[nitrilotris(methylene)]trisphosphonic acid, ammonium salt

Phototransformation in water

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: The study was well documented and meets generally accepted scientific principles, but was not conducted in compliance with GLP.

Study type:

direct photolysis

Principles of method if other than guideline:

Concentrations of 1 mg/l (3.2 uM) irradiated by a middle pressure mercury lamp emitting between 190 and 600 nm. pH 3, 5-6 and 10. Effect of presence of iron at 3.6uM investigated, matching the encountered concentrations in the environment (between 0.2 and 2.5uM Fe in ocean water and an average of 12uM Fe in river). The degradation of phosphonates measured by the release of orthophosphates (PO4-P) and aminomethylphosphonic
acid (AMPA).

GLP compliance:

no

Analytical method:

high-performance liquid chromatography

other: UV-Vis

Light source:

other: Mercury lamp

Light spectrum: wavelength in nm:

>= 190 - <= 600

Details on light source:

- Emission wavelength spectrum: 190nm - 600 nm
- Filters used and their purpose: quartz glass
- Relative light intensity based on intensity of sunlight: similar intensity to natural light in the visible range.

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test apparatus/vessels: reactor is a round-bottomed 2L flask containing the
mercury lamp. Flask is wrapped in aluminium foil to assure light-insulation.
TEST MEDIUM
- Kind and purity of water: distilled water
- Preparation of test medium: iron added to a concentration of 3.6μM
-pH range: 3-10

Duration:

1.5 h

Initial conc. measured:

1 mg/L

DT50:

25 min

Test condition:

pH 5-6

DT50:

15 min

Test condition:

pH 5-6 (in presence of Fe sensitiser)

DT50:

30 min

Test condition:

pH 3

DT50:

10 min

Test condition:

pH 3 (in presence of Fe sensitiser)

DT50:

75 min

Test condition:

pH10

DT50:

60 min

Test condition:

pH10 (in presence of Fe sensitiser)

Reference 2

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Study type:

indirect photolysis

Principles of method if other than guideline:

Method: other (measured)

GLP compliance:

not specified

Radiolabelling:

no

Light source:

sunlight

Details on light source:

Sunlight

Type of sensitiser:

water with additives

Details on sensitiser:

Milli-Q water and tap water with/without added ferric nitrate (as concentration of ferric ion)

Concentration of sensitiser:

0.19 mg/L

Duration:

17 d

Temp.:

23 °C

Initial conc. measured:

10 mg/L

Dark controls:

yes

% Degr.:

0

Sampling time:

17 d

Test condition:

Direct photolysis

% Degr.:

>= 6 - <= 19

Sampling time:

17 d

Test condition:

Indirect photolysis

Transformation products:

yes

No.:

#1

Reference 3

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Test procedure in accordance with national (draft) standard methods with acceptable restrictions.

Study type:

direct photolysis

Principles of method if other than guideline:

Method: other (measured)

GLP compliance:

no

Light source:

sunlight

Type of sensitiser:

water with additives

% Degr.:

<= 2

Sampling time:

17 d

Test condition:

Light conditions, pH7 (no sensitiser present)

% Degr.:

<= 44

Sampling time:

17 d

Test condition:

Light conditions, pH7 (in presence of ferric nitrate as sensitiser)

Transformation products:

yes

No.:

#1

% Transformation (Phosphonate to Orthophosphate) after 17 days sunlight exposure (unless otherwise stated)

	pH4	pH7	pH10
ATMP (light)	0	2	0
ATMP (dark)	<2	<2	<2
ATMP / Ferric nitrate (light)	19 (day 3) 35 (day 9) 45 (day 17)	26 (day 3) 39 (day 9) 44 (day 17)	25 (day 3) 34 (day 9) 38 (day 17)
ATMP / Chromic nitrate (light)	3	1	3
ATMP / Zinc nitrate (light)	0	1	3
ATMP / Cupric nitrate (light)	2	2	3

Conclusions:

Direct photolysis of ATMP is not significant.
Sensitised photolysis was observed in the presence of ferric nitrate.

Description of key information

0 - 45% transformation (phosphonate to orthophosphate) after 17 days under a range of conditions.

Additional information

Three studies are available focussing on stability in water due to photodegradation mechanisms, which have been read-across from ATMP-H. Whilst this is not a conventional pathway for study it brings useful evidence for fate of ATMP in the real environment.

Photodegradation of ATMP-H (6419-19-8) in water was examined (Saeger, (undated, believed to be 1979)). 2% transformation (phosphonate to orthophosphate) was measured after 17 days at pH 7 (0% at pH 4 and 10). Levels of degradation in the presence of ferric (Fe III) nitrate were higher, with 26% transformation by day 3 in the presence of ferric nitrate at pH7 (by day 17: 44% at pH 7, 45% at pH 4 and 38% at pH10). The effect of other metals (chromic, zinc and cupric ions) was insignificant.

In a separate test (Lesueur, 2005), half-lives less than 1 hour were measured in water at pH 3, pH 5-6 and at pH 10, irradiated by a middle pressure mercury lamp emitting between 190 and 600 nm. Half-lives were found to be shorter in the presence of iron ions at environmentally relevant concentrations. Degradation in the presence of ferric (Fe III) ions reflects the ability of that ion to absorb light, and because it can be strongly complexed by ATMP, that energy can be transferred to the complexing anion, resulting in degradation. It is possible that ferrous (Fe II) ions would be formed in this process, and, due to the presence of oxygen, ferric ions would be regenerated. In the environment longer degradation times are to be expected since natural light is weaker by a factor between 125 and 300 in the UVB, a factor between 3 and 8 in the UVA and of the same intensity in the visible range than the light in the study. The iron content in natural waters would be high enough to support the conversion induced by UV light, but due to the fluctuation of pH especially in eutrophic waters and due to buffered systems pH might be out of the optimal range for a rapid phosphonate conversion.

The degradation products identified in this study are orthophosphate and aminomethylphosphonic acid (AMPA). No specific reaction pathway is proposed by the study authors.

In a third study, 6% of the initial dose of ATMP-H was photodegraded in the presence of 0.19 mg/l ferric iron (Monsanto,  1980). In tap water 18% and 19% was photodegraded in the absence and presence of added iron, respectively.

Photodegradation in the presence of common metal ions has been observed. Based on evidence from a number of studies members of this group are considered to be partially degradable over short time periods, and with evidence of mineralisation, particularly in the light, over longer periods.

The acid, sodium, potassium and ammonium salts in the ATMP category are freely soluble in water. The ATMP anion can be considered fully dissociated from its sodium, potassium or ammonium cations when in dilute solution. Under any given conditions, the degree of ionisation of the ATMP 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 ATMP-H, ATMP.4Na, ATMP.7K or another salt of ATMP.

 

Therefore, when a salt of ATMP is introduced into test media or the environment, the following is present (separately):

1. ATMP is present as ATMP-H or one of its ionised forms. The degree of ionisation depends upon the pH of the media and not whether ATMP (3-5K) salt, ATMP (3-5Na) salt, ATMP-H (acid form), or another salt was used for dosing.
2. Disassociated potassium, sodium or ammonium cations. The amount of potassium or sodium present depends on which salt was dosed.
3. It should also be noted that divalent and trivalent cations would preferentially replace the sodium or potassium ions. These would include calcium (Ca²⁺), magnesium (Mg²⁺) and iron (Fe³⁺). These cations are more strongly bound by ATMP than potassium, sodium and ammonium. This could result in ATMP-dication (e.g. ATMP-Ca, ATMP-Mg) and ATMP-trication (e.g. ATMP-Fe) complexes being present in solution.

In this context, for the purpose of this assessment, read-across of data within the ATMP Category is considered to be valid.