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Les radionucléides et le plomb émis par une usine de fertilisants au Liban : Etude de leurs mobilités dans les sols et les plantes pour une évaluation du risque sanitaire.

Abstract : The use of phosphate fertilizers and phosphate rock as raw material by fertilizer plants, and the by-product phosphogypsum, contribute in increasing the levels of natural radionuclides and trace metals in the environment. This may affect the ecosystem and human health.This study evaluates the radiological impact of natural gamma-emitting radionuclides, mainly 238U, 232Th and their decay product, and 40K. As well as, it evaluates the health impact of Pb, present in the raw material and fertilizers produced by a fertilizer plant in Lebanon.The main objective is to characterize the diffuse contamination of these pollutants with a view to assess the health risk in 9 non-cultivated residential sites around the plant. A focus on the quantitative assessment of the health risk is specifically linked to the consumption of the wild plant Dittrichia viscosa and the accidental ingestion of soil dust for the inhabitants of the study area. The concept of bioaccessibility of soil and plant Pb is integrated into these assessments. Chemical extractions using EDTA and the Physiologically Based Extraction Test (PBET) were used for in vitro estimation of available and bioaccessible Pb fractions. These were incorporated into the risk calculations. The radiological risks related to gamma ionizing radiation from radioelements were also estimated via radiological parameters.All of the work has shown that the fertilizer plant generates diffuse contamination that increases the levels of radionuclides and Pb in the near environment, specifically in soils (for 238U, 226Ra and their decay products 214Pb, 212Pb and 210Pb, as well as for Pb), and in the aerial parts of Dittrichia viscosa plants (for Pb and 210Pb). The study of the distribution of 210Pb and PbEDTA fractions provide additional information to characterize the Pb contribution due to the activity of the plant. The results showed that the mean values of activity concentrations of radioelements in soil samples were slightly higher than those determined in other Lebanese regions and worldwide average values. Based on the radiological parameters, no significant risk has been identified for the population frequenting the area.The pseudo-total soil Pb concentrations were below the applied thresholds. Threshold exceedances were observed for Pb levels in Dittrichia viscosa leaves.Two health risk assessment schemes for Pb were studied: a first classical scheme based on the hypothesis of the total ingestion of total Pb levels in soils and plants; a second scheme where only fractions reaching the systemic circulation have been measured and considered in risk calculations. These two schemes were studied for two high-exposure field scenarios. Taking into account the bioaccessible Pb concentrations in the calculations greatly reduces (at least by a factor of 10) the potential risk for both scenarios, whereas the classical risk calculations show a significant risk for the children. Whatever the chosen risk calculation scheme, ingestion of plants remains the main route of exposure for the two maximalist scenarios.
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Submitted on : Friday, January 10, 2020 - 4:45:08 PM
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Dany Saba. Les radionucléides et le plomb émis par une usine de fertilisants au Liban : Etude de leurs mobilités dans les sols et les plantes pour une évaluation du risque sanitaire.. Environnement et Société. Université Paris Saclay (COmUE), 2019. Français. ⟨NNT : 2019SACLA025⟩. ⟨tel-02435279⟩



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