Screening for precancerous anal lesions linked to human papillomaviruses: French recommendations for clinical practice

In France, about 2000 new cases of anal cancer are diagnosed annually. Squamous cell carcinoma is the most common histological type, mostly occurring secondary to persistent HPV16 infection. Invasive cancer is preceded by precancerous lesions. In addition to patients with a personal history of precancerous lesions and anal cancer, three groups are at very high risk of anal cancer: (i) men who have sex with men and are living with HIV, (ii) women with a history of high-grade squamous intraepithelial lesions (HSILs) or vulvar HPV cancer, and (iii) women who received a solid organ transplant more than 10 years ago. The purpose of screening is to detect HSILs so that they can be treated, thereby reducing the risk of progression to cancer. All patients with symptoms should undergo a proctological examination including standard anoscopy. For asymptomatic patients at risk, an initial HPV16 test makes it possible to target patients at risk of HSILs likely to progress to cancer. Anal cytology is a sensitive test for HSIL detection. Its sensitivity is greater than 80% and exceeds that of proctological examination with standard anoscopy. It is indicated in the event of a positive HPV16 test. In the presence of cytological abnormalities and/or lesions and a suspicion of dysplasia on clinical examination, high-resolution anoscopy is indicated. Performance is superior to that of proctological examination with standard anoscopy. However, this technique is not widely available, which limits its use. If high-resolution anoscopy is not possible, screening by a standard proctological examination is an alternative. There is a need to develop high-resolution anoscopy and triage tests and to evaluate screening strategies.

French multicentre prospective evaluation of radiofrequency ablation in the management of haemorrhoidal disease

PURPOSE

The aim of this study was to evaluate the efficacy and safety of radiofrequency ablation (RFA) in the management of haemorrhoidal disease with 1 year's follow-up.

METHOD

This prospective multicentre study assessed RFA (Rafaelo©) in outpatients with grade II-III haemorrhoids. RFA was performed in the operating room under locoregional or general anaesthesia. Primary endpoint was the evolution of a quality-of-life score adapted to the haemorrhoid pathology (HEMO-FISS-QoL) 3 months after surgery. Secondary endpoints were evolution of symptoms (prolapsus, bleeding, pain, itching, anal discomfort), complications, postoperative pain and medical leave.

RESULTS

A total of 129 patients (69% men, median age 49 years) were operated on in 16 French centres. Median HEMO-FISS-QoL score dropped significantly from 17.4/100 to 0/100 (p < 0.0001) at 3 months. At 3 months, the rate of patients reporting bleeding (21% vs. 84%, p < 0.001), prolapse (34% vs. 91.3%, p < 0.001) and anal discomfort (0/10 vs. 5/10, p < 0.0001) decreased significantly. Median medical leave was 4 days [1-14]. Postoperative pain was 4/10, 1/10, 0/10 and 0/10 at weeks 1, 2, 3 and 4. Seven patients (5.4%) were reoperated on by haemorrhoidectomy for relapse, and three for complications. Reported complications were haemorrhage (3), dysuria (3), abscess (2), anal fissure (1), external haemorrhoidal thrombosis (10), pain requiring morphine (11). Degree of satisfaction was high (+ 5 at 3 months on a - 5/+ 5 scale).

CONCLUSION

RFA is associated with an improvement in quality of life and symptoms with a good safety profile. As expected for minimally invasive surgery, postoperative pain is minor with short medical leave.

CLINICAL TRIAL REGISTRATION AND DATE

Clinical trial NCT04229784 (18/01/2020).

Relationships between internalized stigma and depression and suicide risk among queer youth in the United States: a systematic review and meta-analysis

Background

Queer youth experience high rates of depression and suicidality. These disparities stem from stigma-based stressors, including internalized stigma (i.e., negative social views that minoritized individuals internalize about their own identity). Given the importance of this factor in understanding mental health disparities among queer youth, we completed a systematic review and meta-analysis examining the relationships between internalized stigma and outcomes of depression and suicide risk (i.e., suicidal ideation, non-suicidal self-injury, and suicidal behavior).

Methods

We followed the PRISMA standards. Six bibliographic databases were searched for studies in the United States from September 2008 to March 2022. Dual independent screening of search results was performed based on a priori inclusion criteria.

Results

A total of 22 studies were included for data extraction and review. Most studies examined general internalized homophobia, with few examining internalized biphobia or transphobia. Many studies examined depression as an outcome, few studies examined suicidal ideation or behavior, and no studies examined non-suicidal self-injury. Meta-analyses model results show the association between general internalized queer stigma and depressive symptoms ranged r = 0.19, 95% CI [0.14, 0.25] to r = 0.24, 95% CI [0.19, 0.29], the latter reflecting more uniform measures of depression. The association between internalized transphobia and depressive outcomes was small and positive (r = 0.21, 95% CI [-0.24, 0.67]). General internalized queer stigma and suicidal ideation had a very weak positive association (r = 0.07, 95% CI [-0.27, 0.41]) and an even smaller, weaker positive association with suicide attempt (r = 0.02, 95% CI [0.01, 0.03]).

Conclusion

Implications for clinical practice, policy, and future research are discussed.

Environmentally sustainable implementations of two-dimensional nanomaterials

Rapid advancement in nanotechnology has led to the development of a myriad of useful nanomaterials that have novel characteristics resulting from their small size and engineered properties. In particular, two-dimensional (2D) materials have become a major focus in material science and chemistry research worldwide with substantial efforts centered on their synthesis, property characterization, and technological, and environmental applications. Environmental applications of these nanomaterials include but are not limited to adsorbents for wastewater and drinking water treatment, membranes for desalination, and coating materials for filtration. However, it is also important to address the environmental interactions and implications of these nanomaterials in order to develop strategies that minimize their environmental and public health risks. Towards this end, this review covers the most recent literature on the environmental implementations of emerging 2D nanomaterials, thereby providing insights into the future of this fast-evolving field including strategies for ensuring sustainable development of 2D nanomaterials.

Assessment of sexual dysfunction in patients with perianal Crohn's disease

AIM

Over the past 10 years, several studies have focused on sexuality in patients with Crohn's disease. Very few of them specifically focused on perianal disease (PD). This study aimed to compare the prevalence of sexual dysfunction (SD) in Crohn's disease patients with active PD versus controls without active PD.

METHOD

Patients from 14 French centres with active PD, defined by the presence of symptomatic ulceration, fistula or stenosis, were arbitrarily included. They were compared with controls from the existing SEXIA cohort. Men completed the International Index of Erectile Function (IIEF) and women the Female Sexual Function Index (FSFI). The primary end-point was SD defined by FSFI < 26.55 in women and IIEF < 42.9 in men.

RESULTS

Ninety-seven patients (64 women, 33 men) and 238 controls (131 women, 107 men) were included. SD was found in 66% of the female patients versus 50% of the controls (P = 0.04). In the male population, SD was found in 30% of the cases versus 16% of the controls (P = 0.06). Erectile dysfunction affected 46% of the male patients and 43% of the controls (P = 0.8). On multivariate analysis, the predictive factor most strongly associated with SD in women was severely active anal PD defined by a perineal disease activity index > 4 [OR = 13.05 (2.32-73.44)].

CONCLUSION

Women with active PD had an increased prevalence of SD compared with controls without active PD. In the male population, the study was unable to determine whether there was a difference as it was underpowered.

A randomized surgical trial of mitral valve repair with leaflet resection versus leaflet preservation on functional mitral stenosis – primary results of the CAMRA CardioLink-2 trial

Background

The gold standard treatment for mitral valve regurgitation due to prolapse involves surgery with annuloplasty and either leaflet resection or leaflet preservation, with placement of artificial neochordae. It has been suggested that leaflet resection may be prone to functional mitral stenosis, whereby a patient may have a higher mitral gradient at peak exercise compared to a leaflet preservation strategy. Although both techniques are widely used, there has been no prospective randomized study conducted to compare these two techniques, particularly in regard to functional mitral stenosis.

Methods

A total of 104 patients with posterior leaflet prolapse were randomized to undergo mitral repair with either leaflet resection (N=54) or leaflet preservation (N=50) at 7 specialized Canadian cardiac centers. Patient age, proportion of female patients, and mean Society of Thoracic Surgeons risk score was 63.9±10.4 years, 19%, and 1.4% for those who underwent leaflet resection, and 66.3±10.8 years, 16%, and 1.9% for those who underwent leaflet preservation, respectively. The primary endpoint was the mean trans-mitral repair gradient at peak exercise 12-months after repair.

Results

Baseline characteristics were similar between the groups. At 12-months, the mean trans-mitral repair gradient at peak exercise in patients who underwent leaflet resection and preservation was 9.1±5.2 and 8.3±3.3 mmHg (P=0.4), respectively. The two groups had similar mean mitral valve gradient at rest (3.2±1.9 mmHg following resection and 3.1±1.1 mmHg following leaflet preservation, P=0.7). There was no between-group difference for the 6-minute walk distance (451±147 m and 481±95 m for the resection and preservation groups, respectively, P=0.3).

Conclusion

We report the first prospective surgical randomized trial to evaluate commonly used mitral valve repair strategies for posterior leaflet prolapse. Leaflet resection and leaflet preservation both yield acceptable results with no difference in postoperative valve gradient and functional status 12-months after surgical mitral valve repair.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): Heart and Stroke Foundation of Canada

Online training on how to diagnose anoperineal lesions of Crohn's disease: Do pictures matter? A nationwide randomized study

Any gastroenterologist must be trained to properly diagnose anoperineal lesions in patients with Crohn's disease (APLOC). The aim of this study was to establish whether adding pictures would improve teaching effectiveness of the diagnosis of APLOC to French gastroenterology trainees.

METHOD

Trainees were asked to answer a first web-based survey consisting of evaluating 12 pictures of APLOC with a closed answer questionnaire. They were then randomized in 2 groups. Group A received an online teaching with typical pictures and APLOC definitions and group B definitions only. Trainees were asked again seven days later to answer a second survey with 12 other pictures of APLOC and 14 experts also answered this survey. Diagnostic scores were expressed in %. The primary endpoint was the comparison of the score of survey 2 between the two groups of trainees. Secondary endpoints were to compare results of survey 2 between trainees of both groups and experts, and assess diagnosis of each lesion.

RESULTS

Two hundred fourty eight trainees among 465 answered survey 1, and 195 survey 2. The diagnostic score was 71.9% for groups A and B and 74.6% for experts (differences NS). After training diagnosis of ulceration was 72% for group A and 72.9% for group B, fistulae 85.2% versus 85.8%, erythema 44.1% vs. 55.6%, anoperineal scars 67.5% vs. 65.6%, and abscess 100% (differences NS).

CONCLUSION

There was no difference between the two teaching methods. Further research should be performed aiming at improving teaching material and quotation baremes.

How to manage anal ulcerations and anorectal stenosis in Crohn's disease: algorithm-based decision making : French National Working Group Consensus 2018

The French National Society of Coloproctology established national recommendations for the treatment of anoperineal lesions associated with Crohn's disease. Treatment strategies for anal ulcerations and anorectal stenosis are suggested. Recommendations have been graded following international recommendations, and when absent professional agreement was established. For each situation, practical algorithms have been drawn.

Management of anoperineal lesions in Crohn's disease: a French National Society of Coloproctology national consensus

The French National Society of Coloproctology established national recommendations for the treatment of anoperineal lesions associated with Crohn's disease. Treatment strategies for acute abscesses, active fistulas (active denovo and still active under treatment), fistulas in remission, and rectovaginal fistulas are suggested. Recommendations have been graded following the international recommendations, and when absent, professional agreement has been established. For each situation, practical algorithms have been drawn.

Simulating graphene oxide nanomaterial phototransformation and transport in surface water

The production of graphene-family nanomaterials (GFNs) has increased appreciably in recent years. Graphene oxide (GO) has been found to be the most toxic nanomaterial among GFNs and, to our knowledge, no studies have been conducted to model its fate and transport in the environment. Lab studies show that GO undergoes phototransformation in surface waters under sunlight radiation resulting in formation of photoreduced GO (rGO). In this study, the recently updated Water Quality Analysis Simulation Program (WASP8) is used to simulate time-dependent environmental exposure concentrations of GO and its major phototransformation product, rGO, for Brier Creek, GA, USA at two flow scenarios under a constant loading of GO to the river for a period of 20 years. Analysis shows that the degree of phototransformation is closely associated with river flow condition: up to of 40% of GO undergoes phototransformation at low flow condition, whereas only 2.5% of GO phototransformation occurs at mean flow condition. River flow and heteroaggregation exhibit a 'competing' effect in determining the formation of rGO heteroagglomerates. Mass fraction analysis indicates that the vast majority of rGO heteroagglomerates settle to the sediment layers due to the settling of suspended solids. Simulation of natural recovery after removal of the GO source suggests that free GO and rGO are the immediate contaminants of concern in the studied surface water system, while rGO heteroaggregated with suspended solids can have a long-term ecological impact on both the water column and sediments.

Psychometric properties of a questionnaire (HEMO-FISS-QoL) to evaluate the burden associated with haemorrhoidal disease and anal fissures

AIM

Current questionnaires designed to evaluate the burden of haemorrhoidal disease ignore symptoms such as bleeding, pain and itching. A specific questionnaire is needed to evaluate the global impact of anal disorders on patients' daily lives.

METHOD

We developed a questionnaire (HEMO-FISS-QoL) to assess the symptom burden of anal disorders and administered it to 256 patients (mean age 46.2 years; men 60.4%) with haemorrhoidal disease (67.2%), anal fissure (29.3%) or both (3.5%). Psychometric properties were evaluated by testing the acceptability, construct validity and reliability of the questionnaire. Principal components and multi-trait analyses were used to identify dimensions and to assess construct validity. Backward Cronbach alpha curves and a graded response model were used to reduce the number of items and modalities. External validity was evaluated against SF-12 and the Psychological Global Well-Being Index (PGWBI) using Spearman's correlation coefficient.

RESULTS

Principal component analysis defined four dimensions: physical disorders, psychology, defaecation and sexuality. The number of questions was reduced from 38 to 23. The HEMO-FISS-QoL scores correlated well with those of the SF-12 and PGWBI (P < 0.001). Cronbach's coefficients (all > 0.7) reflected good internal reliability of the different dimensions. The total score increased with the severity of the anal disorders and with their consequences (days off work and personal spending related to the disease).

CONCLUSION

The HEMO-FISS-QoL questionnaire reliably evaluates the global impact of haemorrhoids and anal fissures on patients' daily lives. This simple tool may prove useful for treatment evaluation in clinical trials and daily practice.

Environmental fate of multiwalled carbon nanotubes and graphene oxide across different aquatic ecosystems

The industrial use and widespread application of carbon-based nanomaterials have caused a rapid increase in their production over the last decades. However, toxicity of these materials is not fully known and is still being investigated for potential human and ecological health risks. Detecting carbon-based nanomaterials in the environment using current analytical methods is problematic, making environmental fate and transport modeling a practical way to estimate environmental concentrations and assess potential ecological risks. The Water Quality Analysis Simulation Program 8 (WASP8) is a dynamic, spatially resolved fate and transport model for simulating exposure concentrations in surface waters and sediments. Recently, WASP has been updated to incorporate processes for simulating the fate and transport of nanomaterials including heteroaggregation and phototransformation. This study examines the fate and transport of multiwalled carbon nanotubes (MWCNT), graphene oxide (GO) and reduced graphene oxide (rGO) in four aquatic ecosystems in the southeastern United States. Sites include a seepage lake, a coastal plains river, a piedmont river and an unstratified, wetland lake. A hypothetical 50-year release is simulated for each site-nanomaterial pair to analyze nanomaterial distribution between the water column and sediments. For all nanomaterials, 99% of the mass loaded moves though systems of high and low residence times without being heteroaggregated and deposited in the sediments. However, significant accumulation in the sediments does occur over longer periods of time. Results show that GO and rGO had the highest mass fraction in the water column of all four sites. MWCNT were found predominantly in the sediments of the piedmont river and seepage lake but were almost entirely contained in the water column of the coastal plains river and wetland lake. Simulated recovery periods following the release estimate 37+ years for lakes and 1-4 years for rivers to reduce sediment nanomaterial concentrations by 50% suggesting that carbon-based nanomaterials have the potential for long-term ecological effects.

Sensitivity assessment of sea lice to chemotherapeutants: Current bioassays and best practices

Traditional bioassays are still necessary to test sensitivity of sea lice species to chemotherapeutants, but the methodology applied by the different scientists has varied over time in respect to that proposed in "Sea lice resistance to chemotherapeutants: A handbook in resistance management" (2006). These divergences motivated the organization of a workshop during the Sea Lice 2016 conference "Standardization of traditional bioassay process by sharing best practices." There was an agreement by the attendants to update the handbook. The objective of this article is to provide a baseline analysis of the methodology for traditional bioassays and to identify procedures that need to be addressed to standardize the protocol. The methodology was divided into the following steps: bioassay design; material and equipment; sea lice collection, transportation and laboratory reception; preparation of dilution; parasite exposure; response evaluation; data analysis; and reporting. Information from the presentations of the workshop, and also from other studies, allowed for the identification of procedures inside a given step that need to be standardized as they were reported to be performed differently by the different working groups. Bioassay design and response evaluation were the targeted steps where more procedures need to be analysed and agreed upon.

Simulating Multiwalled Carbon Nanotube Transport in Surface Water Systems Using the Water Quality Analysis Simulation Program (WASP)

Under the Toxic Substances Control Act (TSCA), the Environmental Protection Agency (EPA) is required to perform new chemical reviews of nanomaterials identified in premanufacture notices. However, environmental fate models developed for traditional contaminants are limited in their ability to simulate nanomaterials' environmental behavior by incomplete understanding and representation of the processes governing nanomaterial distribution in the environment and by scarce empirical data quantifying the interaction of nanomaterials with environmental surfaces. In this study, the well-known Water Quality Analysis Simulation Program (WASP) was updated to incorporate particle collision rate and particle attachment efficiency to simulate multiwalled carbon nanotube (MWCNT) fate and transport in surface waters. Heteroaggregation attachment efficiencies (α_het) values derived from sediment attachment studies are used to parametrize WASP for simulation of MWCNTs transport in Brier Creek, a coastal plain river located in central eastern Georgia, and a tributary to the Savannah River. Simulations using a constant MWCNT load of 0.1 kg d^-1 in the uppermost Brier Creek water segment showed that MWCNTs were present predominantly in the Brier Creek water column, while downstream MWCNT surface and deep sediment concentrations exhibited a general increase with time and distance from the source, suggesting that MWCNT releases could have increasing ecological impacts in the benthic region over long time frames.

Biomarker analysis of liver cells exposed to surfactant-wrapped and oxidized multi-walled carbon nanotubes (MWCNTs)

Carbon nanotubes (CNTs) have great potential in industrial, consumer, and mechanical applications, based partly on their unique structural, optical and electronic properties. CNTs are commonly oxidized or treated with surfactants to facilitate aqueous solution processing, and these CNT surface modifications also increase possible human and ecological exposures to nanoparticle-contaminated waters. To determine the exposure outcomes of oxidized and surfactant-wrapped multiwalled carbon nanotubes (MWCNTs) on biochemical processes, metabolomics-based profiling of human liver cells (C3A) was utilized. Cells were exposed to 0, 10, or 100ng/mL of MWCNTs for 24 and 48h; MWCNT particle size distribution, charge, and aggregation were monitored concurrently during exposures. Following MWCNT exposure, cellular metabolites were extracted, lyophilized, and buffered for (1)H NMR analysis. Acquired spectra were subjected to both multivariate and univariate analysis to determine the consequences of nanotube exposure on the metabolite profile of C3A cells. Resulting scores plots illustrated temporal and dose-dependent metabolite responses to all MWCNTs tested. Loadings plots coupled with t-test filtered spectra identified metabolites of interest. XPS analysis revealed the presence of hydroxyl and carboxyl functionalities on both MWCNTs surfaces. Metal content analysis by ICP-AES indicated that the total mass concentration of the potentially toxic impurities in the exposure experiments were extremely low (i.e. [Ni]≤2×10(-10)g/mL). Preliminary data suggested that MWCNT exposure causes perturbations in biochemical processes involved in cellular oxidation as well as fluxes in amino acid metabolism and fatty acid synthesis. Dose-response trajectories were apparent and spectral peaks related to both dose and MWCNT dispersion methodologies were determined. Correlations of the significant changes in metabolites will help to identify potential biomarkers associated with carbonaceous nanoparticle exposure.

The outcome of fistulotomy for anal fistula at 1 year: a prospective multicentre French study

AIM

The study aimed to evaluate outcome at 1 year of one- and two-stage fistulotomy for anal fistula in a large group of patients.

METHOD

A prospective multicentre observational study was designed to include patients with anal fistula treated by one- or two-stage fistulotomy. Data were collected using a self-administered questionnaire before surgery, during healing and at 1 year after surgery.

RESULTS

Group A (133 patients) with a low anal fistula underwent a one-stage fistulotomy. The median Wexner scores before and after surgery were 1.0 (0-11) and 2.0 (0-18) (P = 0.032) and the median Vaizey scores were 2.0 (0-14) and 3.0 (0-21) (P = 0.055). The Wexner scores and percentage of patients before and after fistulotomy were as follows: 0-5: 88%, 86%; 6-10: 10.7%, 10.7%; 11-15: 1.0%, 2.6%; and 16-20: 0%, 2%. Eighty-seven per cent of the patients were satisfied. Group B (62 patients) underwent two-stage fistulotomy for a high transsphincteric fistula. The Wexner scores and percentage of patients before the first stage and 1 year after the second stage were as follows: 0-5: 86%, 66%; 6-10: 4.5%, 20%; 11-15: 9%, 11%; and 16-20: 0%, 2%. The median Wexner scores before the first stage and after the second stage were 1 (0-14) vs. 4 (0-19) (P < 0.001), and the median Vaizey scores were 1.5 (0-11) vs. 4 (0-20) (P < 0.001). Eighty-eight per cent of the patients were satisfied.

CONCLUSION

Low transsphincteric anal fistula can be treated by fistulotomy without clinically significant continence disturbance. Treating high transsphincteric anal fistulae with two-stage fistulotomy is followed by mild continence disturbance. Satisfaction rates were high.

Aggregation and Stability of Reduced Graphene Oxide: Complex Roles of Divalent Cations, pH, and Natural Organic Matter

The aggregation and stability of graphene oxide (GO) and three successively reduced GO (rGO) nanomaterials were investigated. Reduced GO species were partially reduced GO (rGO-1h), intermediately reduced GO (rGO-2h), and fully reduced GO (rGO-5h). Specifically, influence of pH, ionic strength, ion valence, and presence of natural organic matter (NOM) were studied. Results show that stability of GO in water decreases with successive reduction of functional groups, with pH having the greatest influence on rGO stability. Stability is also dependent on ion valence and the concentration of surface functional groups. While pH did not noticeably affect stability of GO in the presence of 10 mM NaCl, adding 0.1 mM CaCl2 reduced stability of GO with increased pH. This is due to adsorption of Ca(2+) ions on the surface functional groups of GO which reduces the surface charge of GO. As the concentration of rGO functional groups decreased, so did the influence of Ca(2+) ions on rGO stability. Critical coagulation concentrations (CCC) of GO, rGO-1h, and rGO-2h were determined to be ∼ 200 mM, 35 mM, and 30 mM NaCl, respectively. In the presence of CaCl2, CCC values of GO and rGO are quite similar, however. Long-term studies show that a significant amount of rGO-1h and rGO-2h remain stable in Call's Creek surface water, while effluent wastewater readily destabilizes rGO. In the presence NOM and divalent cations (Ca(2+), Mg(2+)), GO aggregates settle from suspension due to GO functional group bridging with NOM and divalent ions. However, rGO-1h and rGO-2h remain suspended due to their lower functional group concentration and resultant reduced NOM-divalent cation bridging. Overall, pH, divalent cations, and NOM can play complex roles in the fate of rGO and GO.

Sunlight affects aggregation and deposition of graphene oxide in the aquatic environment

In this study, we investigate the role of simulated sunlight on the physicochemical properties, aggregation, and deposition of graphene oxide (GO) in aquatic environments. Results show that light exposure under varied environmental conditions significantly impacts the physicochemical properties and aggregation/deposition behaviors of GO. Photo-transformation has negligible effects on GO surface charge, however, GO aggregation rates increase with irradiation time for direct photo-transformation under both aerobic and anaerobic conditions. Under anaerobic conditions, photo-reduced GO has a greater tendency to form aggregates than under aerobic conditions. Aggregation of photo-transformed GO is notably influenced by ion valence, with higher aggregation found in the presence of divalent ions versus monovalent, but adding natural organic matter (NOM) reduces it. QCM-D studies show that deposition of GO on surfaces coated with organic matter decreases with increased GO irradiation time, indicating a potential increase in GO mobility due to photo-transformation. General deposition trends on Suwannee River Humic Acid (SRHA)-coated surfaces are control GO > aerobically photo-transformed GO ≈ anaerobically photo-transformed GO. The release of deposited GO from SRHA-coated surfaces decreases with increased irradiation time, indicating that photo-transformed GO is strongly attached to the NOM-coated surface.

Photochemical transformation of graphene oxide in sunlight

Graphene oxide (GO) is promising in scalable production and has useful properties that include semiconducting behavior, catalytic reactivity, and aqueous dispersibility. In this study, we investigated the photochemical fate of GO under environmentally relevant sunlight conditions. The results indicate that GO readily photoreacts under simulated sunlight with the potential involvement of electron-hole pair creation. GO was shown to photodisproportionate to CO2, reduced materials similar to reduced GO (rGO) that are fragmented compared to the starting material, and low molecular-weight (LMW) species. Kinetic studies show that the rate of the initially rapid photoreaction of GO is insensitive to the dissolved oxygen content. In contrast, at longer time points (>10 h), the presence of dissolved oxygen led to a greater production of CO2 than the same GO material under N2-saturated conditions. Regardless, the rGO species themselves persist after extended irradiation equivalent to 2 months in natural sunlight, even in the presence of dissolved oxygen. Overall, our findings indicate that GO phototransforms rapidly under sunlight exposure, resulting in chemically reduced and persistent photoproducts that are likely to exhibit transport and toxic properties unique from parent GO.

Interactions of graphene oxide nanomaterials with natural organic matter and metal oxide surfaces

Interactions of graphene oxide (GO) nanomaterials with natural organic matter (NOM) and metal oxide surfaces were investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D). Three different types of NOM were studied: Suwannee River humic and fulvic acids (SRHA and SRFA) and alginate. Aluminum oxide surface was used as a model metal oxide surface. Deposition trends show that GO has the highest attachment on alginate, followed by SRFA, SRHA, and aluminum oxide surfaces, and that GO displayed higher interactions with all investigated surfaces than with silica. Deposition and release behavior of GO on aluminum oxide surface is very similar to positively charged poly-L-lysine-coated surface. Higher interactions of GO with NOM-coated surfaces are attributed to the hydroxyl, epoxy, and carboxyl functional groups of GO; higher deposition on alginate-coated surfaces is attributed to the rougher surface created by the extended conformation of the larger alginate macromolecules. Both ionic strength (IS) and ion valence (Na(+) vs Ca(2+)) had notable impact on interactions of GO with different environmental surfaces. Due to charge screening, increased IS resulted in greater deposition for NOM-coated surfaces. Release behavior of deposited GO varied significantly between different environmental surfaces. All surfaces showed significant release of deposited GO upon introduction of low IS water, indicating that deposition of GO on these surfaces is reversible. Release of GO from NOM-coated surfaces decreased with IS due to charge screening. Release rates of deposited GO from alginate-coated surface were significantly lower than from SRHA and SRFA-coated surfaces due to trapping of GO within the rough surface of the alginate layer.

Deposition and release of graphene oxide nanomaterials using a quartz crystal microbalance

Interactions of graphene oxide (GO) with silica surfaces were investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D). Both GO deposition and release were monitored on silica- and poly-l-lysine (PLL) coated surfaces as a function of GO concentration and in NaCl, CaCl2, and MgCl2 as a function of ionic strength (IS). Under favorable conditions (PLL-coated positive surface), GO deposition rates increased with GO concentration, as expected from colloidal theory. Increased NaCl concentration resulted in a greater deposition attachment efficiency of GO on the silica surface, indicating that deposition of GO follows Derjaguin-Landau-Verwey-Overbeek (DLVO) theory; GO deposition rates decreased at high IS, however, due to large aggregate formation. GO critical deposition concentration (CDC) on the silica surface is determined to be 40 mM NaCl which is higher than the reported CDC values of fullerenes and lower than carbon nanotubes. A similar trend is observed for MgCl2 which has a CDC value of 1.2 mM MgCl2. Only a minimal amount of GO (frequency shift <2 Hz) was deposited on the silica surface in CaCl2 due to the bridging ability of Ca(2+) ions with GO functional groups. Significant GO release from silica surface was observed after adding deionized water, indicating that GO deposition is reversible. The release rates of GO were at least 10-fold higher than the deposition rates under similar conditions indicating potential high release and mobility of GO in the environment. Under favorable conditions, a significant amount of GO was released which indicates potential multilayer GO deposition. However, a negligible amount of deposited GO was released in CaCl2 under favorable conditions due to the binding of GO layers with Ca(2+) ions. Release of GO was significantly dependent on salt type with an overall trend of NaCl > MgCl2 > CaCl2.