Application of internal standard method in recombinant luminescent bacteria test

Mercury and its organic compounds have been of severe concern worldwide due to their damage to the ecosystem and human health. The development of effective and affordable technology to monitor and signal the presence of bioavailable mercury is an urgent need. The Mer gene is a mercury-responsive resistant gene, and a mercury-sensing recombinant luminescent bacterium using the Mer gene was constructed in this study. The mer operon from marine Pseudomonas putida strain SP1 was amplified and fused with prompterless luxCDABE in the pUCD615 plasmid within Escherichia coli cells, resulting in pTHE30–E. coli. The recombinant strain showed high sensitivity and specificity. The detection limit of Hg^2 + was 5 nmol/L, and distinct luminescence could be detected in 30 min. Cd^2 +, Cu^2 +, Zn^2 +, Ca^2 +, Pb^2 +, Mg^2 +, Mn^2 +, and Al^3 + did not interfere with the detection over a range of 10^− 5–1 mM. Application of recombinant luminescent bacteria testing in environmental samples has been a controversial issue: especially for metal-sensing recombinant strains, false negatives caused by high cytotoxicity are one of the most important issues when applying recombinant luminescent bacteria in biomonitoring of heavy metals. In this study, by establishing an internal standard approach, the false negative problem was overcome; furthermore, the method can also help to estimate the suspected mercury concentration, which ensures high detection sensitivity of bioavailable Hg^2 +.     

Role of NO in Hg oxidation over a commercial selective catalytic reduction catalyst V2O5–WO3/TiO2

Experiments were conducted in a fixed-bed reactor that contained a commercial catalyst, V₂O₅–WO₃/TiO₂, to investigate mercury oxidation in the presence of NO and O₂. Mercury oxidation was improved by NO, and the efficiency was increased by simultaneously adding NO and O₂. With NO and O₂ pretreatment at 350°C, the catalyst exhibited higher catalytic activity for Hg⁰ oxidation, whereas NO pretreatment did not exert a noticeable effect. Decreasing the reaction temperature boosted the performance of the catalyst treated with NO and O₂. Although NO promoted Hg⁰ oxidation at the very beginning, excessive NO counteracted this effect. The results show that NO plays different roles in Hg⁰ oxidation; NO in the gaseous phase may directly react with the adsorbed Hg⁰, but excessive NO hinders Hg⁰ adsorption. The adsorbed NO was converted into active nitrogen species (e.g., NO₂) with oxygen, which facilitated the adsorption and oxidation of Hg⁰. Hg⁰ was oxidized by NO mainly by the Eley–Rideal mechanism. The Hg⁰ temperature-programmed desorption experiment showed that weakly adsorbed mercury species were converted to strongly bound ones in the presence of NO and O₂.     

负载NH4+-N生物炭对土壤N2O-N排放和NH3-N挥发的影响

利用生物炭吸附面源污染水体NH₄⁺-N并将其进行还田可实现此氮资源由水体到农田的安全有效迁移,而探索负载NH₄⁺-N生物炭对N₂O-N排放和NH₃-N挥发的影响则对于减施化肥和降低土壤氮素损失意义重大.本研究采用土柱试验,设置4个处理：对照（不施氮肥,CK）、单施化肥（NPK）、负载氮+化学磷钾肥（N-BC+PK）和生物炭+化肥（BC+NPK）.结果表明,相较NPK和BC+NPK处理,N-BC+PK处理N₂O-N累积排放量、NH₃-N累积挥发量、气态氮素累积损失量（以N计）分别显著降低了33.62%和24.64%、70.64%和79.29%、64.97%和73.75%（P<0.05）.特别需要说明的是,BC+NPK处理相比NPK处理显著增加了NH₃-N累积挥发量（P<0.05）.综上所述,负载NH₄⁺-N生物炭可显著减少N₂O-N排放和NH₃-N挥发,且其减排效果显著优于传统的生物炭化肥配施.本研究结果将为富营养化水体NH₄⁺-N农田回用和土壤气态氮素减排提供理论依据和数据支持.     

Temporal and geographical variations of mercury and selenium in eggs of Larus michahellis and Larus audouinii from central Mediterranean islands

In this study, we determined mercury and selenium levels in abandoned unhatched eggs of the yellow-legged gull (Larus michahellis) and Audouin’s gull (Larus audouinii) collected during 2004–2005 from the Tuscan archipelago and Sardinia (Italy). The different feeding habits of the two species probably determine the different uptakes of trace elements, as the study shows highly significant differences for selenium and mercury levels as well as shell thickness and Hg:Se molar ratio values. Audouin’s gulls nesting on the coasts of the Tuscan archipelago showed significantly higher selenium levels than did gulls from colonies from the islands around Sardinia. Comparisons with a similar investigation previously conducted in the same area suggested that mercury and selenium concentrations, although in line with reports in the literature, were significantly lower than levels encountered in gulls in the early 1980s. Mercury (mg/kg d.w.) dropped from 8.631 to 5.030 in Audouin’s gulls and from 2.509 to 0.828 in yellow-legged gulls. The regional decline in mercury levels following reduced use of the metal in industry and the probable food depletion effects linked to the overfishing of fish prey of these two gull species are discussed as hypotheses that could explain the decrease in mercury levels found in eggs.     

Development and case study of a new-generation model-VAT for analyzing the boundary conditions influence on atmospheric mercury simulation

Atmospheric models are essential tools to study the behavior of air pollutants. To interpret the complicated atmospheric model simulations, a new-generation Model Visualization and Analysis Tool (Model-VAT) has been developed for scientists to analyze the model data and visualize the simulation results. The Model-VAT incorporates analytic functions of conventional tools and enhanced capabilities in flexibly accessing, analyzing, and comparing simulated results from multi-scale models with different map projections and grid resolutions. The performance of the Model-VAT is demonstrated by a case study of investigating the influence of boundary conditions (BCs) on the ambient Hg formation and transport simulated by the CMAQ model over the Pearl River Delta (PRD) region. The alternative BC options are taken from (1) default time-independent profiles, (2) outputs from a CMAQ simulation of a larger nesting domain, and (3) concentration files from GEOS-Chem (re-gridded and re-projected using the Model-VAT). The three BC inputs and simulated ambient concentrations and deposition were compared using the Model-VAT. The results show that the model simulations based on the static BCs (default profile) underestimates the Hg concentrations by ~6.5%, dry depositions by ~9.4%, and wet depositions by ~43.2% compared to those of the model-derived (e. g. GEOS-Chem or nesting CMAQ) BCs. This study highlights the importance of model nesting approach and demonstrates that the innovative functions of Model-VAT enhances the efficiency of analyzing and comparing the model results from various atmospheric model simulations.

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摄入负载镉生物炭对斑马鱼的异常行为分析

为了评估生物炭对镉的固定能力,以负载镉生物炭为研究对象,构建大型水蚤(Daphnia magna)-斑马鱼(Zebrafish)的简单食物链,试验周期包括14 d的积累期和7 d的净化期.通过描述鱼群实验(Shoaling)、社会偏好实验(Social Preference)行为变化及斑马鱼中镉的富集量来评估负载镉生物炭的生物毒性.结果表明,在积累期摄入负载镉生物炭会显著抑制斑马鱼的运动能力,而摄入未负载镉生物炭对斑马鱼的活动无明显影响.摄入负载镉生物炭也导致群体偏好显著降低,表现为斑马鱼在社会区域内停留的时间变短,鱼群之间的距离增大.净化期中,斑马鱼的运动能力得到显著提升,同时表现出群聚性的特征.此外,斑马鱼肠道内的镉含量与其行为表现呈显著相关性.生物炭的固定作用和排泄导致不同剂量组斑马鱼肠道内的镉含量相近并缓解了镉在斑马鱼身体内的迁移.本研究揭示负载镉生物炭会破坏斑马鱼的社会行为,但生物炭的固定能力能缓解这种异常变化.     

Mercury removal from flue gas using nitrate as an electron acceptor in a membrane biofilm reactor

Membrane bioreactor achieved mercury removal using nitrate as an electron acceptor. The biological mercury oxidation increased with the increase of oxygen concentration. Ferrous sulfide could make both Hg²⁺ and MeHg transform into HgS-like substances. Nitrate drives mercury oxidation through katE, katG, nar, nir, nor, and nos. Mercury (Hg⁰) is a hazardous air pollutant for its toxicity, and bioaccumulation. This study reported that membrane biofilm reactor achieved mercury removal from flue gas using nitrate as the electron acceptor. Hg⁰ removal efficiency was up to 88.7% in 280 days of operation. Oxygen content in flue gas affected mercury redox reactions, mercury biooxidation and microbial methylation. The biological mercury oxidation increased with the increase of oxygen concentration (2%‒17%), methylation of mercury reduced with the increase of oxygen concentration. The dominant bacteria at oxygen concentration of 2%, 6%, 17%, 21% were Halomonas, Anaerobacillus, Halomonas and Pseudomonas, respectively. The addition of ferrous sulfide could immobilize Hg²⁺ effectively, and make both Hg²⁺ and MeHg transform into HgS-like substances, which could achieve the inhibition effect of methylation, and promote conversion of mercury. The dominant bacteria changed from Halomonas to Planctopirus after FeS addition. Nitrate drives mercury oxidation through katE, katG, nar, nir, nor, and nos for Hg⁰ removal in flue gas.