Estimating overall persistence and long-range transport potential of persistent organic pollutants: a comparison of seven multimedia mass balance models and atmospheric transport models.

Two different approaches to modeling the environmental fate of organic chemicals have been developed in recent years. The first approach is applied in multimedia box models, calculating average concentrations in homogeneous boxes which represent the different environmental media, based on intermedia partitioning, transport, and degradation processes. In the second approach, used in atmospheric transport models, the spatially and temporally variable atmospheric dynamics form the basis for calculating the environmental distribution of chemicals, from which also exchange processes to other environmental media are modeled. The main goal of the present study was to investigate if the multimedia mass balance models CliMoChem, SimpleBox, EVn-BETR, G-CIEMS, OECD Tool and the atmospheric transport models MSCE-POP and ADEPT predict the same rankings of the overall persistence (P(ov)) and long-range transport potential (LRTP) of POPs, and to explain differences and similarities between the rankings by the mass distributions and inter-compartment mass flows. The study was performed for a group of 14 reference chemicals. For P(ov), the models yield consistent results, owing to the large influence of phase partitioning parameters and degradation rate constants, which are used similarly by all models. Concerning LRTP, there are larger differences between the models than for P(ov), due to different LRTP calculation methods and spatial model resolutions. Between atmospheric transport models and multimedia fate models, no large differences in mass distributions and inter-compartment flows can be recognized. Deviations in mass flows are mainly caused by the geometrical design of the models.

Influence of vegetation on the environmental partitioning of DDT in two global multimedia models.

Two multimedia models are used to investigate the effect of a vegetation compartment on the environmental partitioning of dichlorodiphenyltrichloroethane (DDT): a steady-state unit world model using global averages of vegetation cover and land-to-sea ratio and a dynamic model with latitudinal zones and zone-specific vegetation types and annual temperature courses. The vegetation compartment represents canopies of deciduous and coniferous forests and blades of grasses; the organic carbon content of the vegetation-covered soil is higher than in the bare soil. In the steady-state model, transfer from the air to the vegetation and the underlying soil as well as revolatilization from the foliage and reduced deposition to the soil is observed, depending on the chemical's degradation rate constant in vegetation and the deposition velocities of the gaseous and particle-bound fractions. In both models, a significant effect of the organic carbon content of the vegetation-covered soil increasing the effect of the vegetation compartment is observed. In the steady-state model, the changes in the DDT concentrations in air do not exceed 7% difference between the cases with and without vegetation; the soil concentrations differ by maximally a factor of 2.7. In the spatially and temporally resolved model, however, air concentration differences up to 90% are observed, depending on the type and amount of vegetation in the latitudinal zones. Long-range transport is less pronounced in the model with vegetation.

Long-range transport and global fractionation of POPs: insights from multimedia modeling studies.

The long-range transport of persistent organic pollutants (POPs) is investigated with two multimedia box models of the global system. ChemRange is a purely evaluative, one-dimensional steady-state (level III) model; CliMoChem is a two-dimensional model with different temperatures, land/water ratios and vegetation types in different latitudinal zones. Model results are presented for three case studies: (i) the effect of atmospheric aerosol particles on the long-range transport of POPs, (ii) the effect of oceanic deposition on the long-range transport of different PCB congeners, (iii) the global fractionation of different PCB congeners. The model results for these case studies show: (i) the low atmospheric half-lives estimated for several organochlorine pesticides are likely to be inconsistent with the observed long-range transport of these compounds; (ii) export to the deep sea reduces the potential for long-range transport of highly hydrophobic compounds (but does not remove these chemicals from the biosphere); (iii) there are different meanings of the term global fractionation that refer to different aspects of the fractionation process and need to be distinguished. The case-study results further indicate that the influences of varying environmental conditions on the physicochemical properties and the degradation rate constants of POPs need to be determined.

Recovery after total intravenous anaesthesia using combined midazolam/alfentanil infusion and reversal with flumazenil.

One of the major problems with total intravenous anaesthesia (TIVA) is postoperative sedation, possibly with respiratory depression. The aim of the present study was to evaluate the recovery characteristics after TIVA using a continuous infusion of a mixture of midazolam and alfentanil with flumazenil reversal before extubation. This method was compared to balanced anaesthesia using midazolam, alfentanil and nitrous oxide without flumazenil reversal. The degree of sedation was measured by reaction time test, Glasgow Coma Scale, cipher copying test and subtraction test. We found significantly faster reaction times postoperatively in the TIVA group (n = 15) compared to the balanced group (n = 13), despite larger doses of both midazolam (median 21 mg versus 9 mg) and alfentanil (median 5.9 mg versus 4.5 mg). The other tests revealed no difference between the groups. One patient became resedated after flumazenil. We conclude that the TIVA technique described here resulted in slightly better recovery characteristics, offering a usable alternative to balanced anaesthesia.

[Total intravenous anesthesia using ketamine and midazolam. A simple technic]. / Universelle intravenöse Anaesthesie mit Ketamin und Midazolam. Eine einfache Technik.

Forty unpremedicated patients undergoing minor gynecological surgery were anesthetized with 1 mg ketamine and 0.1 mg midazolam per kg bodyweight, if necessary supplemented later with half the initial dose. All patients continued to breathe room air spontaneously with no ventilatory support. There were no incidents of airway obstruction and only 1 case of troublesome airway secretions. The arterial blood gas sample did not show any sign of respiratory depression, but in 11 cases paO2 was lower than normal, though acceptable. The median emergence time was 6 min. The side effects of ketamine were well controlled by midazolam, and patient acceptance of the technique was high. We consider that the technique may be suitable for short procedures under primitive conditions, for example after mass casualties, and that it can, if necessary, be applied by specially trained paramedics.

Sixteen years with the Danish Search and Rescue Helicopter Service.

The Danish helicopter rescue service in its present form was founded in 1966. The use of the Sikorsky (S-61) helicopter has generally been satisfactory. In 1973, the crew was supplemented by an aerospace-medically-educated and helicopter-trained physician. From 1973 to 1989 there were 5,733 missions, of which direct medical intervention occurred in 2075 cases; 94% of the missions supported the civilian public health service in Denmark. Many sorts of diseases and injuries have been seen, but especially trauma, abdominal, and cardiopulmonary diseases. Experience has shown the benefit of having a designated physician, specially trained in aerospace medicine and acute medicine/surgery, as a permanent crewmember.

Aminophylline reduces the depth and duration of sedation with barbiturates.

Aminophylline, an inhibitor of cyclic nucleotide phosphodiesterase, has for many years been used to relieve bronchospasm. Recent reports have shown that aminophylline antagonizes morphine and diazepam sedation. To see if aminophylline acts similarly on barbiturate sedation, we examined 24 women undergoing short general anaesthesia with thiopental (7 mg x kg-1), using a double-blind study design. Evaluated by continuous auditory reaction time measurements, aminophylline (5.6 mg x kg-1) reduces the depth and duration of sedation with thiopental. This suggests that aminophylline could be used to diminish an unwanted effect of barbiturate sedation.