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Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Based on the relevant physical-chemical properties, the known use pattern (release to water) and 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

The distribution in a sewage treatment plant has been estimated using the SimpleTreat model (implemented in EUSES 2.1.2) 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 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.

The acid and salts in the DTPMP category are freely soluble in water and, therefore, the DTPMP anion is fully dissociated from its cations when in solution. Under any given conditions, the degree of ionisation of the DTPMP species is determined by the pH of the solution. At a specific pH, the degree of ionisation is the same regardless of whether the starting material was DTPMP-H, DTPMP (1-3Na), DTPMP (5-7Na), DTPMP (4-8K), DTPMP (xNH4) or another salt of DTPMP.

 

Therefore, when a salt of DTPMP is present in test media or the environment, the following is present (separately):

1. DTPMP is present as DTPMP-H or one of its ionised forms. The degree of ionisation depends upon the pH of the media and not whether DTPMP-H, DTPMP (1-3Na), DTPMP (5-7Na), DTPMP (4-8K), DTPMP (xNH4), or another salt was used for testing.

2. Disassociated ammonium, potassium or sodium cations. The amount of ammonium, potassium or sodium present depends on which salt was added.

3. Divalent and trivalent cations have much higher stability constants for binding with DTPMP than the sodium, potassium or ammonium ions so would preferentially replace them. These ions include calcium (Ca2+), magnesium (Mg2+) and iron (Fe3+). Therefore, the presence of these in the environment or in biological fluids or from dietary sources would result in the formation of DTPMP-dication (e.g. DTPMP-Ca, DTPMP-Mg) and DTPMP-trication (e.g. DTPMP-Fe) complexes in solution, irrespective of the starting substance/test material.