Methyl methacrylate and respiratory sensitization: A Critical review

Methyl methacrylate (MMA) is a respiratory irritant and dermal sensitizer that has been associated with occupational asthma in a small number of case reports. Those reports have raised concern that it might be a respiratory sensitizer. To better understand that possibility, we reviewed the in silico, in chemico, in vitro, and in vivo toxicology literature, and also epidemiologic and occupational medicine reports related to the respiratory effects of MMA. Numerous in silico and in chemico studies indicate that MMA is unlikely to be a respiratory sensitizer. The few in vitro studies suggest that MMA has generally weak effects. In vivo studies have documented contact skin sensitization, nonspecific cytotoxicity, and weakly positive responses on local lymph node assay; guinea pig and mouse inhalation sensitization tests have not been performed. Cohort and cross-sectional worker studies reported irritation of eyes, nose, and upper respiratory tract associated with short-term peaks exposures, but little evidence for respiratory sensitization or asthma. Nineteen case reports described asthma, laryngitis, or hypersensitivity pneumonitis in MMA-exposed workers; however, exposures were either not well described or involved mixtures containing more reactive respiratory sensitizers and irritants.The weight of evidence, both experimental and observational, argues that MMA is not a respiratory sensitizer

Diamond formation by thermal activation of graphite

Synthetic diamond is used in applications ranging from abrasives, tool coatings, bearing surfaces, microelectronics and optics to techniques to produce diamond as the thermodynamically stable form(3), but it can also be grown at low pressures as a metastable carbon phase(1,2). Here we report the production of high-purity cubic diamond microparticles (10-100 mu m), which form in a highly concentrated carbon-vapour phase, followed by deposition of the crystals on the substrate, The carbon-vapour phase is generated by thermal activation of graphite, and the fast initial growth-rates of diamond, in the range 100-500 mu m s(-1), are at least two orders of magnitude higher than previously reported(1,2). We expect that tuning of experimental parameters to optimize the density of the carbon-vapour phase will allow us to grow larger diamond crystals, thereby opening a wider range of potential practical applications