Field measurements of mercury air‐surface exchange from natural settings were made in various Canadian landscapes. Soil and water samples were analyzed for mercury concentrations, and air‐surface exchange fluxes from these substrates were determined using dynamic chamber, micrometeorological, or modeling methods. Environmental variables, including air and soil/water temperature, solar radiation, humidity, and wind speed, were monitored concurrently with the air‐surface exchange to better understand the processes affecting the environmental cycling of mercury. Average mercury fluxes from aquatic landscapes ranged from 0.0 to 5.0 ng m−2 h−1 with total mercury concentration in water ranging from 0.3 to 6.5 ng L−1. A significant correlation (R2 = 0.47) was found between gaseous Hg fluxes and total Hg concentration in water. Mean gaseous Hg fluxes from forest soils varied from −0.4 to 2.2 ng m−2 h−1, while those from agricultural fields ranged from 1.1 to 2.9 ng m−2 h−1. Non‐mineralized bedrock, sand, and till sites yielded fluxes ranging from −0.03 to 5.9 ng m−2 h−1. Mean fluxes from mercuriferous geological substrates at various locations were large compared to non‐mercuriferous sites, ranging from 9.1 to 1760 ng m−2 h−1, and represent natural emissions. The corresponding total mercury substrate concentrations ranged from 0.360 to 180 ppm. A significant correlation (R2 = 0.66) was found between Hg fluxes and total Hg concentrations in mineralized and non‐mineralized substrates. These gaseous Hg flux measurements represent a significant contribution to understanding natural mercury cycling, but there are still insufficient data and knowledge of processes to properly scale up fluxes from natural sources in Canada.

An aerodynamic gradient micrometeorological approach to the measurement of total gaseous mercury (TGM) flux has been developed. This method has been applied in many field studies for the characterization of TGM flux from various mercuriferous substrates. The resolution of the gradient method depends on the sampling systems characteristics and has been demonstrated to be on the order of 0.01 ± 0.01 ng Hg m−3 or better. The method is best suited to measuring high‐emitting sites such as studied here. The TGM flux resolution is based on the gradient resolution and depends on the site characteristics and the atmospheric condition. For a typical friction velocity u* of 0.1 m s−1 and gradient intake heights of 0.15 and 0.4 m the method can resolve a TGM flux on the order of 1.5 ng m−2 h−1. The system can be configured for two‐level or multilevel sampling, as needed. The method compares well with other micrometeorological methods as demonstrated during the Nevada storms intercomparison study. The micrometeorological method is shown to compare well with chamber techniques under comparable conditions.

A new protocol was used to determine biotransformation rate coefficients for volatile organic compounds in activated sludge systems. The values obtained from the protocol were compared to biotransformation rates obtained from a pilot plant. It was seen that biotransformation rates were easier to obtain from the protocol. Observations also showed that acclimation of the microorganisms to the volatile organic compounds did not change the biotransformation rates. The experimental conditions were then modelled using TOXCHEM+, a mechanistic model to predict volatile organic compound behaviour. The TOXCHEM+ predictions, using system default biotransformation rates, compared favourably with the low biotransformation rates measured by the protocol for bromoform and the chlorinated compounds, while under predicting the biotransformation rates for the non-chlorinated volatile organic compounds.

Chamber and micrometeorological mercury flux data collected during the Nevada STORMS intercomparison study were used to identify natural and methodological factors controlling data variability. Micrometeorological and chamber measurements revealed that flux variability at a site is closely related to the Hg concentrations in the substrate, which were found to vary with mineral composition, grain size, and sampling depth. Environmental factors also influenced flux variability. Following two rainfall events, fluxes measured by chamber and micrometeorological methods increased substantially. The micrometeorological flux was enhanced five fold following the rain event. Fluxes measured by both methods were also influenced by net radiation and temperature as evidenced by their tendency to follow the diel cycle in these variables. Daytime fluxes were 6 times greater than nighttime fluxes. Data analysis revealed that interactions between environmental and geochemical variables complicate relationships between the flux and these variables. Understanding the variability at a flux monitoring site is important to establish relationships for scaling up and for the development of consistent sampling protocols that allow comparisons from one study to another and adequately quantify mercury fluxes from natural sites to provide representative emission data that can be used for scaling up to regional and global scales.

A method was developed for determining biotransformation rate coefficients for volatile organic compounds in activated sludge systems. It consisted of a sealed batch reactor containing primary substrate, VOCs and biomass. A bubbleless oxygenation system was used to supply oxygen. Two types of substrate were studied to determine method reliability; domestic wastewater and synthetic wastewater, as were various conditions; abiotic, biotic, anaerobic, anoxic denitrifying and aerobic. The anaerobic and anoxic denitrifying conditions revealed minimal VOC biotransformation, while under aerobic conditions, the method successfully measured mixed second-order biotransformation rate coefficients for the ten VOCs studied. The proposed method will be useful to designers and operators of wastewater treatment plants, who need reliable kinetic parameters to predict the fate of contaminants in wastewater treatment plants. (C) 2000 Elsevier Science Ltd. All rights reserved.

As part of an international Hg flux intercomparison at the Steamboat Springs, Nevada, geothermal area, several dynamic soil flux chambers and micrometeorological gradient systems were operated over desert soils in early September 1997. A series of unanticipated convective rain cells impacted the site with the first rainfall in ∼90 days, and the initial 4‐cm rainfall increased soil moisture from ∼0.01 to 0.06% (vol/vol). Several chambers were operating prior to the events, and two were deployed over wet soils following rainfall. Rainfall resulted in an immediate and steep rise in ambient air Hg concentrations and soil Hg emissions which persisted for 12–24 hours. Fluxes increased most quickly and to a greater degree over the wettest soils, and the rate of increase was related to chamber design and flushing rate. The flux response was also apparent in the micrometeorological data. In general, soil emissions increased by an order of magnitude following the rain, and reached levels ∼6 times above those at the same time the previous day. These fluxes were significantly correlated with temperature, radiation, humidity, wind speed, and soil moisture. After drying for ∼40 hours, selected soil plots were manually irrigated with low‐Hg‐distilled water. Mercury emissions responded similarly across the three treated sites, uniformly increasing from ∼60 ng m−2 h−1 pretreatment to ∼650 ng m−2 h−1 posttreatment, which was a factor of ∼6 higher than adjacent control soils. Possible causes of the increases in flux include soil gas displacement, desorption of Hg° by water molecules, and desorption of Hg(II) and subsequent reduction in solution. The kinetics of the flux response, combined with local soil and climatic conditions, suggest that Hg emissions were responding primarily to soil moisture and solar radiation. These data have interesting implications for the role of changing regional climates on biogeochemical cycling of Hg.

The potential for the use of a laboratory gas exchange system to estimate of mercury emissions from naturally and anthropogenically mercury‐enriched areas was assessed by comparison of mercury fluxes measured from the same substrate in situ and in the laboratory. In general, mercury emissions measured with the laboratory chamber for daytime conditions were of the same magnitude as mean mercury emissions measured in situ with field chambers. Mercury emissions measured with both the field chamber and laboratory chamber were lower than those measured with micrometeorological methods. Within the controlled experimental regime of the laboratory chamber, data were developed that demonstrated that substrate mercury concentrations and light are important parameters in controlling mercury emissions. However, with light and other parameters interacting with the soil, the correlation between mercury fluxes and substrate mercury concentrations declined. Mercury emissions from a variety of substrates in the dark were ∼25% of those emissions measured in the light at the same soil surface temperature.

Diffuse anthropogenic and naturally mercury-enriched areas represent long- lived sources of elemental mercury to the atmosphere. The Nevada Study and Tests of the Release of Mercury From Soils (STORMS) project focused on the measurement of mercury emissions from anaturally enriched area. During the project, concurrent measurements of mercury fluxes from naturally mercury-enriched substrate were made September 1-4, 1997, using four micrometeorological methods and seven field flux chambers. Ambient air mercury concentrations ranged from 2 to nearly 200 ng m- 3 indicating that the field site is a source of atmospheric mercury. The mean day time mercury fluxes, durin p conditions of no precipitation, measured with field chambers were 50 to 360 ng m -2 h - , and with the micrometeorological methods we re 230 to 600 ng m- 2 h -1. This wide range in mercury emission rates reflects differences in method experimental designs and local source strengths. Mercury fluxes measured by many field chambers were significantly different (p < 0.05) but linearly correlated. This indicates that field chambers responded similarly to environmental conditions, but differences in experimental design and site heterogeneity had a significant influence on the magnitude of mercury fluxes. Data developed during the field study demonstrated that field flux chambers are ideal for assessment of the physicochemical processes driving mercury flux and development of an understanding of the magnitude of the influence of individual factors on flux. In general, mean mercury fluxes measured with micrometeorological methods during day time periods were nearly 3 times higher than me an fluxes measured with field flux chambers. Micrometeorological methods allow for derivation of a representative mercury flux occurring from an unconstrained system and provide an assessment of the actual magnitude and variability of fluxes occurring from an area.

Estimates of the total emission of elemental mercury vapour (Hg-0) to the atmosphere from natural sources vary by orders of magnitude. The uncertainty arises from the scarcity of temporally and spatially representative data. This paper describes field studies conducted from July 1996 to September 1997 directed at developing and applying methodologies for measuring atmospheric Hg-0 fluxes from natural sources. Preliminary results for five contrasting geochemical settings in Canada and the USA indicate a positive relationship between He flux and total Hg-0 concentrations in the substrate.

A residential washing machine was studied in order to determine the extent of chloroform formation following the application of a laundry bleach containing sodium hypochlorite. A dynamic model was also developed to estimate chloroform formation, mass transfer, and gaseous emissions during a typical wash cycle. A series of 22 experiments was completed to determine model parameters, including chemical reaction and mass transfer rate coefficients, as well as headspace air exchange rates. Three additional experiments were completed to evaluate model performance. Experimental and model results suggest that washing machine environments are very conducive to chloroform formation, with chloroform levels frequently exceeding 1 mg/L in washwater. Chloroform stripping efficiencies were observed to be greater than those previously reported for ethanol, but less than those reported for radon. Mass emissions of chloroform to indoor air during a ten-minute wash cycle were predicted to be between 5.3 and 9.8 mg. On a unit activity basis, chloroform emissions associated with hypochlorite-containing bleach addition to washing machines far exceeded emissions from showers. Each source was estimated to emit similar quantities of chloroform on an annual basis. Finally, it was estimated that the use of hypochlorite-containing laundry bleaches may contribute a significant fraction of chloroform mass loadings to municipal wastewater.

Intracranial epidural abscess is an uncommon but potentially life-threatening condition requiring prompt recognition and management. Most commonly it arises secondary to infection in the paranasal sinuses, mastoid air cells or the middle ear. It has also been described following craniotomy and trauma. This report describes three cases reported to our institution over a 15 month period, two associated with frontal sinusitis and one with no obvious predisposing factor.

During the period May 1986 to July 1989, a prospective, double blind, randomized trial of antibiotic prophylaxis in colorectal surgery was undertaken at the Royal Brisbane Hospital. Three hundred and thirty patients were considered eligible for the trial. Three regimens were compared: a combination of 2 g ceftriaxone and 1 g metronidazole; a single dose of 2 g ceftriaxone; or 1 g cefazolin and 1 g metronidazole, as antibacterial prophylaxis in colorectal surgery. Fifty patients were excluded from analysis. The overall incidence of wound sepsis was 7.9% (22 patients). There was no statistical difference in the incidence of wound infections between the three groups. The presence of drains and the non-performance of a bowel anastomosis at the time of surgery predisposed patients to wound infection. Staphylococcus aureus or Staphylococcus epidermidis were the cause of wound infection in 16 cases. Patients in the cefazolin and metronidazole group had a significantly higher number of postoperative urinary tract and respiratory tract infections than the other two groups combined (P less than 0.01). There did not appear to be any change in sensitivity patterns to ceftriaxone during the 3 year trial. During the 3 year period of the study, ceftriaxone was found to be a safe and effective drug in antibacterial prophylaxis in colorectal surgery.

Summary Fifty‐seven patients had arterial hypotension induced by a technique with halothane and sodium nitroprusside during operations on the ear, nose and parotid gland. Metoprolol, a cardioselective beta‐adrenergic blocker, was used when required to maintain the pulse rate at 80 beats per minute or less and to assist in reducing the blood pressure. Metoprolol was used in 50 cases while 7 cases remained at a pulse rate of less than 80 bpm spontaneously.

Flash photolysis of VOCl3 vapour under adiabatic conditions yielded in absorption the visible C4Σ––X4Σ– band system of VO, together with eight new, diffuse u.v. spectra of widely varying intensity, in the range 2300–3800 Å. A comparison is made with the known u.v. transitions of the analogous molecule TaO. No trace of a reported u.v. system near 4000 Å, attributed to matrix isolated VO, was observed. Ground and excited state vanadium atoms were detected, and both photolytic and pyrolytic decomposition modes of VOCl3 are postulated.

The flash photolysis of antimony trichloride vapour under isothermal conditions yielded three systems of absorption bands in the ultraviolet region (2168–2421 Å), all being degraded to shorter wavelengths. The bands were somewhat diffuse and no isotope splittings were detectable to check the vibrational assignments. Under adiabatic conditions, only two of the band systems were observed. The known A1, A2→X(?) band systems in the visible region were not present in absorption and it is still not certain whether the lower state of any of the observed transitions of SbCl is the ground state. For all the ultra-violet systems, ω′e∼445 cm–1 and ω″e∼370 cm–1.

AbstractBei der Blitzphotolyse von VOCl3‐Dampf unter adiabatischen Bedingungen werden das sichtbare Absorptionsbandensystem C423 ′‐X42′ von V0 zusammen mit acht neuen diffusen UV‐Spektren mit unterschiedlicher Intensität im Bereich 2 300‐3 800 Å beobachtet.