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Environmental fate & pathways

Phototransformation in water

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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)
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.
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

Description of key information

Photodegradation in water (ATMP): 0 - 45% transformation (phosphonate to orthophosphate) after 17 days under a range of conditions.

Key value for chemical safety assessment

Additional information

Two studies are available focussing on stability in water due to photodegradation mechanisms. Whilst this is not a conventional pathway for study it brings useful evidence for fate of ATMP in the real environment.

Photodegradation of ATMP (6419-19-8) in water was examined (Saeger, Monsanto (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, 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.

Discussion of trends in the ATMP category

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.