Captan

Biodegradation in water and sediment: simulation tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: simulation testing on ultimate degradation in surface water

Type of information:

experimental study

Adequacy of study:

key study

Study period:

21 May 2015 to 19 September 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 309 (Aerobic Mineralisation in Surface Water - Simulation Biodegradation Test)

Version / remarks:

April 2004

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

labelled Test Item: [cyclohexene-14C]Captan
Batch number: 150320
EAS Test item code: 2015-001439
Appearance / colour: Liquid / not available
Specific activity: 55 mCi/mmol
Expiry date: 02 Apr 2016
Storage conditions deep frozen (≤ -18 °C), dark, dry
Additional Properties: Radiochemical purity was checked before application and confirmed to be 100%

Non-labelled Test Item
Batch number: SZB9174XV
Purity analysed: 99.6%
EAS Test item code: 2012-004738
Appearance / colour solid / colourless
Expiry date: 23 Jun 2016

Storage conditions ambient: (≤ +30°C) dark, dry

Radiolabelling:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

natural water

Details on source and properties of surface water:

- Details on collection (e.g. location, sampling depth, contamination history, procedure): Water was sampled from a natural aerobic surface water source in Rhineland-Palatinate (67374 Hanhofen, Germany. Water was sampled from the top 5 to 10 cm of the natural resource, on 26 June 2015. The water was transported in polyethylene containers to the laboratory. Since the transport duration did not exceed 2 to 3 hours, the water samples didn’t have to be cooled to 4 °C. The test water was cooled to 4 °C and aerated prior to use.
- Temperature (°C): 21 °C
- pH at time of collection: 8.18
- Redox potential (mv): 178
- Oxygen (below water surface) [mg/L]: 9.10
- Oxygen (water surface) [mg/L]: 9.58
- Hardness (CaCO3): 10.2 °dH
- Dissolved organic carbon (DOC) [mg/L] at study start: 8.4
- Total Organic Carbon (TOC) [mg/L] at study start: 8.4
- BOD5 [mg/L] at study start: < 1
- Biomass (e.g. in mg microbial C/100 mg, CFU or other):
- Water filtered: yes
- Type and size of filter used, if any: filtration through a filter with 100 μm mesh size

Duration of test (contact time):

60 d

Initial conc.:

93.3 µg/L

Based on:

test mat.

Initial conc.:

9.8 µg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

radiochem. meas.

Details on study design:

TEST CONDITIONS
- Volume of test solution/treatment: To be able to determine the rate and route of degradation, two different test concentrations (9.8 μg/L and 93.3 μg/L) of the radio-labelled test item were used. Based on the specific activity of 6.77 MBq/mg, this corresponds to an applied radioactivity of about 0.033 MBq and 0.32 MBq per vessel, respectively.
- Sampling interval: 0-60 days
- Water condition: Fresh sampled water, biologically active
- Water volume: 500 mL surface water
- Reference substance: 10 μg [ring-U-14C]Benzoic acid, sodium salt / L
- Number of replications (Treatments and Blanks): Duplicates
- Test flasks: Glass flasks (1000 mL)
Each water system included flasks as follows:
- 20 test flasks, treated with 9.8 μg/L [cyclohexene-14C]Captan. 18 test flasks were analysed
- 20 test flasks, treated with 93.3 μg/L [cyclohexene-14C]Captan. 18 test flasks were analysed
- 4 sterile samples, treated with 93.3 μg/L [cyclohexene-14C]Captan. Two sterile samples were analysed
- 6 reference samples, treated with 10 μg/L [ring-U-14C]Benzoic acid, sodium salt. Four reference samples were analysed
- 2 blank controls

TEST ITEM APPLICATION
- Identity of solvent: Ethanol
- Volume of application solution used per treatment: 125 μL A_HT_1; 131 μL A_HT_2
- High application rate (A_HT_1): 4.0 mL [cyclohexene-14C]Captan from the original pot. The solvent was ethanol.
- Low application rate (A_HT_2): 0.34 mL A_HT_1 was dissolved in 3.06 mL ethanol.
- Application method: Drop by drop onto the water phase

EXPERIMENTAL CONDITIONS
- Temperature [°C]: 20 ± 3 °C
- Continuous darkness (Yes/No): Yes
- Aeration: Slightly orbital movement of the test vessel on an orbital
shaker and constant air flow.
- Other details: Samples were equilibrated for 1 day in the dark.

SAMPLING
- Sampling intervals [days after treatment]: 0, 0.04 (1 hour), 0.08 (2 hours), 0.17 (4 hours), 1, 4, 14, 21 and 60.
- Measurement intervals (pH and oxygen): Once a week in the blank controls.
- Sample storage before analysis: The samples were analysed immediately or stored at <-18 °C.

ORGANIC VOLATILES
Tenax® tubes were used to trap the organic volatiles. The tube was extracted with 5 mL acetone for one hour on a flatbed shaker and the amount of radioactivity in the extract was determined in 0.5 mL aliquot by LSC.

CARBON DIOXIDE
The radioactive carbon dioxide was trapped by two flasks containing 2 M sodium hydroxide. 2 x 1 mL aliquot from each sodium hydroxide trap was analysed by LSC.

WATER PHASE
The amount of radioactivity in the test water was determined by LSC measurement. At each sampling, four aliquots (each 2 mL) were taken from the water phase before it was poured out of the incubation flask. Two aliquots served for determination of the total radioactivity within the water phase. The other two aliquots were used for determination of the radioactivity after stripping out the dissolved 14CO2. This was performed by adding 200 μL of acetic acid to each aliquot, shaking vigorously and measuring the remaining radioactivity by
LSC an hour later. In the mass balance, the amount of stripped out 14CO2 was added to the amount of 14CO2 measured in the sodium hydroxide traps.
A further aliquot of the test water was taken for the HPLC-analysis.

Reference substance:

benzoic acid, sodium salt

Compartment:

natural water: freshwater

Sampling date:

2015

% CO2:

1.4

% Other volatiles:

0.1

% Recovery:

100.9

Remarks on result:

other:

Remarks:

Mean recoveries of radioactivity, test concentration 93.3 μg/L: in the range of 97.6% to 104.2% within 60 days of incubation.

Compartment:

natural water: freshwater

Sampling date:

2015

% CO2:

< 5

% Other volatiles:

< 0.1

% Recovery:

101.15

Remarks on result:

other:

Remarks:

Mean recoveries of radioactivity, test concentration 9.8 μg/L: in the range of 97.1% to 105.2% within 60 days of incubation.

Key result

Compartment:

natural water: freshwater

DT50:

< 0.1 h

Type:

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

Temp.:

20 °C

Remarks on result:

other:

Remarks:

Due to the rapid degradation of the test item the performance of kinetic calculations was not possible. Based on the results the DT50-value for [cyclohexene-14C]Captan can be assumed to be < 1 h.

Transformation products:

yes

No.:

#4

No.:

#3

No.:

#2

No.:

#1

Details on transformation products:

MAXIMUM OCCURRENCE OF EACH TRANSFORMATION PRODUCT:

a) Metabolites, maximal mean amounts, test concentration 9.8 μg/L:
THPI 69.2% AR (at 1 hour),
THPAM 77.9% AR (at 14 days),
THCY (M3) of 88.9% AR (at 1 day),
THPAI (M7) 35.8% AR (at 60 days)

b) Metabolites, maximal mean amounts, test concentration 93.3 μg/L:
THPI 36.3% AR (at 1 hour),
THPAM 72.4% AR (at 14 days),
THCY (M3) of 87.2% AR (at 1 day),
THPAI (M7) 14.7% AR (at 60 days)

Results with reference substance:

The reference flasks were sampled and analysed at day 0 and 7 of the incubation. The mean recovery of the applied radioactivity was 100.0% and 96.7% AR at 0 and 7 days after treatment, respectively. 80.0 % AR of the reference item was mineralised on day 7. This indicates that the test system was biologically active. Therefore, the test was valid.

Validity criteria:

Mineralisation within the expected time interval.

Observed value:

The test system was validated by using the reference item [ring-U-14C] Benzoic acid, sodium salt. After 7 days of incubation 80% AR of the reference item was mineralised showing that the test system was biological active.

Validity criteria fulfilled:

yes

Conclusions:

The objective of the study was to determine the time course of biodegradation of Captan in natural aerobic surface water and to evaluate the major pathway of its degradation. The test system was validated with the reference substance [ring-U-14C]Benzoic acid, sodium salt.
Two different test concentrations (9.8 μg/L and 93.3 μg/L) of the radio-labelled test item were used, corresponding to an applied radioactivity of about 0.03 MBq and 0.3 MBq per test vessel, respectively.
The mean recovery of the applied radioactivity (AR) for the whole system and both concentrations was in the range of 97.1% to 105.2% within 60 days of incubation. Five major metabolites were observed for both test concentrations. They were identified as THPI, THPAM, THCY (M3) and THPAI (M7) with maximum amounts of 69.2% AR, 77.9% AR, 88.9% AR and 35.8% AR, respectively.
Co-chromatography failed for identification of the transient metabolite M2 nor could it be related to the mass of one of the reference compounds during LC-MS/MS experiments. Based on sponsor request, the identity of the unknown metabolite M2 (max amount 60.6 and 52.7% AR in the low and high dose, respectively) was not further analytically investigated by LC/MS as this was a transient metabolite rapidly formed and equally rapidly degraded in water.

The DT50-value for the parent substance can be assumed to be < 1 h.
In sterile samples, after 2 days of incubation, [cyclohexene-14C]Captan was degraded to two major metabolites: THPAM (28.7% AR) and THCY (M3) (65.9% AR). The degradation pattern shows an indication that the parent substance was (partially) degraded by hydrolysis.

Executive summary:

The objective of the study was to determine the time course of biodegradation of Captan in natural aerobic surface water and to evaluate the major pathway of its degradation. The study was performed with [cyclohexene-14C]Captan under aerobic conditions using natural aerobic surface water taken from a large water body.

Five major metabolites were detected. In test flasks with the low test concentration THPI and THPAM were found at maximal mean amounts of 69.2% AR (at 1 hour) and 77.9% AR (at 14 days), respectively.

Furthermore, the major metabolites THCY (M3) and THPAI (M7) were observed at maximal mean amounts of 88.9% AR (at 1 day) and 35.8% AR (at 60 days), respectively.

Mineralisation and formation of organic volatiles were negligible for both test concentrations. 14CO2 was detected at maximal mean amounts of 1.4% AR at the end of the incubation. The mean amount of organic volatiles formed at the end of the incubation was < 0.1% AR.

Due to the rapid degradation of the test item the performance of kinetic calculations was not possible. Based on the results the DT50-value for [cyclohexene-14C]Captan can be assumed to be < 1 h.

The mean recovery of radioactivity in the sterile samples was 105% AR after two days of incubation. Two major metabolites were detected; THPAM occurred at mean amounts of 28.7% AR and THCY (M3) at 65.9% AR. The same metabolic pattern was observed as in the non-sterile samples showing that the degradation of the parent and its metabolites to the final metabolite THPAI is due to hydrolysis (abiotic as well as microbial).

Resulting from this study a preliminary pathway for aerobic mineralisation of Captan is proposed.   

Reference 2

Endpoint:

biodegradation in water: sediment simulation testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

April 1992 to March 1993

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods with acceptable restrictions

Remarks:

Guideline not specified, but complies with the SETAC guideline. Deviations: None

Qualifier:

according to guideline

Guideline:

other: SETAC guideline

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

RADIOLABELLED CAPTAN
- Name of test material: Captan, N-(trichloromethylthio)cyclohex-4-ene-1,2-dicarboximide
- Batch no.: 91-140
- Position of radiolabel: [cyclohexene 1,2- 14C]-captan
- Specific activity: 349 Bq/μg
- Radiochemical purity: 98.9 %

Radiolabelling:

yes

Remarks:

14C ring-labelled captan

Oxygen conditions:

aerobic

Inoculum or test system:

natural water / sediment

Details on source and properties of surface water:

Approximately 6 litres of water and 10 litres of sediment were collected from each site and transported in polypropylene containers. The physical state of the sediment and water in situ were noted.

Details on source and properties of sediment:

The metabolism of 14C-ring labelled- captan (ICIA2845) was studied in natural water-sediment systems under laboratory conditions, at 20°C in two water/sediment systems.
One system contained sediment with a high organic matter content ('Old Basing', 21.5% organic matter) and the other sediment with a low organic matter content ('Virginia Water', 5.4% organic matter).
Sterile systems were also set up in order to assess the effect of microbial activity on captan degradation. Each.water-sediment system contained 10% sediment dry matter in stream water.

Duration of test (contact time):

90 d

Initial conc.:

1.2 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

radiochem. meas.

Details on study design:

RADIOLABELLING
In order to obtain a radiolabelled captan solution with the appropriate specific activity for application to the water-sediment systems, an aliquot of the radiolabelled captan stock solution was reduced to dryness under a stream of nitrogen, redissolved in acetone and diluted further with "unlabelled" captan (Ref IC1A2845/01/05) in acetone. The "unlabelled" captan was supplied by the Chemical Development and Characterisation Section at Jealott's Hill (Ref M-1053-C) and was 98.9% pure.

TEST CONDITIONS
- Twenty three Old Basing water-sediment systems and twenty six Virginia Waters water-sediment systems were treated.

- Water-Sediment Systems:
Volume of test solution/treatment: 150 µl application solution (75 kBq annd 215 µg Captan = concentration 1.2 µg/ml
- Sampling after treatment: 1, 3, 7, 14, 30, 59 and 90 days incubation

- Sterile Water-Sediment Systems:
Volume of test solution/treatment: 150 µl application solution (78 kBq annd 225 µg Captan)
- Untreated control systems received 150 µl acetone only.
- Sampling after treatment: 30, 60 and 90 days incubation

Compartment:

natural water / sediment: freshwater

Sampling date:

1994

% Recovery:

95.1

Key result

Compartment:

natural water / sediment: freshwater

DT50:

ca. 1 - < 1.5 h

Type:

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

Temp.:

20 °C

Remarks on result:

other: After 24 hours, captan was not detected in any of the systems, and a DT50 could not be determined. worst-case half-life for captan may be estimated by making the worst-case calculation using zero order hydrolysis kinetics between time 0 and 24 hours.

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

No.:

#5

Evaporation of parent compound:

no

Volatile metabolites:

yes

Remarks:

carbon dioxide

The distribution of radioactivity in the two sediment/water systems is shown in Table 5.2.2-3

The average total recovery for all the systems was 95.1% AR. Recoveries were generally greater than 92%, although day 90 recoveries for both non-sterile systems and day 59 for the Virginia Water non sterile systems were lower at 74.7 - 86.5% AR.

 

The levels of evolved radiocarbon, as¹⁴CO₂were seen to increase throughout the 90-day incubation period. The rate of ¹⁴CO₂evolution was similar for both systems, with approximately 50 % AR mineralised by day 90 of the incubation period. In contrast, < 0.01% AR was mineralised to¹⁴CO₂ in the same 90 day period in the sterile systems.

 

Over the first seven days of incubation, the surface waters in the ‘Old Basing’ systems contained approximately 55 % AR, whereas the ‘Virginia Water’ systems contained approximately 80 % AR. The amount of radioactivity in the surface water fell in both systems after day 7 to < 1.2% AR by day 59 in both non-sterile systems. In the sterile systems, the level of radioactivity in the surface water remained high (> 48 % AR) throughout the incubation period.

At day 0, the majority of the radioactivity in the surface water partitioned into ethyl acetate for both sediment phase types. With incubation of the ‘Old Basing’ system, levels of organosoluble material decreased from 14:1 (organic:aqueous phases) at day 0 to 1:1.5 by day 30. With the ‘Virginia Water’ system, the majority of the radiolabel in the surface water was organosoluble throughout the incubation, although the proportion in the ethyl acetate phase decreased to 2.3:1 on day 1, and remained about this level on day 30. By day 59, there were only negligible amounts of radioactivity in the water phases.

 

In the sterile systems, the majority of the radioactivity in the surface water remained organosoluble throughout the incubation, although by day 90, the ratio in the organic and aqueous phases had fallen to 1.4:1 in the sterile ‘Old Basing’ system and 7.9:1 in the sterile ‘Virginia Water’ systems.

 

The amount of radioactivity extracted from the sediments fell throughout the incubation period, from approximately 40 % AR at day 0, to 3 % AR at day 90, these values being the sum of the first and second sediment extracts. This trend was accompanied by an increase in the unextractable radiocarbon from the sediment from approximately 2 % AR at day 0 to a maximum of 50 % AR at day 59. In the ‘Virginia Water’ system, the amount of radioactivity extracted from the sediment increased from 9 % AR at day 0 to 16 % AR at day 1, and remained at 16 - 18 % AR until day 30. By day 59 the amount of radioactivity extracted from the sediment had fallen to 9.5 % AR and was similar (10.6 % AR) at day 90. The unextractable radiocarbon in the ‘Virginia Water’ sediments remained low (less than or equal to 9 % AR). Until day 59 when levels rose to a maximum of about 30 % AR.

 

The amount of radiolabel extracted from the sterile sediments tended to be higher than the corresponding non-sterile sediments. In the sterile ‘Old Basing’ sediments, 53 % AR was extracted at day 0, and declined to 22 % AR at day 90. Correspondingly, levels of unextracted radioactivity in the sterile ‘Old Basing’ sediment increased to approximately 15 % AR over the 90 day incubation.

 

In the sterile ‘Virginia Water’ sediments, 24 % AR was extracted at day 0, and levels declined over 29 days to 15 % AR, remaining at this level for 90 days. Levels of untextracted radioactivity in the sterile ‘Virginia Water’ sediment remained below 2 % AR.

 

Even at day 0, directly after application, only 5.6 % AR was found to be captan in the ‘Old Basing’ water sediment extracts. Levels of captan extracted on day 0 from the sterile ‘Old Basing’ systems were also low with only 11 % AR in the extracts. In the ‘Virginia Water’ system, captan comprised a greater proportion of the extracted radioactivity in both sterile and non-sterile systems (61 and 54 % AR, respectively). By day 1, captan was not detected in any of the sample extracts, non-sterile or sterile, with either of the sediment types. Captan has been found to degrade rapidly in soil-water mixtures and the degradation rate is pH dependent.

 

The major initial metabolite in both sediment/water systems was THPI. In the ‘Old Basing’ system, the decline of THPI followed first-order kinetics over the first 14 days of incubation, with a half-life of about 5 days. Levels of THPI in the ‘Virginia Water’ systems fluctuated over the first 30 days. However, THPI was reduced to undetectable levels (< 0.1 % AR) in both systems by day 60. In the ‘Old Basing’ systems, THPI was distributed approximately 50:50 between the surface water and sediment phases. In the ‘Virginia Water’ systems, THPI was largely associated with the water phase.

 

THPI was also found in the sterile systems. In the ‘Old Basing’ system, the total amount of extractable THPI was 77 % AR at day 0, which declined to 36 % AR by day 90. In the ‘Virginia Water’ system, the total level of THPI reached a maximum of 80 % AR at day 60, and declined to 64 % AR by day 90.

 

The second highest level of metabolite was that of THPAM, which was found virtually exclusively in the water extracts for all systems. In the ‘Old Basing’ systems, THPAM was found at maximum levels in the water/sediment extracts on day 7 and 14 (approximately 26 % AR) and declined to undetectable levels (< 0.1 % AR) by day 60. In the ‘Virginia Water’ system, levels of THPAM in the water extracts reached a maximum of 25.5 % AR at day 1, and declined to undetectable levels (< 0.1 % AR) by day 60.

 

In the sterile ‘Old Basing’ system, THPAM was detected at a maximum level of 25 % AR after 90 days, whilst in the sterile ‘Virginia Water’ systems, THPAM reached only 6.5 % AR at day 60, and declined to < 1 % AR by day 90.

 

It was shown that under the reflux conditions used for the second sediment extraction, THPAM was converted to THPAI. When in solution, conversion of THPAM to THPAI under reflux conditions was completed in less than 2 hours. It is expected, therefore that levels of THPAM in the second extraction would be reduced as a result of the reflux extraction, and levels of THPAI would be elevated.

 

THPAI reached a maximum level of 11 % AR on day 14 in the ‘Old Basing’ system, and 7.5 % AR on day 30 in the ‘Virginia Water’ system. THPAI was also detected in sterile systems but at very low levels ( < 2.5 % AR). The majority of THPAI was detected in the second sediment extract for all systems, but as previously discussed some of the THPAI in the fraction may have been produced from THPAM during the reflux extraction.

 

Low levels of a fourth metabolite, THPI epoxide, were detected in both non-sterile and sterile

systems. THPI epoxide reached a maximum level of 5 % AR in the Old Basing’ non-sterile system on day 1 and declined to undetectable levels (< 0.1 % AR) by day 60. In the ‘Virginia Water’ system, THPI epoxide also reached its maximum level of 10% AR on day 1. In the sterile systems, the highest levels of THPI epoxide were observed later in the incubation period, at day 90 (10 % AR) in the ‘Old Basing’ system and at day 60 (10 % AR) in the ‘Virginia Water’ system.

No unknown metabolites amounting to > 5 % AR were found in any of the sediment/water systems.

Conclusions:

Captan was hydrolysed very rapidly to THPI in both sterile and non-sterile water/sediment systems. After 24 hours incubation, captan was not detected in any of the systems.In the non-sterile systems, the radioactivity in surface water decreased during the incubation period to levels lower than 2.5 % of the applied radioactivity, although the radioactivity increased in the sediment as bound residues, reaching approximately 25% AR. In the sterile systems, radioactivity remained in the surface water at levels of 63-76% AR after 90 days incubation; in the sediment bound residues were lower than 15%. THPI was observed as main metabolite in all the systems from day 1. It exhibited a DT50 of approximately 5 days in a non-sterile system containing a high organic matter content, high pH sediment, in which it was evenly distributed between sediment and water. In a non-sterile system containing a low organic matter, low pH sediment, THPI was predominantly in the water phase, and a DT50 could not accurately be determined. However, THPI had completely degraded to undetectable levels in both non-sterile systems in 59 days. In sterile systems, THPI degraded more slowly than in non-sterile systems, suggesting that microorganisms enhanced the degradation.Other metabolites detected were THPAM, THPAI and THPI epoxide. In nonsterile systems, maximum levels had been reached by day 14; THPAI and THPI epoxide did not exceed 11% AR, although THPAM reached 22-27% AR. Amounts then declined to undetectable levels after 59 days of incubation for these 3 metabolites.In the sterile systems, THPAM, THPAI and THPI epoxide were also observed after 30 days of incubation, suggesting that the degradation of THPI occurs in the absence of microbial activity, although more slowly. In the non-sterile systems, approximately 50% of the captan applied had been mineralised to 14CO2 after 90 days incubation, whereas in the sterile systems, negligible amounts of 14CO2were evolved throughout the incubation, implying that microbial activity is required for mineralisation.

Executive summary:

The metabolism of ¹⁴C-rlng labelled captan (ICIA2845) was studied in natural water-sediment systems under laboratory conditions, at 20°C. The ¹⁴C-ring labelled captan was applied to two water-sediment "systems.

One system contained sediment with a high organic matter content and the other sediment with a low organic matter content. Sterile systems were also set up in order to assess the effect of microbial activity on captan degradation.

 

In this study captan hydrolysed very rapidly to "THPI" (1,2,3,6-tetrahydrophthaIimide) in both the sterile and non-sterile water-sediment systems. After 24 hours incubation, captan was not detected in any of the systems.

THPI was degraded in all non-sterile water-sediment systems to undetectable levels after 59 days incubation. After 24 hours incubation, three other metabolites were identified in all the water-sediment systems. These metabolites were "THPAM" (6-Carbamoyl-3-CycIohexene-1-carboxylic acid) "THPAL" (3-Cyclohexene-6-Dicarboxylic acid) and "THPI" epoxide (7-oxabicyclo(2,2,1]heptane-2,3-dicarboidmide).

Levels of these metabolites were similar in both non-sterile sediment systems. THPAM reached a maximum level of approximately 25% of applied radioactivity while THPAL and THPl epoxide reached maximum levels of 5 to 11% of applied radioactivity. Maximum levels of these metabolites had been reached by day 14 and amounts then declined to undetectable levels by day 59 of the incubation.

After 90 days incubation, approximately 50% of the Initial ¹⁴C-captan had been mineralised to ¹⁴CO₂ in all non-sterile water-sediment systems. The majority of the remaining radioactivity (approximately 26% of applied radioactivity) was very tightly bound and not extractable from the sediment residue.

In the sterile systems, negligible amounts of ¹⁴CO₂ were evolved throughout the incubation.

After 90 days incubation in the sterile water system, most of-the applied radioactivity was identified as THPl (63.8% of applied radioactivity). After 90 days incubation in the sterile system, THPl levels had fallen to 35.8% of applied radioactivity, THPAM increased to 24.6% of applied radioactivity and levels of the THPl epoxide had reached 9.6% of applied radioactivity.

Results were comparable to mineralisation in aerobic water system (Irmer, 2017).

Description of key information

1. Degradation in sedimentwater systems:
Captan hydrolysed rapidly to THPI in both the non-sterile and sterile water-sediment systems. Amounts of THPI decreased in the nonsterile system to undetectable levels after 59 days incubation. Three other metabolites were produced by the degradation of THPI in these water-sediment systems. These metabolites were THPAM (6-carbamoyl-3-cyclohexene-1-carboxylic acid), THPAL (3-cyclohexene-1,6-carboxylic acid) and THPI epoxide (7-oxabicyclo(2,2,1) heptane-2,3-dicarboximide). Approximately 50% of the radiolabelled captan had been mineralised to 14CO2 after 90 days incubation in both the non-sterile water-sediment system.

2. Aerobic Mineralisation in Surface Water – Simulation Biodegradation Test: The objective of the study was to determine the time course of biodegradation of Captan in natural aerobic surface water and to evaluate the major pathway of its degradation. Captan hydrolysed rapidly to THPI in both the non-sterile and sterile water-systems.
Mineralisation and formation of organic volatiles were negligible for both test concentrations. 14CO2 was detected at maximal mean amounts of 1.4% AR at the end of the incubation. The mean amount of organic volatiles formed at the end of the incubation was < 0.1% AR.
Due to the rapid degradation of the test item the performance of kinetic calculations was not possible. Based on the results the DT50-value for [cyclohexene-14C]Captan can be assumed to be < 1 h at 20°C.

The mean recovery of the applied radioactivity (AR) for the whole system and both concentrations was in the range of 97.1% to 105.2% within 60 days of incubation. Five major metabolites were observed for both test concentrations. They were identified as THPI, THPAM, THCY (M3) and THPAI (M7) with maximum amounts of 69.2% AR, 77.9% AR, 88.9% AR and 35.8% AR, respectively.
In sterile samples, after 2 days of incubation, [cyclohexene-14C]Captan was degraded to two major metabolites: THPAM (28.7% AR) and THCY (M3) (65.9% AR). The degradation pattern shows an indication that the parent substance was (partially) degraded by hydrolysis.