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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:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Principles of method if other than guideline:
To investigate the photodegradation pathway of Fe-EDTA, an aqueous solution of the substance was irradiated with a xenon arc lamp.
The reaction mixture was sampled over a period of 4 days.
GLP compliance:
no
Radiolabelling:
yes
Light source:
Xenon lamp
Details on light source:
Wide spectrum 5500-W Xenon lamp
Details on test conditions:
To determine the extent of ferric EDTA removal from the environment by interaction with sunlight - i.e. photodegradation - the behaviour of aqueous solutions of ferric-1-14C-EDTA at pH 4.5, 6.9, and 8.5 under irradiation from a xenon lamp has been studied. 
Initial conc. measured:
0.002 mol/L
Key result
% Degr.:
100
Sampling time:
24 h
Test condition:
Direct photolysis

Carbon dioxide, formaldahyde, N-carboxy-methyl-N,N'-ethylenediglycine  (ED3A), N,N'ethylenediglycine (EDDA-N,N'), iminodiacetic acid (IMDA),  N-carboxymethyl-N-aminoethyleneglycine (EDDA-N,N), N-aminoethyleneglycine  (EDMA), and glycine have been identified as the major photodegradation products. No nitrilotriacetic acid (NTA) was detected during photodegradation.

The rate of photodegradation was pH dependent, being most rapid at pH 4.5. At a light intensity of 4000-ft candles and an initial concentration of 0.0016 M Fe(III)-EDTA removal was complete after 24 h of irradiation at either pH 4.5 or pH 6.9 and after 32 h at pH 8.5.

Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Study type:
not specified
Principles of method if other than guideline:
EDTA was dissolved in natural lake water and photodegradation over a period of time was determined.
GLP compliance:
not specified
Radiolabelling:
not specified
Analytical method:
high-performance liquid chromatography
Details on sampling:
Exposure to Sunlight: Sampling volume was 10 mL and samples were taken first at the beginning´, second after two weeks and thereafter samples were taken once a week.

Laboratory conditions: Sampling volume was 7 mL, further data are not available
Buffers:
no data availble
Light source:
Xenon lamp
Light spectrum: wavelength in nm:
315 - 400
Details on light source:
laboratory condition: two black lamps (Sylvania F40W/BL, black light 350), yileding 4.8 mW/cm2 at a distance of 100mm.

direct sunlight: The average intensity of solar radiation at the range 290-385 was 0.9 mW/cm2 in June, 0.92 mW/cm2 in July, 0.55 mW/cm2 in August and 0.30 mW/cm2 in September.
Details on test conditions:
laboratory conditions: Test solutionsin 500 mL glass bowls were placed on magnetic stirrers for mixing. Starting concnetration of EDTA was 0.13 mM in destilled and in lake water. The complexation by FeCl3 reduced pH from 6.5 to 3.1 in both media. Therefore one set was carried out where the pH was adjusted to 6.5 using NaOH

Exposure to sunlight: Four 100 L aquariums were used and each held 64 L of the test solution (destilled water in the dark, destilled water in the sunlight, lake water in the dark, lake water in the sunlight). Concentration of EDTA was 0.13 mM. Experiment lasted from June to September.
Duration:
14 wk
Initial conc. measured:
0.13 mmol/L
Reference substance:
not specified
Dark controls:
yes
Computational methods:
The rate of photodegradation of Fe(III)-EDTA seemed to follow first-order kinetics.
Preliminary study:
no data available
% Degr.:
50
Sampling time:
56.8 d
Test condition:
laboratory (lake water)
% Degr.:
50
Sampling time:
45 d
Test condition:
laboratory (distilled water)
% Degr.:
74
Sampling time:
50 d
Test condition:
Exposure to sunlight
Predicted environmental photolytic half-life:
< 50 d without pH adjustment, exposed to direct sunlight.
Transformation products:
not specified
Validity criteria fulfilled:
not specified
Conclusions:
0.13 mM Na2-EDTA did entirely disappear during 50 days from destilled water, wheras 74 % of NA2-EDTA degraded in lake water during this period of time.

Description of key information

Information on phototransformation in water is not required under REACH.

Key value for chemical safety assessment

Additional information

Both HEDTA and its surrogate, EDTA, form complexes with ions. Therefore both exist naturally as a mixture of chelate complexes. Some EDTA species, especially the iron complex, are photolysable (EU Risk Assessment, 2004). Metsärine et al. (2001) have shown that, in natural waters, photodegradation of Na2-EDTA is 74% in 50 days.