Evaluating the PAS-SIM model using a passive air sampler calibration study for pesticides

The main objective of this study was to evaluate the performance of a model for simulating the uptake of various pesticides on passive air samplers (PAS). From 2006-2007 a series of PAS using XAD-resin were deployed at Egbert, a rural agricultural site in southern Ontario, Canada, to measure the uptake of pesticides for time periods ranging from two months to one year. A continuous increase in sequestered amounts was observed for most pesticides, except for trifluralin and pendimethalin, which could conceivably be subject to substantial degradation inside the sampler. Continuous low-volume active air samples taken during the same period, along with data on weather conditions, allowed for the simulation of the uptake of the pesticides using the model (PAS-SIM). The modelled accumulation of pesticides on the PAS over the deployment period was in good agreement with the experimental data in most cases (i.e., within a factor of two) providing insight into the uptake kinetics of this type of sampler in the field. Passive sampling rates (PSR, m(3) d(-1)) were determined from the empirical data generated for this study using three different methods and compared with the PSRs generated by the model. Overall, the PAS-SIM model, which is capable of accounting for the influence of temperature and wind variations on PSRs, provided reasonable results that range between the three empirical approaches employed and well-established literature values. Further evaluation and application of the PAS-SIM model to explore the potential spatial and temporal variability in PAS uptake kinetics is warranted, particularly for established monitoring sites where detailed meteorological data are more likely to be available.

Neutral polyfluoroalkyl substances in the global atmosphere

Concentrations of neutral per- and polyfluoroalkyl substances (nPFAS) in the atmosphere are of interest because nPFAS are highly mobile percursors for perfluoroalkyl acids. Two calibration studies in Ontario, Canada and Costa Rica established the feasibility of using XAD 2-resin based passive air samplers (XAD-PAS) to reliably determine long term average air concentrations of nPFAS under temperate and tropical climatic conditions. The temporal and spatial distribution of nPFAS was investigated by analyzing XAD-PAS deployed for one year at between 17 and 46 sites on six continents between 2006 and 2011 as part of the Global Atmospheric Passive Sampling (GAPS) study. Higher levels of fluorotelomer alcohols (FTOHs) compared to fluorinated sulfonamides (FOSAs), and fluorinated sulfonamidoethanols (FOSEs) were observed at all sites. Urban sites had the highest levels of nPFAS compared to rural and remote sites, which is also apparent in a positive correlation of nPFAS levels with the proximity of a sampling site to areas of high population density. Levels of FOSAs and FOSEs tended to decrease during the six years of measurements, whereas an initial decline in the concentrations of FTOHs from 2006 to 2008 did not continue in 2009 to 2011. A comparison of nPFAS levels measured in national XAD-PAS networks in Costa Rica and Botswana revealed that the GAPS sites in Tapanti and the Kalahari are representative of the more remote regions in those countries. XAD-PAS derived absolute nPFAS levels at GAPS sites are lower than those measured using another PAS, but are within the range of levels measured with active air samplers. Agreement of relative nPFAS composition is better between samplers, suggesting that the discrepancy is due to uncertain sampling rates.

Modeling the uptake of neutral organic chemicals on XAD passive air samplers under variable temperatures, external wind speeds and ambient air concentrations (PAS-SIM)

The main objective of this study was to evaluate the performance and demonstrate the utility of a fugacity-based model of XAD passive air samplers (XAD-PAS) designed to simulate the uptake of neutral organic chemicals under variable temperatures, external wind speeds and ambient air concentrations. The model (PAS-SIM) simulates the transport of the chemical across the air-side boundary layer and within the sampler medium, which is segmented into a user-defined number of thin layers. Model performance was evaluated using data for polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) from a field calibration study (i.e., active and XAD-PAS data) conducted in Egbert, Ontario, Canada. With some exceptions, modeled PAS uptake curves are in good agreement with the empirical PAS data. The results are highly encouraging, given the uncertainty in the active air sampler data used as input and other uncertainties related to model parametrization (e.g., sampler-air partition coefficients, the influence of wind speed on sampling rates). The study supports the further development and evaluation of the PAS-SIM model as a diagnostic (e.g., to aid interpretation of calibration studies and monitoring data) and prognostic (e.g., to inform design of future passive air sampling campaigns) tool.

Comparison of four active and passive sampling techniques for pesticides in air

Four sampling systems were evaluated for their ability to determine the concentrations of pesticides in the atmosphere of rural southern Ontario. Two active air samplers (AAS, high-volume and low-volume pumps) and two passive air samplers (PAS, polyurethane foam disks and XAD-resin) were deployed between March 2006 and September 2007 using different sampling frequencies (biweekly to annually) and durations (24 h to 1 yr). Concentrations of nine pesticides in air determined by the different systems were compared at time scales of two weeks, two months, and one year. Agreement in the average concentrations obtained by different techniques improved with increasing length of the comparison period, especially for pesticides with high short-term temporal concentration variability. Such variability was high for the most volatile and reactive pesticides (trifluralin and pendimethalin). Except for these two pesticides, the annually averaged air concentrations determined by the different systems are within a factor of 2.5 for all pesticides and are not statistically different. Even though the PUF-PAS may have approached equilibrium with the atmosphere during deployment, the air concentrations are not statistically significantly different from those determined by AAS when averaged over longer time scales. Two month XAD-PAS deployments during the second summer resulted in sufficient sampling volumes to reliably establish air concentrations. If the sole purpose of collecting air samples is the assessment of long-term air concentration trends, this can be achieved most cost-effectively, i.e., with the least number of samples with year-long XAD-PAS.

Levels and seasonal variability of pesticides in the rural atmosphere of Southern Ontario

Air samples were collected continuously in Egbert, Ontario, which is in a rural agricultural area north of Toronto, between March 2006 and September 2007 and analyzed for pesticides of both current and historic use. The fungicide chlorothalonil was present in highest abundance with levels exceeding 2000 pg x m(-3) in the summer. Almost as abundant, with summer time concentrations around 400 to 600 pg x m(-3), were the herbicides atrazine, alachlor, and metolachlor. Other pesticides in current use, such as trifluralin, pendimethalin, chlorpyrifos, endosulfan, and disulfoton were consistently present at levels approximately 1 order of magnitude lower. Concentrations of banned pesticides (chlordanes and hexachlorocyclohexane) were generally below 10 pg x m(-3), except for hexachlorobenzene, which was present at the global average of approximately 50 pg x m(-3). These levels and the fact that they are generally lower than what has been reported for the area previously are in agreement with pesticide usage data for Ontario. Only the concentrations of chlorothalonil, chlorpyrifos, and HCB were correlated with air mass origin, as determined by back trajectory analysis. All pesticides had higher levels during the growing season compared to those in winter, but the ratio of concentrations during the different seasons is much higher for the pesticides in current use. That ratio may aid in distinguishing seasonal variability caused by pesticide application during the growing season from that caused by temperature-driven revolatilization. Higher concentrations of the banned pesticides during 2007 compared to those in 2006 may be due to higher volatilization rates caused by higher surface temperatures consistent with the El Nino Southern Oscillation.

Comparative evaluation of three high-performance liquid chromatography-based Kow estimation methods for highly hydrophobic organic compounds: polybrominated diphenyl ethers and hexabromocyclododecane

Three methods for estimating the octanol-water partition coefficient (Kow) based on its relationship with capacity factors on reversed-phase (RP) high-performance liquid chromatography (HPLC) columns were compared in terms of their applicability to highly hydrophobic compounds (HHCs). Methods based on simple isocratic elutions were found to be unsuitable, because the very high organic modifier fractions that are required to elute HHCs from RP columns challenge the basic assumption of the similarity between the octanol-water and RP-eluent systems. Compound planarity was found to exert a considerable influence on the retention of HHCs in RP columns, leading to different linear calibration curves for chlorobenzenes and chlorobiphenyls. Only an empirical exponential regression succeeded in describing the behavior of both groups of compounds during gradient elutions. In a method based on isocratic retention times at multiple temperatures, satisfactory calibration was achieved with a multivariate linear regression that included a numerical indicator of compound planarity. Considering experimental simplicity, speed, precision, and accuracy, with the latter judged by comparison with Kow values for polybrominated diphenyl ethers and polychlorinated naphthalenes as reported in the literature, a gradient elution combined with an exponential calibration curve is recommended for estimating the Kow of HHCs. To our knowledge, the first isomer-specific Kow values for hexabromocyclododecane are reported. Bearing in mind that the influence of structural characteristics on retention is likely to increase with hydrophobicity, it is not justified to judge a HPLC-based Kow estimation method as being suitable for HHCs because it is shown to work well for less hydrophobic substances. Whereas univariate linear regressions often may prove to be sufficient when dealing with substances having a log Kow, of less than five, methods for HHCs need to account for the influence of structure on retention.

Gastroaortic fistula as an early complication of esophagectomy

Gastroaortic fistula following esophagogastrectomy is an uncommon and invariably fatal complication without urgent surgical intervention. We report 1 such case and review the world literature identifying 22 previous cases. It characteristically presents 2 to 3 weeks after esophagogastrectomy with an initial herald bleed, followed by a latent period with a mean duration of 10 hours (range: 30 minutes to 3 days) and final exsanguination. Only 1 patient in this series survived. Awareness is necessary to allow prompt diagnosis and treatment of this almost invariably lethal but curable condition.

Endoscopic palliation and survival in malignant biliary obstruction

Malignant biliary obstruction is a common problem that is regarded as having a poor prognosis and is usually managed with palliation. Our aim was to investigate the survival of 182 consecutive subjects with malignant biliary obstruction where management was palliative with an [corrected] endoscopically placed biliary stent. We undertook a retrospective longitudinal study with date of death or confirmed survival of at least 23 months, as the primary end point. Diagnosis and blood indices from the 24 hr prior to first ERCP were obtained from hospital records. Of the 182 eligible subjects follow-up of date of death or confirmed survival of at least 23 months was obtained in 181 (99.5%). Of these 181 patients, 37 (20.4%) survived for more than one year. Histological confirmation was obtained in 47 of 182 subjects (25.8%). Increased age at first ERCP predicted increased survival (P < 0.05). In conclusion, in patients with malignant biliary obstruction, where management was endoscopic and palliative, 20.4% survived for more than one year with increased age at diagnosis being the only significant predictive marker.

Portal venous collateral drainage in IVC obstruction

Collateral venous drainage via the portal venous system has been demonstrated in three patients with testicular teratoma and IVC obstruction using contrast venography and enhanced computed tomography (CT). The use of CT in assessing the extent of the collateral circulation in IVC obstruction together with implications for surgical management are discussed.

Staging of prostatic carcinoma with radionuclide bone scintigraphy and lymphography

One hundred patients with histologically proven carcinoma of the prostate were examined by radionuclide bone scintigraphy and bipedal lymphography. In 27 cases the bone scintigram and lymphogram were positive, in 16 the bone scintigram only was positive and in 10 the lymphogram only was positive. Although radionuclide bone scintigraphy is the most useful single investigation for detecting metastatic spread from prostatic carcinoma, lymphography should be performed if the bone scintigram is negative, as it is likely to demonstrate nodal metastases in 18% of patients.

Intertrochanteric fractures: a comparison between fixation with a two-piece nail plate and Ender's nails

The progress of 182 patients who presented with intertrochanteric fractures was followed over a six month period. Eighty-seven patients were treated using Thornton/McLaughlin nail plates and 95 were treated using Ender's intramedullary nails. Each fracture was classified according to radiological position and mechanical stability. The results show that the more unstable fractures are more likely to develop unsatisfactory results. Post operatively, the different mechanical complications have been recorded at various stages. Those fractures fixed with a nail plate tended to develop varus deformity resulting from either bony collapse around the implant or implant failure, whereas those fixed with Ender's nails did not develop deformity at the fracture site but encountered distal migration of the nails at the knee. The use of a classification system in predicting post operative mechanical complications is considered, and the comparative merits and disadvantages of the two fixation systems is discussed, with suggestions for improvement in operative technique.