Objectives This study evaluates the possible toxic effects on the peripheral nervous system of tunnel workers exposed to acrylamide and N-methylolacrylamide during grouting work.

Methods Symptoms and nerve conduction velocities (NCV) were recorded for 24 tunnel workers 4 and 16 months after the cessation of exposure during grouting operations. Fifty tunnel workers not involved in grouting operations served as referents. Exposure was assessed by questionnaires, qualitative exposure indices, and measurements of hemoglobin adducts after the cessation of exposure.

Results The exposed workers reported a higher prevalence of symptoms during grouting work than they did in an examination 16 months later. A statistically significant reduction in the mean sensory NCV of the ulnar nerve was observed 4 months postexposure when compared with the values of the reference group (52.3 versus 58.9 m/s, P=0.001), and the mean ulnar distal delay was prolonged (31.1 versus 2.5 ms, P=0.001). Both measures were significantly improved when measured 1 year later. Exposure-related improvements were observed from 4 to 16 months postexposure for both the median (motor and sensory NCV and F-response)and ulnar (sensory NCV, F-response) nerves. A significant reversible reduction in the man sensory amplitude of the median nerve was also observed, while the mean sensory amplitude of the sural nerve was significantly reduced after 16 months.

Conclusions The results indicate demyelinating and axonal changes in peripheral nerves of tunnel workers in relation to exposure to N-methylolacrylamide and acrylamide during grouting operations. The changes were slight, mostly subclinical, and most of the effects were reversible, with normalization after 1 year.

Key terms acrylamide; exposure; grouting agent; hemoglobin adducts; N-methylolacrylamide; nerve conduction velocity; peripheral nervous system; reversibility; symptom; tunnel worker