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
CHINOMETHIONAT
Explanation
Chinomethionat was evaluated by the JMPR in 1968 (as
oxythioquinox), 1974, 1977 and 1981 and a number of maximum residue
limits were recommended (Temporary MRLs, as the AID is temporary).
Information on use patterns on tomatoes and additional residue data
derived from supervised trials were considered desirable by the 1981
JMPR. At the 1983 JMPR limited new data together with those available
to the 1981 meeting were reviewed but the meeting was again unable to
estimate a maximum residue level for tomatoes owing to deficiencies in
the data. The meeting reaffirmed that further data were desirable.
The meeting was informed by the manufacturer that the use of
chinomethionat on tomatoes has generally decreased, with the exception
of two countries from which, however, practically no tomatoes are
exported.
New data on the penetration and metabolism of chinomethionat in
cucumber seedlings, and on its biotransformation by a green alga were
made available by the manufacturer.
FATE OF RESIDUES
In plants.
The biodegradation of chinomethionat by cucumber seedlings
confirms that the thiocarbonate linkage is disrupted during metabolism
of the fungicide by plants (Metche and Piffaut 1982). The sulphur
liberated is principally incorporated into sulphates and sulphur
amino-acids, while the labelled (2,4-14C)-quinoxaline nucleus is
catabolized to 14CO2. Comparison of the results obtained in
sterilized and non-sterilized conditions suggests that micro-organisms
play a large part in the biodegradation.
The metabolites of chinomethionat such as 6-methyl-
2,3-dimercapto-quinoxaline can penetrate more easily through the
roots. This penetration causes the inhibition of some plant metabolic
activities, while there is no inhibitory effect due to chinomethionat
itself.
The biotransformation of chinomethionat by a green alga
(Ankistrodesmus falcatus) has been studied by Piffaut and Metche.
One of the metabolic pathways leads to the transformation of
chinomethionat into an aminochlorinated compound identified as
6-methyl-2 amino-3-chloroquinoxaline. This compound is particularly
phytotoxic to cucumber plants.
APPRAISAL
Chinomethionat was evaluated by the JMPR in 1968, 1974, 1977 and
1981 and a number of temporary MRLs were recommended. Information on
use patterns on tomatoes and additional residue data derived from
supervised trials were considered desirable by the 1981 and 1983
JMPRs.
As a consequence of the withdrawal of the ADI, the existing
temporary MRLs were replaced by guideline levels (GLs).
REFERENCES
Metche, M. and Piffaut, B. Study of the toxicity of chinomethionat.
1983 I. Penetration and metabolism of chinomethionat in cucumber
(Cocumis Sativus) Agric. Biol. Chem. 47, 1725-1732.
Piffaut, B. and Metche, M. Study of the toxicity of chinomethionat.
1983 II. Biotransformation of chinomethionat into toxic derivates
by a green alga (Ankistrodesmus falcatus) Agric. Biol.
Chem. 47, 1733-1740.