Butanal, reaction products with aniline

Phototransformation in water

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods with acceptable restrictions

Remarks:

(Non-GLP)

Study type:

direct photolysis

Principles of method if other than guideline:

The stability of the test substance in aqueous test solutions under irradiation was investigated.
The study was performed in order to examine the stability under conditions simulating those in the environment (pH 7, presence of light and air). Under these conditions, chemicals may be exposed to abiotic degradation by several chemical and physical processes, e.g. hydrolysis, oxidation and photolysis.

GLP compliance:

no

Remarks:

This study was conducted in compliance with ISO/IEC 17025 ‘General requirements for the competence of testing and calibration laboratories’.

Radiolabelling:

no

Analytical method:

high-performance liquid chromatography

Details on sampling:

- Aliquots of the samples were analysed by HPLC and UV/VIS-detection (injection volume: 50 μL)
- Samples were taken at 0 hours, 24, 72, 168, 312 and 480 hours.
- Storage : Routinely, the samples were analysed immediately. Only in exceptional cases, they were stored overnight deep frozen and protected from light.
- Reagents and Solvents: Millipore water / Acetonitrile / sodium sulphate / KH2PO4
- precipitation

Buffers:

- pH: 7

Light source:

not specified

Light spectrum: wavelength in nm:

400 - 700

Details on light source:

A photon flow density ranging from 110 to 140 μE x m-2 x s-1, or an equivalent range of 7300 to 9300 lux, was measured. The light intensity was checked before the start of the test.

Details on test conditions:

- Test 1: buffer pH7
- Test 2: in OECD 201 medium (pH of 7.4 which was adjusted with NaOH solution to pH 8 as required by OECD 201)
- continuous illumination
- 24.8 mg of the test item was dissolved in 100 mL acetonitrile. These stock solutions were 1:100 diluted with buffer solution pH 7 or with OECD 201 medium, leading to a test item concentration of 2.48 mg/L.

- After preparation, the test solutions were deposited in a climate chamber in which a temperature in the range of 22°C +/- 1°C was maintained. Temperature was measured and recorded daily.

- Half-life times and degradation rates of the test substance were calculated from the degradation curves.

Duration:

20 d

Temp.:

22 °C

Initial conc. measured:

2.48 mg/L

Reference substance:

no

Dark controls:

no

Computational methods:

Calculation was done using an external standardization method and a calibration curve. The calibration curve was calculated according to equation (1).
(1) y = a * x + b
where:
y = peak area of test item in injected sample (counts)
x = concentration of test item in injected sample (mg/L)
a = 323.8
b = -0.468
The correlation coefficient R2 was
R2 = 1.0000
To verify the calibration the recovery rate of the verification solution had to be calculated according to equation (2).
(2) recovery % = mean value of assay nominal concentration * 100
The recovery rate was 99.9 % (number of determinations: 7).

DT50:

15 d

Test condition:

Buffer pH7

DT50:

11.8 d

Test condition:

OECD 201 nutrient medium; for the last two sampling times precipitations were observed but have been made available for HPLC detection

Transformation products:

not measured

No.:

#1

No.:

#2

Details on results:

Half-life-times and photolysis rate constants at 22°C:
Test 1 (Buffer pH7):  t (½) = 15 days, k = 3.9 x 10-7 s-1
Test 2 (OECD medium): t (½) = 11.8 * days,  k = 6.8 x 10-7 *
*result to be handled with care:
In test 2, a nutrient-enriched medium containing salts was taken to examine the stability. In comparison to test 1, catalytic processes might reduce the stability. However this effect was not observed as the half-life time of about 11.8 days does not differ significantly from the half-life of 15 days obtained in test 1. However the result of test 2 should be handled with care as at least for the last two sampling times precipitations were observed. If not completely in solution during the test, the substance is hidden for reaction and cannot be degraded photolytically. On the other hand, precipitations of the substance are soluble in the HPLC eluent and have been made available for HPLC detection. For this reason it is assumed that in complete solution the reaction in test 2 should occur even more rapidly than described.

Besides aniline, other degradation products appeared in the HPLC chromatogram. Structure elucidation was not performed. Eluting in the reversed-phase chromatography prio to aniline, it can be supposed that the degradation products have a relatively high polarity.

In the environment chemicals usually occur in dilute solution which means that water is present in large excess and intensive light is available. The concentration of water remains essentially constant during photolysis. The kinetics of photolysis is often zero order or first order at fixed pH and temperature. The concentration of the test substance is determined as a function of time. In case of first order kinetics, the logarithms of the concentrations are plotted against time and the slope of the resulting straight line gives the rate constant from the formula. kobs = - slope * 2.303 (if log10 is used).

The individual results of the test series are listed in the following tables:

a) Results test 1 (Buffer pH7):

time (h)	0	24	72	168	312	480
area of peak at RT 9.6		5.9	6.5
area of peak at RT 12.2	8.8	21.3	13.8	28.2	29.2	18
area of peak at RT 12.7	64.2	15.4
area of peak at RT 13.77	25.6	21.5	22.2	12.8	14.5	9.3
area of peak at RT 15.73 (3-ethyl-4-propyl-quinoline)	21.6	61.2	71.2	53.2	26.5	11.1
area of peak at RT 17.3
area of peak at RT 20.25
area of peak at RT 20.77	6.2
Area sum RT>8 min	126.4	125.3	113.7	94.2	70.2	38.4
c/c0	1	0.99	0.90	0.75	0.56	0.30

RT = retention time in HPLC analysis

The sum of HPLC peak areas is formed by a complex behaviour of several individual components: Some of them disappear rapidly at the beginning of the test (e.g. RT 12.2, 20.77) and others are first formed and then degraded (e.g. RT 9.6, RT 15.73, 3-ethyl-4-propyl-quinoline). It is well known that photochemical reactions often follow a zero order kinetics. The half-life was calculated using the trend line in degradation curve (Figure 1, see Illustration picture below) with the equation: Half-life (h) = 1.0077/0.0015*0.5 = 360 h (15 days).

The photolysis rate constant was calculated using the equation for a zero order kinetics: c (t) = K x t  K = c(t) / t = 3.85 x 10-7 s-1

b) Results test 2 (OECD nutrient medium, pH8):

time (h)	0	24	72	168	312	480
area of peak at RT 9.6			8.5
area of peak at RT 12.2		14.1	11.2	17	16.2	12.8
area of peak at RT 12.7	36.1	11.4
area of peak at RT 13.77	24.8	22.9	18.2	12.7	18.1	18.5
area of peak at RT 15.73 (3-ethyl-4-propyl-quinoline)	17.8	29.5	28.6	15.1	10.2
area of peak at RT 17.3		6.3
area of peak at RT 20.25	24
area of peak at RT 20.77	22.2
Area sum RT>8 min	124.9	84.2	66.5	44.8	44.5	31.3
c/c0	1	0.67	0.53	0.36	0.36	0.25

RT = retention time in HPLC analysis

The sum of HPLC peak areas is formed by a complex behaviour of several individual components: Some of them disappear rapidly at the beginning of the test (e.g. RT 12.7, 20.25, 20.77) and others are first formed and then degraded (e.g. RT 9.6, RT 15.73, 3-ethyl-4-propyl-quinoline). The half-life was calculated using the trend line in degradation curve (Figure 3, see Illustration picture below) with the equation: c (t) = c0 x e-kt, Half-life = 11.8 days.

The photolysis rate constant was calculated using the same equation  K = 6.77 x 10-7 s-1

Validity criteria fulfilled:

not applicable

Conclusions:

The test item is degradable with a half-life of 15 days or less (based on a 24h-day) by direct photolysis.

Executive summary:

The stability of the test item in aqueous test solutions under irradiation was investigated. The tests were performed in order to examine the stability under conditions simulating those in the environment (pH 7, presence of light and air). Under these conditions, chemicals may be exposed to abiotic degradation by several chemical and physical processes, e.g. hydrolysis, oxidation and photolysis. Two tests have been performed at a temperature of 22°C:

- Test 1 was performed under these conditions in buffer solution,

- Test 2 was performed in an algae nutrient medium. The ingredients of the nutrient medium simulate typical environmental conditions concerning occurring traces of inorganic compounds which may influence the chemical stability of the test substance in the environment. Conditions for ventilation and nutrient medium were identical to those used in ecotox testing in accordance with OECD Guideline for Testing of Chemicals No. 201 (2006) ‘Alga, Growth Inhibition Test’.

Both tests were irradiated with illumination of 110-140 µE x m-2 x s-1; (measured in the range 400 to 700 nm) in a test volume of 25 ml in 300 mL Erlenmeyer flasks. The samples were taken at time point 0 and 5 subsequent intervals up to 480 hours (20 days) and analysed using a HPLC method with UV detection.

The degradation of the investigated test substance can be described by zero order kinetics (test 1) and first order kinetics (test 2). Half-life times and degradation rates of the test substance were calculated from the degradation curves. The results of the test series in different media clearly indicate that the test substance in water is photolytically unstable in the presence of light. The test substance is degradable with a half-life of 15 days or less (based on a 24h-day) by direct photolysis.

Description of key information

The test item is degradable with a half-life of 15 days or less (based on a 24h-day) by direct photolysis. 

Key value for chemical safety assessment

Half-life in water:

15 d

Additional information

The stability of the test item in aqueous test solutions under irradiation was investigated. The tests were performed in order to examine the stability under conditions simulating those in the environment (pH 7, presence of light and air). Under these conditions, chemicals may be exposed to abiotic degradation by several chemical and physical processes, e.g. hydrolysis, oxidation and photolysis. Two tests have been performed at a temperature of 22°C:

- Test 1 was performed under these conditions in buffer solution,

- Test 2 was performed in an algae nutrient medium. The ingredients of the nutrient medium simulate typical environmental conditions concerning occurring traces of inorganic compounds which may influence the chemical stability of the test substance in the environment. Conditions for ventilation and nutrient medium were identical to those used in ecotox testing in accordance with OECD Guideline for Testing of Chemicals No. 201 (2006) ‘Alga, Growth Inhibition Test’.

Both tests were irradiated with illumination of 110-140 µE x m-2 x s-1; (measured in the range 400 to 700 nm) in a test volume of 25 ml in 300 mL Erlenmeyer flasks. The samples were taken at time point 0 and 5 subsequent intervals up to 480 hours (20 days) and analysed using a HPLC method with UV detection.

The degradation of the investigated test substance can be described by zero order kinetics (test 1) and first order kinetics (test 2). Half-life times and degradation rates of the test substance were calculated from the degradation curves. The results of the test series in different media clearly indicate that the test substance in water is photolytically unstable in the presence of light.