Microplastics in dust from different indoor environments.

Microplastics (MPs) are present in global indoor dust, which is an important source of MPs for humans. However, few researchers have investigated differences in the abundance and characteristics of MPs in dust in different indoor environments. In this study, we found that residential apartments (mean: 1174 MPs/g; n = 47) had the highest abundance of MPs in indoor dust samples, followed by offices (896 MPs/g; n = 50), business hotels (843 MPs/g; n = 53), university dormitories (775 MPs/g; n = 48), and university classrooms (209 MPs/g; n = 44). The predominant shape of MPs was fiber in most indoor dust samples. The main size fraction of the MPs in the indoor dust samples from university classrooms and business hotels was 201-500 µm, and it was 501-1000 µm in those from offices, university dormitories, and residential apartments. The main MP polymer in indoor dust samples from business hotels, university dormitories, and residential apartments was polyester, whereas those from offices and university classrooms were mainly polyethylene and polypropylene. We calculated the estimated daily intake (EDI) of MPs through the inhalation of indoor dust, and found that infants (7.4 MPs/kg bw/day) had a higher mean EDI of MPs than toddlers (1.4 MPs/kg bw/day), children (0.49 MPs/kg bw/day), adults (0.23 MPs/kg bw/day), and university students (0.22 MPs/kg bw/day). To the best of our knowledge, we are the first to report differences in MP occurrence in dust samples from different indoor environments, and our findings provide a more accurate understanding of exposure risks of MPs to humans.

[Preparation of Modified Watermelon Biochar and Its Adsorption Properties for Pb(â ¡)].

In this study, watermelon rind was used as a raw material to modify watermelon rind biochar (MBC) with ammonium sulphate[(NH4)2S] for adsorption of Pb(Ⅱ) ions. The effects of solution pH, adsorption time, adsorbent addition amount, initial mass concentration of Pb(Ⅱ) ions, and ionic strength on the adsorption of Pb(Ⅱ) ions were investigated. The results show that the saturated adsorption time was 5 h, the optimum pH of the adsorption reaction was 6, and when the initial mass concentration of Pb(Ⅱ) ions were 1000 mg·L-1, and the amount of adsorbent was 2.0 g·L-1. The maximum adsorption amount of MBC to Pb(Ⅱ) ions can reach 97.63 mg·g-1, which is significantly higher than unmodified watermelon husk biochar (BC). The adsorption of Pb(Ⅱ) ions by modified watermelon biochar was in accordance with the Langmuir isotherm adsorption model and the pseudo second-order kinetic model, which proves that adsorption is dominated by monolayer chemical adsorption. The desorption of MBC after adsorption of Pb(Ⅱ) ions was carried out using a sodium hydroxide solution to study the reusability of MBC, and the adsorption amount was still 64.74 mg·g-1 in the sixth cycle. Characterization and analysis of adsorbents by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, nitrogen adsorption, scanning electron microscopy-energy spectroscopy, zeta potential analysis, and X-ray diffraction (XRD) were carried out, which showed that the adsorption mechanism is mainly that MBC oxygen- and MBC sulfur-containing groups adsorb Pb(Ⅱ) through complexation and precipitation. Therefore, ammonium sulfide modified watermelon rind biochar can be used as a highly efficient lead adsorbent.

[Isolation, identification of methyl tert-butyl ether degradation strain and its degradation kinetics].

A methyl tert-butyl ether degradation strain A1 was isolated from the soil under an old Gingko tree. It was identified preliminarily as Comamonas testosterone by 16S rDNA sequence analysis. The main factors including inoculation amount of microbes, pH, temperature and MTBE concentration that may affect the degradation efficiency of MTBE were further studied. The results indicated that the optimum conditions were as following: pH 7.0, temperature 25 degrees C, inoculation amount of microbes was 2 mL (D600 = 2.523 A), initial MTBE concentration 50 mg/L. Under that condition, MTBE can be reduced by 98.89% with seven days (compared with the blank, the volatilization of MTBE was 46.55%). In addition, the biodegradation process of MTBE can be well described by enzymatic reaction of high concentration inhibition, with the maximum substrate utilization rate 0.872 d(-1), Michaelis-Menten constant 7.832 mg x L(-1), inhibitory constant 130.75 mg x L(-1) respectively.

[Degradation of methyl tert-butyl ether (MTBE) by O3/H2O2].

The degradation of methyl tert-butyl ether (MTBE) in water solution has been studied using the combination of ozone/hydrogen peroxide in a bubble column. Effects of air (containing O3) currents, quantities of H2O2, initial concentrations of MTBE, pH values and temperatures on the oxidation of MTBE have been tested, and it is implicated that under the conditions of initial MTBE concentration of 10 mg x L(-1), air current of 0.5 L x min(-1), pH 6.5, 293 K and 2.4 mg x L(-1) H2O2 addition, MTBE can be reduced by 75.5% and the removal rate of COD reaches 68.0% within 30 min. The main of degradation products identified are tert-butyl formate (TBF), tert-butyl alcohol (TBA), acetone (AC) and methyl acetate (MA). On the basis of that, the probable mechanism and pathway of the oxidation of MTBE by ozone/hydrogen peroxide have been proposed.

Photodegradation of methyl tert-butyl ether (MTBE) by UV/H2O2 and UV/TiO2.

Two UV-based advanced oxidation processes (AOPs), UV/H2O2 and UV/TiO2, were tested in batch reactor systems to evaluate the removal efficiencies and optimal conditions for the photodegradation of methyl tert-butyl ether (MTBE). The optimal conditions at an initial MTBE concentration of 1 mM ([MTBE]0=1 mM) were acidic and 15 mM H2O2 in UV/H2O2 system, and pH 3.0 and 2.0 g/l TiO2 in UV/TiO2 suspended slurries system under 254-nm UV irradiation. Under the optimal conditions, MTBE photodegradation during the initial period of 60 min in UV/H2O2 and UV/TiO2 systems reached 98 and 80%, respectively. In both systems, MTBE photodegradation decreased with increasing [MTBE]0. While MTBE photodegradation rates increased with increasing dosage of H2O2 (5-15 mM) and TiO2 (0.5-3 g/l), further increase in the dosage of H2O2 (20 mM) or TiO2 (4 g/l) adversely reduced the MTBE photodegradation. Pseudo first-order kinetics with regard to [MTBE] can be used to describe the MTBE photodegradation in both systems. The pseudo first-order rate constants linearly increased with the increase in the molar ratio of [H2O2]0 to [MTBE]0 in UV/H2O2 system and linearly increased with the decrease in [MTBE]0 in UV/TiO2 system.