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British Journal of Industrial Medicine 1991;48:275-278 4aJ IdiCCufL^ 275 Diurnal variation in peak expiratory flow rate among polyvinylchloride compounding workers H S Lee, T P Ng, Y L Ng, W H Phoon Abstract The diurnal variation in peak expiratory flow rate (PEFR) was studied in 24 mixers and 24 non-mixers in three polyvinylchloride (PVC) aim was to determine whether PVC compounding workers have increased diurnal variation in PEFR suggesting exposure to a potential bronchoactive agent. compounding plants and 24 non-PVC controls from a marine police workshop. The three Materials and Methods groups (all men) were matched for age, race, MANUFACTURING PROCESS and smoking. The mean respirable dust The study was conducted in three PVC compound concentration (essentially PVC dust) was 1-6 mg/m1 for mixers and 0-4 mg/m1 for non mixers. The mean diurnal variation in PEFR of the mixers was 6-5%. This was significantly higher than the 4*8% for non-mixers and 4*3% for the non-PVC controls. Six mixers had a diurnal variation of more than 15% on at least one day compared with none among the other two groups. Twenty nine per cent of mixers complained of wheezing compared with 4% of non-mixers and none among non-PVC work ers. These differences were significant. Forced expiratory volume in one second (FEV,) for the mixers was 10% below the predicted values whereas that of non-PVC workers was 2% below predicted values. The study indicates a significant acute airway constriction from occupational exposure to PVC dust. ing factories. Polyvinylchloride pellets were produced by mixing together PVC resin powder with other additives such as plasticisers (for example di-octylphthalate), stabilisers (for example, lead sulphate), fillers (for example, calcium carbonate), and pigments. Azodicarbonamide (a blowing agent) was not used in the three factories. The bulk of the raw material was the PVC resin powder constituting more than 90% by weight of the mixture. The mixture was then blended and heated up to 170`C and extruded as pellets. The most visibly dusty job was that of the mixers who had to open bags of dry powdered materials and tip them into hoppers. This was carried out on raised platforms (about 8-10 m high)- Temperatures in the hoppers were around 135*C, the result of frictional heat from blending. The hoppers were equipped with local exhaust ventilation. Heating and extrusion took place at the floor level. A case of occupational asthma due to unheated polyvinylchloride (PVC) resin dust has been re ported recently.1 Both obstructive and restrictive ventilatory impairment and a high prevalence of wheezing complaints have been reported among The extruded pellets were collected and packed by the packers who were exposed to a relatively low level of dust. Other less exposed workers were forklift drivers, storemen, meoj^nics, fitters, electricians, material testers, cleaners etc. PVC fabrication workers.*1 Abnormalities of lung STUDY POPULATION function have also been reported in surveys of other A total of72 male workers were studied, consisting of workers exposed to PVC dust.4' 24 mixers, 24 low exposure non-mixers, and 24 non- We studied the diurnal variation in the peak PVC controls. All mixers in the three factories were expiratory flow rate (PEFR) in a group of PVC invited to participate in the study. The 24 mixers compounding workers and in a control group. Our represent 80% of all mixers. The low exposure PVC workers and the non-PVC controls were matched Department of Industrial Health, Ministry of Labour, MOL Building, 18 Havelock Road, Singa pore 0105 H S Lee, WHPhoon Department of Community, Occupational, and Family Medicine, National University of Singapore, Singapore T P Ng, Y L Ng with the mixers for age (five years), race, and smoking sate. The low exposure PVC workers were for example, forklift drivers, storemen, maintenance staff, and material testers from the same three PVC factories. The non-PVC controls were mechanics and maintenance stafffrom a marine police workshop with no exposure to PVC dust or any known asthma inducing agents. BFG21380 22530001 T 276 Lee, AIg, Ng, Phoon PEFR RECORDING Each participant was given a mini-Wright peak flow meter and instructed in its correct use. He was asked to perform three blows after maximal inspiration on each occasion and to record the results on a form. The highest of the three readings was taken. Six daily recordings (every three hours) during the waking hours were made for one week (six working days and one day off). Recording started on a Monday and sampling. Analysis was by liquid chromatography for HC1 and by gas chromatography for VCM. STATISTICAL ANALYSIS Statistical methods to compare exposed workers and controls were analysis of variance (F test), r test for independent quantitative variables, f test, and Fisher's exact test. were made both at the workplace and at home. The diurnal variation in PEFR was calculated as the difference between the highest and lowest PEFR values as a percentage of the highest PEFR on each day. For each worker the mean diurnal variation for the one week period was calculated. Results ENVIRONMENTAL ASSESSMENT Respirable dust concentrations for mixers (21 sam ples) ranged from 0-2 to 2-9 mg/mJ with a mean of 1-6 mg/m1. Respirable dust concentration for nonmixers (24 samples) ranged from 0-1 to 1 -0 mg/m' PULMONARY FUNCTION Forced expiratory volume in one second (FEV,) and forced vital capacity (FVC) were performed on a dry wedge spirometer (Vitalograph) on Monday morn ings when workers began their shifts. The spirometer with a mean of 0-4 mg/m'. Hydrogen chloride and VCM were not detected in any of the eight samples taken (detection limit = 0-03 mg/m1 for both HC1 and VCM). was calibrated before use. The best FEV, and best FVC were taken from three technically satisfactory forced expiratory manoeuvres where the best two recordings were within 5% of each other. All values were corrected to body temperature and pressure saturation. Height (to the nearest centimetre) was measured without shoes. Predicted normal values for FEV, and FVC were calculated based on regression equations developed by Zee* for local Chinese and STUDY POPULATION Among the 72 subjects, 33-3% were Malays and the rest Chinese. Fifty four per cent were smokers (including 17% ex-smokers). Tables 1-3 summarise personal data, prevalence of respiratory symptoms, and results of lung function tests and PEFR monitor ing of these subjects. Non-PVC subjects were taller than those in the other groups. Although they Malay men. Table 1 Characteristics ofstudy population RESPIRATORY QUESTIONNAIRE Each subject was interviewed by a trained field investigator using a structured questionnaire. Data were obtained on pulmonary symptoms, personal biodata, detailed work history including previous employment, past medical history, atopy, and smok ing habits. ENVIRONMENTAL ASSESSMENT High exposure Lots exposure mixers non-mixers (H m 24) tn 24) Age 38-0(8-4) Exposure duration to PVC (y) 11-1(5-7) Height (cm) 165 8(5-8) Cigarette-years 150-1 (258-0) FEV, (1) 2 8 (0-5) FVC (1) 3-2 (<P6) 36-8(8-1) 13-0(5-8) 166-0(7 0) 165-2 (208-7) 3-0(06) 3-4 (0-7) Non-PVC aorkers >n 24) 36-3(8-1) 170-5(5-7)* 186-7(281-1) 3 3(0-5) 3-7 (0-6) A total of 45 personal breathing zone samples of respirable PVC dust were collected over two to four hours on cellulose ester membrane filters of 37 mm diameter and 8-0 /on pore size using SKC personal dust sampling equipment at flow rates of 2 0 1/minute. Twenty one samples were taken from mixers and 24 samples from less exposed workers (non-mixers). A total of eight static samples ofair were collected for analysis of hydrogen chloride (HC1) and vinyl chloride monomer (VCM) (four cadi). Sampling was taken from four points: one near the mixer (on the platform), two near the extruder (floor level), and one outside the factory (ambient air). Sampling duration was three hours. For HC1 sampling, air was drawn through an impinger at 1 1/min. Air was drawn through a charcoal tube at 80 ml/min for VCM Data are given as mean (SD). *p < 0-05 (ANOVA). Table 2 Prevalence ofsymptoms High exposure Lots exposure mixers non-mixers (n - 24) (n - 24) Non-PVC workers (n - 24) Cough Phlegm Rhinitis Eye irritation Breathlessness Wheeze 4(16-7) 6(25-0) 5(20-8) 4(16-7) 3(12-5) 7(29-2)* 2(8-3) 4(16-7) 7 (29-2) 1 (4-2) 2(8-3) I (4-2) 2(8-3) I (4-2) 5 (20-8) 1(4-2) 1 (4-2) 0(0) Diu are given it number (V.) with positive symptoms. *p - 0-002 Ct* test); p - 0-005 compared with non-PVC controls (Fisher's test); p - 0-02 compared with low exposure non-mixers (Fisher's test). BFG21381 22530002 TI Diurnal variation in peak expiratory flow rale among polyvinylchloride compounding workers 277 Table 3 Results of lung function and PEFR High exposure mixers < n = 24} Low exposure non-mixers (n 24) Non-PVC workers fn = 24) "o Predicted FEV, % Predicted FVC FEV, FVC ( j DVPEFR(".i 90 4(10-8)* 90-9(12-5) 86 5 '6 1) 6 5 '4 2)** 94 2(13-7) 93-4(12-6) 87 1 (4 6) 4 8 (2 3) 97-6(10-9) 96-9(10-9) 87-4(5-6) 4 3(2-3) Data arc given as mean SD). *p = 0 03 compared with non-PVC controls (t test). **p = 0 03 compared with non-PVC controls (t test); p = 0 05 compared with low exposure non-mixers (t test). smoked more, this was not statistically significant (table 1). More mixers complained of wheeze than did other subjects. No significant difference was found in the prevalence of other symptoms (table 2). The FEV, of the mixers was 10% below the predic ted values whereas that of the non-PVC subjects was 2% below the predicted values (p = 0 03). The mean diurnal variation in PEFR of the mixers of 6-5% was higher than either of the other control groups (table 3). Six mixers had a diurnal variation of greater than 15% on at least one day compared with none among the other groups (p = 0 01, Fisher's test). The highest diurnal variation in a day was 23-9% in a mixer. Discussion Diurnal variation has been studied in workers exposed to grain dust7 and tobacco dust.* It has been shown that age and smoking were significantly correlated in a positive fashion with diurnal variation in PEFR. The mixers in our study had a higher diurnal variation in their PEFR compared with both low exposure and non-PVC controls matched for age, smoking state, and race. The diurnal variation in PEFR among PVC work ers has not been investigated in any previous study. The median diurnal variation in PEFR of grain elevator workers was 5-9%.7 This is slightly higher than the median diurnal variation in PEFR of 4-8% for PVC mixers. The method for calculating diurnal variation in PEFR, however, for the grain elevator workers was different and resulted in a higher diurnal variation. The diurnal variation in PEFR was cal culated as the difference between the highest and lowest PEFR values as a percentage of the mean PEFR on each day. In our case we expressed the difference as a percentage of the maximum PEFR on each day. Furthermore, the grain elevator workers were older (median age = 44 years) and had higher prevalence of smoking (81 % were smokers). The mean diurnal variation in PEFR in a group of tobacco workers was 14-4% and for their controls, it was 9-5%.' This is much higher than that seen in our subjects although method of calculating diurnal variation in PEFR was similar to ours. Their subjects were mainly women, however, and older (mean age = 43 years). The prevalence of smoking was 43-8%. Also only four PEFR recordings were taken each day. The higher prevalence of wheezing complaints and reduced FEV, (below predicted values) among mix ers compared with non-PVC controls provide fur ther evidence that mixers in the PVC compounding industry may be exposed to a bronchoactive agent. We did not detect any overt cases of occupational asthma. This is however, not unexpected in a cross sectional study since we are likely to be studying a survivor population. We have recently completed a similar study of polyurethane foam operators exposed to toluene diisocyanate (TDI) (not yet published). No overt cases of occupational asthma were detected in this group of workers exposed to a known asthma inducing agent, TDI. Possible asthma inducing agents in the PVC compounding industry include PVC dust, additives, and PVC decomposition products (for example HC1, VCM). Among the additives, only azodicarbonamide is known to cause asthma but azodicarbonamide was not used in the three plants surveyed. So far dioctylphthalate (DOP) and other phthalate esters have not been identified as asthma inducing.10 Furthermore, the DOP was in liquid form. Other additives such as stabilisers (for example, lead, barium, cadmium, and zinc salts) are not likely to cause asthma. Polyvinyl chloride is thermally stable at temperatures below 225*C." Above 225`C, PVC will degrade, releasing first HC1 and then, above 300*C, carbon monoxide, carbon dioxide, benzene, and VCM. Above 600*C small amounts of phosgene and chlorine are formed. Under normal operating conditions, temperatures do not exceed 170*C. At the mixing station, tem peratures do not exceed 135*C. Hydrogen chloride and VCM were not detected in the vicinity of the mixer or the extruder. The bulk of the dust is PVC. That unheated PVC dust can induce asthma t^as been shown by a positive challenge test.' Our study provides further evidence of a significant effect of variable acute airway con striction from exposure to PVC dust. 1 Lee HS, Yep J, Wing YT, Lee CS, Tin KT, Poh SC Occupational ischmi due to unheited polyvinylchloride resin dust. Br J IndMed 1989;46:820-2. 2 Ernst P, De Guire L, Armstrong B, Theriiult G. Obstructive ind restrictive ventilitory impairment in polyvinylchloride fsbricitioa workers. Am J Ind Med 1988;14:273-9. 3 Biser M, Tockmin MS, Kennedy TP. Pulmonary function ind respiratory symptoms in polyvinylchloride fabrication workers. Am Rev Respir Dit 1985;131:203-8. 4 Soutar CA, Copland LH, Thomley PE, Ottery J, Adams WGF, Bcnnet B. Epidemiological study of respiratory disease in workers exposed to polyvinylchloride dust. Thorax 1980;35:644-52. 5 Soutar CA, Gould S. Clinical studies of workers exposed to polyvinylchloride dust. Thorax 1983;38:834-9. 6 Zee KO. Ventilatory function in normal industrial workers in BFG21382 eoooeszz I 278 Lee, Ng, Ng, Phoon Singapore. Proceedings of she XII Singapore-Malaysia Con gress of Medicine, the Academy of Medicine, Singapore, 1977:587-95. 7 Revsbech P, Anderson G. Diurnal variation in peak expiratory flow rate among grain elevator workers. Br J Ind Med 1989;46:566-9. 8 Lander F, Gravesen S. Respiratory disorders among tobacco workers. Br J Ind Med 1988;45:500-2. 9 Slovak AJM. Occupational asthma caused by a plastics blowing agent, azodicarbonamide. Thorax 198136:906-9. 10 Nielsen J, Akesaon B, Skerfving S. Phthalate ester exposure. Air levels and health of workers processing polyvinylchloride. Am Ind Hyg Assoc J 1985;46:643-7. 11 Froneberg B, Johnson PL, Zandrigan PJ. Respiratory illness caused by overheating of polyvinylchloride. Br J Ind Med 198239:239-43. Accepted 1 October 1990 Vancouver style All manuscripts submitted to the Br J Ind Med should conform to the uniform requirements for manuscripts submitted to biomedical journals (known as the Vancouver style). The Br J Ind Med, together with many other international biomedical journals, has agreed to accept articles prepared in accordance with the Vancouver style. The style (described in full in Br Med J, 24 February 1979, p 532) is intended to standardise requirements for authors. References should be numbered consecutively in the order in which they are first mentioned in the text by Arabic numerals above the line on each occasion die reference is cited (Manson1 confirmed other reports*4...). In future references to papers submitted to the Br J Ind Med should include: the names of all authors if there are six or less or, if there are more, the first three followed by et at; the title of journal articles or book chapters; the titles of journals abbreviated according to the style of IndexMedian; and thefirst and finalpage numbers of the article or chapter. Examples of common forms of references are: 1 International Steering Committee of Medial Editors. Uniform requirements for manuscripts submined to biomedical journals. Br Med J 1979;1:532-5. 2 Socer NA, Vasserman SI, Austen KF. Cold urticaria: release into the circulation of histamine and eosino-phil chemotactic factor of anaphylaxis during cold challenge. N Engl J Med 1976394:687-90. 3 Weinstein L, Swam MN. Pathogenic properties ofinvading microorganisms. In: Sodeman WA Jr, Sodcman WA, eds. Pathologic physiology: mechanismsofdisease. Philadel phia: W B Saunders, 1974:457-72. BFG21383