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Classification & Labelling & PBT assessment

PBT assessment

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PBT assessment: overall result

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

Classification of 2,3-xylenol for effects in the environment:

 

The chemical 2,3-xylenol (CAS no. 526-75-0) is used for chemical synthesis as well as a laboratory reagent. The aim was to assess whether the PBT criterion within Annex XIII was fulfilled for 2,3-xylenol. 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 fulfils the P criterion within Annex XIII based on the assessment that here follows:

 

Biotic degradation

 

Various experimental studies for the target compound 2,3-Dimethylphenol (CAS No. 526 -75 -0) were reviewed for the biodegradation end point which are summarized as below:

 

In a key study from peer reviewed journal (E. H. Snider and F. S. Manning, 1982) for target chemical2,3-Dimethylphenol(CAS No. 526-75-0), biodegradation experiment was conducted for evaluating the percentage biodegradability of test substance 2,3-dimethylphenol under aerobic conditions. Activated sludge was used as a test inoculum. The organic analyses in the study were performed by gas chromatography / mass spectrometry (GC/MS) on methylene chloride extracts of the wastewater samples. Three extracts were collected--a neutral extract, an acid extract, and a base extract. Water samples extracted and analysed included the raw wastewater after dissolved air flotation (DAF) treatment, effluent from activated sludge (AS) treatment, and effluent from activated carbon (AC) columns. The percentage degradation of test substance was determined to be 99.98% in 4 days. Thus, based on percentage degradation, test chemical 2, 3-Dimethy phenol was considered to be readily biodegradable in nature.

 

In a supporting biodegradation study was conducted for 28 days for evaluating the percentage biodegradability of test substance 2, 3-dimethylphenol (CAS no. 526-75-0) (HSDB, 2016 and SRC Phys Prop database, 2017). Activated sludge which is acclimated for a period of 2 days was used as a test inoculum for the study. Initial test substance conc. used for the study was 200 mg/l. The percentage degradation of test substance was determined to be 95.5% degradation by COD removal parameter after 5 days. Thus, based on percentage degradation, 2, 3-dimethylphenol is considered to be readily biodegradable in nature.

 

In another supporting data from peer reviewed journal (JAMES G. MUELLER et. al, 1991) for the target chemical 2,3 -Dimethylphenol (CAS No. 526-75-0), biodegradation study was carried out for 14 days for evaluating the percentage biodegradability of test substance 2,3 -dimethylphenol. Micro-organism was used as a test inoculum isolated from surface soil which was freshly obtained from the American Creosote Works site. Microbial inoculum was prepared by mixing 25 g of creosote-contaminated surface soil (17) freshly obtained from the American Creosote Works site with 100 ml of 2.5 mM phosphate buffer (pH 7). After being mixed well, the suspension was centrifuged (2,500 rpm, 10 min) to remove larger soil particles. The resultant supernatant was decanted and used as a source of indigenous, "creosote-adapted" microorganisms for the ground water medium (GWM).Ground water medium (GWM) was used for the study. For the biodegradation study, approximately 400 liters of groundwater contaminated with creosote and PCP was recovered from an on-site sampling well. Groundwater was removed from a depth of 7 m through Teflon-coated Bev-a-line tubing (15 mm inner diameter) by means of an electric pump. Subsamples were stored in darkness at 2°C for subsequent biodegradation studies, toxicity and teratogenicity testing, and chemical analyses.

It contains 2.5 ml of filtered groundwater (passed through a plug of silanized glass wool to remove undissolved solids) plus 12.5 ml of modified Bushnell-Haas medium. Additionally, two clean, sterile, 1.0-liter Wheaton bottles fitted with Teflon-lined screw caps received 200 ml of the same medium. Ground water contains the test chemical 2, 3, 5-trimethylphenol. Wheaton bottles consist of 200 ml of ground water medium (which contain ground water and modified Bushnell-Haas medium. Duplicate 25 ml samples were immediately extracted for time zero analysis. Flasks were incubated at 30°C with shaking (200 rpm) in the dark for 14 days. Killed-cell controls were prepared for each sampling time point by adding 2.5 ml of a 37% formaldehyde solution to five of the shake flasks containing 25 ml of GWM. After 1, 3, 5, 8, and 14 days of incubation, the entire contents of two active flasks and one killed-cell control flask were separately extracted and analysed by GC for the presence of creosote constituents. These data were compared with those obtained from untreated (non-inoculated) GWM that had been stored at 2°C during the 14-day incubation period. As the limit of detection of test chemical by GC is very low during a period 14 days, test chemical 2, 3-dimethylphenol can be considered to be readily biodegradable nature.

 

In an additional supporting data from secondary source (P.C. Singer et. al; 1978) for the target chemical 2,3 -Dimethylphenol (CAS No. 526-75-0), preliminary biodegradability screening test was conducted for 20 days for evaluating the percentage biodegradability of test substance 2,3-dimethylphenol. Domestic sewage was used as a test inoculum was obtained from the Chapel Hill sewage treatment plant. The test compound were added to duplicate, acid-washed, 300 ml BOD bottles at concentration of approximately 5 mg/l. Dilution water was prepared from water which had been passed through activated carbon and ion exchange columns and then glass-distilled. Standard nutrients were added to the water as was 0.5 mg/l allylthiourea for control of nitrification. The dilution water was seeded with 1.5 mg/l of domestic sewage. The BOD bottles were filled, stoppered, and incubated in the dark at 65°F for 20 days. Oxygen uptake was measured at various intervals over the 20 day period by means of a Weston and Stack dissolved oxygen meter. The percentage degradation of test substance was determined to be 91% by O₂uptake parameter in 20 days. Thus, based on percentage degradation, test chemical 2,3-dimethylphenol was considered to be readily biodegradable in nature.

 

Another biodegradation study was conducted according to OECD Guideline 301 C (Ready Biodegradability: Modified MITI Test (I)) for evaluating the percentage biodegradability of test substance 2,3 -dimethylphenol (CAS no. 526 -75 -0) (Kondo, M et. al; 1988). Initial test substance conc. used in the study was 20 mg/l. Namely, a water, acetone or DMSO solution (0.1 ml) of the test chemicals was added to a mixture of river/sea water (4.9 ml) from an unpolluted area and an autoclaved solution (5.0ml) of 0.2% peptone in a sterile test tube with a tight plug. After sealed with film and fixed at an angle of 30°in a dark box, the test tubes were incubated at 30°C and shaked at 120rpm. Inoculum used for the study was mixed culture obtained from different sources (Sea water from Enoshima Beach and River water from Tama River). The percentage degradation of test chemical in river and sea water was determined to be 100 and 54% by BOD parameter in 3 days. Thus, based on percentage degradation, 2,3 -dimethylphenol is considered to be readily biodegradable in nature.

 

On the basis of above results for target chemical 2,3-Dimethylphenol (from peer reviewed journal, authoritative database HSDB and secondary source), it can be concluded that the test substance 2,3-Dimethylphenol can be expected to be readily biodegradable 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 74.1%).In soil, 2, 3-xylenolwas expected to have slow mobility based upon an estimated Log KOC in the range. Thehalf-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, 25.1 % 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 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% when estimated by EPI Suite version 4.1).

 

Hence it has been concluded that 2, 3-xylenol is not 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 BCF value from various databases was determined to be in the range 20 - 57 L/kg wet wt. and theexperimentaloctanol water partition coefficient of the test chemical is 2.48 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 estimation for fish, invertebrates and algae for the substance indicates the LC50/EC50 value to be in the range 6-100 mg/L. These value suggest that the substance is likely to be hazardous to Aquatic organisms at environmentally relevant concentrations. Although the chemical is readily biodegradable in nature, the substance 2, 3-dimethyl phenol has been classified in Aquatic Chronic category 2 as per the Annex VI of the CLP regulation.

 

There are no available long-term toxicity evaluations for 2,3-xylenol. 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.