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

Endpoint summary

Description of key information

Based on the relevant physical-chemical properties, the known use pattern (release to water) and the assuming no biodegradability, DTPMP acid 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%).

Additional information

Because DTPMP acid and its salts behave in aqueous medium in accordance with the pH and composition of the medium, the conclusions in this section apply to both acid and salts.

The compartmental approaches expressed in the Mackay models at Level I and Level III have been used to give an indication of relative partition tendencies, but not predicted concentrations. This qualitative approach is sufficient for the present purpose.

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 1 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

	Release:
	100% To air	100% To water	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.