PESTICIDE RESIDUES IN FOOD - 1984
Sponsored jointly by FAO and WHO
EVALUATIONS 1984
The monographs
Data and recommendations of the joint meeting
of the FAO Panel of Experts on Pesticide Residues
in Food and the Environment and the
WHO Expert Group on Pesticide Residues
Rome, 24 September - 3 October 1984
Food and Agriculture Organization of the United Nations
Rome 1985
FENITROTHION
EXPLANATION
Fenitrothion was evaluated by the Joint Meeting in 1969, 1974,
1976, 1979, 1982 and 1983.1/ Information was required by the 1983
meeting on current good agricultural practices and on the results of
supervised trials carried out on varieties of citrus fruit according
to use recommendations.
RESIDUES IN FOOD AND THEIR EVALUATION
USE PATTERN
The meeting received only minor information on recommended uses,
national maximum residue limits, monitoring data and on the fate of
residues in stored wheat and in chicken tissue. Information on
registered uses has been received from Canada, the Netherlands and New
Zealand. Codex maximum residue limits exist for all uses.
RESIDUES RESULTING FROM SUPERVISED TRIALS
In addition to trials made in Spain on fenitrothion on mandarins,
which were reported in 1983, trials have been made on fenitrothion on
oranges. Sumithion 50 percent EC and Folithion 50 percent EC were
applied in Valencia on oranges at a rate of 4.5 kg a.i./ha in a
concentration of 0.15 percent. The average residue in whole fruit was
1.18 mg/kg and 0.93 mg/kg 14 days and 28 days after treatment. Residue
levels in pulp 14 days and 28 days after both treatments were
0.03 mg/kg or lower.
FATE OF RESIDUES
In Plants
Although the fate of residues of fenitrothion in stored cereals
has been reviewed previously (1974, 1976, 1977 and 1979), additional
information was provided to this meeting. Earlier investigations were
mainly on the degradation rate of the parent compound and to some
minor extent on metabolism of fenitrothion to the oxygen analogue and
3-methyl-4-nitrophenol. An investigation has now been made on the
degradation to other metabolites of fenitrothion in stored wheat. Hard
red spring wheat with a moisture content of 12.5 percent was treated
with fenitrothion to provide a deposit of 12 mg/kg. After mixing, the
wheat was transferred to screw-capped jars and stored in the dark at
1/ See Annex 2 for FAO and WHO documentation.
20°C for 12 months. Samples were taken after 0, 1, 3, 6 and 12
months for quantitative determination of fenitrothion and the
following metabolites: fenitro-oxon, O-dimethyl-fenitrothion,
S-methyl-fenitrothion, 3-methyl-4-nitrophenol,
dimethyl-phosphorothioate and O-dimethyl-S-methyl-fenitrothion.
The samples were extracted with acidified acetone or methanol
and, after concentration, separations were made by partitioning to
organic solvents from acidified or basic aqueous solutions. The
metabolites present were ethylated by diazoethane and clean-up was
made by column chromatography. Determinations were made by GLC using a
flamephotometric detector (phosphorus mode) and an EC-detector. The
presence of the metabolites was confirmed by TLC and for
dimethyl-fenitrothion also by chemical derivatization. After 12
months' storage, fenitrothion residue was decreased to 2 mg/kg.
O-dimethyl-fenitrothion, 3-methyl-4-nitrophenol and dimethyl
phosphorothioate were the major metabolites. The highest levels of
O-dimethyl-fenitrothion and dimethyl-phosphorothioate were found after
six months of storage; the residues, 2.01 mg/kg and 0.55 mg/kg,
respectively, decreased after 12 months to 0.98 mg/kg and 0.21 mg/kg.
Residues of 3-methyl-4-nitrophenol increased during the storage period
from 0.38 mg/kg after one month to 0.96 mg/kg after 12 months. No
fenitrothion or S-methyl-fenitrothion was detected throughout the
study period. Detection limits were 0.001 mg/kg and 0.05 mg/kg,
respectively (Abdel-Kader & Webster, 1982).
In Animals
The fate of residues of fenitrothion in mammals was reviewed in
1969 and 1974. A study has been made on residues of fenitrothion and
its metabolites in chicken tissue after long-term exposure to small
doses. The results from this study show that chicken tissues retain
insignificant amounts of fenitrothion or its metabolites even after a
long exposure to small doses of this insecticide. This is consistent
with earlier observations made on tissues for mammals (Trottier &
Jankowska, 1980).
RESIDUES IN FOOD IN COMMERCE OR AT CONSUMPTION
Monitoring data from 1981-83 have been received from Sweden
(1984a) on fenitrothion in domestic and imported crops of carrot,
dill, lettuce, lemon, mandarin and orange. A total of 483 samples of
domestically grown crops and 1 720 samples of imported crops were
analysed. In 98.5 percent of the samples residues were <0.11 mg/kg.
One sample of dill had a residue higher than 0.5 mg/kg and 14 samples
from 1 032 samples of mandarins and oranges contained residues between
0.29 and 0.8 mg/kg.
NATIONAL MAXIMUM RESIDUE LEVELS REPORTED TO THE MEETING
Updated lists of MRLs were provided to the meeting by the
Netherlands (1984) and Sweden (1984b)
Country Commodity MRL (mg/kg)
The Netherlands Fruit 0.5
Vegetables 0.5
Cereals 0.5
Tea 0.5
Cocoa bean 0.1
Milk 0.002 (limit of
determination)
Meat 0.05 (limit of
determin.)
Other food 0 (0.02) (limit of
determin.)
Sweden Fruits and Vegetables 0.5
Potato 0.2
Cereals and bran 0.5
Flour from cereals 0.2
APPRAISAL
Limited information was received on recommended uses, results of
supervised trials, monitoring data, national maximum residue limits
and the fate of fenitrothion in chickens and in stored wheat.
The meeting received data from a supervised trial with oranges,
which supplemented information received by the 1983 JMPR on trials
with mandarins. Residues in the whole fruit were 1.2 mg/kg after 14
days and 0.93 mg/kg after 28 days. This supports the TMRL for oranges
of 2 mg/kg proposed as an amendment to the Codex MRL. Residues in the
pulp were 0.03 mg/kg or lower.
Studies of the metabolism of fenitrothion in wheat stored at 20°
in the dark showed that levels of O-dimethyl-fenitrothion and
dimethyl-phosphorothioate increased for six months after treatment and
then decreased, but with a considerable residue remaining even after
12 months. Levels of 3-methyl-4-nitrophenol increased during the
whole 12-month period after treatment. No fenitro-oxon or
S-methyl-fenitrothion was observed.
The metabolism of fenitrothion has been investigated in the
chicken after long-term exposure to small doses. No significant
amounts of fenitrothion or metabolites were retained in the tissue.
This is consistent with earlier observations made on mammalian
tissues.
REFERENCES
Abdel-Kader, M.H.K. & Webster, G.R.B. Analysis of fenitrothion and
1982 metabolites in stored wheat. Intern. J. Environ. Anal.
Chem., 11: 153-165.
Netherlands. National maximum residue levels of fenitrothion.
1984
Sweden. Monitoring data from the National Food Administration,
1984a Uppsala.
Sweden. National maximum residue levels of fenitrothion.
1984b
Trottier, B.L. & Jankowska, I. In vivo study on the storage of
1980 fenitrothion in chicken tissues after long-term exposure to
small doses. Bull. Environment. Contam. Toxicol., 24:
606-610.