Pesticide residues in food - 2003 - Joint FAO/WHO Meeting on Pesticide Residues

First draft prepared by
A. Bartholomaeus
Office of Chemical Safety
Therapeutic Goods Administration, Canberra, Australia

Pyraclostrobin is the provisionally approved ISO name for methyl N-{2-[1-(4-chlorophenyl)-1H-pyrazol-3-yloxymethyl]phenyl}(N-methoxy)carbamate (Figure 1). Pyraclostrobin is a member of the strobilurin group of fungicides. The strobilurin fungicides act through inhibition of mitochondrial respiration by blocking electron transfer within the respiratory chain, which in turn causes important cellular biochemical processes to be severely disrupted, and results in cessation of fungal growth. Pyraclostrobin has not been evaluated previously by the JMPR.

Figure 1. Pyraclostrobin and its principle subcomponents

The specifications for the active ingredient, pyraclostrobin, permit a maximum content of 0.0003% (3 mg/kg of feed) of the impurity dimethyl sulfate. Dimethyl sulfate is both mutagenic and carcinogenic. For a substantial proportion of the toxicological studies considered in this monograph, there is uncertainty about the presence and level of this impurity in the pyraclostrobin used, although the studies of mutagenicity were performed with material known to contain dimethyl sulfate at 1 mg/kg of feed. This uncertainty will need to be taken into account when performing risk assessments for pyraclostrobin. The available body of analytical information however, suggests that the concentration of DMS in nearly all batches was less than 0.0001%.

Unless otherwise stated, the studies evaluated in this monograph were certified as having been performed in compliance with good laboratory practice and in accordance with the relevant OECD test guidelines. As these guidelines specify the tissues normally examined and the clinical pathology tests normally performed, only the exceptions to these guidelines are reported here, to avoid repetitive listing of study parameters. For ease of reference, the standard test parameters for studies of repeated doses are provided in Tables 1, 2 and 3.

Table 1. Standard clinical chemistry parameters for studies of repeated doses

Table 2. Organs weighed at sacrifice in studies of repeated doses

Table 3. Tissues examined microscopically in studies of repeated doses

1.1 Absorption distribution and excretion

(a) Oral administration

The absorption, distribution, and elimination of pyraclostrobin were studied in male and female Wistar rats (aged at least 7 weeks) after oral administration of pyraclostrobin (purity, >98%) radiolabelled with ¹⁴C at either the tolyl or chlorophenyl rings.

In a preliminary test, two male and two female rats were assessed for clinical signs for at least 24 h after dosing with unlabelled pyraclostrobin at 50 mg/kg bw; the dose was well tolerated.

In a series of four experiments, the excretion of pyraclostrobin was studied in excreta collected at 6, 12 and 24 h after dosing, and at 24 h intervals thereafter for 168 h, or until 90% of the applied radioactivity had been excreted. In the first three experiments, groups of four male and four female rats were given a single oral dose of [¹⁴C]tolyl- or [¹⁴C]chlorophenyl-labelled pyraclostrobin or unlabelled pyraclostrobin at 50 mg/kg bw. In the fourth experiment, four rats of each sex were given a single oral dose of [¹⁴C]tolyl-labelled pyraclostrobin at 5 mg/kg bw. At the end of each of these experiments, the animals were sacrificed and the heart, liver, spleen, bone, skin, lung, ovaries, bone marrow, carcass, muscle, kidney, testes, brain, pancreas, uterus, adipose tissue, stomach and contents, thyroid glands, adrenal glands, blood/plasma and intestinal tract and contents were assessed for radioactivity. Exhaled air was also collected from two males in each of the two experiments using radiolabelled pyraclostrobin in order to determine exhalation of ¹⁴C-labelled gases.

Two additional experiments were conducted to examine blood concentrations of radioactivity after administration of [¹⁴C]tolyl-labelled pyraclostrobin at 5 or 50 mg/kg bw. Blood samples (100–200 µl) were taken from animals at 0.5, 1, 2, 4, 8, 24, 48, 72, 96 and 120 h after dosing, and the amount of radioactivity in whole blood and plasma was assessed. Tissue distribution was examined in animals sacrificed at 0.5, 8, 20 and 42 h after dosing at 5 mg/kg bw, and at 0.5, 24, 36 and 72 h after dosing at 50 mg/kg bw. The heart, liver, spleen, bone, skin, lung, ovaries, bone marrow, carcass, muscle, kidney, testes, brain, pancreas, uterus, adipose tissue, stomach and contents, thyroid glands, adrenal glands, blood/plasma and intestinal tract and contents were assessed for radioactivity. To examine biliary excretion of pyraclostrobin, bile ducts of the animals were cannulated and bile was collected at 3 h intervals until 48 h after administration of [¹⁴C]tolyl-labelled pyraclostrobin at 5 or 50 mg/kg bw in four animals of each sex at each dose (the duration depended on the health of the animals and the excretion rate at later time-points).

In rats given a single dose of [¹⁴C]tolyl-labelled pyraclostrobin at either 5 or 50 mg/kg bw, plasma concentrations of radioactivity initially peaked after 0.5–1 h; there was a secondary peak after 8 h in males at 5 or 50 mg/kg bw and females given 5 mg/kg bw, and after 24 h in females given 50 mg/kg bw. The magnitude of the difference in the time to peak for females, given the high dose, is likely to be at least partially artifactual owing to the absence of a sampling point between 8 and 24 h. After the second peak, plasma concentrations declined to <0.1 µg equivalent/g after 120 h. The terminal half-lives were similar in males and females, but were 50% longer at 5 mg/kg bw than at 50 mg/kg bw. The area under the curve of plasma concentration–time was approximately proportional to dose for each sex, indicating that absorption was not saturated at the higher dose. Key kinetic data are shown in Table 4.

Table 4. The kinetics of pyraclostrobin in rats

From Leibold et al. (1998)
AUC, Area under curve

After a single oral dose of [¹⁴C]tolyl-labelled pyraclostrobin at 50 mg/kg bw, the highest concentrations of radioactivity were found in the gastrointestinal tract (gut, 28– 39 µg equivalent/g; gut contents, 63–92 µg equivalent/g; stomach, 325–613 µg equivalent/g; stomach contents, 1273–1696 µg equivalent/g) after 0.5 h. The liver (13–25 µg equivalent/g) had higher concentrations of radioactivity than the kidneys (4–7 µg equivalent/g) and plasma (2–6 µg equivalent/g), with lowest values being recorded in the bone (0.1–0.3 µg equivalent/g) and brain (1–2 µg equivalent/g). After 72 h, tissues and organs contained <2.6 µg equivalent/g. After a dose of 5 mg/kg bw, the highest concentrations of radioactivity were also found in the gastrointestinal tract (gut, 5 µg equivalent/g; gut contents, 7–9 µ equivalent/g; stomach, 49–89 µg equivalent/g; stomach contents, 160–205 µg equivalent/g) after 0.5 h. After 42 h, tissues and organs contained <0.7 µg equivalent/g. In rats that were pretreated with unlabelled pyraclostrobin for 14 days and given a single oral dose of [¹⁴C]tolyl-labelled pyraclostrobin at 5 mg/kg bw, the highest concentrations of radioactivity after 120 h were found in the thyroid gland (0.18–0.35 µg equivalent/g) and the liver (0.1 µg equivalent/g). In all other tissues, the concentration of radioactivity recorded was <0.1 µg equivalent/g. The rapid and essentially complete excretion of pyraclostrobin and the decline of tissue concentrations to low levels over the observation period, suggests a low potential for accumulation.

The overall recovery of radioactivity was 91–105% in all experiments. In the first 48 h after a single oral dose of [¹⁴C]tolyl-labelled pyraclostrobin at 5 or 50 mg/kg bw, 10–13% of the administered radioactivity was excreted in the urine and 74–91% was excreted in the faeces. The total amount of radioactivity excreted in the urine and faeces after 120 h was 11–15% and 81–92%, respectively. A similar pattern of excretion was observed in rats that were pre-treated with unlabelled pyraclostrobin for 14 days and given a single oral dose of [¹⁴C]tolyl-labelled pyraclostrobin at 5 mg/kg bw of (12–13% in the urine and 76–77% in the faeces after 48 h; 12–14% in the urine and 79–81% in the faeces after 120 h) and in rats given a single oral dose of chlorophenyl-labelled pyraclostrobin at 50 mg/kg bw (11–15% in the urine and 68–85% in the faeces after 48 h; 12–16% in the urine and 74–89% in the faeces after 120 h). There was no detectable radioactivity in the expired air from rats treated with [¹⁴C]tolyl- or [¹⁴C]chlorophenyl-labelled pyraclostrobin at 50 mg/kg bw. In tissues and organs, the radioactivity that remained after 120 h was <1 mg equivalent/g at 50 mg/kg bw and <0.1 mg equivalent/g at 5 mg/kg bw. Within 48 h after administration of [¹⁴C]tolyl-labelled pyraclostrobin at 5 or 50 mg/kg bw of, 35–38% of the administered radioactivity was excreted via the bile, indicating, in conjunction with observations on urinary excretion, that approximately 50% of the administered dose had been absorbed (Leibold et al., 1998).

(b) Dermal application

The absorption and, to a limited extent, the distribution and excretion of ¹⁴C-labelled pyraclostrobin (in Solvesso) in groups of 16 male Wistar rats was assessed after a single dermal application at a nominal dose of 0.015, 0.075 or 0.375 mg/cm², corresponding to 0.15, 0.75 and 3.75 mg/animal or approximately 0.8, 4 and 18 mg/kg bw. Animals were exposed to the test material for 4 (four rats per group) or 8 (12 rats per group) h and four rats per group were sacrificed at 4, 8, 24 or 72 h after the start of the exposure. An area of approximately 10 cm² on the shoulders was clipped free of hair and was washed with acetone 24 h before dosing. A silicone ring was glued to the skin and the test substance preparation (10 µl/cm²) was administered with a syringe, which was weighed before and after application. A nylon mesh was then glued to the surface of the silicone ring and covered with a porous bandage. After the exposure period, the protective covers were removed and the exposed skin was washed with a soap solution. After sacrifice, the concentration of radioactivity in the excreta, blood cells, plasma, liver, kidneys, carcass, treated and untreated skin was assessed. Radioactivity in the cage and skin wash and the protective covering, including the silicone ring, was also assessed. In all groups, 99–110% of the radioactivity was recovered. At sacrifice at 72 h, after an 8 h exposure, 1.6–2.6% of the administered dose was absorbed, 22–26% was on the skin or in the skin wash, and 72–80% was recovered on the protective cover. Only 0.2–0.4% and 0.9–1.8% was excreted in the urine and faeces, respectively (Leibold & Hoffmann, 1999).

Table 5. Dermal absorption of pyraclostrobin in rats (mean recovery of radioactivity (%))

From Leibold & Hoffmann (1999)
* Radioactivity recovered in excreta, cage wash, blood, kidney, liver and the carcass

In a second study of dermal application, ¹⁴C-labelled pyraclostrobin (in a commercial formulation, details of which were not provided) was applied at a dose of 15, 75 and 375 µg/active ingredient/cm² to the upper surface of epidermal membranes from Wistar rats and human cadavers in vitro, and left unoccluded for 24 h. Skin samples were obtained from the dorsal/dorso-lumbar region from sacrificed rats and human cadavers and were mounted in glass diffusion cells to give a surface area of approximately 1.77 cm². The receptor chamber contained an ethanol/water (1 : 1) mix as the receptor fluid. Ten skin preparations per species and dose were assessed. Only tissues in which the epidermal layer was intact were used in the study. On the day before application of the formulation, the integrity of the skin was assessed by measuring the penetration of tritiated water, which was applied to the epidermal surface. The test material was applied to the upper surface of the epidermal membranes and duplicate aliquots (100 ml) of receptor fluid were taken at 1, 2, 4, 6, 10 and 24 h subsequently. Residual test material was washed from the skin surface with a 10% w/v soap solution, and the washings, remaining receptor fluid, ethanol washings of the dismantled diffusion cells and solubilized skin membranes were retained for analysis of residual radioactivity. During the 24 h after application, 21–51% and 3–8% of the applied [¹⁴C]pyr-aclostrobin was absorbed across the rat and human epidermis respectively, with 13–22% (rat) and 14–17% (human) of the dose recovered on the skin. The majority of absorption by rat skin occurred in the first 6 h, whereas total absorption by human skin increased throughout the entire 24 h period. In total, 91–95% (rat) and 88–106% (human) of the applied dose was recovered (Thomley & Wood, 1999).

Figure 2. Proposed metabolic pathways for pyraclostrobin in rats

From Velic (1999)

1.2 Biotransformation

Tissues, excreta and bile from animals used in the toxicokinetics studies and from additional groups given a single dose at 50 mg/kg bw per day (to provide more material for analysis) were analysed for metabolites of pyraclostrobin. In order to determine the metabolites in the plasma, liver and kidneys, additional groups were treated with a single dose of ¹⁴C]tolyl- or [¹⁴C]chlorophenol ring-labelled pyraclostrobin at 5 and 50 mg/kg bw and sacrificed 8 h later. Metabolites were identified using high-performance liquid chromatography (HPLC), liquid chromatography–mass spectrometry (LC–MS) and nuclear magnetic resonance (NMR). The metabolism of pyraclostrobin proceeded through three main pathways primarily involving alterations to the three major portions of the pyraclostrobin molecule.

The methoxy group on the tolyl-methoxycarbamate moiety was readily lost, with few major metabolites retaining this group. Hydroxylation of the aromatic and/or pyrazole rings was followed by glucuronide and occasionally sulfate conjugation, and many metabolites were derived from the chlorophenol-pyrazole or tolyl-methoxycarbamate moieties of pyraclostrobin, following cleavage of the ether linkage, with subsequent ring hydroxylation and glucuronide or sulfate conjugation. Metabolites were similar in both sexes and at all doses. No unchanged parent compound was found in the bile or urine and only small amounts in the faeces. Compounds dominating the identified metabolites recovered from the urine were: ring-hydroxylated pyraclostrobin; the chlorophenol pyrazole moiety hydroxylated on the pyrazole ring with or without a sulfate conjugate; a glucuronide of the tolyl-methoxycarbamate moiety; and a benzoic acid derivative of the tolyl-methoxycarbamate moiety. In the faeces, the dominant metabolite was a demethoxylated and pyrazole ring hydroxylated pyraclostrobin. In the bile, the primary metabolite was a glucuronide of pyraclostrobin hydroxylated on the pyrazole ring at the 4’ position and this compound, together with the demethoxylated derivative found in the faeces, was also the dominant metabolite isolated from the plasma and the liver. Demethoxylation of the methoxycarbamate moiety appeared to occur primarily in the gut, as the major metabolite in the bile retains this group intact whereas in the faeces the major metabolite is the demethoxylated derivative. Most of the radiolabel isolated from the kidneys was in the form of the unchanged parent compound and a demethoxylated derivative (Velic, 1999).

2.1 Acute toxicity

The acute toxicity of pyraclostrobin is summarized in Table 6.

Table 6. Studies of acute toxicity with pyraclostrobin

^a Dose volume = 10 and 20 ml/kg bw
^b Intact skin, 24 h exposure, 50 cm² area
^c As pyraclostrobin is a viscous fluid with a "negligibly low" vapour pressure (2.6 × 10^-10 hPa), it was dissolved in acetone (4-h LC50, approximately 80 mg/l) or Solvesso to facilitate aerosolization. Mean mass aerodynamic diameter was 1.0, 1.2 and 2.9 µm for the 0.310, 1.070 and 5.270 mg/l groups, respectively, for the study using acetone as the solvent, and between 2.7 and 4.3 µm for the study using Solvesso as the solvent

(a) Oral administration

Clinical signs after oral administration of pyraclostrobin consisted of dyspnoea, staggering, piloerection, and diarrhoea in all animals, resolving by day 6. There were no pathology findings. In a study of acute inhalation using acetone as the solvent, all animals at 1.070 and 5.300 mg/l died on the day of exposure. At 0.310 mg/l, bloody discharge from the nose (two males), piloerection and smeared fur (10 out of 10 animals) were observed. All effects had resolved in surviving animals by day 7. Where Solvesso was used as the solvent, all males and four out of five females at 7.3 mg/l died, and one out of 10 animals died at each of the two lower doses. There were no deaths at 0.89 mg/l.

(b) Dermal irritation

Undiluted pyraclostrobin (500 mg, purity 98.2%) was applied to the shaved, intact skin on the back/flanks of six New Zealand White rabbits under a semi occlusive bandage for 4 h. At the end of the exposure period, the test substance was removed and the treated area was rinsed with polyethylene glycol and water. There were no mortalities. Erythema was observed in all animals from 1 h after removal of the bandage and persisting in most animals until day 8, and in three animals until day 15. The maximum Draize score for erythema was 3 and the average scores at day 1 and 8 were 2 and 1.5 respectively. Oedema with a Draize score of 1 was observed in four out of six rabbits on day 1, resolving in all except two rabbits by day 8, but persisting in one rabbit until day 15. It was concluded that pyraclostrobin is a slight but prolonged skin irritant (Wiemann & Hellwig, 1998c).

(c) Ocular irritation

Pyraclostrobin (0.1 ml; purity, 98.2%) was instilled into the conjunctival sac of the right eye of one male and five female New Zealand white rabbits. After 24 h, the test material was washed out with tap water. The left eye was not treated and served as a control. There were no deaths during the study. Conjunctival redness (score = 1–3) was observed in all animals up to 3 days after treatment, with swelling observed in five out of six rabbits at 1 h (score = 1), six out of six rabbits on day 1 (average score = 1.2), three out of six rabbits on day 2 (score = 1), and two out of six rabbits on day 3 (score = 1). Discharge (score = 1) occurred in one out of six rabbits at 1 h. There were no corneal or iridal effects and all conjunctival effects had resolved by day 8. "Loss of hair at the margins of the eyelids" occurred in six out of six rabbits from 1 day after treatment. Under the conditions of the study, pyraclostrobin was a slight ocular irritant in rabbits (Wiemann & Hellwig, 1998d).

(d) Skin sensitization

In a Magnusson-Kligman maximization test, intradermal injections (2 × 0.1 ml) of Freund adjuvant in a 0.9% aqueous solution of sodium chloride (1 : 1), 5% pyraclostrobin in Freund adjuvant and 5% pyraclostrobin in 1% Tylose CB 30 000 in Aqua bidest (Tylose) were given to the left and right shoulders of each of 20 guinea-pigs. Sites were evaluated 24 h after injections were given. One week later, 5% pyraclostrobin in Tylose (1 ml) was applied to a gauze patch of surface area 2 × 4 cm and administered topically to the same sites, then covered with an occlusive dressing for 48 h, after which time the sites were assessed. On day 22, all animals were challenged with 0.5 ml of 1% pyraclostrobin in Tylose (right flank) and Tylose alone (left flank). A second challenge was performed on day 29, when the test substance was applied to the left flank and the vehicle applied to the right flank. All challenge sites were evaluated 24 and 48 h after removal of the occlusive dressings. There were no deaths and all animals gained body weight normally over the study. Although intradermal injections of Freund adjuvant, 5% pyraclostrobin in Freund adjuvant and 5% pyraclostrobin in Tylose caused moderate and confluent erythema (Draize score = 2) and swelling in all animals, as did an occluded topical application of 5% pyraclostrobin in Tylose, the first and second challenges with 1% pyraclostrobin in Tylose and Tylose alone caused no effect in any animal at 24 or 48 h. The sensitivity of the procedure was confirmed in an assay with the positive controls technical-grade alpha-hexyl cinnamaldehyde technical (85%) and Lutrol E 400 DAB (Lutrol). Pyraclostrobin was not a skin sensitizer in guinea-pigs in this study (Wiemann & Hellwig, 1998e).

2.2 Short-term studies of toxicity

Mice

Groups of five male and five female B6C3F₁ mice were given pyraclostrobin (in 0.5% aqueous carboxymethylcellulose) at a dose of 0 or 4 mg/kg bw per day for 1 week by gavage. Mice were also given diets containing pyraclostrobin at a concentration of 0 or 18 mg/kg of feed for males and 0 or 15 mg/kg of feed for females, for 1 week. Food consumption and body weight were determined daily and animals were examined for mortality and clinical signs of toxicity at least once per day. At the end of the experiment, animals were sacrificed without further examination. Mean intakes of pyraclostrobin were 5.5 mg/kg bw per day in males at 18 mg/kg, and 7.2 mg/kg bw per day in females at 15 mg/kg. After 1 week, food consumption was 31% lower than that of controls in females at 15 mg/kg, but there was no treatment-related effect on body-weight gain and there were no other effects of treatment in any of the treated groups of mice. Data for individual animals were not supplied. This was a supplemental study initiated to address the appropriateness of using an apparently lower body-weight gain in treated animals in a study of developmental toxicity in rabbits as an end-point on which to base an the establishment of an acute reference dose (RfD). In conjunction with similar studies in rabbits and rats, this study was intended to demonstrate the species-specific variability in food intake and body-weight gains in rabbits. Because of the limited parameters examined in this study, it was not adequate for the purposes of risk assessment and a no-observed-adverse-effect level (NOAEL) could not be established (Mellert, 2002a).

Groups of 10 male and 10 female B6C3F₁ mice (aged 47–49 days) were given diets containing pyraclostrobin (purity, 98.5%) at a concentration of 0, 50, 150, 500, 1000, or 1500 mg/kg of feed (equal to 0, 9.2, 30, 120, 270 and 480 mg/kg bw per day) for 3 months. Mice were checked at least once daily for mortality and signs of toxicity, and a comprehensive clinical examination was performed once per week. Body weight and food consumption were recorded once weekly and water consumption was assessed daily. Blood was collected from fasted animals and haematology (excluding prothrombin time) and clinical chemistry (excluding brain, erythrocyte and serum cholinesterases) parameters were assessed in all animals. After 3 months of treatment, all mice were fasted, sacrificed and necropsied. All animals were examined grossly. In the control group and in the group receiving pyraclostrobin at 1500 mg/kg, tissues (including gall bladder) were examined microscopically. The thymus gland, lungs, liver, kidneys, adrenal glands (females), stomach, duodenum, jejunem, ileum and mesenteric lymph nodes were examined microscopically in animals at 50, 150, 500 and 1000 mg/kg, and gross lesions were assessed in all animals affected per group. Organ weights (excluding epididymides, heart and thymus gland) were recorded.

There were no treatment-related clinical signs. Body-weight gain was reduced throughout the study period in males at all doses and in females at >500 mg/kg of feed in a clear dose-related manner, with males at the highest dose experiencing a slight loss in body weight. Reduced weight gains in females at 50 and 150 mg/kg were slight, not statistically significant except at 150 mg/kg on day 77, and were not apparent before day 28 of treatment. Nonetheless a dose-related trend was apparent in females at all doses from day 28 onwards. Although spillage of food hindered interpretation, consistently lower food conversion efficiency values at 1000 and 1500 mg/kg suggested a relationship to treatment. No changes in water consumption between the groups were noted. Reductions were seen at 1500 mg/kg in haemoglobin concentration, MCV and MCH in both sexes, and in erythrocyte volume fraction in males. Platelet counts were increased in both sexes at 1500 mg/kg and in males at 500 and 1000 mg/kg. Haemoglobin concentration was also reduced in females at 1000 mg/kg and erythrocyte volume fraction was reduced in males at 150 mg/kg and above. Leukopenia was seen in both sexes at 1000 and 1500 mg/kg and in females at 500 mg/kg and possibly also 150 mg/kg. There was a reduction in the concentration of eosinophils in males at 50 mg/kg and above, in lymphocytes in both sexes at 1000 and 1500 mg/kg and females at 500 mg/kg, and in monocytes in males at >500 mg/kg. As individual control animals had eosinophil counts ranging from 0 to 0.43 × 10⁹/l the apparent, slight, effect at 50 mg/kg was not considered to be toxicologically significant. Increases were seen in serum cholesterol in females at 1500 mg/kg and urea concentration in both sexes at >150 mg/kg. The values for urea concentration in males at the lowest dose were within the range for historical controls, but in view of the clear increase at >150 mg/kg, a substance-related effect at 50 mg/kg could not be ruled out. Decreases were observed in total protein in both sexes at 1500 mg/kg and in females at 1000 mg/kg, in globulin concentration in both sexes at 1000 and 1500 mg/kg, and in triglyceride concentration in both sexes at >150 mg/kg and in females at 50 mg/kg. Although the reduced concentration of triglyceride in females was not statistically significant a clear dose–response relationship was apparent and examination of values for individual animal confirmed a consistent pattern of reduced values.

A number of organ weight differences between groups were observed which, in the absence of histological alterations in those organs, are likely to be secondary to reduced weight gains and food conversion efficiency in groups receiving pyraclostrobin at >150 mg/kg of feed. Increased relative liver and spleen weights in males at >500 mg/kg could not be readily attributed to altered weight gains, as the relative (to body weight) liver weight tends to remain stable or decline when weight gain is reduced through reduced food intake or reduced food conversion efficiency, and the increased relative spleen weight correlated with the anaemia and leukopenia observed at 1000 and 1500 mg/kg.

Increased incidences and/or severity was seen in the following findings: thickening of the duodenal mucosa in both sexes at >500 mg/kg; erosions or ulcers in the glandular stomach in both sexes at >500 mg/kg and in females at 150 mg/kg; atrophy of the thymus gland in both sexes at >500 mg/kg and in females at 150 mg/kg; apoptotic bodies in follicles of the mesenteric lymph node in both sexes at 1500 mg/kg and in females at 500 and 1000 mg/kg. Decreases were seen in the incidences of vacuolation in cells of the X-zone in the adrenal cortex in females at >150 mg/kg and in males at 1500 mg/kg, lipid vacuoles in the kidneys of males at >500 mg/kg, and fatty infiltration in the liver of both sexes at 1500 mg/kg. A NOAEL was not identified owing to decreased body-weight gains and altered clinical pathology parameters at all doses. (Mellert et al., 1998; Mellert et al., 1999j). Taking into consideration the study of carcinogenicity in mice (doses: 0, 10, 30, 120 mg/kg) the NOAEL for reduced weight gain at 91 days in mice was 30 mg/kg (4 mg/kg bw per day). As the study of carcinogenicity did not examine clinical chemistry parameters, a specific NOAEL for elevated blood urea concentrations could not be identified for this species. Nonetheless, consideration of the dose–response trend in the 3-month study, the observation that the value for this parameter at 50 mg/kg was within the range for historical controls and the absence of abnormal histology and gross pathology in males at 120 mg/kg (17 mg/kg bw per day) and in females at 180 mg/kg (33 mg/kg bw per day) in the study of carcinogenicity in mice suggests that the overall NOAEL in mice of 30 mg/kg (4 mg/kg bw per day) was appropriate.

Table 7. Haematology and clinical chemistry values in mice given diets containing pyraclostrobin for 3 months

From Mellert et al. (1998) and Mellert et al. (1999j)
M, Male; F, Female; MCV, Mean corpuscular volume; MCH, Mean corpuscular haemoglobin; MCHC, Mean corpuscular haemoglobin concentration
* p < 0.05; ** p < 0.02; *** p < 0.002, # An aberrant value of 528 was excluded from the mean to give a mean of 1205 instead of 1137

Table 8. Organ weights in mice given diets containing pyraclostrobin for 3 months

From Mellert et al. (1998) and Mellert et al. (1999j)
Relative organ weight = organ weight (g)/body weight (g) × 100
* p < 0.05; ** p < 0.01

Table 9. Pathology findings in mice given diets containing pyraclostrobin for 3 months

From Mellert et al. (1998) and Mellert et al. (1999j)
Grade 1 = minimal in severity/very few in number/very small in size; grade 2 = slight in severity/few in number/small in size;
grade 3 = moderate in severity and size/moderate to several in number, grade 4 = severe

Rats

Groups of five male and five female Wistar rats were given pyraclostrobin (in 0.5% aqueous carboxymethylcellulose) at a dose of 0 or 4 mg/kg bw per day by gavage for 1 week, or diets containing pyraclostrobin at a concentration of 0 or 34 mg/kg for 1 week. Food consumption and body weight were determined daily and animals were examined for mortality and clinical signs of toxicity at least once per day. At the end of the experiment, animals were sacrificed without further examination. The dietary concentration of 34 mg/kg of feed corresponded to mean intakes of pyraclostrobin of 3.5 mg/kg bw per day in males and 3.8 mg/kg bw per day in females. Lower body-weight gain (up to 33%) was observed in females receiving diet containing pyraclostrobin at 34 mg/kg, but not in females given an equivalent dose of pyraclostrobin by gavage, nor in males given pyraclostrobin either in the diet or by gavage. There were no deaths and no clinical signs of toxicity in any group. Data for individual animals was not supplied. This was a supplemental study initiated to address the appropriateness of using an apparently lower body-weight gain in treated animals in a study of developmental toxicity in rabbits as an end-point on which to base the establishment of an acute RfD. In conjunction with similar studies in rabbits and mice, this study was intended to demonstrate the species-specific variability in food intake and body-weight gains in rabbits. Because of the limited parameters examined in this study, it was not adequate for the purposes of risk assessment and a NOAEL could not be identified (Mellert, 2002b).

Groups of five male and five female Wistar rats (aged 42 days) were given diets containing pyraclostrobin (purity, 94–99%) at a concentration of 0, 20, 100, 500, or 1500 mg/kg of feed (equal to 0, 1.8, 9, 42 and 120 mg/kg bw per day) for 4 weeks. Dose selection was based on the results of a preliminary study (BASF Aktiengesellschaft Project No. 24S0376/96061) in which groups of five male and five female Wistar rats were given diets containing pyraclostrobin at a concentration of 400, 3000 or 15 000 mg/kg of feed for 2 weeks. A separate report was not provided for this study. Rats were checked at least daily for mortality and signs of toxicity, a comprehensive clinical examination was performed weekly, body weight and food consumption were recorded weekly and water consumption was recorded daily. Haematology, urine analysis and clinical chemistry parameters were assessed in all animals, as were gross pathology and organ weights. Histological examination was performed on the liver, spleen, fore-stomach, glandular stomach, duodenum, jejunem, ileum, caecum, colon and rectum of all animals, heart, kidneys, adrenal glands and testes in the control group and at 15 000 mg/kg only, and gross lesions were assessed in all animals affected.

In the preliminary study, all animals at 15 000 mg/kg were sacrificed because of excessive toxicity (no other details provided) and at 3000 mg/kg, body-weight gain and food consumption were reduced, with signs of anaemia apparent at 400 and 3000 mg/kg (no other details provided).

In the main study, there were no deaths or treatment-related clinical signs, but reductions of up to 16% in food consumption at 500 mg/kg and of up to 44% at 1500 mg/kg were observed. Concomittantly, body-weight gain was reduced by 14 to 32% over the study in both sexes at 1500 mg/kg and in males at 500 mg/kg, primarily owing to a pronounced reduction of 51–67% at 1500 mg/kg during the first week of the study. A slight anaemia characterized by reduced erythrocyte numbers and haemoglobin concentration was observed in females at 500 and 1500 mg/kg, with a slight, not statistically significant, reduction in haemoglobin concentration also seen in males at 1500 mg/kg. The anaemia correlated with evidence of extramedullary haematopoiesis in the liver and spleen and with increased relative spleen weights in both sexes at 500 and 1500 mg/kg. Slight decreases were seen in alanine aminotransferase in both sexes at 500 and 1500 mg/kg, and in serum cholinesterase in females at 1500 mg/kg. As decreased alanine aminotransferase activity was observed in the 3-month and long-term studies in rats also, this effect is likely to be treatment-related but, as the magnitude of the effect was small and a decrease is not normally associated with adverse organ or system effects, is unlikely to be toxicologically relevant. This conclusion was further supported by studies indicating that alanine aminotransferase (and alkaline phosphatase) activites can be affected by dietary status, as discussed later in this monograph. Urine volume was increased and specific gravity was decreased in both sexes at 1500 mg/kg.

Table 10. Clinical chemistry findings in rats given diets containing pyraclostrobin for 4 weeks

From Mellert et al. (1999d)
ALT, Alanine aminotransferase; F, female; M, male; MCHC, Mean corpuscular haemoglobin concentration; MCV, Mean corpuscular volume
* p < 0.05; ** p < 0.01

Absolute kidney, adrenal and thymus weights were decreased and relative brain weights were increased secondary to reduced body-weight gains at 1500 mg/kg. Histology did not reveal any alterations in these tissues. An increased relative liver weight correlated with increased hepatocellular hypertrophy in males at 1500 mg/kg, diminished fat storage at 500 and 1500 mg/kg, and altered clinical chemistry values at 1500 mg/kg (increased total bilirubin in males, decreased glucose concentration in both sexes, and decreased globulin concentration in both sexes). The incidence of mucosal hyperplasia in the duodenum was increased at 500 and 1500 mg/kg. Reduced body-weight gains and fat storage in the liver were likely to be secondary to reduced food consumption, which may be related to poor palatability of the treated feed. Consequently, undue weight was not attached to these findings. The NOAEL was 100 mg/kg (equal to 9 mg/kg bw per day) on the basis of anaemia and associated findings, and mucosal hyperplasia at 500 mg/kg (equal to 42 mg/kg bw per day) (Mellert et al., 1999d).

Groups of 10 male and 10 female Wistar rats (aged 9 weeks) received pyraclostrobin (purity, 99%; in 0.5% carboxymethylcellulose) at a dose of 0, 40, 100 or 250 mg/kg bw per day, 5 days per week, for 4 weeks, in an application to the clipped dorsal surface. The test site, approximately 10% of the body surface area, was covered with a semi-occlusive dressing for 6 h after application. Rats were checked at least once daily for mortality and signs of toxicity, detailed clinical examinations were conducted at least once weekly, body weight, food consumption and food conversion efficiency were recorded once per week, and ophthalmoscopy was performed on animals in the control group and in the group at 250 mg/kg bw per day before sacrifice. At study termination, haematology, urine analysis and clinical chemistry parameters were assessed, animals were examined for gross pathology and organs (including uterus) were weighed. In the control group and in the group at 250 mg/kg bw per day only, a standard range of tissues (including nasal cavity, larynx, pharynx and treated skin) were examined microscopically. The uterus, vagina and treated skin were examined microscopically in all animals at 40 and 100 mg/kg bw per day and gross lesions were assessed in all animals affected.

Table 11. Organ weights and histology findings in rats receiving diets containing pyraclostrobin for 4 weeks

From Mellert et al. (1999d)
^aRelative organ weight = organ weight (g)/body weight (g) × 100
* p > 0.05; ** p > 0.01 M, Male; F, Female

There were no mortalities, no treatment-related effects on ophthalmology, haematology, clinical chemistry and urine analysis parameters and no abnormal findings in the open field observations for any animal. On the treated skin, clinical signs included scale formation in most females and some males at 250 mg/kg bw per day, and in some females at 100 mg/kg bw per day. Slight erythema was also seen in most females at 250 mg/kg bw per day. Body-weight gain was reduced by 8% in males at 250 mg/kg bw per day and food conversion efficiency was lower in males at 100 and 250 mg/kg bw per day. Absolute and relative uterus weights were increased by 27% and 30%, respectively, at 250 mg/kg bw per day. Epidermal thickening seen at 100 and 250 mg/kg bw per day was characterized by cloudy swelling of epidermal cells, associated with hyperkeratosis. In the uteri of rats at 250 mg/kg bw per day, dilation of the lumen was more common (two, one, two and six rats at 0, 40, 100 and 250 mg/kg bw per day, respectively; n = 10). After dermal administration of pyraclostrobin to rats for 4 weeks, the NOAEL for systemic toxicity for both sexes was 100 mg/kg bw per day on the basis of effects on the uteri of females and reduced body-weight gains in males at 250 mg/kg bw per day. Signs of dermal irritation occurred in all treated animals (Mellert et al., 1999c).

Groups of 10 male and 10 female Wistar rats (aged 42 days) were given diets containing pyraclostrobin (purity, 98.5%) at a concentration of 0, 50, 150, 500, 1000, or 1500 mg/kg of feed (equal to 0, 3.5, 11, 35, 69 and 106 mg/kg bw per day) for 3 months. Rats were checked at least once daily for mortality and signs of toxicity, and a comprehensive clinical examination was performed once weekly. Body weight and food consumption were recorded once weekly and water consumption was assessed daily. Haematology (including reticulocytes), urine analysis and clinical chemistry (excluding brain cholinesterase) parameters were assessed in all animals. At sacrifice, all animals were examined grossly and organ weights (excluding epididymides, heart and thymus gland) were recorded. A full range of tissues was examined microscopically in the control group and at 1500 mg/kg. The lungs, liver, spleen, kidneys, stomach, duodenum, jejunem, ileum, sternum with marrow and bone marrow from the femur were examined microscopically in animals at 50, 150, 500 and 1000 mg/kg, and gross lesions were assessed in all animals affected per group.

There were no deaths or treatment-related clinical signs. At >500 mg/kg in males and at >1000 mg/kg in females, body-weight gain was reduced. Food consumption was consistently reduced in males, and intermittently in females at >500 mg/kg. Food conversion efficiency was also intermittently reduced at 1000 and 1500 mg/kg. Increased erythrocyte turnover was reflected in a marked increase in reticulocyte counts (41–94%) in males at >1000 mg/kg and in females at 1500 mg/kg, extramedullary haematopoiesis in both sexes at >150 mg/kg and in a slight anaemia in females at 1000 and 1500 mg/kg characterized by reductions of generally 10% or less in erythrocyte counts, haemoglobin concentrations and, at 1500 mg/kg, erythrocyte volume fraction. Other haematological effects consisted of increases in the values for MCV in both sexes at 1000 and 1500 mg/kg and females at 500 mg/kg (3–6%), prothrombin time in males at 1000 and 1500 mg/kg (11 and 13%), leukocyte counts in both sexes at 1500 mg/kg and females at 1000 mg/kg (14–71%), polymorphonuclear neutrophils in both sexes at 1000 and 1500 mg/kg (56–120%), and lymphocytes in females at 1000 and 1500 mg/kg (70–76%). Clinical chemistry changes consisted of increases in bilirubin in both sexes at 1500 mg/kg and males at 1000 mg/kg (30–95%), albumin in males at >500 mg/kg (5–6%) and erythrocyte cholinesterase activity in both sexes at 1500 mg/kg (23–33%), and in decreases in alanine aminotransferase activity in both sexes at >500 mg/kg (20–35%), alkaline phosphatase activity in both sexes at 1000 and 1500 mg/kg and females at 500 mg/kg (14–23%), globulin concentration in both sexes at 1000 and 1500 mg/kg (8–13%), concentration of triglycerides in males at 1000 and 1500 mg/kg (50–61%), cholesterol concentration in males at >500 mg/kg (19–29%), creatinine concentration in females at 1000 and 1500 mg/kg (10%) and serum cholinesterase activity in females at 1000 and 1500 mg/kg (41–49%). As alanine aminotransferase and alkaline phosphatase activities were also reduced in the 28-day and long-term studies in rats, the effect is clearly treatment-related but, given the small magnitude of the effect and as a slight reduction in these parameters is not normally associated with adverse organ or systemic effects, is unlikely to be toxicologically relevant. This conclusion is further supported by studies indicating that alanine aminotransferase (and alkaline phosphatase) activities can be affected by dietary status, as discussed later in this monograph. Males at 1000 and 1500 mg/kg had dark yellow to light red cloudy urine and females at 1500 mg/kg had cloudy urine. In females at 1000 and 1500 mg/kg, urine volume was increased by 48% and 130%, respectively, and specific gravity was decreased slightly. The number of crystals in the urinary sediment was slightly increased in males at 1500 mg/kg. Increased relative liver weights in both sexes at 1500 mg/kg and females at 1000 mg/kg (10–34%), kidney weights in both sexes at 1000 and 1500 mg/kg (8–15%), and spleen weights in both sexes at 1000 and 1500 mg/kg and females at 500 mg/kg (22–74%) were likely to be treatment-related as they correlated with histological and/or clinical pathology findings and/or were inconsistent with normal patterns of organ weight changes associated with reduced body-weight gain. Other organ weight differences were likely to be caused by reductions in body-weight gains (25–42%) in these groups. Thickening of the duodenal wall and discoloration of the spleen were more common at 1500 mg/kg. Microscopic examination demonstrated an increase in the incidence and/or severity of mucosal hyperplasia in the duodenum in both sexes at 1500 mg/kg and in males at 500 and 1000 mg/kg, hepatocellular hypertrophy in the liver of both sexes at 1500 mg/kg and in males at 500 and 1000 mg/kg and, in the spleen, distension of the sinusoids in both sexes at 1000 and 1500 mg/kg, extramedullary haematopoiesis in both sexes at >150 mg/kg and histiocytosis in both sexes at >150 mg/kg. Fat storage in the liver was diminished in both sexes at >150 mg/kg, which is likely to reflect the reduced weight gains observed at >500 mg/kg. In two long-term studies in rats, at intakes of pyraclostrobin of up to 200 mg/kg (9 mg/kg bw per day), no effects on splenic extramedullary haematopoiesis or histiocytosis, or on fat storage in the liver were seen. Consequently the low incidences of these findings at 150 mg/kg were considered to be incidental to treatment. The NOAEL was 150 mg/kg (10.7 mg/kg bw per day in males and 12.3 mg/kg bw per day in females) on the basis of reductions in body weight and food consumption, effects on clinical chemistry parameters, liver hypertrophy, and mucosal hypertrophy in the duodenum at >500 mg/kg (Mellert et al., 1999a, 1999b).

Table 12. Haematology and clinical chemistry findings in rats given diets containing pyraclostrobin for 3 months

From Mellert et al. (1999a, 1999b) ALT, Alanine aminotransferase; AP, Alkaline phosphatase; ECHE, erythrocyte cholinesterase; F, Female; M, Male; MCH, Mean corpuscular haemoglobin; MCHC, Mean corpuscular haemoglobin concentration; MCV, Mean corpuscular volume; SCHE, serum cholinesterase
* p < 0.05; ** p < 0.02; *** p < 0.002

Table 13. Organ weights in rats receiving diets containing pyraclostrobin for 3 months

From Mellert et al. (1999a, 1999b)
F, Female; M, Male
^a Relative organ weight = organ weight (g)/body weight (g) × 100; * p < 0.05; ** p < 0.01

Table 14. Pathology findings in rats receiving diets containing pyraclostrobin for 3 months

From Mellert et al. (1999a, 1999b) F, Female; M, Male
^a Grade 1 = minimal in severity/very few in number/very small in size; grade 2 = slight in severity/few in number/small in size; grade 3 = moderate in severity and size/moderate to several in number

Rabbits

Groups of five male and five female (not pregnant) Himalayan rabbits (Chbb:HM from Charles River Laboratories Germany) were given pyraclostrobin (in a 0.5% aqueous solution of carboxymethylcellulose) at a dose of 0 or 4 mg/kg bw per day for 1 week by gavage. Pyraclostrobin was also administered in the diet at concentrations calculated to provide doses of 0 or 4 mg/kg bw per day for 1 week. Animals were quarantined and acclimatized to standard laboratory conditions for approximately 1 week before the start of the study. Food and water were available ad libitum. Food consumption was determined daily and body weight was recorded on days 0, 2, 4, 6 and 7. Animals were examined for mortality and clinical signs of toxicity at least once per day. At the end of the experiment, animals were sacrificed for necropsy. There were no clinical signs of toxicity and no abnormal macroscopic changes observed at necropsy. From the first day of dosing, mean food consumption was about 15–40% lower in both groups of treated males, but the differences from values in the relevant control groups were not statistically significant. Similarly, in both groups of females mean food consumption was 20–40% lower from the beginning of dosing until day 5. Thereafter, it was similar in control and treated groups. Although there were some apparent differences between mean food consumption and body-weight gains in control and treated groups, there was considerable variation between individuals in all groups and also variation in values obtained for any one individual on different days. Table 15 provides the ranges of values for food consumption and body-weight gain measured in control and treated animals. There was no clear effect of treatment with pyraclostrobin and it is probable that the apparent variation observed was a part of the normal biological variation for this species. This was a supplementary study initiated to address the appropriateness of using an apparently lower body-weight gain in treated animals in a study of developmental toxicity in rabbits as an appropriate end-point on which to base an acute RfD. In conjunction with similar studies in mice and rats, this study was intended to demonstrate the species-specific variability in food intake and body-weight gains of rabbits. Because of the limited parameters examined in this study, it was not adequate for the purposes of risk assessment and a NOAEL could not be identified (Schneider & Hellwig, 2002).

Table 15. Variations in food consumption and body-weight changes in rabbits

From Schneider & Hellwig (2002)
F, Female; M, Male; max/min, maximum/minimum

Dogs

Groups of five male and five female beagle dogs (aged 7–8 months) were given diets containing pyraclostrobin (purity, 97.1%) at a concentration of 0, 100, 200, or 450 mg/kg of feed (equal to 0, 2.8, 5.8 and 13 mg/kg bw per day) for 3 months. Dogs were checked at least once daily for mortality, and clinical signs of toxicity were assessed at least once each working day. Body weight was recorded weekly and food consumption was recorded daily. Haematology (including activated partial thromboplastin time) and clinical chemistry parameters (excluding brain and erythrocyte cholinesterase activity) were assessed in all animals on days 41/43 and 90, and an ophthalmological examination was performed at the end of the study. Urine analysis parameters were assessed in all animals on days 37/38 and 86/87. At sacrifice, all dogs were examined grossly, their tissues (including gall bladder, but excluding seminal vesicles) were examined microscopically and gross lesions were assessed. Organ weights (including parathyroid and thyroid glands, but excluding heart, spleen and thymus gland) were recorded.

There were no deaths, but vomiting (10 out of 10 dogs at 450 mg/kg until week 2) and diarrhoea (10 out of 10 dogs at 450 mg/kg during most of the study) were observed. At 200 mg/kg, diarrhoea also occurred in two out of five males during week 5 only, and sporadically throughout the study in four out of five females. As diarrhoea was observed in a 12-month study in dogs at 400 but not at 200 mg/kg, the occurrences of diarrhoea at 200 mg/kg in this study were regarded as being of no toxicological concern, owing to their isolated occurrence (week 5 only) in almost all affected dogs, or the irregular occurrence in a single animal. All other observations, discussed in the following paragraphs, relate to the treatment at 450 mg/kg only, unless specifically indicated otherwise. Females lost 2% (200 g) of their body weight, and males at 200 and 450 mg/kg gained substantially less weight (up to 31%) than did the controls. The effects in males were greatly influenced by one animal at 200 mg/kg that gained no weight and one at 450 mg/kg that lost weight (1%) during the study. Consequently, the finding in males is of questionable toxicological significance, particularly as no effect on body-weight gains was observed at 200 mg/kg in a subsequent 12-month study in dogs. In females, food consumption (9%) and food conversion efficiency were reduced. There were no treatment-related effects on ophthalmology.

Platelet counts were increased by 47–60% in females, and concentrations of total protein, albumin, globulin (both sexes, 5–12%) and glucose (females, 9–13%) were reduced, and absolute and relative epididymides weights were slightly increased (10–14%). A reduction in absolute and relative liver weights in females is consistent with, and likely to be secondary to, reduced food intake and weight gain. Urine analysis parameters were unaffected by treatment.

In the duodenum of both sexes, thickening of the wall and mucosal hypertrophy, which was characterized by an increased ratio of cytoplasm to nuclei in the villi and a hyperplastic aspect in epithelial cells, were observed. The NOAEL was 200 mg/kg (5.8 mg/kg bw per day) on the basis of increased platelet counts in females, decreased concentrations of total protein, albumin, and globulin in both sexes, decreased concentration of glucose and liver weights in females, and thickening of the wall and mucosal hypertrophy in the duodenum of both sexes at 450 mg/kg (Menges et al., 1999).

Groups of five male and female beagle dogs (aged 5–8 months) were given diets containing pyraclostrobin (purity, 98.7%) at a concentration of 0, 100, 200, or 400 mg/kg of feed (equal to 0, 2.7, 5.4 and 11 mg/kg bw per day) for 12 months. Animals were individually housed in kennels in controlled conditions. Each day, 700 g of food ration was offered to each dog, and water was provided ad libitum. Dogs were checked at least once daily for mortality, and clinical signs of toxicity were assessed at least once each weekday. Body weight and food conversion efficiency were recorded/calculated weekly, while food consumption was recorded daily. An ophthalmological examination was performed at the end of the study. Haematology (including activated partial thromboplastin time) and clinical chemistry (excluding brain, erythrocyte and serum cholinesterase activities) and urine analysis parameters were assessed in all animals at 3, 6 and 12 months. After 12 months of treatment, all dogs were sacrificed and examined grossly. Tissues (including gall bladder, but excluding femur with joint/glenoid surface and seminal vesicles) were examined microscopically and gross lesions were assessed in all animals affected per group. Organ weights (including parathyroid and thyroid glands, but excluding heart, spleen and thymus gland) were recorded.

Table 16. Observations in dogs given diets containing pyraclostrobin for 3 months