Leaching of triphenyl phosphate and tri-n-butyl phosphate from polystyrene microplastics: influence of plastic properties and simulated digestive fluids.

Microplastics have gained considerable attention as a growing environmental problem owing to their potential to serve as vectors for harmful chemicals. However, the leaching of these chemicals from microplastics is unclear. In this study, we investigated the leaching of two organophosphate flame retardants, triphenyl phosphate and tri-n-butyl phosphate, from polystyrene microplastics in simulated digestive fluids and water, and polypropylene microplastics were simultaneously used for comparison with polystyrene microplastics. The results indicated that the first-order kinetic model best explained the leaching process, suggesting that leaching was related to the release of organophosphate flame retardant molecules at the polymer surface. Additionally, the size and crystalline state of the microplastics had a significant effect on the leaching, whereas organophosphate flame retardant content had a minimal impact. Simulated digestive fluids facilitated the leaching to a different extent, and under these influencing conditions, leaching percentages from polystyrene microplastics did not exceed 0.51%. Therefore, leaching from PS microplastics may not be an important source of OPFRs in the environment. However, the release of organophosphate flame retardants can be considerably enhanced with the breakdown of polystyrene microplastics to polystyrene nanoplastics.

Efficient degradation and detoxification of antibiotic Fosfomycin by UV irradiation in the presence of persulfate.

Fosfomycin (FOS) as a widely used antibiotic has been found in abundance throughout the environment, but little effort has been devoted to its treatment. In this study, we systemically looked into the degradation of FOS by ultraviolet-activated persulfate (UV/PS) in aqueous solutions. Our findings demonstrated that FOS can be degraded efficiently under the UV/PS, e.g., >90 % of FOS was degraded with 19,200 mJ cm-2 of UV irradiance and 20 µM of PS. HO was the dominant radical responsible for FOS degradation. FOS degradation increased as PS dosage increased, and higher degradation efficiency was observed at neutral pH. Natural water constitutes either promoted (e.g., Cu2+, Fe3+, and SO42-) or inhibited (e.g., humic acid, HCO3-, and CO32-) FOS degradation to varying degrees. Hydroxyl substitution, CP bond cleavage, and coupling reactions were the major degradation pathways for FOS degradation. Finally, the toxicity evaluation revealed that FOS was toxic to E. coli and S. aureus, but the toxicity of the intermediate products of FOS to E. coli and S. aureus rapidly decreased over time after UV/PS treatment. Therefore, these findings provided a fundamental understanding of the transformation process of FOS and supplied useful information for the environmental elimination of FOS contamination and its toxicity.

Photochemical transformation of C3N4 under UV irradiation: Implications for environmental fate and photocatalytic activity.

In this study, the photo-transformations of bulk C3N4 (CN) and oxidized C3N4 (OCN) under UV-irradiation were examined. Through NO3- release measurements, we found that the photo-transformation rate of OCN is higher than that of CN. Various characterization results revealed the structural and chemical properties changes of CN and OCN after photo-transformation. We proposed that under reactive oxygen species attack, CN and OCN were gradually broken into smaller fragments and finally mineralized into NO3-, CO2, and H2O through the circular reactions of deamination-hydroxylation-decarboxylation. Through the zeta potential measurements and sedimentation experiments, the influence of photo-transformation on the water stabilities of CN and OCN were assessed. The stability of CN in water increased while the water stability of OCN decreased after photo-transformation, implying that the changes to C3N4-based materials caused by photo-transformation may significantly impact their environmental behaviors. Moreover, the photocatalytic activities of the photo-transformed OCN and CN substantially decreased, indicating that the structural changes might be the main reason for their photocatalytic activity loss. These findings highlight the non-negligible influence of photo-transformation on the fate of C3N4 in aquatic environments, as well as on the photochemical stability during its use.

Microplastics in mangrove sediments of the Pearl River Estuary, South China: Correlation with halogenated flame retardants' levels.

Marine microplastic pollution of intertidal mangrove ecosystem is a matter of concern. However, the relationship between microplastic distribution and other pollutants such as halogenated flame retardants (HFRs) is unknown. In this study, forty-eight sediment samples were collected from three mangrove wetlands of the Pearl River Estuary (PRE), South China to investigate the distribution of microplastic and discuss the possible relationship between HFRs and microplastic abundance in mangrove sediments. The abundance of microplastic in mangrove sediments from the PRE ranged from 100 to 7900 items·kg-1 dry weight (dw), with an average of 851 ± 177 items·kg-1 dw, which was at a relatively higher level compared to other regions worldwide. The highest abundance of microplastic was observed in Shenzhen mangrove sediments. The abundance of microplastic was significantly and positively correlated with population density and gross domestic product of the PRE. The microplastics with size <500 µm were predominant in mangrove sediments, accounting for a proportion of 69.4% in all microplastic samples. Polypropylene-polyethylene copolymer, green/black, and fibers/fragments were the dominant type, color and shape in all microplastic samples, respectively. The correlation between HFRs and microplastic abundance demonstrated that polybrominated diphenyl ethers, decabromodiphenyl ethane, 1,2-bis(2,4,6-tribromophenoxy)ethane and hexabromocyclododecane may have the same pollution source as microplastics.

Enhanced adsorption of bisphenol A, tylosin, and tetracycline from aqueous solution to nitrogen-doped multiwall carbon nanotubes via cation-π and π-π electron-donor-acceptor (EDA) interactions.

Doping heteroatoms in carbon nanotubes can substantially enhance the electronic polarizability of the carbon surface and thus may facilitate adsorptive interactions of organic contaminants. Here, the adsorption isotherms of three polar/ionizable emerging organic contaminants, bisphenol A, tylosin, and tetracycline from aqueous solutions to synthesized heteroatom nitrogen-doped multiwall carbon nanotubes (N-MCNT) were compared with those to commercial non-doped multiwall carbon nanotubes (MCNT) at pH ~ 6. N-MCNT exhibited much stronger adsorption (3-4 folds higher sorption distribution coefficients, Kd) towards the three adsorbates than MCNT. The hydroxyl group-substituted bisphenol A molecule is rich in π-electrons and thus interacts with the polarized π-electron-depleted N-heterocyclic aromatic ring on N-MCNT via π-π electron-donor-acceptor (EDA) interaction, whereas the protonated amino group and enone groups in the tylosin molecule are deficient in electrons and interact with the neighboring π-electron-rich aromatic ring on N-MCNT via cation-π and π-π EDA interactions, respectively. The tetracycline molecule contains both electron-rich moiety (phenol ring) and electron-depleted moieties (protonated amino group and enone groups), which interact with the corresponding π-electron-acceptor/donor sites on N-MCNT. The proposed adsorption mechanisms were tested by the effects of ionic strength (NaCl or CaCl2), co-present Cu2+ ion, and changing pH on adsorption, and further by the adsorption behavior of a model organic cation (tetraethylamine). These results indicate that enhanced adsorption of emerging organic contaminants to carbon nanotubes can be achieved by doping with heterocyclic nitrogen atoms to facilitate specific EDA interactions. Capsule: Nitrogen-doped multiwall carbon nanotubes exhibit enhanced adsorptive removal of bisphenol A, tylosin, and tetracycline from aqueous solutions.

Uptake, Elimination, and Biotransformation Potential of a Progestagen (Cyproterone Acetate) in Tilapia Exposed at an Environmental Concentration.

Although the distribution of progestagens in aquatic environments has been widely reported, details on their uptake, elimination, and biotransformation in fish have received little attention. This study investigated the uptake, elimination, and biotransformation potential of a progestagen, cyproterone acetate (CPTA), in Nile tilapia ( Oreochromis niloticus) exposed to an environmentally relevant concentration under semistatic regimes. CPTA in tilapia tissues followed a similar pattern, reaching a concentration plateau within 4 days of exposure, and dropping to below limits of quantitation within 4 days of elimination. The calculated steady-state bioconcentration factors suggest a low bioconcentration potential of CPTA in juvenile tilapia. Results of enzymatic hydrolysis treatments revealed that no conjugates of CPTA were present in tissues, but conjugated biotransformation products of CPTA were found in bile, liver, and muscle. Most CPTA entered tissues and then was biotransformed into seven different products by phase I and phase II metabolism. The concentrations of endogenous cortisol were significantly influenced by CPTA in plasma and liver during the uptake period. These findings suggest that biotransformation products of CPTA should be considered for the assessment of the bioconcentration potential and ecological effects of progestagens.

Halogenated flame retardants in mangrove sediments from the Pearl River Estuary, South China: Comparison with historical data and correlation with microbial community.

Polybrominated diphenyl ethers (PBDEs), decabromodiphenyl ethane (DBDPE), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCDD) and dechlorane plus (DP) were measured in sediments collected from three mangrove wetlands of the Pearl River Estuary (PRE) in South China. This study aims to investigate the distribution of these halogenated flame retardants (HFRs) and the correlations between HFRs and microbial community structure in mangrove sediments. Concentrations of PBDEs, DBDPE, BTBPE, TBBPA, HBCDD and DP in mangrove sediments ranged from 6.97 to 216.1, 3.70-26.0, 0.02-0.73, 0.02-37.5, 0.44-127.5 and 0.07-2.23 ng/g dry weight, respectively. Higher levels of PBDEs, BTBPE, HBCDD and DP were observed in sediments from Futian mangrove wetland of Shenzhen, the only nature reserve located in the downtown of China. The highest concentration of TBBPA found in mangrove sediments from Guangzhou was proximate to a ferry terminal and a dockyard where TBBPA is widely used in the coatings. PBDEs were the predominant HFRs in mangrove sediments, with an average contribution of 63.0%. Mangrove sediments from Guangzhou and Zhuhai showed an enrichment of (-)-α-HBCDD, (-)-ß-HBCDD and (-)-γ-HBCDD. Concentrations of HFRs in mangrove sediments from Guangzhou increased significantly from 2012 to 2015, which was probably due to the establishment and rapid development of Nansha Free Trade Zone of Guangzhou. Redundancy analysis showed that HFRs may cause a shift of microbial community structure in mangrove sediments and the variations were significantly correlated with TBBPA, syn-DP and BTBPE.

Sorption and desorption of phenanthrene on biodegradable poly(butylene adipate co-terephtalate) microplastics.

Biodegradable plastics, as alternatives to conventional plastics, are increasingly used, but their interactions with organic pollutants are still unknown. In this study, the sorption and desorption behaviors on a type of biodegradable plastic-poly(butylene adipate co-terephtalate) (PBAT) were investigated, and at the same time two types of conventional plastics-polyethylene (PEc and PEv) and polystyrene (PS) were used for comparison. Phenanthrene (PHEN) was chosen as one of representative organic pollutants. Results indicated that the sorption and desorption capacities of PBAT were not only higher than those of the other types of microplastics, but also higher than those of carbonaceous geosorbents. The surface area normalized results illustrated that sorption and desorption of the microplastics were positively correlated with their abundance of rubbery subfraction. The sorption kinetic results showed that the sorption rates of PBAT and PEc were higher than PEv and PS. The effects of water chemistry factors including salinity, dissolved organic matter and Cu2+ ion on the sorption process displayed the same trend, but the degrees of influence on the four microplastics differed. The degrees of influence were mainly dependent on the abundance of rubbery subfraction for microplastics. These findings indicate that the biodegradable poly(butylene adipate co-terephtalate) microplastics are actually stronger vectors than the conventional microplastics, and crystallization characteristics of the microplastics have great influences on the vector effect.

Occurrence and distribution of microplastics in an urban river: A case study in the Pearl River along Guangzhou City, China.

Microplastics, as emerging contaminants in the global environment, have become a cause for concern for both academics and the public. The present understanding of microplastic pollution is primarily focused on marine environments, and less attention has been given to freshwater environments, in particular, to urban rivers. In this study, microplastics were sampled from surface water and sediments in 14 sites located in the lower course of the Pearl River. These sampling sites are located along Guangzhou of South China, with built-up areas being the dominant land use. The abundances of microplastics in surface water and sediments ranged from 379 to 7924 items·m-3 and 80 to 9597 items·kg-1, respectively. Polyethylene and polypropylene were the common types of microplastics, together accounting for 64.3% and 73.8% of surface water and sediment samples, respectively. Fibers were the dominant microplastic shapes in both water and sediment samples. The abundances of microplastics varied in surface water and sediments with each site, which might be affected by multiple factors. Our results indicated that wastewater treatment plants (WWTP) could reduce microplastics from municipal sewage which was finally discharged into the Pearl River along Guangzhou.

Halogenated organic pollutants in marine biota from the Xuande Atoll, South China Sea: Levels, biomagnification and dietary exposure.

Six marine biota species were collected from the Xuande Atoll, South China Sea to investigate the bioaccumulation of dichlorodiphenyltrichloroethane (DDT), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), decabromodiphenyl ethane (DBDPE) and dechlorane plus (DP). Pike conger (Muraenesox talabonoides) had the highest concentrations of halogenated organic pollutants (HOPs) among the six marine biota species. DDTs were the predominant HOPs, followed by PCBs and PBDEs, with minor contributions of DBDPE and DP. Twenty-one percent of samples had ratios of (DDE+DDD)/ΣDDTs lower than 0.5, implying the presence of fresh DDT inputs in the environment of the Xuande Atoll. The biomagnification factor values for DDTs, PCBs, PBDEs and DP were higher than 1, suggesting biomagnification of these contaminants in the marine food chains. Consumption of seafood from the Xuande Atoll might not subject local residents in the coastal areas of South China to health risks as far as HOPs are concerned.

Enhanced catalytic degradation of ciprofloxacin with FeS2/SiO2 microspheres as heterogeneous Fenton catalyst: Kinetics, reaction pathways and mechanism.

In this study, the application of FeS2/SiO2 microspheres as a catalyst to activate H2O2 for the degradation of ciprofloxacin (CIP) was systematically investigated. Results demonstrated that the presence of SiO2 microspheres on the surface of FeS2 could effectively make the reaction of aqueous Fe2+ and H2O2 smoothly continuous by controlling the release of aqueous Fe2+ from FeS2. Nearly 100% of CIP was degraded after 60min under the optimum conditions. A superior performance on the CIP degradation and high reusability of the catalyst was obtained in FeS2/SiO2 microspheres activated H2O2 system. A low concentration of ethylene diamine tetraacetie acid (EDTA) did positively affect the degradation rate of CIP. A synergetic effect between adsorption and oxidation processes contributed to the significant enhancement of CIP degradation. Seven oxidation intermediates were identified during the CIP degradation process, and the direct HO oxidation proved to be a main CIP degradation pathway. For degradation pathway of CIP, oxidation of piperazine ring would be its first step, followed by cleavage of the heterocyclic ring. Subsequently, the substitution, hydroxylation and decarboxylation processes occurred. This is the first report on the feasibility of FeS2/SiO2 microspheres activated H2O2 system for the enhanced degradation of CIP.

Enhanced removal of sulfonamide antibiotics by KOH-activated anthracite coal: Batch and fixed-bed studies.

The presence of sulfonamide antibiotics in aquatic environments poses potential risks to human health and ecosystems. In the present study, a highly porous activated carbon was prepared by KOH activation of an anthracite coal (Anth-KOH), and its adsorption properties toward two sulfonamides (sulfamethoxazole and sulfapyridine) and three smaller-sized monoaromatics (phenol, 4-nitrophenol and 1,3-dinitrobenzene) were examined in both batch and fixed-bed adsorption experiments to probe the interplay between adsorbate molecular size and adsorbent pore structure. A commercial powder microporous activated carbon (PAC) and a commercial mesoporous carbon (CMK-3) possessing distinct pore properties were included as comparative adsorbents. Among the three adsorbents Anth-KOH exhibited the largest adsorption capacities for all test adsorbates (especially the two sulfonamides) in both batch mode and fixed-bed mode. After being normalized by the adsorbent surface area, the batch adsorption isotherms of sulfonamides on PAC and Anth-KOH were displaced upward relative to the isotherms on CMK-3, likely due to the micropore-filling effect facilitated by the microporosity of adsorbents. In the fixed-bed mode, the surface area-normalized adsorption capacities of Anth-KOH for sulfonamides were close to that of CMK-3, and higher than that of PAC. The irregular, closed micropores of PAC might impede the diffusion of the relatively large-sized sulfonamide molecules and in turn led to lowered fixed-bed adsorption capacities. The overall superior adsorption of sulfonamides on Anth-KOH can be attributed to its large specific surface area (2514 m(2)/g), high pore volume (1.23 cm(3)/g) and large micropore sizes (centered at 2.0 nm). These findings imply that KOH-activated anthracite coal is a promising adsorbent for the removal of sulfonamide antibiotics from aqueous solution.

Enhanced Adsorption of Hydroxyl- and Amino-Substituted Aromatic Chemicals to Nitrogen-Doped Multiwall Carbon Nanotubes: A Combined Batch and Theoretical Calculation Study.

A large effort is being made to develop nanosorbents with tunable surface chemistry for enhanced adsorption affinity and selectivity toward target organic contaminants. Heteroatom N-doped multiwall carbon nanotubes (N-MCNT) were synthesized by chemical vapor deposition of pyridine and were further investigated for the adsorptive removal of several aromatic chemicals varying in electronic donor and acceptor ability from aqueous solutions using a batch technique. Compared with commercial nondoped multiwall carbon nanotubes (MCNT), N-MCNT had similar specific surface area, morphology, and pore-size distribution but more hydrophilic surfaces and more surface defects due to the doping of graphitic and pyridinic N atoms. N-MCNT exhibited enhanced adsorption (2-10 folds) for the π-donor chemicals (2-naphthol and 1-naphthalmine) at pH ∼6 but similar adsorption for the weak π-donor chemical (naphthalene) and even lower adsorption (up to a 2-fold change) for the π-acceptor chemical (1,3-dinitrobenzene). The enhanced adsorption of 2-naphthol and 1-naphthalmine to N-MCNT was mainly attributed to the favored π-π electron-donor-acceptor (EDA) interaction between the π-donor adsorbate molecule and the polarized N-heterocyclic aromatic ring (π-acceptor) on N-MCNT. The proposed adsorption enhancement mechanisms were further tested through the pH effects on adsorption and the density function theory (DFT) calculation. The results show for the first time that the adsorptive interaction of π-donor aromatic compounds with carbon nanomaterials can be facilitated by N-doping.