In Vivo Mercury Demethylation in a Marine Fish (<i>Acanthopagrus schlegeli</i>)

Mercury (Hg) in fish has attracted public attention for decades, and methylmercury (MeHg) is the predominant form in fish. However, the in vivo MeHg demethylation and its influence on Hg level in fish have not been well-addressed. The present study investigated the in vivo demethylation process in a marine fish (black seabream, <i>Acanthopagrus schlegeli</i>) under dietary MeHg exposure and depuration and quantified the biotransformation and interorgan transportation of MeHg by developing a physiologically based pharmacokinetic (PBPK) model. After exposure, we observed a 2-fold increase of the whole-body inorganic Hg (IHg), indicating the existence of an in vivo demethylation process. The results strongly suggested that the intestine played a predominant role in MeHg demethylation with a significant rate (6.6 ± 1.7 day^–1) during exposure, whereas the hepatic demethylation appeared to be an extremely slow (0.011 ± 0.001 day^–1) process and could hardly affect the whole-fish Hg level. Moreover, demethylation in the intestine served as an important pathway for MeHg detoxification. Our study also pointed out that in vivo MeHg demethylation could influence Hg level and speciation in fish although food is the major pathway for Hg accumulation. Enhancing in vivo MeHg biotransformation (especially in the intestine) could be a potential key solution in minimizing Hg contamination in fish. The related factors involved in intestinal demethylation deserve more attention in the future

The characteristics and two-step reaction model of <i>p</i>-nitroacetophenone biodegradation mediated by <i>Shewanella decolorationis</i> S12 and electron shuttle in the presence/absence of goethite

<div><p>The current study mainly focused on the biodegradation process of <i>p</i>-nitroacetophenone (NP) in the presence and absence of goethite mediated by iron-reducing microbe (<i>Shewanella decolorationis</i> S12) and electron shuttle. The results showed that introduction of electron shuttle could obviously lead to an accumulation of biodegradation intermediate, especially in reaction systems containing high content of electron shuttle in the absence of goethite. Goethite could enhance the degree and rate of NP biodegradation. The microbial reductively generated Fe(II) played an active role in the biodegradation process. The relationship between the concentrations of biodegradation end product and the reaction times could be fitted by a consecutive reaction model with correlation coefficients (adjusted <i>R</i>²) in the range from 0.9241 to 0.9831 during the biodegradation stage from the beginning to about 250 h of incubation. However, during the subsequent biodegradation stages, in the presence and absence of goethite, transitions from the consecutive reaction model to zero-order reaction model and from the consecutive reaction model to exponential growth reaction model were observed, respectively. The newly proposed two-step reaction model will help understand the mechanism of the biodegradation process of nitroaromatic compounds and related pollutants.</p></div

Distinct toxic interactions of TiO₂ nanoparticles with four coexisting organochlorine contaminants on algae

<p>Engineered nanoparticles are increasingly discharged into the environment. After discharge, these nanoparticles can interact with co-existing organic contaminants, resulting in a phenomena referred to as ‘joint toxicity’. This study evaluated joint toxicities of TiO₂ nanoparticles (TiO₂NPs) with four different (atrazine, hexachlorobenzene, pentachlorobenzene, and 3,3′,4,4′-tetrachlorobiphenyl) organochlorine contaminants (OCs) toward algae (<i>Chlorella pyrenoidosa</i>). The potential mechanisms underlying the joint toxicity were discussed, including TiO₂NPs–OC interactions, effects of TiO₂NPs and OCs on biophysicochemical properties of algae and effects of TiO₂NPs and OCs on each other’s bioaccumulation in algae. The results indicate that coexposure led to a synergistic effect on the joint toxicity for TiO₂NPs–atrazine, antagonistic effect for TiO₂NPs–hexachlorobenzene and TiO₂NPs–3,3',4,4'-tetrachlorobiphenyl, and an additive effect for TiO₂NPs–pentachlorobenzene. There was nearly no adsorption of OCs by TiO₂NPs, and the physicochemical properties of TiO₂NPs were largely unaltered by the presence of OCs. However, both OCs and NPs affected the biophysicochemical properties of algal cells and thereby influenced the cell surface binding and/or internalization. TiO₂NPs significantly increased the bioaccumulation of each OC. However, with the exception of atrazine, the bioaccumulation of TiO₂NPs decreased when used with each OC. The distinct joint toxicity outcomes were a result of the balance between the increased toxicities of OCs (increased bioaccumulations) and the altered toxicity of TiO₂NPs (bioaccumulation can either increase or decrease). These results can significantly improve our understanding of the potential environmental risks associated with NPs.</p

Systematic and Quantitative Investigation of the Mechanism of Carbon Nanotubes’ Toxicity toward Algae

Concurrent with the increasing production and application of carbon nanotubes (CNTs) comes an increasing likelihood of CNTs presenting in the aquatic environment, and thereby potentially threatening aquatic organisms via toxic mechanisms that are, at present, poorly understood. This study systematically investigated the toxicity of three multiwalled CNT (MWCNT) samples toward a green alga (<i>Chlorella</i> sp.), focusing on examining and quantifying the contributions of five possible mechanisms to the algal growth inhibition. The results showed that the MWCNTs significantly inhibited the algal growth. The contribution of metal catalyst residues in the MWCNTs to the algal growth inhibition was negligible, as was the contribution from the MWCNTs’ adsorption of nutrient elements. The algal toxicity of MWCNTs could mainly be explained by the combined effects of oxidative stress, agglomeration and physical interactions, and shading effects, with the quantitative contributions from these mechanisms depending on the MWCNT size and concentration. At MWCNT concentrations around 96 h IC₅₀, the oxidative stress accounted for approximately 50% of the algal growth inhibition, whereas the agglomeration and physical interactions, and the shading effects each took approximately 25% of the responsibility

Vertical Distributions of Radionuclides (^239+240Pu, ²⁴⁰Pu/²³⁹Pu, and ¹³⁷Cs) in Sediment Cores of Lake Bosten in Northwestern China

Artificial radionuclides (¹³⁷Cs, ^239+240Pu, ²⁴¹Pu, ²⁴¹Am) deposited in lacustrine sediments have been used for dating as well as radionuclide source identification. In the present work, we investigated the vertical distributions of ^239+240Pu and ¹³⁷Cs activities, ²⁴⁰Pu/²³⁹Pu atom ratios, and ^239+240Pu/¹³⁷Cs activity ratios in sediment cores collected from Lake Bosten, which is the lake closest to the Lop Nor Chinese Nuclear Weapon Test site in northwestern China. Uniformly high concentrations of ^239+240Pu and ¹³⁷Cs were found in the upper layers deposited since 1964 in the sediment cores, and these were controlled by the resuspension of soil containing radionuclides from the nearby land surface. As the Chinese nuclear tests varied remarkably in yield, the mixing of the tropospheric deposition from these tests and the stratospheric deposition of global fallout has led to a ²⁴⁰Pu/²³⁹Pu atom ratio that is similar to that of global fallout and to a ^239+240Pu/¹³⁷Cs activity ratio that is slightly higher than that of global fallout. However, a low ²⁴⁰Pu/²³⁹Pu atom ratio of 0.080 and high ^239+240Pu/¹³⁷Cs activity ratio of 0.087, significantly different from the global fallout values, were observed in one sediment core (07BS10-2), indicating the inhomogenous tropospheric deposition from the Chinese nuclear tests in Lake Bosten during 1967–1973. These results are important to understand the influence of the CNTs on the radionuclide contamination in Lake Bosten

Microplastic-derived dissolved organic matter and its biogeochemical behaviors in aquatic environments: A review

Microplastic-derived dissolved organic matter (MP-DOM) exerts great effects on organic carbon pool and its environmental behaviors in natural waters due to increasing amounts of uncontrolled plastic disposal. However, systematic understanding of chemical composition and environmental impacts of MP-DOM in aquatic systems was limited. In this work, the chemical and molecular structures of MP-DOM derived from diverse characterization methods were examined and synthesized to provide a basis for understanding their environmental processes. Additionally, those factors affecting the quantity and quality of released MP-DOM (e.g., plastic types, water environments, and external weathering conditions) were reviewed. Furthermore, environmental behaviors of MP-DOM including its biological degradation, adsorption on mineral surfaces, and interaction with pollutants, as well as their environmental impacts were comprehensively summarized. Finally, we outlooked the future research directions on MP-DOM studies, aiming to contribute to a deeper understanding of the environmental mechanisms and control of plastic pollution through the analysis of MP-DOM. This review provides information for further understanding the impact of microplastics on natural water, which might have consequences on the fluxes of carbon and biogeochemical behaviors of metal and organic contaminants. The structural features, influence factors, and biogeochemical behavior of MP-DOM were reviewed.Compared with NOM, MP-DOM is dominated by labile aliphatic compounds.UV exposure, high temperature and alkalinity solution could promote MP-DOM release.MP-DOM actively interacts with environmental media and alters their environmental fate. The structural features, influence factors, and biogeochemical behavior of MP-DOM were reviewed. Compared with NOM, MP-DOM is dominated by labile aliphatic compounds. UV exposure, high temperature and alkalinity solution could promote MP-DOM release. MP-DOM actively interacts with environmental media and alters their environmental fate.</p

Predicting Water Quality Criteria for Protecting Aquatic Life from Physicochemical Properties of Metals or Metalloids

Metals are widely distributed pollutants in water and can have detrimental effects on some aquatic life and humans. Over the past few decades, the United States Environmental Protection Agency (U.S. EPA) has published a series of criteria guidelines, which contain specific criteria maximum concentrations (CMCs) for 10 metals. However, CMCs for other metals are still lacking because of financial, practical, or ethical restrictions on toxicity testing. Herein, a quantitative structure activity relationship (QSAR) method was used to develop a set of predictive relationships, based on physical and chemical characteristics of metals, and predict acute toxicities of each species for five phyla and eight families of organisms for 25 metals or metalloids. In addition, species sensitivity distributions (SSDs) were developed as independent methods for determining predictive CMCs. The quantitative ion character–activity relationships (QICAR) analysis showed that the softness index (σp), maximum complex stability constants (log −β_<i>n</i>), electrochemical potential (Δ<i>E</i>₀), and covalent index (<i>X</i>_m²<i>r</i>) were the minimum set of structure parameters required to predict toxicity of metals to eight families of representative organisms. Predicted CMCs for 10 metals are in reasonable agreement with those recommended previously by U.S. EPA within a difference of 1.5 orders of magnitude. CMCs were significantly related to σp (<i>r</i>² = 0.76, <i>P</i> = 7.02 × 10^–9) and log −β_<i>n</i> (<i>r</i>² = 0.73, <i>P</i> = 3.88 × 10^–8). The novel QICAR-SSD model reported here is a rapid, cost-effective, and reasonably accurate method, which can provide a beneficial supplement to existing methodologies for developing preliminarily screen level toxicities or criteria for metals, for which little or no relevant information on the toxicity to particular classes of aquatic organisms exists

Molecular-level exploration of properties of dissolved organic matter in natural and engineered water systems: A critical review of FTICR-MS application

Dissolved organic matter (DOM) contains complex molecular compounds that dominate its heterogeneous dynamics and behaviors in aquatic environments. Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) with ultra-high resolution has proven to be effective in characterizing aquatic DOM. However, a systematic summary of molecular-level compositions and behaviors of DOM in natural and engineered water systems remains insufficient. This study provides a critical review of DOM characterization by FTICR-MS, with emphasis on composition diversity, chemical properties, transformation, and dynamics in the natural and engineered water systems. First, FTICR-MS strategies for DOM characterization are introduced on data interpretation and collaborative analysis of complementary datasets (e.g. spectroscopic data). Second, DOM characteristics, including spatiotemporal distribution, photochemical activity, microbial modification, and interface adsorption in natural water environments were comprehensively summarized based on current FTICR-MS findings. Third, DOM molecular changes caused by different engineered treatment methods were reviewed to highlight the molecular variation, reaction, and transformation by focusing on the FTICR-MS results. Finally, we summarized current limitations, biases, and future directions of FTICR-MS, and future extended studies of natural/engineered-derived DOM behavior. This FTICR-MS application review provides favorable strategies for understanding the molecular chemistry and behaviors of aquatic DOM.</p

Microbial Biomass and Community Composition Involved in Cycling of Organic Phosphorus in Sediments of Lake Dianchi, Southwest China

<p>Organic phosphorus (P_o) was a major fraction of phosphorus (P) in sediments of lakes, and microbes were involved in most of its relevant biogeochemical cycling. Forms and quantification of P_o were investigated by sequential fractionation in 18 sediments of Lake Dianchi, Southwest China. Microbial biomass and community structure in these sediments were determined by phospholipid fatty acids (PLFAs). Distribution of P_o fractions were in the rank order that humic P_o > nucleic acid and polyphosphate > residual P > Ca-Al-P_o > Fe-P_o > sugar P_o > acid soluble P_o > H₂O-P_o. The recoveries of P_o and P_i in these detailed sequential fractions including residual P shows that the total contents of P_o in sediments of lakes were overestimated by the Standards, Measurements and Testing (SMT) protocol (ignition method). Microbial biomass including Gram-positive bacteria (14.4–20.0%), Gram-negative bacteria (32.7–38.4%), microeukaryotes (14.9–24.4%), aerobic bacteria (43.6–55.8%), anaerobic bacteria (0–2.9%) and type І methanotrophs (17.6–24.4%) were assigned. Microbial mass and their composition were strongly correlated with H₂O-P_o, Fe-P_o, nucleic acid and polyphosphate, and humic P_o, though residual P was likely inert for microbes in sediments. The formation and degradation of P_o was closely related with microbial activities in sediments. These findings have implications for understanding the role of microbes on cycling of P_o and organic matter in sediments of lakes.</p

Thermodynamic Study on the Protonation Reactions of Glyphosate in Aqueous Solution: Potentiometry, Calorimetry and NMR spectroscopy

Glyphosate [<i>N</i>-(phosphonomethyl)­glycine] has been described as the ideal herbicide because of its unique properties. There is some conflicting information concerning the structures and conformations involved in the protonation process of glyphosate. Protonation may influence the chemical and physical properties of glyphosate, modifying its structure and the chemical processes in which it is involved. To better understand the species in solution associated with changes in pH, thermodynamic study (potentiometry, calorimetry and NMR spectroscopy) about the protonation pathway of glyphosate is performed. Experimental results confirmed that the order of successive protonation sites of totally deprotonated glyphosate is phosphonate oxygen, amino nitrogen, and finally carboxylate oxygen. This trend is in agreement with the most recent theoretical work in the literature on the subject (J. Phys. Chem. A 2015, 119, 5241−5249). The result is important because it confirms that the protonated site of glyphosate in pH range 7–8, is not on the amino but on the phosphonate group instead. This corrected information can improve the understanding of the glyphosate chemical and biochemical action