PARAQUAT JMPR 1976
Explanation
This compound was evaluated by the Joint FAO/WHO Meeting on
Pesticide Residues in 1970 (FAO/WHO, 1971b) and in 1972 (FAO/WHO,
1973b). Although an acceptable daily intake for man was estimated
(0-0.002 mg/kg body weight), the 1972 Meeting considered it
desirable that the following studies should be undertaken:
1. Detailed comparative toxicity and metabolism studies in order
to elucidate the reason for the comparatively high sensitivity
of man to this compound.
2. Comparative studies on the relationship between lung
concentration and toxicity.
Data on these subjects have now become available.
Moreover, since in addition to its use as a contact herbicide,
which does not usually result in residues in animal feedstuff,
paraquat may also be applied as a harvest aid or desiccant for a
number of animal fodder crops such as grass, maize and alfalfa, a
large number of studies on paraquat in farm animals were reported.
The available data on metabolism in cows, goats, sheep, pigs
and poultry, and on residues in their various organs and milk and
eggs, together with other relevant material, are summarized below.
EVALUATION FOR ACCEPTABLE DAILY INTAKE
BIOCHEMICAL ASPECTS
Absorption, distribution, and excretion
Studies have been carried out to a) compare the metabolism of
paraquat in different species in an attempt to understand their
different susceptibilities to paraquat, and b) to compare the
distribution of paraquat in the organs of the rat to explain the
affinity exhibited by paraquat for the lung.
After oral administration of 14C-paraquat to rats, dogs and
guinea pigs, most of the radioactivity was excreted in 4 days,
mainly in the faeces as unchanged paraquat. The remaining label was
present in urine which contained 12% (rats), 45% (dogs) and 9%
(guinea pigs) of the dose administered.
Thus dogs and guinea pigs absorb very different amounts of
paraquat yet the oral LD50 is the same in the two species.
Paraquat (I) was the main radioactive component of rat and dog
urine (see Figure 1), with monoquat (II) and the dipyridone (IV) of
paraquat accounting for 0.4%, 0.3% and 0.1% of the administered
dose in rat urine and 0.4%, 0.5% and 0% of the dose in dog urine.
Thus, there is very little metabolism of the parent compound
following oral dosing.
After subcutaneous administration of 14C-paraquat into rats
over 90% of the administered radioactivity was excreted in the
urine in 4 days. Whilst this was mainly paraquat, chromatography
indicated that monoquat (II) (1.9%), paraquat monopyridone (III)
(3.2%) and dipyridone (IV) (1.1%) were present.
Although traces of monoquat and paraquat monopyridone were
also found in rat faeces, there was no evidence for extensive
metabolism of paraquat by gut microflora. Intestinal bacteria from
rat caecal contents did not degrade paraquat in vitro to any
measurable extent. It is concluded, therefore, that the previous
observations of Daniel and Gage (1966), indicating a large amount
of degradation by gut microflora were incorrect, and due to
incomplete extraction of paraquat from faeces.
There was no correlation between the toxicity of paraquat to
the 3 species studied and the degree of absorption, rate of
excretion or extent of metabolism. There were no species
differences observed with respect to the metabolic products
detected.
Rat lung slices have been shown to possess an ability to
accumulate paraquat in vitro to concentrations nearly ten times
that of the medium over a period of two hours, brain slices to
concentrations double that of the medium. The accumulation by both
tissues has been shown to be energy, dependent. After oral dosing
of paraquat to rats the lung concentration increased with time to
six times that of plasma after 30 hours. Other organs, with the
exception of the kidney, did not concentrate paraquat to the same
extent.
Lung slices from dog, monkey and rabbit have also been shown
to possess the ability to accumulate paraquat in vitro but to a
much lesser extent when compared with those from rat and man.
Thus from the point of view of paraquat accumulation in the
lung the rat is a good experimental model. Indeed the kinetics (V
max and Km) of the process are very similar in the lung tissues of
both species. (Rose et al., 1976).
The cells in the lung that are damaged by paraquat are
primarily the type I and II alveolar epithelial cells (Vijeyaratnam
and Corrin, 1971). Accumulation of paraquat appears to be
associated with these cells (Sykes et al., 1976) which only
constitute a small fraction of the total cell population of the
lung. After the initial damage of the type I cell, swelling of the
type II cell mitochondria occurs and is followed by more extensive
changes, including loss of microvilli, multivesicular bodies and
electron density with an increase in the number of lipid droplets
and damage.
Thus, the selectivity of paraquat for lung is explained by
accumulation and it is the type I and II cells in lung which
accumulate high concentrations of paraquat via an energy-dependent
process. This leads to the destruction of these cells with
consequent impairment of the air/blood interface and death from
respiratory failure.
Biotransformation
Studies of biotransformation in farm animals and poultry are
described in this section. Further details of residues found in
tissues, milk and eggs are given in the section "Fate of residues".
Cows
When cows were given a single oral dose of 14C-methyl paraquat
at 8 mg/kg, 96% of the radioactivity was recovered in the faeces
during the following 9 days; 0.7% was recovered in urine. Unchanged
paraquat (I) accounted for most of the radioactivity in faeces
(96%) and urine (62-90%), but traces of metabolites II and III were
also detected in the urine.
Only 0.003 - 0.004% of the radioactivity was recovered in
milk; the maximum radioactive residue (0.005 mg/kg, paraquat ion
equivalent) occurred on the day after dosing. About 15% of this
radioactivity was present as unchanged paraquat (I). Compounds II
and III (3-25%) were also found in milk. The radioactivity not
identified as I, II or III was accounted for by incorporation into
natural constituents of milk, resulting from the anabolism of the
radioactive methyl group cleaved from paraquat (Hemingway et al.,
1974).
Cows were fed for three months with diets containing 25, 80
and 170 ppm of paraquat ion (equivalent to 0.8, 2.6 and 5.5 mg/kg
body weight). The paraquat was present as a residue in dried grass
obtained from a pasture which had been sprayed with "Gramoxone" and
subsequently weathered. The diet was accepted satisfactorily and no
toxicological effects were observed during the trial. Pathological
examination of tissues from animals slaughtered within 24 hours of
the end of feeding trial showed no toxic effects attributable to
paraquat. The tissue residues including muscle and liver determined
in cows at the two higher dose rates varied between 0.01 and 0.09
mg/kg except in the kidney where 0.21 - 0.31 mg/kg was found. These
fell to low (0.04 mg/kg in kidney) or non-detectable levels in an
animal fed the high paraquat rate diet for 30 days and then
maintained on an untreated diet for 12 days before slaughter.
Only very low residues of paraquat were present in milk
samples taken weekly during the trial (121 samples <0.0001 -
0.0006 mg/kg: 1 sample = 0.001 mg/kg (Edwards et al., 1974).
Goat
14C ring labelled paraquat was administered to a goat in
mid-lactation twice daily for seven days at a dose equivalent to
100 ppm in the diet. Total radioactive residues in the milk were
less than 0.01 mg/kg paraquat ion equivalent - 76% as unchanged
paraquat. Total radioactive residues were 0.74, 0.56, 0.1 mg/kg in
kidney, liver and muscles respectively. In all samples there was no
significant metabolism of paraquat with the exception of the liver
where 50% of the radioactivity was accounted for as paraquat and
about 5% as each of the metabolites II and III (Hendley et al.,
1976a).
Sheep
A dose of 14C-methyl labelled paraquat administered to a sheep
via a rumen fistula was recovered quantitatively within 10 days.
Approximately 4% of the dose was excreted in the urine and the
remainder in the faeces. More than 95% of the radioactivity in
urine and faeces was present as unchanged paraquat. Small amounts
of compound II (1%) and compound III (2.3%) were also detected.
(Hemingway et al., 1972)
When injected subcutaneously, paraquat is also excreted
rapidly in the urine (over 80% of the dose), 69% within the first
day after treatment. Again unchanged paraquat accounts for most
(90%) of the radioactivity, the monopyridone (III) derivative is
present as 2-3% of the dose and monoquat (II) is a trace
metabolite. This pattern of metabolism is virtually identical to
that seen in the urine following dosing via the rumen. (Hemingway
et al., 1972)
Pigs and hens
Oral dosing and feeding studies with pigs and hens are
described in the section "Fate of residues", p.
TOXICOLOGICAL STUDIES
Acute toxicity
The acute oral toxicity of paraquat was studied comparatively
in rat, guinea pig and monkey. The LD50 was in the order rat monkey
guinea pig. All animal species showed primary lesions in the lung.
Rats and monkeys, but not guinea pigs, developed progressive
interstitial fibrosis of the lung after 7-10 days. Focal necrosis
in liver and kidneys was found in rats and guinea pigs but not in
monkeys (Murray and Gibson, 1972).
TABLE 1. Acute toxicity of paraquat
oral
LD50 (mg/kg
Species body weight) References
Mouse 104 (90-120) Fletcher, 1974
Rat 130 (110-160) "
Guinea pig 30 (22-41) "
Rabbit 126 (69-183) "
Cat 35 "
Hare 35 "
Monkey 75 "
Dog 25-50 "
Sheep 65 "
Cow 35-60 "
Man about 30 "
OBSERVATIONS IN MAN
The potential of lungs from five different species (rat, dog,
rabbit, monkey and man) to accumulate paraquat has been assessed by
measuring the kinetic constants Km and Vmax of the process in lung
slices (Rose et al., 1976). Human lung slices have the highest Vmax
and one of the lowest Km's for this process which indicates that
human lung possesses a very efficient accumulation system for
paraquat. This will tend to make man one of the more sensitive
species to paraquat as the lung will be able to accumulate toxic
amounts of paraquat from very low concentrations present in the
plasma.
In studies of exposure of spray operators to paraquat which
were probably closest to the extremes of exposure likely to occur
in any agricultural operation, measurable levels of paraquat in the
urine of certain workers were found but no noticeable clinical
adverse effects (Staiff et al., 1975).
The ingestion of 10-15 ml of the concentrate supplied to
professional users (containing 20% paraquat cation) can be fatal if
left untreated. The oral LD of paraquat cation to man has been
estimated to be approximately 30 mg/kg body weight (Fletcher, 1974)
which is similar to that measured for dogs and guinea pigs. Rats
are less sensitive, having an oral LD50 of approximately 100 mg
cation/kg body weight.
COMMENTS
In recent feeding studies with paraquat in farm animals, over
90% was excreted within a few days. Thus, tissue accumulation
giving rise to significant tissue residues is unlikely. Paraquat
was only slightly absorbed and was metabolised mainly in the
gastrointestinal tract of the animals. Milk and eggs were found to
contain small residues of two identified metabolites.
The Meeting found the recent data on comparative toxicity and
the metabolic and toxicological studies in laboratory animals
reassuring and reaffirmed the previously established acceptable
daily intake.
TOXICOLOGICAL EVALUATION
Level causing no toxicological effect
Rat: 30 ppm in the diet, equivalent to 1.5 mg/kg bw
Dog: 50 ppm in the diet, equivalent to 1.25 mg/kg bw
ESTIMATION OF ACCEPTABLE DAILY INTAKE FOR MAN
0 - 0.002 mg/kg bw as paraquat dichloride (equivalent to
0 - 0.0014 mg/kg bw, expressed as paraquat ion).
RESIDUES IN FOOD AND THEIR EVALUATION
The use of paraquat as a contact herbicide does not usually
result in residues of this compound animal feeding stuffs. However
paraquat can also be used as a harvest aid or desiccant for a
number of animal fodder crops. such as grass, maize and alfalfa. In
this case paraquat residues of 5-1000 mg/kg may be found in the
resulting feeding stuff; this has stimulated a large number of
studies on the fate of paraquat in farm animals. This work is
described in the section "Biotransformation," p. Some additional
details of residues arising in tissues, organs, milk and eggs are
given in the following section, "Fate of residues".
FATE OF RESIDUES
In animals
Cows
When cows were given a single oral dose of 14C-methyl paraquat
(I) at 8 mg/kg, 96% of the radioactivity was recovered in the
faeces during the following 9 days. 0.7% was recovered in the
urine. Unchanged paraquat accounted for most of the radioactivity
in faeces (96%) and urine (62-90%) but traces of two metabolites
(compounds II and III - Figure 1) were also detected in the urine.
(Hemingway et al., 1974; Leahey et al., 1972; Stevens and Walley,
1966). Only 0.003-0.004% of the radioactivity was recovered in
milk. The maximum radioactive residue (0.005 Ú Úg/g paraquat ion
equivalents) occurred on the day after dosing. Only about 15% of
this radioactivity was present as unchanged paraquat. Compounds II
and III (Figure 1) were also found in the milk in the proportions
shown in Table 2. The radioactivity not identified as I, II or III
was accounted for by incorporation into natural constituents of
milk (Hemingway et al., 1974; Leahey et al., 1972).
TABLE 2. Radioactive compounds detected in the milk of a
cow dosed with 14C-paraquat
Percentage of Radioactivity in milk present as
Day Milk
Collected Paraquat Compound II* Compound III*
1 15 15 3
2 18 18 18
3 9 25 10
* Identified in Figure 1
Cows given 14C-methyl-labelled paraquat orally at 8 mg/kg/day
for three successive days showed a maximum residue in the milk of
0.01 mg/kg paraquat ion equivalents. No paraquat was detected by
residue analysis (limit of detection 0.005 mg/kg) (Daniel et al.,
1971).
In other trials cows were allowed to graze treated grasses
containing up to 1000 mg/kg at the start of the test. A maximum
residue of 0.02 mg/kg paraquat was detected in milk on the first
day after grazing freshly treated fodder; thereafter residues were
less than the normal limit of detection for milk, i.e. below 0.005
mg/kg (Calderbank et al., 1968).
In a trial in which cows were fed for three months with diets
containing 25, 80 and 170 mg/kg of paraquat, only very low residues
of paraquat were found in weekly milk samples (121 samples in the
range, <0.0001 - 0.0006 mg/kg; 1 sample 0.001 mg/kg (Edwards et
al., 1974).
Residues found in the meat, fat and offal of cows fed at
various levels of paraquat in the diet for various periods are
summarized in Table 3.
Similar residue levels were found in the milk and tissues of
two cows maintained for 30 days on a diet containing 150 ug/g of
paraquat (Edwards et al., 1976).
TABLE 3. Residues of paraquat in tissues of cows fed on paraquat-
containing fodder
Paraquat Interval between
ion levels Feeding last feeding on Paraquat residues
in fodder period treated fodder (mg/kg) in
(mg/kg) (days) and sacrifice Liver Kidney Meat Fat
3.6 21 9 days <0.05 <0.05 <0.05 <0.05
25 86-95 <1 day <0.01 <0.06- <0.01 <0.01
0.13
80 " <1 day <0.01 0.14- <0.01 <0.01
0.31
170 " <1 day <0.01- 0.20- <0.01 <0.01
0.09 0.24 -0.02 0.02
135-450 32 3 days <0.01 0.05 <0.01 <0.01
13 days <0.01 <0.01 <0.01 <0.01
220-450 3 1 hour 0.04 0.15 <0.01 <0.01
7 1 hour 0.04 0.16 0.02 <0.01
Calderbank et al., 1968
Edwards et al., 1974
Lazanas, 1969
Litchfield, 1969
Goats
Transfer of residues to the meat and milk of a goat fed on
paraquat was very small, as in the cow. 14C-ring-labelled paraquat
was administered to a goat in mid-lactation, twice daily for seven
days at a dose equivalent to 100 ppm in the diet. Total radioactive
residues in the milk were less than 0.01 mg/kg paraquat ion
equivalents - 76% as unchanged paraquat (Hendley et al., 1976a). Total
radioactive residues in goat tissues were as shown in Table 4.
Unchanged paraquat accounted for at least 50%, and usually almost all,
of these residues.
TABLE 4. Total radiolabelled residues in tissues of a goat
Paraquat Feeding Total radiolabelled residue
ion level Period (mg/kg paraquat ion equivalent)
in diet
(mg/kg) (days) Liver Kidney Muscle Heart Fat
100 7 0.56 0.74 0.08- 0.16 0.02-
0.12 0.03
(Animals sacrificed four hours after receiving last dose.)
Sheep
As with other ruminants, paraquat is rapidly excreted from sheep,
principally in the faeces, and very little metabolism occurs. A dose
of 14C-methyl-labelled paraquat, administered to a sheep via a rumen
fistula, was recovered quantitatively within 10 days. Approximately 4%
of the dose was excreted in the urine and the remainder in the faeces.
More than 95% of the radioactivity in urine and faeces was present as
unchanged paraquat. Small amounts of compound II (1%) and compound III
(2.3%) were also detected (Hemingway et al., 1972).
Pigs
Pigs excrete an oral dose of paraquat, principally in the faeces
as unchanged paraquat. Residues in meat are small. Two pigs were dosed
with 14C-labelled paraquat for seven consecutive days at a rate
equivalent to 50 ppm in the diet. One was dosed with 14C-methyl and
the second with 14C-ring-labelled paraquat. The pigs were sacrificed
two hours after receiving the final dose. At this point 69-73% of the
administered residue had been recovered in the faeces and
approximately 3% in the urine. More than 90% of the radioactivity in
the faeces was present as unchanged paraquat.
Total radioactive residues in the tissues were low (Table 5).
More than 90% of these residues were due to unchanged paraquat except
in liver where approximately 70% was due to unchanged paraquat and
4-7% was due to compound II. (Leahey et al., 1976; Spinks et al.,
1976)
Pigs were also maintained on diets containing 8, 47 and 147 ppm
of non-radioactive paraquat for 30 days. The residues of paraquat in
the tissues of animals sacrificed within 24 hours of the cessation of
feeding were similar to those detected in the experiment with the
radioactive compound. Residues declined to 0.03 mg/kg or below after a
further six days feeding on a control diet (Table 6) (Hemingway et
al., 1975).
TABLE 5. Total radio-labelled residue in tissues of pigs dosed
at 50 ppm in the diet for 7 days, using 14C-labelled
paraquat
Total radio-labelled residue (mg/kg paraquat
ion equivalent)
Radio-label Liver Kidney Muscle Heart Fat
14C-methyl 0.20 0.46 0.03-0.06 0.12 0.02-0.06
14C-ring 0.10 0.38 0.05 0.08 0.01
TABLE 6. Residues of paraquat in tissues of pigs fed on paraquat-containing diet
Paraquat
ion level Paraquat residues (mg/kg) in
in diet
(mg/kg) Feeding Regime Liver Kidney Muscle Heart Fat
8 30 days on treated diet <0.01 <0.01 <0.01 <0.01 <0.01
30 days on treated diet
+
6 days on control diet <0.01 <0.01 <0.01 <0.01 <0.01
47 30 days on treated diet 0.03 0.04 0.02 0.03 <0.01
30 days on treated diet
+
6 days on control diet <0.01 <0.01 <0.01 <0.01 <0.01
147 30 days on treated diet <0.01 0.33 0.04 0.12 0.02
30 days on treated diet
+
6 days on control diet <0.01 0.01- 0.01- 0.02- <0.01
0.03 0.02 0.03
Hens
As in other animals, there is little metabolism of paraquat in
the hen. Residues in meat and eggs are small. When a single oral dose
of 14C-methyl-labelled paraquat was administered to the hen, all of
the dose was recovered quantitatively in the faeces within three days.
At least 98% of the recovered radioactivity was as unchanged paraquat.
Analysis of the tissues of hens after about 3 weeks dosing with
14C-paraquat (6 ppm in the total diet) indicated that it did not
accumulate in the hens (Hemingway and Oliver, 1974).
Continuous dosing of hens with radio-labelled paraquat for up to
22 days, at rates up to 30 ppm in the diet, resulted in total
radioactive residues in the eggs up to approximately 0.05 mg/kg
paraquat ion equivalent. At least 80% of the radioactivity was due to
unchanged paraquat. The residue was present almost entirely in the
yolk rather than in the albumen (Hemingway and Oliver, 1974; Hendley
et al., 1976b).
When hens were maintained for up to 30 days on diets containing
up to 3.6 ppm of unlabelled paraquat, no residues were detected in the
eggs (limit of detection 0.01 mg/kg). At 7.2 and 36 ppm dietary
inclusion levels, paraquat residues were 0.05 mg/kg or below (Leary,
1974).
Paraquat was also administered to hens as a 40 mg/kg solution in
their drinking water for 14 days. Residues in eggs were 0.1 mg/kg or
below and declined rapidly once dosing ceased (Fletcher, 1967).
During the above-mentioned continuous dietary feeding studies
with radio-labelled and with unlabelled material, paraquat residues in
tissues were small (Table 7). In the radio-labelled studies, paraquat
was found to constitute 80% or more of the residue in the tissues.
TABLE 7. Levels of paraquat in tissues of hens
Paraquat
ion level Feeding Paraquat residue (mg/kg) in
in diet Period
(mg/kg) (days) liver Kidney Muscle Heart Fat
1.8 30 <0.01 * <0.01 <0.01 <0.01
3.6 30 <0.01 * <0.01 <0.01 <0.01
7.2 30 <0.01 * 0.01 <0.01 <0.01
36 30 0.01 * 0.01 <0.01 <0.01
30 10 0.06 0.10 <0.01- 0.03 <0.01
0.04
(Animals sacrificed on cessation of dosing)
* Tissue not analysed. Hendley et al., 1976b
NATIONAL TOLERANCES REPORTED TO THE MEETING
The following tolerances have been reported to the Meeting.
Tolerance
Commodity mg/kg
USA
Alfalfa 5
Almond hulls 0.5
Apples 0.05(N)
Apricots 0.05(N)
Avocados 0.05(N)
Bananas 0.05(N)
Barley grain 0.05(N)
Beans (Dry) Exp. 8/28/76 0.5(T)
Birdsfoot Trefoil 5
Cattle (Meat, Fat, Meat By-products) 0.01(N)
Cherries 0.05(N)
Citrus fruit 0.05(N)
Clover 5
Coffee Beans 0.05(N)
Corn fodder 0.05(N)
Corn forage 0.05(N)
Corn fresh (kernels plus cobs) 0.05(N)
Corn grain 0.05(N)
Cottonseed 0.5
Eggs 0.01(N)
Figs 0.05(N)
Guar beans 0.5
Goats (meat, fat, meat by-products) 0.01(N)
Guavas 0.05(N)
Hogs (meat, fat, meat by-products) 0.01(N)
Hops, dried 0.2FA
Hops, vine 0.5
Hops, fresh 0.1
Horses (meat, fat, meat by-products) 0.01(N)
Lettuce 0.05(N)
Melons 0.05(N)
Milk 0.01(N)
Nectarines 0.05(N)
Nuts 0.05(N)
Oat grain 0.05(N)
Olives 0.05(N)
Papayas 0.05(N)
Passion fruit 0.2
Pasture grass 5
Peaches 0.05(N)
Pears 0.05(N)
Peppers 0.05(N)
Pineapples 0.05(N)
Tolerance
Commodity mg/kg
USA
Plums (fresh prunes) 0.05(N)
Potatoes 0.5
Poultry (meat, fat, meat by-products) 0.01(N)
Range grass 5
Rye grain 0.05(N)
Safflower seed 0.05(N)
Sheep (meat, fat, meat by-products) 0.01(N)
Small fruit 0.05(N)
Sorghum forage 0.05(N)
Sorghum grain 0.05(N)
Sorghum grain (animal feed) 2(T)
Soybeans 0.05(N)
Soybean forage 0.05
Sugar beets 0.5
Sugar beet tops 0.5
Sugarcane 0.5
Sunflower seed 2
Sunflower seed hulls 6FA
Tomatoes 0.05(N)
Wheat grain 0.05(N)
Netherlands
Fruit and vegetables 0.05
Cereals 0.05
Potatoes 0.1
FA = Food additive tolerance
(N)= Negligible residue tolerance
(T)= Temporary tolerance
APPRAISAL
Since paraquat was last evaluated by the Joint Meeting in 1972
(FAO/WHO, 1973b) additional studies have been completed on the fate of
paraquat in cows, goats, sheep, pigs and poultry.
Although the use of paraquat as a contact herbicide does not
usually result in residues of this compound on animal feed when it is
used as a harvest aid or desiccant for fodder crops such as grass,
maize or alfalfa residues; of 5-1000 mg/kg may be found in the
resulting feed.
Oral doses of paraquat given to cows are excreted mainly
unchanged in faeces. Residues in milk and meat are extremely small.
When cows were allowed to graze grasses containing up to 1000 mg/kg at
the start of the test, a maximum residue of 0.02 mg/kg paraquat was
detected in milk on the first day after grazing freshly treated
fodder. Thereafter residues were less than the normal limit of
detection for milk, i.e. below 0.005 mg/kg; it was estimated that the
cows consumed one-half of the acute oral LD50 daily. The maximum
residue limit of 0.01 mg/kg for milk, recommended by the Joint Meeting
in 1972, is therefore confirmed. Levels in the meat are often below
0.01 mg/kg and rarely above 0.05, but higher levels are possible
especially in kidney.
Levels in tissues of pigs fed on a paraquat-containing diet were
again generally below 0.01 but sometimes up to 0.05 mg/kg, and in
kidney levels approaching 0.5 mg/kg have been reached. As in other
animals, there was little metabolism of paraquat in the hen: residues
in meat and eggs were small and rarely exceeded 0.01 mg/kg.
Paraquat is also used as a spray directed at the ground to
control weeds, and as a pre-emergence and preplanting spray for cereal
crops. Very small residues at or about the limit of determination can
arise from these uses presumably from adventitious particles of soil
and vegetation adhering to the crop.
RECOMMENDATIONS
The following additional maximum residue limits are recommended.
They refer to paraquat ion.
Commodity Limit, mg/kg
Sunflower seed 2
Kidney of sheep, cattle and pigs 0.5
Dried hops, passion fruit 0.2
Food commodities of plant origin other than
those for which specific recommendations have
been made, meat and edible offals other than
kidney of sheep, cattle and pigs 0.05*
Eggs 0.01*
REFERENCES
Calderbank, A., McKenna, R.H., Stevens, M.A., and Walley, J.K.
1968 Grazing trials on paraquat treated pastures.
J.Sci. Food Agr., 19: 246.
Daniel, J.W., Edwards, M.J., Slade, P., and Walker, G.H.
1971 Milk residues arising from the ingestion of
14C-paraquat by the cow. ICI Plant Protection
Ltd. Report No. AR2282A. (Unpublished)
*at or about the limit of determination
Daniel, J.S., and Gage, J.C. Absorption and excretion of diquat
1966 and paraquat in rats. Brit. J. Indus. Med., 23:
133-136.
Edwards, M.J., Hemingway, R.J., Kinch, D.A., and Slape, P.
1974 Paraquat: residue and toxicology trial with cows
fed a treated grass. ICI Plant Protection Ltd.
Report No. AR2465A(R), (Unpublished)
Edwards, M.J., Hayward, G.J., and Ward, R.J. Paraquat: residues
1976 in milk and tissues of cows fed on paraquat
treated grass. Unpublished report from ICI Plant
Protection Division.
Fletcher, K. Production and viability of eggs from hens treated
1967 with paraquat. Nature, 215: 1407 (Unpublished)
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