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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Endpoint:
biodegradation in water: sediment simulation testing
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the substance is readily biodegradable
Justification for type of information:
Further testing for trioctyl benzene-1,2,4-tricarboxylate is not considered necessary on the basis that the substance is considered readily biodegradable.
In general, achieving the degree and rate of biodegradation necessary to fulfil the readily biodegradable criteria requires that:
a) the structure of the test substance is intrinsically degradable by microorganisms;
b) the individual or consortia of competent microorganisms capable of degrading the test substance are both present in sufficient number at the beginning of the test and they are also viable and active under the conditions of the test, and
c) the test substance is delivered to and maintained in the test system in such a way as to permit sufficient bioavailability to the microorganisms present in the test inoculum.

Information on the structural elements of trioctyl benzene-1,2,4-tricarboxylate and the compound as a whole would suggest the substance to be intrinsically biodegradable, therefore satisfying condition a). This is seen in the EPISUITE BIOWIN v4.10 results for trioctyl benzene-1,2,4-tricarboxylate and its lower and higher TM4 and TM10 analogues, where rapid aerobic biodegradation is predicted for all three structures on the basis that they all contain linear C4 terminal chain [CCC-CH3] and ester [-C(=O)-O-C] fragments. Increasing molecular weight has the effect of lowering probability outcomes, but the effect is trivial, with all three structures predicted to be readily biodegradable, thereby supporting the conclusion that trioctyl benzene-1,2,4-tricarboxylate is readily biodegradable.

More importantly, experimental test data are available for analogue substances for read-across to trioctyl benzene-1,2,4-tricarboxylate, the outcomes of which are additionally influenced by factors b) and c). Available data for tributyl benzene-1,2,4-tricarboxylate (Polynt-IT: 001 Key | Experimental result) show that the core benzene-1,2,4-tricarboxylate entity is readily biodegradable, even under MITI I (OECD 301C) conditions, when dosed in the test system at 100 mg/L. Straight-chain aliphatic alcohols are also readily biodegraded and extending the substituent butyl groups linearly by a further two or four -CH2 units to trihexyl benzene-1,2,4-tricarboxylate (Vertellus-UK: S-01) and trioctyl benzene-1,2,4-tricarboxylate would not be expected to introduce a structural hindrance to biodegradation of the substituent alkyl chains.

However, it is noted that incremental extension of the alkyl chains quickly leads to lower aqueous solubility, thereby influencing bioavailability of the test substance to the microbial inoculum as determined by water solubility. The most soluble, short alkyl chain analogue tributyl benzene-1,2,4-tricarboxylate was completely mineralised (88% in 28 d, based on ThOD) and classified as readily biodegradable in the OECD 301C (MITI I) test, whereas trioctyl benzene-1,2,4-tricarboxylate was not (3% in 28 d, based on ThOD) under identical conditions. Both tests are considered reliable and the collection and preparation of the MITI inoculum is understood to be under centralised control, with distribution to Japanese test facilities following completion of the 3-month adaptation period. Inter-laboratory variation in the composition and biochemical activity of the inoculum was therefore most likely not a decisive factor in the disparate test outcomes. A much higher degree of biodegradation (65% in 28 d based on oxygen consumption, concluding ready biodegradability but failing the 10-d window) was achieved for trioctyl benzene-1,2,4-tricarboxylate by applying the van Ginkel modification of the OECD 301D Closed Bottle Test, with a reduced concentration (2 mg/L as opposed to 100 mg/L in OECD 301C), substitution of the standard, synthetic mineral salts medium with a natural river water containing an indigenous microflora already adapted to its environment, and the application of a poorly degradable dispersing surfactant (Tween 80) to enhance test substance bioavailability.

Moreover, the proposed ester cleavage mechanism that represents the key first step in the biodegradation of TM8 entails the release of 1-octanol and trimellitic acid, and reliable studies are available for octan-1-ol (Kao Chemical Europe S.L.-ES: 001 Key | Experimental result) and trimellitic acid (Polynt-IT: 001 Key | Experimental result) which conclude that both substances are readily biodegradable.
Reason / purpose:
data waiving: supporting information
Endpoint:
biodegradation in water: simulation testing on ultimate degradation in surface water
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the substance is readily biodegradable

Description of key information

Further testing for trioctyl benzene-1,2,4-tricarboxylate is not considered necessary on the basis that the substance is considered readily biodegradable.

In general, achieving the degree and rate of biodegradation necessary to fulfil the readily biodegradable criteria requires that:

a)       the structure of the test substance is intrinsically degradable by microorganisms;

b)       the individual or consortia of competent microorganisms capable of degrading the test substance are both present in sufficient number at the beginning of the test and they are also viable and active under the conditions of the test, and

c)       the test substance is delivered to and maintained in the test system in such a way as to permit sufficient bioavailability to the microorganisms present in the test inoculum.

Information on the structural elements of trioctyl benzene-1,2,4-tricarboxylate and the compound as a whole would suggest the substance to be intrinsically biodegradable, therefore satisfying condition a). This is seen in the EPISUITE BIOWIN v4.10 results for trioctyl benzene-1,2,4-tricarboxylate and its lower and higher TM4 and TM10 analogues, where rapid aerobic biodegradation is predicted for all three structures on the basis that they all contain linear C4 terminal chain [CCC-CH3] and ester [-C(=O)-O-C] fragments. Increasing molecular weight has the effect of lowering probability outcomes, but the effect is trivial, with all three structures predicted to be readily biodegradable, thereby supporting the conclusion that trioctyl benzene-1,2,4-tricarboxylate is readily biodegradable.

More importantly, experimental test data are available for analogue substances for read-across to trioctyl benzene-1,2,4-tricarboxylate, the outcomes of which are additionally influenced by factors b) and c). Available data for tributyl benzene-1,2,4-tricarboxylate (Polynt-IT: 001 Key | Experimental result) show that the core benzene-1,2,4-tricarboxylate entity is readily biodegradable, even under MITI I (OECD 301C) conditions, when dosed in the test system at 100 mg/L. Straight-chain aliphatic alcohols are also readily biodegraded and extending the substituent butyl groups linearly by a further two or four -CH2 units to trihexyl benzene-1,2,4-tricarboxylate (Vertellus-UK: S-01) and trioctyl benzene-1,2,4-tricarboxylate would not be expected to introduce a structural hindrance to biodegradation of the substituent alkyl chains.

However, it is noted that incremental extension of the alkyl chains quickly leads to lower aqueous solubility, thereby influencing bioavailability of the test substance to the microbial inoculum as determined by water solubility. The most soluble, short alkyl chain analogue tributyl benzene-1,2,4-tricarboxylate was completely mineralised (88% in 28 d, based on ThOD) and classified as readily biodegradable in the OECD 301C (MITI I) test, whereas trioctyl benzene-1,2,4-tricarboxylate was not (3% in 28 d, based on ThOD) under identical conditions. Both tests are considered reliable and the collection and preparation of the MITI inoculum is understood to be under centralised control, with distribution to Japanese test facilities following completion of the 3-month adaptation period. Inter-laboratory variation in the composition and biochemical activity of the inoculum was therefore most likely not a decisive factor in the disparate test outcomes. A much higher degree of biodegradation (65% in 28 d based on oxygen consumption, concluding ready biodegradability but failing the 10-d window) was achieved for trioctyl benzene-1,2,4-tricarboxylate by applying the van Ginkel modification of the OECD 301D Closed Bottle Test, with a reduced concentration (2 mg/L as opposed to 100 mg/L in OECD 301C), substitution of the standard, synthetic mineral salts medium with a natural river water containing an indigenous microflora already adapted to its environment, and the application of a poorly degradable dispersing surfactant (Tween 80) to enhance test substance bioavailability.

Moreover, the proposed ester cleavage mechanism that represents the key first step in the biodegradation of TM8 entails the release of 1-octanol and trimellitic acid, and reliable studies are available for octan-1-ol (Kao Chemical Europe S.L.-ES: 001 Key | Experimental result) and trimellitic acid (Polynt-IT: 001 Key | Experimental result) which conclude that both substances are readily biodegradable.

Key value for chemical safety assessment

Additional information

In accordance with REACH Regulation 1907/2006/EC (Annex IX - 9.2.1.2 & 9.2.1.4 - column 2) simulation tests of biodegradation in water and sediment do not need to be conducted as the substance can be regarded as biodegradable via common microbial pathways although the rate of degradation is likely to be limited due to limited bioavailability as a result of low water solubility.