1,3,5-triazine-2,4,6-triamine phosphate

Adsorption / desorption

Description of key information

A log kow of -3.1 (see section 4.7) was determined which indicates low potential for adsorption to soil. In addition a log Koc of  < 1.3 was determined in a study (BASF SE, 2002) performed according to OECD 121 (2001), which supported the low potential for adsorption to soil.

Key value for chemical safety assessment

Koc at 20 °C:

21

Additional information

The estimation of the adsorption coefficient (Koc) in Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC) was based on the following guideline: Organization for Economic Co-operation and Development (OECD), OECD Guideline for Testing of Chemicals, Proposal for a new guideline 121: "Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC)", January 2001.

According to the OECD guidelines, the estimation of the adsorption coefficient (Koc) for test substances that are ionized for at least 10% within pH 5.5 to 7.5, should be performed with both the ionized and non-ionized form.

The test substance is a salt, consisting of an organic part (melamine) and an inorganic part (phosphate). It is not possible to bring both parts into a non-ionized form at the same time but the salt as a whole is neutral.

Therefore it was decided to perform the test at neutral pH without buffering the aqueous part of the mobile phase. Though the response observed is expected to derive from the organic part of the test substance, the response is considered representative for the test substance. Electrical neutrality considerations require that both parts of the salt elute at the same time when testing at neutral pH.

At neutral pH, the adsorption coefficient (Koc) of the test substance is > 4.3x10exp5 (log Koc > 5.6) for the major component and <21, <21 and 5 (log Koc= <1.3, <1.3 and 0.7) for impurities.

Based on pKa calculations for the organic part of the test substance (7.0 and -0.6 for a basic group), it was expected that there might be a pH effect on adsorption. Therefore, it was decided to perform a second test at pH 5 by buffering the aqueous part of the mobile phase. Using these conditions, phosphate and melamine can elute at different times. The melamine peak had a retention time smaller than the retention time of phenol (log Koc - 1 - 32) and phosphate is not expected to adsorb. Therefore, the response observed is considered representative for the test substance. At pH 5, the adsorption coefficient (Koc) of the test substance is < 21 (log Koc < 1.3).

In addition a soil sorption coefficient (Koc) of 53 was calculated in a not reliable study (ECETOC, 1983) with the read across substance melamine (CAS 108 -78 -1) . This indicates that the adsorption of melamine onto soil is not important. A soil with 2 % organic carbon in contact with a 0.1 ppm solution will adsorb melamine to give approximately 0.1 µg/g soil.

[LogKoc: 1.3]