Toxicological evaluation and limit values for Methyl-tertiary-butyl ether (MTBE), Formaldehyde, Glutaraldehyde, Furfural 9. C-value9.1 Quality criteria in soil A limit value of 500 mg/kg has been calculated based on ingestion of soil by children. However, MTBE has a low odour threshold in air. Therefore, to account for discomfort from the odour due to evaporation from the soil, the C-value should not be exceeded in the air above soil surface. Quality criteria Quality criterion for porous air in soil: 0.3 mg/m3 (based on odour). 9.2 Quality criteria in drinking water A limit value of 350 mg/l has been calculated based on intake of drinking water. However, MTBE has a low odour threshold in water. Therefore, to take into account the discomfort from the odour, a quality criterion of 30 mg/l is proposed. This criterion is calculated based on the 50% odour detection limit in water (180 mg/l) and according to the calculation method of the Danish Environmental Protection Agency (conversion of 50% detection value to a 10% detection value = 50% value in mg/m3 x 0.18/ standard deviation for the observations). Quality criteria Quality criterion: 30 mg/l (based on odour). 9.3 C-value A toxicologically based limit value of 0.26 mg/m3 has been calculated. However, MTBE has a low odour threshold in air. Therefore, to account for discomfort from the odour, a limit value of 0.03 mg/m3 is calculated based on the 50% odour threshold in air (0.19 mg/m3) and according to the calculation method of the Danish Environmental Protection Agency (conversion of 50% detection value to a 10% detection value = 50% value in mg/m3 x 0.18/ standard deviation for the observations). For substances, for which odour is the limiting factor, the C-value is set at the odour limit value. Therefore, a C-value of 0.03 mg/m3 is proposed. MTBE should be placed in main group 1, as the substance has shown to be carcinogenic in experimental animals. C-value 0.03 mg/m3 (based on odour), Main Group 1.
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