heptan-2-yl [(5-chloroquinolin-8-yl)oxy]acetate

Biodegradation in water and sediment: simulation tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: sediment simulation testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1991-09-26 - 1992-11-06 (experimental phase)

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: Biologische Bundesanstalt für Land- und Forstwirtschaft, Deutschland. Richtlinien für die Prüfung von Pflanzenschutzmitteln, Teil IV,5 - 1; Abbaubarkeit und Verbleib von Pflanzenschutzmitteln im Wasser/Sediment-System. December 1990

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: Environmental Chemistry and Fate Guidelines for Registration of Pesticides in Canada; Section 6.2. C.2: Biotransformation; 2. Aquatic (Laboratory) - Anaerobic and Aerobic; July 15,1987.

Deviations:

no

GLP compliance:

yes

Radiolabelling:

yes

Oxygen conditions:

aerobic/anaerobic

Inoculum or test system:

natural water / sediment

Details on source and properties of surface water:

Water Characteristics:
Origin: Pond "Judenteich", Rheinfelden, AG, Switzerland
Collection Date: 23 Sep 1991
Analysis Date: 15 Oct 1991
Ntotal (mg / l): 3.1
Ptotal (mg / l): 0.4
TOC (mg / l): 6.8
Hardness:
French Deg. (° f): 21.6 (1 ° f = 0.1 mmol/l)
Oxigen (%, just after sampling): 82
Redox potential (mV, just after sampling): 190

Details on source and properties of sediment:

Sediment Characteristics:
Origin: Pond "Judenteich", Rheinfelden, AG, Switzerland
Collection Date: 23 Sep 1991
Analysis Date: 19 Nov 1991
pH: 6.8
Organic Carbon (%): 9.4
Ntotal (%): 0.87
CaCO3: 5.3
CEC (mmol / z / 100 g sediment): 50.3
Particle Size
Clay (%): 39.8
Silt (%): 44.1
Sand (%): 16.1
USDA classification: silty clay loam
Water Content (g H2O / 100 g dry sediment): 86.2
Microbial Biomass (mg C / 100 g sediment): 466 (after ca 12 months)

Preparation: Before use, the sediment was passed through a 2 mm sieve.

Details on inoculum:

natural water / sediment

Duration of test (contact time):

280 d

Initial conc.:

0.92 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

radiochem. meas.

Details on study design:

Aquatic system: the system consisted of a sediment and the corresponding water as a static system. The incubation apparatus consisted of:
- impinger flask for moistening the incoming air (for experiments under aerobic conditions) or nitrogen (for experiments under anaerobic conditions) (flow adjusted to 60-100 ml/min)
- aquatic metabolism flask (equipped with a magnetic stirrer)
- two NaOH 2N traps in series
- flow meter
The mixture of water and sediment were prepared as follows: Into the 1-liter all-glass metabolism flask wet sediment was filled to a height of about 2 - 2.5 cm (35.6 and 34.1 g based on sediment dry weight for aerobic and anaerobic sediment, respectively). Afterwards 407.3 and 405.1 ml of the pond" water were added, respectively, to reach a height of about 6 cm. The total volume of water per flask was about 491 ml. After preparation, the aquatic systems were equilibrated in climatization chambers under the conditions needed (aerobic, anaerobic) by gentle stirring from the top without disturbing the sediment. During equilibration pH and oxygen content of the water and redox potential of water and sediment were followed. The equilibration time for all conditions was 45 days.

Treatment: each aquatic system flask the test substance (solution in acetone) was applied to the water phase. The resulting concentration was 0.92 mg/l. The concentration of acetone was <0.1% of the aount of water.

Sampling:
A whole flask containing water and sediment was taken for analysis at the following incubation intervals:
- aerobic/20°C: 0, 1, 2, 4, 7, 14, 28, 56, 98, 112 and 280 days after treatment (day 280 was a supplement analysis date and was made to further observe the behaviour of bound residues and volatiles).
- aerobic/10°C: 7, 14, 29, 57, 99, 112, 182 and 358 days after treatment.
- anaerobic/20°C:28, 56, 98, 112 and 238 days after treatment.
- sterile/20°C: 2, 29, 57 and 99 days after treatment.
The microbial biomass was measured on September 18, 1992 (remark: at starting time of the study no adapted method for sediments was available).
Volatiles: The absorption solutions were exchanged and monitored for radioactivity in about weekly intervals during the first month and thereafter in about two weeks intervals.

Extraction Procedure and Sample Preparation
Extraction of Sediment Samples: After separating the water phase from the sediment by suction filtration the wet sediment was transferred into a 250 ml centrifuge tube and extracted twice by shaking at 160 rpm's with 100 ml acetone/buffer pH 4.65 at room temperature. After centrifugation (2500 rpm for 2 min) the radioactivity in each extract was measured by LSC. Afterwards the extracts were combined for TLC - analysis. The extraction was completed by refluxing the sediment with methanol for 4 - 5 hours in a Soxhlet apparatus. The radioactivity was also determined in the Soxhlet extract; afterwards the extract was concentrated in a rotary evaporator and adjusted to 50 ml and then analysed by TLC.
The extracted sediment was air-dried, weighed, homogenized and the residual activity determined by combustion and LSC.

Water phase: In the water phase the radioactivity was measured and the analysis made by TLC.

Compartment:

other: water / sediment, material (mass) balance

Remarks on result:

other: see Tables 1-16

Compartment:

entire system

DT50:

< 1 d

Type:

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

Remarks on result:

other: aerobic conditions, 20 °C

Compartment:

entire system

DT50:

33 d

Type:

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

Remarks on result:

other: aerobic-sterile conditions, 20 °C

Transformation products:

yes

No.:

#1

Details on transformation products:

#1:
IUPAC name: [(5-chloroquinolin-8-yl)oxy]acetic acid
CAS#: 88349-88-6
CAS name: Acetic acid, 2-[(5-chloro-8-quinolinyl)oxy]-
Molecular Formula: C11H8ClNO3
Molar mass: 237.639 g/mol
SMILES notation: O=C(O)COc1ccc(Cl)c2cccnc12
InChI: InChI=1S/C11H8ClNO3/c12-8-3-4-9(16-6-10(14)15)11-7(8)2-1-5-13-11/h1-5H,6H2,(H,14,15)
Structural formula: see attachment in Illustration (picture/graph)

Evaporation of parent compound:

no

Volatile metabolites:

yes

Residues:

yes

Details on results:

Physicochemical Characteristics: During the equilibration and incubation period the water phases of the different aquatic systems were monitored for oxygen content, pH and temperature. Additionally to these parameters, the water phases and the sediments were monitored for the redox potential.
The sediment used can be classified as silty clay loam (USDA classification) with a high amount of organic carbon (9.4%). The biomass was measured after about 12 months after starting the study and showed, at this time, still a high level of 466 mg C/100 g sediment.
The mean redox potential in sediments was found to be -129±71, -54±79 and -338±35 m V under aerobic/20°C, aerobic/10°C and anaerobic/20°C conditions, respectively, demonstrating a reduced state in deeper sediment layers especially under anaerobic conditions. In the corresponding water, a mean redox potential of 213±34, 202±43 and 49±133 mV was measured, respectively, during the equilibration and incubation period, indicating oxidized conditions in the surface layer of the sediments. The pH was nearly constant with mean values of 8.2±0.2 under aerobic/20°C and aerobic/10°C conditions. Under anaerobic conditions a slight increase from 7.4 to 8.5 was observed during the equilibration and incubation period.
The oxygen content in the aerobic/20°, aerobic/10°C and aerobic/sterile water phases was at a constant high level over the whole measuring period (80, 90 and 83 %, respectively). Under anaerobic conditions a mean value of 4 % was found.
The temperatures were monitored during the whole test periods.
The sterility under aerobic/sterile conditions was checked after 29, 57 and 99 days of incubation in the water phases. Any growth was observed on the test slides.
The recoveries ranged from 76.12 to 102.85 % of the radioactivity applied, the low value must be classified as runaway (mean recovery: 93.0±4.8%, n= 28).
The amount of soil-bound radioactivity increased under all conditions with time, under aerobic/20° and aerobic/10°C it reached amounts of 80 to 85% of the dose applied after about 300 days.
The volatile radioactivity was found to be14C02 and increased in all non-sterile experiments with time. 5.85 % of 14C02 was found after 280 days of aerobic/20°C conditions.

Rates of Disappearance and Characterization
CGA185072 disappeared under aerobic/20°C conditions with a half-life (DT50) < 1 day and a DT90 < 2 days. For sterile/aerobic conditions a DT50 of 33 days and a DT90 of 110 days was calculated.
CGA185072 was rapidly hydrolysed to the acid CGA153433, when added to the water phases. The following degradation rates were calculated for CGA153433 under aerobic/20°C conditions: DT50 of 46 days, DT90 of 152 days. In all experiments the acid CGA153433 was strongly bound to the sediment.

Table 1: Distribution Pattern of 14C-Activity for the Degradation of CGA185072 in an Aerobic Aquatic System at 20 °C
(Values given in % of the radioactivity applied, n.d. = not detected)

Time [Days]	Water-phase [%]	Extraction at room temp. [%]	Soxhlet-Extract [%]	Non-Extractable [%]	Volatiles [%]	Recovery [% appl.]
0	58.48	31.83	5.95	6.59	n.d.	102.85
1	30.22	18.96	3.34	41.66	0.02	94.2
2	19.22	11.85	1.42	61.13	<0.01	93.62
4	19.21	9.83	1.36	61.58	<0.01	91.98
7	12.75	9.62	1.10	70.88	<0.01	94.35
14	11.92	9.81	1.33	71.11	0.03	94.2
28	6.63	9.74	0.85	75.92	0.03	93.17
56	4.31	8.75	1.53	78.79	0.20	93.58
98	2.48	9.10	1.26	83.62	0.17	96.63
112	2.05	7.74	1.09	83.73	0.37	94.98
280	0.57	3.34	0.91	80.45	5.85	91.12

 

 

Table 2: Distribution Pattern of CGA185072 and Metabolites in an Aerobic Aquatic System at 20°C
(Values given in % of the radioactivity applied; n.d. = not detected)

Incubation Time (Days)	CGA185072	CGA153433	Unknown Metabolites	Extractables
0	62.71	33.54	n.d.	96.25
1	15.66	36.85	n.d.	52.51
2	3.00	29.48	n.d.	32.48
4	1.58	28.13	0.67	30.38
7	0.85	22.61	n.d.	23.46
14	0.20	22.84	n.d.	23.04
28	0.02	16.45	0.73	17.21
56	n.d.	14.21	0.38	14.59
98	0.01	12.69	0.15	12.84
112	n.d.	10.67	0.19	10.86
280	0.05	3.24	1.53	4.82

 

 

Table 3: Distribution Pattern for CGA185072 and Degradates: Water-Phase of Aerobic Aquatic System at 20°C
Values are given in % of the radioactivity applied.

Time [days]	CGA185072 [%]	CGA153433 [%]	Unknown metabolites [%]	Total in Water-Phase [%]
0	24.94	33.54	n.d.	58.48
1	0.91	29.31	n.d	30.22
2	n.d.	19.22	n.d	19.22
4	n.d.	18.54	0.67	19.21
7	n.d.	12.75	n.d	12.75
14	n.d.	11.92	n.d	11.92
28	n.d.	5.90	0.73	6.63
56	n.d.	3.93	0.38	4.31
98	n.d.	2.33	0.16	2.48
112	n.d.	1.86	0.19	2.05
280	n.d.	0.43	0.14	0.57

n.d. = not detected

 

 

Table 4: Distribution Pattern for CGA185072 and Degradates: Sediment-Phase of Aerobic Aquatic System at 20°C
Values are given in % of the radioactivity applied. 

Time [days]	CGA185072 [%]	CGA153433 [%]	Unknown metabolites [%]	Total in Sediment [%]
0	37.78	n.d.	n.d.	37.78
1	14.75	7.55	n.d.	22.30
2	2.99	10.28	n.d.	13.27
4	1.58	9.61	n.d.	11.19
7	0.85	9.87	n.d.	10.72
14	0.20	10.94	n.d.	11.14
28	0.02	10.57	n.d.	10.59
56	n.d.	10.28	n.d.	10.28
98	0.01	10.35	n.d.	10.36
112	n.d.	8.83	n.d.	8.83
280	0.36	1.86	2.03	4.25

n.d. = not detected

Validity criteria fulfilled:

yes

Conclusions:

The DT50 of the substance in a water/sediment system was less than 1 day under aerobic conditions.

Executive summary:

The degradation of cloquintocet-mexyl was investigated under GLP to test guidlines that are equivalent to OECD TG 308 in an aquatic system, consisting of sediment and water collected from a natural pond, under various conditions (i.e. incubated under aerobic conditions at 20 °C and 10 °C, as well as under anaerobic and sterile / aerobic conditions at 20 °C). The substance dissipated rapidly from the whole system (i.e. water and sediment phases), with a half-life of less than 1 day under aerobic conditions. Dissipation from the whole system was rapid even under sterile conditions, with a half-life of 33 days. The main environmental metabolite of cloquintocet-mexyl degraded less fast, with a calculated degradation half-life of 56.4 days for the whole system under aerobic conditions.

Description of key information

DT50 = 0.2 days for the water phase under aerobic conditions at 20 °C (Keller 1993)

DT50 = 0.7 days for the sediment phase under aerobic conditions at 20 °C (Keller, 1993)

Converting to the EU average outdoor temperature of 12 °C (in accordance with ECHA R.16 guidance) gives normalised half-lives of 0.38 and 1.33 days for the water and sediment compartments, respectively.

The metabolite disappears from the water phase in a few days and persist slightly longer in the whole system (realistic worst case DT50 of 56 days for whole system under aerobic conditions at 20 °C).

Key value for chemical safety assessment

Half-life in freshwater:

0.2 d

at the temperature of:

20 °C

Half-life in freshwater sediment:

0.7 d

at the temperature of:

20 °C

Additional information

The biodegradation of cloquintocet-mexyl in sediments was investigated in two GLP compliant studies conducted to a guideline similar to OECD TG 308 (Biologische Bundesanstalt für Land- und und Forstwirtschaft, Deutschland. Richtlinien für die Prüfung von Pflanzenschutzmitteln, Teil IV,5 - 1; Abbaubarkeit und Verbleib von Pflanzenschutzmitteln im Wasser/Sediment-System. December 1990).

The first study (Keller 1993) investigated the degradation of cloquintocet-mexyl in water-sediment systems at different temperatures and incubation conditions. Cloquintocet-mexyl dissipated very fast under all conditions. The metabolite, Acetic acid, 2-[(5-chloro-8-quinolinyl)oxy]- was formed in up to 37% yield within the first week of incubation. This metabolite was also degraded under aerobic and anaerobic conditions and finally reached 3-8% after 280-358 days. At the beginning of the study, the metabolite was found mainly in the aquatic phase, but became adsorbed to the sediment upon prolonged incubation.

Non-extractable residues were detected in the sediment layers under all conditions. They increased to about 84% of the initial dose within 112 days of aerobic incubation at 20°C, within 358 days of aerobic incubation at 10°C, within 238 days of anaerobic incubation at 20 °C, as well as to 60% after 99 days under sterile anaerobic conditions. As a result of microbial degradation, the bound residues were slowly mineralised. At lower temperature, as well as under anaerobic and sterile conditions, however, the mineralisation was found to be marginal. The formation of 14C-carbon dioxide accounted for 6% in the aerobic experiment at 20 °C, but <0.4% in the other tests.

The second study (Reischmann, 1996) investigated degradation of cloquintocet-mexyl in a natural water-sediment system collected from the Rhine river and incubated under aerobic conditions at 20 °C.

The level of radiocarbon in the aquatic phase decreased to 2% of applied concentration within 125 days. Within the first 7 days, the extractable radioactivity in the sediment increased to 46% and then dropped to 23% at study termination, whereas the non-extractable portions finally reached 63%. 

The disappearance of cloquintocet-mexyl from the system was very fast. The initial quantities accounted for 95% and were distributed between the aquatic phase (75%) and sediment layer (20%). Within 2 days, the amounts in the water declined to 3% and disappeared completely after 14 days. Only one major metabolite was observed, i.e. Acetic acid, 2-[(5-chloro-8-quinolinyl)oxy]-, which reached its highest value of 65% after 2 days, 38% being found in the water and 27% in the sediment. It decreased to 25% in the whole system, 2% in water and 23% in sediment after 125 days. A further metabolite of unknown structure was always <1.4%.

In order to assess the degradation rates of the primary metabolites, the data from the present studies (Keller 1993b, Reischmann 1996) were compiled and re-calculated using the ModelMaker software (Ellgehausen 1998).
From the available data, it can be seen that cloquintocet-mexyl was found to rapidly degrade in aerobic and anaerobic systems (DT50= 0.6 to 2 days in the whole system), but persisted longer under sterile conditions (DT50 = 33 days in whole system), indicating that the most important pathway of dissipation in a viable aquatic environment is microbial degradation. Sterile and anaerobic systems are not considered representative of normal environmental conditions. Therefore, it is proposed that study results for aerobic systems should be used in the Chemical Safety Assessment. Accordingly, the DT50 of 0.2 days for the water phase and 0.7 for the sediment phase under aerobic conditions at 20 °C is selected for the chemical safety assessment. The main environmental metabolite is expected to disappear from the water phase in a few days, but persist longer in the whole system (realistic worst case DT50 of 56 days for whole system under aerobic conditions at 20 °C).