Toxicological evaluation and limit values for Methyl-tertiary-butyl ether (MTBE), Formaldehyde, Glutaraldehyde, Furfural

7. Evaluation

MTBE has shown to cause tumourigenic/ carcinogenic effects in experimental animals as described above. The effects occur at dose levels of considerable organ toxicity. As MTBE was not shown to be genotoxic the tumourigenic effects are considered mediated through non-genotoxic mechanism secondary to organ toxicity. Therefore, a threshold for the tumourigenic effect is anticipated.

From a 90-day oral study a NOAEL of 100 mg/kg/d has been determined as higher dose levels (300 and 900 mg/kg/d) produced kidney toxicity in both male and female rats.

From inhalation studies a NOAEL of 1440 mg/m³ for exposure periods of 6 hours/day, 5 days/week for up to two years was found for female rats (due to occurrence of a2mglobulin accumulation in male rats kidney tubules cells it is not possible to identify a relevant NOAEL for risk assessment in male rats concerning effects on the kidney).

With respect to eye and respiratory tract irritation, studies with human volunteers did not find any signs of irritation up to 180 mg/m³ (the highest level tested). However, the subjective sense of odour from MTBE should be considered when establishing limit values for MTBE in air and water due to the potent terpene-like odour from the substance. In that respect odour detection limits (50% detection limit) of 0.19 mg/m³ and 0.18 mg/l have been determined for MTBE in air and water, respectively.