Mutagenic activity of carbon black dyes used in the leather industry

Seven carbon black pastes used as commercial leather dyes were tested for their mutagenicity in the Salmonella/microsome test (TA98 and TA100 strains). All the samples assayed either directly or after extraction with a 30-min sonication in benzene were devoid of mutagenicity both in the presence and absence of a metabolic activation preparation. After a 48-h extraction with boiling toluene in a Soxhlet apparatus, four samples were mutagenic in TA98 strain in the presence of S9 mix. The activity ranged from 1.3 to 9.6 induced revertants/mg equivalent of extract. A weak direct mutagenic activity in strain TA98 was shown by one extract. Polycyclic aromatic hydrocarbons (PAH) were determined in the toluene extracts by high resolution gas chromatography/mass spectrometry. The presence of PAH could explain the mutagenicity of only one sample (8.79 micrograms of total PAH/100 mg equivalents of extract), while low or undetectable levels of PAH were found in the other mutagenic extracts. The mutagenic activity was evident only after a vigorous extraction process, thus a low bioavailability of the mutagens present in these compounds is suggested.