Are deficits in the equilibrium system relevant to the clinical investigation of solvent-induced neurotoxicity?

Hearing

The main hazard for hearing in the workplace is noise. Organic solvents and heavy metals may increase the danger of developing occupational hearing loss, particularly in the case of co-exposure with noise. While noise produces damage predominantly to the cochlea, chemicals may be responsible for pathologic changes in both peripheral and central parts of the auditory pathway. Noise-induced hearing loss develops slowly over the years, although its progression is most dynamic during the first 10-15 years of exposure. Pure-tone audiometry indicates a bilateral sensorineural hearing loss, affecting predominantly high frequencies, with typical notch at 3-6 kHz in the early stages of the disease. Where there is co-exposure to noise and chemicals, the noise effect on hearing threshold shifts is dominant; however chemicals seem to increase the vulnerability of the cochlea to the damage by noise, particularly at its low and moderate levels. According to European Directive 2003/10/EC, the employer is obliged to implement hearing prevention programs when the A-weighted equivalent 8-hour level of noise (LAEX8 hr) exceeds 80 dB. Since chemicals may impair intelligibility of speech despite a lack of audiometric hearing threshold shift, implementation of speech audiometry, particularly speech in noise tests, is recommended in prevention programs.

Visual search and eye movements in patients with chronic solvent-induced toxic encephalopathy

Various aspects of visual perception have been found to be impaired in patients with occupational chronic solvent-induced toxic encephalopathy (CSE). The purpose of the study was to characterise the changes in eye movements and visual search performance in CSE patients. We measured eye movements of 13 CSE patients and 22 healthy controls during dynamic visual search task by using a fast video eye tracker. The task was to search for and identify a target letter among numerals presented in a rectangular stimulus matrix (3x3-10x10 items). Threshold search time, i.e. the duration of stimulus presentation required for identifying the target with a given probability was determined by using a psychophysical staircase method. The visual search times of the CSE patients were clearly longer, and they needed considerably more eye fixations than healthy controls to find the target. Thus, their reduced performance in this task was mainly related to the reduction in the number of items which could be processed during a single eye fixation (perceptual span). This reduction probably reflects a limited capacity of visual attention, since visual acuity, contrast sensitivity, and the oculomotor saccade velocity were found to be normal. The results suggest that motor slowness or low-level visual factors do not explain the poor performance of CSE patients in visual search tasks. The results are also discussed with respect to the effects of education, and compared to the performance in the widely used neuropsychological Trail Making Test, which uses similar stimuli and requires visual search.

Combined effects of noise and mixed solvents exposure on the hearing function among workers in the aviation industry

This study aims to evaluate the effect of occupational exposure to noise and organic solvents on hearing loss in the aviation industry. The study population comprised 542 male workers, who worked in avionics jobs in Kimhae, Korea, who kept records of work environment evaluations and medical examinations. The Cumulative Exposure Index (CEI) was constructed to assess the lifetime cumulative exposure of the workers, and pure tone audiometry (PTA) data of the workers from their biannual medical surveillance was used to assess hearing loss. The prevalence of hearing loss found in the group exposed to noise and mixed solvents simultaneously (54.9%) was higher than those in the other groups (6.0% in the unexposed, 17.1% in the noise-only, and 27.8 % in the exposed to only a solvents mixture). The relative risks, adjusted for age, were estimated to be 4.3 (95 % CI 1.7-10.8) for the noise-only group, 8.1 (95% CI 2.0-32.5) for the noise and solvents group, and 2.6 (95 % CI 0.6-10.3) for the solvents-mixture group. These suggest that chronic exposure to mixed solvents had a toxic effect on the auditory system. This raises the issue of whether hearing conservation regulations should be applied to all workers exposed to solvents.

Long-term exposure to solvents impairs vigilance and postural control in serigraphy workers

OBJECTIVES

To investigate the effects of solvent exposure (mainly aromatic hydrocarbons) on central regulation of vigilance and postural control, particularly in occasional difficult situations that provide sensorial conflicts.

METHODS

Twenty-two workers occupationally exposed to solvents for an average of approximately 6 years and 21 controls were compared by the use of a questionnaire on their state of vigilance and quality of sleep and on performance measurements of postural control under six different sensorimotor conditions. Their current median exposure levels to aromatic hydrocarbons was 80.1 mg/m(3).

RESULTS

Exposed workers reported reduced alertness but not disturbance of sleep quality compared with controls. Moreover, they had the worst postural performance in all sensory conditions and demonstrated a reduced ability to resolve sensory conflict situations. The precision of stance was clearly affected by solvent exposure in contrast with energy consumption required to regulate proper balance control.

CONCLUSIONS

The depressive effect of aromatic hydrocarbon exposure on cortical and subcortical structures controlling vigilance and postural stability could lead to increased risk of occupational accident, especially due to falls. The detection of central neurotoxic effects by posturographic and vigilance tests could be useful in preventive strategies.

Neurological deficits in solvent-exposed painters: a syndrome including impaired colour vision, cognitive defects, tremor and loss of vibration sensation

Five individuals are described who had participated in a study of former dockyard painters. All had worked between 16 years and 45 years as industrial painters, much of the time inside ships. All underwent structured neurological examination, colour vision testing (allowing calculation of a colour confusion index corrected for age and alcohol), and detailed psychometric testing. An occupational history sufficient to allow estimation of past exposure to solvents was taken. All gave a history of exposure to high concentrations of solvents at work, and several described episodes of acute narcosis. All showed neurological deficits and some had overt neurological disease, although in no case had this previously been linked to their work. The most striking features, sufficient to constitute a syndrome, were acquired blue-yellow colour vision deficits, coarse tremor, impaired vibration sensation in the legs and cognitive impairment. Their estimated cumulative exposures to solvents ranged between the equivalent of 13 and 37 calendar years working at the Occupational Exposure Standard concentration (OES years). This study for the first time gives an indication of the concentrations of solvents likely to lead to serious neurological disease in humans. It serves as a reminder to physicians to take an occupational history from patients with obscure neurological or psychological impairment.