PESTICIDE RESIDUES IN FOOD - 1981
Sponsored jointly by FAO and WHO
EVALUATIONS 1981
Food and Agriculture Organization of the United Nations
Rome
FAO PLANT PRODUCTION AND PROTECTION PAPER 42
pesticide residues in food:
1981 evaluations
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
Geneva, 23 November-2 December 1981
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
Rome 1982
PARAQUAT
Explanation
Paraquat was reviewed at the 1970, 1972, 1976 and 1978 Meetings.*
At the 1972 Meeting a minimum residue limit (MRL) for soybeans of
0.1 mg/kg was recommended. Further information has subsequently become
available that indicates the desirability of reconsidering this
particular recommendation.
RESIDUES IN FOOD
The majority of the existing MRL proposals for paraquat in raw
agricultural commodities are at a value of 0.05 mg/kg, which is at or
about the limit of determination of the residue analytical method
(FAO/WHO, 1973 and 1977). These MRLs derive from pre-plant, pre-
emergency and inter-row weed control uses of the herbicide, which
becomes strongly bound to soil and is thereby rendered unavailable to
plants. The MRLs of 0.1 mg/kg and above, including the existing value
for soybeans, were generally required to cover direct spraying of the
crop shortly before harvest for desiccant and/or harvest aid purposes.
USE PATTERN
Paraquat is applied to the mature soybean crop (seed moisture
level 30-40 percent or when 70 percent or more of pods are brown) at
rates of 140 to 400 g a.i./ha. The crop will normally be ready to
harvest 5 to 10 days later. This use pattern reduces yield losses
through disease and weathering in the field, facilitates mechanical
harvesting and produces a cleaner seed with lower humidity and better
germination and vigour.
The use of paraquat on soybeans shortly before harvest was
developed originally on 'determinate' varieties, where maturity is
reached uniformly throughout the crop. More recently, use has spread
to 'indeterminate' varieties, whose growth and maturation are less
uniform and where seed moisture content near harvest can be greater
than is the case with 'determinate' varieties.
* See Annex II for FAO and WHO documentation.
RESIDUES RESULTING FROM SUPERVISED TRIALS
Data on residues of paraquat in soybeans from plants sprayed
close to harvest from trials conducted in the USA, Brazil, Colombia,
Yugoslavia and Zimbabwe are summarized in Table 1. They show that,
under most conditions, residues are below the MRL of 0.1 mg/kg
proposed by the 1972 Meeting. However, in a few cases notably Texas
1978 and Brazil 1981, levels up to 0.3 mg/kg have been found. These
levels were associated with the spraying of indeterminate varieties
when the seed moisture content was greater than 30 percent.
TABLE 1. Paraquat residues in soybean
Application Pre-harvest Paraquat
Country Year rate interval residue
(kg a.i./ha) (days) (mg/kg)
USA1
Louisiana 1967 0.28 3 0.01, 0.02
0.56 3 0.03, 0.03
Mississippi 1967 0.28 3 <0.01, 0.02,
0.04, 0.05
0.56 3 0.02, 0.03
Arkansas 1968 0.14 6 <0.01,<0.01
0.42 6 <0.01, 0.02
Louisiana 1968 0.14 6 <0.01,<0.01
0.42 6 0.02, 0.06
Mississippi 1968 0.14 6 <0.01, 0.02
0.42 6 0.02, 0.03
Delaware 1978 0.28 8 0.09, 0.15
0.28 11 0.10, 0.10
0.28 36 0.12, 0.12
Georgia 1978 0.28 10 <0.04
Illinois 1978 0.28 7 0.02, 0.03
0.28 15 0.01, 0.02
Nebraska 1978 0.28 14 0.05, 0.06
Texas 1978 0.28 5 0.29, 0.30
Delaware 1979 0.56 19 <0.01, 0.03
TABLE 1. (con't)
Application Pre-harvest Paraquat
Country Year rate interval residue
(kg a.i./ha) (days) (mg/kg)
Florida 1979 0.28 13 0.02, 0.03
0.28 15 0.02, 0.03
Georgia 1979 0.28 12 <0.01,<0.01
Indiana 1979 0.28 6 0.06, 0.08
0.28 7 0.03, 0.05
0.28 8 0.03, 0.04
Iowa 1979 0.28 10 0.07, 0.08
Mississippi 1979 0.28 6 0.01, 0.02
Nebraska 1979 0.28 8 0.07, 0.09
Ohio 1979 0.28 7 0.07, 0.08
0.28 26 0.07, 0.09
S. Carolina 1979 0.28 17 <0.01, 0.02
0.28 31 <0.01,<0.01
Texas 1979 0.28 6 0.03, 0.05
Virginia 1979 0.28 11 0.09, 0.13
0.28 16 0.03, 0.07
0.28 17 0.03, 0.05
0.28 28 0.05, 0.07
Colombia2 1970 0.15 10
<0.05,<0.05,<0.05
0.2 10 <0.05,<0.05,<0.05
0.3 10 <0.05,<0.05,<0.05
0.4 10
1971 0.4 7 <0.05,<0.05
Zimbabwe2 1973 0.56 7 <0.05,<0.05
Yugoslavia2 1977 0.92 8 <0.05
1.10 8 <0.05
1.30 8 <0.05
TABLE 1. (con't)
Application Pre-harvest Paraquat
Country Year rate interval residue
(kg a.i./ha) (days) (mg/kg)
Brazil2 1981 0.4 4 <0.05
0.8 4 <0.05
0.37 5 0.11
0.4 5 0.16
0.4 10 0.08
1 Data from Chevron Chemical Company
2 Data from Imperial Chemical Industries Limited
NATIONAL MAXIMUM RESIDUE LIMITS REPORTED TO THE MEETING
The following national MRLs have been established for soybean:
mg/kg
Australia 0.1
Brazil 0.1
Israel 0.1
USA 0.05
EVALUATION
APPRAISAL
Some additional data on residues of paraquat on soybeans arising
from use close to harvest for desiccation purposes have been received
and reviewed. Apart from two samples from Texas in 1978, all residues
were below 0.2 mg/kg, but several were above the current recommended
maximum residue level (FAO/WHO, 1973) of 0.1 mg/kg. On the evidence
provided, the Meeting agreed that a limit of 0.2 mg/kg would be
appropriate to cover present usage of paraquat on soybeans.
RECOMMENDATION OF RESIDUE LIMITS
It is recommended that the MRL on soybean be revised as follows:
Commodity Limit (mg/kg)
Soybean 0.2
REFERENCES
Chevron Chemical Company. Residue data submitted to the Meeting by ICI
1968-79 Ltd. (Unpublished)
Imperial Chemical Industries Limited. Residue data submitted to the
1970-81 Meeting by ICI Limited (Unpublished),