Fenamiphos

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:

2001-04-03 to 2001-07-12

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Guideline:

other: EU Commission Directive 95/36/EC SETAC, 1995

Version / remarks:

1995

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

- Chemical name: Phosphoramidic acid, (1-methylethyl)-, ethyl (3-methyl-4-methylthio)phenyl ester
- CAS No.: 22224-92-6

Radiolabelling:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

natural sediment: freshwater

Details on source and properties of sediment:

Angler Weiher (AW)
- Details on collection: Surface sediment, wet sieved < 2 mm; sampled on 2001-03-20
- Textural classification (i.e. %sand/silt/clay): classified according to USDA as sand; 93.3 % sand, 1.3 % silt, 5.4 % clay
- pH at time of collection: 6.7 (water), 6.1 CaCl2)
- Organic carbon (%): 1.04
- Redox potential (mv): -166 to -74
- CEC (meq/100 g): 5
- Microbial activity (mg CO2 / hr * kg of sediment): DAT-0 without test item = 8; DAT-100 without test item / with test item = 4 / 6
- Sediment samples sieved: yes, passed wet through a 5-mm sieve and then through a 2-mm sieve


Honniger Weiher (HW)
- Details on collection: Surface sediment, wet sieved < 2 mm; sampled on 2001-03-20
- Textural classification (i.e. %sand/silt/clay): classified according to USDA as loam; 42.9 % sand, 40.2 % silt, 16.9 % clay
- pH at time of collection: 6.0 (water), 5.5 CaCl2)
- Organic carbon (%): 4.41
- Redox potential (mv): -150 to -134
- CEC (meq/100 g): 11
- Microbial activity (mg CO2 / hr * kg of sediment): DAT-0 without test item = 40; DAT-100 without test item / with test item = 16 / 20
- Sediment samples sieved: yes, passed wet through a 5-mm sieve and then through a 2-mm sieve

Details on inoculum:

not aplicable

Duration of test (contact time):

100 d

Initial conc.:

989 µg/L

Based on:

act. ingr.

Remarks:

989 pg/L supernatant, equivalent to a calculated spray of about 10 kg a.s./ha onto a water layer of 100 cm depth

Parameter followed for biodegradation estimation:

radiochem. meas.

Details on study design:

[Phenyl-1-14C]fenamiphos was applied to two different water/sediment systems at a rate of 989 µg/L corresponding to the maximum recommended annual rate of about 10 kg as/ha applied onto a water body of 100 cm depth. The characteristics of the sediments are given in Table CA 7.2.2.3/01-1. Before starting the experiment the wet sediment was sieved (5 and 2 mm sieves) and the dry matter determined. The flasks were filled with about 130 mL wet sediment and 390 mL supernatant water and then pre-incubated in the dark at 20 °C for equilibration and acclimatization of the microflora. The active substance diluted in acetonitrile (stock solution) was pipetted directly onto the surface water (386 µg as/vessel). Then, the vessels were closed with a trap attachment (permeable to O2) filled with quartz wool and soda lime for absorption of volatile compounds and CO2, respectively. The flasks were incubated at a temperature of 20 ± 1 °C in the dark for 100 days. In order to guarantee the uptake of oxygen from the air, the supernatant water was kept in motion without disturbing the sediment layer. Sampling intervals were 0, 2, 8, 20, 58 and 100 days after application. The microbial activity of the systems was measured at the beginning and the end of the study.


At each sampling interval water and sediment of the samples were separated and both phases centrifuged. The combined clear supernatant water was then analysed by liquid scintillation counting for the total radioactivity and diluted CO2, after liberation and absorbtion in a scintillation cocktail. The sediment was extracted twice with a mixture of acetonitrile/water (80:20, v/v) and additionally once with acetonitrile. The combined extracts were analysed for total radioactivity (LSC) and subjected to chromatographic analyses by HPLC and TLC methods (for confirmation). For identification of the as and metabolites, co-chromatography with non-labelled reference compounds was performed with both methods, HPLC as well as TLC (agreement of retention times and Rf-values). Because of the significant radioactivity remaining in the extracted sediment, an additional hot extraction with the acetonitrile/water mixture (under reflux for 2 hours) was performed with the samples of days 8 to 100. After centrifuged, the liquid phase was analysed as described above. Extracted sediment samples were air-dried and the bound radioactivity determined by combustion in an oxidizer followed by liquid scintillation measurement. The CO2 absorbed from the soda lime (trap) was liberated by addition of HCl and absorbed in a scintillation cocktail for subsequent measurement by LSC.

Key result

Compartment:

natural water: freshwater

DT50:

3.6 d

Type:

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

Temp.:

19.87 °C

Remarks on result:

other: Angler Weiher

Key result

Compartment:

natural water / sediment: freshwater

DT50:

9.3 d

Type:

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

Temp.:

19.87 °C

Remarks on result:

other: Angler Weiher

Key result

Compartment:

natural water: freshwater

DT50:

7.9 d

Type:

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

Temp.:

19.87 °C

Remarks on result:

other: Hoenninger Weiher

Key result

Compartment:

natural water / sediment: freshwater

DT50:

111 d

Type:

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

Temp.:

19.87 °C

Remarks on result:

other: Hoenninger Weiher

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#12

No.:

#13

Details on transformation products:

Major metabolites detected were fenamiphos sulfoxide (M01) in both systems and fenamiphos sulfoxide phenol (M12) in the system Angler Weiher (maximum concentration 10.8 %). Fenamiphos sulfoxide (M01) as major metabolite in both systems reached the maximum concentration of 14.6 % in the system Angler Weiher on day 20 and 30.5 % in the system Hoenniger Weiher on day 100. Fenamiphos sulfoxide phenol (M12) was found only in the system Angler Weiher (water phase) exceeding 10 % of the applied amount on day 20. The other metabolites remained below 10 % of the applied amount during the experiment.

Evaporation of parent compound:

not specified

Volatile metabolites:

yes

Remarks:

Carbon dioxide,, max. 14.3 %

Residues:

yes

Remarks:

max. 48.8 %

Table 1: Recovery and distribution of radioactivity [% of applied] after application of [phenyl-1-¹⁴C]fenamiphos to the water/sediment system Angler Weiher (mean of two replicates)

	Incubation time [days]
	0	2	8	20	58	100
Water layer	96.2	71.6	39.9	23.0	11.6	14.9
Sediment (extracted)	4.3	24.2	36.7	27.1	20.7	25.3
Sediment (bound)	0.3	2.2	17.8	41.8	48.8	40.9
^14CO2 : Gas phase	n.m.	< 0.1	0.1	4.4	9.7	13.6
Water phase	n.m.	< 0.1	0.5	0.5	1.5	0.7
Organic volatiles	n.m.	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
Total	100.8	98.0	95.0	96.8	92.3	95.4

n.m. = not measured

 

Table 2: Recovery and distribution of radioactivity [% of applied] after application of [phenyl-1-¹⁴C]fenamiphos to the water/sediment system Hoenniger Weiher (mean of two replicates)

	Incubation time [days]
	0	2	8	20	58	100
Water layer	92.8	62.8	45.1	26.9	18.4	19.5
Sediment (extracted)	5.6	35.0	51.6	65.6	70.7	64.8
Sediment (bound)	0.4	3.1	5.2	4.5	8.6	17.4
^14CO2 : Gas phase	n.m.	< 0.1	< 0.1	0.2	0.7	2.4
Water phase	n.m.	0.3	0.6	0.1	0.1	< 0.1
Organic volatiles	n.m.	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
Total	98.8	101.2	102.5	97.3	98.5	104.1

n.m. = not measured

 

 

Table 3: Distribution of fenamiphos and metabolites [% of applied radioactivity] in the system Angler Weiher after application of [phenyl-1-¹⁴C]fenamiphos

Interval [days]	Fenamiphos		Fenamiphos sulfoxide M01		Fenamiphos sulfone M02		M12	M13	P1 not identified	P2 not identified	Total extracted
	Water	Sediment	Water	Sediment	Water	Sediment	Water	Water	Sediment	Sediment
0	94.1	3.9	2.0	0.4	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	100.4
2	60.9	22.9	10.7	1.2	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.	95.7
8	22.2	31.2	5.4	2.4	7.5	2.2	4.7	n.d.	0.8	n.d.	76.4
20	1.8	17.7	9.2	5.4	0.6	0.6	10.8	0.6	1.1	2.3	50.1
58	n.d.	15.9	5.4	3.5	1.3	0.5	2.4	2.4	0.8	n.d.	32.2
100	0.5	18.8	7.4	4.3	2.2	1.7	2.0	2.8	0.3	0.1	40.1

M01 = Fenamiphos sulfoxide          M12 = Fenamiphos sulfoxide phenol             M12 and M13 were not detected in the sediment

M02 = Fenamiphos sulfone              M13 = Fenamiphos sulfone phenol                P1 and P2 were not detected in the water phase

 

Table 4: Distribution of fenamiphos and metabolites [% of applied radioactivity] in the system Hoenniger Weiher after application of [phenyl-1-¹⁴C]fenamiphos

Interval [days]	Fenamiphos		Fenamiphos sulfoxide M01		Fenamiphos sulfone M02		M12	M13	P1 not identified	Total extracted
	Water	Sediment	Water	Sediment	Water	Sediment	Water	Water	Sediment
0	90.5	5.2	2.4	0.3	n.d.	n.d.	n.d.	n.d.	n.d.	98.4
2	56.8	33.7	6.0	1.3	n.d.	n.d.	n.d.	n.d.	n.d.	97.8
8	42.4	45.8	2.7	5.2	n.d.	0.2	n.d.	n.d.	0.5	96.8
20	17.0	59.2	9.7	6.0	0.2	n.d.	n.d.	n.d.	0.4	92.5
58	6.9	62.2	10.5	7.8	1.0	0.6	n.d.	n.d.	0.1	89.1
100	2.0	45.7	13.7	16.8	2.8	2.3	0.1	0.9	n.d.	84.3

M01 = Fenamiphos sulfoxide          M12 = Fenamiphos sulfoxide phenol             M12 and M13 were not detected in the sediment

M02 = Fenamiphos sulfone              M13 = Fenamiphos sulfone phenol                P1 was not detected in the water phase

n.d. = not detected

 

Table 5: Distribution of fenamiphos and metabolites [% of applied radioactivity] in the entire systems Angler Weiher and Hoenniger Weiher after application of [phenyl-1-¹⁴C]fenamiphos

Interval [days]	Fenamiphos		Fenamiphos sulfoxide M01		Fenamiphos sulfone M02		Fenamiphos sufoxide phenol M12		Fenamiphos sulfone phenol M13
	Angler	Hönniger	Angler	Hönniger	Angler	Hönniger	Angler	Hönniger	Angler	Hönniger
0	98.0	95.7	2.4	2.7	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.
2	83.9	90.6	11.9	7.2	n.d.	n.d.	n.d.	n.d.	n.d.	n.d.
8	53.6	88.2	7.8	7.9	9.8	0.2	4.7	n.d.	n.d.	n.d.
20	19.5	76.2	14.6	15.7	1.2	0.2	10.8	n.d.	0.6	n.d.
58	15.9	69.1	8.9	18.3	1.8	1.6	2.4	n.d.	2.4	n.d.
100	19.3	47.7	11.7	30.5	3.9	5.1	2.0	0.1	2.8	0.9

M01 = Fenamiphos sulfoxide          M12 = Fenamiphos sulfoxide phenol

M02 = Fenamiphos sulfone              M13 = Fenamiphos sulfone phenol

n.d. = not detected

n.d. = not detected

 

Table 6: Degradation of fenamiphos in two water/sediment systems (1^st order kinetics)

System	DT50 [days]	DT90 [days]	r^2	K (1/day)
Angler Weiher: Water	3.6	12.1	0.998	0.191
Entire system	9.3	31.0	0.909	0.074
Hoenniger Weiher: Water	7.9	26.1	0.953	0.088
Entire system	111	367	0.958	0.006

 

Conclusions:

The substance is degraded and mineralised in aerobic water/sediment systems (DT50 in the range of 9.3 to 111 days). The DT50 in the water layer is expected to be in the range of 3.6 to 7.9 days.

Executive summary:

The metabolism of the test item was studied in two different water/sediment systems for a maximum of 100 days under aerobic conditions in the dark at 20 °C. The test systems originated from Angler Weiher (sand, gravel pit, Germany, org. C in sediment = 1.04 %) and Hoenniger Weiher (loam, dammed pond, Germany, org. C in sediment = 4.41 %). The test substance [phenyl-1-14C]Fenamiphos was applied at a dose rate of 989 µg/L supernatant, equivalent to a calculated spray of about 10 kg a.s./ha onto a water layer of 100 cm depth. The experiment was conducted in compliance with the GLP standards and in accordance with EC/SETAC test guidelines. The test system consisted of a glass flask attached with a trap for collection of CO2 and volatile organic compounds. Entire flasks filled with each approx. 130 mL sediment and 390 mL supernatant water were processed and investigated at 0, 2, 8, 20, 58 and 100 days after treatment (DAT) in duplicate. The water layer was decanted and centrifuged, the sediment layer was extracted with organic solvent at room temperature. Aliquots of the organic extracted sediment were combusted for determination of radioactivity (RA), the remaining sediment was further hot extracted with acetonitrile/water (DAT-8, 20, 58 and 100). Water samples and extracts were analysed by LSC and HPLC. The test conditions outlined in the study protocol were maintained throughout the study. During the study the total recovery of applied radioactivity (AR) in test vessels of system Angler Weiher ranged from 92.3 % to 100.8 % (mean of duplicates). In system Hoenniger Weiher the total recovery of AR ranged from 97.3% to 104.1% (mean of duplicates). The material balance found at all sampling intervals demonstrated that no significant RA dissipated from the vessels or was lost during processing. The data gathered in the current laboratory investigation demonstrated that the test item is degraded in both water/sediment systems. The test item disappeared from the water layer by adsorption to the sediment and due to degradation. Although the microbial activity was lower in the system Angler Weiher, the degradation of fenamiphos and the resulting metabolites was faster in this system compared to the system Hoenniger Weiher. In the system Angler Weiher (AW) the DT50 (first-order kinetics) was 3.6 days in the water layer and 9.3 days in entire system, only. The DT50 (first-order kinetics) in the water layer of the loamy system Hoenniger Weiher (HW) was 7.9 days and 111 days in the entire system. Formation of the oxidation product Fenamiphos sulfoxide (FOX) was the initial step of degradation. Then this metabolite was degraded to the respective phenol and finally to carbon dioxide. The main metabolites in both entire systems were Fenamiphos sulfoxide (max. 30.5 %) and Fenamiphos sulfoxide phenol (FOX-PH) (max. 10.8 %). FOX-PH was generated in significant amounts in system Angler Weiher, but not in system Honniger Weiher (max. 0.1 %). Mineralisation to radiolabelled carbon dioxide was detected in both systems indicating further degradation of the strong bound metabolites (system Angler Weiher 14.3 % and system Honniger Weiher 2.4 % of the AR). From the sediment of system AW max. 36.7 % and from system HW max. 70.7 % of the AR were extracted with organic and hot extraction. Main products in the sediment were identified as Fenamiphos (max 31.2 % of AR / AW and max. 62.2 % of AR / HW) and Fenamiphos sulfoxide (max. 5.4 % of AR / AW and max. 16.8 % of AR / HW). In the water layer in general the same degradation products, Fenamiphos sulfoxide and Fenamiphos sulfoxide phenol, were observed. Fenamiphos sulfoxide accounted for max. 10.7 % of the AR in system AW (DAT-2). In case of system HW this metabolite was max. 13.7 % at the end of the test period (DAT-100). Fenamiphos sulfoxide phenol was max. 10.8 % (DAT-20) in the water layer of system AW. In system HW this product was detected only in very low amounts in the water layer (0.1 % at DAT-100). The other metabolites, Fenamiphos sulfone and Fenamiphos sulfone phenol, were detected in max. 7.5 % of the applied RA (Fenamiphos sulfone, system AW, DAT-8). In general, in system Angler Weiher less adsorption but hydrolytic degradation of FOX to FOX-PH in comparison to system HW was observed. Therefore, a high amount of mineralisation was detected. In case of system Honniger Weiher a high amount of RA was adsorbed to the sediment, but hydrolysis and mineralisation was less than in system Angler Weiher. The data demonstrate that the test item is degraded and mineralised in aerobic water/sediment systems (DT50 in the range of 9.3 to 111 days). The DT50 in the water layer is expected to be in the range of 3.6 to 7.9 days.

Description of key information

The substance is degraded and mineralised in aerobic water/sediment systems (DT50 in the range of 9.3 to 111 days at 20 °C). The DT50 in the water layer is expected to be in the range of 3.6 to 7.9 days at 20 °C. For the environmental risk assessment according to Regulation (EC) No 1907/2006 (REACH) the highest DT50 values derived for the water phase and sediment, respectively, are considered.

Key value for chemical safety assessment

Half-life in freshwater:

7.9 d

at the temperature of:

20 °C

Half-life in freshwater sediment:

111 d

at the temperature of:

20 °C

Additional information

The metabolism of the test item was studied in two different water/sediment systems for a maximum of 100 days under aerobic conditions in the dark at 20 °C. The test systems originated from Angler Weiher (sand, gravel pit, Germany, org. C in sediment = 1.04 %) and Hoenniger Weiher (loam, dammed pond, Germany, org. C in sediment = 4.41 %). The test substance [phenyl-1-14C]Fenamiphos was applied at a dose rate of 989 µg/L supernatant, equivalent to a calculated spray of about 10 kg a.s./ha onto a water layer of 100 cm depth. The experiment was conducted in compliance with the GLP standards and in accordance with EC/SETAC test guidelines. The test system consisted of a glass flask attached with a trap for collection of CO2 and volatile organic compounds. Entire flasks filled with each approx. 130 mL sediment and 390 mL supernatant water were processed and investigated at 0, 2, 8, 20, 58 and 100 days after treatment (DAT) in duplicate. The water layer was decanted and centrifuged, the sediment layer was extracted with organic solvent at room temperature. Aliquots of the organic extracted sediment were combusted for determination of radioactivity (RA), the remaining sediment was further hot extracted with acetonitrile/water (DAT-8, 20, 58 and 100). Water samples and extracts were analysed by LSC and HPLC. The test conditions outlined in the study protocol were maintained throughout the study. During the study the total recovery of applied radioactivity (AR) in test vessels of system Angler Weiher ranged from 92.3 % to 100.8 % (mean of duplicates). In system Hoenniger Weiher the total recovery of AR ranged from 97.3% to 104.1% (mean of duplicates). The material balance found at all sampling intervals demonstrated that no significant RA dissipated from the vessels or was lost during processing. The data gathered in the current laboratory investigation demonstrated that the test item is degraded in both water/sediment systems. The test item disappeared from the water layer by adsorption to the sediment and due to degradation. Although the microbial activity was lower in the system Angler Weiher, the degradation of fenamiphos and the resulting metabolites was faster in this system compared to the system Hoenniger Weiher. In the system Angler Weiher (AW) the DT50 (first-order kinetics) was 3.6 days in the water layer and 9.3 days in entire system, only. The DT50 (first-order kinetics) in the water layer of the loamy system Hoenniger Weiher (HW) was 7.9 days and 111 days in the entire system. Formation of the oxidation product Fenamiphos sulfoxide (FOX) was the initial step of degradation. Then this metabolite was degraded to the respective phenol and finally to carbon dioxide. The main metabolites in both entire systems were Fenamiphos sulfoxide (max. 30.5 %) and Fenamiphos sulfoxide phenol (FOX-PH) (max. 10.8 %). FOX-PH was generated in significant amounts in system Angler Weiher, but not in system Honniger Weiher (max. 0.1 %). Mineralisation to radiolabelled carbon dioxide was detected in both systems indicating further degradation of the strong bound metabolites (system Angler Weiher 14.3 % and system Honniger Weiher 2.4 % of the AR). From the sediment of system AW max. 36.7 % and from system HW max. 70.7 % of the AR were extracted with organic and hot extraction. Main products in the sediment were identified as Fenamiphos (max 31.2 % of AR / AW and max. 62.2 % of AR / HW) and Fenamiphos sulfoxide (max. 5.4 % of AR / AW and max. 16.8 % of AR / HW). In the water layer in general the same degradation products, Fenamiphos sulfoxide and Fenamiphos sulfoxide phenol, were observed. Fenamiphos sulfoxide accounted for max. 10.7 % of the AR in system AW (DAT-2). In case of system HW this metabolite was max. 13.7 % at the end of the test period (DAT-100). Fenamiphos sulfoxide phenol was max. 10.8 % (DAT-20) in the water layer of system AW. In system HW this product was detected only in very low amounts in the water layer (0.1 % at DAT-100). The other metabolites, Fenamiphos sulfone and Fenamiphos sulfone phenol, were detected in max. 7.5 % of the applied RA (Fenamiphos sulfone, system AW, DAT-8). In general, in system Angler Weiher less adsorption but hydrolytic degradation of FOX to FOX-PH in comparison to system HW was observed. Therefore, a high amount of mineralisation was detected. In case of system Honniger Weiher a high amount of RA was adsorbed to the sediment, but hydrolysis and mineralisation was less than in system Angler Weiher. The data demonstrate that the test item is degraded and mineralised in aerobic water/sediment systems (DT50 in the range of 9.3 to 111 days). The DT50 in the water layer is expected to be in the range of 3.6 to 7.9 days. For the environmental risk assessment according to Regulation (EC) No 1907/2006 (REACH) the highest DT50 values derived for the water phase and sediment, respectively, are considered.