Total Organic Carbon as a Quantitative Index of Micro- and Nano-Plastic Pollution.

The global pollution of micro- and nano-plastics (MNPs) calls for monitoring methods. As diverse mixtures of various sizes, morphologies, and chemical compositions in the environment, MNPs are currently quantified based on mass or number concentrations. Here, we show total organic carbon (TOC) as an index for quantifying the pollution of total MNPs in environmental waters. Two parallel water samples are respectively filtered with a carbon-free glass fiber membrane. Then, one membrane with the collected particulate substances is treated by potassium peroxodisulfate oxidation and Fenton digestion in sequence for quantifying the sum of MNPs and particulate black carbon (PBC) as TOCMNP&PBC using a TOC analyzer, another membrane is treated by sulfonation and Fenton digestion for quantifying PBC as TOCPBC, and the TOC of MNPs is calculated by subtracting TOCPBC from TOCMNP&PBC. The feasibility of our method is demonstrated by determination of various MNPs of representative plastic types and sizes (0.5-100 µm) in tap, river, and sea water samples, with low detection limits (∼7 µg C L-1) and high spiked recoveries (83.7-114%). TOC is a powerful index for routine monitoring of MNP pollution.

Swelling-Induced Fragmentation and Polymer Leakage of Nanoplastics in Seawater.

Nanoplastics (NPs) have been successively detected in different environmental matrixes and have aroused great concern worldwide. However, the fate of NPs in real environments such as seawater remains unclear, impeding their environmental risk assessment. Herein, multiple techniques were employed to monitor the particle number concentration, size, and morphology evolution of polystyrene NPs in seawater under simulated sunlight over a time course of 29 days. Aggregation was found to be a continuous process that occurred constantly and was markedly promoted by light irradiation. Moreover, the occurrence of NP swelling, fragmentation, and polymer leaching was evidenced by both transmission electron microscopy and scanning electron microscopy techniques. The statistical results of different transformation types suggested that swelling induces fragmentation and polymer leakage and that light irradiation plays a positive but not decisive role in this transformation. The observation of fragmentation and polymer leakage of poly(methyl methacrylate) and poly(vinyl chloride) NPs suggests that these transformation processes are general for NPs of different polymer types. Facilitated by the increase of surface functional groups, the ions in seawater could penetrate into NPs and then stretch the polymer structure, leading to the swelling phenomenon and other transformations.

Digestive Elimination of Coexisting Microplastics for Determination of Particulate Black Carbon in Environmental Waters.

Determination of particulate black carbon (PBC) in the environment is of great importance but faces a new challenge due to the increasing occurrence of coexisting microplastics (MPs), which are an emerging contaminant with properties very similar to those of PBC and cannot be discriminated in the chemical digestion procedure of the reported PBC analysis method. Herein, a comprehensive method has been developed for accurately determining PBC by digestive elimination of the coexisting MPs and other non-black carbon organic matter. Water samples were filtered with a glass fiber membrane (0.3 µm pore size), and the collected substances with the membrane were subjected to sulfonation with chlorosulfonic acid and Fenton digestion in sequence and then to the total organic carbon analyzer for quantification of PBC. Under the optimized conditions, MPs of various sizes and polymer types were efficiently eliminated (>91.0%), whereas various PBC samples were undigested with recoveries over 91.7% except for the relatively low recovery of 65.6% for the PBC prepared at a low pyrolysis temperature of 400 °C. The feasibility of the proposed method was verified by analysis of real water samples with a spike recovery of 88.6-100.2%. We anticipate that this work will pave an avenue for reliable determination of PBC in the presence of MPs.

Sequential Isolation of Microplastics and Nanoplastics in Environmental Waters by Membrane Filtration, Followed by Cloud-Point Extraction.

Respective detection of microplastics (MPs) and nanoplastics (NPs) is of great importance for their different environmental behaviors and toxicities. Using spherical polystyrene (PS) and poly(methyl methacrylate) (PMMA) plastics as models, the efficiency for sequential isolation of MPs and NPs by membrane filtration and cloud-point extraction was evaluated. After filtering through a glass membrane (1 µm pore size), over 90.7% of MPs were trapped on the membrane, whereas above 93.0% of NPs remained in the filtrate. The collected MPs together with the glass membrane were frozen in liquid nitrogen, ground, and suspended in water (1 mL) and subjected to pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) determination. The NPs in the filtrate were concentrated by cloud-point extraction, heated at 190 °C to degrade the extractant, and then determined by Py-GC/MS. For MPs and NPs spiked in pure water, the method detection limits are in the range of 0.05-1.9 µg/L. The proposed method is applied to analyze four real water samples, with the detection of 1.6-7.6 µg/L PS MPs and 0.6 µg/L PMMA MPs in three samples, and spiked recoveries of 75.0-102% for MPs and 67.8-87.2% for NPs. Our method offers a novel sample pretreatment approach for the respective determination of MPs and NPs.

Counting Nanoplastics in Environmental Waters by Single Particle Inductively Coupled Plasma Mass Spectroscopy after Cloud-Point Extraction and In Situ Labeling of Gold Nanoparticles.

The globally raising concern for nanoplastics (NPs) pollution calls for analytical methods for investigating their occurrence, fates, and effects. Counting NPs with sizes down to 50 nm in real environmental waters remains a great challenge. Herein, we developed a full method from sample pretreatment to quantitative detection for NPs in environmental waters. Various NPs of common plastic types and sizes (50-1200 nm) were successfully labeled by in situ growth of gold nanoparticles and counted by single particle inductively coupled plasma mass spectrometry. Sucrose density gradient centrifugation enables the isolation of gold-labeled NPs from homogeneously nucleated Au nanoparticles, enhancing the particle number detection limit to 4.6 × 108 NPs/L for 269 nm spherical polystyrene NPs. For real environmental water samples, the pretreatment of acid digestion with a mixture of 5 mM HNO3 and 40 mM HF eliminates the coexisting inorganic nanoparticles, while the following dual cloud-point extraction efficiently isolates NPs from various matrices and thus improves the Au-labeling efficiency. The high spiked recoveries (72.9%-92.8%) of NPs in different waters demonstrated the applicability of this method in different scenarios.

Comparison of fibrin glue and Vicryl sutures in conjunctival autografting for pterygium surgery.

PURPOSE: To compare clinical parameters and the tear levels of inflammatory cytokines between pterygium surgery using sutures or fibrin glue. METHODS: Fifty-six patients with primary pterygium were divided into the suture group and the glue group, in which the autograft was secured with 10-0 Vicryl sutures and fibrin glue, respectively. A questionnaire, slit-lamp examination, Schirmer test, and visual acuity test were performed in all participants. Real-time quantitative PCR (q-PCR) was used to analyze the expression of genes in pterygium and healthy conjunctival tissues. Based on the qPCR results and literature reports, five inflammatory cytokines, including hepatocyte growth factor (HGF), fibroblast growth factor 2 (FGF2), transforming growth factor-ß1 (TGF-ß1), matrix metalloproteinase 2 (MMP2), and tumor necrosis factor-α (TNF-α), were selected, and their protein levels were measured with enzyme-linked immunosorbent assay (ELISA) in patient tears before surgery as well as at postoperative day 1, 7, and 30. RESULTS: There are 28 patients in either the suture or the glue group. The average duration of surgery was 20.17 ± 3.23 min for the glue group and 32.42 ± 4.47 min for the suture group (p = 0.000). Visual acuity in both groups was improved (p = 0.002) after the surgical procedures. There were more symptoms in the suture group than in the glue group at postoperative day 7 (p = 0.002). Postoperative symptoms disappeared in both groups at 1 month after surgery. Recurrence was observed in one case in the glue group and in two cases in the suture group at the 6 month postoperative follow-up (p = 0.714). In comparison to the preoperative levels (4.33 ± 0.43 ng/ml for the suture group; 4.20 ± 0.26 ng/ml for the glue group), the levels of TNF-α in tears increased in the suture group (5.02 ± 0.49 ng/ml, p = 0.016) and decreased in the glue group (3.84 ± 0.35 ng/ml, p = 0.052) on postoperative day 1. The glue treatment induced higher HGF production (4.78 ± 1.25 ng/ml) than the suture treatment (3.04 ± 1.18 ng/ml) at postoperative day 1 (p = 0.020). Higher levels of TGF-ß1 in the glue group were detected at postoperative day 1 (3.71 ± 0.18 ng/ml) and postoperative day 30 (4.50 ± 0.51 ng/ml), compared to those in the suture group, respectively (2.74 ± 0.21 ng/ml, p = 0.000 for day 1; 3.36 ± 0.96 ng/ml, p = 0.017 for postoperative day 30). CONCLUSIONS: Fibrin glue is effective and safe for attaching conjunctival autografts with an easy surgical procedure, shortened operating time, and less postoperative discomfort. In the early postoperative period, the protein expression of inflammatory cytokines implicates that fibrin glue may induce accelerated healing and subdued inflammation on the ocular surface compared to sutures.

Stretchable solvent-free ionic conductor with self-wrinkling microstructures for ultrasensitive strain sensor.

Stretchable solvent-free ionic conductors with outstanding physicochemical stability are attractive in emerging sensing devices. However, existing ionic conductors struggle to keep high strain sensitivity with a gauge factor (GF) smaller than 4 at a strain range of up to 100%, which seriously affects the reliability of the signal output. Herein, we prepared a novel solvent-free ionic conductor, consisting of a hybrid cross-linked polymer network and mobile ions. Exquisite reticular wrinkling microstructures with ion channels were formed spontaneously by utilizing modulus mismatch in shrinkage during polymerization. The ion channels promote the ionic transport in the polymer, and the reticular wrinkling microstructures dramatically reinforce the mechanical stability and enhance energy dissipation. After being carefully optimized, the as-prepared ionic conductor demonstrated many unique advantages including perfect physicochemical stability, wide operating temperature range, the high ionic conductivity of 1.17 mS cm-1 at 15 °C and excellent sensitivity with GF as high as 7.03 at 100% strain. Moreover, benefiting from the abundant hydrogen bonds and ionic interactions in the polymer network, the ionic conductor also possesses self-healable and adhesion ability. The resulting devices can be used for quantitative evaluation of human joint motion and exhibit great potential in soft electronics or iontronics.

Lightweight and broadband 2D MoS2 nanosheets/3D carbon nanofibers hybrid aerogel for high-efficiency microwave absorption.

Three-dimensional (3D) porous molybdenum disulfide nanosheets/carbon nanofibers (MoS2/CNF) hybrid aerogels were synthesized by using solvothermal method and following carbonization, where two-dimensional (2D) MoS2 nanosheets were homogenously in-situ grown on the interconnected CNF skeleton derived from bacterial cellulose, forming a hierarchical porous structure. This unique heterogeneous structure of the MoS2/CNF hybrid aerogels were conducive to electromagnetic loss, including conduction, polarization, multi-scatterings, and reflections, thus resulting in a balanced impedance matching and microwave attenuation capacity. It was found that the resulted MoS2/CNF hybrid aerogels demonstrate excellent microwave absorbing performance when the only 5.0 wt% fillers were loaded in paraffin. Particularly, MoS2/CNF-2-900 hybrid aerogel displayed an effective absorption bandwidth of 5.68 GHz and minimum reflection loss (RLmin) value of -36.19 dB at a thickness of 2.0 mm. As the thickness increases to 4.4 mm, the RLmin value of MoS2/CNF-2-900 hybrid aerogel reaches -48.53 dB. Electromagnetic loss mechanism analysis indicates that such improved microwave attenuation is attributed to proper component, multiple heterogenous interface and hierarchical porous structures. All the results in this work pave the avenue for the development of ultralight microwave absorber with high absorption capacity as well as broad effective absorption bandwidth.