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
ISOFENPHOS
Explanation
The CCPR, at its sixteenth Session, asked the JMPR to consider
whether the residue definition, currently "sum of isofenphos and its
oxygen analogue" should be extended to include the metabolites
des-N-isopropyl-isofenphos (DNI) and its oxygen analogue (DNIOA).
It was pointed out that crop rotation metabolism studies had suggested
that residues of DNIOA sometimes exceeded those of isofenphos and its
oxygen analogue in some crops.
RESIDUES IN FOOD AND THEIR EVALUATION
Many of the data supporting the 1981 and 1982 evaluations were
based on analyses for isofenphos and its oxon only. When DNI and DNIOA
were also determined, the levels of all four compounds were often
below the limit of determination. Data from supervised trials in which
at least one of them was at a measurable level were available for
maize and sweet corn grain, husks, cobs and forage, wheat, sorghum,
soybeans and onions. Of a total of 93 samples, only one (onion)
contained a measurable level of DNI: it was at the limit of
determination (0.01 mg/kg) and represented about 1 percent of the
residue. DNIOA was measured in 24 samples of corn forage, husks and
kernels at levels ranging from 0.01 to 0.1 mg/kg. It represented 10
percent of the residue or less in 4 samples, and 10-25 percent in 14
samples of forage with total residues of 0.06-0.4 mg/kg. It was found
in forage at 0.02 and 0.08 mg/kg in total residues of 0.07 and
0.17 mg/kg, and was the only residue measured in the remaining
four samples (maize husk, kernels and forage), at levels of
0.01-0.03 mg/kg.
In metabolism studies on sweet corn, onions and cabbage, DNIOA
was a minor metabolite reaching a maximum of 10 percent of the sum of
isofenphos, its oxon and DNIOA in sweet corn, 4 percent in onions and
5 percent in cabbage. DNI was not detected. In feeding studies with
hens and a pig, the main intact ester residue was isofenphos. DNI
accounted for a maximum of about 5 percent of the total
organophosphorus residue in tissues and eggs. DNIOA was not found. In
a cow feeding study, the only identified organophosphorus residue was
isofenphos oxon in liver and kidney.
In metabolism studies with beans, sugar beet and wheat as
rotational crops, isofenphos, its oxon, DNI and DNIOA were determined
by GLC. Isofenphos oxon was the main component of the residue in most
samples. DNIOA accounted for 11 percent, 18 percent and 17 percent of
the total residue in wheat heads, stems and leaves respectively, and
for 75 percent of a total residue of 0.08 mg/kg in sugar beet tops. It
was below the limit of determination in sugar beet roots and bean
forage. DNI was below the limit of determination in all samples.
It is clear that inclusion of DNI in the residue definition is
unnecessary. DNIOA occasionally forms a substantial proportion of the
residue, but only apparently when the total residue is low. It occurs
mainly in forage, for which the JMPR has not proposed an MRL. (There
is a proposed TMRL of 0.5 mg/kg for maize fodder and sweet corn
fodder.)
RECOMMENDATION
The definition of the residue should not be changed.