Verification of effects on the nervous system of low level occupational exposure to CS2.

Neurotoxic effects associated with long term low level occupational exposure to CS2 were reinvestigated four years after the initial study in the same group of workers. The second study concerned 44 exposed and 31 matched control workers. For both studies a personal cumulative exposure Ec was calculated based on function specific exposure levels and the occupational histories, which were carefully re-established. The exposed workers' average Ec was 192 and 213 ppm-years (first and second study respectively). Where possible the values of both data sets were used in a final combined analysis. Effects were found on the motor nerve conduction velocity of the fast (-0.9 m/s) and slow (-1.0 m/s) fibres of the peroneal nerve, the sensory nerve conduction velocity in the hand and arm segment of the median (-2.1 m/s) and ulnar (-1.3 m/s) nerves, and in the sural nerve (-1.3 m/s). An increased refractory period was found in the sural nerve (+ 0.2 ms, + 11%), but not in the peroneal nerve. For the autonomic nervous system an effect was found on the heart frequency response to isometric muscle contraction (-4.7 beats/min, -26%) and maximal forced respiration (-3.2 beats/min, -16%). This study shows the importance of a detailed evaluation of past exposure data. The reinvestigation enabled a more precise estimation of the effects of CS2, which is particularly desirable at around threshold exposure.