Phenol, styrenated

Endpoint summary

Description of key information

Biodegradation in water:

Estimation Programs Interface Suite (EPI suite, 2018) was run to predict the biodegradation potential of the test chemical 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 chemical is expected to be not readily biodegradable.

Biodegradation in water and sediments:

Estimation Programs Interface (EPI Suite, 2018) prediction model was run to predict the half-life in water and sediment for the test chemical. If released in to the environment, 24.8 % of the chemical will partition into water according to the Mackay fugacity model level III and the half-life period of test chemical in water is estimated to be 15 days (360 hrs). 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 low whereas the half-life period of test chemical in sediment is estimated to be 135 days (3240   hrs). However, as the percentage release of test chemical into the sediment is less than 1% (i.e, reported as  0.554 %), indicates that test chemical is not persistent in sediment.

Biodegradation in soil:

The rate and route of transformation of [14C]tristyrenated phenol (TSP) was studied in four European soils: a sandy loam (18 Acres, from the United Kingdom), a silt loam (Gartenacker, from Switzerland), a silt loam (Krone, from the United Kingdom), and a loam (Vetroz, from Switzerland). The radiolabeled carbon atom in [14C]TSP is located randomly at one of the 6 possible locations in the central phenol ring. The study was performed according to OECD TG 307 and in compliance to GLP. The test was run in the dark, under aerobic conditions, at two test temperatures (12 ± 2 °C and 20 ± 2 °C) using a nominal concentration of 0.6 μg/g applied to 100 g of soil. The test duration was ca. 120 days for all soils except 18 Acres, which was continued up to ca. 180d. Tables compiling the results for the different soils are available in the RSS. The main findings are described below. Ultimate degradation of the test item was monitored by means of 14CO2 evolution, which increased in all soil test systems over the course of the incubation period, up to a maximum of 14.3% of applied radioactivity in the test at 12°C and up to 22% of applied radioactivity in the test at 20°C. Small but nevertheless significant mineralization of the test item thus is demonstrated. Decrease of TSP concentration was monitored by means of mild extraction of the soil samples. At incubation start, the radioactivity was (almost) completely extractable from the soil samples (ranging from 94.8% to 105.8%). The radioactive material was confirmed to be the parent chemical, TSP, thus demonstrating that the (mild) extraction protocol does not lead to conversion / transformation of the parent substance. At the end of the incubation period, 11.3 -20.6% and 3.9-­15.6% of applied radioactivity was still present as parent TSP in the test system at 12°C and 20°C, respectively. Primary degradation of the test item was also monitored by means of examination of the mild extraction fractions. Metabolites that were formed at concentrations >10% of applied radioactivity, or >5% in at least 2 consecutive intervals, were identified. The identified primary metabolites are in general oxidation products, i.e. containing additional hydroxyl groups. At day 3 after incubation, up to 22.3% and 22.0% of applied radioactivity was identified as primary metabolites in the 12°C and 20°C experiment, respectively. This indicates that primary degradation of TSP starts quickly after application of the test item to the soil. In total, 9 metabolites were investigated and potential chemical structures were proposed where possible. Any radioactivity not removed during the (mild) extraction process was considered ‘Non-Extractable Residue’ (NER). The extracted soil samples were divided in two parts and submitted either to Soxhlet extraction or to Organic Matter Fractionation (OMF). Soxhleting allowed to further extract 5.8-­11.5% of applied radioactivity from the soil samples. Characterisation of this fraction identified it as polar transformation product. However, as Soxhlet is a harsh technique, it cannot be excluded that conversion of parent chemical occurred during the process. The organic matter fractionation separates the fulvic acid, humic acid and humin fractions of the soil organic matter. For the TSP soil samples, the radioactivity was found to be mainly (present in the insoluble humin fraction: 19.9-­31.1% of applied radioactivity. This indicates that it is not bioavailable. Finally, kinetic modelling was performed in order to obtain the transformation/dissipation rate of [14C]TSP and its major transformation products. All calculations were carried out by means of the TESSELLA model CAKE v3.3 (Computational Assisted Kinetic Evaluation). Three kinetic models were used: i) Single first-­order (SFO), ii) Biphasic double first-­order (DFOP) and iii) First-order multi-­compartment (FOMC).

[14C]Tristyrenated phenol was found to transform rapidly over the incubation period under the conditions of this aerobic soil study, with DT50 ranging from 3.13 to 12.5 days at 12 °C and 2.88 to 8.46 days at 20 °C. The DT50 values of the identified transformation products were also determined by means of the same kinetic model, and ranged from 14.7 to 110 days at 12°C and from 4.78 to 83 days at 20°C.

The rapid degradation of [14C]Tristyrenated phenol, with the formation of several metabolites, combined with a significant amount (≤ 22% of applied radioactivity) of 14CO2 generated over the course of the incubation period, is an indication of significant mineralization and non-persistent nature of the parent compound. The amount of non-­extractable residues increased to a maximum of 51.6% AR. Characterization by organic matter fractionation demonstrated that most of the non-extractable residue is associated with the insoluble humin fraction of the SOM; therefore, it is not bioavailable. The DT50 of TSP is determined to be ranging from 3.13 to 12.5 days at 12 °C and 2.88 to 8.46 days at 20 °C. The DT50 values of the identified transformation products ranged from 14.7 to 110 days at 12°C and from 4.78 to 83 days at 20°C.

 

Additional information

Biodegradation in water:

Predicted data study for test chemical and experimental studies for its read across chemical have been reviewed for Biodegradation in water endpoint and their results are summarized below.

In first study the Estimation Programs Interface Suite (EPI suite, 2018) was run to predict the biodegradation potential of the test chemical 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 chemical is expected to be not readily biodegradable.

In next study Biodegradation experiment was performed according to guideline OECD 301 Manometric Respirometry modified according to EEC Round Robin Test "Assessment of Biodegradability of Chemicals in Water by Manometric Respirometry" DGX 1/283/82 Rev 5, EEC 79/831, Annex 5, Part C. The test chemical undergoes 7 % degradation in 28 days by uisng activated sludge as inoculum in aerobic condition . By considering % degradation value it is concluded that test chemical is not readily biodegradable.

Another study was reviewed from authoritative database (J check, 2018) in this Biodegradation experiment was conducted for 14 days for evaluating the percentage biodegradability of test chemical. 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. The percentage degradation of test substance was determined to be0%, 1.0% and  3% degradation by BOD,  GC(m-) , and GC(p-) parameters respectively  in 28 days.Thus, based on percentage degradation, value test chemical is considered to be not readily biodegradable in nature.

Last study was also reviewed from authoritative database (J check, 2018) in this Biodegradation experiment was conducted for 14 days for evaluating the percentage biodegradability of test chemical. Activated sludge was used as 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 substance was determined to be 0 and 0.3 % by considering BOD and GC parameter in 14 days. Thus, based on percentage degradation, value test chemical is considered to be not readily biodegradable in nature.

By considering results of all above mentioned studies it is concluded that the test chemical is not biodegradable in nature. .

Biodegradation in water and sediments:

Estimation Programs Interface (EPI Suite, 2018) prediction model was run to predict the half-life in water and sediment for the test chemical. If released in to the environment, 24.8 % of the chemical will partition into water according to the Mackay fugacity model level III and the half-life period of test chemical in water is estimated to be 15 days (360 hrs). 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 low whereas the half-life period of test chemical in sediment is estimated to be 135 days (3240   hrs). However, as the percentage release of test chemical into the sediment is less than 1% (i.e, reported as  0.554 %), indicates that test chemical is not persistent in sediment.

Biodegradation in soil:

For 2,4,6­tristyryl phenol (TSP), an aerobic mineralization test in surface water (OECD 309) was requested, if technically feasible. If the OECD 309 test is found to be not feasible, ECHA’s Final Decision Letter provides a soil simulation test (OECD 307) or a sediment simulation test (OECD 308) as alternative options.

The registrants have assessed the technical feasibility of the OECD 309 test, and concluded on the grounds described below, that such a test is not technically feasible, and that, as a result of the anticipated technical difficulties, the outcome of such an OECD 309 test would not contribute to a better understanding of the persistence properties of TSP.

According to OECD Guideline 309, “the principal objective of the simulation test is to determine the mineralisation of the test substance in surface water, and mineralisation constitutes the basis for expressing degradation kinetics. However, an optional secondary objective of the test is to obtain information on the primary degradation and the formation of major transformation products. Identification of transformation products, and if possible quantification of their concentrations, are especially important for substances that are very slowly mineralised (e.g. with half-­lives for total residual 14C exceeding 60 days). Higher concentrations of the test substance (e.g., >100 μg/l) should normally be used for identification and quantification of major transformation products due to analytical limitations.”

For the assessment of (ultimate) degradation kinetics, the OECD 309 guideline prescribes a test concentration of < 1 μg/L in order to ensure that the biodegradation follows first order kinetics. However, when intending for the identification of major transformation products in an OECD 309 test, the test should be run at a higher test concentration. According to the guideline, a concentration > 100 μg/L or sometimes even > 1000 μg/L should be used, due to the analytical limitations related to chemical structure identification techniques. However, 2,4,6-­Tristyrenated phenol has a less water solubility and thereby it is not feasible to obtain sufficiently high test item concentrations in order to allow for the evaluation of primary degradation by means of an OECD 309 test.

The PBT criteria as described in Annex XIII refer to the degradation half-­life of a substance in the different compartments. As further clarified in ECHA Guidance R11: “Degradation may be biotic and/or abiotic (e.g. hydrolysis) and result in complete mineralisation, or simply in the transformation of the parent substance (primary degradation). Where only primary degradation is observed, it is necessary to identify the degradation products and to assess whether they possess PBT/vPvB properties.”

Hence, it is clear that the goal of the requested persistence testing should be to identify a degradation half-­life for the parent substance (TSP), and – in case primary degradation is observed, but not complete mineralization – to identify the degradation products and examine their persistence.

Based on the above, the registrants concluded that:

i) It is technically impossible to assess the primary degradation potential of the parent substance TSP by means of an aqueous OECD 309 test due to the insufficient solubility of the test item in water.