reaction mass of: pentasodium 4-amino-5-hydroxy-3-{(E)-4-[2-(sulfonatooxy)ethylsulfonyl]phenylazo}-6-{(E)-2-sulfonato-4-[2-(sulfonatooxy)ethylsulfonyl]phenylazo}naphthalene-2,7-disulfonate;tetrasodium 4-amino-5-hydroxy-3-{(E)-4-[2-(sulfonatooxy)ethylsulfonyl]phenylazo}-6-[(E)-2-sulfonato-4-(vinylsulfonyl)phenylazo]naphthalene-2,7-disulfonate;tetrasodium 4-amino-5-hydroxy-6-[(E)-2-sulfonato-4-[2-(sulfonatooxy)ethylsulfonyl]phenylazo}-3-[(E)-4-(vinylsulfonyl)phenylazo]naphthalene-2,7-disulfonate;trisodium 4-amino-5-hydroxy-3-[(2-hydroxyethylsulfonyl)-phenylazo]-6-[(E)-2-sulfonato-4-(vinylsulfonyl)phenylazo]naphthalene-2,7-disulfonate;trisodium 4-amino-5-hydroxy-3-[(E)-4-(vinylsulfonyl)phenylazo]-6-[(E)-2-sulfonato-4-(vinylsulfonyl)phenylazo]naphthalene-2,7-disulfonate;trisodium 4-amino-5-hydroxy-3-[(E)-4-(vinylsulfonyl)phenylazo]-6-[-2-sulfonato-4-(2-hydroxyethylsulfonyl)phenylazo]naphthalene-2,7-disulfonate

Adsorption / desorption

Description of key information

The log of the adsorption coefficient (Koc) of Navy MG¡ 1571 was estimated to be <1.32

Key value for chemical safety assessment

Koc at 20 °C:

1.32

Additional information

The determination of the adsorption coefficient (Koc) of Navy MGi 1571 was performed according to the OECD Guideline for the Testing of Chemicals, No. 121.
The test item solution was injected three times and the combined reference solution was injected six times. The log Koc was calculated using a regression curve (log k' vs. log Koc) and was found to be < 1.32 which is equal to a Koc value oÍ < 21. ln the present study the reference items covered the range of log Koc 1.32 to log Koc 5.63.
The *chromatography of the test item resulted in one main peak with a well-defined and reproducible retention time. The HPLC method was therefore considered to be suitable for the purpose of the study. Based on the chromatographic data, Navy MGi 1571 was considered to be stable during the test procedure.
The capacity factor (k') was calculated for each reference item using the retention times. Log Koc was plotted versus log k for each component to obtain a regression curve. The retention time of Navy MGi 1571 in the HPLC chromatogram is shorter than the retention time of the lowest reference item
used.
ln conclusion, the log of the adsorption coefficient (Koc) of Navy MG¡ 1571/REG was estimated to be
log Koc <1.32 which is equalto Koc value of <21 using the HPLC method. This value indicates that Navy MG¡ 1571 is likely not be absorbed by organic carbon in soil. Navy MGi 1571is therefore presumed to be very mobile.

Furthermore, a study according to OECD Guideline No. 106 was carried out. The approach in Tier I showed in none of the soils an equilibrium plateau, however the Tier II part was conducted applying prolonged equilibrium time. The following soils and sediment were used:2.2 (soil I, loamy sand), Attenschwiller (soil II, silt loam), Spra 05 (soil III, sandy clay loam),6S (soil IV, clay), Mechtildshausen (soil V, loam) and a pond sediment (sorbent VI, silty clay loam). The soils and sediment showed a range of different characteristics important for adsorption i.e. organic carbon content, cation exchange capacity, pH , clay content and texture. Soils III and V were treated byγ-irradiation before use in order to limit the impact of microbial activity.

In a preliminary test using two soils and the sediment at a sorbent-to-solution ratio of 1/5(1 g / 5 mL), the adsorption levels increased progressively to 87% (soil I), 75% (soil III) and 99% (sediment) by 48 hours without reaching adsorption plateaus.

The following test was designed to find the absorption equilibrium for all five soils and the pond sediment. The sorbent-to-solution ratio was reduced to 1/25 (1 g / 25 mL) to lower the adsorption levels whereas the time of agitation was extended to 72 hours to allow more time for development of adsorption equilibriums. Under these conditions, adsorption increased progressively to 50%, 67%, 27%, 61%, 47% and 86% by 72 hoursfor soils I-V or the sediment, respectively,without reaching plateaus.

The reasons for not reaching plateaus could be complicating factors, e.g. biodegradation of the test substance (analyte).In presence of the γ-irradiated soils (soils III and V), adsorption was delayed but not slowed down compared to the non-radiated soils. Therefore, restricting microbial activity through γ-irradiation of the sorbent could not be considered as a determining factor in preventing the development of adsorption equilibriums.

Since the adsorption equilibriums could not be reached, the study could not be performed according to OECD 106 nor could the established adsorption data be used for calculating distribution coefficients (e.g. K_d, K_OC,) which by definition are based on adsorption equilibrium.