In a cross-sectional study conducted in the UK, workers at three factory sites producing poly-MMA sheets were assessed (Pickering et al 1993; unpublished report). SCOEL10
Based on workplace station measurements, the workers were divided into three exposure level groups: low (< 1 ppm 8-hr TWA), medium (5 ppm 8-hr TWA) and high (20 ppm 8-hr TWA). However, it was also predicted that the personal exposures at this factory would be similar to that of the study of Pausch et al 1994SCOEL9 (see below),
indicating that a significant proportion of workers would have been exposed to an average concentration of 50 ppm (8h TWA). In addition, a significant proportion of the workers self-reported daily exposure to transiently high levels of MMA as a result of 'cell bursts' or spills; such events have been shown to create transient peaks of several hundreds of ppm (up to 500 ppm).
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The results showed a low prevalence of respiratory symptoms among the workforce with no indication of an exposure-response relationship. The results of spirometry tests showed no exposure-related changes and any differences from expected values were so small as to be of no functional significance. Overall, there were no significant respiratory health effects in this worker population, a significant proportion of whom were thought to have had average exposures of approximately 50 ppm (8h TWA). 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
In another worker survey, a questionnaire study and visual examination of the nasal cavity was performed over a 2-year period on 211 workers at a poly-MMA sheet production factory in Germany (Pausch et al 1994; unpublished report; not available to the SCOEL).SCOEL9 Working areas were classified into the following 8h TWA exposure
ranges (as geometric means) of 3-10 ppm (7 people), 10-20 ppm (128 people), 20-30 ppm (20 people) and 30-40 ppm MMA (56 people). However, about one third of the measurements in the higher exposure category exceeded 40 ppm (up to 50 ppm; and were beyond 50 ppm in 15% of cases).
Small numbers of workers reported respiratory symptoms of "mild" to "moderate" severity; these included impaired nose breathing (6/211), dry nose (6/211), rhinitis (1/211), reduced sense of smell (2/211), eye irritation and lacrimation (3/211) and chronic bronchitis (2/211). The only findings that showed any clear evidence of an association with MMA exposure were those indicative of transient eye and nose irritation, which correlated with short-term peaks of peak exposure (airborne concentrations somewhere between 100 and 680 ppm for periods of 5-15 minutes duration). There were no abnormalities of the nasal cavity in this workforce.
Additional information
lA critical review of the epidemiological literature on potential cancer risks from MMA focused on cast acrylic sheet manufacturing workers. Excesses of respiratory and stomach cancers, observed in some cohorts of workers exposed to MMA, were attributed to lifestyle exposures such as cigarette smoking or diet. An excess of colorectal cancer in one group of workers exposed to high levels of MMA during the 1930s and 1940s remained unexplained. The authors concluded that there is insufficient evidence that MMA is a human carcinogen, based on the lack of
consistency of the various studies, the absence of dose-response relationships and the lack of support from studies in animals.18
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Exposure to MMA and total dust, as well as workers' health symptoms (by
questionnaire), were investigated in twenty dental laboratories in Tehran, Iran. Time- weighted average (8h-TWA) of MMA for technicians with direct and indirect exposure were 327 ± 79 and 283 ± 42 mg/m3, respectively. Peak concentrations (5-15 min) were
337 ± 37 and 329 ± 45 mg/m3, respectively. Cough and skin dryness were the common
health symptoms. Dryness of skin (especially in hands) was associated with MMA concentration (p = 0.03). The prevalence of respiratory symptoms among technicians with direct exposure was 18.4% for cough, 23.7% for phlegm, and 42.1% for asthma. There was a significant difference between smokers or individuals with a history of asbestos exposure and non-smoking individuals without an asbestos exposure
background. In view of the high proportion of smokers (92.9%), and asbestos-exposed individuals (41.9%) in this study, it is concluded that these factors were largely
responsible for the prevalence of respiratory symptoms.6 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 31 32 33 34 35
A study was carried out on 104 employees of a MMA/polymethyl methacrylate (PMMA) production facility in Bulgaria. The control group consisted of 55 healthy employees not working in chemical operations at the plant. Airborne monitoring was conducted over a 10-year period (1983-1993) for MMA and the precursor chemicals methanol and acetone cyanhydrine at the MMA operation, and MMA was monitored at the PMMA operation (potential exposure to this chemical only). Acid-base status of the workers was evaluated (pH, pCO2, pO2 and HCO3 in plasma). Data from retrospective
monitoring of air levels of the chemicals were compared with the acid-base status of workers at the plant. MMA exposure was highest in the PMMA plant and ranged between 24 and 94 mg/m3. In this plant, 8 to 31% of the samples exceeded 50 mg/m3.
Acid-base disruption, indicated by reductions in plasma pH, pO2 and HCO3, was found
for all groups except the control population. The greatest reduction was associated with PMMA production workers (n=13): pH, 7.3±0.02 / 7.4±0.02 mmHg; pCO2, 36.3 ± 6.03 /
41.5 ± 6.8 mmHg; pO2, 36.3 ± 6.03 / 41.5 ± 6.8 mmHg; HCO3, 18.3 ± 4.0 / 23.7 ± 1.9
nmol/L in exposed/control subjects (p < 0.05).13 7.2 Animal experiments
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7.2.1 Irritation and sensitisation
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