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Environmental fate & pathways

Adsorption / desorption

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adsorption / desorption: screening
Type of information:
Adequacy of study:
key study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
Justification for type of information:
Individual model KOCWIN included in the Estimation Programs Interface (EPI) Suite.

2. MODEL (incl. version number)
KOCWIN v2.00 included in EPISuite v 4.11, 2000-2012.

A CAS NUMBER was entered in the initial data entry screen. In the structure window, the molecular weight, structural formula and the structure of the input SMILES notation is shown.

a. Defined endpoint: Organic carbon partition coefficient, given as log Koc.
b. Dependent variable: KOCWIN estimates log Koc with two separate estimation methodologies:
(1) Estimation using first order Molecular Connectivity Index (MCI),
(2) Estimation using log Kow (octanol-water partition coefficient)
c. Algorithm:
Log Koc according to MCI method is calculated using the formula:
log Koc = 0.5213 MCI + 0.60 + ΣPfN
(ΣPfN is the sum of all relevant correction factor coefficients multiplied by the number (N) of that factor in each chemical structure)
Log Koc according to the log Kow method is calculated using two formulas (depending on the polarity of the substance):
log Koc = 0.8679 log Kow - 0.0004 (Non-polar substances)
log Koc = 0.55313 log Kow + 0.9251 + ΣPfN (polar substances)

d. Descriptor values:
Log Kow method:
The independent variable input parameter (log Kow) can be either be estimated directly by the programme using the related model KOWWIN v1.68 input model or can be user-entered based on measured experimental data, as applicable.

e. Applicability domain: The minimum and maximum values for molecular weight are the following:
Training Set Molecular Weights: 32.04-665.02 g/mol,
Validation Set Molecular Weights: 27.03-991.15 g/mol

f. Statistics for goodness-of-fit:

Statistical accuracy of MCI methodology for training and validation set:
i. Training without corrections:
Number: 69
R^2 correction coefficient: 0.967
Standard deviation (log Koc): 0.247
Average deviation (log Koc): 0.199

ii. Training with corrections:
Number: 447
R^2 correction coefficient: 0.900
Standard deviation (log Koc): 0.340
Average deviation (log Koc): 0.273

iii. Validation data set:
Number: 158
R^2 correction coefficient: 0.850
Standard deviation (log Koc): 0.583
Average deviation (log Koc): 0.459

Statistical accuracy of Log Koc methodology:
i. Training without corrections:
Number: 68
R^2 correction coefficient: 0.877
Standard deviation: 0.478
Average deviation: 0.371

ii. Training with corrections:
Number: 447
R^2 correction coefficient: 0.855
Standard deviation (log Koc): 0.396
Average deviation (log Koc): 0.307

iii. Validation data set:
Number: 150
R^2 correction coefficient: 0.778
Standard deviation (log Koc): 0.679
Average deviation (log Koc): 0.494

g. Mechanistic interpretation: Log Koc is estimated based on the likeliness of a substance for sorption to surfaces of soil/sediment particles. This characteristic is triggered by lipophilic character of substances but may be modified by certain molecular fragments that need to be considered by application of correction factors. The Log Koc is a physical inherent property used extensively to describe a chemical’s likeliness to adsorb to organic carbon.
h. The uncertainty of the prediction (OECD principle 4): Tris(2-ethylhexyl) phosphate is not highly complex and the rules applied for the substance appear appropriate. An individual uncertainty for the investigated substance is not available.

a. Descriptor domains:
i. Molecular weights: With a molecular weight of g/mole the substance is within / out of the range of the training set (32 - 665 g/mol) as well as in the range of the validation set (27 -– 991 g/mol).
ii. Structural fragment domain: Regarding the structure of Tris(2-ethylhexyl) phosphate the fragment descriptors found by the program are complete. For log Koc estimation according to MCI method and log Kow method, one fragment descriptor was applied (OrganoPhosphorus, aliphatic). For estimation of log Koc according to log Kow method the log Kow estimated directly by the programme using the related model KOWWIN v1.68 input model was used.
iii. Mechanism domain: No information available.
iv. Metabolic domain: Not relevant.
b. Structural analogues: not applicable
i. Considerations on structural analogues: not applicable

a. Regulatory purpose: The data may be used under any regulatory purpose.
b. Approach for regulatory interpretation of the model result: If no experimental data are available, the estimated value may be used to fill data gaps needed for hazard and risk assessment, classification and labelling and PBT / vPvB assessment. Further the value is used for other calculations.
c. Outcome: The prediction of organic carbon partition coefficient yields a useful result for further evaluation.
d. Conclusion: The result is considered as useful for regulatory purposes.
other: REACH Guidance on QSARs R.6
Principles of method if other than guideline:
Estimation Program Interface EPI-Suite version 4.11: KOCWIN (v2.00) for the estimation of the organic carbon-normalized sorption coefficient for soil and sediment (Koc).
The Estimation Program Interface was developed by the US Environmental Agency's Office of Pollution Prevention and Toxics, and Syracuse Research Corporation (SRC). © 2000 - 2012 U.S. Environmental Protection Agency for EPI SuiteTM (Published online in November 2012).

Scientific Papers:
Boethling R.S., Howard PH and Meylan W. 2004, Finding and estimating chemical property data for environmental assessment. Environ. Toxicol. Chem. 23: 2290-3308).
Doucette, W.J.  2000.  Soil and sediment sorption coefficients.  In: Handbook of Property Estimation Methods, Environmental and Health Sciences. R.S. Boethling & D. Mackay (Eds.), Boca Raton, FL: Lewis Publishers (ISBN 1-56670-456-1). 
Meylan, W., P.H. Howard and R.S. Boethling.  1992.  Molecular topology/fragment contribution method for predicting soil sorption coefficients. Environ. Sci. Technol. 26: 1560-1567.
Sabljic, A. 1984.  Predictions of the nature and strength of soil sorption of organic pollutants by molecular topology. J. Agric. Food Chem. 32:243-246.
Sabljic, A. 1987.  On the prediction of soil sorption coefficients of organic pollutants from molecular structure: application of molecular topology model. Environ. Sci. Technol. 21:358-66.
Sabljic, A., H. Gusten, H. Verhaar and J. Hermens.  2005.  QSAR modeling of soil sorption. Improvements and systematics of log Koc vs. log Kow correlations. Chemosphere 31:4489-4514. (see also Chemosphere 33: 2577).
Schuurmann, G., R. Ebert and R. Kuhne.  2006.  Prediction of the sorption of organic compounds into soil organic matter from molecular structure. Environ. Sci. Technol. 40:7005-7011
Software Package:
Estimations Programs Interface for Windows (EPI Suite) v4.11 (November 2012)
Available at:
GLP compliance:
Type of method:
other: Estimation
Specific details on test material used for the study:
Key result
2 468 000 L/kg
Remarks on result:
other: QSAR predicted value
MCI Method
1 895 000 L/kg
Remarks on result:
other: QSAR predicted value
KOW Method

KOCWIN predicted that tris(2 -ethylhexyl) phosphate has a Koc = 2.468E+06 L/kg, when using the MCI method.

KOCWIN predicted that tris(2 -ethylhexyl) phosphate has a Koc = 1.895E+06 L/kg, when using the log Kow method.

KOCWIN predicts a KOC value of 2.468E+06 L/kg for the registered substance, based on the first-order Sabljic molecular connectivity index (MCI), and a KOC value of 1.895E+06 L/kg based on the log Kow methodology.

Executive summary:

The adsorption coefficient (KOC) of the registered substance was estimated using the KOCWIN v2.00 QSAR model available from the US EPA.

The estimated adsorption coefficient of the registered substance, based on the first-order Sablljic molecular connectivity index is 2.468E+06 L/kg. Additionally, log Kow methodology predicted a KOC value of 1.895E+06 L/kg, for the registered substance.

According to the Koc values, the registered substance is considered as immobile in soils (McCall et al. 1981).

McCall P.J., Laskowski D.A., Swann R.L., and Dishburger H.J., (1981), “Measurement of sorption coefficients of organic chemicals and their use, in environmental fate analysis”, in Test Protocols for Environmental Fate and Movement of Toxicants. Proceedings of AOAC Symposium, AOAC,Washington DC.

Description of key information

KOCWIN predicted that tris(2 -ethylhexyl) phosphate has a Koc = 2.468E+06 L/kg, when using the MCI method.

KOCWIN predicted that tris(2 -ethylhexyl) phosphate has a Koc = 1.895E+06 L/kg, when using the log Kow method.

Key value for chemical safety assessment

Koc at 20 °C:
10 000

Additional information

Two acceptable (Q)SAR predictions for tris(2 -ethylhexyl) phosphate indicate that the soil adsorption coefficient (Koc) is >10,000 L/kg. When used in exposure modelling, a Koc of 6,000 L/kg results in close to 99 % adsorption and doesn't significantly rise with increasinf Koc. Therefore, the generally accepted limit value of Koc = 10,000 L/kg is used for chemical safety assessment, which is the limit value for EUSES modelling.

[LogKoc: 4.0]