D-gluconic acid, compound with N,N''-bis(4-chlorophenyl)-3,12-diimino-2,4,11,13-tetraazatetradecanediamidine (2:1)

Phototransformation in water

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2008-2009

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Study type:

direct photolysis

Qualifier:

according to guideline

Guideline:

OECD Guideline draft (Phototransformation of Chemicals in Water - Direct and Indirect Photolysis)

Version / remarks:

August 2000

Deviations:

yes

Remarks:

During the kinetic study, the temperature was > 30 °C for 4 hours, due to breakdown of the cooling aggregate of the thermostat.

GLP compliance:

yes (incl. QA statement)

Remarks:

Dr. U. Noack Laboratorien

Radiolabelling:

no

Analytical method:

high-performance liquid chromatography

Details on sampling:

- Sampling intervals for the parent/transformation products: at test start and at 10 spaced points over 15 d
Buffer solution was analysed to exclude possible analytical interferences with the test item.

Buffers:

- pH: 7
- Type and final molarity of buffer: 0.06 mol/L KH2PO4
- Composition of buffer: 500 mL 0.1 mol/L of potassium dihydrogenphosphate (KH2PO4) in double distilled water and 291 mL 0.1 mol/L sodium hydroxide (NaOH), bubbled with air for 5 min and adjusted to pH 7 with 0.1 mol/L sodium hydroxide.

Light spectrum: wavelength in nm:

280 - 800

Details on light source:

- Light intensity at sample and area irradiated: 3140 μEinstein / s m2

Details on test conditions:

TEST SYSTEM
- Temperature: 26.2°C (mean)
The temperature was > 30 °C for 4 hours during the study, due to breakdown of the cooling aggregate of the thermostat. Due to this, illumination was stopped for an hour until the aggregate worked on. This interruption was taken into account for evaluation.
- Test concentration: 50 mg/L in kinetic study, 250 mg/L in scan for transformation products (both related to Chlorhexidine digluconate Solution 20%)

REPLICATION
- No. of replicates (irradiated): 1 for each measuring time point

Reference substance:

no

Dark controls:

yes

Remarks:

Test and actinometer solution, not irradiated

Preliminary study:

The theoretical maximum photolysis loss over a 30 day/night period at latitude 50°N was calculated to be 100 %.

Quantum yield (for direct photolysis):

7.353

DT50:

> 69.1 d

Test condition:

in winter, 50° N, near surface

Transformation products:

yes

Details on results:

Three additional signals at RRT (relative retention time based on Chlorhexidine) 0.406, 0.761 and 0.827 were observed at all sampling intervals. All detected signals were < 10 % of the initial Chlorhexidine signal and therefore no major degradation products were determined.
A possible structure of the degradation product at RRT 0.827 (most intense signal) was postulated: N-(4-chlorophenyl)-N'-[6-({imino¬[(iminomethylene)amino] methyl}amino)hexyl]imidodicarbonimidic diamide.
For the degradation product at RRT 0.406 mass signals at 212.2 and 273.3 Da and for the degradation product at RRT 0.761 mass signals at 503.2, 354.3 and 252.3 Da were observed. No structures were postulated for these signals.

Photolysis Results for the PNAP Actinometer; laboratory conditions (Simulated sunlight, 3140 µmol photons / s m²)

 

Photolysis time [h]	Concentration [mg/L]
0.00	3.26
17.50	2.57
91.92	1.78
113.42	1.60
140.83	1.26
185.08	0.795
262.50	0.503
283.25	0.537
354.92	0.358

 

Hydrolysis Results forChlorhexidine Digluconate Solution 20 %(dark control)

Photolysis time [h]	Concentration [mg test item/L]
0.00	43.8
91.92	57.2
140.83	55.7
262.50	56.4
283.25	55.6
308.50	57.4
354.92	58.7

Photolysis Results forChlorhexidine Digluconate Solution 20 %; laboratory conditions (Simulated sunlight, 3140 µmol photons / s m²)

 

Photolysis time [h]	Concentration [mg test item/L]	ln Concentration (ln c)
0.00	43.8	3.780
17.50	53.3	3.976
42.42	48.5	3.882
91.92	40.7	3.706
113.42	38.7	3.656
140.83	23.6	3.161
185.08	21.1	3.049
262.50	8.82	2.177
283.25	11.5	2.442
308.50	5.14	1.637
354.92	0.822	-0.196*

*) = Outlier, not taken into account for evaluation

Estimated Direct Photolysis Rate Constants of Chlorhexidine Digluconate Solution 20 % in Near Surface Clear Natural Water at Latitude 50° N:

	Spring	Summer	Fall	Winter
Rate constant [1/h]	2.101 · 10^-3	3.369 · 10^-3	1.046 · 10^-3	4.177 · 10^-4
Half-life t1/2[d]	13.7	8.6	27.6	69.1

Validity criteria fulfilled:

yes

Conclusions:

Direct photolysis rate constants and half lives for near surface clear natural water during spring, summer, fall, and winter at latitude 50° N were estimated based on the laboratory data. The estimated half-lifes were between 8.6 d in summer and 69.1 d in winter. A reaction rate for natural water bodies was not determined. Under natural conditions photolysis occurs exclusively near the water surface. In deeper water layers photolysis is inhibited by dullness and light disperion. Therefore, the determined reaction rates cannot be adopted for environmental half-lifes.

Description of key information

Direct photolysis rate constants and half-lives for near surface clear natural water during spring, summer, fall, and winter at latitude 50° N were estimated based on the laboratory data. The estimated half-lifes were between 8.6 d in summer and 69.1 d in winter. A reaction rate for natural water bodies was not determined. Under natural conditions photolysis occurs exclusively near the water surface. In deeper water layers photolysis is inhibited by dullness and light dispersion. Therefore, the determined reaction rates cannot be adopted for environmental half-lives. 

Key value for chemical safety assessment

Half-life in water:

8.6 d

Additional information

The value for summer is reported as key value.