53 

## 1. Exposure Data

1.1 Identification of the agents

1.1.1 Benzidine

Chem. Abstr. Serv. Reg. No .: 92-87-5

Chem. Abstr. Serv. Name : [1,1 ′ -Biphenyl]-4,4 ′ -diamine

NH 2 H 2 N



### C

12 

### H

12 

### N

2 

### Relative molecular mass: 184.24
Description : White to slightly reddish, crystalline powder; darkens on exposure to air and light ( O’Neil, 2006 ). Solubility : Slightly soluble in water, diethyl ether, and dimethyl sulfoxide (DMSO); soluble in ethanol ( Lide, 2008 )



## 1.1.2 Benzidine dihydrochloride

Chem. Abstr. Serv. Reg. No .: 531-85-1

Chem. Abstr. Serv. Name : [1,1 ′ -Biphenyl]-

4,4 ′ -diamine, dihydrochloride

NH 2 . 2HCl H 2 N 

### C

12 

### H

10 

### N

2 

### .2HCl

Relative molecular mass: 257.18
Description : Crystalline solid ( O’Neil,

2006 ) Solubility : Soluble in water and alcohol ( O’Neil, 2006 )



## 1.2 Uses

Benzidine has been used since the 1850s as the reagent base for the production of a large number of dyes, particularly azo dyes for wool, cotton, and leather ( IARC, 2010 ). In the past, benzidine also

has been used in clinical laboratories for detec

tion of blood, as a rubber compounding agent, in the manufacture of plastic films, for detection of hydrogen peroxide in milk, and for quantita

tive determination of nicotine. Most of these uses have been discontinued because of toxicological concerns. Some dyes used as stains for micros

copy and similar laboratory applications may contain benzidine as an impurity ( ATSDR, 2001 ; NTP, 2005 ). Manufacture of benzidine is prohibited in several individual countries (e.g. Japan, Republic of Korea, Canada, and Switzerland) and in Europe through European Union (EU) legisla

tion. It has not been manufactured on a large scale for commercial purposes in the United 

# BENZIDINE

Benzidine was considered by previous IARC Working Groups in 1987 and 2008 ( IARC, 1987

, 2010 ). Since that time new data have become available, which have been incorporated in

this Monograph, and taken into consideration in the present evaluation.

### IARC MONOGRAPHS – 100F

States of America (USA) since 1976, although small quantities remain available for diagnostic testing. It is reportedly produced and/or supplied in research quantities in Germany, Hong Kong Special Administrative Region, India, the People’s Republic of China (China), Switzerland, and the USA ( IARC, 2010 ). Production and use of benzidine in dye production has been reported in some developing countries, as has the transfer of benzidine production from other European countries to the former Serbia and Montenegro and to the Republic of Korea ( Carreón et al

. , 2006a ). In 1994, the German Government prohib

ited the use of certain azo dyes in consumer goods that come in direct, prolonged contact with human skin (e.g. clothing, bedding, foot

wear, gloves, etc.). The dyes affected are those that, after reduction of one or more azo groups, may release one or more of 20 specific aromatic amines (including benzidine) in detectable concentrations (i.e. > 30 parts per million (ppm)). In 2002, a EU Directive (76/769/EEC) expanded coverage to articles that come in contact with the oral cavity and added two amines to the list ( Ahlström et al

. , 2005 ; ETAD, 2008 ). The US Food and Drug Administration limits benzi

dine content in food colourants to 1 part per billion (ppb). While exposure via ingestion is considered highly unlikely, other impurities in synthetic colouring agents may be metabolized to benzidine after ingestion ( ATSDR, 2001 ). 

## 1.3 Human exposure

1.3.1 Occupational exposure

Estimates of numbers of workers potentially exposed to benzidine have been published by CAREX (CARcinogen EXposure) in Europe. CAREX is an international information system that provides selected exposure data and docu

mented estimates of the number of exposed workers by country, carcinogen, and industry ( Kauppinen et al

. , 2000 ). Based on data on occupational exposure to known and suspected carcinogens collected from 1990 to 1993, it

is estimated from the CAREX database that 6900 workers were exposed to benzidine in the
European Union. Table  1.1 presents the results for benzidine by industry in the EU ( CAREX,

1999 ). NIOSH (1984) estimated from the US National Occupational Exposure Survey (1981–83) that 1554 workers (including 426 women) were poten

tially exposed to benzidine and 2987 workers (2464 women) to benzidine dihydrochloride. Studies that reported airborne or urinary concentrations and results of dermal wipes of

benzidine or benzidine derivatives in the benzi

dine-based dye industry have been reviewed ( IARC, 2010 ).



## 1.3.2 Non-occupational exposure

Because benzidine may be produced only for captive consumption (i.e. in-house by the producer only, in closed systems with stringent controls), its direct release into the environment is expected to be low. Benzidine-based dyes can contain various

amounts of benzidine as a contaminant. The general population can be exposed to benzidine when in contact with consumer goods containing benzidine or benzidine based-dyes such as leather products ( Ahlström et al

. , 2005 ), clothes and toys ( Garrigós et al

. , 2002 ). Some food colourants such as tartrazine and sunset yellow FCF have been

54 

### Table 1.1 Estimated numbers of workers exposed to benzidine in the European Union

Industry, occupational activity

Manufacture of textiles 160

Education services 3700

Research and scientific institutes 1900

Medical, dental, other health &
veterinary services 1300

TOTAL 6900

From: CAREX (1999)

### Benzidine

reported to contain trace amounts of benzidine (< 5 to 270 ng/g) ( Lancaster & Lawrence, 1999 ).



## 2. Cancer in Humans

In a previous IARC Monograph ( IARC, 2010 )

it was concluded that there is sufficient evidence in humans for the carcinogenicity of benzidine in the human bladder. Numerous case reports from different countries have been published ( IARC, 1972

, 1982

, 1987

, 2010 ). In one extreme instance, all five of a group of workers perma

nently employed in the manufacture of benzi

dine for 15 years or more developed bladder cancer ( IARC, 1982 ). Vigliani & Barsotti (1962) reported on 20 workers with tumours of the urinary bladder between 1931 and 1948 among 83 Italian dyestuff workers involved in benzidine production and use. Case et al

. (1954) found 10 bladder-cancer deaths among dyestuff workers exposed only to benzidine (standardized mortality ratio (SMR) 13.9 [95%CI: 6.7–25.5]). In benzidine-exposed workers in the chemical dye industry in China, the morbidity from bladder cancer increased with increasing duration of exposure (p for trend < 0.01) ( Sun & Deng, 1980 ),

while in a cohort of benzidine manufacturers in the USA, risks were significantly elevated for those with ≥2 years exposure to benzidine (SMR 13.0 [95%CI: 4.8–28.4]) ( Meigs et al

. , 1986 ). In a cohort of dyestuff workers in Torino, Italy, the SMR was 100.8 [95%CI: 60.8–167.2] during exposure and 14.8 [95%CI: 71–31.0] at 20 or more years after exposure ceased ( Piolatto et al

. , 1991 ). In a study of workers from a chemical manu

facturing plant in Shanghai, China, an interac

tion was found between benzidine exposure and cigarette smoking in the development of bladder cancer ( Wu, 1988 ). Relative to those who did not smoke and had no exposure to benzidine, the risks (RR) for bladder cancer were 6.2 ( P = 0.05) for smokers who were not exposed to benzidine; 63.4 ( P < 0.05) for non-smokers exposed to benzi

dine; and 152.3 ( P < 0.01) for smokers exposed to benzidine. In another study of Chinese workers in benzidine production and use facilities, the odds ratios (OR) for bladder cancer were 1.0, 2.7 (1.1– 6.3) and 4.4 (1.8–10.8) for low, medium and high cumulative exposure to benzidine, respectively, after adjustment for life-time cigarette smoking ( Carreón et al

. , 2006b ). In a case–control study in
Canada, excesses of renal cell cancer in relation to duration of exposure to benzidine ( P < 0.004) were noted, but other consistently supporting data were not found ( Hu et al

. , 2002 ).

Overall, case reports and epidemiological investigations from several countries show strong

and consistent associations between benzidine exposure and risk for bladder cancer.



## 3. Cancer in Experimental Animals

Studies on the carcinogenicity of benzidine in the mouse, rat, hamster, rabbit, dog, and frog by oral, subcutaneous injection, intraperitoneal injection, or inhalation routes of exposure have been reviewed by previous IARC Working Groups ( IARC, 1972

, 1982

, 1987

, 2010 ). There have been no additional carcinogenicity studies in animals reported since the most recent evaluation ( IARC,

2010 ). Results of adequately conducted carcino

genicity studies are summarized in Table 3.1

. Benzidine and its dihydrochloride were adequately tested for carcinogenicity by oral administration (feed, drinking-water or gavage) in eight experiments in mice and one experi

ment in rats; by subcutaneous injection in one experiment in rats and one experiment in frogs; and in rats in one experiment by intraperitoneal
injection. Following oral administration to male and
female mice, newborn and adult, of different strains, benzidine significantly increased the

55

### IARC MONOGRAPHS – 100F

56Table 3.1 Carcinogenicity studies of benzidine in experimental animalsSpecies, strain(sex)DurationReferenceRouteDosing regimen,Animals/group at startIncidence of tumoursSignificanceCommentsMouse, B6C3F1(M)90 wkVesselinovitchetal. (1975)FeedFour groups of 50 M mice were fed 150 ppmbenzidine as the dihydrochloride (certified ACSgrade) in the diet for 45 wk. Groups of 50 micewere sacrificed at 45, 60, 75, and 90 wk of age. Agroup of 100 male mice that were sacrificed at 90wk of age served as untreated controlsHepatocellular carcinomas: 1/98, 2/50, 5/50$,14/50*, 24/50*Hepatocellular adenomas: 1/98, 6/50$, 15/50*,17/50*, 11/50**[P< 0.0001],$[P< 0.05]Mouse, B6C3F1(M)90 wkVesselinovitchetal. (1975)FeedThree groups of 50 M mice were fed 150 ppmbenzidine as the dihydrochloride salt (certifiedACS grade) in the diet for 39, 54, or 84 wk. Allanimals were sacrificed at 90 wk of age. A groupof 100 M mice that were sacrificed at 90 wk ofage served as untreated controls.Hepatocellular tumours [benign andmalignant]:1/98, 35/50*, 25/50*, 44/50**[P< 0.0001]Mouse, B6C3F1(M, F)90 wkVesselinovitchetal. (1979)FeedGroups of 43–65 M and F offspring mice werefed and/or exposed to a diet containing 150 ppmbenzidine as the dihydrochloride (1) through fedmothers from the 12th d of gestation (prenatal)to delivery; (2) through fed mothers with littersfrom delivery to weaning; (3) to offspring fromweaning to 90 wk of age; (4) during the prenatal and pre-weaning period; or (5) prenatally,during pre-weaning and in adulthood.Groups 98 M and 100 F mice served as untreatedcontrols.Hepatocellular tumours [benign andmalignant]:Group 1–17/55* (M), 2/62 (F)Group 2–62/65*, 2/43Group 3–25/44*, 48/50*Group 4–49/49*, 12/48*Group 5–50/50*, 47/50*Controls–1/98, 0/100*[P< 0.0001]Age NRPurity NRMouse, B6C3F1(M, F)90 wkVesselinovitch(1983)FeedGroups of pregnant F or weanling M + F B6C3F1mice were fed diets containing 150 ppm ofbenzidine as the dihydrochloride:group 1–prenatal exposure (12th d of gestationto delivery)group 2–pre-weaning exposure (delivery toweaning)group 3–from weaning to 90 wkGroups of 98 M + 96 F mice were sacrificed at 90wk and served as controls.Hepatocellular adenomas and carcinomas:Group 1: 8/36* (M), 2/56 (F)Group 2: 35/52$, 9/43$Group 3: 22/26$, 16/25$Controls: 1/98, 0/96Hepatocellular carcinomas:Group 1: 3/36* (M), 1/56 (F)Group 2: 26/52$, 5/43*Group 3: 17/26$, 16/25$Controls: 0/98, 0/96*[P< 0.05],$[P< 0.0001)Liver was the onlytissue examined.Purity NR

### Benzidine

57Species, strain(sex)DurationReferenceRouteDosing regimen,Animals/group at startIncidence of tumoursSignificanceCommentsMouse , F1(C57BL/6JfC3Hf/Nctrfemales × BALB/cStCrLfC3Hf/Nctr males) andmono-hybrid (F1females and F1males)up to 80 wkNelsonet al.(1982)Drinking-waterGroups of M + F mice (F1) and MC micewere given drinking-water containing 0, 30,60, 120, 200, or 400 ppm of benzidine as thedihydrochloride. Groups of mice were sacrificedafter 40, 60, or 80 wk of treatment.Hepatocellular adenomas and carcinomas:F1M, 40 wk–0/49, 0/98, 0/72, 0/51, 3/50, 1/28F1F, 40 wk–0/48, 2/98, 1/72, 0/49, 5/50, 13/29F1M, 60 wk–1/48, 0/73, 4/49, 9/48, 9/47, 12/23F1F, 60 wk–1/48, 3/74, 4/52, 24/58, 54/61, 41/41F1M, 80 wk–0/46, 5/44, 6/47, 13/45, 8/21, 16/20F1F, 80 wk–0/47, 9/43, 23/43, 34/37, 9/9, 0/1MC M, 40 wk–0/50, 1/101, 0/71, 1/48, 0/52, 1/27MC F, 40 wk–0/48, 0/97, 0/72, 3/51, 6/50, 10/26MC M, 60 wk–0/48, 3/69, 3/46, 8/50, 8/43, 7/26MC F, 60 wk–1/48, 7/72, 12/54, 26/56, 47/60,33/38MC M, 80 wk–2/45, 2/41, 7/43, 14/44, 7/19, 11/17MC F, 80 wk–0/48, 12/43, 20/42, 31/32, 7/8, 5/6No statisticsprovided[significant formany groups]Age NRPurity NRInitial number ofanimals unclearMouse, F1(C57BL/6JfC3Hf/Nctrfemales × BALB/cStCrLfC3Hf/Nctr males) andmono-hybrid (F1females and F1males)33 mo (Lifetime)Littlefieldet al.(1983,1984)Drinking-waterGroups of 72–120 M + F mice (F1) and MC micewere given drinking-water containing 0, 30,40, 60, 80, 120, or 160 ppm (M) and 0, 20, 30,40, 60, 80, or 120 ppm (F) of benzidine as thedihydrochloride.Hepatocellular carcinomas:F1M: 14/125, 24/119, 30/96, 23/71, 35/71, 51/71,49/71F1F: 3/124, 51/120, 52/95, 45/72, 55/71, 60/69,64/72MC M: 17/123, 20/118, 20/95, 23/72, 24/71,37/71, 32/71MC F: 10/125, 54/119, 43/95, 31/71, 37/72, 51/69,56/72The authors also noted that a dose effect wasobserved for Harderian gland adenomas in F1and MC males (P= 0.02) and females (P= 0.02)and for angiomas of the uterus in F1and MCfemales (P= 0.07).Authors indicatethat for allfour strain/sexcombinations,there was asignificant doserelated trend forfatal liver tumours,incidental livertumours, and thepooled estimateusing Peto’s test,however details onstatistics were notprovided.Purity NRMouse, B6C3F1(M, F)90 wkVesselinovitchetal. (1975)GavageGroups of 75 M and 75 F mice were given 0.5or 1.0 mg benzidine as the dihydrochloride salttwice weekly. All animals were sacrificed at90 wk of age. Groups of 100 M and 100 F miceserved as untreated controls, killed at 90 wk.Hepatocellular tumours [benign andmalignant]:M–1/98, 3/75, 12/75*F–0/100, 4/75$, 17/75*No statisticsprovided*[P< 0.0005],$[P< 0.05]Purity NRVehicle NRTable 3.1 (continued)

### IARC MONOGRAPHS – 100F

58Species, strain(sex)DurationReferenceRouteDosing regimen,Animals/group at startIncidence of tumoursSignificanceCommentsMouse, ICR (F)63 wkMiyakawa &Yoshida (1980)FeedGroups of F mice were implanted with a 45-mgglass bead in the urinary bladder and dividedinto three groups: 30 were fed basal diet; 60 werefed diet containing 0.2% benzidine; and 60 werefed diet containing a mixture of 0.2% benzidineand 2%dl-tryptophan. Treated groups receiveddiets starting at six wk of age for 20 wk and werethen fed the control diet for 40–43 wk.Hepatomas [adenomas]: 0/30, 34/41*, 24/51No bladder tumours were found in any of theanimals.*P< 0.01,compared withcontrol andtryptophan treatedgroupsPurity NRMouse, StrainNR (M, F)LifetimeBonseret al.(1956)Subcutaneous InjectionGroups of 30 M and 30 F mice received 0.1 ml ofa freshly made 3% solution of benzidine (purityNR) in arachis oil by subcutaneous injection,twice/wk for 50 wk, and were then observed forlife. Groups of 30 M and 30 F mice served asvehicle controls.Hepatomas:M–0/30, 4/30;F–0/30, 3/30No statisticsprovidedAge NRRat, SpragueDawley (F)9 moGriswoldet al.(1968)GavageFour groups of 10–20 F rats were given benzidineat doses of 12, 25, 35 or 50 mg/rat in sesame oilby stomach tube, daily for 30 d, and sacrificedafter a 9-mo observation period. A group of 140F rats served as vehicle controls.Mammary carcinomas:3/132, 5/10*, 7/9*, -, 4/5*No statisticsprovided*[P< 0.0001]Small number ofanimals per group,high mortality intop 2 dose groups.Purity NRRat, Sherman(M, F)LifetimeSpitzet al.(1950)Subcutaneous injectionGroups of 45 to 155 M and F rats were injectedwith 15 mg/rat of “technical” benzidine, “pure”benzidine, or benzidine sulfate, dissolved in 1mL of olive oil once/wk throughout life. A groupof 50 rats served as vehicle controls.Hepatomas:Technical–8/78 (M), 0/155 (F); Pure–5/45 (M),1/107 (F); Sulfate–not tested (M), 1/153 (F)External auditory canal carcinomas (M+F):Technical −54/233*; Pure −32/152*; Sulfate−16/153*None of the above tumours were reported in the50 control animals.No statisticsprovided*[significant]Survival at 300 dwas 56% for controlsand 15% to 3% fortreated rats. Poorsurvival due to heat(no air conditioningin animal rooms).Sex of controlanimals NRTable 3.1 (continued)

### Benzidine

59Species, strain(sex)DurationReferenceRouteDosing regimen,Animals/group at startIncidence of tumoursSignificanceCommentsRat, CD (F)46 wkMortonet al.(1981)Intraperitoneal injectionThree groups of 30 F rats were given injections of0, 10, or 30 μmol/kg bw benzidine in trioctanoinsuspensions, twice/wk for 4 wk.Mammary gland tumours (all): 3/30, 7/30,12/29*Mammary gland adenocarcinomas: 1/30, 2/30,7/29**Zymbal gland tumours (benign and malignant):1/30, 1/30, 7/29**No tumours of the liver were found.*P< 0.01 **P< 0.05Purity NRFrog,Ranatemporaria38 wkKhudoley (1977)Subcutaneous injectionA group of 37 frogs (1–1.5 yr old) received asubcutaneous injection, once/wk, of 0.2–0.5 mLof a 0.5% solution of benzidine in mineral oil, forup to 38 wk (total dose, 45–114 mg/animal). Agroup of 67 frogs given subcutaneous injectionsof 0.2–0.5 mL mineral oil once weekly for 42 wkserved as vehicle controls.Liver tumours: 0/67, 3/14*Tumours of the haematopoietic system: 0/67,4/14**[P< 0.01]Fourteen animalsin the treated groupwere still alive whenthe first tumourappeared at 16 wk.The high mortalitywas the result ofexceeding themaximum tolerateddose. Sex NR. PurityNR. Histopathologynot further specifiedbw, body weight; d, day or days; F, female; M, male; MC, monohybrid cross; mo, month or months; NR, not reported; d, day; wk, week or weeksTable 3.1 (continued)

### IARC MONOGRAPHS – 100F

incidence of hepatocellular tumours (benign and/or malignant) in both sexes ( Vesselinovitch

et al

. , 1975

, 1979 ; Miyakawa & Yoshida, 1980 ; Vesselinovitch, 1983 ; Nelson et al

. , 1982 ; Littlefield

et al

. , 1983

, 1984 ). Oral administration of benzi

dine caused a markedly increased incidence of mammary carcinomas in female rats ( Griswold

et al

. , 1968 ). Subcutaneous administration of

benzidine or its sulfate to male and female rats produced a high incidence of external audi

tory canal carcinomas ( Spitz et al

. , 1950 ), while

subcutaneous administration of benzidine to frogs caused an increase in tumours of the liver and haematopoietic system ( Khudoley, 1977 ). The intraperitoneal administration of benzidine

to female rats resulted in an increase in the inci

dence of mammary gland adenocarcinomas and combined benign and malignant Zymbal gland tumours ( Morton et al

. , 1981 ). Other studies were found to be inadequate for evaluation.



## 4. Other Relevant Data

A general section on “Aromatic amines: metabolism, genotoxicity, and cancer suscepti

bility” appears as Section 4.1 in the Monograph on 4-aminobiphenyl in this Volume.
Benzidine, N -acetylbenzidine, and

N,N ′ -diacetylbenzidine have been detected in the urine of workers exposed to benzidine. The predominant DNA adduct identified in exfo

liated bladder cells was N ′ -(deoxyguanosin8-yl)- N -acetylbenzidine ( Rothman et al

. , 1996a ). Thus, N -monoacetylation of benzidine

does not interfere with the formation of a DNA-reactive intermediate, and may occur before the cytochrome P450-catalysed forma

tion of N ′ -hydroxy- N -acetylbenzidine. In

contrast, N

, N ′ -diacetylation may be a detoxi

fication pathway. N -Acetylbenzidine may be

N

-glucuronidated or N -hydroxylated in the liver.
In the bladder, the N ′ -hydroxyl- N -acetylbenzidine or N ′ -acetoxy- N -acetylbenzidine formed by

NAT-mediated O -acetylation may react with

DNA to form covalent adducts. NAT1 is more effi

cient than NAT2 in catalysing the N -acetylation

of benzidine or of N -acetylbenzidine ( Zenser et al

. , 1996 ). At low exposure levels,

N

-acetylation of benzidine is favoured over

that of N -acetylbenzidine. Human neutrophils

can also form N ′ -(deoxyguanosin-8-yl)- N

acetylbenzidine from N -acetylbenzidine by a reaction catalysed by myeloperoxidase ( Lakshmi

et al

. , 2000 ). N ′ -hydroxy- N -acetylbenzidine may also be formed through peroxidative acti

vation by prostaglandin H synthase ( Zenser

et al

. , 1999a

, b ). Levels of benzidine-related DNA adducts in exfoliated urothelial cells among exposed workers were not affected by acetylator phenotype ( Rothman et al

. , 1996a ), or GSTM1 genotype ( Rothman et al

. , 1996b ). For several benzidine-based azo dyes, both metabolism and molecular changes identical to

those of benzidine have been observed. Metabolic
conversion of Direct Black 38, Direct Blue 6, and

Direct Brown 95 to benzidine has been observed in the Rhesus monkey ( Rinde & Troll, 1975 ). Azoreductase activity in intestinal bacteria and in the liver catalyses the formation of benzidine from benzidine-based dyes ( Cerniglia et al

. , 1982 ;
Bos et al

. , 1986 ). Benzidine is a multiorgan carcinogen in experimental animals; it induces bladder tumours in dogs, liver tumours in mice and hamsters, and mammary gland tumours in rats. In the presence of a liver-derived metabolic activation system – which in some cases leads to reduc

tive metabolism followed by oxidative metabo

lism – benzidine and benzidine-based dyes (e.g.
Direct Black 38, CI Acid Red 114, CI Direct Blue 15, and CI Pigment Red) were mutagenic

in several strains of S. typhimurium. Benzidine,

N

-acetylbenzidine, and N,N ′ -diacetylbenzidine

have been measured in the urine of workers exposed to Direct Black 38, and benzidine- or 4-ABP-related haemoglobin adducts have been

60

### Benzidine

measured in blood ( Dewan et al

. , 1988 ; Beyerbach

et al

. , 2006 ). Significant increases in the inci

dence of chromosomal aberrations in peripheral lymphocytes have been observed in workers exposed to benzidine or benzidine-based dyes ( Mirkova & Lalchev, 1990 ). In workers exposed to benzidine, the accumulation of mutant p53 protein increased with increasing exposures ( Xiang et al

. , 2007 ). Similarly, benzidine induced

DNA lesions in TP53 in the bladder, liver, and lung of exposed rats ( Wu & Heng, 2006 ), increased the frequency of micronucleated bone-marrow cells and induced unscheduled DNA synthesis in
mice, and increased DNA strand-breaks in the liver of exposed rats. Based on bio-monitoring studies in workers, animal carcinogenicity data and genotoxicity
data, it is reasonable to use the same carcino

genic hazard classification for benzidine-based dyes that are metabolized to benzidine as for

benzidine.



## 5. Evaluation

There is sufficient evidence in humans for the carcinogenicity of benzidine. Benzidine causes cancer of the urinary bladder.

There is sufficient evidence in experimental animals for the carcinogenicity of benzidine. There is strong mechanistic evidence indi

cating that the carcinogenicity of benzidine in humans operates by a genotoxic mechanism of
action that involves metabolic activation, forma

tion of DNA adducts, and induction of mutagenic and clastogenic effects. Metabolic activation to DNA-reactive intermediates occurs by multiple pathways including N -oxidation in the liver,

O -acetylation in the bladder, and peroxidative activation in the mammary gland and other

organs. Benzidine is carcinogenic to humans (Group 1)

. 

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