Lixuan Zeng

Concentration and transportation of heavy metals in vegetables and risk assessment of human exposure to bioaccessible heavy metals in soil near a waste-incinerator site, South China

There is limited study focusing on the bioaccumulation of heavy metals in vegetables and human exposure to bioaccessible heavy metals in soil. In the present study, heavy metal concentrations (Cr, Ni, Cu, Pb and Cd) were measured in five types of vegetables, soil, root, and settled air particle samples from two sites (at a domestic waste incinerator and at 20km away from the incinerator) in Guangzhou, South China. Heavy metal concentrations in soil were greater than those in aerial parts of vegetables and roots, which indicated that vegetables bioaccumulated low amount of heavy metals from soil. The similar pattern of heavy metal (Cr, Cd) was found in the settled air particle samples and aerial parts of vegetables from two sites, which may suggest that foliar uptake may be an important pathway of heavy metal from the environment to vegetables. The highest levels of heavy metals were found in leaf lettuce (125.52μg/g, dry weight) and bitter lettuce (71.2μg/g) for sites A and B, respectively, followed by bitter lettuce and leaf lettuce for sites A and B, respectively. Swamp morning glory accumulated the lowest amount of heavy metals (81.02μg/g for site A and 53.2μg/g for site B) at both sites. The bioaccessibility of heavy metals in soil ranged from Cr (2%) to Cu (71.78%). Risk assessment showed that Cd and Pb in soil samples resulted in the highest non-cancer risk and Cd would result in unacceptable cancer risk for children and risk. The non-dietary intake of soil was the most important exposure pathway, when the bioaccessibility of heavy metals was taken into account.

Adsorption of Cd(II), Cu(II) and Ni(II) ions by cross-linking chitosan/rectorite nano-hybrid composite microspheres.

Chitosan/rectorie (CTS/REC) nano-hybrid composite microsphere was prepared by changing the proportion of CTS/REC with 2:1, 3:1 and 4:1. Compared with the pure cross-linking chitosan microsphere, the nano-hybrid composite microsphere was proved to have better sorption capacity of Cd(II), Cu(II) and Ni(II), especially 2:1(CTS/REC-1). The adsorption behavior of the microsphere of Cd(II), Cu(II) and Ni(II) was investigated in single and binary metal systems. In single system, the equilibrium studies showed that the adsorption of Cd(II), Cu(II) and Ni(II) followed the Langmuir model and the pseudo-second-order kinetic model. The negative values of (ΔG) suggested that the adsorption process was spontaneous. In binary system, the combined action of the metals was found to be antagonistic and the metal sorption followed the order of Cu(II)>Cd(II)>Ni(II). The regeneration studies indicated that EDTA desorbed Cd(II), Cu(II) and Ni(II) from cross-linking microspheres better than HCl. The FT-IR and XPS spectra showed that coordination bonds were formed between Cd(II), Cu(II) and Ni(II) and the nitrogen atoms of cross-linking CTS/REC nano-hybrid composite microspheres.

Bioaccessibility of polychlorinated biphenyls in workplace dust and its implication for risk assessment

Human exposure to bioaccessible PCBs via indoor dust is limited around the world. In the present study, the workplace dust sample from commercial office, hospital, secondary school, shopping mall, electronic factory and manufacturing plant were collected from Hong Kong for PCBs analyses. Total PCBs concentrations ranged from 46.8 to 249 ng g(-1), with a median of 107 ng g(-1). Manufacturing plant showed the highest concentration among all of sampling sites. PCB 77 was found as the dominant congeners. The bioaccessibility of PCBs in small intestinal juice ranging from 8.3% to 26.0% was significantly higher than that in gastric condition, ranging from 4.8% to 12.4%. In addition, significant negative correlations (p<0.05) were observed between KOW and bioaccessibility for all workplace dust samples. Risk assessment indicated that the averaged daily dose of dioxin-like PCBs via non-dietary intake of workplace dust, considering the bioaccessibility of PCBs, were much lower than the TDI of dioxins (2.3 pg WHO-TEQ kgbw(-1)d(-1)) established by Joint FAO/WHO Expert Committee on Food Additives.

Catalytic ozonation of 2,4-dichlorophenoxyacetic acid over novel Fe–Ni/AC

Iron and nickel based bimetallic loaded activated carbon (Fe–Ni/AC) prepared by an impregnation method was employed as a heterogeneous catalyst for the ozonation of 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous solution. The Fe–Ni/AC was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption–desorption, and atomic absorption spectrometry (AAS). The results indicated that the degradation and mineralization efficiencies of 2,4-D were considerably improved in the presence of Fe–Ni/AC. During the ozonation (50 mg h−1 ozone flow rate) of 2,4-D aqueous solution (10 mg L−1, pH = 4.18) in the presence of Fe–Ni/AC, the TOC removal rate reached 72% at 60 min reaction time, while the rate was 60% with Fe/AC, 62% with Ni/AC, 50% with activated carbon (AC), and only 34% by ozonation alone. The 2,4-D removal process followed the pseudo first order reaction model well, its degradation rate constant with Fe–Ni/AC/O3 was 1.6 times higher than that with AC/O3, and 1.9 times than that by O3 alone. The Fe–Ni/AC showed much better catalytic activity and stability based on the seven times repetition of the ozonation of 2,4-D. In addition, the effects of 2,4-D initial concentration, pH value and reaction temperature on catalytic ozonation of 2,4-D over Fe–Ni/AC were also investigated. The addition of tert-butanol (TBA) strongly inhibited the catalytic degradation of 2,4-D, which suggests that the degradation reaction follows the mechanism of hydroxyl radical (HO˙) oxidation.

Adsorption of congo red by cross-linked chitosan resins

AbstractIn this study, cross-linked chitosan resins were prepared through inverse suspension and were used to adsorb congo red (CR). FT-IR spectra and SEM technique characterized the chitosan resins. The influences of contact time, temperature, adsorbent dose, initial concentration of CR, and pH of CR solution on the adsorption behavior were investigated. The results showed that the chitosan beads made from 5% chitosan in 2% aqueous acetic acid had smooth surface and strong mechanical strength. When the contact time was 60 min, temperature was 50°C, adsorbent dose was 0.02 g, initial concentration of CR was 80 mg/L, and pH of CR solution was 7, the best adsorption capacity was obtained. The adsorption behavior can be fitted well by the Langmuir isotherm and also obeyed the pseudo-second-order kinetic expression. The intra-particle diffusion studies indicate that the diffusion step was not the only rate-limiting step. Thermodynamic studies illustrated that the adsorption reactions are exothermic and sponta...

In vitro digestion and absorption of BDE-28, -47, -99 and -153 in indoor dust and its implication in risk assessment.

The bioaccessibility of polybrominated diphenyl ethers (PBDEs) in indoor dust was estimated by a series of in vitro digestion methods. However, the absorption of PBDEs by intestinal cells after in vitro digestion was seldom studied. In the present study, the bioaccessibility of BDE-28, 47, 99 and 153 in indoor dust was firstly investigated by using the in vitro digestion method. Bioaccessibility in intestinal phase (BDE-28: 24.5-30.1%; BDE-47: 6.99-13.0; BDE-99: 1.61-14.2%; and BDE-153 5.97-24.4%.) was higher than that in gastric phase (BDE-28: 38.3-58.0; BDE-47: 9.62-30.9%; BDE-99: 9.71-24.3%; and BDE-153: 13.8-57.4%). The organic matter contents in indoor dust showed variable influence on the bioaccessibility of PBDEs. For the Caco-2 uptake assay, the BDE-28 showed greatest transport rate from medium to cell (Kmc: 0.525h-1), followed by -47, -99 and -153. The Kmc of PBDEs was significantly negative correlated with its corresponding KOW value. Similar pattern was found for the maximum uptake flux (Ju, max) and the transport rate from cell to medium (Kcm). The combination of bioacessibility and the absorption factor by Caco-2 cells could be used to estimate human intake of PBDEs via indoor dust would avoid overestimate the health risk.

Daphnia magna May Serve As a Powerful Tool in Screening Endocrine Disruption Chemicals (EDCs)

Guangdong Technology Research Center for Ecological Management and Remediation of Urban Water System, and Key Laboratoryof Theoretical Chemistry of Environment, Ministry of Education, School of Chemistry & Environment, South China NormalUniversity, Higher Education Mega Center, Guangzhou 510006, ChinaDaphnia magna has been widely applied in aquatic toxicityincluding acute and chronic toxicity test. However, its asexualand sexual reproduction in life cycle is usually ignored. Underfavorable environmental condition, Daphnia magna showsasexual reproduction only producing female offspring. Theenvironmental stressor could stimulate the Daphnia magna toproduce male or gynandromorphism offspring. Male and femaleoffspring can be determined by the presence of two elongatedfirst antennae two rudimentary first antennae, respectively, at10× magnification.Endocrine disruption chemicals (EDCs) such as vinclozolinand dicofol, as an environmental stressor, are also observed tobe able to alter the sex ratio of Daphnia magna offspring.

Synergistic effect of co-exposure to cadmium (II) and 4-n-nonylphenol on growth inhibition and oxidative stress of Chlorella sorokiniana

Toxicological effect of freshwater algae co-exposure to Cd and 4-n-nonylphenol (4-n-NP) was seldom reported. In the present study, Chlorella sorokiniana was selected for testing the single and combined effect of Cd and 4-n-NP by detecting the growth inhibition and oxidative stress after exposure for 48 h, 72 h, and 96 h. The combined effects were evaluated by using toxic units (TU) method and concentration addition（CA）model. The synergistic effect of mixture on algal growth inhibition was both observed at 48 h and 72 h, and the additive effect was observed at 96 h. In addition, the significant alterations of superoxide, thiobarbituric acid reactive substances and antioxidant defenses (superoxide dismutase, catalase, glutathione) have been detected. It could be observed that the mixture predominantly lead to synergistic effects in superoxide induction, and the antagonistic effects in the GSH induction. A similar trend between the superoxide induction and growth inhibition were observed, which may indicate that the oxidative effects of Chlorella sorokiniana contributed to the growth inhibition after exposure to Cd and 4-n-NP. These findings may have important implications in the risk assessments of heavy metals and endocrine disruptors in the aquatic environment.

Fabrication and Adsorption Behavior for Congo Red of Chitosan and Alginate Sponge

With chitosan and sodium alginate as the main raw material, the sponge adsorbents were satisfactorily prepared by freeze-drying and curing molding by CaCl2. The structure of sponge was characterized by FTIR and SEM and its physical property was measured. In addition, the different influences on absorbability of CR and analyzing the dynamics and thermodynamics of the adsorption process have been studied, thus it can provide theoretical foundation for the practical application of azo-dye wastewater treatment. The results are as follows: 0.10 g CTS/SA sponge adsorbent has the best absorbability on CR in the condition of 30°C, pH value is range from 6.00 to 7.00, and adsorption time is 45 min and stirring speed of 200 rpm. The adsorption kinetic followed the pseudo-second-order dynamics and it shows good relevance. The CR adsorption of CTS/SA sponge adsorbent can be described as Freundlich isotherm model (R2 > 0.94) and Langmuir isothermmodel (R2 > 0.99). The maximum adsorption capacity of CTS/SA sponges at 30°C can be obtained from the Langmuir model was 121.95 mg/g.

Study on Adsorption of Methylene Blue with Organic Rectorite

The natural rectorite (REC) is a clay mineral with regular interlayer structure. The special structure of rectorite rendered it strong adsorption capacity. According to the cation-exchange mineral characters, rectorite was inserting-layer modified with three novel Gemini surfactants by conventionl method to form three kinds of organic-modified rectorite (OREC), termed (12-2-12)-REC, (12-3-12)-REC, (18-3-18)-REC. Through FTIR and XRD analysis, it confirmed the cation exchange reaction between REC and surfactant. This paper studies on the adsorption of REC and three kinds of OREC for methylene blue and the influence of main factors were discussed. The results indicated that the interlayer distance of the three ORECs((12-2-12)-REC, (12-3-12)-REC, (18-3-18)-REC) were enlarged from 2.49 nm to 3.77 nm, 3.00 nm, 3.33 nm, respectively. Besides, the adsorption results showed that the OREC with larger interlayer spacing displayed more excellent adsorption capacities than the OREC with smaller interlayer spacing in the same work condition. The MB adsorption of three kinds of OREC can be described as Freundlich isotherm model and Langmuir isotherm model, but the adsorption of (18-3-18)-REC is more likely described as Freundlich isotherm model. The max adsorption amount of the three ORECs((12-2-12)-REC, (12-3-12)-REC, (18-3-18)-REC) can be reached 45.56 mg/g, 37.81 mg/g, 40.82 mg/g at 25°C, respectively.