PHD defense of Ronagul Turganova

This thesis explores the bioavailability of soil-bound trace elements (TEs) and persistent organic pollutants (POPs), focusing on their widespread occurrence in soil matrices and potential risks to the environment and human health. ETs such as chromium (Cr) and nickel (Ni) occur naturally in the earth's crust and are essential micronutrients in small quantities. However, industrial activities such as metallurgical processes, leather tanning and inappropriate waste disposal have led to soil contamination. Cr and Ni exist in different forms, with Cr (III) and Cr (VI) and Ni (II) being of particular concern due to their toxicity and carcinogenic potential. Cr (VI) and Ni (II) are highly toxic and present significant environmental risks, which underlines the need to accurately estimate their presence in soils. Soil contamination is complex, with the simultaneous presence of various compounds. Among these, POPs such as polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) are of particular concern because of their high lipophilicity, bioaccumulation potential and resistance to degradation. Although PCBs and DDT have been banned for decades, they persist in the environment and continue to present health risks.Currently, bioavailability is often estimated on the basis of the total concentration of contaminants in the soil, which can lead to an overestimation of the risks. This study therefore aims to integrate precise methods for assessing the bioavailability of ETs and POPs and to explore strategies for reducing their impact on the environment. In vivo and in vitro models were used. The bioavailability of Cr and Ni was assessed in piglets after oral exposure, by extending a model previously used to assess the bioavailability of Cd and Pb (Caboche, 2009). With regard to POPs, the bioavailability of highly hydrophobic compounds such as PCBs was studied using an improved physiological extraction test relative to Tenax (rTI-PBET), using Tenax as the adsorbent. In addition, bioavailability reduction strategies, in particular the use of biochar (BC) and activated carbon (AC), were tested for DDT and its metabolites in order to reduce the risk of soil contamination. To complete these assessments, the mutagenicity of NDL-PCB and DDT was evaluated using the Ames test, including tests on DDT-contaminated soil treated with BC and AC. The results showed that the relative bioavailability of Cr was lower than that of Ni in different types of soil, indicating that Cr is less mobile in soils. In contrast, in vitro assessments of NDL-PCBs showed low bioaccessibility (BA%) compared to in vivo ABR results, suggesting the need for further refinement of the assay to obtain more accurate predictions. Reducing the bioavailability of DDT using BC and AC proved effective, particularly at higher amendment rates (2%) and with finely ground particles. Mutagenicity tests showed that soils contaminated with PCBs and DDTs had mutagenic activity, while soils treated with BC and AC showed no mutagenic effects, confirming the effectiveness of the reduction strategy.Overall, these results improve understanding of bioavailability and its reduction, contributing to more accurate risk assessments and effective mitigation strategies for soil contamination, ultimately supporting efforts to protect human health.