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Classification & Labelling & PBT assessment

PBT assessment

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Administrative data

PBT assessment: overall result

PBT status:
the substance is not PBT / vPvB

Classification of 1-phenylazo-2-naphthol for effects in the environment:


The chemical 1-phenylazo-2-naphthol (CAS no. 842-07-9) is used for dyestuff application. The aim was to assess whether the PBT criterion within Annex XIII was fulfilled for 1-phenylazo-2-naphthol. The PBT criterion was herein assessed based on experimental data in conjunction with standardized environmental fate models. Here follows a description of the PBT assessment.



Persistence assessment

The tested substance fulfils the P criterion within Annex XIII based on the assessment that here follows:


Biotic degradation

The carbon dioxide evolution test (former Sturm test) is a static method to evaluate the ultimate aerobic biodegradability of a test substance Sudan Orange 220 (CAS no. 842-07-9) in water (Sustainability Support Services (Europe) AB has letter of access, Experimental report no. 03/0063/36/1, 2003). Activated sludge was obtained from laboratory wastewater plant treating municipal sewage. Activated sludge of a concentration of 30 mg/I dry substance was pre-aerated for about two days before the start of the test. Mixtures of the test substance, a defined inorganic medium and a non-pre-adapted inoculurn (e .g. activated sludge or effluent of a municipal or laboratory waste water treatment plant) are incubated and aerated at room temperature up to 28 days. The biologically produced carbon dioxide is trapped in a 0.25 mol. potassium hydroxide solution. The production of carbon dioxide (C02) is a clear indication of biodegradation. The measured amount of carbon dioxide at the end of the test is compared with the calculated maximal theoretical production (ThC02) and indicated as biodegradation degree in percent. The conductivity shift of the absorption solution is used for calculating of the C02 production. Biodegradation degree of the reference substance after 14 days (% CO2/ThCO2): 60 - 70%. The percentage degradation of the test substance was determined to be <10% in 28 days by CO2/ThCO2 parameter. Thus, the test substance is considered to be not readily biodegradable according to OECD criteria.


Biodegradation study of Sudan I was performed (Haiyan Xu et. a; 2010) (CAS no. 842-07-9). The test is carried at a temperature of 37ᵒC with a duration period of 2 days. The anaerobic bacterial species used in the study were obtained from the American Type Culture Collection (ATCC). All strains were preserved at -80ᵒC in 10 to 15% glycerol stocks and revived as needed. The bacterial strains were grown anaerobically at 37ᵒC by using BHI broth or MRS supplemented with various Sudan dye. A loopful for each strain was cultured in static conditions at 37ᵒC for 24 h in an Erlenmeyer flask containing 10 ml medium for use as a seed culture. The bacterial seed cultures of 1.5 ml were inoculated into flasks containing 100 ml BHI broth. Dye stock solutions were added to the medium at final concentrations of 10µg/ml, the cultures were incubated at 37ᵒC in an anaerobic chamber for 2 days without agitation. Metabolites of the reduction of the test compound Sudan I were isolated and identified by HPLC andLiquid chromatography/ electrospray ionization mass spectrometric (LC/ESI-MS).Reduction of the dyes was determined by measuring the disappearance of the absorbance at 500 nm immediately after extraction with ethyl acetate as well. The results are presented in percentage (%) obtained by the means from triplicate incubations. Among the tested bacterial strains, B.ovatus, B. uniformis, B. distasonis, B. fragilis, B. thetaiotaomicron, B. caccae, B. infantis, C. perfringens, C. butyricum, C. difficle, C. indolis, C. clostridioforme, E. aerofaciens, E. faecalis, E. faecium, F. russi, F. nucleatum, L. paracasei, L. rhamnosus, R. obeum and R. gnavus were able to completely degrade (100%) the test substance Sudan I.

The bacteria which are unable to degrade the Sudan I are Bifidobacterium longum, B. Adolescentis, B. catenulatum, B. angulatum, Clostridium ramosum, Clostridium leptum, Eubacterium tenue, Escherichia coli, Lactobacillus bifidus, Lactobacillus reuteri, Lactobacillus ruminis, and Peptostreptococcus magnus, respectively. The metabolite produced from Sudan I by E. faecalis was identified as aniline, based on an identical retention time of 4.05 min and ions atm/z94 [MH+] and 135 [MH++acetonitrile].1 -amino-2 -naphthol from Sudan I dye could not be detected in the extracted samples. No metabolites of Sudan I dye produced by E. coli was detected by LC/ESI-MS, indicating that the dyes were not degraded by the bacterium. Thus, based on percentage degradation of test substance, Sudan I is considered to be readily biodegradable in nature.


Although publication study result indicates that the chemical is readily biodegradable in anaerobic conditions, but based on the experimental result for aerobic biodegradation (key study), it is concluded that the test substance C.I. Solvent Yellow 14 is considered to be not readily biodegradable in nature.


Environmental fate

According to the fugacity model levels III, the most likely environmental fate for this test chemical is soil and sediment (i.e.estimated to 70.4% and 22.0 % respectively). In sediment and soil, the substance was expected to have low mobility based upon a Log KOC of 4.72. The half-life in sediment and soil (337.5 days and 75 days, respectively estimated by EPI suite) indicates that the chemical is persistent in sediment but not persistent in soil.


If released in to the environment, 7.59 % of the chemical will partition into water according to the Mackay fugacity model level III in EPI suite version 4.1 (2016). However, the half-life (37.5 days estimated by EPI suite) indicates that the exposure risk to aquatic animals is low.


Hence it has been concluded that 1-phenylazo-2-naphthol is persistent in nature.  



Bioaccumulation assessment

The tested substance does not fulfil the B criterion within Annex XIII based on the assessment that here follows:


The estimated bioaccumulation factor (BCF) was determined to 10 L/kg wet wt. If this chemical is released into the aquatic environment, there should be a moderate risk for the chemical to bioaccumulate in fish and food chains.


Toxicity assessment

The tested substance fulfils the T criterion within Annex XIII based on the assessment that here follows:



The tested chemical is regarded to be classified for mutagenicity in Mutgenic Category 2 and Carcinogenic Category 2 as per theHarmonised classification - Annex VI of Regulation (EC) No 1272/2008 (CLP Regulation)

The tested chemical is regarded to be not classified for reprotoxicity, Further, there is no evidence of chronic toxicity, as identified by the classifications STOT (repeated exposure), category 1 (oral, dermal, inhalation of gases/vapours, inhalation of dust/mist/fume) or category 2 (oral, dermal, inhalation of gases/vapours, inhalation of dust/mist/fume).


Aquatic organisms

All of the available short-term eco-toxicity estimation for invertebrates and algae for the substance indicates the LC50/EC50 value to be in the range >10 - > 100 mg/L. These value suggest classification in Aquatic chronic 3 category but since it is classified in Aquatic chronic category 4 as per the Harmonised classification - Annex VI of Regulation (EC) No 1272/2008 (CLP Regulation), the same has been considered for the dossier.


There are no available long-term toxicity evaluations for 1-phenylazo-2-naphthol. By speculation, adverse effects at environmentally relevant concentrations in freshwater species were not expected for 1-phenylazo-2-naphthol since all the effect concentrations are well above 10 mg/L.

The chemical was therefore not considered as hazardous to aquatic environments as per the criteria set out in Annex XIII.




Based on critical, independent and collective evaluation of information summarized herein, the tested compound fulfils the P and T criterion but does not fulfil the B criterion and has therefore not been classified as a PBT compound within Annex XIII.