Trixylyl phosphate

Endpoint summary

Additional information

The test substance, trixylyl phosphate, 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 1.6 E-06 kPa at 20 °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 one of the possible isomers of trixylyl phosphate between four environmental compartments (air, water, soil, sediment) at steady state in a unit world.

Partitioning is detailed to be:

-        Air 2.4%

-        Water 29.7%

-        Soil 0.812%

-        Sediment 67.1%

 It should be noted that as the majority of the substance distributes to the sediment compartment; and the low solubility in water (measured at < 0.02 mg/l), this indicates that the substance is likely to persist in this compartment rather than distribute. Trixylyl phosphate displays a low ready biodegradability in that it achieved 14% biodegradation in a 28-day study closed bottle test, and a half life of > 60 days within fresh water.

 

The substance is also not expected to hydrolyse under normal environmental conditions.  Experimental studies on hydrolytic effects demonstrated that the substance was stable to hydrolysis at environmentally relevant pH’s, with a half life of > 1year days at pH 7. As such, negligible to nil degradation is anticipated via this route. Studies on direct phototransformation in water are not available but it is assumed on the basis of chemical structure that the substance is not degraded by direct photolysis. It is concluded, therefore, that abiotic processeswould not contribute significantly to the depletion of the substance within the environment. 

 

Trixylyl phosphate has a measured log Pow of >6.2, extrapolated to 6.38 via calculation. This value indicates that possible bioaccumulation in the food chain could be anticipated. However, review of the phosphates as a group, which included read across, existing literature data and effective QSAR determination concluded that the substance is not bioaccumulative.  A value BCF of 922 is therefore applied for the purposes of hazard assessment on the basis of the information available. The substance is not considered to be “bioaccumulative” or “very bioaccumulative” on the basis of the available data.

 

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 5.08 at 25 °C with Koc of 119941. As such, adsorption to soil is deemed to be high, based on this study assessment. Such a high potential indicates that the substance would bind tightly to soils and sediments and thus, reduce overall exposure potential to aqueous organisms. However, exposure related effects to sediment and soil dwelling organisms is considered to be minimal. This is on the basis of the existing classification and labelling as “hazardous” to the environment. Risk Management Measures ensure that there should be no release to the environment. Hence exposure is considered to be mitigated.

 

Based on its limited water solubility high partition coefficient and low biodegradability, it can be concluded that trixylyl phosphate could potentially be persistent within the environment. However, abiotic effects within the environment will result in eventual removal from the environment. The substance is also not considered to be bioaccumulative on the basis of the data available. Hence significant contact with the organisms in the food chain can considered to be minimised.

 

 Finally, trixylyl phosphate demonstrates low acute toxicity in mammalian studies, but some extended effects, in chronic studies. Effects on terrestrial organisms are not anticipated on the basis of the available data set.