Fenamiphos

Biodegradation in soil

Description of key information

Based on a study according to OECD TG 307 the DT50 (20 °C pF2/10kPa) of the test item was determined to be 0.71 days. The normalized geometric mean DT50 (20 °C pF2/10kPa) values of its metabolites are considered to be < 120 days. This conclusion is in full compliance with the EFSA Conclusion on the peer review of the pesticide risk assessment of the active substance (European Food Safety Authority, 2019; EFSA Journal 2019;17(1):5557, 49 pp.).

Key value for chemical safety assessment

Half-life in soil:

0.71 d

at the temperature of:

20 °C

Additional information

Simulation tests on the biodegradability in soil is not a data requirement according to Annex VII-VIII of Regulation (EC) 1907/2006 (REACH). Therefore, no IUCLID endpoint study record was prepared. However, two route and rate of degradation studies of Simon (1990) and Brumhard (2002) on mineralisation of the test item in soil are available and discussed below. The studies had been submitted in accordance with Directive 91/414/EEC and were evaluated in the Draft Assessment Report (DAR) for Fenamiphos (Vol. 3, Annex B, Point 8.1.1, November 2003).

The Simon study covered a large number of soils from different locations around the world. These studies were conducted in the frame of a PhD dissertation and were not GLP compliant nor did they follow any particular Regulatory Guideline. For this reason it was concluded that the Simon study should only be used in providing supportive information on the aerobic route of degradation of the test substance. The study is not considered to be of sufficient quality and reliability to obtain DegT₅₀ endpoints for modelling and risk assessment purposes, especially for consideration of the major degradates. In conclusion, this study is intended to be only used to support the rate of degration of Fenamiphos in soil of the active substance.

Sufficiently reliable information exists in the Brumhard study to conclude on the route of degradation of the test substance in soil and obtain a DegT₅₀ for the test item. For the major soil degradates the Brumhard results are additionally supported by a number of new rate of degradation in soil studies.

Four major soil metabolites were identified in these studies and included in the residue definition for risk assessment of the EFSA Scientific Report (2006) 62, 1-81, which is as follows: Fenamiphos (FEN), fenamiphos-sulfoxide (FOX) , fenamiphos-sulfone (FON), fenamiphos-sulfoxide phenol (FOXP) and fenamiphos-sulfone phenol (FONP). The biodegradation of the metabolites of Fenamiphos were further investigated in studies of Matthews (2015a-e) and Abu (2016).

 

Key information

Brumhard (2002) carried out a GLP-compliant study according to OECD TG 307 (2000). This information had been submitted in the EU in 2002 for inclusion of Fenamiphos to Annex I of Directive 91/414/EEC and has been previously evaluated in the Draft Assessment Report (see above) and was subject to peer review by EFSA and Member States.

 

In this study the metabolism and degradation behaviour of [phenyl-1-¹⁴C]fenamiphos was investigated in four agriculturally relevant soils: sandy loam, silt loam, silt and sand. An overview about the soil characteristics is given in the tables below.

Table 1: Characteristics of the soils used

Origin	Soil type*	org. C [%]	Textural analysis*			pH	CEC	WHC
			Clay [%]	Silt [%]	Sand [%]	(water)	[meq/ 100g soil]	[g H2O/ 100g dry soil]
Laacher Hof AXXa	Sandy loam	1.02	5.0	22.6	72.4	7.2	8	34.4
Laacher Hof AIII	Silt loam	0.83	12.0	51.1	36.9	7.4	8	36.4
Hoefchen am Hohenseh 4a	Silt	2.11	10.2	81.3	8.5	7.6	15	63.1
Standard soil BBA 2.1	Sand	0.38	2.3	8.1	89.6	5.9	5	27.6

 

Table 2: Microbial biomass [mg org. C/kg dry soil] of the soils incubated at 20 °C used

Day	Conditions	Laacher Hof AXXa	Laacher Hof AIII	Hoefchen am Hohenseh 4a	Standard soil BBA 2.1
0	without as	616	228	950	85
60	with as	349	231	671	52
120	without as	290	209	544	41
120	with as	267	217	602	41

 

One tenth of the maximum agricultural application rate of 10 kg as/ha was used in the experiments. This corresponds to an application rate of 0.67 mg as/kg dry soil. Before starting the tests, the soils were air dried, sieved to a size ≤ 2 mm and the soil moisture then adjusted to 40% of the maximum water holding capacity. The active substance diluted in acetonitrile (stock solution) was pipetted onto soil subsamples and the solvent allowed to evaporate while mixing the treated soil samples with a spatula. The soil subsamples were then completed with the corresponding soils to the total soil amount and mixed in a tumbling mixer (approximately 1 h) in order to achieve a homogeneous distribution of the as. Soil samples corresponding to 100 g dry matter were filled in Erlenmeyer flasks which were closed with a trap attachment containing a polyurethane foam plug and soda lime for adsorption of organic volatiles and CO₂, respectively. The vessels were incubated in the dark at 20 °C under aerobic conditions for 120 days. Samples were taken for analysis on days 0, 0.25, 1, 2, 4, 7, 14, 30, 60 and 120. The microbial biomass of the soils was determined at the beginning, on day 60 and at the end of incubation time, with and without the active ingredient.

The soil samples were extracted three times with a solvent mixture of acetonitrile/water (1:1) and finally with pure acetonitrile. After each shaking procedure the slurry was centrifuged, the supernatant was filtered and the radioactivity of the combined clear supernatants determined by liquid scintillation counting. Extracted soil subsamples were then subjected to a hot extraction with acetonitrile/water (1:1) for 2 hours under reflux and processed as described above. Subsamples of the cold and hot extracts were evaporated to dryness and redissolved in acetonitrile for HPLC analysis. The different fractions from the HPLC runs (with same Rf) were purified by preparative TLC cut out and eluted with acetonitrile. After another purification by HPLC methods, the radioactive fractions were separated and evaporated for structure elucidation by spectroscopic methods. Different TLC methods were used for quantification and identification of metabolites by co-chromatography with authentic reference compounds. The distribution of the radioactive zones was obtained by use of a Bio-Imaging Analyzer and the quantification carried out with the software TINA. Reversed phase HPLC was applied for isolation/purification as well as for identification and quantification of metabolites (HPLC combined with a radioactivity monitor and scintillation flow-through detector Raytest). For confirmation of the quantitative and qualitative results, TLC methods were used. All metabolites except U2 and U3 were identified by mass spectroscopy (LS-MS/MS including NMR-spectrums) additionally to confirmations obtained by TLC and HPLC methods. ¹⁴CO₂ absorbed from the soda lime (trap) was liberated with HCl and absorbed in a scintillation cocktail for subsequent measurement of radioactivity via LSC. The bound residues remaining in the extracted soil samples were determined by combustion in an oxidizer, i.e. measurement of the formed ¹⁴CO₂ absorbed in a scintillation cocktail by liquid scintillation counting.

The recovery rate during the test period ranged on average from 98.5 to 101.1% of the applied radioactivity in the four soils investigated. The values demonstrate that no significant loss occurred during the incubation process.

With ongoing incubation time the mineralisation to ¹⁴CO₂ increased steadily in all soils and ranged from 23.0 to 52.1% of the applied radioactivity at the end (day 120) of the experiment. There is a good correlation between mineralisation rate and microbial biomass (% org. C) of the soils. Other volatiles remained below 0.1% of the applied radioactivity at any time of the study.

The extractable radioactivity in the four soils exceeded 96% of the applied radioactivity in the four soils at the beginning of incubation (on day 0) and decreased to a range of 10.4 to 58.7% depending on the mineralisation and formation of residues bound to the soil. The lowest extractable part of the applied radioactivity at the end of the study was found in the soil Hoefchen Hohenseh 4a (10.4%) due to the strong mineralisation (52% CO₂) and high content of bound residues (34.7%). In contrast, in the sand the highest extractable part of the applied radioactivity was found at the end of the study (58.7%) and the lowest mineralisation rate (23% CO₂) and amount of bound residues (16%) (for details see Tables CA 7.1.1.1/02-6 to -9). This is in accordance with the significantly higher biological activity and content of organic carbon of the soil Hoefchen Hohenseh 4a compared to the soil BBA 2.1. Also in the other two soils, the degradation behaviour of fenamiphos was well correlated to their biological activity.

The bound residues increased in all soils during the time course of the study and reached their maximum concentration in three soils at the end of incubation (16.0 to 33.1%), while in the soil Hoefchen Hohenseh 4a the maximum amount of 35.8% was observed on day 30, remaining nearly constant till to the end of the experiment (34.7% on day 120). Due to this fact, it is supposed that the bound residues in this soil become bio-available again contributing thus also to mineralisation.

Fenamiphos was rapidly degraded and metabolized in all soils investigated. A total of seven metabolites were found in the soils during the time course of the experiment. Five compounds could be clearly identified of which three were major metabolites found in quantities exceeding 10% of the applied amount. Major metabolites were fenamiphos sulfoxide (M01), fenamiphos sulfone (M02) and fenamiphos sulfone phenol (M13). Other metabolites found in quantities below 10% of the applied amount were fenamiphos sulfoxide phenol (M12) and fenamiphos sulfone anisole (M14).

Fenamiphos sulfoxide (M01) reached its maximum concentration in all soils within 4 days and declined then till to the end of incubation (day 120) to a range of 2.1 to 19.3% of the applied radioactivity. The highest concentration was detected in the sand soil BBA 2.1 amounting to 77.2% on day 4 of incubation, while in the other three soils a maximum level of about 66% was found. Fenamiphos sulfone (M02) reached the maximum concentration of 15.3 to 24.9% in three soils within 7 days and declined then till to the end of incubation (day 120) to a range of 0.4 to 6.7% of the applied radioactivity. Only in the less active sand soil (BBA 2.1) the maximum amount of 29.3% was found later on day 60 of incubation (25% on day 120). The third major metabolite Fenamiphos sulfone phenol (M13) reached the maximum concentration of 20 to 25.1% in three soils between days 7 and 14 and declined then till to the end of incubation (day 120) to a range of 2 to 10.4% of the applied radioactivity. Also in this case, in the less active sand soil (BBA 2.1) the maximum amount of 5.4% was found only at the end of the experiment (on day 120).

The minor metabolite Fenamiphos sulfoxide phenol (M12) reached its maximum concentration of 2.7 to 6.5% in all soils between days 7 and 14 of incubation and declined till to the end of the study to a level of about 1% of the applied amount. The second minor metabolite Fenamiphos sulfone anisole (M14) was detected at a later stage of the experiment (up from day 14). In the soils Laacher Hof AIII (silt loam) and BBA 2.1 (sand) the maximum concentration of 8.2 and 1.4%, respectively, was measured only at  the end of incubation (day 120). In the soils Hoefchen Hohenseh 4a (silt) and Laacher Hof AXXa (sandy loam) the maximum concentration of 3.5 and 5.1%, respectively, was found on days 14 and 60, respectively. A more significant decrease of this metabolite to 0.8% on day 120 was observed in the silt soil (Hohenseh 4a), indicating that also this metabolite was subjected to mineralisation. A not identified degradation compound (U3) was detected at concentrations < 1% only once in each soil, Laacher Hof AIII and Hoefchen Hohenseh 4a.

 

Table 3: Carbon dioxide and bound residues

soil type	max. CO2 (day)	max. bound residue (day)
sandy loam	38.4% (120)	28.5% (120)
silt loam	27.8% (120)	33.6% (120)
silt	52.1% (120)	36.2% (30)
sand	23.0% (120)	17.5 (30)

 

 

Table 4: Maximum formation rate of metabolites

Metabolite	soil type	max % after (..) days	% after 120 days
fenamiphos-sulfoxide	sandy loam	65.4 (1)	7.4
	silt loam	65.4 (2)	11.7
	silt	66.9 (1)	2.1
	sand	77.2 (4)	19.3
fenamiphos-sulfone	sandy loam	24.9 (4)	6.7
	silt loam	17.7 (7)	1.9
	silt	15.3 (2)	0.4
	sand	29.3 (60)	25.0
fenamiphos-sulfoxide-phenol	sandy loam	3.7 (7)	1.2
	silt loam	4.0 (7)	0.7
	silt	6.5 (7)	0.4
	sand	2.7 (14)	1.0
fenamiphos sulfone phenol	sandy loam	20.0 (7)	5.7
	silt loam	23.7 (30)	10.4
	silt	25.1 (7)	2.0
	sand	5.4 (120)	5.4
fenamiphos-sulfone anisole	sandy loam	5.1 (60)	4.5
	silt loam	8.2 (120)	8.2
	silt	3.5 (14)	0.8
	sand	1.4 (120)	1.4

 

Table 5: Aerobic degradation rates for fenamiphos in four soils.

Substance		sandy loam	silt loam	silt	sand
Fenamiphos	DT50 [d]	0.6	1.0	0.4	1.4
	r^2	0.971	0.996	0.992	0.981

 

Supporting information

The study of Simon (1990) did show that fenamiphos was degraded to FOX, FON, FOX P and FONP (no FANON was reported as being identified as a degradate of fenamiphos) carbon dioxide and bound residues.

The available data were assessed by the EFSA and a conclusion on the biodegradation of Fenamiphos aa well as its metabolites was drawn in the EFSA Conclusion on the peer review of the pesticide risk assessment of the active substance Fenamiphos (European Food Safety Authority, 2019; EFSA Journal 2019;17(1):5557, 49 pp.). The key information needed for the persistence assessment and exposure assessment according to Regulation (EC) 1907/2006 (REACH) is summarized in table 6 and 7 below.

 

Table 6: Route of degradation (aerobic) of Fenamiphos in soil (Regulation (EU) N° 283/2013, Annex Part A, point 7.1.1.1) as cited in the appendix to EFSA Conclusion on the peer review of the pesticide risk assessment of the active substance Fenamiphos (European Food Safety Authority, 2019; EFSA Journal 2019;17(1):5557, 49 pp.).

Mineralisation after 100 days	23-52.1 % after 120 days at 20 ºC (n=4)
Non-extractable residues after 100 days	34.7 % after 120 days at 20º C (n=4)
Metabolites requiring further consideration - name and/or code, % of applied (range and maximum)	Fenamiphos-sulfoxide (FOX – M01): 65.4 – 77.2 % at day 4 (n=4) Fenamiphos-sulfone (FON – M02): 24.9 – 29.3 % at day 60 (n=4) Fenamiphos-sulfoxide-phenol (FOXP – M12): 2.7 – 6.5 % at day 7 (n=4) Fenamiphos-sulfone-phenol (FONP - M13): 5.4 – 25.1 % at day 14 (n=4) Fenamiphos-sulfone-anisole (FANON – M14): 1.4 – 8.2 % at day 120 (n=4)

 

Table 7: Rate of degradation in soil (aerobic) laboratory studies active substance and its metabolites (Regulation (EU) N° 283/2013, Annex Part A, point 7.1.2.1.1 and Regulation (EU) N° 284/2013, Annex Part A, point 9.1.1.1) as cited in the appendix to EFSA Conclusion on the peer review of the pesticide risk assessment of the active substance Fenamiphos (European Food Safety Authority, 2019; EFSA Journal 2019;17(1):5557, 49 pp.). The table summarizes highest normalized DT50 values and the geometric mean value or each species.

Substance	DT50 (days) 20 °C pF2/10kPa (max. value)	DT50 (days) 20 °CC pF2/10kPa (geom. mean)
Fenamiphos	2.01	0.71
M01 (FOX)	21.3	9.6
M02 (FOΝ)	80	9
M12 (FOXP)	23.5	6.2
M13 (FONP)	83.6	25.5
M14 (FANON)	184	119

 

Conclusion

The available data provide robust laboratory derived DegT₅₀ values for use in risk assessments according to Regulation (EC) No 1907/2006 (REACH). In the study of Brumhard (2002) it was demonstrated that Fenamiphos is rapidly degraded and metabolized in soil. In the to EFSA Conclusion on the peer review of the pesticide risk assessment of the active substance Fenamiphos (European Food Safety Authority, 2019; EFSA Journal 2019;17(1):5557, 49 pp.) a normalized DT50 (20 °C pF2/10kPa) of 0.71 days is indicated. A total of seven metabolites were found in the soils during the time course of the experiment. Five compounds could be clearly identified of which three were major metabolites found in quantities exceeding 10% of the applied amount. Major metabolites were Fenamiphos sulfoxide (M01), Fenamiphos sulfone (M02) and Fenamiphos sulfone phenol (M13). Other metabolites found in quantities below 10% of the applied amount were Fenamiphos sulfoxide phenol (M12) and Fenamiphos sulfone anisole (M14). The normalized geometric mean DT50 (20 °C pF2/10kPa) values of these metabolites are considered to be < 120 days. Hence, neither the parent compound Fenamiphos, nor its metabolites are persistent according to the criteria based on Annex XIII of REACH.

 

References:

Abu, A. (2016). Aerobic Soil Degradation Kinetic Assessment of Fenamiphos and its Metabolites FOX, FON, FOXP AND FONP. Cambridge Environmental Assessments project number CEA.1693.

Brumhard, B. (2002). Aerobic degradation of fenamiphos in four soils. Bayer AG report number MR-587/01.

Matthews, J. (2015a). Fenamiphos-sulfoxide (a degradate of fenamiphos): rate of degradation in soil. Envigo project number JDV0127.

Matthews, J. (2015b). Fenamiphos-sulfone (a degradate of fenamiphos): rate of degradation in soil. Envigo project number JDV0128.

Matthews, J. (2015c). Fenamiphos-sulfoxide phenol (a degradate of fenamiphos): rate of degradation in soil. Envigo project number JDV0129.

Matthews, J. (2015d). Fenamiphos-sulfone phenol (a degradate of fenamiphos): rate of degradation in soil. Envigo project number JDV0130.

Matthews, J. (2015e). Fenamiphos-sulfone anisol (a degradate of fenamiphos): rate of degradation in soil. Envigo project number JDV0131.

Simon, L. (1990). Metabolism of Fenamiphos (Nemacur) in soil types of different geographic origin. Report number M5680.