FENAMIPHOS JMPR 1977
Explanation
Arising out of the list of requirements for further work or
information published in the Report of the 1974 Joint Meeting
(FAO/WHO, 1975a) some data on residues of fenamiphos in oranges and
potatoes wore referred to the FAO Panel of &ports; reports of a very
limited number of analyses of snap beans, broccoli, carrots, kiwifruit
and tomatoes were also received but these added nothing of value to
the data already available (FAO/WHO, 1975b). Some further information
on the metabolism of fenamiphos in bean plants and on its uptake from
soils was also made available to the Meeting.
RESIDUES IN FOOD AND THEIR EVALUATION
RESIDUES RESULTING FROM SUPERVISED TRIALS
The residues of fenamiphos, together with its sulphoxide and sulphone,
resulting from supervised trials on oranges and potatoes (Anonymous,
1977) are shown in Table 1. Residues in potatoes were generally below
0.2 mg/kg. In oranges, observed levels were mostly between 0.6 and 2.6
mg/kg in the peel and between 0.01 and 0.25 mg/kg in the flesh of the
fruit. These figures would correspond to a maximum of about 0.7 mg/kg
in the whole fruit, most being below 0.5 mg/kg. No further data on
other citrus fruits was available to the Meeting. Table 2 lists the
limited data provided on residues in other crops (Anonymous, 1977).
FATE OF RESIDUES
In plants
Waggoner (1972) indicated the presence of two unidentified
organosoluble metabolites (IV and V) of fenamiphos isolated from
treated plant products. Work by Pither and Gronberg (1977) on the
characterisation of these compounds has now been reported. Bean plants
were treated, by stem injection or solution uptake, with various
combinations of fenamiphos labelled with tritium or carbon-14 in
various positions and the metabolites were isolated. Metabolite IV was
identified as des-isopropyl fenamiphos sulphoxide; metabolite V was
shown to contain the ethyl-O-P-O-ring structural backbone but the
presence or absence of the isopropyl-N-P moiety could not be
determined. Observed concentrations of these transient metabolites
(0.6-3.8% metabolite IV and 0-0.7% metabolite V) confirmed those
previously reported. These metabolites contribute little to the total
residue which comprises mainly fenamiphos, fenamiphos sulphoxide,
fenamiphos sulphone and some hydrolysis products.
TABLE 1. Residues of fenamiphos resulting from supervised trials (oranges and potatoes)
Application
rate Interval Residues2/found
Crop Country Formulation1/ (kg a.i./ha) (days)(mg/kg)
Fruit Peel Flesh
Oranges ( USA 15% G 100 0 <0.01 <0.01
( 27 <0.01 <0.01
( 33 <0.01 <0.01
( 61 1.50 0.02
( 90 1.66 0.07
( 118 1.78 0.13
( 153 1.65 0.04
( 159 1.56 <0.01
( 189 2.60 0.25
( 194 1.52 0.03
( 215 1.57 0.03
( 238 0.85 0.03
( 456 0.78 0.02
( 483 0.87 0.02
( 513 0.63 0.01
( Spain 5% G 10 97 0.17
( 104 0.12
( 111 0.06
( 118 0.04
Potatoes( Netherlands 5% G 10 107 0.15
( 137 0.12
( 40% EC 10 107 0.06
( 137 0.05
TABLE 1. (Continued)
Application
rate Interval Residues2/found
Crop Country Formulation1/ (kg a.i./ha) (days)(mg/kg)
Fruit Peel Flesh
( Federal Republic 40% EC 8 153 0.02
( of Germany 8 157 0.08
( 8 146 0.22
( 10 159 0.07
( 8 159 0.02
( 6 159 0.03
( 10 156 <0.01
( 8 156 0.06
( 6 156 0.05
( 10 133 0.05
( 10 163 0.01
1/ G = granules; EC = emulsifiable concentrate.
2/ Residues comprise fenamiphos, its sulphoxide and sulphone, determined. and expressed as fenamiphos sulphone.
TABLE 2. Residues of fenamiphos resulting from supervised trials (miscellaneous)
Application
rate Interval Residues2/found
Crop Country Formulation1/ (kg a.i./ha) (days) (mg/kg)
Beans USA 3% SC 6.7 411 < 0.01
(Snap) 431 < 0.01
Broccoli USA 15% G 10 112 0.03
Carrots N. Zealand - 8 76 0.03
98 <0.01
- 12 76 0.05
98 <0.01
Kiwifruit N. Zealand 8 185 <0.01
16 185 <0.01
Tomatoes N. Zealand 40% EC 8 97 <0.01
1/ SC = spraying concentrate; G = granules; EC = emulsifiable concentrate.
2/ Residues comprise fenamiphos, its sulphoxide and sulphone, determined
and expressed as fenamiphos sulphone.
In soils
The persistence of fenamiphos in soil and its uptake by certain crops
was investigated by Shaw (1975). Technical fenamiphos was mixed with
fenamiphos labelled with tritium in the S-CH3 position and with
fenamiphos uniformly labelled with carbon-14 in the ring. The effects
of plant growth and time on fenamiphos residues in soil treated with
this doubly labelled material were studied. Corn and cotton were grown
in the treated soil and harvested. After the soil had lain fallow, com
and soybeans were grown in the treated soil, a portion of which had
been extracted with methanol/water, and subsequently harvested. The
tritium/carbon-14 ration of 4:1 was consistent throughout the study
indicating no hydrolysis of the methylthio group from the ring
structure.
Fenamiphos - 14C, 3H-treated soils contained 47% of the
radioactivity as residue when the initial corn and cotton plants were
harvested. The quantity of absorbed material was four times greater in
corn plants (20%) than in cotton plants (5%). Soils still contained
29% of the original radioactivity (18.5% was bound) one year after
treatment. Rotational crops of soybeans and cotton, grown in extracted
and non-extracted soils, took up less than 1.2% and 0.17% respectively
of the applied material. No significant difference in residue uptake
was detected between plants from in extracted or non-extracted soil. A
difference in residue uptake clue to a plant species difference was
detectable because cotton absorbs less fenamiphos residues than do
corn or soybeans.
NATIONAL TOLERANCES REPORTED TO THE MEETING
National tolerances and associated pre-harvest intervals reported to
the Meeting are shown in Table 3.
TABLE 3. National tolerances reported to the Meeting
Tolerance Pre-harvest
Country Commodity (mg/kg) interval (days)
Australia Tomatoes, brassicas,
cucurbits, lettuce, citrus 0.05
pineapples, grapes,
bananas, ginger
Federal Republic Potatoes, tomatoes 0.2
of Germany Bananas (with peel), raw
coffee, grapes 0.1
TABLE 3. (Continued)
Tolerance Pre-harvest
Country Commodity (mg/kg) interval (days)
Other food of plant
origin 0.05
South Africa General 0.1
Potatoes 42
Spain General 60
USA Bananas, Brussels sprouts,
cabbage 0.1
Cottonseed 0.05
Peanuts 0.02
Peanut hulls 0.4
Soybeans 0.05
APPRAISAL
Residues of fenamiphos observed in potatoes were generally below the
level of 0.2 mg/kg and the new data were in accord with those
previously available. For oranges, however, the latest data conflicted
appreciably with those for a number of citrus fruits in 1974. Up to
2.6 mg/kg was observed in the peel and up to 0.25 mg/kg in the flesh
of the fruit; the maximum corresponds to about 0.7 mg/kg on the whole
fruit, but the majority of results would be less than 0.5 mg/kg. These
levels are an order of magnitude higher than the previously reported
maxima of 0.3 mg/kg (peel) and 0.03 mg/kg (flesh) for tangerines;
residues on grapefruit, lemons, limes and oranges were previously
reported at levels at or only slightly above the limit of
determination. Limited data on residues in other crops added nothing
of value to those previously available. Further observations have
helped to clarify the fate of residues in plants and soil.
RECOMMENDATIONS
The recommendation for potatoes made by the 1974 Meeting is confirmed
as no longer being temporary. The previous recommendation for citrus
fruits is withdrawl and replaced by a maximum residue limit for
oranges and a temporary maximum residue limit for other citrus fruits.
The other recommendations remain unchanged.
The following limits refer to the sum of fenamiphos, its sulphoxide
and its sulphone, expressed as fenamiphos.
Maximum residue limits
Commodity Limit, mg/kg
Oranges, whole fruit 0.5
flesh of fruit 0.1
Potatoes 0.2
Temporary maximum residue limit
Commodity Limit, mg/kg
Citrus fruits
(other than oranges),
whole fruit 0.05*
* At or about the limit of determination.
FUTURE WORK OR INFORMATION
REQUIRED (by 1980)
Further data on which to assess the residues in or on citrus fruits
other than oranges and on tomatoes.
DESIRABLE
1. Information on brain cholinesterase and behavioural studies in
animals exposed to low levels for extended periods.
2. Observations in humans.
3. Additional studies on the potentiation effects with other
organophosphorus pesticides.
4. Residue data for raw agricultural products moving in commerce.
5. Further residue data for different crops from supervised trials,
especially for beans, cucumbers, lettuce, peppers and strawberries.
REFERENCES
Anonymous. (1977) Data on residues of fenamiphos in oranges, potatoes
and other crops. Submitted by Bayer A.G. (Unpublished).
Pither K.M. and Granberg, R.R. (1977) The metabolism of (R) Nemacur in
plants. Chemagro Report No. 52257. (Unpublished).
Shaw II, H.R. (1975) Determination of soil-borne residues and uptake
by rotational crops from soil treated with (R)Nemacur. Chernagro
Report No. 44226. (Unpublished).
Waggoner, T.B. (1972) Metabolism of Nemacur (ethyl 4-(methylthio)-m-
olyl isopropylphosphoramidate) and identification of two metabolites
in plants. J. Agr. Food Chem., 20 (l): 157-160-
FAO/WHO (1975a) 1974 evaluations of some pesticide residues in food.
FAO/AGP/1974/M/11; WHO Pesticide Residue Series No. 4.
FAO/WHO (1975b) Pesticide residues in foods Report of the 1974 Joint
FAO/WHO Meeting. FAO Agricultural Studies No. 97; Wld. Hlth. Org.
techn. Rep. Ser., No. 574. WHO Technical Reports Series.