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We studied the environmental impact (gaseous emissions) of using scrap tires as a fuel substitute at a cement plant that produces one million tons of cement per year. Using a combination of tires and coal as opposed to only coal caused variations in the pollutant emission rate. The study recorded a 37% increase in the rate of emission for CO, a 24% increase for SO2, an 11% decrease for NOx, and a 48% increase for HCl when tires were included. The rate of emission for metals increased 61% for Fe, 33% for Al, 487% for Zn, 127% for Pb, 339% for Cr, 100% for Mn, and 74% for Cu, and decreased 22% for Hg. On the other hand, the emission rate of organic compounds dropped by 14% for polycyclic aromatic hydrocarbons, 8% in naphthalene, 37% in chlorobenzene, and 45% in dioxins and furans. We used a Gaussian model of atmospheric dispersion to calculate the average pollutant concentration (1-h, 24-h, and annual concentrations) in the ambient air at ground level with the help of the ISC-ST2 software program developed by the USEPA. When tires were used, we observed (i) a 12 to 24% increase in particulate matter, this range considering the concentration variation depending on the average used (1-h, 24-h, and annual basis), 31 to 52% in CO, 22 to 34% in SO2, 39 to 52% in HCl, 12 to 27% in Fe, -3 to 8% in Al, 30 to 37% in Zn, and 270 to 885% in Pb; (ii) a decrease of 8 to 13% in NOx, 9 to 13% in polycyclic aromatic hydrocarbons, 6 to 7% in naphthalene, 32 to 39% in chlorobenzene, and 32 to 45% in dioxins and furans. The results obtained showed that the maximum ground-level concentrations were well within the environmental standards (for operation with only coal as well as for operation with a combination of coal and tires).

This paper is declicntecl t o Professor Sigeru Huzinaga on the occnsion ($his 65th birthdclyANDRE G. MICHEL, CHAKIB AMELIANE-HASSANI, and NATHALIE BREDIN. Can. J. Chenl. 70, 596 (1992). In the framework of molecular mechanics conformational energy calculations, a random-search and minimization procedure is presented to characterize low-energy domains of polypeptidic structures. Rather than striving for global minima, populations of conformers are randomly generated, and their energy is minimized in order to study their intrinsic properties. The application to the opioid peptide Met-Enkephalin allowed the identification of low-energy domains that are compared with previous results of conformational studies on this molecule. Our method gives a complete overview of the conformational behaviour of the polypeptide under study, including previously reported structures as determined from experimental and theoretical studies. To illustrate the usefulness of this method to determine bioactive peptidic structures and their active conformers, the application to geometrically constrained chemotactic tripeptides is presented.Key words: peptides, conformation, theoretical prediction.ANDRT. G. MICHEL, CHAKIB AMEZIANE-HASSANI et NATHALIE BREDIN. Can. J. Chem. 70, 596 (1992). Une mCthode thCorique de caractCrisation des domaines conformationnels des molCcules polypeptidiques est presentee. Les calculs d'Cnergie conformationnelle sont effectuCs dans le cadre empirique de la mCcanique molCculaire. PlutBt que chercher B localiser le minimum global d'une hypersurface CnergCtique, des populations de conform6res sont gCnCrees en vue d'en Ctudier les propriCtCs intrinskques. L'application au peptide opiact Met-Enktphaline a permis d'identifier des domaines dans la population gCnerCe et de comparer ces rCsultats des Ctudes conformationnelles antkrieures. On dCmontre que cette approche fournit une vue complkte du comportement conformationnel du polypeptide, incluant les structures proposkes par des travaux thCoriques ou expCrimentaux. Afin d'illustrer I'applicabilitC de la mCthode pour I'identification de conformation d'intCr&t biologique, une Ctude a kt6 menCe sur des tripeptides chimiotactiques a gCometrie restreinte.

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