Influence of hydrogen peroxide on isotactic polypropylene degradation into micro/nano-plastics under thermal oxidative reaction

The influence of aggregate gradation (11 gradations with volume moment mean diameter ranging from 192 to 398 μm) and hydrogen peroxide (HP) dosage (0%, 0.8%, 1.6%, 2.4%, and 3.2% by weight of cement) on the fluidity, strength, and microstructure of cemented foam backfill (CFB) was comprehensively evaluated in this study. The fluidity, expansion ratio, and water film thickness for fresh CFB and 28-day strength and microstructural properties for hardened CFB were compared as a function of aggregate gradation and HP dosage. The end results reveal that the fluidity of fresh CFB decreases with finer aggregate and higher HP dosage due to their effect on water film thickness, but the expansion ratio increases. The strength for hardened backfill without foaming agent increases with coarser aggregate, but that for cemented foam backfill decreases. Additionally, the mercury intrusion porosimetry (MIP) results denote that the variation of aggregate gradation and HP dosage mainly influences the volume of large pores (>1 μm) and consequently the overall porosity of CFB, resulting in the strength variation. The linear relationship between compressive strength and averaged fractal dimensions of cross-sections obtained from X-ray CT indicates that the number of extra-large pores (100~500 μm) determines the strength of CFB. The influence of HP on the hydration reaction of backfill and the potential application of CFB in mining practices are also discussed.

Oxidative stress in clinical situations - fact or fiction?

The emission from low‐pressure microwave plasmas in the vacuum‐ultraviolet (VUV) region (λ < 200 nm) was investigated in order to use these plasmas as light sources for the study of the VUV photochemistry of polyethylene (PE) and polypropylene (PP) as part of the study of plasma‐polymer interaction. These polymers, immersed in low‐presure oxygen, were exposed to radiation with wavelengths down to 112 nm, the cut off of magnesium fluoride used as a window to separate the polymer specimen from the plasma light source. Total oxygen incorporation in the surface [O], and the formation of hydroxyl, carbonyl, and carboxyl groups were measured using XPS in combination with chemical derivatizations, particularly their dependence upon the radiation spectrum and the oxygen pressure around the sample. In most experiments the surface oxygen concentration [O] attained a constant value that appears to be related to the initial oxidation rate; this suggests a competition between oxygen incorporation and chain scission reactions, followed by the removal of volatile oxidation products. PE is usually oxidized to a higher level than PP, the latter appearing to be more susceptible to reaction with atomic oxygen than PE. A general initiation mechanism for the VUV experiments is proposed that allows us to explain the observed differences in behavior between PE and PP, and the results obtained under different irradiation conditions. The nature of oxidation products is in both cases very similar to what is observed after direct plasma treatment of the polymers. We conclude that short wavelength radiation contributes very appreciably to the observed surface modification effects during plasma treatment of PE and PP. © 1995 John Wiley & Sons, Inc.

Plastic pollution is a pressing global environmental challenge, and low-density-polyethylene (LDPE) is among the most persistent synthetic polymers. This study investigates the in vitro biodegradation of LDPE by native Aspergillus strains isolated from plastic-contaminated soils in Trujillo, Peru. Molecular techniques were used to identify the Aspergillus species. The LDPE strips were incubated for 50 days, and biodegradation was evaluated by weight loss (%), pH variation, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Likewise, the reduction rate and half-life of the polymer (t1/2) were calculated. Three strains of Aspergillus—A. niger H1C, A. ochraceopetaliformis H3C, and A. tamarii H6C—were isolated and evaluated for their ability to LDPE under in vitro conditions. A. niger H1C exhibited the most weight reduction (4.25 ± 1.67%) and a polymer half-life of 897.89 days, while A. tamarii H6C demonstrated a comparable loss (3.79 ± 1.52%) with a half-life of 901.6 days. A. ochraceopetaliformis H3C exhibited a moderate degradation (1.98 ± 0.37%), with the longest half-life recorded at 1757.33 days. The process was supported by pH variations. Furthermore, FTIR and SEM analyses revealed structural modifications in LDPE including formation of hydroxyl, carbonyl, and ether groups, suggesting oxidative and enzymatic activity-possibly mediated by lipases induced under lipid-rich conditions. This is the first report of A. ochraceopetaliformis and A. tamarii, highlighting their potential in sustainable plastic bioremediation strategies aligned with SDG 13 (Climate Action).

Although wood–plastic composites have become more accepted and used in recent years and are promoted as low‐maintenance, high‐durability building products, they do experience a color change and a loss in mechanical properties with accelerated weathering. In this study, we attempted to characterize the modulus‐of‐elasticity (MOE) loss of photostabilized high‐density polyethylene (HDPE) and composites of wood flour and high‐density polyethylene (WF/HDPE) with accelerated weathering. We then examined how weathering changed the surface chemistry of the composites and looked at whether or not the surface changes were related to the MOE loss. By examining surface chemistry changes, we hoped to begin to understand what caused the weathering changes. The materials were left unstabilized or were stabilized with either an ultraviolet absorber or pigment. After 1000 and 2000 h of accelerated weathering, the samples were tested for MOE loss. Fourier transform infrared (FTIR) spectroscopy was employed to monitor carbonyl and vinyl group formation at the surface. Changes in the HDPE crystallinity were also determined with FTIR techniques. It was determined that structural changes in the samples (carbonyl group formation, terminal vinyl group formation, and crystallinity changes) could not be reliably used to predict changes in MOE with a simple linear relationship. This indicated that the effects of crosslinking, chain scission, and crystallinity changes due to ultraviolet exposure and interfacial degradation due to moisture exposure were interrelated factors for the weathering of HDPE and WF/HDPE composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2263–2273, 2004

We report the new insight into the dielectric barrier discharge (DBD) induced inactivation of Microcystis aeruginosa, the dominant algae which caused harmful cyanobacterial blooms in many developing countries. In contrast with the previous work, we employed flow cytometry to examine the algal cells, so that we could assess the dead and living cells with more accuracy, and distinguish an intermediate state of algal cells which were verified as apoptotic. Our results showed that the numbers of both dead and apoptotic cells increased with DBD treatment delay time, and hydrogen peroxide produced by DBD was the main reason for the time-delayed inactivation effect. However, apart from the influence of hydrogen peroxide, the DBD-induced initial injures on the algal cells during the discharge period also played a considerable role in the inactivation of the DBD treated cells, as indicated by the measurement of intracellular reactive oxygen species (ROS) inside the algal cells. We therefore propose an effective approach to utilization of non-thermal plasma technique that makes good use of the residual inactivation effect to optimize the experimental conditions in terms of discharge time and delay time, so that more efficient treatment of cyanobacterial blooms can be achieved.

Biodegradation is an eco-friendly measure to address plastic pollution. This study screened four bacterial isolates that were capable of degrading recalcitrant polymers, i.e., low-density polyethylene, polyethylene terephthalate, and polystyrene. The unique bacterial isolates were obtained from plastic polluted environment. Dermacoccus sp. MR5 (accession no. OP592184) and Corynebacterium sp. MR10 (accession no. OP536169) from Malaysian mangroves and Bacillus sp. BS5 (accession no. OP536168) and Priestia sp. TL1 (accession no. OP536170) from a sanitary landfill. The four isolates showed a gradual increase in the microbial count and the production of laccase and esterase enzymes after 4weeks of incubation with the polymers (independent experiment set). Bacillus sp. BS5 produced the highest laccase 15.35 ± 0.19 U/mL and showed the highest weight loss i.e., 4.84 ± 0.6% for PS. Fourier transform infrared spectroscopy analysis confirmed the formation of carbonyl and hydroxyl groups as a result of oxidation reactions by enzymes. Liquid chromatography-mass spectrometry analysis showed the oxidation of the polymers to small molecules (alcohol, ethers, and acids) assimilated by the microbes during the degradation. Field emission scanning electron microscopy showed bacterial colonization, biofilm formation, and surface erosion on the polymer surface. The result provided significant insight into enzyme activities and the potential of isolates to target more than one type of polymer for degradation.

The chemical and physical changes occurring during U.V. degradation of high impact polystyrene

Photostabilization of poly-(2,6-dimethyl-1,4-phenylene oxide) films by metal dialkyl dithio-phosphate

Aims; It has been reported that hepatitis C virus (HCV) core expression causes hepatocellular carcinoma (HCC) in transgenic mice by reactive oxygen species (ROS). On the other hand, we have reported that loss of signals of retinoic acid (RA), a metabolite of vitamin A, leads to steatohepatitis, eventually to HCC in the receptor for RA (RARα)-knocked-down mice. We have demonstrated that the mechanism by which loss of RA signal causes HCC is mediated by increased oxidative stress via impaired metabolisms of fatty acids and iron. In turn, the effect of oxidative stress on RA signals remains to be clarified. The present study aims to explore the effect of oxidative stress and HCV core expression on RA signals in the context of hepatocarcinogenesis. Methods; The first parts of experiments were done using hydrogen peroxide as the source of ROS Human HCC cell lines HuH7, HLF, HepG2, Hep3B, Li7, Alexander and HuH6 were used. The expression level of RARα and activation of MAPKs such as ERK, JNK and p38, and RA signal by DR5-reporter assay were examined with 0.1∼1μM hydrogen peroxide. Anisomycin, an activator of JNK signal, SP600125, an inhibitor of JNK, and constitutive active MKK7-JNK1 was explored on level of RARα and activation of MAPKs. Phosphorylation and ubiquitination of mutant RARα, of which three phosphorylation sites by JNK are changed from serines to alanines, were examined. The second parts of experiments were performed using tetracycline-inducible HCV core system (Tet-On system), which is constructed in HuH7 cells. The intensity of RA signal after induction of HCV core protein was measured by DR5-reporter assay. The expression Sp101b, which is induced by RA and an adaptive protein of HCV core, was examined on expression and cellular translocation. The level of SRC-3, a coactivator of RAR/RXR, and p38 MAPK, an upstream signal of SRC-3 and a downstream signal of oxidative stress, were examined. The cellular antioxidative ability and hydroxyl radical formation were measured during this process. Results; In the first parts experiment using hydrogen peroxide, oxidative stress suppressed RA signal through degradation of RARα. The degradation of RARα was mediated by its phosphorylation by JNK and followed by ubiquitination. In the second parts of experiments, expression of HCV core protein reached its maximum at 72 h at 5 μg/ml of Tet. RA signal increased at 36 h, however then decreased at 48 h and 72 h. The decreased RA signal was reverted by N-acetyl cystein (NAC), an antioxidative protein. The cellular antioxidative ability was decreased at 24h, and hydroxyl radical formation was increased at 48 h. Activation of p38 and SRC-3 was observed after induction of HCV core expression, however it was inhibited by NAC. Conclusions; The data of the present study suggest that RA plays an important role in preventive effect of hepatitis C virus- and oxidative stress-related hepatocarcinogenesis Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5723.

Identification of plastic-degrading bacteria in the human gut

The use of self-medication, which includes dietary supplements and over-the-counter drugs, is still on the rise, while safety issues are not well addressed yet. This especially holds for combinations. For example, iron supplements and magnesium peroxide both produce adverse effects via the formation of reactive oxygen species (ROS). This prompted us to investigate the effect of the combination of three different iron supplements with magnesium peroxide on ROS formation. Hydroxyl radical formation by the three iron supplements either combined with magnesium peroxide or alone was determined by performing a deoxyribose assay. Free iron content of iron supplements was determined using ferrozine assay. To determine hydrogen peroxide formation by magnesium peroxide, a ferrous thiocyanate assay was performed. Finally, electron spin resonance spectroscopy (ESR) was performed to confirm the formation of hydroxyl radicals. Our results show that magnesium peroxide induces the formation of hydrogen peroxide. All three iron supplements induced the formation of the extremely reactive hydroxyl radical, although the amount of radicals formed by the different supplements differed. It was shown that combining iron supplements with magnesium peroxide increases radical formation. The formation of hydroxyl radicals after the combination was confirmed with ESR. All three iron supplements contained labile iron and induced the formation of hydroxyl radicals. Additionally, magnesium peroxide in water yields hydrogen peroxide, which is converted into hydroxyl radicals by iron. Hence, iron supplements and magnesium peroxide is a hazardous combination and exemplifies that more attention should be given to combinations of products used in self-medication.

Background: Dental bleaching agents show the ability to permeate through dental hard tissues, which may lead to pulp tissue changes. This systematic review (PROSPERO register: CRD42020213767) is aimed at understanding the effects of bleaching agents on the process of mineralization of the pulp tissue.Methods: Only in vitro studies evaluating the influence of hydrogen peroxide (HP) on mineralization in dental pulp cells were included. Studies without a non-bleached control group or cells after co-treatment with a bleaching agent other than HP and/or carbamide peroxide were excluded. The primary outcomes evaluated were alkaline phosphatase (ALP) activity and mineralized nodule deposition. The mineralization markers analysis in dental pulp cells and the cell viability were considered secondary outcomes. Two independent authors conducted a systematic search (PubMed/MEDLINE, Scopus, Embase, Cochrane Library, and OpenGrey until January 2021) with no language restrictions and performed data extraction. The quality assessment was appraised according to a modified Joanna Briggs Institute critical appraisal checklist.Results: The search resulted in 473 studies, and 11 were considered eligible. Overall, a reduction in the process of mineralization was observed among pulp cells after bleaching. A reduction in the ALP activity was reported in the mostly bleached groups using different protocols and analysis periods of nine studies. Regarding mineralized nodule deposition, 6 studies reported a significant reduction from 7 to 21 days among bleached groups. Of those three studies that investigated other mineralization markers, two found a reduction in the expression of dentin matrix acidic phosphoprotein (DMP)-1, dentin sialophosphoprotein (DSPP), and matrix extracellular phosphoglycoprotein (MEPE) among some bleaching gel concentrations. In contrast, one study showed a greater expression of osteopontin (OPN) and osteocalcin (OCN) in 100 μmol/L HP after 5 or 10 min of exposure, and another study showed significant induction of DSPP in concentrations of up to 0.5 mmol/L HP.Conclusion: Especially, high concentrations of bleaching gel reduce the potential of mineralization in pulp cells in in vitro studies; however, different HP concentrations, bleaching protocols, and analysis periods can influence this outcome.

Reaction patterns in photooxidative degradation of two herbicides

Dose-dependent degradation and long-term ageing effects in electron beam-irradiated natural rubber latex catheters