Tris(methylphenyl) phosphate

Endpoint summary

Additional information

The test substance, TCP, is a liquid under all environmental conditions and only sparingly soluble in water. It has a low volatility (based on a vapour pressure result of 0.0002 Pa at 25 °C). As such, any environmental release will result in virtually all of the substance compartmentalising into soil and water compartments, with little release directly to atmosphere. Any potential exposure to the environment would result in rapid redistribution from soil and water due to its volatility. The high adsorption to soil (based on the soil adsorption study, discussed below) indicates that the majority of the substance will partition to soil and sediment rather than water should it be released to the environment. 

This is supported by a Level III fugacity model in the US EPA EPISUITE (Mackay,) which assumes steady-state but not equilibrium conditions. The Level III model in EPI Suite predicts partitioning between air, soil, sediment and water using a combination of default parameters and various input parameters. This model has been used to calculate the theoretical distribution of the main isomers of the substance between four environmental compartments (air, water, soil, sediment) at steady state in a unit world.

Partitioning is detailed to be:

	Mass Amount (%)
	tri-m-tolyl phosphate	Di-m Cresyl p Cresyl Phosphate	Di-p Cresyl m Cresyl Phosphate
Air	0.354	0.521	0.636
Water	9.89	8.26	8.25
Soil	66.2	71.6	71.5
Sediment	23.5	19.6	19.6

 It is proposed that as the majority of the substance distributes to the soil compartment; and the low solubility in water, this indicates that the substance is likely to persist in this compartment rather than distribute to the soil pore water.

The substance is considered to be readily biodegradable. The key study, OECD 301C (Bayer 1987) gave 80% biodegradation within 28 days. Further evidence is presented in two inherent biodegradation tests (both MITI 1992) with biodegradation of ca. 80 to 100% after 28 days observed. Saeger (1979)shows >97% primary biodegradation after 28 days and 82% ultimate biodegradation, the latter performed with adapted sludge. There are also numerous additional studies that indicate biodegradation effects, both inherent and ultimate.On the basis of the available data set, it is proposed that the isomers of TCP will undergo significant biodegradation under environmentally relevant conditions.An additional contributor to environmental removal is that the fact that the substance will also hydrolyse slowly under normal environmental conditions.  Experimental studies on hydrolytic effects demonstrated that the substance does undergo hydrolysis at environmentally relevant pH’s, with a half life of 44 days at pH 7. As such, some degradation can also be anticipated via this route. There is also a study available that demonstrated that the substance underwent rapid hydrolysis within a lake water type environment after an initial lag period of approximately 48 h, the substance was shown by GLC-FPD to have completely disappeared after 120 h. 

No specific information on the hydrolysis of the individual above components is available; however assessment using the EPISUITE HYDROWIN v2.00 tool provides the following results:

 

pH	Estimated half life
	tri-m-tolyl phosphate	Di-m Cresyl p Cresyl Phosphate	Di-p Cresyl m Cresyl Phosphate
5	170.7 years	210.9 years	259.1 years
6	18.02 years	21.89 years	26.59 years
7	1.812 years	2.198 years	2.666 years
8	66.17 days	80.25 days	97.33 days
9	6.617 days	8.025 days	9.733 days
10	15.88 hrs	19.26 hrs	23.36 hrs

 

The above QSAR results endorse the conclusion of the test conducted that the hydrolysis rate of commercial TCP products are pH dependant, but are somewhat higher for results at pH 7 than those noted within the test.

 

TCP has a measured log Pow of 5.93. This value indicates that possible bioaccumulation in the food chain could be anticipated. However, review of the data set for the substance, which includes existing literature data and effective QSAR determination concludes that the substance is not bioaccumulative.  On the basis of a weight of evidence approach, there is sufficient information available to state that the substance is not bioaccumulative. Whilst it is not possible to provide a definitive BCF value for the substance, due to the variation in the results, none of these are above the threshold value quoted in the Regulation of 2000 or 5000 which indicates the potential to bioaccumulate.  A summary of the results is as follows:

  

Endpoint study	Result (BCF)	Notes
EPIWIN BCFBAF Results [L/kg]	568.5	None
BCF Read-Across (version 1.0.2) [L/kg]	127-128	None
BCF model (CAESAR) (version 2.1.13) [L/kg]	77	None
BCF model (Meylan) (version 1.0.0)	1064	None
US EPA (T.E.S.T) v4.1	83.09 – 95.92
Bengtsson et all - Bioaccumulation and effects of some technical triaryl phosphate products in fish and Nitocra spinipes - Alburnus alburnus	>= 400 — <= 800
Muir Et Al; Environmental Dynamics Of Phosphate Esters. Comparison Of The Bioconcentration Of Four Triaryl Phosphates By Fish	>= 1162 — <= 1653*	Initial rate (mTCP)
	>= 596 — < 784	static test (mTCP)
	>= 385 — <= 1102	Biofac (mTCP)
	>= 2199 — <= 2768*	Initial rate (pTCP)
	>= 928 — <= 1420	static test (pTCP)
	>= 588 — <= 1466	Biofac (pTCP)
	>= 709 — <= 770	static test (p-TCP)
	>= 310 — <= 462	static test (m-TCP)
Veith et al (1979) – assessment of commercial TCP in Fathead minnows (pimephales promelas)	165
Sitthichaikasem (1978) – assessment of p-isomer in Bluegill (Leptomis macrochirus)	1589

 

*The authors states the results of the initial rate as less valid as the substance decreased rapidly in the water phase.

In addition, this material has been assessed by the UK Environment Agency Member State Authority, 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

 

The position of theUK Environment Agency Member State Authority is that this substance is not bioaccumulative.For the purposes of assessment, a BCF value of 800 is applied.

 A screening organic carbon-water partitioning coefficient (Koc) is available for the substance, using a HPLC Estimation method. This resulted on a log Koc value of 4.31 at 25 °C with Koc of 20489. This is indicative of a moderate to high potential to bind tightly to soils and sediments. Such a potential indicates that the substance would bind tightly to soils and sediments and thus, reduce overall exposure potential to pelagic aqueous organisms. While no specific biomagnification study is available the data set indicates that it is not expected to biomagnify into higher trophic pelagic aqueous organisms.

Based on high biodegradability and low bioaccumulation potential, it can be concluded that the substance is not persistent within the environment. Biodegradation and abiotic effects within the environment will result in rapid removal from the environment and hence significant contact with the organisms in the food chain can considered to be minimised.

Finally, the substance demonstrates low acute toxicity in mammalian studies, but some extended effects in prolonged studies. However, effects due to exposure via the environment are not anticipated, as the substance is not persistent, nor can it enter the food chain via bioaccumulation.