassifiablea     30 28.9 104    (70–148) 2.6 154 (42–392) 
   No work history    116 136.4 85    (71–102) 10.6 75 (33–149) 
Type of work         
   Managers     35 41.5 85    (61–119) 2.8 179 (58–418) 
   Engineers    862*** 747.7 115 (108–123) 79 65.7 120 (96–150) 
   Admin, clerical    384* 347.4 111 (100–122) 30 31.1 96 (65–138) 
   Industrial 2018** 1902.0 106 (102–111) 155 165.7 94 (80–109) 
   Building construction     37 34.2 108    (78–149) 2.8 36    (1–199) 
   Not known    120 142.5 84    (70–101) 11.0 73 (31–144) 
Total 3456*** 3215.2 107 (104–111) 278 279.0 100 (88–112) 

NS, not significant.

aUnclassifiable work history.

*P < 0.05, **P < 0.01, ***P < 0.001.

Corresponding findings for leukaemia are shown for males and females combined in Table 6. There was a significant positive trend (P < 0.05) with year of hire, and a significant negative trend (P < 0.01) with period from hire. The negative trend with period from leaving employment was not significant. The main leukaemia sub-types showed similar patterns of SRRs by period from hire and by period from leaving employment (data not shown).

Table 6.

Incidence of leukaemia in UK electricity generation and transmission workers (71 360 males and 10 482 females), by year of commencing employment, period from hire, period from leaving employment, industry sector and type of work, 1973–2008

 Obs Exp SRR (95% CI) 
Year of hire 
   1926–39 7.4 68 (22–158) 
   1940–49 29 36.6 79 (53–114) 
   1950–59 63 72.8 87 (68–111) 
   1960–69 134 148.1 90 (76–107) 
   1970–82 126 116.6 108 (91–129) 
P-value for trend 
Period from first employment (years)  
   0–19 82* 62.3 132 (105–163) 
   20–29 85 103.0 83 (66–102) 
   30–39 110 114.5 96 (79–116) 
   ≥40 80* 101.8 79 (62–98) 
P-value for trend ** 
Period from leaving employment (years) 
   <5 84 80.6 104 (84–129) 
   5–14 137 138.2 99 (83–117) 
   15–24 117 135.3 86 (72–104) 
   ≥25 19 27.4 69 (42–108) 
P-value for trend NS 
Industry sector 
   Power stations 239 254.9 94 (83–106) 
   Transmission 15 17.7 85 (47–140) 
   Non-operational 80 87.8 91 (73–113) 
   Unclassifiablea 3.6 56 (7–201) 
   No work history 21 17.6 119 (74–182) 
Type of work 
   Managers 4.8 62 (13–183) 
   Engineers 62(*) 86.5 72 (56–92) 
   Administration, clerical 37 39.9 93 (67–128) 
   Industrial 229 228.0 100 (88–114) 
   Building, construction. 4.1 122 (40–285) 
   Not known 21 18.3 115 (71–175) 
Total 357 381.5 94 (84–104) 
 Obs Exp SRR (95% CI) 
Year of hire 
   1926–39 7.4 68 (22–158) 
   1940–49 29 36.6 79 (53–114) 
   1950–59 63 72.8 87 (68–111) 
   1960–69 134 148.1 90 (76–107) 
   1970–82 126 116.6 108 (91–129) 
P-value for trend 
Period from first employment (years)  
   0–19 82* 62.3 132 (105–163) 
   20–29 85 103.0 83 (66–102) 
   30–39 110 114.5 96 (79–116) 
   ≥40 80* 101.8 79 (62–98) 
P-value for trend ** 
Period from leaving employment (years) 
   <5 84 80.6 104 (84–129) 
   5–14 137 138.2 99 (83–117) 
   15–24 117 135.3 86 (72–104) 
   ≥25 19 27.4 69 (42–108) 
P-value for trend NS 
Industry sector 
   Power stations 239 254.9 94 (83–106) 
   Transmission 15 17.7 85 (47–140) 
   Non-operational 80 87.8 91 (73–113) 
   Unclassifiablea 3.6 56 (7–201) 
   No work history 21 17.6 119 (74–182) 
Type of work 
   Managers 4.8 62 (13–183) 
   Engineers 62(*) 86.5 72 (56–92) 
   Administration, clerical 37 39.9 93 (67–128) 
   Industrial 229 228.0 100 (88–114) 
   Building, construction. 4.1 122 (40–285) 
   Not known 21 18.3 115 (71–175) 
Total 357 381.5 94 (84–104) 

NS, not significant.

aUnclassifiable work history.

*P < 0.05, **P < 0.01;() indicates deficit.

Discussion

The important overall findings of this study were an excess of mesothelioma with no matching excess of lung cancer and unexceptional findings for leukaemia and brain tumours. The strengths of the study were its size and length of follow-up, leading to an unusually large number of cancer cases, even for rare sites of cancer. The key study limitation was that first known job has been used to categorise individuals by industry sector and type of work, and 55% of the cohort had some employment within the industry before personnel records were computerized with a resultant misclassification in the sub-group analyses.

The incidence of all cancers combined was a little below expected, and morbidity from lung cancer was markedly below expectation. The findings for other smoking-related cancers were consistent with the hypothesis that this skilled workforce had below average smoking habits. Direct evidence of a low prevalence of smoking in this industry was sought from records of annual company medicals. One of the CEGB successor companies had computerized data for 2724 male and 284 female employees with at least one medical in the period 1990–2004; some 90% of employees accepted the offer of a medical. Based on data from the first medical, 19% of the male employees and 21% of the female employees were current smokers (cigarettes, pipe or cigars). Expected percentages were 34 and 26%, respect ively, based on national data from the General Lifestyle Surveys, taking calendar year into account. Only some of these employees with medicals would have been in the study cohort. Nevertheless, these data suggest that employees in this industry had a lower proportion of smokers than the general population. The cohort may also have had other lifestyle influences associated with higher socio-economic status and lower cancer risk.

The ‘Helsinki report’ states that ‘currently about 10,000 mesotheliomas and 20,000 asbestos-induced lung cancers are estimated to occur annually’ in the populations of Western Europe, North America, Japan and Australia [16]. Ignoring the totals, the Helsinki experts consider that there will be two lung cancers for every mesothelioma caused by asbestos, and a 2005 review of 31 cohort studies of male asbestos workers reached the same conclusion [17]; the ratio of 2:1 for excess lung cancers/mesotheliomas is a reasonable overall figure, certainly for high exposure studies. However, an earlier review noted that five cohort studies have ‘produced mesothelioma in conditions where no excess lung cancer was seen’ [18]. To this list could be added two cohort studies of petroleum industry workers [19,20]. It would seem that the 2:1 ratio is not universally applicable and certainly not to UK electricity supply industry workers. The numbers in this study are so large that the absence of a lung cancer excess cannot be a chance finding; the low prevalence of smoking in the cohort would explain, at least to some extent, such an absence.

Mesothelioma was significantly elevated in all industry sectors and in all types of work except administration and clerical work, and there is still no sign of the effects of the asbestos risk having played itself out. Hodgson et al. [21] have estimated that such an effect will not start, nationally, until 2011–15 or thereabouts. It is suspected that the excess mesotheliomas in workers at non-operational sites is a consequence of occasional or earlier periods of working at power stations where asbestos was used to lag pipes and boilers [13].

The excess of cancer of the small intestine in female employees with no comparable excess in male employees suggests that occupational exposures are not important in the female excess, as it is difficult to imagine exposures that would be received by female workers only. There were no important contrasts in the more detailed analyses that were carried out for this excess. Some chance excesses are to be expected, possibly this is one.

The excess of nasal cancer was most unexpected, particularly as it was present for female employees only. Nasal cancer, particularly adenocarcinoma, is known to be associated with some occupational exposures including hard wood dust, leather dust and hexavalent chromium exposure [22]. Exposures to leather dust and hexavalent chromium are not present in the industry under study here, although there are carpentry shops in power stations. However, none of the female cases ever worked in such shops and bystander exposure to hard wood dust seems an unlikely explanation for the female excess when there was no corresponding excess in male workers. There were no important contrasts in the more detailed analyses that were carried out for this excess, and it seems highly unlikely that the whole of the excess is due to occupational exposures in this industry, given the variety of histologies for the nine cases. It remains possible that some of the nasal cancers in females are occupational in origin and for unknown reasons.

Exposure to sunlight is an accepted risk factor for skin cancer (non-melanoma), and one could easily attribute the higher risk in transmission workers to outdoor working. Unfortunately, individual data on occupational and non-occupational sun exposure are not available for study.

Several studies of workers potentially exposed to electromagnetic fields have reported increased risks of male breast cancer [23–26], although three cohort studies of electric utility workers reported no overall excess for this disease [2–4]. There were no important contrasts in the more detailed analyses that were carried out for male breast cancer in this study, and it seems unwise to attach too much importance to the non-significant excess shown.

A possible relationship between occupational EMF exposure and risks of brain cancer has been investigated in many studies, although a causal relationship has not been established. There were no important contrasts in the more detailed analyses that were carried out for brain cancer in this cohort.

A possible relationship between occupational EMF exposure and risks of leukaemia has also been investigated in many studies without a causal relationship being established. In this study, leukaemia risks declined with period from hire, and it is unclear, at this stage, as to how such an observation is consistent with occupational causation.

The overall elevated incidence found for mesothelioma (close to 4% of all cancers in male employees) almost certainly reflects the late health effects of earlier incidental asbestos exposure received in this industry.

Key points
  • The workforce has suffered an occupational excess of mesothelioma without any matching excess of lung cancer.

  • Overall, this workforce had unexceptional findings for leukaemia and brain tumours but outdoor working may have been a factor in the excess of skin cancer (non-melanoma).

  • Novel excesses in females for nasal cancer and cancer of the small intestine were not matched by similar findings in males.

Acknowledgements

I thank the Information Centre for Health and Social Care and its forerunners for supplying follow-up details, and the pensions and human resources departments of the participating companies for solving data queries. Constructive criticisms of an earlier draft of this paper were received from members of the Mortality Study Steering Group; responsibility for the final version remains with the author.

Funding

Research award from companies in the electricity industry, administered by the Energy Networks Association.

Conflicts of interest

The author’s university salary is defrayed by a research award from the Energy Networks Association (ENA).

References

1.
Thériault
G
Goldberg
M
Miller
AB
et al
Cancer risks associated with occupational exposure to magnetic fields among electrical utility workers in Ontario and Quebec, Canada and France: 1970–1989
Am J Epidemiol
 
1994
139
550
––
572
2.
Savitz
DA
Loomis
DP
Magnetic field exposure in relation to leukaemia and brain cancer mortality among electric utility workers
Am J Epidemiol
 
1994
141
123
––
134
3.
Kelsh
MA
Sahl
JD
Mortality among a cohort of electric utility workers, 1960–1991
Am J Ind Med
 
1997
31
534
––
544
4.
Johansen
C
Olsen
JH
Risk of cancer among Danish utility workers – a nationwide cohort study
Am J Epidemiol
 
1998
147
548
––
555
5.
Harrington
JM
Nichols
L
Sorahan
T
van Tongeren
M
Leukaemia mortality in relation to magnetic field exposure: findings from a study of United Kingdom electricity generation and transmission workers, 1973–97
Occup Environ Med
 
2001
58
307
––
314
6.
Sorahan
T
Nichols
L
van Tongeren
M
Harrington
JM
Occupational exposure to magnetic fields relative to mortality from brain tumours: updated and revised findings from a study of United Kingdom electricity generation and transmission workers, 1973–97
Occup Environ Med
 
2001
58
626
––
630
7.
Sorahan
T
Nichols
L
Mortality from cardiovascular disease in relation to magnetic field exposure: findings from a study of UK electricity generation and transmission workers, 1973–1997
Am J Ind Med
 
2004
45
93
––
102
8.
Sorahan
T
Kheifets
L
Mortality from Alzheimer’s motor neuron and Parkinson’s disease in relation to magnetic field exposure: findings from the study of UK electricity generation and transmission workers, 1973–2004
Occup Environ Med
 
2007
64
820
––
826
9.
Santibanez
M
Bolumar
F
Garcia
AM
Occupational risk factors in Alzheimer’s disease: a review assessing the quality of published epidemiological studies
Occup Environ Med
 
2007
64
723
––
732
10.
National Radiological Protection Board
ELF Electromagnetic Fields and the Risk of Cancer: Report of an Advisory Group on Non-ionising Radiation
 
Chilton, Oxfordshire
NRPB
2001
11.
International Agency for Research on Cancer
IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Non-ionising Radiation. Part 1: Static and Extremely Low Frequency (ELF) Electric and Magnetic Fields
 
Vol. 80
Lyon
IARC Press
2002
12.
Kheifets
L
Bowman
JD
Checkoway
H
et al
Future needs of occupational epidemiology of extremely low frequency electric and magnetic fields: review and recommendations
Occup Environ Med
 
2009
66
72
––
80
13.
Nichols
L
Sorahan
T
Mortality of UK electricity generation and transmission workers
Occup Med (Lond)
 
2005
55
541
––
548
14.
Coleman
M
Douglas
A
Hermon
C
Peto
J
Cohort study analysis with a Fortran computer program
Int J Epidemiol
 
1986
15
134
––
137
15.
International Agency for Research on Cancer
IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Tobacco Smoke and Involuntary Smoking
 
Vol. 83
Lyon
IARC Press
2004
16.
Consensus Report
Asbestos, asbestosis, and cancer: the Helsinki criteria for diagnosis and attribution
Scand J Work Environ Health
 
1997
23:
311
––
316
17.
Hessel
PA
Gamble
JF
McDonald
JC
Asbestos, asbestosis, and lung cancer: a critical assessment of the epidemiological evidence
Thorax
 
2005
60
433
––
436
18.
Hodgson
JT
Darnton
A
The quantitative risks of mesothelioma and lung cancer in relation to asbestos exposure
Ann Occup Hyg
 
2000
44
565
––
601
19.
Gun
RT
Pratt
NL
Griffith
EC
Adams
GG
Bisby
JA
Robinson
KL
Update of a prospective study of mortality and cancer incidence in the Australian petroleum industry
Occup Environ Med
 
2004
61:
150
––
156
20.
Sorahan
T
Nichols
L
Harrington
JM
Mortality of United Kingdom oil refinery and petroleum distribution workers, 1951–1998
Occup Med (Lond)
 
2002
52
333
––
339
21.
Hodgson
JT
McElvenny
DM
Darnton
AJ
Price
MJ
Peto
J
The expected burden of mesothelioma mortality in Great Britain from 2002 to 2050
Br J Cancer
 
2005
92
587
––
593
22.
International Agency for Research on Cancer
IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. A Review of Human Carcinogens: Arsenic, Metals, Fibres, and Dusts
 
Vol. 100C
Lyon
IARC Press
2011
23.
Tynes
T
Andersen
A
Langmark
F
Incidence of cancer in Norwegian workers potentially exposed to electromagnetic fields
Am J Epidemiol
 
1992
136:
81
––
88
24.
Demers
PA
Thomas
DB
Rosenblatt
KA
et al
Occupational exposure to electromagnetic fields and breast cancer in men
Am J Epidemiol
 
1991
134
340
––
347
25.
Matanoski
GM
Breysse
PN
Elliott
EA
Electromagnetic field exposure and male breast cancer
Lancet
 
1991
337
737
26.
Pollán
M
Gustavsson
P
Floderus
B
Breast cancer, occupation and exposure to electromagnetic fields among Swedish men
Am J Ind Med
 
2001
39
276
––
285