Toxicology of Industrial Compounds

302 SPECIAL POINTS IN THE TOXICITY ASSESSMENT OF COLORANTS
Table 21.1 Number of azo colorants based on cancerogenic aromatic amines (2napthylamine,
benzidine and its derivatives) listed in Colour Index (3rd edn, 3rd
Rev., 1987)
The problem of carcinogenic azo colorants
In the past, azo colorants based on benzidene, 3,3′-dichlorobenzidine, 3,3′dimethylbenzidine
(o-tolidine), and 3,3'-dimethoxybenzidine (odianisidine)
have been synthesized in large amounts and numbers,
especially in the German chemical industry. The Colour Index (1987) lists
a total number of more than 2000 azodyes, 452 of them being based on 2naphthylamine,
benzidine, or benzidine derivatives (Table 21.1).
Azo colorants have a number of properties that have made them
invaluable for dyeing a wide variety of materials, including natural and
artificial fibres, plastics, resins, textiles, leather, paper, glass, ceramics,
cement, inks, printing inks, chalks, crayons and carbon papers, as well as
cosmetics, food and beverages. Interesting with respect to potential
exposure of painters is the use of azo colorants in the coloring of oil-,
resins-, emulsion-, lime-, and other aqueousbased paints, distempers,
transparent laquers, spirit and oil wood stains, and varnishes (Colour
Index, 1987). In all these fields, particularly benzidine-based azo colorants
have found widespread use (Gregory, 1984).
In the UK, the Carcinogenic Substances Regulation led in 1967 to
discontinuation of the use of benzidine in the production of azo colorants
(Martin and Kennelly, 1985). The US government in 1974 promulgated
regulations to control benzidine at the workplace (Gregory, 1984).
Nevertheless, in the period of 1972–4, more than 150000 persons in the
USA were potentially occupationally exposed to benzidine-based colorants
(Gregory, 1984); in 1978, approximately 1.7 million US pounds of
benzidine-based azo colorants were manufactured, and a further 1.6
million pounds were imported into the USA (Lynn et al., 1980).
In Germany, over 30 different benzidine-based azo colorants were
manufactured in the early 1960s. The manufacture of these colorants was
stopped in 1971, with the exception of one dye (Direct Black 4; C.I. No.
30245); the manufacture of the latter was continued until 1973. Azo