Thermodynamic aspects in the adsorption of polynuclear aromatic hydrocarbons on chrysotile and silica – possible relation to synergistic effects in lung toxicity

Abstract

. 67,289 (1989).This study is to compare the adsorption of phenanthrene -a polynuclear aromatic hydrocarbon -(apolar molecule) and water (polar molecule) on chrysotile, a mainly ionic solid and on one silica (Aerosil), a covalent solid. The adsorption of water shows that the adsorption capacity and the interaction energies are much higher for chrysotile than for silica. With phenanthrene, the adsorption mechanism on these two materials is very different: on chrysotile-a solid with a surface having a basic character -there is a multilayer adsorption, with lateral interactions between PAH molecules vertically oriented with regard to solid surface, whereas on silica (acidic solid), the PAH molecules are adsorbed flat and form only one layer. Chrysotile turns out to be a much more powerful adsorbent than silica towards both polar molecules and apolar molecules. The calorimetric data concerning the adsorption of phenanthrene on chrysotile in xylene reveal three thermal stages, showing the influence of preadsorbed water and solvent and permit to propose a model of adsorption mechanism. The formation of multilayers of phenanthrene on chrysotile converts its marked hydrophilic surface into a hydrophobic one which may act as a carrier of organic molecules and slowly release them into the biological medium. These phenomena may provide a possible interpretation for some synergistic effects concerning lung cancers observed after asbestos and cigarette-smoke exposure.Key words: adsorption, phenanthrene, chrysotile, silica, water.JEANINE FOURNIER, BICE FUBINI, VERA BOLIS et HENRI PEZERAT. Can. J. Chem. 67,289 (1989).La comparaison des propriCtCs d'adsorption d'un solide ionique, le chrysotile avec celles d'un solide covalent, une silice (ACrosil), est fondCe sur 1'Ctude de l'adsorption d'un hydrocarbure polycyclique aromatique, le phknanthrkne (molCcule apolaire) dans le xylkne et d'une molCcule polaire a 1'Ctat gazeux, l'eau. L'adsorption de l'eau montre que la capacite' d'adsorption et 1'Cnergie d'interaction (solide-H20) sont beaucoup plus importantes dans le cas du chrysotile que dans le cas de la silice. L'adsorption du phenanthrkne differe selon le matCriau CtudiC. En effet, pour le chrysotile dont la surface prCsente un caractkre basique, les isothermes rCvklent une adsorption en multicouches avec la presence d'interactions IatCrales entre les moltcules adsorbies, ces molCcules Ctant orientCes verticalement par rapport la surface. Par contre, pour la silice, seule une monocouche est formCe avec des molCcules adsorbtes 2 plat. Tous ces rCsultats font apparaitre que le chrysotile a une capacitC d'adsorption pour le phknanthrkne et pour l'eau trks supCrieure a celle de la silice. La presence de trois Ctapes thermiques lors de I'adsorption du phinanthrkne sur le chrysotile rCvkle l'influence du solvant et de l'eau prCadsorbCe. Ces donnCes calorimttriques permettant de proposer un modkle de mecanisme d'adsorption. La surface du chrysotile, initialement hydrophile devient hydrophobe du fait de la prksence de multicouches de ...

Exposure to Diesel Motor Exhaust and Lung Cancer Risk in a Pooled Analysis from Case-Control Studies in Europe and Canada

“…[113][114][115][116] The mechanism may be linked to the strong ability of asbestos fibres to effectively bind PAHs and to deliver them to cells of the lung. [117][118][119] However, our results concerning a synergistic effect were not statistically significant and therefore need to be replicated in other populations before a conclusion can be reached. Table 5 shows the OR for lung cancer following occupational exposure to individual agents, groups of agents, and for the group of agents overall in men.…”

Surface reactivity in the pathogenic response to particulates.

“…On leached fibers, strong adsorption of proteinaceous material may take place, which eventually would protect the body from direct contact with the fiber. However, adsorption of PAHs is weaker with leached than with the original chrysotile, which suggests that solids with a basic character (asbestos, magnesia) have more affinity for PAHs than those with an acidic one (silica, alumina) (14).…”

“…Polyaromatic hydrocarbons (PAHs) are adsorbed at the asbestos surface to a larger extent than on other solids such as silica or glass fibers (12)(13)(14). The surface concentration of PAHs attained is higher because on asbestos the PAH molecule is polarized and adsorbed vertically and not horizontally, as on silica.…”

“…The surface concentration of PAHs attained is higher because on asbestos the PAH molecule is polarized and adsorbed vertically and not horizontally, as on silica. Multiple layers of vertically packed molecules build up and bind strongly to the surface (14). This may be related to the well-established synergistic effect of tobacco smoking and asbestos exposure on the risk of lung cancer; the relevant mechanism in still under debate (15 (16).…”

Surface Reactivity in the Pathogenic Response to Particulates

“…The surface concentration of PAHs attained is higher because on asbestos the PAH molecule is polarized and adsorbed vertically and not horizontally, as on silica. Multiple layers of vertically packed molecules build up and bind strongly to the surface (14). This may be related to the well-established synergistic effect of tobacco smoking and asbestos exposure on the risk of lung cancer; the relevant mechanism in still under debate (15).…”