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Discussion of potentially applicable B criterion for PBT assessment

A study on the bioaccumulation potential of the substance is not required for a registration in the tonnage band 10 - 100 t p.a.. As the substance however fulfils (v)P screening assignment criteria, as well as T criteria, the endpoint bioaccumulation should be assessed with reference to the vPvB and PBT discussion.

Measured log Kow data

The available information on the octanol-water partition coefficient of the submission item indicates log Kow >6.2 (study of O'Connor 2002) and tends thus to show that the substance may have the potential to bioaccumulate. It has however to be stressed that this log Kow measurement was conducted via the HPLC method at pH 11, i.e. the log Kow of the non-ionised form of the different components of the substance was being determined. As will be shown below, at the environmentally relevant pH range 5 - 9 the ionised forms of the substance are the prevailing substance species, which subsequently leads to lower bioaccumulation potential estimates.

Computed BCF data (based on log Kow values for non-ionised substance species)

For PBT discussions under the REACH Regulation, a log BCF of 3.3 is the cut-off value for the applicability of the B criterion. Table 1 demonstrates the estimated log BCF values for the three major components (total compositional proportion > 90 %) of the submission item (computation via BCFWIN, EPI Suite 4.1). For component 1, which has a compositional proportion of ca. 50 %, the calculated log BCF is rather small with 1.37. For the two other major components the calculated log BCF values (2.99 and 2.82, respectively) are already rather close to the regulatory cut-off value for the B criterion of log BCF 3.3. The BCFWIN-computed data still can be considered as valid, as they include a number of worst case assumptions, as will be demonstrated below.

Table 1: Log BCF values as computed via BCFWIN (EPI Suite 4.1)

Component

1

2

3

CAS registry number

404825-11-2

111182-04-8

404825-12-3

Compositional proportion in [%]

ca. 47 %

ca. 32 %

ca. 13 %

Log BCF

1.37

2.99

2.82

Log Kow values used for calculation (non-ionised substance species)

2.59

5.03

4.78

Equation used to calculate: Log BCF = 0.6598 log Kow - 0.333 + Correction(s)

(No Applicable Correction Factors)

Computed pKa data

As log Kow values for non-ionised substance species are higher than the log Kow values for ionised species, the BCF-computations based on non-ionised log Kow values subsequently tend to produce higher log BCF values (i.e. leading to worst case estimates).

Table 2 however demonstrates that within the environmentally relevant pH range 5 - 9, for all three major components the fully (double) protonated form is dominating the system (Marvin Sketch version 5.3.6). Only between pH 8.5 and pH 9 the percentages of partially (single) protonated forms and of the non-ionised forms are gaining.

Table 2: Microspecies distribution estimate based on pKa data as computed via Marvin Sketch version 5.3.6

pH

Component 1

Component 2

Component 3

Frequency of protonated molecule sites at respective pH value [%]

0

1

1

2

0

1

2

0

1

1

2

5.00

0.00

0.00

0.00

99.99

0.00

0.00

100

0.00

0.00

0.00

99.99

6.00

0.00

0.02

0.04

99.94

0.00

0.03

99.97

0.00

0.01

0.04

99.95

7.00

0.00

0.17

0.39

99.45

0.00

0.34

99.66

0.00

0.11

0.41

99.47

8.00

0.05

1.61

3.67

94.67

0.02

3.28

96.70

0.04

1.07

3.95

94.94

8.20

0.13

2.47

5.64

91.76

0.06

5.10

94.84

0.09

1.64

6.08

92.19

8.40

0.31

3.72

8.52

87.44

0.14

7.84

92.02

0.21

2.49

9.21

88.09

8.60

0.73

5.48

12.54

81.24

0.35

11.86

87.80

0.49

3.68

13.63

82.20

8.80

1.65

7.79

17.81

72.76

0.81

17.49

81.70

1.11

5.26

19.48

74.15

9.00

3.53

10.50

24.03

61.94

1.83

24.87

73.31

2.41

7.17

26.58

63.84

10.00

46.40

13.82

31.62

8.15

36.19

49.28

14.53

37.50

11.17

41.39

9.94

11.00

90.93

2.71

6.20

0.16

87.70

11.94

0.35

87.50

2.61

9.66

0.23

12.00

99.03

0.30

0.67

0.00

98.65

1.34

0.00

98.62

0.29

1.09

0.00

13.00

99.90

0.03

0.07

0.00

99.86

0.14

0.00

99.86

0.03

0.11

0.00

14.00

99.99

0.00

0.01

0.00

99.99

0.01

0.00

99.99

0.00

0.01

0.00

Computed Log D data

Based on the above, it is much more reasonable to use pH-depending log D values for PBT discussion, rather than log Kow values for the non-ionised species (which only are existing to some minor extent at pH 5 - 9).

Log D values are shown in Table 3. With computed log D values for the three major substance components of 1.22, 3.38, and 3.45, respectively (worst case scenario at pH 9), all these log D values are well below the value of 4.5, which is the cut-off value for the B screening assignment in PBT discussions.

Table 3: Log D data as computed by Marvin Sketch version 5.3.6

pH

Component 1

Component 2

Component 3

5.00

-3.57

-1.34

-1.43

5.50

-3.51

-1.29

-1.36

6.00

-3.34

-1.15

-1.18

6.50

-2.97

-0.81

-0.78

7.00

-2.33

-0.21

-0.13

7.50

-1.50

0.61

0.72

8.00

-0.57

1.53

1.65

8.50

0.36

2.48

2.58

9.00

1.22

3.38

3.45

10.00

2.34

4.68

4.64

11.00

2.63

5.06

5.01

12.00

2.67

5.11

5.06

13.00

2.67

5.12

5.07

14.00

2.67

5.12

5.07

Computed BCF data (based on log D values for ionised substance species)

In Table 4 the computed log BCF values are shown, which are based on pH-dependent log D data (Table 3). The data are demonstrated for pH 9, which is the worst case when referring to the environmentally relevant pH range 5 - 9. The log D-based BCF estimates are all well below the regulatory cut-off value for the B criterion of 3.3.

Table 4: Log BCF values as computed via the equation used by BCFWIN (EPI Suite 4.1)

Component

1

2

3

CAS registry number

404825-11-2

111182-04-8

404825-12-3

Compositional proportion in [%]

ca. 47 %

ca. 32 %

ca. 13 %

Log BCF

0.36

1.9

1.94

Log D values at pH 9 (see Table 3) used for calculation of (partially) ionised substance species

1.22

3.38

3.45

Equation used to calculate: Log BCF = 0.6598 log D - 0.333 + Correction(s)

(No Applicable Correction Factors)

Conclusions on the applicability of the B criterion for potential PBT discussions

The submission item shall not be considered to fulfil the B criterion of PBT substances, based on the following:

1) BCFWIN computations lead to log BCF results of 1.37, 2.99, and 2.82, respectively, for the three major substance components. These results all below the cut-off value for the B criterion of log BFC 3.3 (BCF 2000).

These BCFWIN-computed data even are to be seen as worst case results (i.e. tendency of overestimation of the BCF results as computed via BCFWIN), as they include a number of worst case assumptions:

2) In the environmentally relevant pH range 5 - 9, the ionised species of the three major components of the submission item are prevailing, whereas the BCFWIN computation was based on log Kow estimates of the non-ionised species (Kow estimates for non-ionised species are higher than for the ionised species).

3) Computed pH-dependent log D values show clearly that these log D data within the environmentally relevant pH range 5 - 9 are much lower than the BCFWIN estimates for log Kow (and lower as the HPLC-based log Kow results, which also were being obtained with non-ionised substance species).

4) BCF computations based on log D values reveal log BCF results of 0.36, 1.9, and 1.94, respectively, which all are well below the regulatory cut-off value for the B criterion of 3.3.

With the evidence provided it safely can be assumed that the substance is not fulfilling the B criterion, and that the submission item therefore shall not be considered as a PBT or vPvB substance. Based on these grounds, a study on bioaccumulation can be waived, what further can be supported by the fact that (referring to the restricted industrial uses of the substance, and based on the high adsorption potential) a direct or indirect exposure to the aquatic environment is unlikely.