Summary Our study included 27 polyurethane foam workers exposed to MDI only at low concentrations. (ranging from 0 0005 to 0 001 ppm) and 27 clerks from.
Intt Arch Occun Environ Health (,91990) 2:521-524 Arh c ro a t 25
InternationalArchives of
OeCUpatinan
Environmental Health l © Springer-Verlag 1990
Short-term respiratory changes in polyurethane foam workers exposed to low MDI concentration F Sulottol, C Romano l , G Piolattol, M Coggiola l , S Polizzi 2 , C Ciacco l , and A Berra3 'Istituto di Medicina del Lavoro dell'Universita' di Torino C T O Health Service USSL 31 Carmagnola, Italy Director Fiat Auto Health Services Turin, Italy
2 National 3
V Zuretti 29, I-10126 Torino, Italy
Received February 13 / Accepted August 22, 1990
Summary Our study included 27 polyurethane foam workers exposed to MDI only at low concentrations (ranging from 0 0005 to 0 001 ppm) and 27 clerks from the same factory matched by age Respiratory function tests were performed on a Monday and Friday of the same week at shift onset, 4 h later and at shift end The subjects under study were asymptomatic for asthma The two groups had quite similar spirometric values with minimal functional impairment A statistical analysis was carried out by Student's t-test for matched pairs and two-way analysis of variance (ANOVA), in order to take into account both occupational exposure and smoking habits No significant differences between the two groups were observed with paired t-tests in the respiratory parameter trend during both the Monday and Friday work shift Nor were differences observed within the two groups when Friday's and Monday's results were compared No significant differences between the two groups were found in paired comparisons between Friday and Monday for respiratory parameters ANOVA demonstrated that the FEV 1 and FEF25-75 reduction present on Friday, when compared to Monday, was related to smoking and not to occupational exposure In conclusion our findings showed no short-term respiratory changes in subjects exposed to low MDI concentration. Key words: MDI
Respiratory changes
Smoking
Introduction Short-term spirometric parameter variations occurring during a shift or a working week in asymptomatic isocyanate workers have been studied as an index of a possible long-term worsening evolution of respiratory function, in order to identify subjects at risk. Such an approach is not confined to polyurethanes. In fact the available literature also refers to other exOffprint requests to: F Sulotto
posed populations such as coal miners l 13l, cotton workers l 1l, grain handlers l3 l. A significant reduction, mainly in FEV 1, during a work shift has been reported to follow TDI exposure l20 l Such an observation appears to be correlated to the reduction in the above parameter six months l19 l or some years l18 l later The severity of respiratory worsening seems to be related to the task l11 l and moreover to exposure level l22l In fact, the results of those studies that rule out short-term respiratory effects among workers with low exposure to either TDI and/or MDI l14, 15 l may be explained, at least in theory, in terms of ambient air isocyanate concentration so low as to cause no adverse effects to nearly all workers However, this may also be due to the fact that daily variations of the parameters in non-sensitized subjects are not large enough so as to make the standard spirometric tests sensitive in all cases l16l. It must be noted that almost all the data in the literature refer to TDI; the few referring to low exposure either to MDI l 14, 15 l or NDI l10l seem to rule out any significant long or short-term respiratory impairment, in particular with regard to FEV 1. The very few data on low environmental exposure to isocyanate in general, the paucity of data on MDI in literature, the discrepancy between the results for TDI and those for other isocyanates, led us to carry out this study on respiratory parameter variations during a working week in a group of polyurethane foam producers exposed to an MDI concentration known to be constantly low In fact most processes in the study factory were carried out in closed systems and with effective aspiration in the presence of fumes. Materials and methods The study included 31 male polyurethane foam workers exposed to MDI only, in a factory producing finished parts for the car industry It is worth noting that the foam production, until 1980, was carried out by TDI only, which was subsequently gradually substi-
522 tuted by MDI Since 1984 MDI became the only isocyanate in use. In order to rule out the role of other factors affecting the withinsubject reproducibility over short periods of time of spirometric measurements, it seemed suitable to measure the same parameters in a control, unexposed sample The group of the workers not directly involved in foam operations was first considered as appropriate However the high prevalence of possible previous or concomitant exposure to MDI, even occasional, excluded the possibility of obtaining a sufficient number of controls among those workers Therefore 31 clerks from the same factory were matched by age (+/ 2 years) according to the following procedure: exposed workers and clerk controls were randomly listed; the first clerk meeting the age criterion was selected as the first matched control. The procedure was then repeated to obtain 31 matched pairs. All the exposed subjects were asymptomatic for asthma, this last being a motive for removal from isocyanate exposure The removal from further exposure of 17 workers occurred before 1984, i.e during periods in which TDI or TDI-MDI were used Therefore there was no selection within our MDI worker group Consequently, any asthmatic clerk was excluded from matching A history of seasonal rhino-conjunctivitis was present in five polyurethane workers and in three clerks These subjects were not excluded, as the study was carried out during autumn and winter (a surely asymptomatic period). A Vicatest dry spirometer was used to carry out functional tests on all subjects, at shift onset, 4 h later and at shift end respectively Measurements were performed on each subject on Monday and Friday during the same week The study started in September 1988 and was completed by February 1989 All tests were performed by the same trained technician Each time every subject was requested to perform five maximal expiratory manoeuvres; the curve with the highest sum of FVC and FEV 1 was chosen for calculations. MDI-exposed subjects were tested during the morning shift and therefore, approximately 2 h before the control group, due to a different working schedule. The results of spirometric tests were unreliable in either one or both subjects included in four matched pairs, which were consequently discarded, thus leaving 27 pairs for analysis The following parameters were measured: FVC, FEV 1, FEF 25-75 ECCS 1971 l4l reference values were adopted for volumes and Knudson et al 1976 l 12l values for flow. Since there was no means of including height in the matching procedure, the percentage of theoretical values rather than absolute volumes or flows were used for statistical analysis. The Monday shift onset value for the three parameters was taken as the baseline, departures from which, expressed as percent values, (according to the following formula: Xpost-X pre / X baseline* 100), were calculated for all six tests carried out during the week. The following scheme was then applied: 1-DIFI: 2-DIF2: 3-DIF3: 4-DIF4: 5-DIF 5: 6-DIF6: 7-DIF7:
Monday mid-shift value vs Monday shift onset value Monday shift end value vs Monday shift onset value Friday mid-shift value vs Friday shift onset value Friday shift end value vs Friday shift onset value Friday shift onset value vs Monday shift onset value Friday shift end value vs Monday shift end value Friday shift end value vs Monday shift onset value.
Paired t-tests and two-way analysis of variance (ANOVA), in order to take into account both occupational exposure and smoking habits, were used for statistical analysis Environmental analyses to asses MDI concentration were carried out by continuous tape monitoring (7005 FR Rankon Analyzer) during the same period when functional tests were performed. The values ranged from 0 0005 to 0 001 ppm Band type routine method for isocyanate monitoring may underestimate MDI atmosphere under certain conditions l2l, as compared to HPLC. However, based on the recorded data, they are well below the TLV Therefore it can be considered a low MDI exposure.
Results Table 1 shows mean values and standard deviation of baseline lung function parameters and years at work in addition to smoking habits No significant differences were found by paired t-tests between the two groups under study; nor where there significant differences in baseline values when controlling by two-way ANOVA either for occupational exposure, smoking or the combined effect. It must be noted that the proportion of smokers was much lower than non smokers within clerical workers (5 smokers vs 22 non smokers), whereas it was similar within exposed workers (12 vs 15). In Table 2 the two groups are classified according to their spirometric results Subjects were deemed normal when FVC, FEV 1, FEV 1%/FVC, FEF 25-75 were all within the confidence limits of the predicted values The functional impairment was classified as: isolated FEF2575 reduction, obstruction (FEV 1%/FVC reduction), FVC and/or FEV 1 reduction (whether or not associated to FEF 25-75 reduction) Lung function characteristics were similar in exposed and control subjects Both showed a high prevalence of normal subjects and the presence of a low number of cases with reduction in FEF 25-75 only, all of which were non smokers Three exposed workers and two clerks showed a slight reduction of FVC and/or FEV 1; the three exposed workers were smokers, and the two clerks non smokers. Table 3 shows the mean values of percent variations of the studied parameters at mid-shift and shift end on Monday (DIF 1, DIF 2) and on Friday (DIF 3, DIF4), in both exposed and clerical workers. The paired t-tests showed no significant differences between the two groups in the corresponding time intervals; nor were differences observed within the two groups when comparing the variations observed on Monday and Friday respectively, at the same time intervals. Further splitting of exposed and clerical worker results according to smoking is not reported in Table 3 for
Table 1 Personal details of the study groups Group
Total N in study
Nof current smokers
Years at work
FVC % predict
FEV 1 % predict
FEF25-75 % predict.
Exposed workers Clerks
27 27
12 5
14 0 (4 5)a 16 4 (6 2)
95 7 (11 3) 97 3 (11 5)
102 3 (14 5) 103 6 (11 7)
87 5 (27 0) 90 0 (20 4)
a
In parentheses indicate SD
523 Table 2 Distribution of lung function results as recorded at baseline test Exposed workers
Clerks
Smokers
Non smokers
Smokers
Non smokers
N
N%
N
%
N
100
19
Normal FEF25-75
9
reduction Obstructive
0 0
% 75
%
12
80
5
86
3 O
20
0 O
1 O
O
2
9
22
100
5 -
FVC and/or FEV 1 reduction
Total
3
25
0
12
100
15
100
5
100
Table 3 Percentage changes in lung function on mid-shift and shift end tests carried out on Monday and Friday in exposed and clerk groups Param eters
Exposed workers
Clerks
Monday
Monday
Friday
Friday
the sake of simplicity However, testing the effect of exposure and smoking by two-way ANOVA did not provide evidence of significant variations. Table 4 shows the mean values of percent spirometric changes during the week (i e comparison between Friday and Monday results) None of the paired comparisons between the two groups gave significant differences in the t-tests. The results of the same comparisons, carried out by taking into account by ANOVA both exposure and smoking habit, are reported in Table 5 The outcome of the tests which showed no significant differences was not included in this table The only significant effect due to the job category was that of an increase in FEF25-75 in the exposed group, when comparing Friday shift end with Monday shift onset values (DIF7). FEV 1 reduction was related to smoking when comparing Friday shift end values with both Monday shift end (DIF6) and Monday shift onset (DIF 7) values A significant effect of smoking was also observed on FEF2575 reduction, when comparing Friday shift onset with Monday shift onset (DIF5) as well as Friday shift end with Monday shift onset (DIF7) In no case was there a statistically significant exposure-smoking interaction effect.
DIF 1 DIF2 DIF3 DIF4 DIF 1 DIF 2 DIF 3 DIF4 FVC 01 FEV 1 14 FEF25-75 4 8 DIF 1: DIF 2: DIF 3: DIF 4:
-0 9 -1 7 -0 9 -0 1 0 5 07 05 14 0 2 05 31 72 51 14 05
02 13 46
-0 1 06 23
Monday mid-shift value vs Monday shift onset value Monday shift end value vs Monday shift onset value Friday mid-shift value vs Friday shift onset value Friday shift end value vs Friday shift onset value
Table 4 Percentage changes in lung function when comparing the values obtained at beginning and end of working week Parameters FVC FEV 1 FEF25-75
Exposed workers
Clerks
DIF 5
DIF6
DIF 7
DIF 5
DIF 6
DIF 7
-0 7 -0 8 -3 7
-0 7 -0 2 -2 0
-1 7 05 11
-0 2 -0 7 -2 5
-0 8 -0 7 -2 1
-0 3 -0 2 -1 9
DIF 5: Friday shift onset value vs Monday shift onset value DIF 6: Friday shift end value vs Monday shift end value DIF 7: Friday shift end value vs Monday shift onset value
Discussion Our polyurethane foam producer group included asymptomatic subjects with minimal functional impairment in as much as the baseline spirometric values were almost normal and the data obtained from exposed workers and clerks were very similar The trend of the values obtained during one shift with elapsing working hours was also very similar in the two groups, with very small differences between the Monday and the Friday trends within each single group This result is in agreement with the absence of any significant difference in the weekly trend of spirometric data between exposed and control subjects. The 2-h difference in the time of execution of each test, tied to the same difference in shift onset for exposed workers and clerks, did not seem to affect the results In fact, the trend of the values obtained with elapsing working hours in both groups seems to be in agreement with that found in the literature reporting a slight increase in FEV 1 in the morning shift l8, 21 l and a decrease in FEV 1
Table 5 Comparison of values obtained at beginning and end of working week List of the significant results obtained by testing both job and smoking effect by two-way ANOVA A) Independent variable: Effect:
MDI exposure FEF 25-75 increase:
Friday shift end vs Monday shift onset (DIF 7)
P = 0 009
B) Independent variable: Effect:
Smoking FEV 1 decrease: FEV 1 decrease: FEF25-75 decrease: FEF25-75 decrease:
Friday Friday Friday Friday
P= P= P= P=
shift shift shift shift
end vs Monday shift end (DIF 6) end vs Monday shift onset (DIF7) onset vs Monday shift onset (DIF 5) end vs Monday shift onset (DIF 7)
0 037 0 050 0 041 0 021
524
and maximal expiratory flows in late shift and furthermore in the night shift l6 l. The smoking factor has some relevance in our groups. Data available in the literature mostly show an effect of smoking on long-term functional worsening in workers exposed to isocyanates l14, 15, 19 l or to other occupational noxae (e g grain silo workers) l3 l However, this seems to be less evident in workers exposed to low isocyanate concentrations l5 l. Data available in the literature on short-term effects (1 shift or 1 working week) of smoking differ from each other In fact no association was found between smoking and FEV 1 trend in TDI workers l20, 22 l, whereas the relationship found among cotton and grain silo workers was so close as to consider smoking as a predictor of FEV 1 worsening during a working shift This seems to be due to the bronchial obstruction frequently associated with the higher circadian variability of maximal expiratory flows l 7l. In our group the significant Friday reduction in FEV 1 an FEF25-75 with reference to baseline values (Monday) found by ANOVA as due to smoking rather than to job is not supported by specific short-term data in the literature However this result is in general agreement with the notion of a combined adverse effect of smoking and occupational broncoirritants The contribution given by clerks to the total variance due to smoking is less easy to explain l9, 13 l and, owing to the small number of smokers in this group, may be reasonably regarded as an occasional finding in a small set of data. Seasonal rhino-conjunctivitis (likely to have been caused by atopia) seems to have no relevance in our subjects, as the study was carried out in an asymptomatic period Furthermore literature data rule out any relationship between atopia and both short l17 l and longterm l5l pulmonary changes caused by isocyanates Moreover, the absence of asthmatics in our two groups, not due to before or during work selection, further reduces the possibility of any confounding effect of atopia on our data. Our findings are in agreement with those of Musk l14, 15 l who does not report any short-term respiratory changes in subjects exposed to low MDI concentrations very similar to those found in our working environment.
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