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Theses

Tracking trace elements from soil to Lebanese bread and Populations Exposure

Abstract : In Lebanon, the agri-food industry represents 18% of the industrial sector and yet food safety remains a major problem. In this interdisciplinary thesis, we followed the Trace Elements (TEs) in the Lebanese white bread sector "from farm to fork" based on the reality on the ground, and on two links in the sector: (i) the geogenic or anthropogenic origin of TEs present in the soil and their transfer to the wheat grain, for which 10 plots cultivated in wheat, covering the diversity of soils, irrigation practices and anthropogenic environments of the central Bekaa were chosen ; (ii) the exposure of populations to TEs present in bread, for which a survey of consumption habits across Lebanon was carried out on 992 individuals (children, adolescents, women and men) and the quantification of TEs present in bread from the 3 biggest bakeries.A new microwave digestion with H2SO4 + H2O2 combined with flame - Atomic Absorption Spectrometry measurement was validated with Certified Reference Material and after comparison with Hydrofluoric-based digestion. It allows routine but accurate quantification of TEs As, Cd, Cu, Co, Cr and Pb, “green” and inexpensive, suitable for calcareous or calcium-saturated Mediterranean soils.In soils, the total TE contents and the bioavailable quantity by DTPA extraction are not correlated. Thus, the B5 and B8 sites have the highest total contents, probably of geogenic origin, but B8 is richer in bioavailable forms linked to industrial activities. Likewise, the B3 and B9 sites, which have low to medium total TE contents, have on the contrary the highest bioavailable TE contents of anthropogenic origin.In wheat, the level of Cd, As and Pb was studied in roots, stems, leaves and grains. The As contents in grains are high and correlate with the DTPA-extractable As in soil, while the Pb contents in the grain are very low. The Cd content in grains is close to the threshold values. Root Cd content correlates with extractable Cd and translocation factors are often greater than 1, showing that Cd is easily transferred to grain. The high Cd content (20 mg kg-1) of phosphate fertilizers imported into Lebanon is the plausible source of this contamination, hence the importance of its monitoring.The Lebanese bread consumption survey showed that white bread is consumed the most and men the greatest consumers (282 g d-1). Arsenic, Cd, Co, Cr, Hg, Ni and Pb have been analyzed in white bread from the 3 most consumed brands. There is no health risk with respect to the elements Hg, Cd, Cr and Co, with the exception of the 95th percentile of 6-9 years old children. Exposure to nickel, on the other hand, showed an excess of total food intake up to 4 times for the most exposed populations (95th percentile). There are food safety issues related to As and Pb because the exposure margins are very low.Given the current crisis in Lebanon where it will be necessary to rely more on local production, it is important to monitor the levels of As, Cd and Pb in wheat, the relationships with the soil and environmental factors, to assess the risks to human health and identify ways to limit potential exposure to metals and metalloids. To our knowledge, this is the first time that exposure to Arsenic has been studied in the Lebanese population. These observations need to be confirmed, and there is an urgent need to determine the speciation of inorganic arsenic forms in bread.
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Submitted on : Wednesday, June 22, 2022 - 4:40:12 PM
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Nada Lebbos. Tracking trace elements from soil to Lebanese bread and Populations Exposure. Environmental and Society. Université Bourgogne Franche-Comté, 2021. English. ⟨NNT : 2021UBFCK061⟩. ⟨tel-03702029⟩

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