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Suitable studies are presented in support of the ready biodegradation status as follows:

 

Key study;

Bayer 1987 [K1 - key]

Allocated K1. 

Method: OECD Guideline 301 C (Ready Biodegradability: Modified MITI Test (I)):

result: 80% degradation in 28-days.

Notes: Conducted on commercially available TCP; isomeric composition not specified, - (synthesised from 70% m-, 30% p-cresol, only traces of o-cresol (<0.05 wt%) present in starting reagents);

 

Supporting studies:

 

Allocated K2

Method: River die-away method; Semicontinuous Activated Sludge (SCAS) Method; Die-away test with acclimated bacterial seed

Results: %Degr.  

> 97 4 wk; (SCAS); addition rate 3 mg/l

> 99 4 wk; (SCAS); addition rate: 13 mg/l

82.1 4 wk; 

78.6 7 d                        

Notes: Conducted on commercially available TCP; isomeric composition not specified

 

Allocated K2

Method: OECD Guideline 302 C (Inherent Biodegradability: Modified MITI Test (II))

Results: %Degr.  

65.7; O2 consumption; 4 wk  

82.6; Test mat. analysis; 4 wk;        GC-analysis

81.6; Test mat. analysis; 4 wk;        UV-VIS analysis

                            

Notes: Conducted on o-TCP; an isomer of commercially available TCP at the time the test was conducted. Note that this isomer is not present in commercially available TCP in current day commercial TCP; however it is considered an appropriate indicator of the propensity of the isomers of TCP to biodegrade in appropriate study conditions.

 

Allocated K2

Method: OECD Guideline 302 C (Inherent Biodegradability: Modified MITI Test (II))

Results: %Degr.  

100; O2 consumption; 4 wk   

100; Test mat. analysis; 4 wk;GC-analysis

81.6;Test mat. analysis; 4 wk;UV-VIS analysis

                            

Notes: Conducted on p-TCP; an isomer of commercially available TCP at the time the test was conducted.. Note that this isomer is a minor component in current day commercially available TCP; however it is considered an appropriate indicator of the propensity of the isomers of TCP to biodegrade in appropriate study conditions.

 

Allocated K3

Method: OECD Guideline 301 D (Closed Bottle test)

Results: %Degr.  

24.2; O2 consumption; 28 d; based on its ThODNH4s

 

Notes: GLP study conducted to recognised guidelines. However, OECD 301D Guideline states that insoluble and volatile substances may be assessed using this method provided that precautions are taken. Degradation values for insoluble substances may be falsely low unless the bottles are agitated periodically during the incubation. No agitation was undertaken during the study. As a result, and given the information on the analogue materials, it is considered that the lack of agitation has affected the outcome of the studies. This study is therefore deemed "not reliable" when considering the propensity of this material to biodegrade.

 

Supporting K2 - Ku, Y. & Alvarez, G. H 1982.; Biodegradation of [14C]Tri-p-Cresyl Phosphate in a Laboratory Activated-Sludge System

Results: %Degr.  

In 24-h experiments, 70 to 80% of tri-p-cresyl phosphate, added at the 1 ug/ml ,level was degraded. The average overall recovery of added radioactivity was 84%.

 

Supporting K2 - Kawagoshi, Y et al. 2002; Degradation of organophosphoric esters in leachate from a sea-based solid waste disposal site

Results: %Degr.  

Tricresyl phosphate, in leachate rapidly decreased to less than the detection limit within 20 days under aerobic condition, suggesting high biodegradability.                        

 

In addition, this material has been assessed by the UK Environment Agency, in their report references as “Environmental risk evaluation report: Tricresyl phosphate (CAS no. 1330-78-5)”. This report is available at:https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/290861/scho0809bquj-e-e.pdf

 

This report lists the following additional data endpoints for consideration:

 

WHO (1990) reports that several old (1960s) SCAS studies showed a high level of degradation (around 99 per cent) over a 24-hour period at a feed level of 3 to 13 mg/l.

 

IUCLID (1998) reports that Ishikawaet al.(1985a) found around 60 per cent

degradation of tricresyl phosphate after two days using unacclimated activated sludge and around 90 per cent degradation after two days using acclimated activated sludge.

 

Boethling and Cooper (1985) report the results of an unpublished study using tri-ocresyl phosphate and a commercial tricresyl phosphate. In this study, activated sludge mixed liquor was acclimated to progressively higher concentrations of the test substance. At the start of the test, the acclimated liquor was diluted 1:10 with a mineral salts medium and the test substance was added as the sole source of carbon. The initial concentrations used were 271 mg/l for tri-o-cresyl phosphate and 524 mg/l for the commercial tricresyl phosphate and the substances were 98 per cent and 87 per cent degraded respectively within seven days. The same report indicates that tri-o-cresyl phosphate was found to be extensively degraded in a river die-away test over seven days (97 per cent degraded in seven days). The half-life for commercial tricresyl phosphate in the river die-away test was around three days.

 

Xing and Raetz (2001) showed that tricresyl phosphate, as part of a contaminated ground water (contaminated with phenols and benzene, toluene, ethylbenzene and xylene (BTEX)), was effectively biodegraded using a bench-scale pressurised fluidised bed reactor. The reactor was initially seeded with mixed phenol-degrading bacteria. The system was found to degrade tricresyl phosphate from an influent concentration of 2,500μg/l to an effluent concentration of below 40μg/l (above 98 per cent removal). The effect of temperature and redox potential on the degradation of several phosphate esters, including tri-m-cresyl phosphate, in two natural sediments was investigated by

 

Hattoriet al.(1981, cited in WHO 1990) investigated the degradation of tricresyl phosphate in river water and sea water from Osaka, Japan. The substance was tested at an initial concentration of 1 mg/l. Tricresyl phosphate was found to degrade rapidly in river water after a lag period of one to two days, and was almost completely degraded within five days. No degradation was seen over 15 days in heat sterilised river water indicating that the degradation seen was due mainly to biotic processes. In contrast to this, tricresyl phosphate was found to degrade only slowly in sea water.

 

Boethling and Cooper (1985) estimated that the removal of tricresyl phosphate during biological waste water treatment at a production plant in the United States was 96 per cent, based on the average concentration in waste water (6.23 mg/l) and the average concentration in effluent from the treatment plant (0.23 mg/l). The removal was thought to be due to biodegradation since air stripping was not thought to be an important removal mechanism, and sludge wastage was not practiced at the facility. However, it was also indicated that the results of this study should be treated with caution as the recoveries found for the effluent samples were generally much lower than found for the waste water samples (27 per cent overall versus 89 per cent overall). Thus, the concentrations in the effluent may have been higher than indicated (and hence the removal lower than indicated).

 

QSAR- The UM-BBD Minnesota University model is not a model widely used in the context of regulatory ecotoxicity. It is mainly used for scientist and researchers. The UM-BBD thus represents the current state of knowledge in order to get information about the biodegradation pathway. Although the substance is known to be readily biodegradable, a prediction of the biodegradation pathway was performed using the EAWAG/University of Minnesota model:

 

The main pathways for primary degradation predicted by the model are:

1. Hydroxylation at one of the phenyl rings leading to a dihydroxylated structure (likely pathway)

2. Cleavage of 1 ester group leading to cresol and to a phosporic acid di-ester (likely pathway)

3. Hydroxylation at one of the alkyl (here: methyl) groups (neutral pathway)

 

Thus it is shown that the Minnesota model predicts the same biodegradation pathway for Tris-methylphenyl phosphate (TCP) and for Tris-isopropylphenyl phospate (TIPPP).

 

On the basis of the above data set, it is proposed that the isomers of TCP will undergo significant biodegradation under relevant conditions. The substance is considered to be readily biodegradable.

 

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