Student Number : 0110634H - MPH research report - School of Public Health - Faculty of Sciences / During October 1996 to December 1999, isocyanates were the most frequently reported causative agent for occupational asthma cases (16.7% of all cases) submitted to the Surveillance of Work-Related and Occupational Respiratory Diseases in South Africa registry (SORDSA). Occupational disease surveillance registries in other countries also identified isocyanates as the most important occupational sensitiser. Asthma caused by isocyanates exposure may be severe and may persist even after exposure ceases. For this reason, it is important to identify the potentially hazardous isocyanate exposure settings, and to prevent sensitisation and asthma development where possible. Auto body repair shops, typically small, medium or micro enterprises (SMMEs), were the focus group in this study. Due to the paucity of medical surveillance and occupational hygiene programmes, there is likely to be over-exposure to isocyanates in such workplaces. The aim of this study was to identify and quantify exposure to HDI in auto body repair shops, and secondly, to describe the control measures currently used in these repair shops. The study investigated hexamethylene diisocyanate (HDI) exposure in the spray-painting processes of automotive repair shops in Gauteng. The repair shops were selected from the Highveld South African Motor Body Repairers’ Association (SAMBRA) membership list. Ten repair shops were included in this cross sectional study. Twelve subjects directly or indirectly involved in spray-painting in each repair shop had HDI exposure measured, resulting in a total of 113 HDI measurements. HDI monomers, prepolymers and total isocyanates determined using the National Institute for Occupational Safety and Health (NIOSH) draft method 5525 for analysis of monomeric and TRIG aliphatic isocyanates. Eighty one percent of workers were over-exposed to HDI monomers (exposure limit of 0.02mg/m3) and 3.4% to HDI prepolymers (exposure limit of 0.5mg/m3). Ninety percent of the establishments’ HDI monomer airborne concentration exceeded the OEL and 30% the prepolymer HDI concentrations. Workers were divided into 12 occupation categories according to the extent of their direct contact with the HDI-based paint and the three highest exposed groups were panel beaters, spray painters and dent-fillers. Workers directly and indirectly in contact with paint, in the auto body repair shops registered with SAMBRA were exposed to high levels of HDI during the spray painting operation. Insufficient and incorrect control measures were in place to control HDI exposure. The findings of this study confirm the risk of exposure to HDI in the automotive repair industry and the need for occupational hygiene control measures. In conclusion, high concentrations of HDI were common and even indirectly exposed workers were at risk of excessive exposure to HDI. Inadequate exposure control methods were widespread.

No description available.

The desirable properties of polyurethanes (PUs) such as mechanical flexibility associated with chemical versatility make these polymers attractive in the development of biomedical devices. In this study, various segmented polyurethanes were synthesized through polymerization reactions between polycaprolactone (PCL) diol or triol and excess hexamethylene diisocyanate (HDI) with varying NCO/OH ratios and the effect of composition on the properties of the resultant polyurethane films were examined. Initially, isocyanate terminated prepolymers were synthesized through one-shot polymerization, and then these prepolymers were cured by introducing crosslinkages into the structure and thus PUs were obtained. In order to enhance biocompatibility and hydrophilicity of the resulting polymers, heparin was added into the prepolymer before the curing process. The influence of excess HDI as a crosslinker on the degree of H-bond formation between hard-hard segments or hard-soft segments was examined by using Fourier transform infrared-Attenuated total reflectance spectroscopy (FTIR-ATR). Also the effects of HDI content on the chemical, physical and mechanical properties of the polyurethanes were examined with differential scanning calorimetry (DSC), X-Ray diffraction spectroscopy (XRD), dynamic mechanical analyzer (DMA), mechanical tester and goniometer. FTIR- ATR, DSC and DMA analyses showed that use of triol resulted in better network formation and homogenous distribution of hard segments within soft segment matrix. Incorporation of heparin into the polymer matrix produced more hydrophilic films (water contact angle reduced from 80 to 60). Polyurethanes from PCL and HDI in the absence of any solvent, initiator, catalyst or chain extender were successfully synthesized and this kind of synthesis enhanced biocompatibility and increased the potential of polymers for use in biomedical applications.

Diisocyanates (dNCO) such as methylene diphenyl diisocyanate (MDI) are used primarily as cross-linking agents in the production of polyurethane products such as paints, elastomers, coatings and adhesives, and are the most frequently reported cause of chemically induced immunologic sensitization and occupational asthma (OA). Immune mediated hypersensitivity reactions to dNCOs include allergic rhinitis, asthma, hypersensitivity pneumonitis and allergic contact dermatitis. There is currently no simple diagnosis for the identification of dNCO asthma due to the variability of symptoms and uncertainty regarding the underlying mechanisms. Immunological sensitization due to dNCO exposure is traditionally thought to require initial conjugation of the dNCO to endogenous proteins to generate neoantigens, which trigger production of dNCO specific T lymphocytes and ultimately dNCO specific IgE. Testing for dNCO-specific IgE, for diagnosis of dNCO asthma is however, only specific (96-98%) but not sensitive (18-27%). The low prevalence of detectable dNCO specific IgE has been attributed to both assay limitations and a potential IgE-independent dNCO asthma mechanism(s). The identity of the conjugated proteins responsible for the sensitization also remains unknown. It is also not clear whether dNCOs bind to extracellular, cell membrane, or intracellular proteins as a way of triggering non-IgE asthma. Standardization and optimization of immunoassays used to screen for dNCO specific antibodies in sera is important if its utility as a dNCO asthma diagnostic tool is to be achieved. This will potentially improve sensitivity and allow comparison of results across studies. Current studies on assays of dNCO-specific IgE and IgG lack or have limited characterization of the conjugates used. Diisocyanates bound to hemoglobin (Hb), human serum albumin (HSA), and THP-1 proteins were quantified by HPLC with fluorescence detection. Proteomic tandem mass spectrometry (MS) was used to delineate TDI and MDI specific amino acid binding sites on Hb as well as identification of proteins from MDI exposed THP-1 cells. The trinitrobenzene sulfonic acid assay (TNBS) and SDS gel electrophoresis were used to evaluate extent of intra and intermolecular cross-linking in dNCO-HSA conjugates. Binding of monoclonal antibodies (mAbs) to dNCO bound proteins in enzyme-linked immunosorbent assay (ELISA) was used to evaluate antigenicity of dNCO-protein conjugates. The amount of dNCO binding to HSA and Hb increased with the concentration of the dNCO used for conjugation. All the dNCOs reacted with HSA more than with Hb. Eight binding sites were observed with both MDI and TDI on Hb. The N-terminal valines of both the alpha and beta subunits on Hb, lysine 40 of the alpha subunit and lysine 61 of the beta subunit were common binding sites for both TDI and MDI. Lysine 7 of the alpha subunit and lysines 8, 65 and 66 of the beta subunit were unique to MDI. On the other hand, lysines 11, and 16 of the alpha subunit and lysines 17 and 144 of the beta subunit were unique to TDI. Protein bound MDI was detected in a dose-dependent manner in membrane and cytoplasm fractions of MDI exposed THP-1 cells. MDI was also detected in 11 of the 13 cytoplasmic protein bands. The extent of MDI intracellular protein binding was not affected by cytochalasin D, a chemical that binds actin filaments and inhibits active uptake into cells. The extent of cross-linking shown using the TNBS assay was found to increase with amount of dNCO used. Clear bands from both intra and intermolecular cross-linking were observed on all dNCO-Hb/HSA SDS gels. Using ELISA, both TDI-Hb and TDI-HSA conjugates were reactive to monoclonal antibodies produced against TDI conjugated HSA indicating that dNCO-Hb is also antigenic. The best characterization of dNCO-protein conjugates is achieved by the quantitative determination of conjugated dNCO per mole of protein as well as determining the extent of dNCO cross-linking. Although HSA is more reactive to dNCOs than other serum proteins such as Hb, contribution from other serum proteins to development of OA should not be overlooked as dNCO-Hb was found to be reactive to dNCO specific mAbs. dNCO-conjugated proteins identified in the soluble fraction of MDI exposed THP-1 cells were all of intracellular origin suggesting that MDI can cross the cell membrane and react with intracellular proteins. The entry of MDI into live cells is a passive process, as the extent of intracellular binding was not affected by cytochalasin D. The present study support the potential involvement of dNCO-haptenated membrane and intracellular proteins in development of non-IgE dNCO asthma.

D. Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology / In the present era of water resources scarcity, efficient treatment of wastewater is a major prerequisite especially for growing economy. Numerous approaches have been studied for the development of cheaper and more effective adsorbents for removal of both organic and inorganic pollutants from wastewater. The present study seeks to harness the potential of biosorption and nanotechnology by producing more efficient, selective, mechanically stable and effective adsorbents for removal of organic and inorganic pollutants. The biosorbent-magnetic nanomaterial was synthesized by coating magnetite nanoparticles with sodium hydroxide treated pine cone by co-precipitation method. Magnetite coated pine bio-composite was then modified by cross-linking with hexamethylene diisocyanate and epichlorohydrin to the molecular recognition compound “cyclodextrin”. These novel biosorbent-magnetic nanoparticle materials were explored in overcoming the drawbacks of the biosorbent alone and selectively remove inorganic and organic pollutants from complex matrices. The synthesized materials were characterized by several analytical techniques including, Fourier Transformed Infrared Spectroscopy (FTIR), Thermogravimetric analysis (TGA), X-Ray Diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM–EDX), Transmission Electron Microscopy (TEM), Brunauer, Emmett and Teller Isotherm (BET) surface area analysis, X-ray Photoelectron Spectroscopy (XPS), Vibrating Sample Magnetometer (VSM) and pH at point of zero charge (pHpzc). Sodium hydroxide treated pine cone and magnetite coated pine cone were applied for both chromium(VI) and arsenic(III) adsorption while the magnetite coated pine cone, magnetite coated pine cone crosslinked to cyclodextrin using both epichlorohydrin and hexamethylene diisocyanate were applied for 4-nitrophenol removal from aqueous solution. Batch adsorption studies were performed to optimize operating parameters such as solution pH, adsorbent dose, contact time, temperature and initial concentration. Pseudo first, pseudo second, intraparticle diffusion, pore and film diffusion kinetic models were determined to investigate the mechanism of adsorption process. Coefficient of correlation, r2, and variable error, methods were also applied in the determination of the best fit of the kinetic method. Structural characterization of magnetite coated pine cone and the magnetite coated pine crosslinked to cyclodextrin using 1,6-hexamethylene diisocyanate and epichlorohydrin were confirmed by characterization techniques applied. The adsorption of Cr(VI), As(III) and 4-nitrophenol was found to be dependent on the solution pH, adsorbent dose, initial concentration, temperature and ionic strength. Kinetic modelling revealed that the adsorption of Cr(VI), As(III) and 4-nitrophenol is controlled by pseudo second order kinetic model suggesting surface adsorption and intraparticle diffusion model. Intraparticle, pore and film diffusion models gave further insight into the controlling diffusion mechanism involved in the adsorption process for all pollutants investigated. Equilibrium studies indicated that the adsorption of all pollutants followed Langmuir isotherm indicating that adsorption sites are homogeneous in nature. The obtained thermodynamic parameters demonstrated that the adsorption of Cr(VI), As(III) and 4-nitrophenol were spontaneous, favourable and endothermic in nature. Anionic effect positively affected Cr(VI) and As(III) removal but had a negative effect on the 4-nitrophenol adsorption. Adsorption of 4-nitrophenol onto the nanocomposite adsorbents was attributed to multiple adsorbent-adsorbate interactions such as hydrogen bonding, hydrophobic attraction and guest host interaction. Magnetite coated pine better removed Cr(VI) and As(III) from aqueous solution than NaOH treated pine cone biomaterial while the magnetite coated pine crosslinked to cyclodextrin using 1,6-hexamethylene diisocyanate exhibited better adsorption performance for 4-nitrophenol removal than the nanocomposite crosslinked using epichlorohydrin and the magnetite coated pine cone.