An assessment of dermal exposure to semi-synthetic metal working fluids by different methods to group workers for an epidemiological study on dermatitis.

BACKGROUND: Assessment of exposure assessment to metal working fluids (MWF) has almost exclusively focused on inhalation exposure. AIMS: To assess levels of, and factors affecting, dermal and inhalation exposure to semi-synthetic MWF, and to identify suitable dermal exposure grouping schemes among metal workers for an epidemiological survey on dermatitis of hands, forearms, and head. METHODS: A cross-sectional survey was conducted in four metal working machining departments of a truck manufacturing plant, estimating dermal and inhalation exposure levels to semi-synthetic metal working fluids (SMWF) in machine operators. Dermal exposure levels to SMWF were estimated by three different methods for dermal exposure assessment (VITAE, surrogate skin pad method, and a semi-quantitative dermal exposure assessment method (DREAM)). RESULTS: The identified factors affecting dermal exposure were similar for the three methods, although differences were found for estimated variability in dermal exposure levels between groups, within groups (among workers), and from day to day. With the VITAE method differences in exposure levels were detected between workers that were not detected with the surrogate skin pad method, and only partly with the DREAM method. CONCLUSIONS: Considering the additional effort and costs that use of the VITAE method entailed, the observational semi-quantitative DREAM method appeared to be more efficient for grouping of dermal exposure levels for the epidemiological study on dermatitis.

Beneficial effects of TCP on soman intoxication in guinea pigs: seizures, brain damage and learning behaviour.

Poisoning with the potent nerve agent soman produces a cascade of central nervous system (CNS) effects characterized by severe convulsions and eventually death. In animals that survive a soman intoxication, lesions in the amygdala, piriform cortex, hippocampus and thalamus can be observed. In order to examine the mechanisms involved in the effects of soman and to evaluate possible curative interventions, a series of behavioural, electrophysiological and neuropathological experiments were carried out in the guinea pig using the NMDA antagonist N-[1-(2-thienyl)cyclohexyl] piperidine (TCP) in conjunction with atropine and pyridostigmine. The NMDA antagonist TCP appeared to be very effective in the treatment of casualties who suffered from soman-induced seizures for 30 min: (i)Seizures were arrested within minutes after the TCP injection, confirmed by quantitative electroencephalogram (EEG), after fast Fourier analysis. Three hours after TCP the quantitative EEGs were completely normal in all frequency bands and remained normal during the entire 3-week intoxication period. The power shift to the lower (delta) frequency bands, indicative for neuropathology and found in control animals intoxicated only by soman, was not observed in the soman-TCP group. (ii)The gross neuropathology found in soman control animals within 48 h after soman was prevented in soman-TCP animals and was still absent in 3-week survivors. Instead, ultrastructural changes were observed, indicative of defense mechanisms of the cell against toxic circumstances. (iii)Twenty-four hours after soman, soman-TCP animals were able to perform in the shuttle box and Morris water maze. The beneficial effects of TCP on the performance in these tests during the 3-week intoxication period were very impressive, notwithstanding (minor) deficits in memory and learning. (iv)The increase in excitability after TCP was confirmed by an increase in the acoustic startle response. Taken together, these results confirmed the involvement of NMDA receptors in the maintenance of soman-induced seizures and the development of brain damage. They underline the current hypothesis that cholinergic mechanisms are responsible for eliciting seizure activity after soman and that, most likely, the subsequent recruitment of other excitatory neurotransmitters and loss of inhibitory control are responsible for the maintenance of seizures and the development of subsequent brain damage.

Implementation and evaluation of the fluorescent tracer technique in greenhouse exposure studies.

Knowledge of the level of exposure is important for health risk estimation and risk management. Recently, the occurrence of dermal exposure in many situations has been recognized and estimated to be relevant for worker health. Dermal exposure measurement techniques are therefore needed and several approaches have been taken to assess this type of exposure. The purpose of the present study was to apply and evaluate the fluorescent tracer technique, being one of the most promising and innovative techniques to estimate dermal exposure. The image acquisition is fully calibrated and validated. The most significant aspects of the image analysis process are validated in laboratory settings. The system is applied in a field study to estimate dermal exposure of operators and harvesters in greenhouses, while chemical analysis of clothing exposure is also performed. For operators, the correlation coefficient between the active substance (propoxur) and the fluorescent compound (Tinopal) was 0.92, and for harvesters 0.85. It is concluded that the variability in the analytical technique used is insignificant with respect to the variability in exposure within and between workers. Instead of improving the measuring technique, one might better lower the variability by measuring, for instance, a larger number of workers and/or by standardizing work procedures. The fluorescent tracer technique, being a fast method to estimate dermal exposure, enables the estimation of larger numbers of individuals. Furthermore, the qualitative use of this technique can lead to a more efficient sampling strategy since the exposed body area to evaluate can easily be visualized and selected.

A critical evaluation of methods for estimating the numerical density of synapses.

Several methods for estimating the numerical density (NV) of particles are described. The usefulness and the limitations of different methods with respect to the estimation of synaptic densities are discussed. These methods are: the discrete unfolding technique, the serial section technique and the disector technique. From the results it is concluded that it is not advisable to use an unfolding technique to estimate the number and size of synapses since all sorts of assumptions regarding the shape, truncation and overprojection are hazardous. Consistently lower values for NV were obtained with the disector technique compared with the results of the serial section technique. This difference, obtained with two unbiased techniques, is discussed. The main conclusion with respect to this point is that both techniques can be used to estimate synaptic densities, provided a reliable estimate of the section thickness is obtained and an appropriate sampling procedure is used.

The complex-shaped 'perforated' synapse, a problem in quantitative stereology of the brain.

Failure to appreciate the consequences for stereological work of the simultaneous presence of complex-shaped perforated and disc-like non-perforated synapses in brain tissue results in underestimation of synaptic profile length and overestimation of synaptic density when measured in randomly selected ultrathin E-PTA slices. This problem can be solved by using serial slices and a calculation method which makes no assumptions about synaptic size and shape. A three-dimensional reconstruction is unnecessary.