Teflubenzuron

Biodegradation in water and sediment: simulation tests

Description of key information

The DT50 of teflubenzuron was investigated in two water/sediment systems. In water  the DT50 ranged between 4.9 and 9.7 days, in total system between 11.4 and 21.4 days. The geomean DT50 of teflubenzuron at 20 °C in freshwater was determined to be 6.9 days. The geomean DT50 in whole system was determined to be 15.6 days at 20 °C.

The geometric mean DT50 of teflubenzuron was calculated to be 33.1 days at 12 °C in total system and 14.6 days at 12 °C in water (Chapter R.7b, p.222: Endpoint specific guidance Version 4.0 – June 2017).

Key value for chemical safety assessment

Half-life in freshwater:

14.6 d

at the temperature of:

12 °C

Whole System

Half-life in whole system:

33.1 d

at the temperature of:

12 °C

Type of system:

fresh water and sediment

Additional information

Three studies were performed to address the behaviour in water/sediment systems. One of the studies was carried out according to Dutch biological guidelines and does not cover the current requirements for water/sediment studies with regard to organic matter content and water/sediment ratio. It is therefore not described here. A second study was performed in marine water/sediment systems and is described below as supporting information, as well as its kinetic assessment. The third study is the key study, performed according to current guidelines and is summarized below.

 

For details please refer to Draft Assessment Report for teflubenzuron prepared according to the Commission Regulation (EU) No 1107/2009, Volume 3 – B.8 (AS) (October 2007).

 

Key study

 

Batelle (2006): [14C]-teflubenzuron: (benzoyl and aniline labelled) Degradation and Retention in Two Water/Sediment Systems. DocID according to Draft Assessment Report prepared in compliance with Regulation (EC) No 1107/2009: 20061024568; crossreference to Draft Assessment Report according to Regulation (EU) No 1107/2009: CA 7.2.1.3.2/03

 

The route and rate of degradation of [¹⁴C]-teflubenzuron (benzoyl and aniline labelled) has been investigated in two water-sediment systems collected from sites in the UK. The sediments were characterised as a sand (pH in water 5.5, % OC 0.7) and a clay (pH in water 7.1,%OC 5.0).

The systems were incubated in glass flasks containing sediment and associated water at a ratio of 1:4 (w/w). Throughout the experiment the flasks were maintained in the dark at 20 ± 2°C whilst attached to an incubation system allowing air to be bubbled through the surface water and a series of traps for trapping volatile degradates. The water/sediment systems were incubated for approximately 10 days prior to application of teflubenzuron to enable acclimatisation to occur. The redox potential of the sediment and water in control flasks was measured at regular intervals prior to dosing and during incubation. The pH and dissolved oxygen content of the water was also measured.

Teflubenzuron was applied to the water surface at an application rate equivalent to 120 g/ha and water and sediment samples were incubated for 120 days. At intervals (0, 1, 3, 7, 14, 30, 60 and 120 days) throughout the study single flasks and their corresponding traps were removed from the incubation system. The water was decanted off and extracted, and the sediment extracted using a range of suitable solvents and conditions. Following concentration, the components present in the water (solvent extracts and residual water) and in the sediment extracts were characterised and quantified by HPLC. In addition, selected extracts were analysed by LC-MS to provide confirmation of structural identity. The redox potential of the sediment and water, and the pH and dissolved oxygen content of the water were measured at each sampling point.

The total material balance in the samples treated with the benzoyl labelled teflubenzuron were 101.2% mean (range 90.2 to 121.3%) in system 05/011 and 94.7% mean (range 88.5 to 101.4%) in system 05/024. The total material balance in the samples treated with the aniline labelled teflubenzuron were 93.6% mean (range 73.0 to 100.0%) in system 05/011 and 94.1% mean (range 83.2 to 99.5%) in system 05/024. The mass balance in individual samples only fell significantly below 90% at late time points and was shown to be due to loss of known volatile components from the sediment fraction during extraction and drying prior to combustion.

The concentration of teflubenzuron in the water decreased from >99% (mean value) at day 0 to <0.5% (mean value) of the applied amount by study termination at 120 days in both systems. The concentration of teflubenzuron in the sediment increased to a maximum value of 38.6% of applied (mean) at day 7 in system 05/011 and 36.2 % (mean) at day 14 in system 05/024. In both systems the concentration of teflubenzuron in the sediment then fell steadily reaching 2.5% of applied (mean) in system 05/011 and 5.4% (mean) in system 05/024 by study termination at 120 days.

The major transformation products detected in the water were 3,5-dichloro-2,4-difluorophenylurea (22.5% maximum), 3,5-dichloro-2,4-difluoroaniline (26.4% maximum), 2,6-difluorobenzoicacid (13.8% maximum) and dissolved ¹⁴CO₂ (14.1% maximum). One additional metabolite detected in the samples dosed with the aniline label at up 19.1% of applied radioactivity in system 05/011, was identified in additional experiments as 5-chloro-2.4-difluoroaniline. This metabolite was not persistent and declined to only 2% by 120 days in system 05/011 and was only actually observed in one sample in system 05/024. Six minor unknowns were also detected but none ever exceeded 6% of applied radioactivity.

The majority of the radioactivity detected in the sediment phase was teflubenzuron. Significant transformation products detected in the sediment were 3,5-dichloro-2,4-difluoroaniline (maximum 12.8%), 5-chloro-2,4-difluoroaniline (maximum 10.3%) and 3,5-dichloro-2,4-difluorophenylurea (maximum 3.8%).

Non-extractable residues in the sediment increased to a maximum of 34% in the samples treated with the benzoyl labelled teflubenzuron and 60% in the aniline labelled samples. At the end of the study > 60% of the applied radioactivity had been transformed into ¹⁴CO₂ in both samples treated with the benzoyl labelled teflubenzuron (total in volatile traps and retained in water) and 12.3-13.5% in the aniline labelled samples.

The half-lives of teflubenzuron in the water phase and in the total system, using a first-order
kinetic analysis of the results, were determined to be as follows:

		DT50(Days)	Significance level (%)	r^2
Sediment 05-011	Water	5.0	>99	0.960
	Total System	11.4	>99	0.969
Sediment 05-024	Water	9.7	>99	0.976
	Total System	21.5	>99	0.987

 

Overall it can be concluded that the degradation of teflubenzuron in water sediment systems under aerobic conditions at 20 ± 2°C occurs at a fast rate and that the compound will not be persistent in the environment. Mineralisation of both rings to carbon dioxide proceeds via initial cleavage of the teflubenzuron to form 3,5-dichloro-2,4-difluorophenylurea and 2,6-difluorobenzoicacid. The urea is further degraded via the anilines 3,5-dichloro-2,4-difluoroaniline and 5-chloro-2,4-difluoroaniline ultimately forming unextractable residues and carbon dioxide. The benzoic acid is also further degraded to form unextractable residues and carbon dioxide.

 

 

 

Supporting information

 

Huntingdon Life Sciences (1997): Teflubenzuron: A Study of the Degradation and Retention of Teflubenzuron in the Marine Water/Sediment System. DocID according to Draft Assessment Report prepared in compliance with Regulation (EC) No 1107/2009: TZ-630-004; crossreference to Draft Assessment Report according to Regulation (EU) No 1107/2009: CA 7.2.1.3.2/02

 

And

 

Batelle (2003b): Teflubenzuron: Kinetic Modelling Analysis of Data from laboratory Water/Sediment Studies. DocID according to Draft Assessment Report prepared in compliance with Regulation (EC) No 1107/2009: 2003/1028439; crossreference to Draft Assessment Report according to Regulation (EU) No 1107/2009:

 

These studies are summarized in the following for sake of completeness but have however not been documented in separate IUCLID Endpoint Study Records.

 

The study in the marine water/sediment systems was performed according to UK Veterinary Medicines Directorate. It was not evaluated fully by the RMS during Annex I procedure since the relevance of the study was not justified by the Notifier and it was therefore not used for regulatory purposes.

The metabolism, degradation and partitioning behaviour of [¹⁴ C]-teflubenzuron uniformly labelled in the benzoyl and in the aniline ring was determined in 2 marine water/sediment systems. A sandy silt loam and a sandy silt loam/silt loam were taken with their associated water from 2 sites. The test substances were added at 0.019 mg/L, close to the water solubility of teflubenzuron. The water/sediment systems were incubated in aerobic conditions at 10 °C in the dark for 100 days, the duration of the study. Sterile samples were also prepared. For the test with the aniline labelled compound, samples were taken on days 0, 1, 2, 7, 14, 30, 50, 75 for the sandy silt loam /silt loam and 78 for the sandy silt loam, and 100. For the test with the benzoyl labelled compound, sampling was on days 0, 1, 2, 7, 14, 30, 50 for the sandy silt loam /silt loam and 68 for the sandy silt loam, 75 for the sandy silt loam /silt loam and 78 for the sandy silt loam, and 100. The aqueous phase and the sediments were analyzed at selected intervals up to 100 days for teflubenzuron and metabolites by HPLC and TLC. Half-lives for the parent in the different compartments were calculated on the assumption that biodegradation followed first-order kinetics.

The following results were achieved: Partitioning of radioactive material into the sediment phase occurred relatively rapidly. After 2 days the level of teflubenzuron and its metabolites in the aqueous phase was less than 50% of applied radioactivity, and by 100 days virtually all the radioactivity was associated with the sediment phase. Very little degradation was detected in the sterile samples indicating that the degradation observed was largely biological.

For the majority of the systems radiochemical mass balance was good. 0.1% and 0.4% of applied radioactivity was collected as [¹⁴C]-CO₂ during the study from the sandy silt loam and sandy silt loam/silt loam sediment/water systems fortified with [¹⁴C-aniline]-teflubenzuron. However, 27.6% and 11.0% of applied radioactivity was collected as [¹⁴C]-CO₂ during the study from the sandy silt loam and sandy silt loam/silt loam sediment/water systems fortified with [¹⁴C-benzoyl]-teflubenzuron. This shows a more rapid degradation of the benzoyl portion of teflubenzuron compared to the aniline portion. Only 0.1% of applied radioactivity, or less, was collected as [¹⁴C]-CO₂ from the sterilised water/sediment systems fortified with either [¹⁴C-aniline]-teflubenzuron or [¹⁴C-benzoyl]-teflubenzuron showing little or no mineralisation in the sterile systems.

[¹⁴C-aniline]-teflubenzuron was metabolised to 3,5-dichloro-2,4-difluorophenylurea and 3,5-dichloro-2,4-difluoroaniline in the marine water/sediment systems.

In the marine water/sandy silt loam sediment system levels of the metabolites reached a maximum at 50 days (10.1% AR and 0.4% AR for 3,5-dichloro-2,4-difluorophenylurea and 3,5-dichloro-2,4-difluoroaniline respectively) and also in the marine water/sandy silt loam/silt loam sediment system levels of the metabolites a maximum was reached at 50 days (11.7% AR for 3,5-dichloro-2,4-difluorophenylurea) and 100 days (1.6% AR for 3,5-dichloro-2,4-difluoroaniline).

[¹⁴C-benzoyl]-teflubenzuron was metabolised to [¹⁴C]-CO₂ (27.6% AR and 10.7% AR at 100 days in the sandy silt loam and sandy silt loam/silt loam systems respectively) and to 2,6-difluorobenzoic acid. The level of 2,6-difluorobenzoic acid reached a maximum at 30 days (14.9% AR) and 75 days (5.5% AR) in the sandy silt loam and the sandy silt loam/silt loam sediment/water systems respectively.

The overall recoveries were in the range of 91.7 to 99.8% of applied radioactivity, except at 14 days, when the recovery was 74.1% AR. It is possible that methane was a degradation product, but this would not have been collected in the trapping solutions.

Levels of teflubenzuron were plotted against time to determine with computerized statistical models half-lives from the degradation curves.

Sandy silt loam system	DT50 (days)
Water phase Sediment phase Total system	1 40 - 67 41 - 75
Sandy silt loam/silt loam system	DT50 (days)
Water phase Sediment phase Total system	1 38 – 60 48 - 60

 

 

A second kinetic assessment on the marine water/sediment data was performed by Batelle (2003b), to obtain kinetic rate constants and first-order half-life values for teflubenzuron and its metabolites by a series of formulas using Excel spreadsheets.

The DT₅₀ values obtained from the model fits compare well with the experimental data, except for the late occurrence of the benzoic acid maximum in the sandy silt loam / silt loam system. For the two water/sediment studies, the conversion percentage (CP) of the parent to the phenylurea metabolite was found to be high (ie 75% to 100%). These percentage were assumed for the subsequent metabolite analyses.

The observed phenylurea metabolite concentrations correspond to DT₅₀ values of 13 to 23 days, with a maximum after 40 to 60 days. The observed aniline concentrations, formed by degradation of the phenylurea metabolite, and directly from teflubenzuron degradation correspond to a short DT50 values of <1 to 3 days. The amide metabolite was not observed (< 0.1 %) which postulates either a very low formation rate and/or a very short DT₅₀. The observed non-occurrence fits to a DT₅₀ of <2days. The benzoic acid metabolite can be formed by degradation of the amide metabolite and directly from teflubenzuron degradation. The observed concentrations correspond to a DT₅₀ of 8 to 13 days in the sandy silt loam experiment and to 3 to 4 days in the sandy silt loam / silt loam system.

 

It can be concluded that the first order model fits of the experimental data describe the behaviour of teflubenzuron and its metabolites well. DT₅₀ values could be estimated for teflubenzuron and all metabolites. All metabolites can be assumed to have short or very short half-lives in water sediment systems, with the phenylurea metabolite degradation being the time limiting step.

 

System	DT50 (days) whole system
	Teflubenzuron	3,5-dichloro-2,4-difluorophenylurea	3,5-dichloro-2,4-difluoroaniline	2,6-difluorobenzamide	2,6-difluorobenzoic acid
Sandy Silt loam	41 - 75	13 - 21	≤ 1	2	8 - 13
Sandy Silt Loam/Silt loam	48 - 60	17 - 23	1 - 3	≤ 2	3 - 4

 

 

 

Conclusion

Three studies were performed to investigate the behaviour in water/sediment systems. The use and relevance of the marine water/sediment systems (HRC, 1997 and kinetic assessment Batelle 2003b) was not fully justified by the Notifier. Therefore the study was not fully evaluated and not used in the risk assessment. However, examination of the results in the study summary indicates teflubenzuron and its metabolites rapidly dispersed from water and were declining in sediment at study end. The study performed by Dutch guidelines was not compatible with the 91/414 requirements and not used in the risk assessment and is not described here. Only the study (Batelle, 2006) was conducted to current guidelines, considered valid and used in the risk assessments.

The RMS calculated water phase DT₅₀ values of 4.9 and 9.7 days (as a mean of the results from both labelled rings), in the 05-011 and 05-024 water/sediment systems respectively. Corresponding DT₅₀ values of 11.4 and 21.4 days were calculated for the total water/sediment systems.

 

The geomean DT50 of teflubenzuron was calculated to be 29.6 days at 12 °C in total system and 13.1 days at 12 °C in water using the EUSES formula (640):

 

DT50bio_{water_temp env} = DT50bio_{water_temp test *} e ^{(0.08*(TEMPtest-TEMPenv))}

 

Input
DT50biowater_temp test	half-life for biodegradation in water at a temperature of the data set	[d]
TEMPtest	temperature of the measured data in simulation test	[K]
TEMP	environmental temperature	[K]
Output
DT50biowater_temp env	half-life for biodegradation in water at the environmental temp.	[d]