Desmedipham

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2012-05-03 to 2013-06-28

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Version / remarks:

2004

Deviations:

not specified

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Analytical monitoring:

yes

Details on sampling:

- Sampling intervals for the parent/transformation products: Three samples were taken immediately after application (0 h) whereas two samples were taken at the respective sampling intervals (Table 1).

Buffers:

- pH: pH4, pH7, pH7 repetition & pH 9

- Composition of buffer:
pH 4:
500 mL potassium hydrogen phthalate solution (10.21 g C8H5KO4 / 500 mL pure water) was mixed with 40 mL sodium hydroxide solution (0.1 mol/L NaOH) and filled up to 1000 mL with pure water.

pH 7:
500 mL potassium dihydrogen phosphate solution (6.81 g KH2PO4 / 500 mL pure water) was mixed with 296 mL sodium hydroxide solution (0.1 mol/L NaOH) and filled up to 1000 mL with pure water.

pH 7-Repetition:
125 mL potassium dihydrogen phosphate solution (3.395 g KH2PO4 /250 mL pure water) was mixed with 74 mL sodium hydroxide solution (0.1 mol/L NaOH) and filled up to 250 mL with pure water.

pH 9:
500 mL boric acid solution (3.09 g H3BO3 / 500 mL KCl 0.1 mol/L) was mixed with approx. 213 mL sodium hydroxide solution (0.1 mol/L NaOH) and filled up to 1000 mL with pure water.
:

Details on test conditions:

EXPERIMENTAL CONDITIONS:
The main tests were performed in buffered solutions at pH 4, 7 and 9 at three different temperatures each (pH 4: 20, 50 and 60°C; pH 7, 9: 20, 25 and 30°C). To verify the results obtained at pH 7 the test was repeated under almost equal conditions. Stoppered glass flasks were used for carrying out the tests and all glassware was sterilised. The test vessels were maintained at constant temperature in the dark. Considering a rapid degradation of the test item at pH 7 and 9 at 20 °C a preliminary test was performed only for the labelled test item at pH 4 and at 50 °C.

Solutions for each temperature of different pH values were prepared separately. The concentrations ranged from 1.25 mg/L to 1.33 mg/L. The maximum concentration of 1.33 mg/L was below half of the saturation concentration of the test item in water (7 mg/L at 25°C). The percentage of organic co-solvent in the test solution was < 1% (v/v).

OTHER TEST CONDITIONS
- pH: The test was carried out with buffer solutions at three pH-values (pH 4, 7 and 9).
- Dissolved oxygen: To avoid oxidation or microbial degradation reactions by oxygen and microorganisms respectively, the buffer solutions were purged with nitrogen gas and sterilized before use by heating them in an autoclave or pressure cooker.

Number of replicates:

The main tests were performed in buffered solutions at pH 4, 7 and 9 at three different temperatures each (pH 4: 20, 50 and 60°C; pH 7, 9: 20, 25 and 30°C). To verify the results obtained at pH 7 the test was repeated under almost equal conditions. The degradation rate of Desmedipham and transformation product pattern was almost equal for both approaches.

Transformation products:

yes

Remarks:

Desmedipham was hydrolysed to form two metabolites, EHPC and aniline in equal amounts.

No.:

#2

No.:

#1

Key result

pH:

4

Temp.:

12 °C

DT50:

10 368.2 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Calculated from result at 20 °C

Key result

pH:

7

Temp.:

12 °C

DT50:

2.1 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Calculated from result at 20 °C and 19 °C

Key result

pH:

9

Temp.:

12 °C

DT50:

0.02 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Calculated from result at 20 °C

Details on results:

MAJOR TRANSFORMATION PRODUCTS
At pH4:
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed:
At pH 4 aniline was the only known major degradation product detected at each temperature. Percentages (referred to the entire radioactivity within the samples) of aniline found at the end of incubation were 1% (mean value) at 20 °C, 52% at 50 °C and 68% at 60 °C. In case of pH 4 at 50 °C and 60 °C an unknown degradation product emerged after 5 and 3 days of incubation, respectively. The compounds' percentage of 8% and 9% (mean) respectively remained steady until the end of incubation. No efforts were made to characterise the unkown degradation product further as i) the percentage of the compound was in average below 10% of the entire radioactivity and ii) could only be found under harsh conditions (50 °C and 60 °C).

At pH7:
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed:
Samples at pH 7 were incubated at 20°C, 25°C and 30°C for 36 h, 25 h and 16 h, respectively. The test was repeated once to verify the results obtained during the first approach. For the repetition, samples were incubated at 19°C, 25°C and 30°C for 45 h, 30 h and 14 h, respectively. The degradation rate of desmedipham and degradation product pattern was almost equal for both approaches. Aniline was detected as known major degradation product at each temperature. Percentages (referred to the entire radioactivity within the samples) of aniline found at the end of incubation were 52% (mean) at 20 °C, 69% at 25 °C and 86% at 30 °C for the first approach and 65% (mean) at 19 °C, 83% at 25 °C and 81% at 30 °C for the repeated test. Additionally, EHPC was detected as known major degradation product at each temperature. Percentages (referred to the initially applied amount) of EHPC found at the end of incubation were 66% (mean) at 20 °C, 80% at 25 °C and 87% at 30 °C for the first approach and 69% (mean) at 19 °C, 86% at 25 °C and 85% at 30 °C for the repeated test.

In both approaches an unknown degradation product was found at each temperature with an average percentage at the end of incubation of 14% (mean) at 20 °C, 14% at 25 °C and 6% at 30 °C for the first approach and 8% (mean) at 19 °C, 6% at 25 °C and 9% at 30 °C for the repeated test.

Repetition at pH 7:
Samples were analysed immediately after sampling and individual samples were re-analysed after approx. 60 days in case of the first test approach and after 48 h in case of the repeated approach to verify the stability of the unknown transformation product. Results indicate a degradation of the unknown product to aniline during storage of the samples at approx. 4°C in the dark. Thus, it can be proposed that the structure of the unknown degradation product was closely related to aniline. No efforts were made to characterise the unknown transformation product further as the compound was not stable during storage at low temperature. Under general environmental conditions (i.e. 20 °C), a rapid transformation of the unknown product would occur.

At pH9:
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed:
At pH 9 the only detected major degradation product was aniline which was detected via HPLC coupled with radiodetection at each temperature. Percentages (referred to the entire radioactivity within the samples) of aniline found at the end of incubation were 72% (mean value) at 20 °C, 82% at 25 °C and 92% at 30 °C. EHPC was detected as known major degradation product at each temperature. Percentages (referred to the initially applied amount) of EHPC found at the end of incubation were 77% (mean) at 20 °C, 89% at 25 °C and 100% at 30 °C. No unknown transformation product could be observed in course of incubation.

Material balance

Mean material balances were 101% AR for pH 4 at 20 °C, 97% AR for pH 4 at 50 °C and 91% AR for pH 4 at 60 °C (overall for pH 4 96% AR). For pH 7 mean material balances were 98% AR at 20 °C, 96% AR 25 °C and 91% AR at 30 °C (overall for pH 7 95% AR). For repetition of pH 7 mean material balances were 102% AR at 19 °C, 97% AR 25 °C and 98% AR at 30 °C (overall for pH 7 99% AR). For pH 9 mean material balances were 112% AR at 20 °C, 110% AR 25 °C and 89% AR at 30 °C (overall for pH 9 103% AR).

 

The hydrolysis of aniline labelled desmedipham is presented in Tables from 2 to 6. 

Table 2: Hydrolysis of aniline labelled desmedipham at pH 4 (values expressed as % nominal for desmedipham and in % peak of entire chromatogram for aniline and unknown)

20 °C
Compound	Replicate No.	Interval [days]
		0	1	2	10	15	20	24	30
	A	104	105	95	102	98	92	97	99
desmedipham	B C	94 102	92 -	98 -	91 -	95 -	94 -	99 -	98 -
	Mean	100	99	97	97	97	93	98	99
aniline		n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	2
unknown ^1		n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.
50 °C
Compound	Replicate No.	Interval [days]
		0	1	2	10	15	20	24	30
	A	101	88	75	68	57	54	44	39
desmedipham	B C	103 96	86 -	85 -	70 -	59 -	51 -	46 -	41 -
	Mean	100	87	80	69	58	52	45	40
aniline		n.d.	13	24	28	38	45	50	52
unknown ^1		n.d.	n.d.	n.d.	n.d.	8	5	7	10
60 °C
Compound	Replicate				Interval [days]
	No.	0	1	2	10	15	20	24	30
	A	100	78	55	27	19	21	20	27
desmedipham	B C	99 101	83 -	56 -	30 -	25 -	22 -	20 -	20 -
	Mean	100	81	56	29	22	21	20	24
aniline		n.d.	17	40	64	71	70	72	68
unknown ^1		n.d.	n.d.	n.d.	9	9	10	8	11

n.d.: not detected

¹ could only be found under harsh conditions at 50°C and 60°C, which are nor representative for environmental

 

Table 3: Hydrolysis of aniline labelled desmedipham at pH 7 (values expressed as % nominal for desmedipham and EHPC, and in % peak of entire chromatogram for aniline and unknown)

20 °C
Compound	Replicate No.	Interval [hours]
		0	4	8	12	20	24	28	32	36
	A	101	80	77	64	52	49	43	40	32
desmedipham	B C	99 100	89 -	77 -	68 -	54 -	47 -	38 -	35 -	34 -
	Mean	100	85	77	66	53	48	41	38	33
	A	N/A	9	19	29	42	49	61	65	62
EHPC	B C	N/A N/A	9 -	24 -	29 -	43 -	52 -	55 -	60 -	71 -
	Mean	N/A	9	21	29	43	50	58	62	66
aniline		n.d.	10	16	25	35	43	46	51	52
unknown ^1		n.d.	4	6	8	9	10	10	11	14
25 °C
Compound	Replicate No.	Interval [hours]
		0	2.5	5	7.5	10	12.5	20	22.5	25
	A	101	88	71	56	47	37	21	19	16
desmedipham	B C	99 100	89 -	75 -	57 -	51 -	37 -	25 -	16 -	15 -
	Mean	100	89	73	57	49	37	23	18	16
	A	N/A	15	29	44	50	57	72	78	82
EHPC	B C	N/A N/A	21 -	32 -	48 -	49 -	60 -	87 -	82 -	78 -
	Mean	N/A	18	30	46	50	58	80	80	80
aniline		n.d.	14	25	35	42	51	63	68	69
unknown ^1		n.d.	5	6	9	8	10	13	13	14
30 °C
Compound	Replicate No.	Interval [hours]
		0	2	4	6	8	10	12	14	16
	A	96	77	55	41	30	19	14	12	8
desmedipham	B C	103 101	72 -	52 -	39 -	26 -	20 -	14 -	12 -	6 -
	Mean	100	75	54	40	28	20	14	12	7
EHPC	A B C Mean	N/A N/A N/A N/A	30 29 - 29	50 52 - 51	60 61 - 60	70 68 - 69	76 79 - 78	85 82 - 84	82 96 - 89	89 86 - 87
aniline		n.d.	25	40	55	63	72	80	83	86
unknown ^1		n.d.	6	9	9	10	8	6	6	6

n.d.: not detected; N/A: not applicable

¹: The unkown transformation product was not stable during storage at low temperature. Under general environmental conditions (i.e. 20°C), a rapid transformation of the unknown product would occur.

 

Table 4:  Hydrolysis of aniline labelled desmedipham at pH 7, repetition (values expressed as % nominal for desmedipham and EHPC and in % peak of entire chromatogram for aniline and unknown)

19 °C
Compound	Replicate No.	Interval [hours]
		0		5		10		21		25		30		34		45
	A	101		78		71		51		45		41		36		23
desmedipham	B C	100 99		86 -		70 -		55 -		47 -		40 -		38 -		27 -
	Mean	100		82		71		53		46		41		37		25
	A	N/A		N/A		24		45		51		55		60		69
EHPC	B C	N/A N/A		N/A N/A		23 -		46 -		50 -		55 -		59 -		70 -
	Mean	N/A		N/A		23		46		51		55		59		69
aniline		n.d.		15		22		43		47		52		56		65
unknown		n.d.		n.d.		0		4		6		5		6		8
25 °C
Compound	Replicate No.	Interval [hours]
		0	2.5		5		7.5		10		21		23		26		30
	A	100	78		64		62		49		22		19		15		12
desmedipham	B C	98 102	85 -		70 -		58 -		48 -		20 -		16 -		12 -		12 -
	Mean	100	82		67		60		49		21		18		14		12
	A	N/A	N/A		33		44		50		77		83		85		85
EHPC	B C	N/A N/A	N/A N/A		35 -		44 -		51 -		76 -		84 -		84 -		87 -
	Mean	N/A	N/A		34		44		51		77		83		85		86
aniline		n.d.	17		26		36		44		72		75		80		83
unknown		n.d.	4		6		7		9		8		8		8		6
30 °C
Compound	Replicate No.	Interval [hours]
		0		1		2		4		6		8		12		14
	A	101		75		64		49		32		24		12		10
desmedipham	B C	96 103		78 -		67 -		46 -		32 -		23 -		14 -		10 -
	Mean	100		77		66		48		32		24		13		10
	A	N/A		N/A		27		48		62		71		84		85
EHPC	B C	N/A N/A		N/A N/A		28 -		48 -		62 -		72 -		83 -		85 -
	Mean	N/A		N/A		28		48		62		72		84		85
aniline		n.d.		13		25		40		55		65		76		81
unknown		n.d.		4		6		10		11		11		11		9

n.d.: not detected; N/A: not applicable

¹ The unkown transformation product was not stable during storage at low temperature. Under general environmental conditions (i.e. 20°C), a rapid transformation of the unknown product would occur.

 

Table 5: Hydrolysis of aniline labelled desmedipham at pH 9 (values expressed as % nominal for desmedipham and EHPC and in % peak of entire chromatogram for aniline and unknown)

20 °C
Compound	Replicate No.	Interval [hours]
		0	2.5	5		7.5		10		12.5		15		17.5		20		22.5
	A	79	66	90		49		45		40		52		27		28		21
desmedipham	B C	90 130	64 -	55 -		50 -		47 -		56 -		57 -		30 -		28 -		29
	Mean	100	65	73		50		46		48		55		29		28		25
	A	8	29	60		44		58		59		96		68		73		74
EHPC	B C	6 11	30 -	39 -		47 -		53 -		88 -		104 -		69 -		73 -		76 -
	Mean	8	29	49		45		55		73		100		68		73		75
aniline		6	28	37		44		50		55		61		68		68		72
25 °C
Compound	Replicate No.	Interval [hours]
		0	2		4		6		8		10		12		14		16
	A	134	55		48		49		47		27		24		16		18
desmedipham	B C	85 81	53 -		45 -		36 -		45 -		25 -		19 -		26 -		16 -
	Mean	100	54		47		43		46		26		21		21		17
EHPC	A B C Mean	11 6 6 8	36 36 - 36		49 49 - 49		77 59 - 68		104 107 - 106		73 74 - 74		79 78 - 78		84 127 - 105		88 87 - 87
aniline		8	36		46		58		65		71		76		81		82
30 °C
Compound	Replicate No.	Interval [hours]
		0	1.5		3		4.5		5		7.5		9		10.5		12
	A	98	87		46		35		25		18		15		10		9
desmedipham	B C	101 101	60 -		43 -		37 -		28 -		17 -		19 -		15 -		10 -
	Mean	100	73		45		36		26		18		17		12		10
	A	9	68		61		74		83		83		92		97		96
EHPC	B C	8 8	47 -		64 -		74 -		107 -		89 -		133 -		137 -		99 -
	Mean	8	57		63		74		95		86		113		117		98
aniline		8	46		61		68		79		84		88		92		92

n.d.: not detected

 

Table 6: Hydrolytic kinetics of aniline-labelled desmedipham in buffer (pseudo first order)

pH	Temperature [°C]	DT50 ^1	rate constant Kobs ^2
4	20	4884 days	0.0001 days^-^1
	50	7 days	0.0932 days^-^1
	60	4 days	0.1647 days^-^1
7	20	23 hours	0.030 hours^-1
	25	9 hours	0.077 hours^-1
	30	4 hours	0.163 hours^-1
7 (repetition)	19	24 hours	0.029 hours^-1
	25	9 hours	0.074 hours^-1
	30	4 hours	0.159 hours^-1
9	20	14 minutes	0.0508 minutes^-^1
	25	8 minutes	0.0890 minutes^-^1
	30	4 minutes	0.1847 minutes^-^1

1 t1/2 = ln2/kobs ² K_obs = slope

Validity criteria fulfilled:

yes

Conclusions:

RMS comments and conclusion: The study followed the OECD test guideline 111 (2004) and fulfilled the validity criteria for material balance. The temperature was maintained within ± 0.2 to ± 0.6 °C during the study which is line line with the recommended ± 0.5 °C in the guideline. The sterility was maintained throughout the study and was checked with a commercially available dip slide kit (Hycon GKT/HS, Heipha Dr. Müller GmbH, Eppelheim, Germany) which was used for a total count of microorganisms (GK-T agar) and to determine the total count of yeast and moulds (HS agar). No colonies on the agar were observed. The study is considered valid. The study was performed with aniline ring labeled desmedipham, but EHPC in test samples were co- cromatograhped with EHPC standard. The hydrolytic degradation of desmedipham is strongly dependent on the pH of the solution. Desmedipham was hydrolysed to form two metabolites, EHPC and aniline quite in equal amount which is also the assumption based on the molecular structure of desmedipham. The mean calculated half-lives for desmedipham were 4884 days (stable), 23.5 hours and 14 min at pH 4, 7 and 9, respectively at 20 °C. The results also show that the amount of aniline and EHPC increased towards the end of the study in all test pH showing that these metabolites do not hydrolyse. Hence, no separate hydrolysis study needs to be performed with metabolites. The unknown degradation product found at pH 7 was rapidly transformed to aniline and therefore would be assumed to be the unstable intermediate phenyl carbamic acid which will be transformed under CO2 elimination to aniline.

Executive summary:

The purpose of the study was to determine the rate of hydrolysis of [aniline-UL-¹⁴C] desmedipham at different pH-values by quantifying the test item concentration after different incubation periods and at different temperatures. Considering a rapid degradation of the test item at pH 7 and 9 at 20 °C the main test were carried out without performing a preliminary test at those specific pH-values. In case of pH 4 the pre-test was conducted. For this, the test item was dissolved in an aqueous solution buffered at pH 4 and incubated at 50°C ± 0.9°C for a maximum of 5 days. At the end of the test 39% of the initial concentration (average) of the test item was degraded and thus a main test at pH 4 had to be performed.

 

Screening for degradation products was performed by HPLC-UV and HPLC/radiodetection. Only degradation product, aniline was found during the preleminary test. Due to the high absorption of the buffer solution at 210 nm, no information about further degradation products were obtained from HPLC-UV measurements.

 

The main tests were performed in buffered solutions at pH 4, 7 and 9 at three different temperatures each (pH 4: 20, 50 and 60 °C; pH 7, 9: 20, 25 and 30 °C). To verify the results obtained at pH 7 the test was repeated under almost equal conditions. The degradation rate of desmedipham and transformation product pattern was almost equal for both approaches. Desmedipham was found to be hydrolytically stable at pH 4 and 20 °C. At pH 4: 50 °C and 60 °C; pH 7: 20 °C, 25 °C and 30 °C and pH 9: 20 °C, 25 °C and 30 °C a significant degradation of the test item was observed. Reaction rate constants and corresponding half-lives at 20 °C were calculated to be 1.42*10^-4 d^-1 and 4884 days at pH 4, 0.030 d^-1 and 23 hours at pH 7 and 0.051 d^-1 and 14 minutes at pH 9.

 

Screening for degradation products was performed by HPLC-UV and HPLC/radiodetection. As major transformation products aniline and EHPC were characterised by co-chromatography with available reference compounds at each pH-value. At pH 7 an unknown transformation product was found. Repeated measurements of the samples stored at approx. 4 °C in the dark showed a rapid transformation of the unknown product to aniline and therefore it would be assumed that the unknown transformation product will be most probably the intermediate phenyl carbamic acid.

Description of key information

The key value for chemical safety assessment is 1.91 days at 12 °C, based on four hydrolysis studies giving a range of DT50 values from 1.66 to 2.08 days at 12 °C and pH 7.

 

In the table below all available studies are listed. For some studies only the results are presented since they are not considered relevant due to the reasons given under “Assessment”. All available studies have been evaluated within the scope of Plant Protection Regulation in the respective Draft Renewal Assessment Report (DAR) under Regulation (EC) 1107/2009.

Test type	Result for pH 7 calculated for 12 °C	Assessment	Reference
Carried out following OECD 111 guidelines, at pH 4, 7 and 9 and 20 °C	2.08 days	Key study	Riefer and Telscher (2013)
Carried out following EPA guidelines, at pH 4, 5, 7 and 9 and 25 °C	1.66 days	Supporting study	Andre (2003)
Carried out following OECD 111 guidelines, at pH 4, 5, 7 and 9 and 25 °C	1.84 days	Supporting study	Derz (2005)
Carried out following OECD 111 guidelines, at pH 4-8	2.05 days	Supporting study	Traub (2015)

Key value for chemical safety assessment

Half-life for hydrolysis:

1.91 d

at the temperature of:

12 °C