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
PARATHION
Explanation
The CCPR at its fourteenth Session asked the JMPR to reconsider
the definition of the residue, currently "sum of parathion and its
oxygen analogue".
RESIDUES IN FOOD AND THEIR EVALUATION
In most of the data supplied for evaluation, residue analysis was
by a method which does not differentiate between parathion and its
oxygen analogue, or the oxygen analogue was not determined. Separate
determinations of the thion and oxon on lettuce, however, showed that
the half-life of paraoxon was much shorter than parathion. Parathion
residues decreased from 1.7 mg/kg on the day of treatment to
0.02 mg/kg 14 days later, whereas the oxon residue was 0.01 mg/kg, the
limit of determination, on the day of treatment and was not detectable
thereafter. In spinach the parathion residue on the day of treatment
was 1.5 mg/kg while the oxon was 0.05 mg/kg.
In supervised trials with cottonseed, residues of parathion and
its oxon in cottonseed and cottonseed oil were mainly below the limit
of determination (0.05 mg/kg). Measurable residues of parathion found
in 14 samples of seed ranged from 0.05 to 0.66 mg/kg, while all the
oxon residues were below the limit of determination. In cottonseed
oil, measurable thion residues were 0.10-0.27 mg/kg (4 samples) and
all oxon residues were below 0.05 mg/kg.
Extensive monitoring data from several countries, based on
analytical methods which would determine the thion and oxon
separately, show that residues of parathion are occasionally found,
but the oxon has never been reported.
Gunther et al. (1977) reviewed studies of dislodgable residues
on citrus foliage after treatment with parathion (to assess the
hazards of the re-entry of workers to treated orchards) which showed
that residues of paraoxon could sometimes exceed those of the parent
compound and could persist for several weeks. This situation is
however peculiar to desert conditions where the normally unstable oxon
residues are protected from degradation by soil dust covering the leaf
surfaces. Residues are largely adsorbed by the dust and are
effectively removed from fruit by post-harvest washing in packing
houses. The meeting concluded that these dislodgable residues were
therefore not relevant in the context of residues in or on food
commodities.
RECOMMENDATION
The oxygen analogue should be excluded from the definition
without changing the numerical values of the MRLs.
REFERENCES
Gunther, F.A., Iwata, Y., Carman, G.E. & Smith, C.A. The Citrus
1977 re-entry problem: Research on its causes and effects, and
approaches to its minimization. Res. Rev. 67: 1-132.