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PBT assessment

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PBT assessment: overall result

Reference
Name:
dimethyl sulphone
Type of composition:
boundary composition of the substance
State / form:
solid: bulk
Reference substance:
Composition 1
PBT status:
the substance is not PBT / vPvB
Justification:

Classification of Dimethyl sulfone for effects in the environment:

 

The chemical Dimethyl sulfone(CAS no. 67-71-0) is used as a solvent. The aim was to assess whether the PBT criterion within Annex XIII was fulfilled forDimethyl sulfone. 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 does not fulfil the P criterion within Annex XIII based on the assessment that here follows:

 

Biotic degradation

In an experimental key study from NTRL report (1991), biodegradation study was conducted for evaluating the percentage biodegradability of test chemical. The study was performed under aerobic conditions at a pH range 6.9 to 7.2.1 lt cylinder with bottom diffusers was used as a test vessel for the study. Activated sludge taken from the bench-scale completely mixed activated sludge system (CMAS) was used as test inoculums for the study. Test inoculum was further settled, decanted, washed with 20 mM pH 7.0 phosphate buffer, and resuspended in the same buffer solution. Initial test substance conc. used in the study was 100 mg/l. The removal of the test chemical and TOC were analyzed over several days. All the oxygen uptake tests were done with a 250-m1 BOO bottle and an Orbisphere oxygen probe equipped with an adapter. Endogenous rates were taken after 30-min aeration without feed. When substrate was included, the sludge was washed twice with 10 or 20mM pH7 phosphate buffer. The BOD5 and COO (dichromate) analyses were done according to the Standard Methods. TOC was analyzed with a Beckman TOCAMASTER Model 915-B. Sulfate was determined by ion exchange chromatography (Dionexl.Inorganic sulfate has been identified as a degradation product of test chemical. The percentage degradation of test chemical was determined to 87-100% by using test material analysis & TOC removal parameter in 48 hrs. Thus, based on percentage degradation, test chemical is considered to be readily biodegradable in nature.

 

In a supporting weight of evidence study from authoritative databases (2018) for the test chemical,biodegradation experiment was conducted for 28 days for evaluating the percentage biodegradability of test chemical. The study was performed according to OECD Guideline 301 C (Ready Biodegradability: Modified MITI Test (I) under aerobic conditions. Activated sludge was used as a test inoculums for the study. Concentration of inoculum i.e, sludge used was 30 mg/l and initial test substance conc. used in the study was 100 mg/l, respectively. The percentage degradation of test chemical was determined to 106 and 89% by BOD, TOC removal and CE parameter in 28 days Thus, based on percentage degradation, test chemical is considered to be readily biodegradable in nature.

 

Experimental results from the read across substance also indicate that it is readily biodegradable.

 

Thus, based on the available information, it indicates that chemical Dimethyl sulfone can be considered to be readily biodegradable in water and thus likely to be not persistent (Not P) in nature

 

Environmental fate

According to the fugacity model levels III, the most likely environmental fate for this test chemical is soil (i.e.estimated to 49.9%). In soil,Benzyl isovaleratewas expected to have moderate mobility based upon a Log KOC value of 1.809± 0.001at 25°C. The half-life in soil (30 days estimated by EPI suite) indicates that the chemical is not persistent in soil and the exposure risk to soil dwelling animals is moderate to low.

 

If released in to the environment, 43.7% of the chemical will partition into water according to the Mackay fugacity model level III in EPI suite version 4.1 (2017). However, the half-life (15 days estimated by EPI suite) indicates that the chemical is not persistent in water and the exposure risk to aquatic animals is moderate to low.

 

Moreover, its persistent characteristic is only observed in the sediment compartment but Fugacity modelling shows that sediment is not an important environmental fate (less than 1% i.e reported as 0.0838% when estimated by EPI Suite version 4.1).

 

Hence it has been concluded that chemical Dimethyl sulfone is not persistent (notP) in nature.

 

Bioaccumulation assessment

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

 

Theoctanol water partition coefficient of the test chemical from authoritative and modelling databases was determined to be ranges from -1.41 to -1.34, respectively 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 does not fulfil the T criterion within Annex XIII based on the assessment that here follows:

 

Mammals

The tested chemical is regarded to be not classified for carcinogenicity, 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 data for fish, aq. invertebrates and algae for the substanceDimethyl sulfoneindicates the LC50/EC50 value to be in the range > 100 – 1000 mg/L. These value suggest that the substance is not likely to be hazardous to aquatic organisms at environmentally relevant concentrations and can be considered to be ‘not classified’ as per the CLP regulation.

 

There are no available long-term toxicity evaluations for Dimethyl sulfone. By speculation, long-term NOEC for aquatic organisms were not expected for the substance at concentration below 0.01 mg/L based on the data mentioned above.

 

The chemical was therefore not 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 does not fulfil the P, B and T criterion and has therefore not been classified as a PBT compound within Annex XIII.