Study of fifteen respirable aerosol samplers used in occupational hygiene.

European and international standards lay down criteria for the size-selective aerosol sampling in occupational hygiene. Aerosol samplers are supposed to match these target sampling criteria. This study focused on 15 aerosol samplers used to sample the conventional respirable fraction. An aerodynamic particle sizer (APS) method was used to measure the sampling efficiency of the samplers in a low-velocity wind tunnel. Polydisperse coal dust was generated as the test aerosol. The data were fitted by an appropriate mathematical model. For some instruments the results show serious deviations from the conventional target curve, whereas other devices meet the convention quite well. The flow rate of certain cyclone-separator-based instruments was optimized to adjust their sampling efficiency. The mass concentration bias and accuracy of the samplers were calculated for a number of ranges of particle size distributions of aerosols commonly found in industrial workplaces. Finally, the performance of each sampler was evaluated using bias and accuracy maps. Most of these samplers are suitable for sampling the CEN-ISO-ACGIH respirable fraction of aerosols, but several require modification of the flow rate. For real industrial situations, the rough knowledge of the aerosol size distribution can guide the choice of an appropriate sampling technique.

Personal thoracic CIP10-T sampler and its static version CATHIA-T.

A specific version of the personal aerosol sampler CIP 10 was designed, named CIP10-T, for sampling the conventional CEN thoracic fraction. A static sampler, named CATHIA, was also designed. It uses the same sampling head, but the size selected particles are collected onto a filter. The combined particle efficiency of the aspiration slot and the selector was measured in a horizontal wind tunnel at low air velocity, close to 16 cm s-1. The flow rate of both samplers was fixed at its nominal value, i.e., 71 min-1. Two different methods were used: the former was based on the Aerodynamic Particle Sizer (TSI); the latter used the measurement of particle size distribution of the collected samples by the Coulter technique. For the CIP10-T sampler, the particle collection efficiency onto the rotating cup was also measured. For both samplers bias and accuracy maps have been calculated, following the recommendations of a new CEN standard about sampler performance. The bias does not exceed 10% in absolute value for both samplers, within a large range of particle size distribution of the total aerosol. For the CIP10-T sampler, the accuracy map exhibits a large area where the accuracy is better than 10%, corresponding for example to 4 microns < or = MMAD < or = 14 microns for GSD = 2. For the same geometric standard deviation, the accuracy is still better than 20% for 15 microns < or = MMAD < or = 21 microns. For the CATHIA-T sampler, the accuracy map can be roughly divided into two parts. The accuracy remains better than 10% for MMAD < or = 12 microns, and it remains between 10 and 20% for coarser aerosols, with 13 microns < or = MMAD < or = 20 microns, provided GSD > or = 2.

Innervation patterns of the lateral line stitches of the clawed frog, Xenopus laevis, and their reorganization during metamorphosis.

We quantitatively examined the afferent innervation pattern of the lateral line stitches of both larval and postmetamorphotic clawed frogs, Xenopus laevis, using a silver staining technique. We also studied the relevance of the number of neuromasts in a stitch to physiological properties, recording afferent activity with an electrode inserted directly into the neuromast. The innervation pattern changed during early metamorphosis, the fiber thickness increasing after the reorganization. We found three different innervation patterns: in type A stitches, the same two afferent fibers innervate all neuromasts; in type B stitches, one or two fibers innervate more than one stitch; in type C stitches, three to six fibers innervate a stitch. The distribution of the different types of stitches varied in different parts of the body. The frequency of type A stitches differed between larval trunk and larval head. For both larvae and juveniles, type B stitches were more frequent on ventral than dorsal areas, while type C stitches were more frequent on the head than on the trunk. Electrophysiological experiments indicated that the sensitivity of an afferent fiber increases with the number of neuromasts it innervates. This increase and the variation in innervation patterns shows that the single afferent fiber, not the stitch, is the functional unit of the lateral line periphery.

Sensory activity in the telencephalon of the clawed toad, Xenopus laevis.

In this study data are presented providing evidence that the striatum of the clawed toad, Xenopus laevis, processes mechanosensory, acoustic, and visual information and that multisensory interaction takes place in this telencephalic structure. Multimodal processing as well as the considerable effects of stimulus repetition rate on response amplitudes are in line with the finding that the striatum of Xenopus mediates attentional processes (Traub & Elepfandt, 1990). Further physiological studies are needed to delineate the functional organization of the striatum in amphibians.

Reaction to surface waves by Xenopus laevis Daudin. Are sensory systems other than the lateral line involved?

The turning response to surface waves of clawed toads (Xenopus laevis) with an inactivated lateral line was reinvestigated to examine whether sensory systems other than the lateral line ("second systems") are involved. Two methods were used to block the lateral line input: selective and reversible inactivation of the lateral line periphery using CoCl2 or chronic destruction with thermocautery. The time-course of the response recovery (response frequency, turning accuracy and reaction time) was recorded. Following CoCl2 inactivation 10 out of 13 animals did not respond to surface waves for at least 2 days. The remaining 3 animals gave sporadic turning responses. It is assumed that in these individuals a "second system" is permanently involved in the detection of surface waves parallel to the lateral line. Five days after the chronic destruction of the lateral line all animals again turned to the centre of surface waves. It is suggested that by this time the "second system" had become capable of substituting for the missing lateral line input. The response frequency and the accuracy of the turning response of lesioned animals varied considerably among individuals but was always lower than in untreated animals (tested up to 120 days).

Exposure to sulphuric acid and sulphur dioxide in the manufacturing of titanium dioxide.

An assessment of exposure to sulphuric acid and sulphur dioxide was performed in the French titanium dioxide manufacturing industry. The three plants use the sulphuric acid process, with potential exposure mainly to sulphur dioxide and sulphuric acid. The exposures found were below the French limit values, except for some employees using the Moore filtration process in one plant. For sulphuric acid sampling, a comparison was made between thoracic particulate mass and inhalable particulate mass, from samples taken with a Marple cascade impactor. This comparison shows that the suggested new limit value (0.1 mg m-3 in thoracic particulate mass) would be much more severe than the present one (1.0 mg m-3 with no restriction as to the droplet size).

Multisensory interaction in the torus semicircularis of the clawed toad Xenopus laevis.

Interactions between the lateral-line, general somatosensory and auditory system were studied using field potential analysis and single unit recordings in the torus semicircularis of the clawed toad Xenopus laevis. As a response to paired stimuli (electric shocks applied to the peripheral nerves or acoustic clicks), in all systems a reduction of the second evoked potential occurred for intervals of up to 5 s. Following consecutive stimulation of two different systems, the amplitude of the second evoked potential was also reduced, indicating mutual interaction of different systems. Single unit recordings revealed the existence of both inhibitory and excitatory interaction between different modalities.