Diisopropylbiphenyl and triisopropylbiphenyl

Endpoint summary

Description of key information

Alkylation and transalkylation products of biphenyl with propene is considered not readily biodegradable based on a weight of evidence assessment for main constituents of the UVCB substance (including QSAR estimates). Based on the information on screening test level persistence can only be excluded for MIPB, whereas a final conclusion on persitence cannot be drawn for the main constituents DIPB and TIPB.

Alkylation and transalkylation products of biphenyl with propene is an UVCB substance composed of different constituents. Each constituent is present as a mixture of isomers with unknown constituents. Based on the complex composition in combination with the physico-chemical properties of the substance biodegradation simulation testing is technically not feasible. This was assessed within a feasibility study conducted according to OECD 309 guideline. In a weight of evidence approach, considering study results and QSAR estimates for the main constituents of the UVCB, it was concluded that alkylation and transalkylation products of biphenyl with propene is potentially persistent or very persistent.

Additional information

Persistence screening assessment (ready biodegradability)

On the biodegradation screening test level experimental data are available for the constituent MIPB. In an OECD 310 headspace test with a prolonged test duration of 45 days 67% degradation of MIPB was observed. The 10 % adaption phase was reached on day 10, the pass level of 60% was reached on day 30. Based on the result it can be concluded that MIPB does not meet the persistence criteria and can be fully mineralized within a short period of time at environmental conditions.

The ready biodegradability of the main constituents DIPB and TIPB was estimated by QSAR (VEGA 1.1.4; Ready Biodegradability model (IRFMN) 1.0.9). For DIPB the QSAR model was outside of the applicability domain and no prediction on biodegradability was performed. However, the data on similar substances listed in the training set of the model provide valuable information. In the training set experimental data are reported for the biphenyl (CAS 92-52-4) and for 1,4-diisopropylbenzene (CAS 100-18-5) which consists of only one phenyl ring with two isopropyl side chains. According to the presented experimental results the aromatic biphenyl ring system without isopropyl side chains is readily biodegradable, whereas 1,4-diisopropylbenzene is not readily biodegradable. The presented data in combination with the experimental result of the OECD 310 study with MIPB (see above) indicate that the degradability of the biphenyl derivatives decreases with an increasing number of isopropyl chains (biphenyl > MIPB > DIPB > TIPB). This is in line with the QSAR calculation for TIPB predicting no ready biodegradability. The QSAR prediction for TIPB is considered reliable and falls within the applicability domain of the model.

Based on the information on screening test level persistence can only be excluded for MIPB, whereas a final conclusion on the P/vP criterion cannot be drawn for the main constituents DIPB and TIPB.

 

Biodegradation simulation tests (feasibility test in surface water)

Simulation degradation tests were performed in surface water according to OECD 309 with non-labeled test item.

The substance is a complex UVCB comprising a high number of stereoisomers. Since not all of the stereoisomers can be technically identified and quantified it was necessary to select representative analytes (isomers) for the degradation measurement. One criterion for the selection of representative analytes was the limit of detection (LOD) and quantification (LOQ). Due to the low solubility of the test item of approximately 33 µg/L an application rate of 15 µg/L was chosen as high application rate in the feasibility test which is below the standard rate of 100 µg/L. The low application rate was set to 3 µg/L. Due to these low concentrations it was necessary to find appropriate extraction methods for quantification and identification of the analytes. This required a series of pre-tests, in order to develop appropriate instrumental and extraction methods to identify and subsequently analyse the test item. The four most abundant isomers of DIPB (i.e. DIPB1, DIPB2, DIPB3 and DIPB4; arbitrary names) and the most abundant isomer of TIPB (TIPB1) were selected as representatives for the UVCB substance (>90% of the constituents of the UVCB substance are covered). Finally, the chromatographic conditions were optimized in GC-MS analysis and a column with a different stationary phase (DB-5MS, J & W Scientific) was further used for a better peak resolution. A LOQ value of 0.3 µg/L was set for all five selected analytes. A LOD value of 0.03 µg/L was set for DIPB isomers and a LOD value of 0.1 µg/L was set for TIPB1. The conduction of the pre-tests took more than a year to complete.

The repeatability of the extraction method was performed by analysing five replicates at 0.3 µg/L (10 % of lowest application rate) and five replicates at 16.5 µg/L (110% of the highest application rate). Mean recoveries ranged from 108 % to 117 % and between 100 % and 109 % for the low and high application rates, respectively. Relative standard deviation values ranged from 2 % to 12 %. An overall mean recovery of 108 % ± 7 % was obtained, thus showing that the extraction method is repeatable. The mean procedural recovery values on the day of extraction were within 70-110% and the method is therefore considered to be reliable.

The feasibility of the test was assessed in three main types of experimental designs: open system, closed system with tubes (Tenax® or activated carbon) and closed system with solvent (toluene) traps. The test water (natural surface water) was incubated in the dark at 12 ±2°C with slightly constant orbital movement of the test vessel. The incubation period after treatment was 78 days for the open system and 7 days for the closed systems. Duplicate samples were taken for analysis at specified intervals for 0, 8, 13 and 78 days after treatment (DAT) for the open system and for 0 and 7 DAT for the closed systems. The identification and quantification of the selected analytes was done by using GC-MS as analytical method.

There was a significant decrease in test item concentration at 6 DAT in the open and 7 DAT in the closed systems. Recoveries of the test item in the water phase ranged between 4.1 % and 20 % for the open system and between 3.2 % and 43 % for the closed systems. This decrease was similar in the sterile samples, which indicates the absence of biological degradation. The presence of test item in the different traps for volatile compounds observed a loss by evaporation. The recovery of the applied analytes in the traps ranged from <LOD to 12 % for the Tenax® tubes, from <LOD to 1.2 % in the activated carbon tubes and from <LOD to 0.44 % in the solvent traps.

It can be concluded that the experimental designs, which were tested in this study, were not suitable for determining the degradation rate of the test item in natural aerobic surface water. In the open system, the constant gas phase exchange between the bottle gas phase and the air produces a high loss of the test item. In the closed system, the test item is confined to the bottle headspace. From the three different traps for volatiles tested in this study, the Tenax® tubes showed the highest trapping efficiency. However, the amount of test item recovered from the gas phase by the Tenax® tubes did not account for the total decrease of test item in the water phase. Based on the results of this study, it is not possible to provide conclusive remarks about the reason for the incomplete mass balance. The loss of test item might be due to incomplete trapping efficiency of the Tenax® tubes. The absence of biological degradation was indicated by the analysis of sterile samples.

In conclusion, an aerobic mineralisation study in surface water according to OECD 309 can be considered technically not feasible due to the physico-chemical properties of the substance (e.g. evaporation of the substance from the water phase takes place). Furthermore, based on the low solubility of the substance in combination with the complex composition of this UVCB substance, the adequate analytical methods on the identification and quantification of the substance are only limited to some of the most abundant constituents. For these reasons no further simulation tests for alkylation and transalkylation products of biphenyl with propene were conducted.

 

Biodegradation simulation tests (QSAR predictions for sediment/water system and soil)

Based on the complex composition in combination with the physico-chemical properties of the substance biodegradation simulation testing is considered as technically not feasible. This was assessed within a feasibility study conducted according to OECD 309 guideline (see above). Persistence in sediment and soil was estimated by QSAR calculations for the two main constituents DIPB and TIPB. These QSAR results were used in a weight of evidence approach for the persistence assessment of the UVCB substance.

For the prediction of the persistence of DIPB and TIPB in sediment/water systems the VEGA 1.1.4 “Persistence sediment model” (IRFMN) 1.0.0 was used. Both constituents (DIPB and TIPB) fall within the applicability of the model. The prediction is persistent (P) and/or very persistent (vP) for DIPB and very persistent (vP) for TIPB, respectively. For performance of the model on similar molecules is good (DIPB) to moderate (TIPB), even though isopropyl chains are missing in the list of the most similar substances in the training set of the model. The prediction is considered to be valid and is used as information within a weight of evidence approach for the persistency assessment of the substance.

The persistence of the main constituents DIPB and TIPB in soil was estimated using the QSAR model VEGA 1.1.4 “Persistence (soil) model” (IRFMN) 1.0.0. For DIPB the model predicts no persistence (nP) whereas the prediction for TIPB is very persistent (vP). The QSAR estimate for DIPB should be considered with caution, since the substance does not fall within the applicability domain of the model. For both isomers, DIPB and TIPB, the performance of the model on similar molecules is good, even though isopropyl chains are missing in the list of the most similar substances in the training set. The use of the prediction as supporting information within a weight of evidence approach for the persistency assessment of the UVCB substance is considered acceptable.