Chronic exposure

Inhalation

There is no information on the effects of chronic inhalation of NMP in humans. Rats exposed to 0.1, 0.5 or 1.0 mg/l (25, 123 or 247 ppm) aerosol-vapour mixture of NMP for six hours per day, for five days per week for four weeks, developed lethargy and respiratory effects. Effects developed three to four hours after onset of exposure, continued throughout exposure and into the recovery period. The severity of clinical effects was dose related, with excessive mortality at the highest concentration. Only a few rats at the highest dosage had recovered by 18 hours post exposure. No effects were reported in the control group. Marked pulmonary oedema and congestion were found at postmortem examination in animals that died. Those killed in extremis were found to have focal interstitial pneumonitis, increased neutrophils in alveolar capillaries and bone marrow haemorrhage. Rats surviving 1.0 mg/l and those killed in extremis had bone marrow hypoplasia, haematopoietic cell necrosis and atrophy of lymphoid tissue in thymus, spleen and lymph nodes. Increases in relative and absolute numbers of neutrophils and decreased relative numbers of lymphocytes in rats surviving 1.0 mg/l, returned to normal values following 2 weeks of recovery. These abnormalities were not found in rats exposed to 0.1 or 0.5 mg/l (Lee et al., 1987).

Exposure of rats to NMP vapour for six hours per day, five days per week for two years, at concentrations of 0.04 or 0.4 mg/l (10 or 100 ppm) resulted in no life threatening toxic effects. Dose related darker yellow urine was reported. In the absence of a similar increase in renal lesions, this change was considered to be of no biological significance. Males in the highest treatment group had a slightly reduced mean bodyweight (6% less than controls) (Lee et al., 1987).

There were no effects on food consumption or bodyweight gain of rats exposed to 165 ppm for 6 hours each day on days 4 to 20 of gestation (Hass et al., 1995).

Dermal

No information available. Eye

Eye irritation described as uncomfortable after half an hour, was reported by some employees after occupational exposure to as little as 0.72 ppm NMP vapour (8 hour TWA) for full shifts (Beaulieu and Schmerber, 1991). However, it is not clear how this concentration was derived from the data reported.

Ingestion

No information available.

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