Multiple lines of evidence to demonstrate vinyl chloride aerobic biodegradation in the vadose zone, and factors controlling rates

A field-based investigation was conducted at a contaminated site where the vadose zone was contaminated with a range of chlorinated hydrocarbons. The investigation consisted of groundwater and multilevel soil-gas monitoring of a range of contaminants and gases, along with isotope measurements and microbiology studies. The investigation provided multiple lines of evidence that demonstrated aerobic biodegradation of vinyl chloride (VC) was occurring in the vadose zone (i) above the on-site source zone, and (ii) above the downgradient off-site groundwater plume location. Data from both the on-site and off-site locations were consistent in showing substantially greater (an order of magnitude greater) rates of VC removal from the aerobic vadose zone compared to more recalcitrant contaminants trichloroethene (TCE) and tetrachloroethene (PCE). Soil gas VC isotope analysis showed substantial isotopic enrichment of VC (δ¹³C -5.2 to -10.9‰) compared to groundwater (δ¹³C -39.5‰) at the on-site location. Soil gas CO₂ isotope analysis at both locations showed that CO₂ was highly isotopically depleted (δ¹³C -28.8 to -33.3‰), compared to soil gas CO₂ data originating from natural sediment organic matter (δ¹³C= -14.7 to -21.3‰). The soil gas CO2 δ¹³C values were consistent with near-water table VC groundwater δ¹³C values (-36.8 to -39.5‰), suggesting CO₂ originating from aerobic biodegradation of VC. Bacteria that had functional genes (ethene monooxygenase (etnC) and epoxyalkane transferase (etnE)) involved in ethene metabolism and VC oxidation were more abundant at the source zone where oxygen co-existed with VC. The distribution of VC and oxygen vadose zone vapour plumes, together with long-term changes in soil gas CO₂ concentrations and temperature, provided information to elucidate the factors controlling aerobic biodegradation of VC in the vadose zone. Based on the overlapping VC and oxygen vadose zone vapour plumes, aerobic vapour biodegradation rates were independent of substrate (VC and/or oxygen) concentration. The high correlation (R=0.962 to 0.975) between CO₂ concentrations and temperature suggested that aerobic biodegradation of VC was controlled by bacterial activity that was regulated by the temperature within the vadose zone. When assessing a contaminated site for possible vapour intrusion into buildings, accounting for environmental conditions for aerobic biodegradation of VC in the vadose zone should improve the assessment of environmental risk of VC intrusion into buildings, enabling better identification and prioritisation of contaminated sites to be remediated.

Pilonidal sinus disease

Pilonidal disease is a frequent suppurative condition that occurs twice as often in men as in women, usually between the ages of 15 and 30. Pilonidal disease is located beneath the skin of the sacro-coccygeal region. It presents acutely as an abscess under tension while the chronic form gives rise to intermittent discharge from pilonidal sinus(es). Diagnosis is clinical and usually straightforward. In the large majority of cases, treatment is surgical but there is no consensus as to the 'ideal' technique. Acute abscess must be evacuated and an off-midline incision seems preferable. Excision is the standard definitive treatment but the choice of wide versus limited excision depends on the school of thought. The widespread practice in France is to leave the wound open, relying on postoperative healing by secondary intention. This technique has a low rate of recurrence but has the disadvantages of requiring local nursing care; the healing process is prolonged, usually associated with a temporary but prolonged cessation of activity. Primary wound closure techniques are less restrictive but their recurrence rate is probably higher. A direct midline suture is best after a small excision, but for a more extended wound, plastic reconstruction techniques are preferred; data in the literature favor asymmetric closure techniques such as those described by Karydakis and Bascom.

A rapid screening technique for estimating nanoparticle transport in porous media

Quantifying the mobility of engineered nanoparticles in hydrologic pathways from point of release to human or ecological receptors is essential for assessing environmental exposures. Column transport experiments are a widely used technique to estimate the transport parameters of engineered nanoparticles in the subsurface environment, but this technique is often time-consuming, labor-intensive, and of low sample throughput. Thus, the traditional column experiment is unlikely to be a viable tool for processing the large numbers of engineered nanomaterials in various types of porous media that will be needed for environmental impact assessment and regulatory activities. Here we present a high throughput screening technique for nanoparticle transport using 96 deep well plate columns packed with porous media. The technique was tested for the transport of 60-nm polystyrene microspheres, fullerene C60 nanoparticles (aq/nC60), and surfactant-wrapped single-walled carbon nanotubes (SWNTs) in 0.001-0.1% sodium dodecyl sulfate (SDS) through Iota quartz sand and Calls Creek sediment. Our results showed that this screening technique produced highly reproducible column hydrodynamic properties as revealed by conservative tracer tests and precise measurements of nanoparticle transport parameters. Additionally, all nanoparticles exhibited greater retention in the sediment than in Iota quartz, and the retention of SDS-SWNTs decreased with increasing SDS concentrations, which is consistent with the existing literature. We conclude that this technique is well suited for rapidly screening the mobility of engineered nanomaterials in porous media.

Colloidal properties and stability of graphene oxide nanomaterials in the aquatic environment

While graphene oxide (GO) has been found to be the most toxic graphene-based nanomaterial, its environmental fate is still unexplored. In this study, the aggregation kinetics and stability of GO were investigated using time-resolved dynamic light scattering over a wide range of aquatic chemistries (pH, salt types (NaCl, MgCl2, CaCl2), ionic strength) relevant to natural and engineered systems. Although pH did not have a notable influence on GO stability from pH 4 to 10, salt type and ionic strength had significant effects on GO stability due to electrical double layer compression, similar to other colloidal particles. The critical coagulation concentration (CCC) values of GO were determined to be 44 mM NaCl, 0.9 mM CaCl2, and 1.3 mM MgCl2. Aggregation and stability of GO in the aquatic environment followed colloidal theory (DLVO and Schulze-Hardy rule), even though GO's shape is not spherical. CCC values of GO were lower than reported fullerene CCC values and higher than reported carbon nanotube CCC values. CaCl2 destabilized GO more aggressively than MgCl2 and NaCl due to the binding capacity of Ca(2+) ions with hydroxyl and carbonyl functional groups of GO. Natural organic matter significantly improved the stability of GO in water primarily due to steric repulsion. Long-term stability studies demonstrated that GO was highly stable in both natural and synthetic surface waters, although it settled quickly in synthetic groundwater. While GO remained stable in synthetic influent wastewater, effluent wastewater collected from a treatment plant rapidly destabilized GO, indicating GO will settle out during the wastewater treatment process and likely accumulate in biosolids and sludge. Overall, our findings indicate that GO nanomaterials will be stable in the natural aquatic environment and that significant aqueous transport of GO is possible.

One-year outcome of haemorrhoidectomy: a prospective multicentre French study

AIM

An evaluation was performed of the 1-year outcome of open haemorrhoidectomy (Milligan and Morgan alone or with posterior mucosal anoplasty [the Leopold Bellan procedure]).

METHOD

A prospective, multicentre, observational study included all patients having a planned haemorrhoidectomy from January 2007 to June 2008. Data were collected before surgery, and at 3 months and 1 year after surgery. Patients assessed their anal symptoms and quality of life (SF-36).

RESULTS

Six-hundred and thirty-three patients (median age = 48 years, 56.5% women) underwent haemorrhoidectomy either by the Milligan and Morgan procedure alone (n = 231, 36.5%) or together with the Leopold Bellan procedure (posterior mucosal anoplasty) for resection of a fourth haemorrhoid (n = 345, 54.5%), anal fissure (n = 56, 8.9%) or low anal fistula (n = 1, 0.16%). The median healing time was 6 weeks. Early complications included urinary retention (n = 3), bleeding (n = 11), local infection (n = 7) and faecal impaction (n = 9). At 1 year, the main complications included skin tags (n = 2) and anal stenosis (n = 23). There were three recurrences requiring a second haemorrhoidectomy. On a visual analogue scale, anal pain at 1 year had fallen from a median of 5.5/10 before treatment to 0.1/10 (p < 0.001), anal discomfort from 5.5/10 to 0.1/10 (P < 0.001) and the Knowles-Eckersley-Scott Symptom (KESS) constipation score from 9/45 to 6/45 (P < 0.001). The median Wexner score for anal incontinence was unchanged (2/20). De-novo anal incontinence (a Wexner score of >5) affected 8.5% of patients at 1 year, but preoperative incontinence disappeared in 16.7% of patients with this symptom. All physical and mental domains of quality of life significantly improved, and 88% of patients were satisfied or very satisfied.

CONCLUSION

Complications of open haemorrhoidectomy were infrequent. Anal continence was not altered. Comfort and well-being were significantly improved at 1 year after surgery. Patient satisfaction was high despite residual anal symptoms.

Effects of humic and fulvic acids on aggregation of aqu/nC60 nanoparticles

Aggregation of fullerene nanoparticles (nC(60)) is a fundamental process influencing its environmental fate and transport, and toxicity. Using time-resolved dynamic light scattering we systematically investigated aggregation kinetics of nC(60) generated from extended mixing in water (termed as aqu/nC(60)) in a range of symmetrical monovalent (NaCl) or divalent (MgSO(4)) electrolyte concentrations with the presence/absence of model natural organic matter (NOM), i.e., Suwannee River humic acid (SRHA) and fulvic acid (SRFA), at three pH levels (4, 7.8, 9.8). Electrophoretic mobility (EPM) data were interpreted according to the Ohshima's soft particle theory to obtain average characteristics of the adsorbed NOM layers, which was then used to explain the observed aggregation profiles. Results indicate that the presence of NOM stabilized aqu/nC(60), and SRHA was more effective than SRFA in suppressing aqu/nC(60) aggregation. The stabilization effect of NOM in the presence of NaCl was less pronounced than in the presence of MgSO(4), likely as a result of high aggregation potential of aqu/nC(60) in the presence of MgSO(4) due to effective charge screening and neutralization. The differential stabilization capacity between SRHA and SRFA could be explained by the structural and conformational characteristics of the adsorbed NOM layers by invoking steric repulsion, as determined by both the adsorbed layer thickness and the NOM affinity to aqu/nC(60). While this was true under most conditions, the discrepancy observed in the presence of MgSO(4) at pH 9.8 may be attributed to inter-particle aggregation through Mg(2+) binding with SRFA that is not included in steric repulsion theory.

Sphincter-sparing anal-fissure surgery: a 1-year prospective, observational, multicentre study of fissurectomy with anoplasty

AIM

Internal sphincterotomy is the standard surgical treatment for chronic anal fissure, but is frequently complicated by anal incontinence. Fissurectomy is proposed as an alternative technique to avoid sphincter injury. We describe 1-year outcomes of fissurectomy.

METHOD

This was a prospective, multicentre, observational study. All patients with planned surgery for chronic anal fissure were included and had fissurectomy. Data were collected before surgery, at healing, and 1 year after fissurectomy. Patient self-assessed anal symptoms and quality of life (using the 36-item short-form health survey [SF-36] questionnaire). Presurgical and postsurgical variables were compared using the Wilcoxon signed-rank test for paired samples.

RESULTS

Two-hundred and sixty-four patients were included (median age, 45 years; 52% women). Anoplasty was associated with fissurectomy in 83% of the 257 documented cases. The main complications were urinary retention (n = 3), local infection (n = 4) and faecal impaction (n = 1). Healing was achieved in all patients at a median of 7.5 weeks after surgery. No recurrence occurred. At 1 year, 210 (79%) questionnaires were returned. Median anal pain had dropped from 7.3/10 to 0.1/10 (P < 0.001), anal discomfort had decreased from 5.0/10 to 0.1/10 (P < 0.001) and the Knowles-Eckersley-Scott Symptom constipation score had decreased from 9/45 to 5/45 (P < 0.001). There was a nonsignificant increase in the Wexner anal incontinence score, from 1/20 to 2/20. De-novo clinically significant anal incontinence (Wexner score > 5) affected 7% of patients at 1 year, but presurgical incontinence had disappeared in 15% of patients. All SF-36 domains significantly improved. Anoplasty did not impact any result.

CONCLUSION

Given its high rate of healing and low rate of de-novo anal incontinence, fissurectomy with anoplasty is a valuable sphincter-sparing surgical treatment for chronic anal fissure.

Do we have to stop anticoagulant and platelet-inhibitor treatments during proctological surgery?

AIM

This prospective observation study evaluated the incidence of secondary bleeding after proctological surgery without interruption of oral anticoagulant or platelet-inhibitor treatments.

METHOD

The number of episodes of postoperative bleeding was identified prospectively from the day of surgery to the last follow-up visit in consecutive patients operated on during 2010 in two units dedicated to proctology.

RESULTS

A total of 2513 procedures were performed in 2314 patients (1379 men), 46 ± 16 years of age. Secondary bleeding occurred after 115 (4.6%) procedures, no later than day 24 after surgery, requiring rehospitalization in 86% of cases and further surgery and/or transfusion in 36%. The highest frequency was noted after surgery for haemorrhoids (haemorrhoidopexy, 7.9%; haemorrhoidectomy, 6.2%) (P = NS and transanal excision of rectal tumours (6.5%). On multivariate analysis, the frequency was significantly increased by clopidogrel (15%) [relative risk (RR) = 10). In patients on oral anticoagulants, bleeding occurred in 23% (RR = 5.8) if the anticoagulants were not interrupted and in 57% (RR = 42) if the anticoagulants were discontinued and replaced with heparin.

CONCLUSION

During proctological surgery the overall risk of postoperative bleeding is low, but it can occur up to 3 weeks after surgery and is often severe. Maintenance treatment with oral anticoagulants is the most important risk factor, aggravated by a change to heparin. Clopidogrel also significantly increases the bleeding risk.

Fullerene nanoparticles exhibit greater retention in freshwater sediment than in model porous media

Increasing production and use of fullerene-based nanomaterials underscore the need to determine their mobility in environmental transport pathways and potential ecological exposures. This study investigated the transport of two fullerenes (i.e., aqu/C(60) and water-soluble C(60) pyrrolidine tris-acid [C(60) PTA]) in columns packed with model porous media (Iota quartz and Ottawa sand) and a sediment from Call's creek under saturated and unsaturated steady-state flows. The fullerenes had the least retention in Iota quartz, and the greatest retention in the sediment at near neutral pH, correlating with the degree of grain surface chemical heterogeneity (e.g., amorphous Al hydroxides concentration increasing in the order of Iota quartz<Ottawa sand<sediment). Surface roughness was elucidated as another important factor responsible for the greatest fullerene retention in the sediment. In accordance with the XDLVO energy calculations, C(60) PTA was less retained than aqu/C(60) at near neutral pH, due to its greater hydrophilicity measured by tolune-water partition coefficient, as well as smaller particle sizes revealed by atomic force microscopy. Fullerene retention exhibited a strong dependency on solution pH that could be explained partly by the pH-dependent surface charge of fullerenes and grain surface, and partly by increased hydrophobicity of C(60) PTA when solution pH approaches its isoelectric point (IEP). Finally, fullerene retention was enhanced in unsaturated media, implying that fullerenes may be more attenuated in the vadose zone than in groundwater.

Aggregation kinetics and transport of single-walled carbon nanotubes at low surfactant concentrations

Little is known about how low levels of surfactants can affect the colloidal stability of single-walled carbon nanotubes (SWNTs) and how surfactant-wrapping of SWNTs can impact ecological exposures in aqueous systems. In this study, SWNTs were suspended in water with sodium dodecylsulfate (SDS) as a surface-active dispersing agent. The effect of SDS concentration on SWNT suspension stability was investigated with time-resolved dynamic light scattering (TRDLS) initial aggregation studies utilizing both monovalent (Na(+)) and divalent (Ca(2+)) cations. The critical coagulation concentration (CCC) values increased with SDS concentration for the Na(+) treatments, but the Ca(2+) treatments were less sensitive to SDS concentration changes. Longer term stability studies with SDS concentrations orders of magnitude below the SDS critical micelle concentration demonstrated that SWNTs remained suspended for over six weeks in a surface water. Transport studies in a freshwater sediment similarly showed a SDS concentration-dependent mobility of SDS-wrapped SWNTs in that SWNTs showed a relatively greater retention at lower SDS concentrations (0.001%-0.05% w/v) than at a higher SDS concentration (0.1%). It is hypothesized that the stability and mobility of SWNT suspensions is directly related to the surface coverage of SDS on the SWNT surface that simultaneously increases electrosteric repulsion and decreases surface chemical heterogeneity. Overall, these studies demonstrate that low levels of surfactant are effective in stabilizing and mobilizing SWNTs in environmental media.