MALATHION JMPR 1973
Malathion has been reviewed each year 1965/1971 (FAO/WHO 1965b,
1967b, 1968b, 1969b, 1970b, 1971, 1972b). In the monographs of the
1966 meeting (FAO/WHO 1967b) reference is made to the use of malathion
for the treatment of dried beans as protection against damage by
stored product pests. However, no recommendation appears to have been
made for an appropriate residue limit.
Many countries in tropical regions, especially in Asia and the
Far East are heavily dependent upon dried beans (lentils, pulses) as a
food staple, principle source of protein and valuable export
commodity. In some areas the economy is largely dependent on the
production and sale of dried beans (pulses). Export markets demand
high quality standards and freedom from insect pests and their damage.
Deterioration of quality in storage is entirely due to attack by
pests. Damage is caused by a number of insect species which produce
obvious holes in the beans. Unless the produce is fumigated regularly
approximately 5% of the pulses are holed by insects during each month
of storage. Too frequent fumigation causes tainting, loss of quality
and excessive fumigant residues. The holes cause severe downgrading in
the quality and price of the beans and greatly increase local costs
because of the need for hand sorting.
Lindane dusts and sprays are used in some areas but some species
of pests have developed lindane resistant strains, To prevent
infestation it is desirable to admit an acceptable insecticide.
Malathion is the only product which could be considered at the present
time. Malathion should also be applied to the outside of bags and
stacks following fumigation.
The addition of malathion in the form of dust or dilute emulsion
spray is effective at rates of the order of 8 ppm on the weight of the
beans. Extensive experience with malathion on wheat, oats, barley,
rice and maize indicates that such treatment would remain effective
for five to six months by which time the residue level would have
declined to approximately 2-4 ppm.
Extensive work (refer to the several JMPR monographs) indicates
that malathion is readily removed from the surface of grain by washing
and processing. It has been shown that simple cooking removes or
destroys virtually all trace of malathion residues from cereal
products, beans, peas and fruits. It may be assumed that a similar
loss would occur from the normal cooking to which pulses are always
That an additional tolerance be recommended as follows:
Pulses (dried beans, lentils) 8 ppm