Effect of pH on binding of pyrene to hydrophobic fractions of dissolved organic matter(DOM) isolated from lake water

In order to better understand the compositional and structural complexity of dissolved organic matter(DOM) macromolecules and provide mechanistic information on the binding of hydrophobic organic contaminants(HOCs) to DOM, we fractionated large amounts of lake water into three hydrophobic DOM-fractions. The variation of the partitioning coef?cients(K_(DOC)) of pyrene at different p H levels was examined by ?orescence quenching titration. Results show that, relative to the more polar acidic DOM-fractions, the hydrophobic neutral fraction exhibits a higher sorption ability to pyrene. Generally, the sorption of pyrene to the three hydrophobic fractions is strongly pH-dependent. The K_(DOC) values of pyrene generally increase with decreasing p H levels, which is especially obvious in the sorption of pyrene to the fulvic acid fractions, suggesting that the binding is controlled by hydrophobic interactions. The mechanisms underlying the binding of pyrene to the hydrophobic fractions were also discussed. Our data are bene?cial to further understanding the binding of HOCs to DOM and how it has been affected,which may result in more accurate predictions of K_(DOC).

Fluorescence regional integration and differential fluorescence spectroscopy for analysis of structural characteristics and proton binding properties of fulvic acid sub-fractions

Structural characteristics and proton binding properties of sub-fractions（FA3–FA13） of fulvic acid（FA）, eluted stepwise by pyrophosphate buffer were examined by use of fluorescence titration combined with fluorescence regional integration（FRI） and differential fluorescence spectroscopy（DFS）. Humic-like（H-L） and fulvic-like（F-L） materials, which accounted for more than 80% of fluorescence response, were dominant in five sub-fractions of FA. Based on FRI analysis, except the response of F-L materials in FA9 and FA13, maximum changes in percent fluorescence response were less than 10% as pH was increased from 2.5 to 11.5.Contents of carboxylic and phenolic groups were compared for fluorescence peaks of FA sub-fractions based on pH-dependent fluorescence derived from DFS. Static quenching was the dominant mechanism for binding of protons by FA sub-fractions. Dissociation constants（p Ka） were calculated by use of results of DFS and the modified Stern-Volmer relationship. The p Kaof H-L, F-L, tryptophan-like and tyrosine-like materials of FA subfractions exhibited ranges of 3.17–4.06, 3.12–3.97, 4.14–4.45 and 4.25–4.76, respectively, for acidic pHs. At basic pHs, values of p Ka for corresponding materials were in ranges of 9.71–10.24, 9.62–10.99, 9.67–10.31 and 9.33–10.28, respectively. At acidic pH, protein-like（P-L）materials had greater affinities for protons than did either H-L or F-L materials. The dicarboxylic and phenolic groups were likely predominant sites of protonation for both H-L and F-L materials at both acidic and basic pHs. Amino acid groups were significant factors during proton binding to protein-like materials of FA sub-fractions at basic pH.

A review of atmospheric benzene homologues in China: Characterization, health risk assessment, source identification and countermeasures

Benzene homologues are important chemical precursors to the formation of ground-level ozone and secondary organic aerosol(SOA) in the atmosphere,in addition,some toxic species are harmful to human health.Strict countermeasures have been taken to fight air pollution since 2013,and total amount control of volatile organic compounds is being promoted in China at present.Therefore,it is important to understand the pollution situation and the control status of ambient benzene homologues in China.This paper reviews research progress from published papers on pollution characteristics,atmospheric photochemical reactivity,health risk assessment and source identification of ambient benzene homologues in recent years in China,and also summarizes policies and countermeasures for the control of ambient benzene homologues and the relevant achievements.The total ambient levels of benzene,toluene,ethylbenzene and xylenes(BTEX) shows a declining tendency from 2001 to 2016 in China.The mass concentrations of BTEX are generally higher in southern regions than in northern regions,and they present vertical decreasing variation characteristics with increasing altitude within the height range of about 5500 m.Toluene has the highest ozone formation potential and SOA formation potential both in urban areas and background areas,while benzene poses an obvious carcinogenic risk to the exposed adult populations in urban areas.Source identification of ambient benzene homologues suggested that local governments should adopt differentiated control strategies for ambient benzene homologues.Several recommendations are put forward for future research and policy-making on the control of ambient benzene homologues in China.

Three decades of changes in water environment of a large freshwater Lake and its relationship with socio-economic indicators

Tai Lake(Ch: Taihu) has attracted international attention forcyanobacteria blooms.However, the drivers of cultural eutrophication, especially long-term socio-economic indicators have been little researched. The results of research demonstrate how socioeconomic development affected quality of water and how it has been improved by anthropogenic activities. This study described variability in indicators of water quality in Tai Lakeand investigated thedrivers. Significant relationships existed between concentrations of annual mean total nitrogen(TN), total phosphorous(TP), chemical oxygen demand(COD) and biological oxygen demand(BOD), and population, per capital gross domestic production(GDP) and sewage discharge(p < 0.05). However, mechanisms causing change varied among TN, TP, COD and BOD. Before 2000, the main contributors to increases in concentrations of TN were human population, GDP and volumes of domestic sewage discharges. After 2000, discharges of industrial sewage become the primary contributor. After 1998, the regressions of annual mean TN, TP and COD on per capital GDP, population and domestic sewage discharge were reversed compared to the former period. Since 1999, an apparent inverted U-shaped relationship between environmental pollution and economic development has developed, which indicated that actions taken by governments have markedly improved quality of water in Tai Lake. The statistical relationship between BOD and per capital GDP didn't conform to the Kuznet curve. The Ushaped Kuznet curve may offer hope for the future that with significant environmental investments a high GDP can be reached and maintained without degradation of the environment, especially through appropriate management of industrial sewage discharge.

New insights on the enhanced non-hydroxyl radical contribution under copper promoted TiO_(2)/GO for the photodegradation of tetracycline hydrochloride

TiO_(2)/graphene oxide(GO)as photocatalyst in the photo-degradation of multitudinous pollutants has been extensively studied.But its low photocatalytic efficiency is attributed to the high band gap energy which lead to low light utilization.Cu-TiO_(2)/GO was synthesized via the impregnation methods to enhance the catalytic performance.The Cu-TiO_(2)/GO reaction rate constant for photo-degradation of pollutants(tetracycline hydrochloride,TC)was about 1.4 times that of TiO_(2)/GO.In 90 min,the removal ratio of Cu-TiO_(2)/GO for TC was 98%,and the maximum degradation ratio occurred at p H 5.After five cycles,the removal ratio of Cu-Ti O_(2)/GO still exceeded 98%.UV-visible adsorption spectra of Cu-Ti O_(2)/GO showed that its band gap was narrower than TiO_(2)/GO.Electron paramagnetic resonance(EPR)spectra test illustrated the generation rate of·O_(2)^(-)and·OH was higher in Cu-TiO_(2)/GO system than TiO_(2)/GO and TiO_(2) system.The contribution sequence of oxidative species was·O_(2)^(-)>holes(h+)>·OH in both TiO_(2)/GO and Cu-Ti O_(2)/GO system.Interestingly,the contribution of·OH in Cu-TiO_(2)/GO was less than that in TiO_(2)/GO during the photo-degradation process.This phenomenon was attributed to the better adsorption performance of Cu-Ti O_(2)/GO which could reduce the accessibility of TC to·OH in liquid.The enhanced non-hydroxyl radical contribution could be attributed to that the more other active species or sites on(nearby)the surface of Cu-TiO_(2)/GO generated after doping Cu.These results provide a new perspective for the tradition metal-doped conventional catalysts to enhance the removal of organic pollutants in the environment.

Simulated photo-degradation of dissolved organic matter in lakes revealed by three-dimensional excitation-emission matrix with regional integration and parallel factor analysis

Simulated photo-degradation of fluorescent dissolved organic matter(FDOM) in Lake Baihua(BH) and Lake Hongfeng(HF) was investigated with three-dimensional excitationemission matrix(3 DEEM) fluorescence combined with the fluorescence regional integration(FRI),parallel factor(PARAFAC) analysis,and multi-order kinetic models.In the FRI analysis,fulvic-like and humic-like materials were the main constituents for both BH-FDOM and HF-FDOM.Four individual components were identified by use of PARAFAC analysis as humic-like components(C1),fulvic-like components(C2),protein-like components(C3) and unidentified components(C4).The maximum 3 DEEM fluorescence intensity of PARAFAC components C1-C3 decreased by about 60%,70% and 90%,respectively after photo-degradation.The multi-order kinetic model was acceptable to represent the photo-degradation of FDOM with correlation coefficient(Radj2)(0.963-0.998).The photo-degradation rate constants(kn) showed differences of three orders of magnitude,from 1.09 × 10-6 to 4.02 × 10-4 min-1,and half-life of multi-order model(T1/2n)ranged from 5.26 to 64.01 min.The decreased values of fluorescence index(FI) and biogenic index(BI),the fact that of percent fluorescence response parameter of Region I(PⅠ,n) showed the greatest change ratio,followed by percent fluorescence response parameter of Region II(PⅡ,n,while the largest decrease ratio was found for C3 components,and the lowest T1/2n was observed for C3,indicated preferential degradation of protein-like materials/components derived from biological sources during photodegradation.This research on the degradation of FDOM by 3 DEEM/FRI-PARAFAC would be beneficial to understanding the photo-degradation of FD OM in natural environments and accurately predicting the environmental behaviors of contaminants in the presence of FDOM.

Plasmonic silver/silver oxide nanoparticles anchored bismuth vanadate as a novel visible-light ternary photocatalyst for degrading pharmaceutical micropollutants

The degradation of pharmaceutical micropollutants is an intensifying environmental problem and synthesis of efficient photocatalysts for this purpose is one of the foremost challenges worldwide.Therefore,this study was conducted to develop novel plasmonic Ag/Ag2O/BiVO4 nanocomposite photocatalysts by simple precipitation and thermal decomposition methods,which could exhibit higher photocatalytic activity for mineralized pharmaceutical micropollutants.Among the different treatments,the best performance was observed for the Ag/Ag2O/BiVO4 nanocomposites (5 wt.%;10 min’s visible light irradiation)which exhibited 6.57 times higher photodegradation rate than the pure BiVO4.Further,the effects of different influencing factors on the photodegradation system of tetracycline hydrochloride (TC-HCl) were investigated and the feasibility for its practical application was explored through the specific light sources,water source and cycle experiments.The mechanistic study demonstrated that the photogenerated holes (h^+),superoxide radicals (·O2^-)and hydroxyl radicals (·OH) participated in TC-HCl removal process,which is different from the pure BiVO4 reaction system.Hence,the present work can provide a new approach for the formation of novel plasmonic photocatalysts with high photoactivity and can act as effective practical application for environmental remediation.

Are current Chinese national ambient air quality standards on 24-hour averages for particulate matter sufficient to protect public health？

With rapid economic development and urbanization in recent decades, China has experienced the worsening of ambient air quality. For better air quality management to protect human health, Chinese government revised national ambient air quality standards （NAAQS） for particulate matter （PM） in 2012 （GB3095-2012）. To assess the effectiveness of current NAAQS for PM on public health in Chinese population, we conducted a meta- analysis on published studies examining the mortality risk of short-term exposure to PM with aerodynamic diameters less than 10 and 2.5μm （PM10 and PM2.5） in China. The reported 24-hour concentrations of PM10 and PM2.5 in studies ranged from 43.5 to 150.1 μg/m^3 and 37.5 to 176.7 μg/m^3. In the pooled excess, mortality risk estimates of short-term exposure to PM. In specific, per 10 μg/m^3 increase in PM10, we observed increases of 0.40% （95%CI： 0.33%, 0.47%）, 0.57% （95%CI： 0.44%, 0.70%） and 0.49% （95%CI： 0.40%, 0.58%） in total, respiratory and cardiovascular mortality, per 10/μg/m^3 increase in PM2.5, we observed increases of 0.51% （95% CI： 0.38%, 0.63%）, 0.62% （95%CI： 0.52%, 0.73%） and 0.75% （95%CI： 0.54%, 0.95%） in total, respiratory and cardiovascular mortality. Finally, we derived 125 μg/m^3 for PM10 and 62.5 μg/ m^3 for PM2.5 as 24-hour recommendation values based on the pooled estimates. Our results indicated that current Chinese NAAQS for PM could be sufficient in mitigating the excess mortality risk from short-term exposure to ambient PM. However, future research on long-term exposure cohort studies in Chinese population is also essential in revising annual averages for PM in Chinese NAAQS.

Organophosphate esters cause thyroid dysfunction via multiple signaling pathways in zebrafish brain

Organophosphate esters(OPEs)are widespread in various environmental media,and can disrupt thyroid endocrine signaling pathways.Mechanisms by which OPEs disrupt thyroid hormone(TH)signal transduction are not fully understood.Here,we present in vivo-in vitro-in silico evidence establishing OPEs as environmental THs competitively entering the brain to inhibit growth of zebrafish via multiple signaling pathways.OPEs can bind to transthyretin(TTR)and thyroxine-binding globulin,thereby affecting the transport of TH in the blood,and to the brain by TTR through the blood-brain barrier.When GH3 cells were exposed to OPEs,cell proliferation was significantly inhibited given that OPEs are competitive inhibitors of TH.Cresyl diphenyl phosphate was shown to be an effective antagonist of TH.Chronic exposure to OPEs significantly inhibited the growth of zebrafish by interfering with thyroperoxidase and thyroglobulin to inhibit TH synthesis.Based on comparisons of modulations of gene expression with the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases,signaling pathways related to thyroid endocrine functions,such as receptor-ligand binding and regulation of hormone levels,were identified as being affected by exposure to OPEs.Effects were also associated with the biosynthesis and metabolism of lipids,and neuroactive ligand-receptor interactions.These findings provide a comprehensive understanding of the mechanisms by which OPEs disrupt thyroid pathways in zebrafish.

A preliminary study on pollution characteristics of surfactant substances in fine particles in the Beibu Gulf Region of China

The pollution characteristics of surfactant substances in fine particles(PM_(2.5))in spring were studied in the Beibu Gulf Region of China,68 samples of PM_(2.5)were collected at Weizhou Island in Beihai City from March 12 to April 17,2015.The Anionic Surfactant Substances(ASS)and Cationic Surfactant Substances(CSS)in the samples were analyzed using Byethyl Violet Spectrophotometry and Disulfide Blue Spectrophotometry,respectively.Combined with the data from backward trajectory simulation,the effects of air pollutants from remote transport on the pollution characteristics of surfactant substances in PM_(2.5)in the Beibu Gulf Region were analyzed and discussed.The results showed that the daily mean concentrations of ASS and CSS in spring in the Beibu Gulf Region were 165.20 pmol/m^(3)and 8.05 pmol/m^(3),and the variation ranges were 23.21–452.55 pmol/m^(3)and 0.65–31.31 pmol/m^(3),accounting for 1.82‰±1.65‰and 0.12‰±0.11‰of the mass concentration of PM_(2.5),respectively.These concentrations were lower than those in comparable regions around the world.There was no clear correlation between the concentrations of ASS and CSS in PM_(2.5)and the mass concentrations of PM_(2.5).Tourism and air transport had a positive contribution on the concentrations of ASS.The concentration of surfactant substances in PM_(2.5)was significantly impacted by wind speed and wind direction.Atmospheric temperature,air pressure and precipitation had little effect on the concentrations of surfactant substances.Surfactant substances in PM_(2.5)significantly impacted visibility.Results also showed that the main sources of surfactant substances were from the southern China and Southeast Asia.