in most cases , nitrosamines were not detected in laboratory air , but levels of 200-800 micrograms/m3 ( 42 to 180 ppb ) of n-nitrosomethyl-tert-butylamine were measured during animal treatment , 0.8-8.6 micrograms/m3 ( 0.3 to 2.8 ppb ) of ndma during mutagenesis assays , 12-22 micrograms/m3 ( 4-7 ppb ) of ndma during in vitro metabolism studies and 11 micrograms/m3 ( 3.6 ppb ) of ndma in a walk-in refrigerator .
C0028197
nitrosamines
C0012431
ndma