P. D. Winter

Cancer mortality among man-made vitreous fiber production workers.

We have updated the follow‐up of cancer mortality for a cohort study of man‐made vitreous fiber production workers from Denmark, Finland, Norway, Sweden, United Kingdom, Germany, and Italy, from 1982 to 1990. In the mortality analysis, 22,002 production workers contributed 489,551 person‐years, during which there were 4,521 deaths. Workers with less than 1 year of employment had an increased mortality [standardized mortality ratio (SMR) = 1.45; 95% confidence interval (CI) = 1.37–1.53]. Workers with 1 year or more of employment, contributing 65% of person‐years, had an SMR of 1.05 (95% CI = 1.02–1.09). The SMR for lung cancer was 1.34 (95% CI = 1.08–1.63, 97 deaths) among rock/slag wool workers and 1.27 (95% CI = 1.07–1.50, 140 deaths) among glass wool workers. In the latter group, no increase was present when local mortality rates were used. Among rock/slag wool workers, the risk of lung cancer increased with time‐since‐first‐employment and duration of employment. The trend in lung cancer mortality according to technologic phase at first employment was less marked than in the previous follow‐up. We obtained similar results from a Poisson regression analysis limited to rock/slag wool workers. Five deaths from pleural mesothelioma were reported, which may not represent an excess. There was no apparent excess for other categories of neoplasm. Tobacco smoking and other factors linked to social class, as well as exposures in other industries, appear unlikely to explain the whole increase in lung cancer mortality among rock/slag wool workers. Limited data on other agents do not indicate an important role of asbestos, slag, or bitumen. These results are not sufficient to conclude that the increased lung cancer risk is the result of exposure to rock/slag wool; however, insofar as respirable fibers were an important component of the ambient pollution of the working environment, they may have contributed to the increased risk.

Mortality of tanners.

The mortality of 833 male tannery workers known to have been employed in the industry in 1939 and who were followed up to the end of 1982 was studied. A total of 573 men had been employed in making leather tanned by vegetable extracts for soles and heels, and 260 men had used chrome tanning to make leather for the upper parts of shoes. No significant excesses of deaths were found for any of the common sites of cancer in either group of workers. One death from nasal cancer (0.21 expected) was reported among the men who worked with sole and heel leather.

Non-neoplastic mortality of European workers who produce man made vitreous fibres.

We were intrigued by the report and findings from Elliott et al of overall mortality, cancer incidence, and stroke mortality in Shipham village. Their findings are similar to the conclusions we reported in 1982 after work funded by the Department of Health and Social Security. We noted that “the failure to demonstrate any excess morbidity requiring hospital admission is reassuring for Shipham residents”. We identified a small but significant excess of carcinoma of the ovary but thought it extremely unlikely that this could be explained by exposure to cadmium; the histology of the two reported neoplasms was diVerent and one of the patients resided at an address with a normal soil cadmium content. Hospital admissions were not increased for essential benign hypertension, hypertensive heart disease, acute nephritis, other nephritis and nephrosis, and calculus of the urinary system, or from gastric cancer which had in North Wales been associated with similar patterns of contamination of the soil with heavy metal. These findings are not explored by Elliott et al. Although they explore biomarkers of blood and urine, they do not discuss the worth of in vivo neutron activation analysis or dental studies. Yet, in 1979, it was reported that the mean (SD) liver cadmium concentrations of 21 Shipham residents was 11.0 (2.0) ppm, which was significantly higher (p<0.001) than that of 10 nonShipham controls (2.2 (2.0) ppm). These researchers also reported values of up to 260 ppm in industrially exposed workers, and that neither the workers nor the Shipham residents showed any evidence of cadmium toxicity. These findings were considered reassuring. The dental health of Shipham children was reported to be similar to children in neighbouring villages without the soil contamination, although increased concentrations of cadmium had been found in their teeth. One other background study of the villagers, also not cited by Elliott et al, reported widespread morbidity among 22 of 31 village residents. Its methodology has, however, been severely criticised. There is no doubt that the more extensive and detailed follow up by Elliott et al must again be reassuring to this residential population. However, as they point out, the intervening two decades since public health studies began in this village have seen enormous changes in the composition of its residents. Moreover, the soil concentrations of cadmium within Shipham vary considerably between gardens of adjacent houses (Department of the Environment, unpublished data). Doseresponse relations for the population of Shipham residents to all sources of cadmium are extremely diYcult to estimate. This public health interest in the soil concentrations of cadmium in Shipham village first arose in 1979 as a response by the United Kingdom Government Central Directorate on Environmental Pollution, Department of the Environment, to widespread news media coverage of work being undertaken by the Department of the Environment for the distribution of cadmium in the environment. This work followed up findings reported in the Wolfson geochemical atlas of England and Wales. At that time the contamination which had been widely known for generations within the village was not considered to present any known health risks for the population. Elliott et al do not seem to be aware of this background or of the findings from earlier studies. Such an introduction would have helped to set the context of their own study. The earlier publications also helped to make the study of Elliott et al possible by reporting the huge time costs needed for manual record linkage. For example, they reported that “the postcode of residence was used to identify cases from the national cancer and mortality databases, held by the United Kingdom Small Area Health Statistics Unit (SAHSU). Back in 1976, the need for record linkage was discussed. Our study of Shipham residents “was, in part, a response to the challenge that further interest should be stimulated in the use of Hospital Activity Analysis data” (HAA). We also reported that “for HAA purposes addresses of patients are coded by local authority districts. Health problems, however, are often restricted to much smaller geographical areas. Before we could calculate standardised admission ratios for Shipham, 451 hours of clerical work were required to identify the 201 records of HAA data for Shipham residents”. At that time the need to produce statistics for small areas had been recognised and the then OYce of Population, Censuses and Surveys was introducing a postcode system for vital statistics in England and Wales. Postcoding of hospital patient data and record linkage followed in the late 1980s. Elliott et al were able to use these developments. We thought that public health fears generated for this population had been allayed by studies reported in the 1980s for their sources of exposure, dietary intake of cadmium, body burden of cadmium, morbidity, and mortality experience. What Elliott et al now report is further evidence from longitudinal studies. The worth of such follow up studies is considerably weakened by knowledge that on average, 10% of the population move house each year, and diYculties estimating total body burden of cadmium. We think that much can be learned from the experience of studies involving this population. In particular, any such long term follow up studies should be sensitive to their public health needs. As Elliott et al and ourselves have noted, the methodological problems associated with interpreting findings from the use of routinely available data are considerable. It is therefore important for researchers, with the ready availability of powerful, computer based literature searching facilities and library held compendia— such as the Index Medicus—to be able to reassure readers that they have considered all the relevant background information and that their findings are being fully discussed in the context of other published work. Questions the informed reader will ask include: has a comprehensive risk assessment been undertaken? Has all the evidence been considered and is it coherent? Are there anomalies and can they be explained? What fresh insights has the study yielded? And what are the implications of the findings? In this instance we are left asking why was this recent study undertaken and what has it added to existing knowledge? Or, in other words, why has this soil been turned over again? It should be realised that in 1979, as a consequence of the news media scare and without any public health evidence, property values in the village dropped to half their market value. They took years to recover. Accordingly, we need to remind ourselves that we have a duty of care in planning research to ensure that our eVorts to better understand occupational and environmental health problems are intended for the public good.

Updating lung cancer mortality among a cohort of man-made mineral fibre production workers in seven European countries

A historical cohort of 21,967 workers ever employed in 13 European factories manufacturing various types of man-made mineral fibres (MMMF) was observed until 1982. Overall there were 2719 deaths (standardised mortality ratio (SMR) = 111) of which 189 were from lung cancer (SMR = 125). For the glasswool and rockwool/slagwool production subcohorts the lung cancer SMRs rose with time since first exposure, exceeding 170 for the period of 30 or more years. Adjustment for regional variations in mortality substantially reduced the excess in the glasswool group, but not in the rockwool/slagwool. In neither subgroup was there any relationship of lung cancer mortality with length of employment. During the early years of rockwool/slagwool production there was the potential for much higher fibrous dust exposure than at present, because of the absence of dust suppressing oil and/or the use of a batch production process. In addition slag was widely used as a raw material. Amongst workers employed during the early phase, there were 10 lung cancer deaths giving SMRs of 270 and 244 for the periods 20-29 and 30 or more years since first exposure. This group accounts for most of the absolute excess of lung cancer for the rockwool/slagwool plants.