Nordic experience: expected decline in the incidence of mesotheliomas resulting from ceased exposure?

BACKGROUND: As a result mainly of information to workers and the public on prevention of effects of asbestos exposure, the use of asbestos for insulation was reduced to a minimum in the Nordic countries during the second half of the 1970's and the early 1980's. Stringent regulations when handling asbestos were introduced, and prohibition of use began in the early 1980's. Depending on the duration of the latency period between first exposure and the period of most intense exposure, a decline might be expected in the incidence of Malignant Mesothelioma (MM) 20-45 years after interruption of exposure. OBJECTIVES: to describe the incidence of MM after cessation of asbestos exposure in Nordic countries. METHODS: Nordic countries have cancer registers with information on all new cases of all cancers, over the past 4-6 decades. Cancer incidence data in these registers could describe long-term effects of interruption of asbestos exposure. RESULTS: Current male and female incidence in Norway is about 1.5 x 10(-5)/year and 0.2 x 10(-5)/year respectively, and appears to be increasing. Based on personal observations among 32 MM cases, a number of which resulting from low total asbestos exposure with mean latency of about 45 years, examples are presented of the MM incidence in Nordic countries, illustrating when a significant decline in MM incidence may be expected. CONCLUSIONS: 25 years after interruption of asbestos exposure, the expected rapid decline in MM incidence is still lacking, which appears to agree with population-based selection phenomena, with survival of a large pool of asbestos-exposed subjects with minimal exposure.

Risk of fatal industrial accidents and death from other external causes among asphalt workers.

The hypothesis that asphalt workers are at increased risk of mortality from industrial accidents and other external causes was tested. Mortality rates for external and violent causes of death in a cohort of asphalt industry employees from seven European countries and Israel were compared to that of the general population. There was no evidence that mortality from external causes was increased among long term employees in asphalt application and mixing. There was an increased risk for mortality due to external causes among short term workers. However, none of the fatal accidents among short term workers appear to have occurred during employment in the studied asphalt companies. Overall, no evidence was found supporting the hypothesis that asphalt workers are at increased risk of fatal industrial or road accidents. Mortality from other external causes did not increase in this population as a whole, but increased risks among short term workers deserve further attention.

Update of the follow-up of mortality and cancer incidence among European workers employed in the vinyl chloride industry.

Although vinyl chloride is an established cause of liver angiosarcoma, the evidence is inconclusive on whether it also causes other neoplastic and nonneoplastic chronic liver diseases as well as neoplasms in other organs. Furthermore, the shape of the dose-response relation for angiosarcoma is uncertain. We have extended for approximately 8 years the mortality and cancer incidence follow-up of 12,700 male workers in the vinyl chloride industry in four European countries. All-cause mortality was lower than expected, whereas cancer mortality was close to expected. A total of 53 deaths from primary liver cancer (standardized mortality ratio 2.40, 95% confidence interval = 1.80-3.14) and 18 incident cases of liver cancer were identified, including 37 angiosarcomas, 10 hepatocellular carcinomas, and 24 liver cancers of other and unknown histology. In Poisson regression analyses we observed a marked exposure response for all liver cancers, angiosarcoma, and hepatocellular carcinoma. The exposure-response trend estimated for liver cancer in analyses restricted to cohort members with cumulative exposures of <1,500 parts per million-years was close to that estimated for the full cohort (relative risk of 2.0 per logarithmic unit of cumulative dose). No strong relation was observed between cumulative vinyl chloride exposure and other cancers. Although cirrhosis mortality was decreased overall, there was a trend with cumulative exposure.

Incidence of cancer among workers exposed to vinyl chloride in polyvinyl chloride manufacture.

Based on results from two previous studies where an excess of melanomas was found in a cohort of workers exposed to vinyl chloride (VCM), a follow up of the incidence of cancer in the same cohort of 428 workers was carried out to scrutinize whether or not the excess could be confirmed by new cases. The total number of deaths in the study group from 1953 to the end of 1993 was 132 v 141 expected, and the total number of incident cancer cases was 56 v 57 expected. There were 11 cases of lung cancer v eight expected, seven cases of melanomas v 2.07 expected, and two cases of thyroid cancer v 0.34 expected. Five of the seven melanoma cases had occurred in the group that had been most heavily exposed to VCM v 0.7 expected. In the present follow up we also found five cases of the spinocellular cancer of the skin v 1.7 expected. Out of these five cases four were diagnosed after 1984. Two of the five cases v 0.7 expected had occurred in the most heavily exposed group. The total number of skin cancers (melanomas and spinocellular cancers) were 12 v 3.7 expected. There was one new case of melanoma between 1985 and 1993 v 0.7 expected. Hence, the strength of the relation between the observed and expected number of cases was reduced compared with the last follow up, and does not strengthen the previously indicated causal relation between exposure to VCM and development of malignant melanoma. There was no excess of testicular cancers in this study. The present results may indicate that occurrence of spinocellular skin cancer could bear some relation to work in the manufacture of polyvinyl chloride (PVC). Confirmation is needed from studies on other cohorts exposed to VCM.

Incidence of cancer among welders and other shipyard workers with information on previous work history.

The incidence of cancer among 4480 shipyard workers, including 861 welders, was investigated for a potential relationship between exposure to welding fumes and lung cancer. A subcohort of 3150 workers with information on previous work history was studied separately. This investigation is a historical prospective cohort study. Environmental air samples were collected in 1973, 1977, and 1989. Information on smoking habits was surveyed in 1976 and 1984. The employment work histories were collected from the personnel register. There were 411 observed cancers of all sites versus 387.5 expected, and 45 cases of lung cancer versus 51.3 expected. Nine cases of lung cancer were found among the welders versus 7.1 expected. Among 310 former seamen with welding experience, there was 1 case of lung cancer versus 2.1 expected. These shipyard workers showed no excess risk of lung cancer. Tobacco smoking and asbestos exposure are potential confounders in the study. There was no clear relationship between exposure to welding fumes and lung cancer, but welders with the longest experience had a relative risk of 1.9 for lung cancer. The differences in lung cancer incidence among the different shipyard workers could not be attributed to differences in recruitment patterns or previous work history.

A Neuropsychological Study of Patients Exposed to Organic Solvents.

Sixty-seven male patients exposed to organic solvents were neurospychologically examined. Twenty-five subjects had possible causes of encephalopathy other than solvent exposure, leaving 42 patients for the study of the association between exposure and neuropsychological test results. The patients had been heavily exposed for, on average, 24.6 years (range 2-46). The main clinical findings were impairments of psychomotor function, short-term memory, and attention. The results suggest an association between impaired psychomotor speed and exposure duration (r = 0.41; p = 0.007), with moderate to severe impairment occurring after at least 15 years. Forty percent of the patients exposed for more than 30 years had moderate to severely impaired psychomotor speed. The results suggest declining test performance on Trail Making Test B related to exposure duration (r = -0.34; p = 0.03). Further, the individual age-adjusted score on the Digit Span task (WAIS) was reduced when compared with the individual age-adjusted score on the Picture Completion task (WAIS). This reduction was related to exposure duration (r = -0.48; p = 0.002).

Fatal accident resulting from methyl bromide poisoning after fumigation of a neighbouring house; leakage through sewage pipes.

An intoxication after using methyl bromide (CH3Br) in fumigation is reported. The accident resulted in the death of a newborn infant within 12-13 h after exposure, as well as clinical intoxication of the infant's parents. The concentration of bromide ion in the infant's blood was 170 mg l-1 and in the parents blood it was 130 and 110 mg l-1. Autopsy showed that the cause of death was acute pneumonia due to aspiration, most likely resulting from vomiting and aspiration after inhalation of CH3Br. The clinical symptoms of the parents are reported, as well as a brief survey on the kinetics and CH3Br toxicity in animals and humans. Reconstruction of the events prior to the intoxication revealed that the sewage pipes serving the two houses had been sucked empty only 1-2 h prior to the start of fumigation, resulting in an open sewage connection between the houses and permitting CH3Br to leak from the treated house into the house of the affected family.

Incidence of cancer among Norwegian boiler welders.

OBJECTIVES: The cancer incidence among 2957 boiler welders was investigated. The subjects were registered electrical welders from 1942 to 1981. A subcohort of 606 stainless steel welders was studied separately. METHODS: The investigation was a historical prospective cohort study based on a national registry. The loss of follow up was 4.9%. RESULTS: There were 625 deaths (659 expected). There were 269 cancer cases (264 expected). An excess of lung cancer was found; 50 cases v 37.5 expected. There were three cases of pleural mesotheliomas v 1.1 expected. The subcohort of stainless steel welders had six cases of lung cancer v 5.8 expected, and one case of pleural mesothelioma v 0.2 expected. CONCLUSIONS: The welders in the study were assumed to represent a qualified work force. These welders had a small excess risk of lung cancer. The excess risk did not seem to be associated with stainless steel welding. Smoking and asbestos exposure were potential confounders.

Cancer risk for European asphalt workers.

OBJECTIVES: The feasibility of a European epidemiologic study of cancer risk among asphalt workers was examined in Western Europe. The study was motivated by occupational and public health concern about possible health risk from exposure to bitumen fumes. METHODS: Information on the accessibility and quality of epidemiologic resources, retrospective worker records, mortality and cancer incidence records, and exposures was requested from research institutes and road paving and asphalt mixing companies in 15 European countries. RESULTS: Research institutes and asphalt companies in 12 countries responded. It was found that at least 44 companies in seven countries can be included in a retrospective mortality study of a minimum of 32,000 employees with 356,000 person-years (over 100 lung cancers). Coal tar will be an important confounder for these data. The power of a cohort study of workers who have never worked with tar-containing materials remains insufficient. Even in an ambispective study extending to the year 2005, the expected lung cancer deaths in a tar-free cohort would be only four. CONCLUSIONS: The results suggest that a case-referent study of lung cancer, nested in an international cohort of asphalt workers, represents the design of choice, conditionally on the possibility of assessing relevant individual life-time exposures. A cross-sectional determination of relevant biomarkers of exposure such as adducts in lymphocytes or the presence of metabolites of polycyclic aromatic compounds in urine in a group of workers exposed to bitumen fumes will provide further relevant information.

Cytogenetic studies of stainless steel welders using the tungsten inert gas and metal inert gas methods for welding.

Cytogenetic damage was studied in lymphocytes from 23 welders using the Tungsten Inert Gas (TIG), and 21 welders using the Metal Inert Gas (MIG) and/or Metal Active Gas (MAG) methods on stainless steel (SS). A matched reference group I, and a larger reference group II of 94 subjects studied during the same time period, was established for comparison. Whole blood conventional cultures (CC), cultures in which DNA synthesis and repair were inhibited (IC), and the sister chromatid exchange (SCE) assay were applied in the study. For the CC a statistically significant decrease in chromosome breaks and cells with aberrations was found for both TIG/SS and MIG/MAG/SS welders when compared with reference group II. A non-significant decrease was found for the corresponding parameters for the two groups of welders when compared with their matched referents. A statistically significant negative association was found between measurements of total chromium (Cr) in inhaled air and SCE, and a weaker negative correlation with hexavalent Cr (Cr(VI)) in air. In conclusion, no cytogenetic damage was found in welders exposed to the TIG/SS and MIG/MAG/SS welding fumes with low content of Cr and Ni. On the contrary, a decline in the prevalence of chromosomal aberrations was indicated in the TIG/SS and MIG/MAG/SS welders, possibly related to the suggested enhancement of DNA repair capacity at slightly elevated exposures.

Asbestos-related radiographic changes by ILO classification of 10 x 10 cm chest X-rays in a screening of the general population.

A sample of 1388 10 x 10 cm chest X-rays from a previous population screening of males aged 40+ years were reevaluated by use of the ILO classification. There were 1036 films of subjects from an industrialized town, and 352 from a rural community. The observed rates of parenchymal changes (profusion > or = 1/0) at the reevaluation were 1.3% in the urban community and 3.4% in the rural community. The corresponding figures for pleural changes were 5.0% and 0.6%, respectively. Based on additional questionnaire information on asbestos exposure, it was found that the radiographic changes were probably related to past asbestos exposure for 2.3% of the subjects from the urban community and 0.6% from the rural community. In cases of asbestos-related illnesses the mean time since first exposure to asbestos was 35.9 years, whereas the mean duration of the exposures was 11.4 years. The results seem to indicate that the ILO reassessment of the radiographs was more sensitive in detecting pleural changes than the previous clinical screening of both small and large films.

Occupational and environmental medicine in Norway.

A short review is presented on the field of occupational health services (OHSs) and occupational medicine in Norway, with due attention to their history. The current Work Environment Act of 1977 requires management in various industries and enterprises to establish and finance OHSs to obtain advice on matters relating to the work environment. The advisory role of the OHSs, with a focus on prevention, has not yet been adequately implemented. A brief report is given on the current status of occupational health, institutions, teaching in medical faculties, and research activities. As work-related and environmental exposures interact in the causation of diseases, integration of the preventive activities within occupational and environmental medicine is foreseen.

Nickel-related cancer in welders.

During stainless steel (SS) welding, solid aerosols are generated from elemental compounds which are generally considered to be human carcinogens; i.e. compounds of hexavalent chromium (CrVI) and nickel. Epidemiological studies among groups of SS-welders have indicated that they may carry a higher risk of acquiring lung cancer than mild steel (MS) welders using the same welding techniques. This excess risk has been demonstrated in cohort as well as by case-control studies. The present evidence does not support the view that exposure to SS-welding fumes poses a hazard of cancer at any other site. Exposure to asbestos and smoking are generally major confounders in these studies. The number of SS-welders world-wide seems to be increasing, thus these findings may be of significance to SS-welders and to the welding industry. Despite the information on the possible cancer hazard among SS-welders, current epidemiological data on cancer incidence and mortality do not offer clear evidence to determine whether exposure to nickel or CrVI compounds constitutes the more important risk factor for lung cancer.

Chromosome damage in lymphocytes of stainless steel welders related to past and current exposure to manual metal arc welding fumes.

Cytogenetic damage was studied in lymphocytes from 42 welders using the manual metal arc (MMA) method on stainless steel (SS). A detailed characterization of previous exposure by job interviews, and for current exposure with personal air sampling and biological monitoring of chromium (Cr) and nickel (Ni) in blood and urine, was done for 32 of these welders. A subgroup of 20 welders was studied before and after 1-4 months of MMA/SS welding. A matched reference group I, and a larger reference group II were established for comparison. A significant increase in chromatid breaks (1.4 vs. 0.9 and 0.8 for group I and II) and for cells with aberrations (2.2 vs. 1.6 in group II) was found in the welders. An even larger difference was found when comparing non-smoking welders with their non-smoking referents. No synergistic effect between smoking and MMA/SS welding fumes was observed for any type of aberrations. Current welding fume exposure during the week before sampling was not associated with increases in any type of cytogenetic damage. The results indicated that the increase in chromatid breaks was associated with cumulated welding fume exposure for more than a year, and with not using respirators. Exposure to MMA/SS welding fumes for up to 4 months gave a slight, but significant increase in chromatid breaks when using the welders as their own referents. However, when using matched referents in the study after exposure, no difference was found between these welders and their matched referents. No differences between the groups were observed in the DNA synthesis and repair-inhibited cultures or for SCE.

Incidence of cancer among nitrate fertilizer workers.

The results are presented from a historical prospective cohort study on the incidence of cancer among 1756 male workers at a nitrate fertilizer plant. Workers employed for 1 year or more between 1947 and 1980 were included in the cohort. Surrogates for individual exposure to nitrogen derivatives and asbestos dust were recorded to identify subgroups. There were 195 cases of cancer observed versus 208.8 expected, as based on the rates among age-adjusted rural Norwegian males. A slight increase in stomach cancer was found: 28 observed versus 19.9 expected.

Prevention of lung cancer through the use of knowledge on asbestos and other work-related causes--Norwegian experiences.

This review attempts to estimate the contribution of different known work-related causes of lung cancer in the Norwegian male population in order to predict the potential of prevention of work-related cases. The presented estimates are based on data from epidemiologic studies made in Norway, but may be of significance for other countries with a similar work-force structure. Over the past decade asbestos-related lung cancer appears to have contributed about two-thirds of the lung cancers that have been related to work exposure in Norway, for example, possibly 125-175 of the 1100 cases that occurred among Norwegian men in 1987. The potential for prevention is, however, greater due to synergism. To a less extent compounds of nickel and chromium have also contributed, along with exposure to polycyclic aromatic hydrocarbons, radon daughters, seafaring work, and other, less significant specific and nonspecific determinants of lung cancer.

Incidence of cancer among welders of mild steel and other shipyard workers.

The incidence of cancer among 4571 shipyard workers with first employment between 1940 and 1979, including 623 welders of mild steel, was investigated in a historical cohort study. The loss to follow up was 1.1%. The total number of deaths was 1078 (974.5 expected) and there were 408 cases of cancer v 361.3 expected. Sixty five cases of lung cancer were found v 46.3 expected based on the national rates for males. Four pleural mesotheliomas had occurred (1.2 expected), none among the welders. An excess of lung cancers was found among the welders (nine cases v 3.6 expected). There were six cases of lung cancer v 1.6 expected in a high exposure group of 255 welders. A survey of the smoking habits as of 1984 indicated 10%-20% more daily smokers among the shipyard production workers than among Norwegian males. Exposure to smoking and asbestos were confounding variables in this study.

Urinary mercury excretion in chloralkali workers after the cessation of exposure.

Seventeen former chloralkali workers were followed through the regular determination of urinary mercury for nearly two years after the cessation of exposure to mercury vapor in a study of the time course of urinary mercury elimination. Their duration of exposure ranged from 3 d to 35.5 years. A one-compartment model for urinary mercury elimination was applied. The urinary mercury concentration declined at a rate indicating a half-time of 91 d. When corrected for an individual base-line level of urinary mercury resulting from sources of mercury intake not related to work, the half-time was 72.4 [95% confidence interval (95% CI) 63.2-81.7] d, with a mean elimination rate constant of 0.011 (95% CI 0.008-0.013).d-1. The day-to-day variability of the urinary mercury concentration averaged 22%, expressed as the coefficient of variation between urine samples delivered on three consecutive days.