Theoretical study of the O2 interaction with a tetrahedral Al4 cluster.

Employing both multireference configuration interaction (MRCI) and density functional theory (DFT) methods, we have studied the interaction of O2 with a tetrahedral Al4 cluster in the total spin triplet state. For a parallel to the base approach of O2 facing an apex of the pyramid, the O2 adsorption is hindered by a barrier. Both the MRCI and the DFT calculations show that after a small barrier, there are two local energy minima: a shallow one just above the apex atom and another deeper one below the apex atom. The latter corresponds to dissociative O2 adsorption. We discuss the implications of these findings for the understanding of O2 adsorption on defect sites of Al surfaces.

Theoretical investigation of the interaction of CH(4) with Al(2) and Al(3) neutral and charged clusters.

We have studied the interaction of CH(4) with Al(2) and Al(3) neutral and charged clusters in the two lowest lying spin states using density functional theory. These calculations, via extended search, are used to determine the stable positions of H and CH(3) near the cluster, and the transition state to break the H-CH(3) bond. In all cases, stable methyl-aluminum-hydrides are possible. The H desorption is studied by means of vibration analysis and application of transition state theory. A common observed trend is that, in breaking the H-CH(3) bond, the interacting H atom is attached to the "surface" of the clusters attracting some negative charge of approximately 0.2e. The charge transfer is illustrated using the corresponding orbitals near the transition state in conjunction with the computed Mulliken population analysis. Thermal vibrations, generally, do not enhance the reaction. In all exothermic cases, the binding energy toward CH(3)+HAl(n) (charge) increases with increasing charge of the original Al(n) ((q=-1,0,1)) cluster. Although Al lacks occupied d-orbitals, the small Al clusters reduce the (free methane) CH(3)-H dissociation barrier except for Al(3) ((q=-1,0)). The relevant reactions in desorption require approximately 400-700 degrees C.

Biomonitoring human exposure to environmental carcinogenic chemicals.

A coordinated study was carried out on the development, evaluation and application of biomonitoring procedures for populations exposed to environmental genotoxic pollutants. The procedures used involved both direct measurement of DNA or protein damage (adducts) and assessment of second biological effects (mutation and cytogenetic damage). Adduct detection at the level of DNA or protein (haemoglobin) was carried out by 32P-postlabelling, immunochemical, HPLC or mass spectrometric methods. Urinary excretion products resulting from DNA damage were also estimated (immunochemical assay, mass spectrometry). The measurement of adducts was focused on those from genotoxicants that result from petrochemical combustion or processing, e.g. low-molecular-weight alkylating agents, PAHs and compounds that cause oxidative DNA damage. Cytogenetic analysis of lymphocytes was undertaken (micronuclei, chromosome aberrations and sister chromatid exchanges) and mutation frequency was estimated at a number of loci including the hprt gene and genes involving in cancer development. Blood and urine samples from individuals exposed to urban pollution were collected. Populations exposed through occupational or medical sources to larger amounts of some of the genotoxic compounds present in the environmental samples were used as positive controls for the environmentally exposed population. Samples from rural areas were used as negative controls. The project has led to new, more sensitive and more selective approaches for detecting carcinogen-induced damage to DNA and proteins, and subsequent biological effects. These methods were validated with the occupational exposures, which showed evidence of DNA and/or protein and/or chromosome damage in workers in a coke oven plant, garage workers exposed to diesel exhaust and workers exposed to ethylene oxide in a sterilization plant. Dose reponse and adduct repair were studied for methylated adducts in patients treated with methylating cytostatic drugs. The biomonitoring methods have also demonstrated their potential for detecting environmental exposure to genotoxic compounds in nine groups of non-smoking individuals, 32P-postlabelling of DNA adducts being shown to have the greatest sensitivity.

Impact of human activities on the quality of river water: The case of Evrotas River catchment basin, Greece.

The impact of point (domestic and industrial effluents) and non-point (agricultural land runoff) pollution sources on the quality of the receiving waters of the Evrotas River (Laconia, Greece) was investigated during a monitoring study from August 1991 to August 1992. The part of the river which was located near the city of Sparta was seasonally influenced by the discharge of effluents from orange juice plants (operating during winter) and by the discharge of septage for the emptying of cesspools which are serving part of the city. The low dilution of incoming pollutants (septage) during the low water flow in summer lead to the decreasing self-purification capacity of the river and the development of septicity conditions in some of its parts. In the vicinity of intensively cultivated areas, the high concentrations of nitrogen and phosphorus which were detected in the river water during winter and spring may be partly attributed to the leaching of the applied fertilizers because of nirogen mobilization and soil erosion, following the season's precipitations. The protection of the Evrotas River water Quality must therefore include adequate treatment of the septage produced in the area, as well as the construction of wastewater treatment plants for the major industries of the area. The non-point pollution could be controlled by the restoration of the Evrotas riparian vegetation, together with a more rational use of fertilizers in the area.