Diphosphoric acid, compound with 1,3,5-triazine-2,4,6-triamine

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

16 December 2003 and 11 March 2004

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP study conducted in accordance with an internationally recognised method

Qualifier:

according to guideline

Guideline:

OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))

GLP compliance:

yes (incl. QA statement)

Type of method:

HPLC estimation method

Media:

other: HPLC column with nitrile stationary phase (soil simulation)

Radiolabelling:

no

Test temperature:

40°C organic component
30°C pyrophosphate

Details on study design: HPLC method:

Analysis (organic component) at pH 5.5:

Column: Genesis 4µ, CN (250 x 4.6 mm id)
Column temperature: 30°C
Mobile phase: methanol:water (55:45 v/v) adjusted to pH 5.5 with 0.02M hydrochloric acid
Flow-rate: 1.0 ml/min
UV detector wavelength: 210 nm deadtime and reference standards, 205 nm sample
Injection volume: 10.0 µl
Deadtime standard: formamide

Analysis (organic component) at pH ~7.5:

Column: Genesis 4µ, CN (250 x 4.6 mm id)
Column temperature: 40°C
Mobile phase: methanol:water (55:45 v/v) adjusted to pH 7.6 using 0.1M and 1M sodium hydroxide
Flow-rate: 1.0 ml/min
UV detector wavelength: 210 nm deadtime and reference standards, 205 nm sample
Injection volume: 10.0 µl
Deadtime standard: formamide


Analysis (pyrophosphate) at pH 7.5

Column: Zorbax SB-CN, 5µ (250 x 4.6 mm id)
Column temperature: 30°C
Mobile phase: methanol:water (55:45 v/v) adjusted to pH 7.5 with 35% ammonia solution
Flow-rate: 1 ml/minute
Injection volume: 10 µl
Deadtime standard: formamide
Mass selective detector: electrospray, single ion mode, negative polarity

Details on sampling:

- Concentrations:
- Sampling interval:
- Sample storage before analysis:

Type:

Koc

Value:

129

Temp.:

40 °C

Remarks on result:

other: Organic component pH 5.5 (partially ionised)

Type:

Koc

Value:

26.7

Temp.:

40 °C

Remarks on result:

other: Organic component pH ~7.5 (unionised)

Type:

Koc

Value:

< 17.8

Temp.:

30 °C

Remarks on result:

other: Pyrophosphate pH 7.5 (ionised)

The method guideline states that the measurement of adsorption coefficient should be carried out on substances in their ionised and unionised forms. The pKa of the organic component was known to be 5.16 (see Dissociation Constant, page 41), therefore testing was performed at pH 5.5, at which the organic component would be expected to be partially ionised and pH 7.5, where it would be in its unionised form.

However, testing would be required at less than pH 0 to obtain pyrophosphate in its unionised form. As this was outside the specified pH range for the test (5.5 to 7.5) and not possible experimentally, testing was performed at approximately neutral pH, with the pyrophosphate component ionised.

Validity criteria fulfilled:

yes

Conclusions:

The adsorption coefficient (Koc) of the organic component of MPP (melamine) is 129 at pH 5.5 and 26.7 at pH 7.5
The adsorption coefficient (Koc) of pyrophosphate is <17.8 at pH 7.5)
However, it is possible that the MPP shows different physico-chemical properties from melamine and pyrophosphate because MPP is not inorganic salt of melamine or pyrophosphate but organic salt constituted by both of them. And according to these differences, it may also show different environmental and metabolic pathway from melamine and pyrophosphate. Therefore, adsorption/desorption measurement will be conducted by MPP itself and its result will be used for this conclusion.

Description of key information

The adsorption coefficient for MPP has been determined as Koc = 26.7 as represented by the measurement of the adsorption coefficient of the organic component of MP at pH 7.5. According to the McCall classification criteria for soil mobility potential (McCall et al Proc. of Assoc. of Official Analytical Chemists, 1980), MPP is highly mobile in soil.

Key value for chemical safety assessment

Koc at 20 °C:

26.7

Additional information

The soil adsorption coefficient (Koc) of the organic component of MPP has been determined as 26.7 at pH 7.5, where it exists in unionised state and 129 and at pH 5.5 where it exists in partially unionised state.

Pyrophosphate exists in ionised state at all environmentally relevant pHs and has a Koc value of <17.8.

For the purposes of risk assessment the Koc value of pyrophosphate will be disregarded as it is known to eventually hydrolyse in the environment to produce phosphate salts that are ubiquitous in nature, forming part of the natural background level of such compounds.

The value of Koc 26.7 is taken forward into the risk assessment on the basis that this value for Koc is representative of the unionised, state which is the simplest and most definable form of the organic component of MPP. The Log Pow is also determined on the organic component of MPP in unioinised state (at pH7). The fact that the Koc is slightly higher for the partially ionised form suggests that the mechanism of interaction with soil may involve ion exchange, but the value of 129 observed at pH 5.5 is not sufficiently different from the value obtained at pH 7.5 to affect the outcome of the risk assessment.

However, it is possible that the MPP shows different physico-chemical properties from melamine and pyrophosphate because MPP is not inorganic salt of melamine or pyrophosphate but organic salt constituted by both of them. And according to these differences, it may also show different environmental and metabolic pathway from melamine and pyrophosphate. Therefore, adsorption/desorption measurement will be conducted by MPP itself and its result will be used for this conclusion.