CARBARYL JMPR 1977
Explanation
When carbaryl was last reviewed in 1976 (FAO/WHO, 1977b) the use and
fate on stored grain were evaluated in the light of extensive
information and maximum residue limits were recommended for carbaryl
on barley, oats, rice, rye and wheat.
Information has since become available on the level and fate of
carbaryl following its use on stored sorghum, together with further
data on the rate of disappearance of carbaryl on stored raw cereals
generally. The following monograph addendum summarises that
information.
RESIDUES IN FOOD AND THEIR EVALUATION
RESIDUES RESULTING FROM SUPERVISED TRIALS
The use of carbaryl for the control of Rhyzoperta domenica which
is not sufficiently sensitive to organophosphorus insecticides to be
controlled effectively by approved grain protectant insecticides
including malathion, dichlorvos, fenitrothion, clorpyrifos-methyl,
bromophos and pirimiphos-methyl was referred to in the 1976 monograph
(FAO/WHO, 1977b). Bengston at al. (1977a) have reported the results of
commercial-scale trials in which carbaryl was applied at the rate of 6
mg/kg in conjunction with pirimiphos-methyl at 4 mg/kg to 18 silos
each holding approximately 2000 tons of wheat. Table 1 gives the
results obtained by analyzing samples of grain drawn at intervals
(generally monthly) over periods up to 9 months. The average grain
temperature over the storage period ranged from 22° to 30° C and
average relative humidity in the inter-grain space calculated from
grain moisture (9-11%) ranged from 35 to 49%. The residue data were
used to calculate the half-life of the deposit which was found to
range from 22 to 50 weeks.
Bengston at al. (1977b) report the outcome of extensive experiments
with a range of grain protectants for the control of
malathion-resistant insects in stored sorghum. Carbaryl applied at a
nominal rate of 8 mg/kg controlled Rhyzopertha domenica for more
than 24 weeks (work still in progress). Table 2 indicates the level of
carbaryl residues in samples of sorghum dram from treated silos and
analysed by the method of Desmarchelier (1977a).
Desmarchelier (1977b) has measured the rate of loss of carbaryl
residues under 12 fixed sets of laboratory conditions and has derived
a general model relating the half-life to temperature and relative
humidity. The model is indicated in a graph which is reproduced as
Figure 1. From this model it is possible to predict the residue level
after any interval of storage from a knowledge of temperature and the
relative humidity of the intergrain space and thus to determine the
rate of application required to provide the requisite level of
protection for the anticipated period of storage. Application of the
TABLE 1. Residues of carbaryl in stored wheat 1976-77 Pilot studies (Australia) ( from Bengston et al., 1977a)
Site Bin
No. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept.
1 8 3-5 5-6 4-6 4-6 2-4 2-4 2-4 2-4 2-4
2 1 1-2 - 1-2
3 8 2-4 -
4 8 3-5 5-6 2-4 2-4 1.5-3 1-2
5 8-10 6-8 6-8
6 93* 3-5 3-5 3-5 2-4 1-2 1.5-3
" 98 3-5 3-5 3-5 2-4 1-2 1-2 1.5-3
" 99 2-4 3-5 2-4 2-4 2-3 2-4
7 1-3 6-8 4-6 4-6 4-6 4-6 4-6
" 2-3 5-7 5-7 4-6 3-5 4-6 3-5
" 3-3 4-6 4-6 4-6 3-5 2-4 2-4
8 4-6 2-4 2-4 1.5-3 1.5-3
9 5-7 3-5 - 4-6
10 5-7 4-6 3-5 2-4 2-4
11 19 4-6 2-4 1.5-3
12 4-6 2-4 2-4 2-4
13 4-6 4-6 2-4 2-4
14 5 samples, April-May: 1-2, 2-4, 4-6, 5-7, 5-7 4-6 4-6
* Aerated
TABLE 2. Residues of carbaryl in sorghum stored in bulk silos stored at various times prior to assay (Bengston et al., 1977b)
Site Grain Average Application Residue, mg/kg, at week
Temp. Moisture Rate mg/kg 1 4 8 12 18 24
1 26°C 12.4% 8.7 6-8 4-6 3-5 2-4 1.5-3 0.6-.08
2 27°C 12.2% 7.8 2-4 4-6 - 1.5-3 0.75-1.5 0.4-0.6
model to extensive field trial data on wheat, barley and sorghum has
confirmed the practical validity of the prediction. The use of this
model should enable residue levels to be maintained as low as possible
consistent with obtaining adequate insect control.
The new information indicates that the maximum residue limit
recommended previously for carbaryl on sorghum from pre-harvest use is
appropriate to cover residues resulting from post-harvest application.
FURTHER WORK OR INFORMATION
Desirable
See Report of 1976 Meeting (FAO/WHO, 1977a, p. 29)
NOTE.
In the Report of the 1977 Meeting (FAO/WHO, 1978a, Annex 1), the
recommended maximum residue limit for carbaryl in meat of cattle,
goats and sheep is recorded both as 1 mg/kg and 0.2 mg/kg. The correct
limit is 0.2 mg/kg; the recommendation was lowered from 1 to 0.2 mg/kg
by the 1973 Meeting. A correction will be published in Annex 1 of the
Report of the 1978 Meeting.
REFERENCES
Bengston, M., Connell, M., Desmarchelier, J., Phillips, M., Ridley,
E., Ripp, B., Snelson, J. and Sticka, R. (1977a) Report of pilot-scale
studies of grain protectants on wheat. Report to Australian Wheat
Board, July 1977 (to be published).
Bengston, M., Cooper, L.M., Davies, R.A.H., Desmarchelier, J.M., Hart,
R.J. and Phillips, M. (1977b) Grain protectants for the control of
malathion-resistant insects in sorghum J. Stored Prod. Res. (in
press).
Desmarchelier, J.M. (1977a) Simultaneous clean-up and esterification
of phenols, at residue levels, by reaction with anhydrides in dilute
base. Residue Vol. 4 (in press).
Desmarchelier, J.M. (1977b) (CSIRO Division of Entomology, Canberra)
Loss of carbaryl on grains in storage (in press).
FAO/WHO (1977a) Pesticide residues in food. Report of the 1976 Joint
Meeting of the FAO Working Party of Experts on Pesticide Residues and
the WHO Expert Committee on Pesticide Residues. FAO Plant Production
and Protection Series No. 8; WHO Technical Report Series No. 612.
FAO/WHO (1977b) 1976 evaluations of some pesticide residues in food.
FAO/AGP:1977/M/5.