Yulin Tang

Combined effects of graphene oxide and Cd on the photosynthetic capacity and survival of Microcystis aeruginosa

In this work, the combined effects of graphene oxide (GO) and Cd(2+) solution on Microcystis aeruginosa were investigated. Chlorophyll fluorescence parameters were measured by a pulse-amplitude modulated fluorometer. GO at low concentrations exhibited no significant toxicity. The presence of GO at low concentrations significantly enhanced Cd(2+) toxicity as the 96 h half maximal effective concentration of the Cd(2+) reduced from 0.51 ± 0.01 to 0.474 ± 0.01 mg/L. However, concentrations of GO above 5mg/L did not significantly increase the toxicity of the Cd(2+)/GO system. Observations through scanning and transmission electron microscopy revealed that GO, with Cd(2+), easily attached to and entered into the algae. Reactive oxygen species and malondialdehyde were measured to explain the toxicity mechanism. The photosynthetic parameters were useful in measuring the combined toxicity of the nanoparticles and heavy metals.

The influence of humic acid on the toxicity of nano-ZnO and Zn2+ to the Anabaena sp.

This study explored the effects of humic acid (HA) on the toxicity of ZnO nanoparticles (nano‐ZnO) and Zn2+ to Anabaena sp. Typical chlorophyll fluorescence parameters, including effective quantum yield, photosynthetic efficiency and maximal electron transport rate, were measured by a pulse‐amplitude modulated fluorometer. Results showed that nano‐ZnO and Zn2+ could inhibit Anabaena sp. growth with the EC50 (concentration for 50% of maximal effect) of 0.74u2009±u20090.01 and 0.3u2009±u20090.01 mg/L, respectively. In the presence of 3.0 mg/L of HA, EC50 of nano‐ZnO increased to 1.15u2009±u20090.04 mg/L and EC50 of Zn2+ was still 0.3u2009±u20090.01 mg/L. Scanning electron microscopy observation revealed that HA prevented the adhesion of nano‐ZnO on the algae cells due to the increased electrostatic repulsion. The generation of intracellular reactive oxygen species and cellular lipid peroxidation were significantly limited by HA. Nano‐ZnO had more damage to the cell membrane than Zn2+ did, which could be proven by the malondialdehyde content in Anabaena sp. cells.

Synergistic Effects of Nano-Sized Titanium Dioxide and Zinc on the Photosynthetic Capacity and Survival of Anabaena sp.

Anabaena sp. was used to examine the toxicity of exposure to a nano-TiO2 suspension, Zn2+ solution, and mixtures of nano-TiO2 and Zn2+ suspensions. Typical chlorophyll fluorescence parameters, including effective quantum yield, photosynthetic efficiency and maximal electron transport rate, were measured by a pulse-amplitude modulated fluorometer. Nano-TiO2 particles exhibited no significant toxicity at concentrations lower than 10.0 mg/L. The 96 h concentration for the 50% maximal effect (EC50) of Zn2+ alone to Anabaena sp. was 0.38 ± 0.004 mg/L. The presence of nano-TiO2 at low concentrations (<1.0 mg/L) significantly enhanced the toxicity of Zn2+ and consequently reduced the EC50 value to 0.29 ± 0.003 mg/L. However, the toxicity of the Zn2+/TiO2 system decreased with increasing nano-TiO2 concentration because of the substantial adsorption of Zn2+ by nano-TiO2. The toxicity curve of the Zn2+/TiO2 system as a function of incremental nano-TiO2 concentrations was parabolic. The toxicity significantly increased at the initial stage, reached its maximum, and then decreased with increasing nano-TiO2 concentration. Hydrodynamic sizes, concentration of nano-TiO2 and Zn2+ loaded nano-TiO2 were the main parameters for synergistic toxicity.

A review of the environmental distribution, fate, and control of tetrabromobisphenol A released from sources

Tetrabromobisphenol A (TBBPA), a high use brominated flame retardant (BFR), raising concerns of widespread pollution and harm to human and ecological health. BFR manufacturing, TBBPA-based product manufacturing, e-waste recycling, and wastewater treatment plants have been identified as the main emission point sources. This paper discusses the occurrence, distribution, and fate of TBBPA from source to the environment. After release to the environment, TBBPA may undergo adsorption, photolysis, and biological degradation. Exposure of humans and biota is also discussed along with the role of treatment and regulations in reducing release of TBBPA to the environment and exposure risks. In general this review found stronger enforcement of existing legislation, and investment in treatment of e-waste plastics and wastewater from emission point sources could be effective methods in reducing release and exposure of TBBPA in the environment.

Facile ultrasonic synthesis of novel zinc sulfide/carbon nanotube coaxial nanocables for enhanced photodegradation of methyl orange

Zinc sulfide (ZnS) has been widely studied due to its versatile application in photocatalysis. A facile, one-pot, ultrasonic-assisted approach was developed to synthesize coaxial nanocables consisting of highly conductive multi-walled carbon nanotube (CNT) cores and well-crystalline ZnS sheaths. The morphology and structural features of the materials were characterized using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. The photoluminescence and optical properties of the CNT/ZnS coaxial nanocables are characterized by photoluminescent spectrum and UV–Vis spectroscopy. Methyl orange (MO) dye was chosen as a model for organic pollutants and was used to evaluate the photocatalytic performance of the CNT/ZnS nanocables. CNT/ZnS showed significant visible-light activity in the degradation of MO. Compared with the ZnS powders, the novel CNT/ZnS coaxial nanocables exhibited much higher performance as a photocatalyst. The enhanced performance arises from the structural advantages of the nanocables. First, the CNT cores effectively improved the electronic conductivity of the hybrid materials. Second, the CNT coaxial nanocables had rich hierarchical pores of ZnS sheath and large surface area.

Enhanced inactivation of E. coli by pulsed UV-LED irradiation during water disinfection

Pulsed ultraviolet (UV) irradiation has presented enhanced inactivation efficiency in water disinfection and food decontamination. As an emerging UV source, UV light-emitting diodes (UV-LEDs) are an attractive alternative for pulsed irradiation because they can be turned on and off with a high and adjustable frequency. In this study, disinfection efficiencies of pulsed and continuous UV-LED irradiation were compared for Escherichia coli (E. coli) inactivation in water using a high power 285u202fnm LED and low power 265 and 280u202fnm LEDs. Factors including various duty cycles, pulse frequencies and UV irradiances were evaluated. The log-inactivation of E. coli increased substantially as the duty cycle decreased from 100% to 5% at the same UV dose. For 265 and 280u202fnm LEDs, the log-inactivation enhancements of pulsed UV irradiation were similar. When a higher irradiance was applied, the energy efficiency enhancement of pulsed UV irradiation became more obvious. The log-inactivation of E. coli enhanced remarkably using high current pulsed irradiation of 280u202fnm LEDs. Compared to continuous UV irradiation, pulsed UV-LED irradiation is an attractive alternative for E. coli inactivation in water considering energy efficiency.

Environmental risks of ZnO nanoparticle exposure on Microcystis aeruginosa: Toxic effects and environmental feedback

The vast majority of studies measure the toxic effect of organisms exposed to nanoparticles (NPs) while there is still a lack of knowledge about the influence of NPs on the aquatic environment. It is unknown whether or not the interaction between NPs and algae will result in the variation of algal organic matter (AOM) and stimulate the production of more algal toxins. In this study, zinc oxide nanoparticles (nano-ZnO) as a typical representative of metal oxide NPs were used to evaluate the toxic effects and environmental feedback of Microcystis aeruginosa. Reactive oxygen species (ROS) and malondialdehyde (MDA) were measured to explain the toxicity mechanism. Changes of AOM, including the production of toxins, the molecular weight distribution and the excitation-emission matrices of algal solution were also studied as environmental feedback indicators after nano-ZnO destroyed the algae. As the nano-ZnO exceeded the comparable critical concentration (1.0u2009mg/L), the algae were destroyed and intracellular organic matters were released into the aquatic environment, which stimulated the generation of microcystin-LR (MC-LR). However, it is worth noting that the concentration of nano-ZnO would need to be high (at mg/L range) to stimulate more MC-LR production. These findings are expected to be beneficial in interpreting the toxicity and risks of the releasing of NPs through the feedback between algae and the aquatic environment.

The Toxicity of Nanoparticles to Algae

Nanoparticles (NPs) display unique physical and chemical properties to the toxicity of algae. Among the NPs, metal oxide NPs such as titanium dioxide (nano-TiO2), zinc oxide (ZnO NPs), and copper oxide (CuO NPs) are the most used nanomaterials. Silver nanoparticles (Ag NPs), gold nanoparticles (Au NPs), and zero-valent iron nanoparticles (nZVI) have received considerable attention among noble metal materials. Besides, Quantum dots (QDs) and carbon-based nanoparticles are also common. To assess the ecological response of algae to NPs, we provide an overview of NPs ecotoxicological effects on algae from existing data and focus on the effect of different NPs on algae, the underlying mechanisms of NPs toxicity and their toxic effects on algae. Among the data available, NPs have been shown to exert from inhibitive to lethal effects on algae due to a high surface area, nanoscale size effects, and quantum effects.