FENITROTHION JMPR 1976
Explanation
In 1969 the Joint Meeting evaluated fenitrothion in the light
of the information then available;(FAO/WHO 1970). In 1974 extensive
new information was evaluated and recommendations were made for
maximum residue limits on a number of raw agricultural commodities
including raw grains and milled cereal products as a result of
post-harvest use of fenitrothion as a grain protectant insecticide
(FAO/WHO 1975),
The 1974 meeting listed several items of further work or
information as desirable. These included results from studies on
the effect of cooking on fenitrothion residues in rice, further
studies to determine the fate of residues from cooking other cereal
products from wheat and rye and information on the level and fate
of residues following post-harvest use on oats, barley and rye. A
considerable amount of additional research has been carried out to
provide information on these points. The results of these studies
have been made available for evaluation by the Meeting and the
following monograph addendum has been prepared.
USE PATTERN
Post-harvest treatments
No new use patterns have been developed for the postharvest
application of fenitrothion as a grain protectant but several of
the reports which were available only in manuscript form in 1974
have now been published or submitted for publication.
Ardley and Sticka (1974) compared fenitrothion applied at 2.5,
5, 6 and 10 mg/kg with malathion applied at 12 and 18 mg/kg for the
protection of bulk wheat in vertical bin silos and horizontal bulk
depots of conventional construction. The results suggest that in
both types of storage the persistence of the insecticides can be
correlated with the temperature and moisture content of the grain.
Under the conditions of silo storage both protectants remained
effective for as long as 19 months; under the more severe
conditions of horizontal bulk storage the higher applications were
effective for only 6-7 months. Fenitrothion at one-half the
application rate of malathion appears to give equivalent protection
against attack from stored product insect pests.
Bengston et al. (1976a) compared fenitrothion with three other
new grain protectant insecticides and with malathion in extensive
studies in Australia. The effects of concentration of insecticide
and storage conditions on the biological performance of each
compound were evaluated by bio-assay using both susceptible and
organophosphorous-resistant strains of many different stored
product pests. Fenitrothion was shown to give superior performance
to malathion and comparable protection to chlorpyrifos-methyl,
pirimiphos-methyl and methacriphos (CGA-20168).
Further extensive trials carried out in 20 regional locations
throughout Australia evaluated a mixture of fenitrothion and
bioresmethrin against a combination of pirimiphos-methyl and
bioresmethrin under a wide variety of storage conditions,
temperatures, and moisture (Bengston et al., 1976b). These studies
showed fenitrothion to be effective against all stored product
species including numerous organophosphorus-resistant strains. The
lesser grain borer Rhyzopertha dominica, which is not
adequately controlled by fenitrothion, was completely inhibited by
the addition of 1-2 mg/kg bioresmethrin. Extensive data were
obtained on the effect of temperature, moisture and aeration on the
durability of such grain protectants.
RESIDUES RESULTING FROM SUPERVISED TRIALS
Table 1 from the work of Desmarchelier et al. (1976) shows the
effects of storage time and temperature on the levels of residues
of fenitrothion applied to grain stored in 20 different localities
in Australia. It was known from previous studies that a
concentration of approximately 5 mg/kg of fenitrothion in grain is
required to control effectively the invasion of stored product
pests. It was found by challenging sample insects under laboratory
conditions that the application of Fenitrothion at a level within
the range 10-12 mg/kg ensured complete protection of stored grain
for approximately 20 weeks. However, under field conditions
effective protection would be considerably longer. In extensive
field trials from which these data were derived, wheat did not
become infested even after 30 weeks. During this time, wheat in
adjoining silos became invaded by pests, although it had been
treated with malathion.
FATE OF RESIDUES
General
Desmarchelier et al (1977) reported a collaborative study of
residues on wheat of methacriphos, chlorpyrifoamethyl,
fenitrothion, malathion and pirimiphos-methyl during 6 months'
storage. These workers developed formulae by which it is possible
to calculate the level of residues at any particular time following
storage at known temperatures and humidity. The half-life at 30°C
of fenitrothion was calculated to be 16.2 weeks. This compared with
12.6 weeks for malathion and 69 weeks for pirimiphos-methyl.
Desmarchelier (1976a) in a study of the kinetic constants for
breakdown of fenitrothion on grains in storage, found that the
breakdown on wheat, rice paddy, oats and sorghum in storage at four
temperatures, was first order with respect to fenitrothion and to
grain moisture. At a given moisture content, water activities were
TABLE 1. Fenitrothion residues in stored wheat: Effects of time and temperature on residue levels
Grain Fenitrothion residues after various intervals at indicated temperatures
Location Moisture, %
Interval 0 4 weeks 7 weeks 10 weeks 13 weeks 16 weeks 21 weeks
mg/kg °C mg/kg °C mg/kg °C mg/kg °C mg/kg °C mg/kg °C mg/kg °C
1 9.4 10.7 36 6.4 4.4 4.7 35
2 9.4 11.8 33 8.3 8.3 6.6 30
3 9.4 12.8 35 6.9 5.5 34 5.2 34
4 9.0 12.0 29 8.3 8.8 27
5 11.2 9.8 31 9.8 29 8.8 29 7.0 29 7.2 30 5.7 29
6 - 11.9 28 11.2 28 4.7 28 8.2 28 7.4 27 7.5 28
7 11.0 10.8 30 9.5 28 5.6 27 6.2 27 3.4 27 3.8 27
8 11.9 12.8 31 10.2 22 10.6 24 9.0 24 7.0 24 7.6 23
9 10.4 12.4 35 8.0 28 8.2 28 7.4 24 8.0 24
10 10.8 12.3 34 9.6 28 7.1 28 8.8 29 8.0 24
11 9.6 10.4 - 3.3 25 2.8 23 2.1 23 2.5 22
12 9.4 10.4 - 2.7 30 2.1 30 1.6 30 1.5 27
13 10.4 10.0 34
14 9.9 11.2 7.8 34
15 10.1 11.5 7.1 4.3
16 10.1 13.0 12.2 6.8
17 11.4 12.2 7.0 3.8
18 9.3 10.7 9.4 6.6
19 10.4 11.6 7.9
20 10.2 11.3 7.2
dependent upon, but rate constants ware independent of grain type. The
effect of temperature on breakdown was of the form of the Arrhenius
equation. A simple expression was derived from these basic concepts of
kinetics which accurately predicted residues under 24 different
conditions set by altering grain type, moisture content and
temperature.
In processing and cooking
Barley
A number of studies have been made into the fate of fenitrothion
residues when treated grain is subjected to normal processing,
preparation and cooking. These studies are discussed separately
according to the grains involved.
Desmarchelier (1976b) studying the decay of five insecticides
during the storage and melting of barley, carried out experiments in
triplicate on samples of barley with a moisture content of 13% held at
25°C. After three months storage the barley was malted by a primitive
process and after 6 months by a commercial process. In neither case
was germination affected by any of the pesticides, including
fenitrothion. An initial application of 15 mg/kg fenitrothion had
declined to 6.8 and 3.1 mg/kg after 3 and 6 months respectively. When
subjected to the primitive malting process, barley containing 6.8
mg/kg fenitrothion produced malt containing 2.9 mg/kg. The barley
containing 3.1 mg/kg fenitrothion, when submitted to the commercial
malting process, produced malt containing only 0.55 mg/kg of
fenitrothion. Under similar conditions, barley containing 6.4 mg/kg of
malathion produced malt which still contained 0.8 mg/kg of malathion.
More extensive studies are currently under way in conjunction
with the Australian Barley Board and co-operating maltsters but the
data are not expected to be available until mid-1977.
Oats
Desmarchelier (1976c) studied the decay of five insecticides
following the storage and cooking of oats. Duplicate samples of oats
with a moisture content of 12% were stored at 25°C and were analysed
after 3 and 6 months. Oats treated with fenitrothion at the rate of 15
mg/kg were found to contain 6.9 and 4.2 mg/kg fenitrothion at the end
of 3 and 6 months respectively. Some of the oats which had been stored
for 3 months were cooked in a minimum amount of boiling water for 5
and 15 minutes without prior de-husking. The original residue level of
6.9 mg/kg was found to have fallen to 4.6 mg/kg after 5 minutes
cooking and to 4.0 mg/kg after 15 minutes cooking.
A more extensive study in which the oats are to be de-husked,
milled and rolled before cooking, is planned to be completed during
1977.
Rice
Desmarchelier (1976d) studying the decay of five pesticides on
rice during storage and processing, treated duplicate samples of rice
in husk with fenitrothion at a concentration of 15 mg/kg. The rice had
a moisture content of 13% and was stored at 25°C for 3 and 6 months by
which time the residue level had declined to 6.2 and 3.5 mg/kg
respectively. After 6 months storage, the rice was milled and the
resulting husked and polished rice analysed. It was found that the
residue had been reduced to 0.62 mg/kg on the husked rice and 0.27
mg/kg on the polished rice. Samples of husked and polished rice were
cooked by boiling in a minimum amount of water for 15 minutes. Such
cooking further reduced the residue level on the husked rice to 0.39
mg/kg and on the polished rice to 0.13 mg/kg.
In a series of parallel studies Desmarchelier (1976d) applied
fenitrothion to husked (brown) rice which was stored at 25°C for 6
months. The rice, which had a moisture content of 12.5%, was treated
at a concentration of 18.0 mg/kg. Samples were examined after 3 and 6
months, by which time the fenitrothion concentration had declined to
11.5 and 8.0 mg/kg respectively. Some of the rice which had been in
storage for 3 months was cooked in a minimum amount of boiling water
for 5 and 15 minutes after which it was found that the residue level
had declined from 11.5 mg/kg to 5.3 and 3.8 mg/kg respectively. When
rice which had been in storage for 6 months was similarly cooked for
25 minutes, the fenitrothion concentration declined from 8.0 to
4.2 mg/kg.
The effect of storing and cooking polished (white) rice treated
with fenitrothion was studied by Desmarchelier (1976d). Polished rice
treated at 15 mg/kg still retained 10 mg/kg after 3 months and 7.5
mg/kg after 6 months. When rice which had been in storage for 3 months
was cooked in a minimum amount of boiling water for 5 and 15 minutes,
the fenitrothion content declined to 5.0 and 3.0 mg/kg respectively.
These studies on rice indicate that the fate of fenitrothion is
not particularly different from that of pirimiphos-methyl,
methacriphos or malathion which were examined concurrently, but its
stability is somewhat greater than that of carbaryl or bioresmethrin.
Ito et al (1976) carried out an extensive and detailed study on
the fate of Fenitrothion residues in rice. Following the application
of Fenitrothion to husked rice the grain was stored for 12 months,
then milled under standard conditions which yielded 87% polished rice
and 13% bran. During the milling process the major portion of the
residue in the husked rice was removed in the bran and this feature
was independent of the storage period or the amount of fenitrothion
applied. Only a minor proportion of the fenitrothion remained in the
polished rice and even this was reduced by washing the grains before
cooking. The residue in the washed grain was reduced to about half by
cooking. The higher the temperature and pressure applied during
cooking, the greater was the reduction in the fenitrothion residue.
Table 2, summarising this work, shows that the ratio of the
fenitrothion concentrations in polished rice and bran remains
constant, irrespective of the amount of fenitrothion applied to the
husked rice or found after prolonged storage. Only about 10% of the
quantity occurring in the husked rice remains in the polished rice
after milling. The polished rice was then washed and cooked, with the
results shown in Table 3. Three types of cooking were employed in
these studies. Cooking condition 1 represents the typical method of
cooking rice in the home and consists of boiling the rice in an
approximately equal weight of water at atmospheric pressure for 15
minutes, followed by a further 15 minutes at a temperature of 80°C.
Cooking condition 2 consists of boiling the rice in an equal quantity
of water for 10 minutes at 110°C under a pressure of 1.5 atmospheres
in an autoclave. Condition 3 consists of cooking for 10 minutes at a
temperature of 120°C under a pressure of 2.1 atmospheres. The
increased temperature and pressure had a slight but significant effect
upon the destruction of the remaining small quantity of fenitrothion
in the cooked rice.
TABLE 2. Fate of fenitrothion applied to husked (brown)
rice during milling and cooking (Ito et al, 1976
Amount Storage Residues (mg/kg) in
Applied Period
mg/kg Months Husked Rice Polished Rice* Rice Bran*
15 0 9.38 1.02 65.0
2 12 0.61 0.09 4.03
6 12 1.66 0.25 11.7
15 12 4.39 0.55 31.6
*Ratio polished rice to bran = 87:13
TABLE 3. Effect of cooking on fenitrothion residues in rice
(Ito et al, 1976)
Amount Storage Cooking** Residue
applied period Residues (mg/kg) in Condition in cooked
mg/kg months Polished Washed Wash* rice (mg/kg)
Rice grains water
15 0 1.02 - 0.60 1 0.26
2 12 0.09 0.03 0.05 1 0.02
2 0.01
3 0.01
6 12 0.25 0.08 0.16 1 0.05
2 0.03
3 0.01
15 12 0.55 0.18 0.37 1 0.12
2 0.07
3 0.04
* Concentration expressed as mg/kg in grains before washing.
** For explanation see text.
Wheat
In a series of three trials, Desmarchelier (1976e) determined the
fate of fenitrothion residues on wheat during milling and cooking.
Table 4 shows the results, indicating that when wheat is milled for
the production of white flour, only about 10% or less of the
fenitrothion present in the raw grain is carried into the flour, the
bulk being concentrated in the bran with a lesser amount in the shorts
(pollard). When white bread is prepared from the flour, there is a
further significant loss of fenitrothion so that the residue remaining
in the bread is of the order of 1-2% of that present in the raw wheat.
In the case of wholemeal bread, however, there is a significant
carry-over of the residue from the grain, equivalent to 20-25% of the
original fenitrothion concentration. In these trials, only a small
proportion of the original residue remained as residual phenol
(3-methyl-4-nitrophenol).
TABLE 4. Fate of fenitrothion residues on wheat during milling and
cooking
Trial 3
Trial 1 Trial 2 Fenitrothion 3-methyl-
4-nitrophenol
Time after
application 19 13 10 -
(weeks)
Residue, mg/kg, in
wheat 6.5 9.6 7.6 -
wholemeal flour 3.5 4.8 6.1 -
wholemeal bread 1.5 1.8 1.72 0.05
bran 19.5 22.6 20.8 0.25
shorts 5.8 11.0 3.3 0.12
white flour 0.53 0.74 0.25 0.06
white bread 0.09 0.21 0.08 0.06
Ardley (1976) studied the level and fate of fenitrothion residues
in wholemeal and wholemeal bread. For comparison, similar grain
treated with malathion was also processed. Separate lots of clean
wheat were treated with fenitrothion and malathion at the rate of 10
mg/kg, using pilot scale facilities. The grain was stored at room
temperature (approximately 20°C) and was analysed 7 days later for
fenitrothion and malathion by GLC using both flame ionization and
thermionic phosphorus detectors. The results were comparable by both
methods.
Part of the grain was milled into wholemeal on a disc mill and
part was converted into white flour on a roller mill. The wholemeal
flour was combined with white flour prepared from untreated grain in
the ratio of 90% wholemeal : 10% white flour and the products of the
roller milling were recombined to give a similar blend containing the
bran, shorts (pollard) and white flour in the same 90:10 proportion.
The loaves were baked by standardised procedures and the bread and
flour were subjected to residue analysis in the same way as the raw
grain. Table 5 indicates the level of residues found in the wheat,
wholemeal and bread. It will be observed that only about 50% of the
residue was lost in the baking of wholemeal bread but fenitrothion was
no different in this respect from malathion. It is now known that much
of the residue data published on the level and fate of malathion in
cooked cereal products is inaccurate because the extraction procedures
used to recover the residue were incapable of removing the residue
occluded in or combined with components of the prepared or cooked
cereal.
METHODS OF RESIDUE ANALYSIS
Although no new basic concepts in residue analysis affecting the
determination of fenitrothion residues in grain and milled cereal
products have been noted since the previous monograph was prepared,
two reports pointing to the problems involved in the sampling and
extraction of grain and milled cereal products are worthy of
attention.
Snelson and Desmarchelier (1975) in a paper presented at the
First International Working Congress of Stored Product Entomology,
discussed the significance of pesticide residue analysis, and pointed
to the wide variations in results between analysts and the unresolved
variation between methods, making the meaning of analytical figures
somewhat uncertain. The paper surveys the results of a collaborative
programme of analysis of wheat for malathion and discusses sources of
variance between analysts and between methods, the errors due to lack
of primary analytical standards, and the variance caused by sampling,
and points to the need for eliminating as many of these variations as
possible.
In an extensive report of a collaborative study of the analysis
of residues in wheat of five grain protectant insecticides including
fenitrothion, Desmarchelier et al (1977a), point particularly to the
lack of consideration of the difference between the ease of extraction
of freshly applied and "aged" or "weathered" deposits not withstanding
the fact that techniques for accurately analysing aged deposits have
been well documented.
This work was undertaken to develop methods suitable for the
determination of the insecticides in wheat and to assess the broader
problem of variations among results, by means of a panel of analysts
who studied, over a 6 month period, the breakdown of residues in grain
from field trials. The error of basing recoveries on the analysis of
fortified samples is particularly important in the case of stored
grain.
Because of the international movement of grain and the acceptance
of maximum residue limits for a number of grain protectant
insecticides, the methods of analysis should ideally be rapid and as
independent as possible of special equipment. Extraction by standing
whole grain in methanol is simpler than most procedures. From the
extensive results of the study by Desmarchelier et al (1977a) there
would seem to be no major errors associated with different conditions
TABLE 5. Fate of fenitrothion and malathion on wheat used for the production of wholemeal bread
Insecticide Amount Residue in Residue Residue in bread made from
treatment applied grain 7 days in flour
mg/kg later Disc milled Roller milled
None - ND ND ND ND
Malathion 10 5.0 2.0 2.7 2.4
Fenitrothion 10 5.5 2.6 3.2 3.1
ND - Residue below limit of determination (0.05 mg/kg)
for GLC or different types of specific phosphorus detectors. The
method used works well with fenitrothion residues in grain even over a
range of operating conditions.
APPRAISAL
Following the evaluation in 1974 (FAO/WHO 1975) the Joint Meeting
considered that further work or information on the occurrence and fate
of fenitrothion residues in stored products and milling products of
stored grain was desirable. This information has been generated and
evaluated. The data indicate that fenitrothion residues from
treatments applied to the various raw grains in storage, are largely
removed during processing, preparation and cooking except in the case
of wheat converted into whole meal bread. In this case, 20-50% of the
original deposit appears to remain in the bread after baking. Parallel
studies have indicated that fenitrothion is little different in this
respect from malathion, the detection of undecomposed residues in the
prepared bread reflecting improved methods of extraction and analysis
rather than greater stability on the part of fenitrothion.
A number of studies point to the importance of the correct choice
of extraction techniques, solvents and analytical methods for
determining grain protectant insecticide residues on stored grain and
particularly in milled and cooked cereal products.
The new data confirm the recommendations for maximum residue
limits made in 1974 and justify recommendations which would permit the
use of fenitrothion for the postharvest protection of rice.
RECOMMENDATIONS
The following maximum residue limits are recommended. The limit
for rice bran is new: the others replace recommendations made in 1974.
In keeping with previous practice the limits are for the sum of
fenitrothion and its oxygen analogue expressed as fenitrothion.
Commodity Limit, mg/kg
Rice bran 20
Rice (in husk and hulled) 10
Rice (polished) 1
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