How iron-bearing minerals affect the biological reduction of Sb(V): A newly discovered function of nitrate reductase

As a toxic element of global concern, the elevated concentration of antimony (Sb) in the environment has attracted increasing attention. Microorganisms have been reported as important driving forces for Sb transformation. Iron (Fe) is the most important metal associated element of Sb, however, how Fe-bearing minerals affect the biological transformation of Sb is still unclear. In this study, the effects of Fe-bearing minerals on biological Sb(V) reduction were investigated by employing a marine Shewanella sp. CNZ-1 (CNZ-1). Our results showed that the presence of hematite, magnetite and ferrihydrite (1 g/L) resulted in a decrease in Sb(III) concentration of ~19-31 % compared to the Fe(III)-minerals free system. The calculated Sb(V) reduction rates are 0.0256 (R2 0.71), 0.0389 (R2 0.87), 0.0299 (R2 0.96) and 0.0428 (R2 0.95) h-1 in the hematite-, magnetite-, ferrihydrite-supplemented and Fe(III)-minerals free systems, respectively. The cube-shaped Sb2O3 was characterized as a reductive product by using XRD, XPS, FTIR, TG and SEM approaches. Differential proteomic analysis showed that flagellar protein, cytochrome c, electron transfer flavoprotein, nitrate reductase and polysulfide reductase (up-regulation >1.5-fold, p value <0.05) were supposed to be included in the electron transport pathway of Sb(V) reduction by strain CNZ-1, and the key role of nitrate reductases was further highlighted during this reaction process based on the RT-qPCR and confirmatory experiments. Overall, these findings are beneficial to understand the environmental fate of Sb in the presence of Fe-bearing minerals and provide guidance in developing the bacteria/enzyme-mediated control strategy for Sb pollution.

alterniflora and mudflat regions

Elevated sediment-bound trace elements and iron-bearing minerals in intertidal habitats have been drawing more attention, but there is rarely a comparative study assessing these features between halophyte plants habitat and mudflats. In this paper, sediment samples were collected in S. alterniflora and the corresponding mudflat at 7 typical intertidal habitats (Chongming, Xiapu, Yueqing, Yunxiao, Zhanjiang, Beihai, and Zhuhai) from north to south of China, respectively. Trace element concentrations, including arsenic (As), mercury (Hg), cadmium (Cd), antimony (Sb) and scandium (Sc), and magnetic characteristics were determined. Variations in sediment-bound As, Hg, Cd, Sb were associated with S. alterniflora. Accumulations of sediment-bound As, Hg, Sb, Cd and Sc in S. alterniflora in Beihai were much higher than those in the mudflat. Concentration of sediment-bound As, Hg, Sb, Cd and Sc in S. alterniflora and mudflat were comparable in Yueqing, Xiapu, Yunxiao and Zhanjiang, respectively. Variations in low-frequency susceptibility, susceptibility of anhysteretic remanence magnetization, saturation isothermal remanence magnetization and frequency dependent susceptibility can explain the site-dependent accumulation of magnetic minerals in intertidal habitats. S. alterniflora tend to deplete sediment magnetic concentration and enhance sediment-bound As, Hg, and Sb concentration. The results of our study further revealed the coexistence of trace elements and magnetic minerals between the sampling sites and vegetative in intertidal habitats.

Soluble Fe release from iron-bearing clay mineral particles in acid environment and their oxidative potential

Soluble iron from atmospheric aerosol particles has toxicological effects on ambient environment due to their oxidative potential. However, the dissolution process and factors affecting this process are poorly understood. In this study, by solid phase characterization and aqueous dissolution experiments, we investigated the influence of acids, including HCl, H₂SO₄ and HNO₃, and H⁺ concentration on iron dissolution rate, solubility and speciation of iron in chlorite, illite, kaolinite and pyrite. The dissolution of iron-bearing clay minerals, i.e. chlorite, illite and kaolinite, was a multi-stage process with a rapid rate in the initial stage and then decreasing rate in the following stages. In contrast, the regularly crystallized pyrite proceeded with an extremely rapid dissolution rate at very beginning and then remained almost constant. In all acid solutions, the dissolution rate was in the order of pyrite > illite > chlorite > kaolinite. H₂SO₄ was stronger than HCl and HNO₃ in the destruction of mineral structures to release iron, while HNO₃ dissolved more iron in pyrite (FeS₂). High H⁺ concentration easily destroyed the mineral structures to release the structural or interlayer iron, whereas low H⁺ concentration increased the proportion of Fe (II) in clay minerals. Non-linear fitting of continuous dissolution models showed that the iron dissolution rates and iron redox speciation as functions of time were well predicted, with r² > 0.99 for chlorite and illite, and r² > 0.96 for kaolinite. Oxidative potential analysis proved that the dissolved iron possessed a considerable potential to generate reactive oxygen species.

Facile and large-scale fabrication of (Mg,Ni)(Fe,Al)2O4 heterogeneous photo-Fenton-like catalyst from saprolite laterite ore for effective removal of organic contaminants

A facile and cost effective acid leaching-coprecipitation method was developed to prepare spinel-type (Mg,Ni)(Fe,Al)₂O₄ from saprolite laterite ore in large scale. The as-prepared (Mg,Ni)(Fe,Al)₂O₄ exhibited excellent photo-Fenton-like catalytic activity in decomposing different kinds of organic dyes and antibiotic tetracycline in the present of oxalic acid (H₂C₂O₄). The influential factors of RhB degradation efficiency were investigated, including the (Mg,Ni)(Fe,Al)₂O₄ dosage, H₂C₂O₄ concentration and the intensity of simulated sunlight. Meanwhile, the reaction mechanism of (Mg,Ni)(Fe,Al)₂O₄/H₂C₂O₄/simulated sunlight system was also proposed. As the formation of highly photochemical [≡Fe(C₂O₄)₃]^3- complex ions on the surface of the (Mg,Ni)(Fe,Al)₂O₄, the obtained (Mg,Ni)(Fe,Al)₂O₄ showed degradation efficiency (η) over 90.0 % for common organic dyes and antibiotic tetracycline within 180 min under the optimum conditions. The η and TOC removal for RhB were still over 98.0 % and 46.0 % after five reuse cycles, respectively. The excellent catalytic performance and recyclability make the (Mg,Ni)(Fe,Al)₂O₄ fabricated from natural saprolite laterite ore more competitive in dealing with wastewaters contaminated by organic pollutants.