U.S. Environmental Protection Agency 8/18/2010

Dyes Derived from Benzidine and Its Congeners

I. Overview

 This Action Plan addresses the use of benzidine-based dyes and benzidine congenerbased dyes, both metalized and non-metalized, in products that would result in consumer 

exposure, such as for use to color textiles. There is a well-established concern for the potential 

carcinogenic effects presented by exposure to benzidine-based and benzidine congener-based 

dyes, and this Action Plan focuses on human carcinogenicity issues. EPA intends to address risk 

concerns from potential exposures by initiating rulemaking to add four benzidine-based dyes to 

an existing TSCA section 5(a)(2) significant new use rule (SNUR) for benzidine-based 

substances at 40 CFR 721.1660; and by initiating rulemaking to establish a new TSCA section 

5(a)(2) SNUR for benzidine congener-based dyes, including 44 specific such dyes. 

 

 Because there may be concern for exposure to these dyes on imported finished textiles, 

EPA may also consider proposing to eliminate the article exemption applied to SNURs. If EPA 

learns that such activities are ongoing, EPA intends to consider initiating action under TSCA 

section 6. Furthermore, should EPA determine that there are other ongoing uses for these dyes, 

EPA intends to consider additional regulatory action to obtain information necessary to 

determine whether the uses present concerns which need to be addressed. 

 As part of the Agency's efforts to address benzidine-based and benzidine congener-based 

dyes, EPA also intends to evaluate the potential for disproportionate impact on children and 

other sub-populations. 

 

II. Introduction 

 As part of EPA's efforts to enhance the existing chemicals program under the Toxic 

Substances Control Act (TSCA)1, the Agency identified an initial list of widely recognized 

chemicals, including benzidine-based and benzidine congener-based dyes, for action plan 

development based on their presence in human blood; persistent, bioaccumulative, and toxic 

(PBT)2

 characteristics; use in consumer products; production volume; and other similar factors. 

This Action Plan is based on EPA’s initial review of readily available use, exposure, and hazard 

information3

 on the dyes. EPA considered which of the various authorities provided under TSCA 

and other statutes might be appropriate to address potential concerns with the dyes in developing 

the Action Plan. The Action Plan is intended to describe the courses of action the Agency plans 

to pursue in the near term to address its concerns. The Action Plan does not constitute a final 

Agency determination or other final Agency action. Regulatory proceedings indicated by the 

 

1 15 U.S.C. §2601 et seq. 2

 Information on PBT chemicals can be found on the EPA website at http://www.epa.gov/pbt/. 3

 Information sources customarily employed include Inventory Update Reporting (IUR) submissions; Toxic Release 

Inventory (TRI) reporting; data submitted to the HPV Challenge Program; existing hazard and risk assessments 

performed by domestic and international authorities including but not limited to U.S. Federal government agencies, 

the Organization for Economic Cooperation and Development, the Stockholm Convention on Persistent Organic 

Pollutants, Health and Environment Canada, the European Union; and others. Action plans will reference specific 

sources used. 
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Action Plan will include appropriate opportunities for public and stakeholder input, including 

through notice and comment rulemaking processes.

III. Scope of Review

 Benzidine and its congeners constitute a family of similar synthetic aromatic amines 

which are important precursors in the synthesis of dyes. Some of these dyes have the potential to 

metabolize to aromatic amines that are considered to be carcinogenic (NTP, 2005). Benzidine 

and dyes metabolized to benzidine are considered "known human carcinogens". Benzidine's 

congeners, 3,3'-dichlorobenzidine, 3,3'-dimethylbenzidine, and 3,3'-dimethoxybenzidine and 

dyes metabolized to the latter two congeners have all been classified as "reasonably anticipated 

to be human carcinogens" (NTP, 2005). 

 The 2006 Inventory Update Report (IUR) indicated that a number of benzidine-based or 

congener-based dyes and pigments were produced in high volumes. This observation resulted in 

a decision to review the current status of the category of dyes and pigments derived from 

benzidine and its congeners in products that could result in potential consumer exposure. In 

reviewing the benzidine congener-based pigments, EPA believes that the presence of pigments in 

such consumer products as printing inks, paints, plastics, and textiles was unlikely to present an 

exposure concern, because the pigments are not bioavailable and are not absorbed into the body 

(Environment Canada, 2009, Golka, et al, 2004, OECD, 2003, ). Additionally EPA believes that 

some of the congener-based dyes reported to the 2006 IUR were not likely to degrade to 

carcinogenic amines (Jung, R., et al, 1992). 

 EPA therefore decided to focus on dyes derived from benzidine and its congeners that are 

listed on the non-confidential business information (CBI) TSCA Inventory and have the potential 

to degrade to carcinogenic amines. A search of the non-CBI TSCA Inventory found 48 

substances not already subject to TSCA SNUR authority. These are divided among two lists (see 

Appendix 1.): 

 List 1. Benzidine Based Dyes -- 4 substances 

 List 2. Benzidine Congener-Based Dyes -- 44 substances 

 As these dyes all have the potential to degrade to benzidine or a benzidine congener, EPA 

chose to consider whether there are concerns about consumer exposure to the dyes in products 

that need to be addressed. 

IV. Uses and Substitutes Summary

 Benzidine-based and congener-based dyes (also called azo dyes) are used in the 

production of textiles, paints, printing inks, paper, and pharmaceuticals. They are also used as 

reagents and biological stains in laboratories, are used in the food industries, and have more 

recent uses in laser, liquid crystal displays, ink-jet printers, and electro-optical devices (Dapson, 

2009, Kamboh, et al, 2009, Oomen, et al, 2004). 

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Dye production in the U.S. has been steadily declining for the past decade, largely due to 

the increase in imported finished textiles. Most of the imported volume comes from China and 

India and other less developed countries which may have less stringent regulations on dye 

intermediates (Dapson, 2009). No List 1 dyes were reported and only two List 2 dyes were 

reported on the 2006 IUR and since their volume was below 500,000 pounds per year, no 

exposure and use data was reported. Only 12 of the List 2 and none of the List 1 dyes were 

believed to be available in the U.S., and two others are available internationally but could end up 

in U.S. products. Given that dyes are quite often available from importers, reformulators and 

others who distribute in small volumes, it is assumed that there are a number that were not 

readily identified, because they are produced in volumes below the 2006 IUR reporting threshold 

(25,000 pounds per year). Because the European Union has had a ban on the use of certain azo 

dyes, such as those on Lists 1 and 2, in textiles and leather that are in prolonged contact with 

human skin, there are readily available substitutes for the use of benzidine and congener dyes in 

textiles and leather. 

 

V. Hazard Identification Summary

 The 1980 EPA Preliminary Risk Assessment on derivatives of benzidine and its 

congeners established that the primary hazard concern was for the carcinogenic effects to 

humans from exposure to specific metabolites of the dyes (EPA, 1980). Therefore, the hazard 

review for this Action Plan focuses on human carcinogenicity issues. Azo dyes are biologically 

active through their metabolites. Azoreduction of these compounds occurs in humans by an 

enzyme-mediated reaction. Azoreductases are found in the liver, in gut bacteria, and in skin 

bacteria. The result of this azoreduction is the release of the carcinogenic aromatic amine from 

the dye. Studies have demonstrated that the azoreduction of benzidine-based dyes occurs in the 

human body as well as on the skin (Golka, et al, 2004). Therefore, the primary human health 

concern for consumers is exposure to the benzidine-based and benzidine-congener-based dyes 

through oral, dermal or inhalation routes. Evidence from animal studies suggests that there is 

early life susceptibility to benzidine carcinogenesis. Cancer potency for benzidine was 

substantially increased when the dose was given in early life as compared to adults (EPA, 2005). 

 It appears that metal chelation does not completely eliminate the carcinogenic effects of 

metalized dyes derived from bendizine congeners; therefore, the metalized congener dyes have 

been included in List 2 (Morgan, et al, 1994). The four dyes on List 1 have the potential to 

degrade to benzidine. List 2 includes 17 dimethylbenzidine-based dyes, 26 dimethoxybenzidinebased dyes and 1 dichlorobenzidine-based dye, all of which would be expected to degrade to 

their carcinogenic precursors and would therefore present a potential exposure concern in 

consumer products 

VI. Fate Characterization Summary

 Azo dyes have been expected to resist biodegradation, because they are synthetic. 

However, the problems of discharge of dye contents to wastewaters from textile and other 

industries have resulted in extensive research for biological methods to degrade dyes and other 

organic pollutants. Under certain environmental conditions, various fungi, bacteria, yeasts and 

algae have been found to be capable of decolorizing and sometimes completely mineralizing 

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many azo dyes. Different trophic groups of microorganisms are capable of degrading azo dyes 

under anaerobic, anoxic and aerobic conditions (Pandey, et al, 2007). 

VII. Exposure Characterization Summary

 The main routes of consumer exposure to azo dyes are (Zeilmaker, et al, 1999, 

Zeilmaker, et al, 2000): 

 Dermal absorption is the primary route from wearing azo-dyed clothing or footwear 

and using azo-dyed materials such as paper and inks. 

 Oral ingestion is an additional route for babies and young children who suck on 

clothing, blankets, and other non-food products which might contain azo dyes. 

 Inhalation exposure is a more important route in occupational settings; however, it 

can also occur from the use of azo-dyed inks during "air brushing" or from offgassing from azo-dyed carpets to indoor air. 

 Contact with azo dyes entering the environment through the whole life cycle of azo 

dyes in textiles is an additional potential source of exposure. 

 Actual dermal exposure does occur from the leaching of azo dyes by sweat in contact 

with the dyed textiles. Studies have shown that various types of human skin bacteria possess the 

azo reductases necessary to breakdown azo dyes to release the carcinogenic amines, which can 

be absorbed. Additionally, once on the skin, the dye itself may be absorbed. It is well established 

that azoreduction also occurs internally in the gut and the liver (Zeilmaker, et al, 1999, 

Zeilmaker, et al, 2000). 

 Three European studies experimentally examined the leaching of amines and azo dyes 

from consumer textile products, including leather. Two of the studies used a variety of 

assumptions to estimate life-long daily uptake values for dermal exposure to various pieces of 

azo-dyed clothing and footwear shown to contain benzidine or a congener. When comparing 

their values to EPA's acceptable 10-6 level for benzidine (and extrapolated to the other 

congeners), they determined that exposure to the azo-dyed clothing and footwear would result in 

a cancer risk above the "negligible risk level" (NRL). (Zeilmaker, et al, 1999, Zeilmaker, et al, 

2000). In addition to the fact that the studies reported data from dyed products purchased in 

Europe, many assumptions were used, often worst cases assumptions which may overestimate 

exposure. Also, it was noted that the main factors determining dye releases from textiles to the 

skin include the type of dyed textile, contact with other substrates, amount of dye applied to the 

textile, and number of previous washings. 

 Nevertheless, during a similar time period as the studies discussed above, a risk 

committee for the European Commission reviewed a report on consumer exposure to diazo 

textile dyes (unavailable) and agreed with the report's conclusion that while consumer exposure 

is likely to be very low, the associated cancer risks give enough cause for concern that the use of 

azo dyes which can degrade to 22 carcinogenic aromatic amines be restricted to the lowest 

possible levels or banned (European Commission, 1999). 

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VIII. Risk Management Considerations

Current Regulatory Status in North America and Europe 

 Occupational exposure to some dyes derived from benzidine and its congeners has been 

regulated for many years; however, the potential for consumer exposure to products containing 

these products is still a potential concern. The EU has banned in textile and leather articles which 

may come into direct and prolonged contact with humans the use of azo dyes which can break 

down to release any of 22 listed carcinogenic aromatic amines (includes benzidine and its 

congeners) in amounts above 30 ppm in finished articles or the dyed parts (See Restriction 43 in 

REACH Annex XVII, European Commission, 2009). Canada has also expressed concern about 

the potential release of benzidine or its congeners from azo dyes and is evaluating potential 

approaches for addressing azo dyes (Environment Canada, 2009). 

 In 1995, when EPA proposed a significant new use rule (SNUR) on benzidine-based 

substances, EPA indicated that this was the first step in a risk management strategy to reduce the 

risks associated with the manufacture and use of benzidine-based and benzidine congener-based 

dyes and pigments (60 FR 45119, 8/30/95). The SNUR at 40 CFR §721.1660 is for any use of 22 

benzidine-based substances. These substances were not included in this Action Plan. Exempt 

from the SNUR were minor ongoing specified uses as analytical reagents and biological stains. 

 When EPA finalized that first SNUR, EPA recognized that additional benzidine-based 

substances would need to be added. The four benzidine-based dyes on List 1 had been included 

in draft additions to §721.1660 which were never finalized (61 FR 52287, 10/7/96). With the 

exception of the seven metalized congener dyes and the one DCB-based dye, the other 37 dyes 

on List 2 had been included in a draft of a proposed SNUR for non-metalized dyes based on 

dimethylbenzidine and dimethoxybenzidine that was never finalized. 

Benzidine-based and congener-based dyes -- Potential concerns for humans 

Risk from consumer use of products containing dyes. Because of the azoreductases 

present in the human body and in bacteria on the skin, consumer products using the dyes could 

present a concern. The main products presenting a concern would be textiles and leather products 

that are in prolonged contact with human skin. The other products are either not available to 

consumers (laboratory chemicals) or would not likely be readily accessible in significant 

quantities (printing ink or LCD displays) to present an exposure concern. 

Risk to the general population from dyes released to the environment. Biodegradation 

studies indicate that the dyes would be expected to biodegrade at negligible to slow rates under 

aerobic conditions in the environment. However, in anaerobic soils the dyes are likely to undergo 

azo reduction to benzidine and/or congeners depending on structure. It is unclear whether 

metabolites from these reductions would be available in large concentrations or locations to be of 

concern to the general population. 

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Assumptions and Uncertainties 

Based on market information and the fact that the 2006 IUR had no reports for the 

benzidine-based dyes, it appears that if the dyes are used at all, they would be used in small 

volumes, making it difficult to access production and use information. Additionally, it appears 

that new uses of azo dyes in high tech applications have been developed since EPA last 

examined the market. Although it is unclear whether the dyes on Lists 1 and 2 are used in these 

applications, it is assumed that these new uses would be less likely to result in significant 

consumer exposure to the dyes. 

 As many of the Direct Blue dyes on List 2 have been identified as having potential uses 

as biological stains and as having anti-viral activity, it is unknown how much of the production 

volume would be attributed to those uses, which would generally not be a concern for consumers 

or not subject to TSCA (e.g., pharmaceuticals). The only consumer exposure data available for 

analysis comes from a few European studies which may or may not be applicable in the U.S. 

Those studies also used many assumptions to prepare their estimates and identified important 

variables which affect the amount of dye released from textiles to the skin. However, given the 

evidence for early life susceptibility to benzidine, EPA believes that it is important to consider 

actions to address children's potential exposure to dyes which can metabolize to benzidine and 

benzidine-based congeners. 

 Given that dye production has been shifting to Asia and importation of finished textiles 

has increased, it is possible that the risk of exposure to azo dyes in the U.S. would be more from 

dyes on imported finished textiles than from dyes manufactured or imported and used to finish 

textiles in the U.S. 

IX. Next Steps

List 1 Benzidine-Based Dyes 

EPA intends to initiate rulemaking to add the four List 1 dyes to the existing TSCA section 

5(a)(2) significant new use rule for benzidine-based substances at 40 CFR 721.1660. 

 In order to use the SNUR authority, EPA must be aware that the uses it chooses to regulate 

are not ongoing or exempt ongoing uses. 

 The existing SNUR at 40 CFR 721.1660 already covers listed benzidine-based substances. 

EPA could choose to add the four List 1 benzidine-based dyes to that SNUR. 

 Request comment on whether there are for ongoing uses as analytical reagents and lab stains 

and indicate that the exemption at 721.1660 would likely continue to apply. 

 There is some uncertainty about the extent of current uses; however, the market profile did 

not find information indicating that any of the four List 1 substances are available in the U.S. 

Therefore, it is clear that any uses would be very small quantities. 

 If public comments on the proposed SNUR indicate that there are existing uses beyond minor 

laboratory uses, EPA may need to consider additional action such as TSCA section 6 

rulemaking, depending on the potential exposure scenarios presented by any existing uses. 

In making such a consideration, EPA would evaluate whether those existing uses indicated 

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the potential to present an unreasonable risk, in coordination with CPSC and/or other 

agencies where appropriate. 

List 2 Benzidine Congener-Based Dyes 

EPA intends to prepare a new proposed TSCA section 5(a)(2) significant new use rule for 

benzidine congener-based dyes and include the List 2 dyes. 

 In order to use the SNUR authority, EPA must be aware that the uses it chooses to regulate 

are not ongoing or exempt ongoing uses. 

o Some of the Direct Blues appear to have application as biological stains and 

pharmaceuticals. The stain uses could be exempted and the pharmaceutical uses are 

not subject to TSCA. 

o There is much uncertainty about the uses of and potential exposures to the dyes in 

both textiles and the newer high tech fields. 

 EPA could draft a proposed benzidine congener-based SNUR for the List 2 dyes, indicating 

an intention to exempt minor laboratory uses that are reported during the comment period. 

 If ongoing uses in high technology applications, such as LCD displays, are reported, EPA 

could further evaluate potential exposure concerns before addressing those uses. 

 EPA will search the CBI TSCA Inventory to identify benzidine-based and benzidine 

congener-based dyes that could be added to List 1 or List 2 and included in the above SNURs. 

 Because there is concern for exposure to azo dyes on imported finished textiles, EPA 

could propose eliminating the article exemption applied to the above SNURs. 

 If EPA determines that List 1 and/or 2 dyes are currently coming into the U.S. on 

imported finished textiles, EPA intends to consider initiating regulatory action under TSCA 

section 6. In making such a consideration, EPA would evaluate whether those existing uses 

indicated the potential to present an unreasonable risk, in coordination with CPSC and/or other 

Agencies where appropriate. 

 When EPA proposes the SNURS, EPA will request comment on using TSCA section 6 as 

an alternative approach to the SNUR process. 

X. References

Dapson, R.W. 2009. Benzidine-based dyes: effects of industrial practices, regulations, and world trade on the 

biological stains market. Biotechnic & Histochemistry 84(3): 95-100. 

Environment Canada. 2009. Strategic options for the management of toxic substances benzidine and 3,3-

dichlorobenzidine. Accessed 10/9/09 at: http://www.ec.gc.ca/toxics/docs/sor/bdine/EN/sum.cfm

EPA. 1980. Preliminary Risk Assessment: Phase I. Benzidine, its congeners, and their derivative dyes and pigments. 

EPA-560/11-80-019, June 1980. 

EPA. 2005. Supplemental Guidance for Assessing Susceptibility from Early Life Exposure to Carcinogens. EPA 

630/R-03/003F, March 2005. 

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European Commission. 1999. Opinion of risk of cancer caused by textiles and leather goods coloured with azo-dyes 

expressed at the 7th CSTEE plenary meeting, Brussels, 18 January 1999. Accessed 9/18/09 at 

http://ec.europa.eu/health/ph_risk/committees/sct/docshtml/sct_out27_en.htm

European Commission. 2009. Commission Regulation EC No. 552/2009 

Commission Regulation (EC) No 552/2009 of 22 June 2009 amending Regulation (EC) No 1907/2006 of the 

European Parliament and of the Council on REACH as regards Annex XVII. 

Golka, K., Kopps, S., Myslak, Z.W. 2004. Carcinogencitiy of azo colorants: influence of solubility and 

bioavailability. Tox Lett 151:203-210. 

Jung, R., D. Steinle, R. Anliker. 1992. A compilation of genotoxicity and carcinogenicity data on aromatic 

aminosulphonic acids. Fd.Chem.Toxic. 30(7):635-660. 

Kamboh, M.A., Solangi, I.B., Sherazi, S.T.H., Memon, S. 2009. Synthesis and application of caliz[4]arene based 

resin for the removal of azo dyes. 

Morgan, D.L., J.K. Dunnick, T. Goehl, M.P. Jokinen, H.B. Matthews, E. Zeiger, J.H. Mennear. 1994. Summary of 

the National Toxicology Program Benzidine Dye Initiative. Environ.HealthPerspect. 102(Suppl 2):63-78. 

NTP. 2005. Report on Carcinogens, 11th edition. 

OECD. 2003. SIDS Initial Assessment Profile for Diarylide Yellow Pigment Category, SIAM 16, 27-30 May 2003. 

Oomen, A.G., Versantvoort, C.H.M., Duits, M.R., van de Kamp, E., van Twillert, K. 2004. Application of in vitro 

digestion models to assess release of lead and phthalate from toy matrices and azo dyes from textile. RIVM Report 

320102003/2004. Netherlands. 

Pandey, A., Singh, P., Iyengar, L. 2007. Bacterial decolorization and degradation of azo dyes. Int. Biodeterioration 

& Biodegradation 59:73-84. 

Zeilmaker, M.J., Rosese, E.D., van Haperen, P., van Veen, M.P., Bremmer, H.J., van Kranen, H.J., Wouters, 

M.F.A., Janus, J.A. 1999. Cancer risk assessment of azo dyes and aromatic amines from garment and footwear. 

RIVM Report 601503014. Netherlands. 

Zeilmaker, M.J., van Kranen, H.J., van Veen, M.P., Janus, J.A. 2000. Cancer risk assessment of azo dyes and 

aromatic amines from tattoo bands, folders of paper, toys, bed clothes,

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Appendix 1.

Benzidine-Based and Congener-Based Dyes

With Potential to Degrade to Carcinogenic Amines 

List 1: Benzidine-Based Dyes on the Non-CBI TSCA Inventory 

CAS NO CHEMICAL NAME1 

117-33-9 1,3-Naphthalenedisulfonic acid, 7-hydroxy-8-[[4'-[(4-hydroxyphenyl)azo][1,1'-biphenyl]-

4-yl]azo]- 

65150-87-0 1,3,6-Naphthalenetrisulfonic acid, 8-hydroxy-7-[[4'-[(2-hydroxy-1-naphthalenyl)azo][1,1'-

biphenyl]-4-yl]azo]-, trilithium salt 

68214-82-4 2,7-Naphthalenedisulfonic acid, 5-amino-3-[[4'-[(7-amino-1-hydroxy-3-sulfo-2-

naphthalenyl) azo][1,1'-biphenyl]-4-yl]azo]-4-hydroxy-, disodium salt [CI Direct Navy 

BH] 

72379-45-4 2,7-Naphthalenedisulfonic acid, 4-amino-5-hydroxy-3-[[4'-[[2-hydroxy-4-[(2-

methylphenyl) amino]phenyl]azo] [1,1'-biphenyl]-4-yl]azo]-6-(phenylazo)- 

List 2: Benzidine Congener-Based Dyes on the Non-CBI TSCA Inventory

CAS NO CHEMICAL NAME1 

72-57-1 2,7-Naphthalenedisulfonic acid, 3,3'-[(3,3'-dimethyl[1,1'-biphenyl]-4,4'-diyl)bis(azo)]bis[5-

amino-4-hydroxy-, tetrasodium salt 

[CI Direct Blue 14, tetrasodium salt; Trypan Blue]

117-32-8 1,3-Naphthalenedisulfonic acid, 7-hydroxy-8-[[4'-[(4-hydroxyphenyl)azo]-3,3'-

dimethyl[1,1'-biphenyl]-4-yl]azo]- 

314-13-6 1,3-Naphthalenedisulfonic acid, 6,6'-[(3,3'-dimethyl[1,1'-biphenyl]-4,4'-diyl)bis(azo)]bis[4-

amino-5-hydroxy-, tetrasodium salt 

[CI Direct Blue 53, tetrasodium salt; Evans Blue] 

992-59-6 1-Naphthalenesulfonic acid, 3,3'-[(3,3'-dimethyl [1,1'-biphenyl]-4,4'-diyl)bis(azo)] bis[4-

amino-, disodium salt 

[CI Direct Red 2, disodium salt; Benzopurpurin 4B] 

2150-54-1 2,7-Naphthalenedisulfonic acid, 3,3'-[(3,3'-dimethyl [1,1'-biphenyl] -4,4'-diyl)bis(azo)] 

bis[4,5-dihydroxy-, tetrasodium salt 

[CI Direct Blue 25, tetrasodium salt;p Benzo Sky Blue] 

2429-71-2 1-Naphthalenesulfonic acid, 3,3'-[(3,3'-dimethoxy [1,1'-biphenyl]-4,4'-diyl)bis(azo)]bis [4-

hydroxy-, disodium salt 

[CI Direct Blue 8, disodium salt; Benzoazurine G] 

2429-74-5 2,7-Naphthalenedisulfonic acid, 3,3'-[(3,3'-dimethoxy[1,1'-biphenyl]-4,4'-

diyl)bis(azo)]bis[5-amino-4-hydroxy-, tetrasodium salt 

[CI Direct Blue 15, tetrasodium salt; Direct Sky Blue] 

2586-57-4 1,3-Naphthalenedisulfonic acid, 4-amino-5-hydroxy-6-[[4'-[(2-hydroxy-1-naphthalenyl) 

azo]-3,3'-dimethoxy [1,1'-biphenyl]-4-yl]azo]-, disodium salt 

[CI Direct Blue 22, disodium salt; Chicago (Niagra) Blue RW] 

2610-05-1 1,3-Naphthalenedisulfonic acid, 6,6'-[(3,3'-dimethoxy[1,1'-biphenyl]-4,4'-

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List 2: Benzidine Congener-Based Dyes on the Non-CBI TSCA Inventory

CHEMICAL NAME1 CAS NO 

diyl)bis(azo)]bis[4-amino-5-hydroxy-, tetrasodium salt 

[CI Direct Blue 1, tetrasodium salt; Chicago/Sky Blue 6B] 

3841-14-3 1,3-Naphthalenedisulfonic acid, 6,6'-[(3,3'-dimethoxy[1,1'-biphenyl]-4,4'-

diyl)bis(azo)]bis[4-amino-5-hydroxy- 

[CI Direct Blue 1, free acid; Chicago Sky Blue 6B] 

4198-19-0 2,7-Naphthalenedisulfonic acid, 3,3'-[(3,3'-dimethoxy [1,1'-biphenyl]-4,4'-diyl)bis(azo)] 

bis[4,5-dihydroxy-, tetrasodium salt 

[CI Direct Blue 10; Dianil Blue G] 

6358-29-8 1,3-Naphthalenedisulfonic acid, 8-[[4'-[(4-ethoxyphenyl) azo]-3,3'-dimethyl[1,1'-

biphenyl]-4-yl]azo]-7-hydroxy-, disodium salt 

[CI Direct Red 39, disodium salt] 

6405-94-3 Benzenesulfonic acid, 3,3'-[(3,3'-dimethyl [1,1'-biphenyl]-4,4'-diyl)bis(azo)] bis[2,4-

diamino-5-methyl-, disodium salt 

[CI Direct Orange 10] 

6449-35-0 1-Naphthalenesulfonic acid, 3-[[4'-[(6-amino-1-hydroxy-3-sulfo-2-naphthalenyl) azo]-3,3'-

dimethoxy[1,1'-biphenyl]-4-yl]azo]-4-hydroxy-, disodium salt 

[CI Direct Blue 151, disodium salt] 

6459-94-5 1,3-Naphthalenedisulfonic acid, 8-[[3,3'-dimethyl-4'-[[4-[[(4-methylphenyl)sulfonyl] 

oxy]phenyl]azo] [1,1'-biphenyl]-4-yl]azo]-7-hydroxy-, disodium salt 

[CI Acid Red 114, disodium salt; Milling Red B] 

6548-29-4 2,7-Naphthalenedisulfonic acid, 4,4'-[(3,3'-dichloro[1,1'-biphenyl]-4,4'-diyl)bis(azo)] 

bis[3-amino-, tetrasodium salt 

[CI Direct Red 46, tetrasodium salt] 

6739-62-4 Benzoic acid, 2-[[2-amino-6-[[4'-[(3-carboxy-4-hydroxyphenyl)azo]-3,3'-dimethoxy[1,1'-

biphenyl]-4-yl]azo]-5-hydroxy-7-sulfo-1-naphthalenyl]azo]-5-nitro-, trisodium salt 

[CI Direct Black 91] 

12222-00-3 Cuprate(4-), [.mu.-[[4,4'-[[3,3'-di(hydroxy-.kappa.O) [1,1'-biphenyl]-4,4'-diyl]bis(azo-

.kappa.N1)]bis[3-(hydroxy-.kappa.O)-2,7-naphthalenedisulfonato]](8-)]]di-, tetrasodium 

[CI Direct Blue 80] 

17011-51-7 Ethanesulfonic acid, 2,2'-[(3,3'-dimethoxy-4,4'-biphenylylene)bis[azo(methylimino)]]di-, 

disodium salt 

28407-37-6 

(former = 

10401-50-0) 

Cuprate(4-), [.mu.-[[3,3'-[[3,3'-di(hydroxy-.kappa.O) [1,1'-biphenyl]-4,4'-diyl]bis(azo-

.kappa.N1)]bis[5-amino-4-(hydroxy-.kappa.O)-2,7-naphthalenedisulfonato]](8-)]] di-, 

tetrasodium 

[CI Direct Blue 218] 

64743-15-3 Benzoic acid, 5-[[4'-[[2,6-diamino-3-methyl-5-[(4-sulfophenyl)azo]phenyl]azo]-3,3'-

dimethyl [1,1'-biphenyl]-4-yl]azo]-2-hydroxy-, disodium salt 

[CI Direct Brown 222] 

65151-33-9 2,7-Naphthalenedisulfonic acid, 4,4'-[(3,3'-dimethoxy[1,1'-biphenyl]-4,4'-

diyl)bis(azo)]bis[3-hydroxy-, tetrasodium salt 

65152-14-9 1,6-Naphthalenedisulfonic acid, 4-amino-3-[[4'-[(1-amino-4-sulfo-2-naphthalenyl)azo]-

3,3'-dimethyl[1,1'-biphenyl]-4-yl]azo]-, trisodium salt 

10
U.S. Environmental Protection Agency 

List 2: Benzidine Congener-Based Dyes on the Non-CBI TSCA Inventory

CHEMICAL NAME1 CAS NO 

65152-15-0 1,7-Naphthalenedisulfonic acid, 4-amino-3-[[4'-[(1-amino-4-sulfo-2-naphthalenyl)azo]-

3,3'-dimethyl[1,1'-biphenyl]-4-yl]azo]-, trisodium salt 

66214-51-5 2,7-Naphthalenedisulfonic acid, 5-amino-3-[[4'-[(7-amino-1-hydroxy-3-sulfo-2-

naphthalenyl) azo]-3,3'-dimethyl[1,1'-biphenyl]-4-yl]azo]-4-hydroxy-, trisodium salt 

66225-65-8 Cuprate(2-), [5-[[4'-[[2,6-dihydroxy-3-[(2-hydroxy-5-sulfophenyl)azo]phenyl]azo]-3,3'-

dimethyl[1,1'-biphenyl]-4-yl]azo]-2-hydroxybenzoato(4-)]-, disodium 

66418-17-5 Cuprate(3-), [.mu.-[4-[[4'-[(6-amino-1-hydroxy-3-sulfo-2-naphthalenyl)azo]-3,3'-

dihydroxy[1,1'-biphenyl]-4-yl]azo]-3-hydroxy-2,7-naphthalene disulfonato(7-)]]di-, 

trisodium 

66418-18-6 Cuprate(4-), [.mu.-[3-[[3,3'-dihydroxy-4'-[(2-hydroxy-3,6-disulfo-1-

naphthalenyl)azo][1,1'-biphenyl]-4-yl]azo]-4-hydroxy-2,7-naphthalene disulfonato(8-)]]di-

, tetrasodium 

67893-48-5 Benzoic acid, 5-[[4'-[(2,4-diamino-5-sulfophenyl) azo]-3,3'-dimethyl[1,1'-biphenyl]-4-

yl]azo]-2-hydroxy-, disodium salt 

68084-09-3 2,7-Naphthalenedisulfonic acid, 5-amino-4-hydroxy-3-[[4'-[(2-hydroxy-3,6-disulfo-1-

naphthalenyl)azo]-3,3'-dimethoxy[1,1'-biphenyl]-4-yl]azo]-, tetrasodium salt 

68084-21-9 1,3-Naphthalenedisulfonic acid, 4-amino-5-hydroxy-6-[[4'-[(2-hydroxy-3,6-disulfo-1-

naphthalenyl)azo]-3,3'-dimethoxy[1,1'-biphenyl]-4-yl]azo]-, tetrasodium salt 

68084-22-0 2,7-Naphthalenedisulfonic acid, 4-[[4'-[(6-amino-1-hydroxy-3-sulfo-2-naphthalenyl)azo]-

3,3'-dimethoxy[1,1'-biphenyl]-4-yl]azo]-3-hydroxy-, trisodium salt 

68084-23-1 1,3-Naphthalenedisulfonic acid, 4-amino-6-[[4'-[(1,8-dihydroxy-3,6-disulfo-2-

naphthalenyl)azo]-3,3'-dimethoxy[1,1'-biphenyl]-4-yl]azo]-5-hydroxy-,tetrasodium salt 

68140-31-8 Cuprate(3-), [.mu.-[3-[[3,3'-di(hydroxy-.kappa.O) -4'-[[2-(hydroxy-.kappa.O)-8-hydroxy6-sulfo-1-naphthalenyl]azo-.kappa.N1][1,1'-biphenyl]-4-yl]azo-.kappa.N1]-4-(hydroxy-

.kappa.O)-5-hydroxy-2,7-naphthalenedisulfonato(7-)]]di-, trisodium [CI Direct Blue 

214] 

68345-21-1 2,7-Naphthalenedisulfonic acid, 3-[[3,3'-dimethyl-4'-[[4-[[(4-methylphenyl)sulfonyl]oxy] 

phenyl] azo][1,1'-biphenyl]-4-yl]azo]-4-hydroxy-5-[[(4-methylphenyl) sulfonyl]oxy]-, 

disodium salt 

68966-43-8 2,7-Naphthalenedisulfonic acid, 3,3'-[(3,3'-dimethoxy [1,1'-biphenyl]-4,4'-diyl)bis(azo)] 

bis[5-amino-4-hydroxy-, sodium salt, compd. with 2,2'-iminobis[ethanol] 

68966-50-7 2,7-Naphthalenedisulfonic acid, 3,3'-[(3,3'-dimethoxy[1,1'-biphenyl]-4,4'-diyl)bis(azo)] 

bis[5-amino-4-hydroxy-, sodium salt 

70210-32-1 Benzenesulfonic acid, 3-(benzoylamino)-4-hydroxy-5-[[1-[[[4'-[[2-[[2-hydroxy-5-(methyl 

sulfonyl)phenyl]azo]-1,3-dioxobutyl]amino]-3,3'-dimethoxy[1,1'-biphenyl]-4-yl]amino] 

carbonyl]-2-oxopropyl]azo]-, monosodium salt 

70632-09-6 Benzoic acid, 5-[[4'-[[2,6-diamino-3-[(4-sulfophenyl) azo]phenyl]azo]-3,3'-dimethyl [1,1'-

biphenyl]-4-yl]azo]-2-hydroxy-, dilithium salt 

71550-22-6 2,7-Naphthalenedisulfonic acid, 3,3'-[(3,3'-dimethoxy[1,1'- biphenyl]-4,4'-diyl)bis(azo)] 

bis[5-amino-4-hydroxy -, tetralithium salt 

[CI Direct Blue 15 or Trypan Blue, tetralithium salt] 

71566-41-1 Benzoic acid, 2-[[2-amino-5-hydroxy-6-[[4'-[(2-hydroxy-6-sulfo-1-naphthalenyl)azo]-3,3'-

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12

List 2: Benzidine Congener-Based Dyes on the Non-CBI TSCA Inventory

CAS NO CHEMICAL NAME1 

dimethoxy[1,1'-biphenyl]-4-yl]azo]-7-sulfo-1-naphthalenyl]azo]-5-nitro-, trisodium salt 

71701-30-9 2,7-Naphthalenedisulfonic acid, 3-[[3,3'-dimethyl -4'-[[4-[(phenylsulfonyl)oxy] 

phenyl]azo] [1,1'-biphenyl]-4-yl]azo]-4-hydroxy-, disodium salt 

71873-63-7 

(former = 

12217-56-0) 

Cuprate(4-), [.mu.-[7-[[3,3'-di(hydroxy-.kappa.O) -4'-[[4-(hydroxy-.kappa.O)-2-sulfobenzo 

[a]phenazin-3-yl]azo-.kappa.N1] [1,1'-biphenyl]-4-yl]azo-.kappa.N1]-8-(hydroxy-

.kappa.O)-1,3,6-naphthalene trisulfonato(8-)]]di-, tetrasodium 

[CI Direct Blue 90] 

101200-51-

5 

Benzoic acid, 2-[[2-amino-5-hydroxy-6-[[4'-[(2-hydroxy-6-sulfo-1-naphthalenyl)azo]-3,3'-

dimethoxy[1,1'-biphenyl]-4-yl]azo]-7-sulfo-1-naphthalenyl]azo]-5-nitro-, disodium salt 

1

Common names are not unique identifiers as they may be applied to more than one CAS No.; 

however, they are frequently used, even in peer-reviewed literature.