I A Calvert

University of Birmingham, Birmingham, England, United Kingdom

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Publications (24)84.72 Total impact

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    ABSTRACT: Equations using variance components in exposure data to predict attenuation and standard error of exposure--response slopes have been published recently. However, to date, no comparisons have been made between results of applying these equations to a real data set with the exposure-response relations estimated directly. Data on lung function parameters and personal inhalable and respirable dust exposure levels from the European carbon black respiratory health study were used. The predicted attenuation and standard error of the relation between current inhalable and respirable dust levels and lung function parameters (FVC and FEV(1)) were calculated for various exposure grouping schemes. These results were compared with the observed exposure-response relations. Workers were grouped by Job Category, the combination of factory and Job Category and five a posteriori created Exposure Groups. In addition, the individual approach was also used, as exposure data were available for each worker. The rank orders of the coefficients from the regression analyses using the different grouping schemes were similar to those predicted by the equations, although the differences were larger than predicted. When using inhalable dust exposure, the predicted standard errors of the exposure-response slopes were slightly lower than those estimated directly; for respirable dust the predicted standard errors were about a factor two to three smaller than those from the regression analyses. When considering FVC, the predicted exposure-response relations were all statistically significant, whilst the observed relation was only significant when using the five a posteriori Exposure Groups. When reviewing the relations between dust exposure and level of FEV(1), all relations were statistically significant, with the exception of the (observed) relation between respirable dust and FEV(1), when the individual approach was used. Using different grouping schemes for estimating exposure can have large effects on the slope and standard error of the exposure-response relation. It is, therefore, important that the effect of the different grouping schemes on the level and precision of the exposure-response slope be estimated. Despite violation of most of the assumptions when applying the equations to predict attenuation and the standard error of the exposure-response slope, the similarities in predicted and observed exposure-response relations and standard errors are indicative of the robustness of these equations. Therefore, the equations appear to be a useful tool in establishing the most efficient way of utilizing exposure measurements.
    American Journal of Industrial Medicine 12/1999; 36(5):548-56. · 1.97 Impact Factor
  • American Journal of Industrial Medicine 36 (1999). 01/1999;
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    ABSTRACT: The aim of this study was to assess the theoretical efficiencies of different grouping strategies and its effect on the exposure-response relation in a study of respiratory morbidity associated with exposure to total inhalable and respirable carbon black dust. A large epidemiological study is being undertaken to investigate the respiratory health of employees in the European carbon black manufacturing industry in relation to exposure to carbon black dust. In phase 2 of the study, repeated measurements of total inhalable and respirable dust were taken which enabled estimation of various components of variability in the exposure data (within and between worker variance and within and between group variance). These variance components were used to calculate the contrast in exposure between the groups in various classification schemes and to calculate the theoretical attenuation of the exposure-response relation and the standard error (SE) of the slope. High contrast in exposure was found when workers were classified according to the combination of their factory and job category as well as when these combinations were amalgamated into five exposure groups. Attenuation was minimal with most grouping schemes; only with the individual based strategy was the attenuation large. The SE of the theoretically attenuated exposure-response slope was smallest for the strategy based on individual people followed by the classification scheme based on factory and job category. It was concluded that, although some assumptions for the calculations of the attenuation of the exposure-response slope were not met, the most appropriate classification scheme of the worker seems to be by the combination of factory and job category.
    Occupational and Environmental Medicine 11/1997; 54(10):714-9. · 3.22 Impact Factor
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    E E Clarke, L S Levy, A Spurgeon, I A Calvert
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    ABSTRACT: The use of pesticides in Ghanaian agriculture, though beneficial in reducing crop loss both before and after harvest, has been associated with threats to human health often due to the misapplication of the chemicals. This study was an initial attempt to explore the knowledge, attitudes and practices of 123 farm workers on three irrigation project areas in the Accra Plains, Ghana, regarding the safe handling and use of pesticides, to assess the prevalence of symptoms associated with organophosphorus pesticides (OPs) and carbamates and to determine the prevalence of pesticide-related symptoms, and blood cholinesterase. The study design was cross-sectional in type. Methods used were interviews and observation, and biological monitoring. The results revealed moderate levels of knowledge of the routes of absorption of pesticides and of potential symptoms following exposure. Knowledge of personal protective measures was poor to moderate. High risk practices included frequent handling of the chemicals, home storage of pesticides and short re-entry intervals. Despite knowledge of some health risks associated with pesticides, the use of personal protective equipment (PPE) was minimal due primarily to financial constraints. The prevalence of symptoms was higher and cholinesterase levels lower than in a control group of teachers. It is suggested that there is a need for more epidemiologic studies to investigate the problems associated with pesticide induced ill health as well as research into appropriate and affordable PPE. PPE needs to be subsidized. Training of agriculture and health workers in safety precautions, recognition, and management of pesticide-related ill health is a matter of urgency.
    Occupational Medicine 08/1997; 47(5):301-8. · 1.45 Impact Factor
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    J M Harrington, I A Calvert
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    ABSTRACT: A Delphi survey was carried out in an attempt to identify areas of priority in occupational health that should be targeted by research. Previously 53 occupational physicians identified and ranked these areas. These were then assessed by personel managers. There was considerable agreement on priorities between the two groups with musculoskeletal disorders and stress securing the highest ranking.
    Occupational and Environmental Medicine 10/1996; 53(9):642-4. · 3.22 Impact Factor
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    ABSTRACT: Organophosphates are effective pesticides which are frequently used in several agricultural settings. Although their acute effects are well characterised, it remains unclear whether long term exposure can damage the human nervous system. This study sought to investigate their long term effects by comparing abnormalities on neurological examination between groups of workers exposed to organophosphates and an unexposed group. 146 exposed sheep farmers and 143 unexposed quarry workers were recruited into a cross sectional study of symptoms and neuropsychological effects of long term exposure to organophosphates in sheep dip. From a symptom questionnaire given immediately after dipping the 10 most symptomatic and 10 least symptomatic farmers were selected. Several months later each of these, along with 10 of the unexposed quarry workers, underwent a standardised neurological examination similar to that which might be used in clinical practice, at at time as remote as possible from recent exposure to organophosphates so as to exclude any acute effects. All 30 selected subjects agreed to participate. The components of the examination which showed a significant difference were two point discrimination on the dorsum of the hand (symptomatic farmers 22 mm; asymptomatic farmers 13 mm; quarry workers 8 mm) and the dorsum of the foot (symptomatic farmers 34 mm; asymptomatic farmers 10 mm; quarry workers 11 mm), and mean calf circumference (symptomatic farmers 35.0 cm; asymptomatic farmers 36.3 cm; quarry workers 38.6 cm). Overall the prevalence of neurological abnormalities was low. The differences in neurological examination detected between groups were subtle and their clinical significance was unclear. However, they do suggest evidence of an adverse neurological effect from exposure to organophosphates. Further, larger scale studies will be required before it is possible to confirm or refute the differences detected.
    Occupational and Environmental Medicine 09/1996; 53(8):520-5. · 3.22 Impact Factor
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    ABSTRACT: Carbon black is a very pure form of very finely divided particulate carbon used mainly in the automotive tyre industry. Its carbonaceous nature and submicron size (unpelleted) have raised concerns with regard to its ability to affect respiratory morbidity. This paper describes the exposure to carbon black dust in the first and second phase of a large multi-national epidemiological study investigating the magnitude of these exposure-related effects. In Phase I, 1278 respirable dust samples were taken (SIMPEDS cyclone) which increased to 2941 in Phase II with a similar rise in the number of total inhalable dust samples (IOM head) from 1288 in Phase I to 3433 Phase II. Exposure dropped markedly between the two phases with total inhalable dust showing a bigger reduction (49.9%) than respirable dust (42%), although the mean exposure for certain factories and job categories dropped more than others. The data are presented by the 14 job titles/numbers (21-34). The highest mean exposure in both phases and for both dust fractions is experienced by the warehouse packers and they are also most likely to exceed the OES of 3.5 mg m-3 (35.1% of samples in Phase I and 12.0% in Phase II).
    Annals of Occupational Hygiene 03/1996; 40(1):65-77. · 2.16 Impact Factor
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    ABSTRACT: This study was undertaken to assess whether contaminated personal clothing worn beneath a coverall (normal workwear) is a source of potentially significant dermal exposure to polycyclic aromatic hydrocarbons (PAHs) in coal liquefaction workers. An intervention study was conducted over a two week period involving 10 workers that reflected the range of activities performed at the factory. A cross over design was used to examine the influence of normal workwear (personal clothing worn beneath a coverall) and intervention workwear (new coverall, shirt, trousers, underwear, socks, and boots) upon excretion of urinary 1-hydroxypyrene (1-OHP) and skin pad deposition of pyrene. The impact of intervention was noted in three ways: (1) A notable reduction (55%) in the mass of 1-OHP excreted on the first day of the intervention phase was found. The median reduction in mass excreted (22.7 nmol) was significant from zero at the 5% level; (95% confidence interval (95% CI) 9.5-40.8 nmol). (2) A notable reduction (82%) in skin pad deposition of pyrene on the first day of the intervention phase was found. The median reduction of 13.20 ng.cm-2 was significant from zero at the 5% level; (95% CI 7.3-26.4 ng.cm-2). (3) About a 50% reduction in 1-OHP concentration over the working week occurred during the intervention phase; an increase of 2.07 mumol/mol creatinine was found from the start to the end of the work period during the intervention phase compared with an increase of 4.06 mumol/mol creatinine during the normal phase. This reduction was not significant at the 5% level. The results indicate that on the first day of the working week investigated, significant reductions in absorbtion (as measured by excretion of urinary 1-OHP) and deposition of PAHs (as measured by skin pad deposition of pyrene) can be effected by improvements in workwear policy. The impact of the improved workwear regimen was also detected by reduction in spot urinary 1-OHP concentrations, although this effect was less pronounced. One implication of the findings is that exposure to PAHs may arise from workers' own contaminated personal clothing. As a consequence of this study an improved workwear policy has been implemented at the factory.
    Occupational and Environmental Medicine 10/1995; 52(9):600-5. · 3.22 Impact Factor
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    ABSTRACT: Studies in coal liquefaction workers were conducted to examine relationships between work activities, exposure to polycyclic aromatic hydrocarbons (PAHs) and excretion of urinary 1-hydroxypyrene (1-OHP). In a single-week study in operators, the end of work period 1-OHP excretion was an order of magnitude higher than in a shadow control subject, who experienced exposure by inhalation only (shadowed operator = 15.8 mumol mol-1 creatinine; shadow control = 1.07 mumol mol-1 creatinine). Dermal exposure was estimated to account for over 70% of excreted 1-OHP in exposed workers. A second study over 4 consecutive weeks (multi-week study) showed consistency in 1-OHP excretion from week to week both in operators and laboratory technicians, indicating little variation in weekly exposures for these workers. Excretion levels in maintenance workers however, showed some week to week variation, consistent with the variable nature of exposures associated with this type of work. A further study involving an end of work period spot assessment for all personnel showed a clear distinction between exposed workers (operators and maintenance staff) and other workers not thought to be exposed (laboratory technicians and office staff). Findings in the course of these studies indicated that there is no loss of 1-OHP at 4 degrees C, compared with -20 degrees C. On the basis of work to date at the coal liquefaction facility, hygiene control strategies have been proposed involving periodic urinary 1-OHP monitoring.
    Annals of Occupational Hygiene 07/1995; 39(3):329-46. · 2.16 Impact Factor
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    ABSTRACT: Organophosphate-based pesticides are widely used throughout the world. The acute effects of over-exposure to such compounds are well known. Concern has also been expressed that long-term exposure may result in damage to the nervous system. In a cross-sectional study, we compared neuropsychological performance in 146 sheep farmers who were exposed to organophosphates in the course of sheep dipping with 143 non-exposed quarry workers (controls). The farmers performed significantly worse than controls in tests to assess sustained attention and speed of information processing. These effects remained after adjustment for covariates. The farmers also showed greater vulnerability to psychiatric disorder than did the controls as measured by the General Health Questionnaire. There were no observed effects on short-term memory and learning. Repeated exposure to organophosphate-based pesticides appears to be associated with subtle changes in the nervous system. Measures should be taken to reduce exposure to organophosphates as far as possible during agricultural operations.
    The Lancet 06/1995; 345(8958):1135-9. · 39.21 Impact Factor
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    ABSTRACT: This study was undertaken to assess the suitability of urinary 1-hydroxypyrene (1-OHPyr) as a biological marker of polycyclic aromatic hydrocarbon (PAH) exposure in coal liquefaction workers. This is believed to be the first evaluation of the method in coal liquefaction workers. Ten workers were selected from a group of 30 workers considered likely to be at risk of contamination from PAHs by virtue of their jobs. Spot urine samples were collected at the start of a work period and at the end of each work shift, with analysis of 1-OHPyr being undertaken by high-performance liquid chromatography linked to a fluorescence detector. Exposure was assessed by the completion of questionnaires. Excretion of 1-OHPyr increased significantly over the working period, and there was a significant increase in 1-OHPyr where start-shift and end-shift samples were taken over one shift. A significant decrease in 1-OHPyr was found during breaks away from work.
    Occupational Medicine 05/1995; 45(2):63-8. · 1.45 Impact Factor
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    ABSTRACT: To determine whether the respiratory symptoms and decrements in lung function found in manufacturers of ceramic fibres are related to exposure to the respirable fibre or inspirable mass constituents of the air in the working environment. Cross sectional survey of all current European primary producers of ceramic fibre was carried out, with measurement of exposure to respiratory fibres by personal samplers that measured inspirable and total mass, together with a health survey with an expanded respiratory questionnaire and standardised measurement of lung function. Odds ratios were calculated for symptoms and current exposure by multiple logistic regression, and multiple linear regression coefficients for lung function related to cumulative exposures controlled for the effects of respirable fibre and inspirable mass separately and together. Significant effects of current exposure to both inspirable dust and respirable fibres were related to dry cough, stuffy nose, eye and skin irritation and breathlessness. The decrements found in smokers and to some extent in ex-smokers in forced expiratory volume in one second and forced expiratory flow from 25% to 75% of expiratory volume, seem to be related to the respirable fibres rather than the inspirable mass constituents of the environment. Current symptoms were related to both current exposure to inspirable dust and respirable fibre. The decrements in lung function were related to the fibre constituent of the exposure.
    Occupational and Environmental Medicine 03/1995; 52(2):105-9. · 3.22 Impact Factor
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    ABSTRACT: To study the relation between occupational exposure to ceramic fibres during manufacture and respiratory health. The respiratory health of 628 current employees in the manufacture of ceramic fibres in seven European plants in three countries was studied with a respiratory questionnaire, lung function tests, and chest radiography. Simultaneous plant hygiene surveys measured subjects' current exposure to airborne ceramic fibres from personal samples with optical microscopy fibre counts. The measured exposures were combined with occupational histories to derive estimates of each subject's cumulative exposure to respirable fibres. Symptoms were related to current and cumulative exposure to ceramic fibres and lung function and findings from chest radiographs were related to cumulative exposure. The mean duration of employment was 10.2 years and mean (range) cumulative exposure was 3.84 (0-22.94) (f.ml-1.y). Eye and skin symptoms were frequent in all plants and increased significantly, as did breathlessness and wheeze, with increasing current exposure. Dry cough and stuffy nose were less common in the least exposed group but did not increase with increasing exposure. After adjustment for the effects of age, sex, height, smoking, and past occupational exposures to respiratory hazards, there was a significant decrease in both forced expiratory volume in one second (FEV1) and forced midexpiratory flow related to cumulative exposure in current smokers (P < 0.05) and in FEV1 in ex-smokers (P < 0.05). Small opacities were found in 13% of the chest radiographs; their prevalence was not related to cumulative exposure to ceramic fibres. It is concluded that exposure to ceramic fibres is associated with irritant symptoms similar to those seen in other exposures to man made mineral fibres (MMMFs) and that cumulative exposure to respirable ceramic fibres may cause airways obstruction by promoting the effects of cigarette smoke.
    Occupational and Environmental Medicine 02/1995; 52(2):97-104. · 3.22 Impact Factor
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    ABSTRACT: A cross sectional study was carried out to compare 110 paintmakers exposed to solvents with 110 age matched controls for outcome measures designed to assess cognitive performance and mental health. Hygiene data available for the paintmakers allowed the development of individual indices of solvent exposure and the analyses of health effects in relation to both duration and intensity of exposure. No effects on cognitive functioning or mental health were found in the paintmakers. For most of their period of employment the exposure of the paintmakers had been below current occupational exposure limits. The results are therefore interpreted as providing support for the view that long term exposure at or below current compliance levels does not result in damage to the central nervous system.
    Occupational and Environmental Medicine 10/1994; 51(9):626-30. · 3.22 Impact Factor
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    ABSTRACT: This paper describes how exposure to solvents at two large paint making sites was assessed in a study carried out to investigate the possibility of neuropsychological effects resulting from long term exposure to organic solvents. A job exposure matrix was constructed by buildings and year. A detailed plant history was taken and this was used to identify uniform exposure periods during which workers' exposure to solvents was not thought to have changed significantly. Exposure monitoring data, collected by the company before the study, was then used to characterise exposure within each uniform exposure period. Estimates were made for periods during which no air monitoring was available. Individual detailed job histories were collected for subjects and controls. The job histories were used to estimate exposure on an individual basis with the job exposure matrix. Exposure was expressed as duration, cumulative dose, and intensity of exposure. Classification of exposure by duration alone was found to result in misclassification of subjects.
    Occupational and Environmental Medicine 10/1994; 51(9):617-25. · 3.22 Impact Factor
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    ABSTRACT: A study population of 3086 employees was identified in 18 carbon black production plants in seven European countries. Respiratory health questionnaires, spirometry, and chest radiographs were used to estimate effects on health and personal monitoring procedures were employed to measure current exposure to inspirable and respirable dust along with sulphur and carbon monoxide. The low concentrations of gaseous contaminants made the generation of their current and cumulative exposure indices impossible. Low responses from some plants restricted the final analysis to 1742 employees in 15 plants (81% response rate) for respiratory symptoms and spirometry, and 1096 chest radiographs from 10 plants (74% response rate). In total, 1298 respirable and 1317 inspirable dust samples, as well as 1301 sulphur dioxide and 1322 carbon monoxide samples were collected. This study is the first to include a comprehensive and concurrent assessment of occupational exposure to carbon black dust and its associated gaseous contaminants. Cough, sputum, and the symptoms of chronic bronchitis were found to be associated with increasing indices of current exposure. Lung function tests also showed small decreases in relation to increasing dust exposure in both smokers and non-smokers. Nearly 25% of the chest radiographs showed small opacities of category 0/1 or greater. These were strongly associated with indices of cumulative dust exposure. The findings are consistent with a non-irritant effect of carbon black dust on the airways combined with dust retention in the lungs. Further cross sectional studies are planned to investigate whether long term exposure to carbon black dust causes damage to the lung parenchyma.
    British journal of industrial medicine 01/1994; 50(12):1082-96.
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    ABSTRACT: In 1987, the first phase of a study was initiated to investigate respiratory morbidity in the European Carbon Black Industry The study is co-ordinated from a research centre which also prepares and analyses the dust samples Filters and cassettes are sent by post to the factories and returned after sampling To find out whether weight loss occurs in transit 180 filter samples (60 controls and 120 loaded with respirable carbon black dust) were sent to and returned unopened from 12 factories Only 89 valid samples were obtained, the others were rejected due to gross dislodgement of particulates after transit An average weight loss of 0.04 mg was found, although this was not statistically significant Weight loss of filters with an initial carbon black load of more than 2 mg can be considerable A regression model using only filters with an initial carbon black load of less than 2 mg, showed that weight loss increased with increasing carbon black loads It was concluded that weight loss of filters loaded with respirable carbon black can occur causing some additional sampling error However, these minor losses and inaccuracies are far outweighed by the benefits of being able to collect large datasets simultaneously in 18 factories using one standard method of exposure assessment and a uniform rigorous quality control scheme
    Annals of Occupational Hygiene 01/1994; · 2.16 Impact Factor
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    ABSTRACT: Levels of airborne dust have been measured in the breathing zone of five warehouse packers in a carbon black manufacturing plant on consecutive days over 1 week. Post-shift urine samples were collected on individuals over the week and the concentration of the pyrene metabolite 1-hydroxypyrene have been measured. A questionnaire was used to assess the likelihood of potential confounding factors, such as direct exposure to feedstock oil, as well as smoking and diet. The arithmetic mean both of airborne dust and of excreted 1-hydroxypyrene for each individual have been correlated (a) with the constraint that the regression line pass through the origin, and (b) without this constraint. The slope of the regression through the origin was significant and that of the second regression (not through the origin) was not. The statistical test to determine whether excretion on days after Monday was higher than that on Monday itself proved highly significant. The results suggest that 1-hydroxypyrene may be a useful indicator of exposure to the PNAs adsorbed onto carbon black.
    Annals of Occupational Hygiene 01/1993; 36(6):681-8. · 2.16 Impact Factor
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    ABSTRACT: Carbon black is manufactured by the vapour phase pyrolysis of heavy aromatic hydrocarbon feedstocks. Its manufacture is worldwide and the majority of its production is for use in the rubber industry especially tyre manufacture. Its carbonaceous nature has led many to investigate the occurrence of exposure-related medical conditions. To quantify any such relationships, it is necessary to assess exposure accurately. As part of such an epidemiological investigation survey involving the measurement both of respirable and of total inhalable carbon black was undertaken in 18 plants in seven European countries between mid-1987 and mid-1989. A total of 1298 respirable samples (SIMPEDS cyclone) and 1317 total inhalable samples (IOM head) were taken and deemed of sufficient quality for inclusion in the study. The distributions of the time-weighted average values were assessed and found to be best described by a log-normal distribution, and so exposure is characterized by geometric means and standard deviations. The data are presented in terms of 13 separate job titles for both dust fractions and shows a wide variation between job titles, with the highest mean exposure experienced by the site cleaners, and 30% of the samples taken from the warehouse packers being in excess of the relevant countries' occupational exposure limits for total inhalable dust. The quality and extent of this data allows both for comparison with exposure standards and for generation of occupational exposure indices, which will be presented in another paper (Gardiner et al., in preparation).
    Annals of Occupational Hygiene 11/1992; 36(5):477-96. · 2.16 Impact Factor
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    ABSTRACT: The manufacture of carbon black is known to generate carbon monoxide and sulphur dioxide in the 'production gas' and the pyrolysis products of the 'production gas', respectively. Adverse health effects have been reported as associated with both contaminants (coronary heart disease with carbon monoxide and respiratory morbidity with sulphur dioxide). A major cross-sectional and longitudinal respiratory morbidity study is being conducted to assess the effects of exposure to carbon black on lung function, on chest X-rays and on responses to a questionnaire. The questionnaire includes questions on respiratory and cardiovascular symptoms, so that information regarding confounding exposure is essential. The working population of 18 manufacturing plants in seven European Countries was split into 13 job title numbers (1-13) which were then amalgamated into five job categories (A-E), with an appropriate (statistically) number of samples taken from each plant-job category. In total, 1322 carbon monoxide samples and 1301 sulphur dioxide samples were taken, using actively pumped longterm colorimetric tubes. In the majority of cases, more than half of the samples in each plant-job category were either zero or trace, thereby preventing the accurate estimation of the average exposure. The highest median carbon monoxide concentration was from the amalgamated data from all 18 plants in job number 9 (furnace operators), the highest median sulphur dioxide concentration was only 'trace'. The large number of zero and trace values also precluded the generation of current and retrospective exposure indices.
    Annals of Occupational Hygiene 09/1992; 36(4):363-72. · 2.16 Impact Factor