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PBT assessment

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PBT assessment: overall result

PBT status:
the substance is not PBT / vPvB
Justification:

Classification of [4-[4,4'-bis(dimethylamino)benzhydrylidene]cyclohexa-2,5-dien-1-ylidene]dimethylammonium chloride for effects in the environment:

 

The chemical [4-[4,4'-bis(dimethylamino)benzhydrylidene]cyclohexa-2,5-dien-1-ylidene]dimethylammonium chloride (CAS no. 548-62-9) is used in the dyestuff industry in the manufacture of inks. The aim was to assess whether the PBT criterion within Annex XIII was fulfilled for the substance [4-[4,4'-bis(dimethylamino)benzhydrylidene]cyclohexa-2,5-dien-1-ylidene]dimethylammonium chloride. 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

In an experimental study done by Clariant Chemical (India) limited in 2010. The test chemical 4-{bis[4-(dimethylamino)phenyl]methylidene}-N,N-dimethylcyclohexa-2,5-dien-1-iminium chloride (CAS no. 548-62-9) showed 3.6 % biodegradation by using parameter CO2 evolution in 28 days. By this percent biodegradation value this chemical is considered as not readily biodegradable.

 

In another study done by Chiing-Chang Chen, et.al. published in journal Biotechnology letters in 2007 biodegradation experiment was performed to test biodegradability of test chemical (4-(4,4'-Bis(dimethylamino)benzhydrylidene)cyclohexa-2,5-dien-1-ylidene)dimethylammonium chloride (CAS no. 548-62-9) by taking bacteria Pseudomonas putidaas a inoculum isolated from waste water of dye manufacturing company at concentration of 6×107cfu/mL. Prior to the experiment, the bacterial cells were pre-cultivated in nutrient broth for 12 h. The initial concentration of test chemical taken was 0.022 mg/L and pH was 7.5 and temperature was 37 o C. After 7 days amount of residual chemical was analysed by using HPLC and percent biodegradation was calculated. Percent Biodegradation of test chemical (4-(4,4'-Bis(dimethylamino)benzhydrylidene)cyclohexa-2,5-dien-1-ylidene)dimethylammonium, chloride obtained was 78.5 % by test material analysis parameter. By percent biodegradation this test chemical is considered as readily biodegradable byPseudomonas putida.

 

In next study prediction was done to check biodegradability of test chemical N-(4-{bis[4-(dimethylamino)phenyl]methylene}cyclohexa-2,5-dien-1-ylidene)-N-methylmethanaminium chloride ( CAS no. 548-62-9) using OECD QSAR tool box v.3.3 using log kow as primary descriptor. The biodegradation percentage of test chemical N-(4-{bis[4-(dimethylamino)phenyl]methylene}cyclohexa-2,5-dien-1-ylidene)-N-methylmethanaminium chloride obtained was only 3 %  by considering BOD parameter  and microorganisms as inoculum in 28 days. By considering this value of percent biodegradability it is concluded that test chemical N-(4-{bis[4-(dimethylamino)phenyl]methylene}cyclohexa-2,5-dien-1-ylidene)-N-methylmethanaminium chloride is not readily biodegradable.

 

Another prediction done by using Estimation Programs Interface Suite (EPI suite, 2017)to predict the biodegradation potential of the target chemical N-(4-{bis[4-(dimethylamino)phenyl]methylene}cyclohexa-2,5-dien-1-ylidene)-N-methylmethanaminium chloride (CAS No: 548-62-9) in the presence of mixed populations of environmental microorganisms. The biodegradability of the substance was calculated using seven different models such as Linear Model, Non-Linear Model, Ultimate Biodegradation Timeframe, Primary Biodegradation Timeframe, MITI Linear Model, MITI Non-Linear Model and Anaerobic Model (called as Biowin 1-7, respectively) of the BIOWIN v4.10 software. The results indicate that the chemicalN-(4-{bis[4-(dimethylamino)phenyl]methylene}cyclohexa-2,5-dien-1-ylidene)-N-methylmethanaminium chloride is not readily biodegradable.

 

Experimental study on read across substances (CAS: 2465-27-2 and 1100-88-5) also indicate the substances to be not readily biodegradable

 

By considering all the results of above mentioned study of target chemical 4-{bis[4-(dimethylamino)phenyl]methylidene}-N,N-dimethylcyclohexa-2,5-dien-1-iminium chloride (CAS no. 548-62-9) and supporting weight of evidence study of its read across chemicals percentage of biodegradation was very low ( below 20 %) therefore it is concluded that this test chemical not readily biodegradable but in one study of target chemical published in Biotechnology letters journal shows contradicting results i.e., target chemical readily biodegradable as its degradation percentage was very high ( 78.5%) in 7 days by bacteria pseudomonas putida the probable reason for this result is that the target chemical shows cytotoxicity to many microorganisms as reported by Michaels and Lewis (1986) and gram negative bacteria Pseudomonas putidais resistance to many antibiotics and chemical hence it is able to degrade it.

 

However in environment there are many type of microorganisms which not resistance to target chemical which shows cytotoxicity to many organisms. Hence by considering results of other above mentioned studies and studies of read across chemicals it is concluded that target chemical 4-{bis[4-(dimethylamino)phenyl]methylidene}-N,N-dimethylcyclohexa-2,5-dien-1-iminium chloride (CAS no. 548-62-9) is expected to be not readily biodegradable.

 

Environmental fate

According to the fugacity model levels III, the most likely environmental fate for this test chemical is sediment and soil (i.e.estimated to 49% and 48.8% respectively). In soil, [4-[4,4'-bis(dimethylamino)benzhydrylidene]cyclohexa-2,5-dien-1-ylidene]dimethylammonium chloride was expected to have negligible mobility based upon an estimated Log KOCas 5.78.Thehalf-life in soil (541.66 days in sediment and 120 days in soil estimated by EPI suite) indicates that the chemical is persistent in sediment but not persistent in soil.

 

If released in to the environment, 2.22% of the chemical will partition into water, respectively according to the Mackay fugacity model level III in EPI suite version 4.1 (2017). Moreover, the half-life (60 days estimated by EPI suite) indicates that the chemical is persistent in water and the exposure risk to aquatic animals is moderate to high.

 

Hence it has been concluded that the [4-[4,4'-bis(dimethylamino)benzhydrylidene]cyclohexa-2,5-dien-1-ylidene]dimethylammonium chloride is likely to be persistent in nature.  

 

Bioaccumulation assessment

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

 

Theestimated BCF value from various databases was determined to be in the range 3.0 – 39.5 and the estimatedoctanol water partition coefficient of the test chemical is 1.172 which is less than the threshold of 4.5. If this chemical is released into the aquatic environment, there should be a low 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:

 

Mammals

The tested chemical is regarded to be classified for carcinogenicity in category 2 as per theAnnex VI of Regulation (EC) No 1272/2008 (CLP Regulation)but not for mutagenicity and 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 0.70 – 0.79 mg/L. These value suggest that the substance is likely to be hazardous at environmentally relevant concentrations and can be classified in Aquatic acute category 1 as per the CLP regulation.

 

There are no available long-term toxicity evaluations for [4-[4,4'-bis(dimethylamino)benzhydrylidene]cyclohexa-2,5-dien-1-ylidene]dimethylammonium chloride. By speculation, long-term NOEC for aquatic organisms can be expected for the substance at concentration below 0.01 mg/L based on the data mentioned above.

 

The chemical was therefore considered as hazardous to aquatic environments as per the criteria set out in Annex XIII.

 

 

Conclusion

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.