Wenjing Guo

Copper and zinc, but not other priority toxic metals, pose risks to native aquatic species in a large urban lake in Eastern China ☆

Over the past 20 years, global production of copper (Cu) and zinc (Zn) rank in the top three compared to other metals such as Pb, Cd, Cr, Ni, As and Hg. However, due to the potential for exposure and toxicity to humans, more attention of environmental pollution was paid to other metals such as Cd and Hg. Aquatic organisms are sensitive to Cu and Zn. Even though internal concentrations of these required elements are homeostatically controlled, toxic effects can occur at the fish gill surface. In this work, concentrations in surface waters and toxic effects of Cu, Zn, Ni, Cr, Pb, Cd, As, Hg were determined and risk of various metals in Tai Lake, China were evaluated using both risk quotients and joint probability distributions. Two transition metals, Cu and Zn posed the greatest risks to aquatic organisms while measured concentrations of other metals were less than thresholds for adverse effects. Approximately 99.9% and 50.7% of the aquatic organisms were predicted to be affected by Cu and Zn in surface water of Tai Lake respectively. Our results highlight ecological risks of Cu and Zn in water of a typical, large, urban lake in Eastern China, which was ignored in the past.

Refocusing on Nonpriority Toxic Metals in the Aquatic Environment in China

in China Zhiyou Fu,† Wenjing Guo,† Zhi Dang,‡ Qing Hu, Fengchang Wu,*,† Chenglian Feng,† Xiaoli Zhao,† Wei Meng,† Baoshan Xing, and John P. Giesy †State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China ‡School of Environment and Energy, South China University of Technology, Guangzhou 510006, China School of Environmental Science & Engineering, Southern University of Science and Technology, Shenzhen 518055, China Department of Plant, Soil, and Insect Sciences, University of Massachusetts, Amherst, Massachusetts 01003, United States Department of Veterinary Biomedical Sciences and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan Canada

Effects of monovalent and divalent metal cations on the aggregation and suspension of Fe3O4 magnetic nanoparticles in aqueous solution.

There has been limited research investigating how the mechanisms of aggregation of magnetic nanoparticles (MNPs) are affected by inorganic ions. In this study, Na+, Mg2+, Ca2+, Sr2+ and Ba2+ were selected to systematically study the aggregation mechanisms of Fe3O4 MNPs. The results indicated that divalent cations more significantly affected the stabilities of MNPs than Na+ at low concentrations (e.g., 0.1mM) in a decreasing order of Ba2+>Sr2+>Ca2+>Mg2+>Na+. Extended DLVO theory did not offer a satisfactory explanation for the above difference due because it ignores specific ion effects. It was also found that the initial adsorption ratios of these metals by Fe3O4 MNPs were linearly proportional to the hydrodynamic diameter (HDD) of Fe3O4 MNPs before aggregation occurred. In addition to the valence states, the hydration forces and ionic radii of the metal cations were proposed to be other factors that significantly affected the interactions of metal cations with Fe3O4 MNPs based on the excellent linear relationships of the HDD of Fe3O4 MNPs and these three factors. Moreover, a bridging function of divalent cations might develop after aggregation occurred based on the increases in their adsorption amounts and intensities for binding oxygen-containing functional groups. In addition, an increase in the positive ζ potential of MNPs was observed with the addition of divalent cations until 10.0mM at a pH of 5.0, which potentially enhances the resistance of MNPs to aggregation in aquatic systems compared with Na+. Consequentially, the effects of metal cations on the aggregation of MNPs are determined by the hydration forces, valance states, ionic radii and bond types formed on the MNPs. Thus, the specific ion effects of these cations should be considered in predicting the environmental behaviors of specific nanomaterials.

Using solid (13)C NMR coupled with solution (31)P NMR spectroscopy to investigate molecular species and lability of organic carbon and phosphorus from aquatic plants in Tai Lake, China.

Forms and labilities of plant-derived organic matters (OMs) including carbon (C) and phosphorus (P) were fundamental for understanding their release, degradation and environmental behaviour in lake ecosystems. Thus, solid 13C and solution 31P nuclear magnetic resonance (NMR) spectroscopy were used to characterize biomass of six aquatic plants in Tai Lake, China. The results showed that carbohydrates (61.2% of the total C) were predominant C functional group in the solid 13C NMR spectra of plant biomass, which may indicate high lability and bioavailability of aquatic plants-derived organic matter in lakes. There was 72.6–103.7% of the total P in aquatic plant biomass extracted by NaOH–EDTA extracts. Solution 31P NMR analysis of these NaOH–EDTA extracts further identified several molecular species of P including orthophosphate (50.1%), orthophosphate monoesters (46.8%), DNA (1.6%) and pyrophosphate (1.4%). Orthophosphate monoesters included β-glycerophosphate (17.7%), hydrolysis products of RNA (11.7%), α-glycerophosphate (9.2%) and other unknown monoesters (2.1%). Additionally, phytate, the major form of organic P in many lake sediments, was detected in floating plant water poppy. These inorganic P (e.g. orthophosphate and pyrophosphate) and organic P (e.g. diester and its degradation products) identified in plant biomass were all labile and bioavailable P, which would play an important role in recycling of P in lakes. These results increased knowledge of chemical composition and bioavailability of OMs derived from aquatic plants in lakes.

Protonation-dependent heterogeneity in fluorescent binding sites in sub-fractions of fulvic acid using principle component analysis and two-dimensional correlation spectroscopy

Heterogeneous distributions of proton binding sites within sub-fractions of fulvic acid (FA3-FA13) were investigated by use of synchronous fluorescence spectra (SFS), combined with principle component analysis (PCA) and two-dimensional correlation spectroscopy (2D-COS). Tryptophan-like, fulvic-like and humic-like materials were observed in SFS. Tyrosine-like materials were identified by use of SFS-PCA analysis. Combined information from synchronous-asynchronous maps and dissociation constants (pKa) was used to describe heterogeneity of binding sites for protons within each sub-fraction. Heterogeneous distributions of proton binding sites were observed in fulvic-like, humic-like, tryptophan-like, and tyrosine-like materials of five sub-fractions and even in the single fulvic-like materials in FA3 and tryptophan-like materials in FA9 and FA13. Values of pKa of sub-fractions ranged from 2.20 to 5.29, depending on associated wavelengths in synchronous-asynchronous maps and use of the modified Stern-Volmer equation. The larger values of pKa (4.17-5.29) were established for protein-like materials (including tryptophan-like and tyrosine-like materials) in comparison to those (2.20-3.38) for humic-like and fulvic-like materials in sub-fractions. Sequential variations of 274nm (pKa 4.15-5.29)→360-460nm (pKa 2.78-2.39) for FA5-FA13 revealed that binding of protons to tryptophan-like materials appeared prior to humic-like/fulvic-like materials. In FA9, protons were preferentially binding to tryptophan-like materials than tyrosine-like materials. In FA3, protons were preferentially binding to humic-like materials than fulvic-like materials. Relative differences of values of pKa for fluorescent materials within each sub-fraction were consistent with sequential orders derived from asynchronous maps. Such an integrated approach, SFS-PCA/2D-COS, has superior potential for further applications in exploring complex interactions between dissolved organic matter and contaminants in engineered and natural environments.

Removal of antimonate (Sb(V)) and antimonite (Sb(III)) from aqueous solutions by coagulation-flocculation-sedimentation (CFS): Dependence on influencing factors and insights into removal mechanisms

This study investigates the effects of different influence factors on the removal of inorganic Sb species using coagulation-flocculation-sedimentation (CFS) and establishes the mechanism of the process. Thus, the influence of pH, initial Sb concentrations, coagulant dosages and competitive matters on Sb(V) and Sb(III) removal via CFS with polymeric ferric sulfate (PFS) was investigated systemically. Competition experiments and characterization methods, including X-ray diffraction (XRD), energy dispersive spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS), were performed to determine the mechanisms of the process. The main conclusions included: (i) Optimum Sb removal was observed at a pH range of 4-6 and dosages of 4 × 10-4 mol/L and 8 × 10-5 mol/L for Sb(V) and Sb(III), respectively. Additionally, both Sb(V) and Sb(III) removal could be inhibited by the presence of phosphate and humic acid (HA). (ii) A higher priority was observed for the removal of Sb(III) over Sb(V). (iii) After excluding precipitation/inclusion/occlusion, coprecipitation involving chemical bonding played a significant role in both Sb(V) and Sb(III) removal, and electrostatic force served another significant role in Sb(V) removal. The Sb(V) and Sb(III) contamination in real contaminated waters was successfully removed using PFS via CFS process. The results of this study provide insights into the removal mechanisms of inorganic Sb species via CFS.

Using dual isotopes and a Bayesian isotope mixing model to evaluate sources of nitrate of Tai Lake, China

AbstractIdentification and quantification of sources of nitrate (NO3–) in freshwater lakes provide useful information for management of eutrophication and improving water quality in lakes. Dual δ15N- and δ18O-NO3– isotopes and a Bayesian isotope mixing model were applied to identify sources of NO3– and estimate their proportional contributions to concentrations of NO3– in Tai Lake, China. In waters of Tai Lake, values for δ15N-NO3– ranged from 3.8 to 10.1‰, while values of δ18O ranged from 2.2 to 12.0‰. These results indicated that NO3– was derived primarily from agricultural and industrial sources. Stable isotope analysis in R called SIAR model was used to estimate proportional contributions from four potential NO3– sources (agricultural, industrial effluents, domestic sewage, and rainwater). SIAR output revealed that agricultural runoff provided the greatest proportion (50.8%) of NO3– to the lake, followed by industrial effluents (33.9%), rainwater (8.4%), and domestic sewage (6.8%). Contributions of those primary sources of NO3– to sub-regions of Tai Lake varied significantly (p < 0.05). For the northern region of the lake, industrial source (35.4%) contributed the greatest proportion of NO3–, followed by agricultural runoff (27.4%), domestic sewage (21.3%), and rainwater (15.9%). Whereas for the southern region, the proportion of NO3– contributed from agriculture (38.6%) was slightly greater than that contributed by industry (30.8%), which was similar to results for nearby inflow tributaries. Thus, to improve water quality by addressing eutrophication and reduce primary production of phytoplankton, NO3– from both nonpoint agricultural sources and industrial point sources should be mitigated. Graphical abstractᅟ