Modelling Zn (II) sorption onto clayey sediments using a multi-site ion-exchange model

International audienceIn environmental studies, we need to be able to predict the behaviour of contaminants in more or less complex physico-chemical contexts. The improvement of this prediction partly depends on establishing thermodynamic models that can describe the behaviour of these contaminants and, in particular, the sorption reactions on mineral surfaces. In this way, based on the mass action law, it is possible to use surface complexation models and ion exchange models. Therefore, the aim of this study is i) to develop an ion-exchange model able to describe the sorption of transition metal onto pure clay minerals and ii) to test the ability of this approach to predict the sorption of these elements onto natural materials containing clay minerals (i.e. soils/sediments) under various chemical conditions. This study is focused on the behaviour of Zn(II) in the presence of clayey sediments. Considering that clay minerals are cation exchangers containing multiple sorption sites, it is possible to interpret the sorption of Zn(II), as well as competitor cations, by ion-exchange equilibria with the clay minerals. This approach is applied with success to interpret the experimental data obtained previously in the Zn(II)-H+-Na+-montmorillonite system [Baeyens, B., Bradbury, M.H., 1997. A mechanistic description of Ni and Zn sorption on Na-montmorillonite. Part I: Titration and sorption measurements. J. Contam. Hydrol. 27, 199–222]. Our research team has already studied the behaviour of Na+, K+, Ca2+ and Mg2+ versus pH in terms of ion exchange onto pure montmorillonite, leading us to develop a thermodynamic database including the exchange site concentrations associated with montmorillonite and the selectivity coefficients of Na+, K+, Ca2+, Mg2+, and Zn2+ versus H+. In the present study, we report experimental isotherms of Zn(II) on two different sediments in batch reactors at different pH and ionic strengths, using NaCl and CaSO4 as electrolytes. Assuming clay minerals are the main ion-exchanging phases, it is possible to predict Zn(II) sorption onto sediments under different experimental conditions, using the previously obtained data base on montmorillonite. Whatever the physico-chemical conditions tested, we observe a relatively good agreement between experimental results and the predicted sorption behaviour

Detection and long-term quantification of methane emissions from an active landfill

Landfills are a significant source of fugitive methane (CH4) emissions, which should be precisely and regularly monitored to reduce and mitigate net greenhouse gas emissions. In this study, we present long-term, in situ, near-surface, mobile atmospheric CH4 mole fraction measurements (complemented by meteorological measurements from a fixed station) from 21 campaigns that cover approximately 4 years from September 2016 to December 2020. These campaigns were utilized to regularly quantify the total CH4 emissions from an active landfill in France. We use a simple atmospheric inversion approach based on a Gaussian plume dispersion model to derive CH4 emissions. Together with the measurements near the soil surface, mainly dedicated to the identification of sources within the landfill, measurements of CH4 made on the landfill perimeter (near-field) helped us to identify the main emission areas and to provide some qualitative insights about the rank of their contributions to total emissions from the landfill. The two main area sources correspond, respectively, to a covered waste sector with infrastructure with sporadic leakages (such as wells, tanks, pipes, etc.) and to the last active sector receiving waste during most of the measurement campaigns. However, we hardly managed to extract a signal representative of the overall landfill emissions from the near-field measurements, which limited our ability to derive robust estimates of the emissions when assimilating them in the atmospheric inversions. The analysis shows that the inversions based on the measurements from a remote road further away from the landfill (far-field) yielded reliable estimates of the total emissions but provided less information on the spatial variability of emissions within the landfill. This demonstrates the complementarity between the near- and far-field measurements. According to these inversions, the total CH4 emissions have a large temporal variability and range from ∼ 0.4 to ∼ 7 t CH4 d−1, with an average value of ∼ 2.1 t CH4 d−1. We find a weak negative correlation between these estimates of the CH4 emissions and atmospheric pressure for the active landfill. However, this weak emission–pressure relationship is based on a relatively small sample of reliable emission estimates with large sampling gaps. More frequent robust estimations are required to better understand this relationship for an active landfill.</p

Preclinical pharmacokinetics and metabolism of a novel prototype DNA-PK inhibitor NU7026

In this study we investigated the in vitro time dependence of radiosensitisation, pharmacokinetics and metabolism of NU7026, a novel inhibitor of the DNA repair enzyme DNA-dependent protein kinase (DNA-PK). At a dose of 10 μM, which is nontoxic to cells per se, a minimum NU7026 exposure of 4 h in combination with 3 Gy radiation is required for a significant radiosensitisation effect in CH1 human ovarian cancer cells. Following intravenous administration to mice at 5 mg kg−1, NU7026 underwent rapid plasma clearance (0.108 l h−1) and this was largely attributed to extensive metabolism. Bioavailability following interperitoneal (i.p.) and p.o. administration at 20 mg kg−1 was 20 and 15%, respectively. Investigation of NU7026 metabolism profiles in plasma and urine indicated that the compound undergoes multiple hydroxylations. A glucuronide conjugate of a bis-hydroxylated metabolite represented the major excretion product in urine. Identification of the major oxidation site as C-2 of the morpholine ring was confirmed by the fact that the plasma clearance of NU7107 (an analogue of NU7026 methylated at C-2 and C-6 of the morpholine ring) was four-fold slower than that of NU7026. The pharmacokinetic simulations performed predict that NU7026 will have to be administered four times per day at 100 mg kg−1 i.p. in order to obtain the drug exposure required for radiosensitisation

The transcriptional landscape of polyploid wheat

Ramirez-Gonzalez RH, Borrill P, Lang D, et al. The transcriptional landscape of polyploid wheat. SCIENCE. 2018;361(6403): eaar6089

"Adaptive response" - some underlying mechanisms and open questions

Organisms are affected by different DNA damaging agents naturally present in the environment or released as a result of human activity. Many defense mechanisms have evolved in organisms to minimize genotoxic damage. One of them is induced radioresistance or adaptive response. The adaptive response could be considered as a nonspecific phenomenon in which exposure to minimal stress could result in increased resistance to higher levels of the same or to other types of stress some hours later. A better understanding of the molecular mechanism underlying the adaptive response may lead to an improvement of cancer treatment, risk assessment and risk management strategies, radiation protection, e. g. of astronauts during long-term space flights. In this mini-review we discuss some open questions and the probable underlying mechanisms involved in adaptive response: the transcription of many genes and the activation of numerous signaling pathways that trigger cell defenses - DNA repair systems, induction of proteins synthesis, enhanced detoxification of free radicals and antioxidant production.Publisher PDFPeer reviewe