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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail
Justification for type of information:
The Read Across Justification is attached in Section 13.
Reason / purpose:
read-across source
Qualifier:
according to
Guideline:
OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))
Version / remarks:
Adopted January 22nd, 2001
Deviations:
yes
Remarks:
mobile phase was changed
GLP compliance:
yes (incl. certificate)
Type of method:
HPLC estimation method
Test temperature:
25.0 °C
Details on study design: HPLC method:
EQUIPMENT
- Apparatus: HPLC-pumps (Waters 510), HPLC-autosampler (Waters 712 WISP).
- Type, material and dimension of analytical column: 250 mm x 3 mm, Nucleosil 100-5 CN (particle size 5 μm, pore size 100 Å), Macherey-Nagel. The analytical column (based on silica matrix) packed with a cyanopropyl (CN-) solid phase containing non-polar and polar moieites.
- Type, material and dimension of guard column: 8 mm x 3 mm, Nucleosil 100-5 CN (particle size 5 μm, pore size 100 Å), Macherey-Nagel.
- Detection system: UV-detector, Waters 484 Tunable Absorbance detector.

MOBILE PHASES
- Type: acetonitrile : water (containing 2 g/l NaH2PO4), 20 : 80 (% v/v).
- Experiments with additives carried out on separate columns: no.

ANALYSIS CONDITIONS
- Injection volume: 50 μl.
- Colum temperature: 25.0 °C.
- Run time: 40 min.
- Flow: 0.50 ml/min.
- Wavelength: 214 nm.

DETERMINATION OF DEAD TIME
- Method: by inert substances which are not retained by the column. Sodium nitrate (1 mg/l) was used. The mean value was calculated.

TEST SUBSTANCE
- Concentration of the test substance: 5 mg/l.
- Solutes for dissolving test substance: acetonitrile: water (containing 2 g/l NaH2PO4), 20 : 80 (% v/v).

REFERENCE SUBSTANCES
- Identity: Acetanilid (CAS No: 103-84-4, purity 99.9 %), Atrazin (CAS No: 1912-24-9, 98.4 %), Triadimenol (CAS No: 55219-65-3, 98.0 %), a-Endosulfan (CAS No: 959-98-8, 97.0 %), Pyrazophos (CAS No: 13547-18-6, 97.0 %), 2-Nitrobenzamide (CAS No: 610-15-1, 99.9 %).
- Concentration: 1 mg/l of each reference item in separate solution.
- Solutes for dissolving substances: acetonitrile: water (containing 2 g/l NaH2PO4), 20 : 80 (% v/v).

DETERMINATION OF RETENTION TIMES
- Intervals of calibration: the reference substance was analysed before and after the analysis of the test substance.

REPETITIONS
- Number of determinations: three injections of the test solution, two injections of the reference standard solutions.

EVALUATION
- Calculation of capacity factors k': the capacity factor was calculated according to the equation k'= ((tR-t0)/t0), where: tR = Retention time of test or reference substance, t0 = Dead time.
- Determination of the log Koc value: the log Koc values and the coresponding capacity factors of the reference items are correlated by plotting a calibration graph of log Koc versus log k'. The measured HPLC-retention data of the test item are calculated with the correlation to get the adsorption coefficient Koc.
Type:
log Koc
Value:
1.54 - 1.78 dimensionless
Temp.:
25 °C
Remarks on result:
other: SD = 0.006
Details on results (HPLC method):
- Retention times of reference substances used for calibration: 2-Nitrobenzamide: 4.252 min, acetanilide: 5.036, atrazine: 6.962 min, triadimenol: 11.426 min, pyrazophos: 23.353 min, a-endosulfan: 31.160 min
- Details of fitted regression line (log k' vs. log Koc): y = 2.4469x + 1.5567, R^2 = 0.9873
- Average retention data for test substance: peak I (5.878 ± 0.019) min, peak II (6.630 ± 0.022) min
- Dead time of sodium nitrate (min): 2.964 ± 0.002

Calibration data of the Reference Items

Reference item tR(min) tRMean(min) k' log k' logKoc (1)
2-Nitrobenzamide 4.250 4.252 0.435 -0.362 0.75
4.254
Acetanilide 5.038 5.036 0.699 -0.156 1.25
5.034
Atrazine 6.964 6.962 1.349 0.13 1.81
6.959
Triadimenol 11.432 11.426 2.855 0.456 2.4
11.42
Pyrazophos 23.289 23.353 6.879 0.838 3.65
23.416
a-Endosulfan 31.098 31.16 9.513 0.978 4.09
31.221

(1) Log Koc of 2 -Nitrobenzamide is the mean value of batch experiments on five soils adopted from Gawlik & Muntau (1999) (1)

(2) The Log Koc values of the rest of the reference items are taken from the guideline OECD 121.

Table: Retention time, Capacity Factors and Adsorption Coefficient of Test item

Reference item tR(min) k' log k' logKoc
2-Nitrobenzamide 5.892 0.988 -0.005 1.54
5.885 0.985 -0.007 1.54
5.856 0.976 -0.011 1.53
Mean  5.878 0.983 -0.008 1.54
SD 0.019 0.006 0.003 0.006
Acetanilide 6.630 1.237 0.092 1.78
6.622 1.234 0.091 1.78
6.589 1.223 0.087 1.77
Mean  6.614 1.231 0.090 1.78
SD 0.022 0.007 0.003 0.006

Validity criteria

Partially not fullfiled: retention time difference between the two injections for the reference substances Pyrazophos and a-Endosulfan was slightly higher than 0.1 min, 0.13 and 0.12 respectively.

(1) Gawlick, B.M and Muntau, H. Eurosoils II. Laboratory Reference Materials for Soil-related studies. Joint Researc Centre, European Commision, EUR 18983 EN (1999)

(2) OECD/OCDE 121 Guideline for the testing of chemicals- Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage using High Perfomance Liquid Chromatography (HPLC) (Draft dated 2001 -01 -222)

Validity criteria fulfilled:
no
Remarks:
retention time difference between the two injections for the Pyrazophos and a-Endosulfan was slightly higher than 0.1 min, 0.13 and 0.12 respectively
Conclusions:
log Koc: 1.54 - 1.78 at 25 °C
Executive summary:

The estimation of the adsorption coefficient (Koc) on soil and on sewage sludge using high performance liquid chromatography (HPLC) was carried out according to the principles of the OECD Guideline 121. Calibration was performed using six reference items with known values of log Koc and the capacity factor k' was calculated from the dead time of the HPLC-system for each reference item. The measured HPLC - retention data of the test item were calculated and were used for the estimation of the adsorption coefficient from the calibration graph (Log Koc versus log k').

The estimated range of log Koc for the test item is 1.54 -1.78, SD = 0.006 which corresponds to a Koc range of 35 - 60.

Conclusion

log Koc: 1.54 - 1.78 at 25 °C

Description of key information

Low potential for adsorption.

Key value for chemical safety assessment

Koc at 20 °C:
35

Other adsorption coefficients

Type:
log Kp (solids-water in suspended matter)
Value in L/kg:
0.25

Other adsorption coefficients

Type:
log Kp (solids-water in soil)
Value in L/kg:
0.15

Additional information

Direct Black 168 is expected to have a low potential for absorption, on the basis of the partition coefficient; the log Pow was determined to be lower than 4 at 20 °C and pH 6. The organic carbon-water partition coefficient was estimated using EUSES v.2.1 to be 0.09 (log koc: -1.06).

In order to deeper investigate the substance characteristics, the available data on the structural analogous Similar Substance 01 has been considered. Similar Substance 01 shares with Direct Black 168 the same scaffold chemical structure base; the differences are considered to be not able to impact the study outcomes, thus the read across can be considered as reliable and apporopriated to evaluate the endpoint (details on read-across approach are given in the IUCLID section 13).

The estimation of the adsorption coefficient (Koc) of Similar Substance 01 was carried out using high performance liquid chromatography (HPLC), according to the OECD Guideline 121. Calibration was performed using six reference items with known values of log Koc and the capacity factor k' was calculated from the dead time of the HPLC-system for each reference item. The estimated range of log Koc for the test item was 1.54 -1.78 (SD = 0.006), which corresponds to a Koc range of 35 - 60.

Despite the difference in values recorded, both estimated values on Direct Black 168 and Similar Substance 01 agree to define the same behaviour, i.e. that the substance can be considered as mobile in soil.

Therefore, the experimental data on the analogous has been used in order to estimate the suspended matter-water and soil-water partition coefficients, which are needed to the calculation of the PNECs for sediment and soil, according to the equilibrium partitioning method.

Suspended matter-water partition coefficient: 1.78 - 2.4 (log Ksusp 0.25 - 0.38)

Soil-water partition coefficient: 1.43 - 2.18 (log Ksoil 0.15 - 0.34)