No abstract

As the largest container and resource of metals, sediment has a special role in the fate of metals. Factors influencing bioavailability of heavy metals in sediment have never been comprehensively considered and the sediment properties still fail to understand and even controversial. In this review, the mechanisms of sediment properties such as acid-volatile sulfides (AVS), organic matter, texture (clay, silt or sand) and geology, organism behaviors as well as those influencing the bioavailability of metals were analyzed. Under anoxic condition, AVS mainly reduce the solubility and toxicity of metals, while organic matters, Fe-Mn oxides, clay or silt can stabilize heavy metals in elevated oxidative-reductive potential (ORP). Other factors including the variation of pH, redox potential, aging as well as nutrition and the behavior of benthic organism in sediment also largely alter metals mobility and distribution. These factors are often inter-related, and various toxicity assessment methods used to evaluate the bioavailability of trace metals have been also discussed. Additionally, we expect that some novel synthetic materials like polysulfides, nano-materials, provide the substantial amendments for metals pollution in sediment.

Antimicrobial resistance (AMR) poses a worldwide threat to human health and biosecurity. The spread of antibiotic resistance genes (ARGs) via conjugative plasmid transfer is a major contributor to the evolution of this resistance. Although permitted as safe food additives, compounds such as saccharine, sucralose, aspartame, and acesulfame potassium that are commonly used as nonnutritive sweeteners have recently been associated with shifts in the gut microbiota similar to those caused by antibiotics. As antibiotics can promote the spread of antibiotic resistance genes (ARGs), we hypothesize that these nonnutritive sweeteners could have a similar effect. Here, we demonstrate for the first time that saccharine, sucralose, aspartame, and acesulfame potassium could promote plasmid-mediated conjugative transfer in three established conjugation models between the same and different phylogenetic strains. The real-time dynamic conjugation process was visualized at the single-cell level. Bacteria exposed to the tested compounds exhibited increased reactive oxygen species (ROS) production, the SOS response, and gene transfer. In addition, cell membrane permeability increased in both parental bacteria under exposure to the tested compounds. The expression of genes involved in ROS detoxification, the SOS response, and cell membrane permeability was significantly upregulated under sweetener treatment. In conclusion, exposure to nonnutritive sweeteners enhances conjugation in bacteria. Our findings provide insight into AMR spread and indicate the potential risk associated with the presence of nonnutritive sweeteners.

This study reports creative preparation of MnO 2 -biochar (MBR) via MnO 2 modification of biochar (BR) derived from aerobically composted swine manure. SEM coupled with EDX analyzer, TEM, XRD, BET, and FT-IR were employed to examine the surface properties and pore structures of MBR and BR. Adsorption experiments of Pb(II) and Cd(II) including isotherms, kinetics, and thermodynamics as well as the influence of pH on zeta-potential were also investigated. The results indicated that MBR showed rougher and larger surface area and pore volume than BR. In batch adsorption, MBR showed superior adsorption performance (maximum capacity for Pb 268.0 mg/g and Cd 45.8 mg/g) to BR (Pb 127.75 and Cd 14.41 mg/g). The adsorption process was pH-dependent, and the removal efficiency reached its maximum at 0.2 g/L dosage of MBR, after which it declined. Finally, X-ray photoelectron spectrometer (XPS) studies indicated the oxidative Mn 4+ on MBR, and suggested that apart from electrostatic attachment, specific adsorption (i.e., Pb/Cd−O or hydroxyl binding) and ion exchange were the removal mechanisms of metal ions. Therefore, this modification method toward BR was promising for wastewater treatment of heavy metal pollution.