MALATHION JMPR 1977
Malathion was last evaluated by the Joint Meeting in 1975 (FAO/WHO
1976). Further information was desirable on residues in stored grains
resulting from god storage practice including storage at relatively
low temperature and humidity and on the effects of milling, cooking
and baking on these residues. Information was sought especially on
residues after long-term storage of grain. Some information on these
points, and on levels of malathion in rye and wheat moving in
commerce, has been provided and is reviewed below.
RESIDUES IN FOOD AND THEIR EVALUATION
FATE OF RESIDUES
In storage and processing
As stated in the 1976 evaluation of fenitrothion (FAO/WHO 1977, P.370)
residues of malathion 7 days after treatment in wheat which initially
contained 10 mg malathion/kg were 5 mg/kg in the grain, 2 mg/kg in the
flour, 2.7 mg/kg in bread made from disc-milled flour and 2.4 mg/kg in
bread made from roller-milled flour.
In a similar trial with rye grain two 3-ton lots of rye, each at 13.2%
humidity, were treated with malathion in dust and emulsifiable
concentrate formulations, at 10-11 mg/kg and stored in hoppers up to
34 months. The temperature was initially 20°C and varied between 20
and 4°C during storage. After eleven months storage the grain was
mixed and samples of 100 kg from each lot were cleaned by aspiration
and milled. Malathion levels were determined in different milling
fractions and in bread made from two types of flour (grey flour, type
1150 and white flour, type 815). Malathion was determined by a
colorimetric method similar to that recommended by the "Malathion
Panel" (1960). The results are summarized in Tables 1-3.
Flat bread made from flour containing 1 and 2 mg malathion/kg
contained residues between 0.2 and 0.6 mg/kg, after baking for 15
minutes and drying.
The longer the storage period the more malathion penetrates the grain.
Residues in stored rye declined fairly rapidly for 3-6 months after
treatment and then remained fairly constant. Eleven months after
storage only 10% of the residues in raw grain could be removed by
aspiration. After milling, residue levels in the different milling
fractions decreased in the order: bran > whole meal >white flour.
After baking, small amounts of malathion were still present in bread.
No off-flavour in grain, milling fractions or bread was observed
TABLE 1. Residues of malathion (mg/kg) in stored rye
Type of formulation
Storage period dust emulsifiable
0 days a) 10-11 10-11
3 days 9.5 10.2
2 Weeks 5.3 7.2
5 weeks 5.0 6.2
3 months 3.3 -
5 months 2.9 4.0
6 months 2.6 5.4
7 months 2.7 5.2
8 months 2.4 5.0
11 months b) 3.3c) 3.5c)
13 months 3.3 3.6
34 months 1.9 2.5
a) 13.2% humidity in grain
b) 12.2% humidity in grain
c) after mixing the stored lot
TABLE 2. Residues of malathion (mg/kg) in rye fractions
Fraction/% dust emulsifiable
aspirated grain /97 30 3.2
crushed grain /2.3 6.7 4.1
dust (waste) /0.3 60 38
* aspirated after 11 months storage. The malathion residue was
33-35 mg/kg before aspiration.
TABLE 3. Residues of malathion (mg/kg) in milling fractions of
Fraction/% dust emulsifiable
Flour (grey type 1150) /84-85 1.9 1.9
Flour (white type 815) /1 1.2 1.0
Shorts and pollards/5.2-10 13.5 11.8
Bran/2.5-6.2 16.8 15.5
RESIDUES IN GRAIN MOVING IN COMMERCE
In a total of 51 samples of German rye and 153 samples German wheat
moving in commerce, residue levels of malathion were all below 0.001
mp/kg. In 16 of a total of 18 samples of wheat of unknown origin,
residues were also below 0.001 mg/kg. The other 2 samples contained
residues of 0.006 and 0.011 mg/kg. (Ocker, 1976).
Since the last evaluation of malathion by the 1975 Joint Meeting,
further information which was requested on the fate of residues in rye
during storage, milling and baking has been received.
Initial residues of 10-11 mg/kg decreased steadily during the first
3-6 months of storage, and much more slowly thereafter, being about
3.5 mg/kg after 11 months and 2-2.5 mg/kg after 34 months. Milling the
grain containing 3.5 mg/kg produced flour containing 1-2 mg/kg and
bran containing about 16 mg/kg. Bread baked from the flour contained
residues of 0.2-0.6 mg/kg. It appears therefore that the limit of 2
mg/kg for malathion in whole meal and flour from rye and wheat
recommended in 1968 might be exceeded in rye.
The Meeting noted that the 1976 evaluation of fenitrothion included
information on residues of malathion in stored wheat. Initial residues
of 10 mg/kg decreased to 5 mg/kg grain in 7 days. Flour milled from
this grain contained 2 mg/kg.
In the course of reviewing the above data, the Meeting was informed of
the existence of other data on this subject which also suggested that
a limit higher than 2 mg/kg was likely to be required. It therefore
decided to defer a decision pending a full review of the subject at a
Some data on residues of malathion in rye and wheat moving in commerce
were received. Levels in 220 of 222 samples were below 0.001 mg/kg,
the other two being close to 0.01 mg/kg.
The following maximum residue limit for bran of rye and wheat is
recommended. It is additional to the limits recommended previously.
Commodity Limit, mg/kg
Bran of rye and wheat 20
FURTHER WORK OR INFORMATION
1. Further residue data from supervised trials of malathion on stored
grains including data on the fate of malathion during milling, baking
Bresssau, G. Uber Rückstände (1966) von
Vorratschutzmitteln-insbesondere Malathion - in Getreide. Deutache
Lebenmdttel-Rdsch. 62, (1966), 390-95.
Ocker, H.D. (1976) Pflanzenschutzmittelrückstände und
Schwermetallgehalt in der deutschen Getreidernte. 1976.
Bundesforschungsanstalt für Getreide-und Kartoffelnerarbeitung.
Institut für Biochemie und Analytik, Detmold, Fed. Rep. of Germany.
FAO/WHO (1976) 1975 evaluations of some pesticide residues in food.
AGP:1975/M/13; WHO Pesticide Residues Series No. 5.
FAO/WHO 1976 evaluations of some pesticide residues in food;