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Background & Aims of the Study: Heavy metals pollution in aquatic ecosystems threats living organisms' health and environment. Hence, the present study aims to assess concentration of lead, chromium, copper, zinc and their ecological risk in the surface sediments of the Bashar River during the summer and winter seasons. Materials & Methods: This is a field study; sampling of surface sediment was done in 8 stations in 2016. The samples were digested by the composition of ratio of 1:4 Percholoric acid and Nitric acid and then were analyzed by atomic absorption spectrophotometry. Statistical analysis of all data was also done using SPSS 21 and various criteria were used to fine the amount of contamination of heavy metals. Results: The results showed that the average total concentration of Zn, Cu, Pb and Cr in the summer were (48.16, 39.2, 14.45 and 10.35) and as for winter was (39.88, 26.93, 12.23 and 10.301) mg/kg respectively. In addition, evaluating geo-accumulation indexes, pollution load and pollution factor indicated the low pollution status of the area in both seasons. Conclusions: According to the results, pollution status and the RI level of heavy metals in the Bashar River is low and similar in summer and winter. Also, the sources and changes in elements concentration in different stations and seasons may be as a result of the institution of various urban and industrial contamination sources along the river, and its physical and geobiochemical changes in water flow volume entering the river, especially in winter.

The unique porosity of single-and multi-walled carbon nanotubes has prompted considerable interest in their gas adsorption properties. Among all gases, the interactions of oxygen with single-wall carbon nanotubes are widely studied. Sensitivity of their electronic properties to oxygen exposure can be used as the basis for a chemical sensor. Recent studies have shown that the transport properties of single-walled nanotubes change dramatically upon exposure to oxygen molecules. Practical applications for the production of better gas sensors as thermoelectric nano-nos is a key issue in the subject. Also, oxygen molecules could affect transport properties indirectly, by binding to donor or acceptor centers in the substrate or at the contacts or directly, by binding to the nanotube. Oxygen gas could be physisorbed via dispersive van der Waals forces or chemisorbed via formation of a chemical bond, and adsorption could take place either on perfect nanotube walls or at defect sites. We review the recent works published on the both theoretical and experimental study of adsorption data concerning the oxygen gas on the carbon nanotube materials.

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