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Radiocarbon content in biogenic samples is widely used to study the variation of atmospheric CO 2 due to anthropogenic activities. A total of 26 samples of evergreen and deciduous tree leaves, as well as seasonal small plant leaves, were analyzed for this study. Sampling was carried out at the end of the vegetation season from rural villages surrounding a cement factory in Mount Lebanon Province, Lebanon. Reference samples of identical species were collected during the same period from a clean zone. The conventional 14 C method was used for the determination of Δ 14 C values. The data showed that the 14 C concentration in the studied sites was significantly lower than the clean area, due to the release of anthropogenic CO 2 . In order to estimate the Suess effect, the fossil fuel fraction was determined based on equations of mass balance for CO 2 concentration, stable isotopic composition of carbon, and 14 C concentration. The results showed that selected locations are affected differently according to their distance from the factory and the wind direction.

Abstract:A new radiocarbon laboratory has been established recently at the Lebanese Atomic Energy Commission. This laboratory consists of benzene synthesis line and a low background liquid scintillation counter, Tri-Carb 3180 TR/SL for measurements with Bismuth Germanate (BGO) guard detector. The effectiveness of the benzene line was tested firstly by preparing benzene from a wood sample after carbide and acetylene receiving. Normalization and standardization of the liquid scintillation counter was carried out, as well as the Factor of Merit (E2/B) was determined for three different counting regions. To assure accuracy and reliability of results, reference materials were used. Based on z-score and u-score evaluation, as well as Student's t-test, acceptable data were obtained from travertine and wood samples available through the International Atomic Energy Agency (IAEA-C2 and IAEA-C5), and humic acid (U) and murex shell (R) from the Fifth International Radiocarbon Intercomparison (VIRI). After that, a preliminary study was done, which is the base for future research in order to assess the anthropogenic impact and degree of environmental pollution in terms of radiocarbon isotope ratio (Δ 14 C) deduced from the Percent Modern Carbon or PMC. This work represents the results of four reference materials and those of five green grass samples. The Δ 14 C of green grass samples collected from two different clean zones were found to be 50‰ and 52‰, while the values of those collected from different polluted zones were 23‰, 7‰ and 15‰.

The determination of radiocarbon content in biogenic samples such as tree leaves and short-lived plants is crucial when studying the anthropogenic impact on the ecosystem and for detecting any alteration in stable and radioactive CO 2 . A total of 76 samples of evergreen and deciduous tree leaves as well seasonal plants were collected in winter, spring, and summer. Sampling was carried out from rural villages located in Mount Lebanon Province, Lebanon. Based on the data obtained from a previous study carried out in autumn, which showed that the selected sites are characterized by depletion of 14 C caused by the releases of pollutants and CO 2 from a cement factory in the region, further investigation was carried out in the present work to determine possible significant seasonal variations in Δ 14 C values. Reference samples of identical species were collected in the same period from a clean zone. The conventional 14 C method was used to determine the carbon isotopic ratio. Δ 14 C data are compared to those obtained in autumn. 14 C concentration in the studied sites was significantly lower than in the clean area in all seasons. ANOVA tests showed that there is a significant seasonal variation for deciduous leaves and seasonal plants, while this difference was not significant in evergreen leaves. In addition, no significant variation was recognized for different species in the same season.

Since the primary factor contributing to the internal effective dose in the human organism is contaminated food, the control of radionuclides in food represents the most important means of protection. This study was conducted to determine the levels of the dietary exposure of the Lebanese population to gamma-emitting radioisotopes. The activity concentrations of gamma-emitting radioisotopes have been measured in food samples that represent the market basket of an adult urban population in Lebanon. The artificial radionuclide (137)Cs was measured above detection limits in only fish, meat and milk-based deserts. The most abundant natural radionuclide was 40K (31-121 Bq kg(-1)), with the highest content in fish and meat samples. The annual mean effective dose contributed by 40K in the reference typical diet was estimated equal to 186 microSv y(-1), a value reasonably consistent with findings reported by several other countries.