Phosphoric acid, P,P'-[2,2-bis(chloromethyl)-1,3-propanediyl] P,P,P',P'-tetrakis(2-chloro-1-methylethyl) ester

Adsorption / desorption

Key value for chemical safety assessment

Koc at 20 °C:

245

Additional information

Read Across with 2,2 -bis(chloromethyl)trimethylene bis[bis(2-chloroethyl)phophate.

Weight of evidence

The understanding of the adsorption behaviour of 2,2-bis(chloromethyl)trimethylene bis(bis(2-chloroethyl)phosphate), and the structurally-related substances Tris[2-chloro-1-(chloromethyl)ethyl] phosphate (TDCP) and Tris(2-chloro-1-methylethyl) phosphate (TCPP), is based on the following data:      -Measured adsorption coefficient in soils, sediment and sludge for TDCP, in accordance with OECD guideline 106

        -Estimated adsorption coefficient by HPLC measured with all three substances, in accordance with EU Method C.19

        -Prediction by standard QSAR methods, from the EU Technical Guidance Document (TGD).

 

The Koc of the structurally-related substance TDCP has been determined to be 1780 in a reliable study. The Koc of TDCP predicted using the TGD equation for phosphates is 950 and using the 'hydrophobics' equation is 1230. These are somewhat lower than the measured value, suggesting that TDCP is adsorbing to organic matter more strongly than predicted by these equations.

 

From the OECD 106 study on TDCP, a regression equation was derived, in order to derive a Koc also for the test substance. Based on the measured log Kow of 3.69 and the measured log Koc of 3.25 from the OECD 106 study, the following empirical relationship can be derived:

log Koc = -0.44 + log Kow

 

It is assumed that the same relationship can be applied to 2,2-bis(chloromethyl)trimethylene bis(bis(2 -chloroethyl)phosphate)

Applying the same equation (with the Log Kow of 2.83), gives the result : log Koc = 2.39, Koc = 245.

The basis of such an approach is the structural analogy between the substances and is justified because the most reliable information of the whole dataset is the measured Koc of TDCP.

 

The result of the HPLC adsorption-desorption screening test (EC method C.19) is Koc - 1.1 x 10exp4, log Koc = 4.04 for 2,2-bis(chloromethyl)trimethylene bis(bis(2-chloroethyl)phosphate. This value applies to the main component and would not have been affected by the impurities present.

 

For the substance TDCP it was found that the HPLC test resulted in a 7-fold higher Koc than was found in the OECD 106 study. This suggests some specific interaction with the HPLC column, possibly involving the phosphate group, had occurred; binding to the natural substrates in the OECD 106 test system was much lower than to the HPLC column substrate. This interpretation is further supported in that 2,2-bis(chloromethyl)trimethylene bis(bis(2-chloroethyl)phosphate), which has 2 phosphate groups, is the substance for which the HPLC estimate is most out of line, relative to the Kow. Adsorption behaviour in the OECD 106 study was proportional to organic carbon content as expected suggesting that adsorption to components other than organic carbon was not significant.

 

The TGD gives a method for estimating the value of Koc based on log Kow. The most appropriate equation is that for phosphates:

Log Koc = 0.49 log Kow + 1.17 (n=41, r2 = 0.73, s.e. = 0.45)

The log Kow = 2.83 +/- 0.05. From the above equation, Koc = 360.3 (range 340.6 - 381.2).

The HPLC-estimated Koc value is somewhat higher than the predicted value from the TGD method. This is consistently true for this group of substances.  

 

Conclusions:

The estimates from HPLC are consistently out of line with the other approaches. Both the phosphates and hydrophobics equations predict statistically similar Koc values to the value derived using the OECD 106 measured value for TDCP. It is considered that the uncertainty in reading across from TDCP to 2,2-bis(chloromethyl)trimethylene bis(bis(2-chloroethyl)phosphate) is less than or similar to the uncertainty in applying the QSAR methods, especially given the relatively low value of r2 for the phosphates equation.

 

This leads to a Koc of 245 for 2,2-bis(chloromethyl)trimethylene bis(bis(2-chloroethyl)phosphate)

 

The following partition coefficients are derived from this value, using default conversion factors:

 

Partition coefficient	Symbol	Values used
Organic carbon - water partition coefficient	Koc	245 l/kg
Solids - water partition coefficient for soil	Kpsoil	4.9 l/kg
Solids - water partition coefficient for sediment	Kpsed	12.2 l/kg
Solid - water partition coefficient for suspended matter	Kpsusp	24.5 l/kg
Soil - water partition coefficient	Ksoil-water	7.55 m^3/m^3
Sediment - water partition coefficient	Ksed-water	6.93 m^3/m^3
Suspended matter - water partition coefficient	Ksusp-water	7.03 m^3/m^3

 

 

References:

- European Commission (2003),Technical Guidance Document on Risk Assessment (TGD). 2^ndedition, Part II

- European Union Risk Assessment Report "2,2-Bis(chloromethyl)trimethylene bis[bis(2-chloroethyl)phophate]" (V6), CAS 38051-10-4, May 2008

- European Union Risk Assessment Report“tris[2-chloro-1-(chloromethyl)ethyl] phosphate” (TDCP), CAS 13674-87-8, May 2008