[[(phosphonomethyl)imino]bis[ethane-2,1-diylnitrilobis(methylene)]]tetrakisphosphonic acid

Distribution modelling

Administrative data

Endpoint:

distribution modelling

Type of information:

calculation (if not (Q)SAR)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

accepted calculation method

Materials and methods

Model:

calculation according to Mackay, Level III

Media:

air - biota - sediment(s) - soil - water

Test material

Test material information

Constituent 1

Reference substance name:

[[(phosphonomethyl)imino]bis[ethane-2,1-diylnitrilobis(methylene)]]tetrakisphosphonic acid

EC Number:

239-931-4

EC Name:

[[(phosphonomethyl)imino]bis[ethane-2,1-diylnitrilobis(methylene)]]tetrakisphosphonic acid

Cas Number:

15827-60-8

Molecular formula:

C9H28N3O15P5

IUPAC Name:

[(bis{2-[bis(phosphonomethyl)amino]ethyl}amino)methyl]phosphonic acid

Test material form:

not specified

Study design

Test substance input data:

- Molar mass: 573.2
- Data temperature: 20˚C
- Water solubility: 500 000 mg/l
- Vapour pressure: 2.7E-09 Pa
- log Pow: -3.4 initially (minimum limit accepted by the software), although a surrogate value is preferred when the program used does not allow input of Koc (see below).

- Reaction half-life estimates for
- Air: assumed negligible
- Water: assumed negligible
- Soil: assumed negligible
- Sediment: assumed negligible
- Suspended sediment: assumed negligible
- Aerosols: assumed negligible
- Aquatic biota: assumed negligible

Environmental properties:

As default

Results and discussion

Percent distribution in media

Air (%):

0

Water (%):

58.9

Soil (%):

0

Sediment (%):

41.1

Any other information on results incl. tables

Using a fugacity based model (Mackay level 1) DTPMP (15827-60-8) is predicted to migrate entirely to the aqueous compartment (100%) with 9E-5% in the soil, 6E-11% in air and 2E-06% in sediment.

However, in this model, Level 1 is modelling a very low soil and sediment adsorption, known not to be correct. Therefore further level 1 modelling using a substitute log K_ow= 4.38 has been performed. This value of log K_ow, set to obtain the correct K_oc(9748) within the Level 1 program, gives:

Table: Level I outputs using an adjusted log K_ow

Air	3E-12%
Soil	93.5%
Water	4.4%
Sediment	2.1%

 

The Level III program has also been applied, with the default model, using the same input parameters and the adjusted log K_ow. The resulting distribution between compartments is as follows:

Table: Level III outputs using an adjusted log K_ow

 

Distribution	Release: 100% To air	Release: 100% To water	Release: 100% To soil
% in air	0%	0%	0%
% in soil	99.6%	0%	99.6%
% in water	0.24%	58.9%	0.23%
% in sediment	0.17%	41.1%	0.16%

For the known use pattern, the most likely emission route will be directly to water. Direct emission to soil via spreading of sludge from waste water treatment plants is also possible.

The results reflect that most DTPMP found in air would be precipitated to soil, and that there is very little movement between soil and water, because transfer via the air compartment is very slow, for a substance of low volatility. In water, the adsorption coefficient of DTPMP results in significant adsorption to sediment.

The distribution in a sewage treatment plant has been estimated using the SimpleTreat model (implemented in EUSES 2.1.1) to be 0% degraded, 20% to water, 80% to sewage sludge. These outputs are based on non-biodegradability, and the properties given above for the fugacity-modelling of distribution. There is evidence from literature that wastewater treatment plants using a purification step with iron and aluminium salt additives to remove phosphorus, can be expected to achieve more than 90% removal of DTPMP, attributed largely to adsorption to amorphous precipitated iron oxides (Nowack, 2002). Measurements of one WWTP performance (Weil) showed a removal of 93%; another WWTP site showed 95% removal at the biological treatment stage with a further 2% removal at the flocculation (iron salts treatment) step.

Applicant's summary and conclusion

Conclusions:

Based on the relevant physical-chemical properties, the known use pattern (release to water) and the fact that it is non-biodegradable, DTPMP and its salts will partition primarily to water and suspended sediments. In the sewage treatment plant the substance is not expected to degrade, but will be removed on sewage sludge (80%) and be present in the effluent (20%).