C16-(branched), C20-(branched) and C24-(branched)-alkanes

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

(Q)SAR

Adequacy of study:

key study

Study period:

N/A

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with limited documentation / justification

Justification for type of information:

SOFTWARE
EpiSuite v4.11, US EPA, 2012

MODEL (incl. version number)
KOCWIN v2.00 (MCI method)

SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
- Defined endpoint: Koc
MCI (molecular connectivity index) method
The equation derived by the non-polar (no correction factor) regression is:
log Koc = 0.5213 MCI + 0.60
(n = 69, r2 = 0.967, std dev = 0.247, avg dev = 0.199)
for comparison, the previous version of PCKOCWIN used a very similar equation:
log Koc = 0.53 MCI + 0.62
Adding in the correction factor regression yields the final MCI equation:
log Koc = 0.5213 MCI + 0.60 + ΣPfN
where ΣPfN is the summation of the products of all applicable correction factor coefficients multiplied by the number of times (N) that factor is counted for the structure.

- Defined domain of applicability:
Currently there is no universally accepted definition of model domain. However, users may wish to
consider the possibility that log P estimates are less accurate for compounds outside the MW
range of the training set compounds, and/or that have more instances of a given fragment than the
maximum for all training set compounds. It is also possible that a compound may have a functional
group(s) or other structural features not represented in the training set, and for which no fragment
coefficient was developed. These points should be taken into consideration when interpreting
model results.

Training Set Molecular Weights:
Minimum MW: 32.04
Maximum MW: 665.02
Average MW: 224.4
Validation Molecular Weights:
Minimum MW: 73.14
Maximum MW: 504.12
Average MW: 277.8

- Appropriate measures of goodness-of-fit and robustness and predictivity:
Overall, the MCI methodology is somewhat more accurate than the Log Kow methodology, although both methods yield good results. If the Training datasets are combined in to one dataset of 516 compounds (69 having no corrections plus 447 with corrections), the MCI methodology has an r2, standard deviation and average deviation of 0.916, 0.330 and 0.263, respectively.

APPLICABILITY DOMAIN
- Descriptor domain: The components of the substance are within the molecular weight range of the training set compounds, and all fragments are represented in the training set. Thus, it is concluded, that the substance is within the applicability domain.
- Similarity with analogues in the training set: several linear and branched alkanes and alkenes, which are considered to be similar, are present in the training set.

ADEQUACY OF THE RESULT
The QSAR prediction is valid and of good reliability. Thus, the result is adequate for chemical safety assessment.

Qualifier:

according to guideline

Guideline:

other: Computer model

Principles of method if other than guideline:

The calculated value was determined using PCKOCWIN version 2.00, a subroutine within the computer program EPI SuiteTM version 4.0.

GLP compliance:

no

Radiolabelling:

no

Test temperature:

N/A

Analytical monitoring:

no

Computational methods:

The calculated value was determined using Soil Adsorption Coefficient Program (PCKOCWIN) version 2.00, a subroutine within the computer program EPI SuiteTM version 4.0.

PCKOCWIN estimates the soil adsorption coefficient (Koc) of organic compounds. Koc can be defined as "the ratio of the amount of chemical adsorbed per unit weight of organic carbon (oc) in the soil or sediment to the concentration of the chemical in solution at equilibrium" (Lyman, 1990); it is represented by the following equation (Lyman, 1990):

Koc = (ug adsorbed/g organic carbon) / (ug/mL solution)

Type:

Koc

Value:

51 910 000

Type:

log Koc

Value:

7.715

Validity criteria fulfilled:

yes

Conclusions:

Estimated Tetrabutane log Koc is 7.7.

Executive summary:

Estimated Tetrabutane log Koc is 7.7.

Description of key information

Estimated log Koc = 7.7 ( EpiSuite v4.11, US EPA, 2012; KOCWIN v2.00 (MCI method)).

Key value for chemical safety assessment

Koc at 20 °C:

7.7