Reaction mass of 3-phenoxybenzyl (1R,3R)-2,2-dimethyl-3-(2-methylprop-1-en-1-yl)cyclopropanecarboxylate and 3-phenoxybenzyl (1R,3S)-2,2-dimethyl-3-(2-methylprop-1-en-1-yl)cyclopropanecarboxylate (4:1)

Repeated dose toxicity: oral

Administrative data

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Oct 2011 - Jan 2012

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP / guideline study without deficiencies

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2012

Report date:

2012

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity Study in Rodents)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

d-Phenothrin

IUPAC Name:

d-Phenothrin

Constituent 2

Reference substance name:

Cyclopropanecarboxylic acid, 2,2-dimethyl-3-(2-methyl-1-propenyl)-, (3-phenoxyphenyl) methyl ester, (1R)

IUPAC Name:

Cyclopropanecarboxylic acid, 2,2-dimethyl-3-(2-methyl-1-propenyl)-, (3-phenoxyphenyl) methyl ester, (1R)

Constituent 3

Reference substance name:

188023-86-1

Cas Number:

188023-86-1

IUPAC Name:

188023-86-1

Test material form:

other: liquid

Details on test material:

- Name of test material (as cited in study report): d-Phenothrin
- Physical state: yellow to brown transparent viscous liquid
- Purity test date: 20 January 1011
- Lot/batch No.: R1101004
- Expiration date of the lot/batch: January 2014
- Stability under test conditions: test material stability in feed was verified
- Storage condition of test material: room temperature

Test animals

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Crl:WI rats
- Source: Charles River Laboratories, 97633 Sulzfeld, Germany
- Age at study initiation: ca. 6 weeks
- Weight at study initiation: males 201 - 221 g, females: 150 - 181 g
- Housing: Type II and/or III polycarbonate
- Diet (e.g. ad libitum): rabbit pellet feed ad libitum
- Water (e.g. ad libitum): charcoal filtered and UV sterilised tap water ad libitum
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 - 23
- Humidity (%): 65 - 66
- Air changes (per hr): 15
- Photoperiod (hrs dark / hrs light): 12 / 12

IN-LIFE DATES: From: 2006-04-20 To: 2006-04-25

Administration / exposure

Route of administration:

oral: feed

Details on oral exposure:

DIET PREPARATION
- Rate of preparation of diet (frequency): once
- Mixing appropriate amounts with (Type of food): ssniff® SM R/M-Z+H “Autoclavable Complete Feed for Rats and Mice – Breeding and Maintenance” by ssniff Spezialdiäten GmbH, D-59494 Soest Germany
- Storage temperature of food: room temperature

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Test item concentration and/or homogeneity in feed were determined on 3 analytical occasions, twice at receipt of the diets (concentration and homogeneity), and once towards completion of the treatment (concentration of remaining diet and stability from the animal room).
The samples were extracted and analysed by HPLC using UV detection based on a validated analytical method (CiToxLAB Hungary Ltd. study 11/089-316AN).
d-Phenothrin proved to be stable in diet under ambient storage conditions in the animal room (approximately 22 ±3 °C) for at least 14 days
and in the diet storage room (approximately 15 - 21 °C) for at least 8 weeks.

Duration of treatment / exposure:

90 days

Frequency of treatment:

via diet, ad libitum

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

1 000 ppm

Remarks:

nominal in diet
equivalent to 67 and 84 mg/kg bw/d in males and females, respectively

Doses / concentrations 2

Dose / conc.:

3 000 ppm

Remarks:

nominal in diet
equivalent to 202 and 252 mg/kg bw/d in males and females, respectively

Doses / concentrations 3

Dose / conc.:

10 000 ppm

Remarks:

nominal in diet
equivalent to 685 and 1030 mg/kg bw/d in males and females, respectively

No. of animals per sex per dose:

10

Control animals:

yes, plain diet

Details on study design:

- Dose selection rationale: DRF study (Kuszky, 2012a)
- Rationale for selecting satellite groups: no satellite groups were maintained

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Animals were inspected for signs of morbidity and mortality twice daily (at the beginning and end of each working day). General clinical observations were made at least once a day at approximately the same time, with minor variations as practical.
- Cage side observations checked in table 1 were included.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Detailed clinical observations were made on all animals outside the home cage at randomisation (Day -7), on the first day of treatment (Day 0) and at least once a week afterwards.

BODY WEIGHT: Yes
- Time schedule for examinations: Day -7, Day 0, then at least weekly, including on Day 89, and prior to scheduled necropsy (fasted, on Day 90)

FOOD CONSUMPTION AND COMPOUND INTAKE:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: Yes

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: Yes

OPHTHALMOSCOPIC EXAMINATION: Yes
- Ophthalmoscopy was conducted in all animals before treatment (Day -8), and in the Control Group 1 and High dose Group 4 animals, during Week 13 (Day 88).

HAEMATOLOGY: Yes
- Time schedule for collection of blood: at termination
- Anaesthetic used for blood collection: Yes (pentobarbital)
- Animals fasted: Yes, overnight
- How many animals: all survivors
- Parameters checked in table 2 were examined.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: at termination
- Animals fasted: Yes
- How many animals: all survivors
- Parameters checked in table 3 were examined.

URINALYSIS: Yes
- Time schedule for collection of urine: Day 90, prior to necropsy
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes
- Parameters checked in table 4 were examined.

NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations: Day 84
- Dose groups that were examined: all
- Battery of functions tested: sensory activity / grip strength / motor activity / landing foot splay

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (see table 5)
HISTOPATHOLOGY: Yes (see table 6)

Statistics:

Evaluation was made by comparing the data for each of the Groups 2 to 4, respectively, against the Control Group 1. The heterogeneity of variance between groups was checked by Bartlett's homogeneity of variance test. Where no significant heterogeneity was detected, a oneway analysis of variance was carried out. If the obtained result was positive, Duncan's Multiple Range test was used to assess the significance of inter-group differences.
Where significant heterogeneity was found, the normal distribution of data was examined by Kolmogorov-Smirnov test. In case of abnormal distribution, the nonparametric method of Kruskal-Wallis One-Way analysis of variance was applied. If there was a positive result, the inter-group comparisons were performed using MannWhitney U-test. The mean and standard deviations values, the frequency of clinical observations, macroscopic and microscopic findings were calculated as applicable.

Results and discussion

Results of examinations

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

reduced BW gain at high dose

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

no effects observed

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

no effects observed

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

WBC was increased in the Mid and High dose males. Decreased neutrophils in High dose females.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

Increased phosporus in High dose animals.

Urinalysis findings:

no effects observed

Behaviour (functional findings):

no effects observed

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Increased liver, kidney and thyroid weights in High dose animals.

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

Bilateral enlargement of the thyroids in High dose males

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

High dose animals: Hypertrophy of the follicular cells in the thyroids, hepatocellular centrilobular hypertrophy in the liver and cortical tubular proteinaceous casts in the kidney.

Histopathological findings: neoplastic:

no effects observed

Details on results:

BODY WEIGHT AND WEIGHT GAIN
Lower than control body weight gain was noted for the 90 day period of treatment in the High dose group, with a weight gain suppression of approximately 8.5% in the males and 16.2% in the females. Body weights of the High dose group of both sexes consistently remained below control, approximately after Week 6 (males) or Week 2 (females), to termination. None of these changes were statistically significant.

HAEMATOLOGY
White blood cell count (WBC) was 76% and 91% higher than control in the Mid and High dose males, with increases of 18% in the High dose females only, without attaining statistical significance. In the females, decreases in the neutrophils of approximately 36%, p<0.01 and increases in the lymphocytes (18%, p<0.01) were observed at 10'000 ppm. In the males, the APTT was approximately 7% lower than control at 10'000 ppm. At 3000 and 10'000 ppm, the PT was 6% and 10% lower than control, changes considered to reflect a possible effect of the test item at these dose levels. There were no similar effects in the females, which showed minor variations only, up to 3%.

CLINICAL CHEMISTRY
Phosphorus was approximately 22% higher than control in the High dose males and 33% in the High dose females. At 3000 ppm, the mean value was 23% higher than control in the males with no effect in the females. A 12% increase occurred in the Low dose males only, however, the mean and individual values remained within the normal ranges, not considered toxicologically significant or to reflect an adverse effect. Bile acids were higher than control at 3000 and 10'000 ppm in both males and females, although without a clear dose response, up to 51% in the males and up to 45% in the females, with statistical significance in the Mid dose females only. Total protein, albumin and A/G ratio were marginally lower in the High dose females only, 7%, 11% and 9% lower than the control values, respectively. No statistically or toxicologically significant changes were recorded in these parameters in the males. Calcium mean concentration Ca++ was 5% and 7% higher than control in the High dose males and females, respectively.

ORGAN WEIGHTS
Possible treatment-related increases were noted in the liver, kidney and thyroid weights in the males and/or females mostly in the High dose group and on occasion in the Mid dose group. The mean absolute kidney weight was 17% higher than control in the High dose males and 14% higher than control when adjusted for the brain weight, with no changes in the females. When adjusted for the terminal body weight, the relative kidney weight was up to 21% higher than control in both male and female High dose animals. Statistically higher than control liver weights were noted at 10'000 ppm, 23% higher in the females only, when evaluated as absolute values, and in males and/or females when adjusted for the body or brain weights (up to 33% and 20% higher, respectively).
Absolute thyroid weights were 26% and 23% higher than control in the High dose males and females, respectively and 21% higher in the Mid dose females. When
adjusted for the brain weight, the mean relative thyroid weights were 24% (High dose males), 19% (High dose females) and 20% (Mid dose females) higher than control.
When adjusted for the terminal body weight, the mean value in the 10'000 ppm males was 31% higher than control, without attaining statistical significance. In the females, statistically higher values were noted at 3000 and 10'000 ppm, up to approximately 26% and 32% higher, p<0.05, respectively.

GROSS PATHOLOGY
Bilateral enlargement of the thyroids was observed in 2/10 High dose males.

HISTOPATHOLOGY: NON-NEOPLASTIC
Minimal to mild microscopic findings were observed in three tissues. These were hypertrophy of the follicular cells in the thyroids, hepatocellular centrilobular hypertrophy in the liver and cortical tubular proteinaceous casts in the kidney predominantly in the High dose group.
In the thyroid gland, minimal hypertrophy of the follicular cells was seen in 4/10 males and 3/10 females from the High dose group and in 1/10 Mid dose female. No hypertrophy was observed in Mid dose males. These findings correlated with the organ weight data. Based on the isolated occurrence in 1/10 Mid dose females only and in the absence of any indication of thyroid weight changes in Low dose females, histopathological examination was not considered necessary at the Low dose. In the liver, minimal hepatocellular centrilobular hypertrophy affected 4/10 High dose females but not males. No hypertrophy was noted in Mid dose females duringadditional microscopic evaluation.
In the kidney, minimal to mild bilateral cortical tubular proteinaceous casts were observed in 8/10 High dose males. Minimal bilateral/left casts in 2/10 Mid dose males were noted during additional examination. In the males, casts were not seen in controls; however one control female had also bilateral minimal casts.

Effect levels

1

Dose descriptor:

LOAEL

Effect level:

202 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: gross pathology; organ weights; histopathology

2

Key result

Dose descriptor:

NOAEL

Effect level:

67 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: gross pathology; organ weights; histopathology

3

Dose descriptor:

LOAEL

Effect level:

252 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

female

Basis for effect level:

other: gross pathology; organ weights; histopathology

4

Dose descriptor:

NOAEL

Effect level:

84 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

female

Basis for effect level:

other: gross pathology; organ weights; histopathology

Target system / organ toxicity

Critical effects observed:

not specified

Any other information on results incl. tables

Table 7: Haematology changes in males
DOSE GROUP n=10		APTT sec.	PT sec.	WBC 10^9/L	LUC %
Control	MEAN	18.96	24.40	3.67	0.23
1000 ppm	MEAN	18.69	23.51	3.99	0.41
	±%	-1.4	-3.6*	8.7	2.9
3000 ppm	MEAN	18.98	22.94	6.48	0.41
	±%	0.1	-6**	76*	78**
10’000 ppm	MEAN	17.71	21.87	7.01	0.42
	±%	-7**	-10**	91*	83**

 

Table 8: Haematology changes in females
DOSE GROUP n=10		NE %	LY %
Control	MEAN	32.19	62.80
1000 ppm	MEAN	26.56	68.65
	±%	-17	9.3
3000 ppm	MEAN	27.76	67.64
	±%	-14	7.7
10’000 ppm	MEAN	20.63	74.03
	±%	-36**	18**

 

Table 9: Clinical-chemical changes in males
DOSE GROUP n=10		CL^- mmol/L	Ca^++ mmol/L	Phos. mmol/L	Tot. prot g/L	Alb. g/L	A/G	Bile acids µmol/L
Control	MEAN	105.98	2.50	2.05	55.40	28.42	1.05	11.68
1000 ppm	MEAN	105.25	2.56	2.30	55.64	28.75	1.07	11.87
	±%	-0.7	2.2*	12**	0.4	1.2	1.9	1.6
3000 ppm	MEAN	103.92	2.57	2.53	56.24	29.59	1.11	17.66
	±%	-1.9**	2.6*	23**	1.5	4.1	5.7	51**
10’000 ppm	MEAN	103.34	2.64	2.49	53.81	28.10	1.10	15.29
	±%	-2.5**	5.3**	22**	-2.9	-1.1	4.8	31**

 

Table 10: Clinical-chemical changes in females
DOSE     GROUP n=10		CL^- mmol/L	Ca^++ mmol/L	Phos. mmol/L	Tot. prot g/L	Alb. g/L	A/G	Bile acids µmol/L
Control	MEAN	103.74	2.48	1.71	60.52	33.77	1.26	9.91
1000 ppm	MEAN	103.31	2.56	1.82	59.56	33.68	1.30	11.42
	±%	-0.4	3.3	6.4	-1.6	-0.3	3.2	15
3000 ppm	MEAN	102.86	2.54	1.69	58.29	32.86	1.29	14.41
	±%	-0.8	2.5	-1.3	-3.7	-2.7	2.4	45**
10’000 ppm	MEAN	104.66	2.65	2.28	56.37	30.18	1.15	12.90
	±%	0.9	6.7**	33**	-6.9*	-11*	-8.7*	30

 

Table 11: Effects on absolute organ weights (g)
DOSE GROUP n=10		Terminal bw		Kidney		Liver		Thyroid w/ parathyroids
		♂	♀	♂	♀	♂	♀	♂	♀
Control	MEAN	544.2	291.9	3.212	1.946	14.470	8.114	0.0232	0.0168
1000 ppm	MEAN	526.9	301.9	3.088	1.990	14.496	8.572	0.0250	0.0193
	±%	-3.2	3.4	-3.9	2.3	0.2	5.6	7.8	15
3000 ppm	MEAN	520.8	283.2	3.259	1.905	14.220	7.898	0.0242	0.0203*
	±%	-4.3	-3.0	1.5	-2.1	-1.7	-2.7	4.3	21
10’000 ppm	MEAN	519.9	272.6	3.751*	1.974	15.703	9.985**	0.0292**	0.0206*
	±%	-4.5	-6.6	17	1.4	8.5	23	26	23

 

Table 12: Effects on relative organ weight changes (% BW)
DOSE GROUP n=10		Brain		Kidney		Liver		Thyroid w/ parathyroids
		♂	♀	♂	♀	♂	♀	♂	♀
Control	MEAN	0.41430	0.69864	0.59328	0.66376	2.66125	2.76754	0.00427	0.00573
1000 ppm	MEAN	0.42344	0.70934	0.58769	0.66901	2.75474	2.86573	0.00477	0.00646
	±%	2.2	1.5	-0.9	0.8	3.5	3.5	12	13
3000 ppm	MEAN	0.42794	0.73030	0.62285	0.67411	2.71609	2.80329	0.00467	0.00720*
	±%	3.3	4.5	5.0	1.6	2.1	1.3	9	26
10’000 ppm	MEAN	0.43889	0.77274**	0.72189**	0.72501*	3.01784**	3.66899**	0.00561	0.00757 *
	±%	5.9	11	22	9.2	13	33	31	32

Applicant's summary and conclusion

Conclusions:

In conclusion, under the conditions of this study based on the potentially treatment related findings noted at 3000 and 10'000 ppm, the NOAEL of d-Phenothrin administered in the diet to Wistar rats for 90 consecutive days is considered to be 1000 ppm, equivalent to approximately 67 and 84 mg/kg bw/day achieved dose levels in males and females, respectively.

Executive summary:

The objective of this study was to obtain information on the toxicity of d-Phenothrin administered in diet, pelleted by simple compression, daily for 90 days according to the following experimental design:

Control group: basal diet (0 mg d-Phenothrin/kg bw/d) 10 males/10 females

Low dose group: 1000 ppm in diet (~75 mg d-Phenothrin/kg bw/d) 10 males/10 females

Mid dose group: 3000 ppm in diet (~227 mg d-Phenothrin/kg bw/d) 10 males/10 females

High dose group: 10000 ppm in diet (~857 mg d-Phenothrin/kg bw/d) 10 males/10 females

 

Parameters monitored during this study were mortality and clinical observations, including neurological assessment and ophthalmoscopy, towards the end of the treatment period and examination of the vaginal smears prior to necropsy for evaluation of the oestrus cycle phase. Body weights and food consumption were measured weekly and food conversion efficiency and test item intake were calculated.

Clinical pathology (haematology, clinical chemistry and urinalysis) was conducted prior to necropsy on Day 90, followed by necropsy with macroscopic examination and selected organ weight measurements. Full histopathology was performed for Groups 1 (Control) and 4 (High dose) and any organs showing macroscopic findings. Following initial examination, additional slide preparation and examination was conducted for Group 3 Mid dose animals, on the liver from females, thyroids from males and females and kidneys from males only. 

Test item content and/or homogeneity in the diet were determined by HPLC using UV detection based on a validated analytical method, twice at receipt of the diet and once towards completion of the treatment period, within the stability interval The samples were extracted and analysed by d-Phenothrin proved to be stable in ssniff® SM R/M-Z+H “Autoclavable Complete Feed for Rats and Mice – Breeding and Maintenance” under ambient storage conditions in the diet storage room at approximately 15 - 21 °C for at least 8 weeks and in the animal room at approximately 22 ±3 °C for at least 14 days. No d-Phenothrin was detected in the control samples. Test item-diets were homogeneous and had measured concentrations within 95 - 102% of the nominal concentrations, within the intended range of ±10% nominal.

No unscheduled mortality, clinical signs, or toxicologically significant changes were noted in the animal behaviour, general physical condition, in the reactions to different type of stimuli, landing foot splay or grip strength or motor activity.

There were no test item related changes at ophthalmoscopy or in the oestrus cycle phases evaluated prior to necropsy.

Lower than control body weight gain was noted for the 90-day period of treatment in the High dose group, with a weight gain suppression of approximately 8.5% in the males and 16.2% in the females. Body weights of the High dose group of both sexes consistently remained below control, approximately after week 6 (males) or week 2 (females), to termination. None of these changes were statistically significant. There were no test item related adverse effects on the animal mean daily food consumption or food conversion efficiency.

The test item intake calculated between Days 0 and 89 was approximately 67, 202 and 685 mg/kg bw/day in the Low, Mid and High dose groups males and 84, 252 and 1030 mg/kg bw/day in the females, with mean group values of 75, 227 and 857 mg/kg bw/day achieved dose levels at 1000, 3000 and 10000 ppm.

In the haematology, the white blood cell count (WBC) was 76% and 91% higher than control in the Mid and High dose males, with increases of 18% in the High dose females only, without attaining statistical significance. In the females, decreases in the neutrophils of approximately 36%, p<0.01 and increases in the lymphocytes (18%, p<0.01) were observed at 10000 ppm. In the males, the APTT was approximately 7% lower than control at 10000 ppm. At 3000 and 10000 ppm, the PT was 6% and 10% lower than control, changes considered to reflect a possible effect of the test item at these dose levels. There were no similar effects in the females, which showed minor variations only, up to 3%.

Clinical chemistry evaluation did not reveal any obvious toxicity for d-Phenothrin. Phosphorus was approximately 22% higher than control in the High dose males and 33% in the High dose females. At 3000 ppm, the mean value was 23% higher than control in the males with no effect in the females. A 12% increase occurred in the Low dose males only, however, the mean and individual values remained within the normal ranges, not considered toxicologically significant or to reflect an adverse effect. Bile acids were higher than control at 3000 and 10000 ppm in both males and females, although without a clear dose response, up to 51% in the males and up to 45% in the females, with statistical significance in the Mid dose females only. Total protein, albumin and A/G ratio were marginally lower in the 10000 ppm High dose females only, 7%, 11% and 9% lower than the control values, respectively. No statistically or toxicologically significant changes were recorded in these parameters in the males. Calcium mean concentration Ca++ was 5% and 7% higher than control in the High dose males and females, respectively.

There were no adverse effects in the haematology or clinical chemistry parameters evaluated in the 1000 ppm Low dose group. There were no d-Phenothrin-related, or adverse effects at urinalysis performed prior to necropsy at any of the dose levels tested.

Possible treatment-related increases were noted in the liver, kidney and thyroid weights in the males and/or females mostly in the 10000 ppm High dose group and on occasion in the 3000 ppm Mid dose group and these correlated with the macroscopic and/or microscopic findings.

The mean absolute kidney weight was 17% higher than control in the High dose males and 14% higher than control when adjusted for the brain weight, with no changes in the females. When adjusted for the terminal body weight, the relative kidney weight was up to 21% higher than control in both male and female High dose animals.

Statistically higher than control liver weights were noted at 10000 ppm, 23% higher in the females only, when evaluated as absolute values, and in males and/or females when adjusted for the body or brain weights (up to 33% and 20% higher, respectively).

Absolute thyroid weights were 26% and 23% higher than control in the High dose males and females, respectively and 21% higher in the Mid dose females. When adjusted for the brain weight, the mean relative thyroid weights were 24% (High dose males), 19% (High dose females) and 20% (Mid dose females) higher than control. When adjusted for the terminal body weight, the mean value in the 10000 ppm males was 31% higher than control, without attaining statistical significance. In the females, statistically higher values were noted at 3000 and 10000 ppm, up to approximately 26% and 32% higher, p<0.05, respectively.

At macroscopic evaluation performed during necropsy on Day 90, bilateral enlargement of the thyroids was observed in 2/10 High dose males. This was subsequently found to be correlated with microscopic changes. There were no other macroscopic findings which appeared to be treatment related.

At histopathological evaluation, minimal to mild microscopic findings were observed in three tissues. These were hypertrophy of the follicular cells in the thyroids, hepatocellular centrilobular hypertrophy in the liver and cortical tubular proteinaceous casts in the kidney predominantly in the High dose group.

In the thyroid gland, minimal hypertrophy of the follicular cells was seen in 4/10 males and 3/10 females from the High dose group and in 1/10 Mid dose female. No hypertrophy was observed in Mid dose males. These findings correlated with the organ weight data. Based on the isolated occurrence in 1/10 Mid dose females only and in the absence of any indication of thyroid weight changes in Low dose females, histopathological examination was not considered necessary at the Low dose. In the liver, minimal hepatocellular centrilobular hypertrophy affected 4/10 High dose females but not males. No hypertrophy was noted in Mid dose females during additional microscopic evaluation.

In the kidney, minimal to mild bilateral cortical tubular proteinaceous casts were observed in 8/10 High dose males. Minimal bilateral/left casts in 2/10 Mid dose males were noted during additional examination. In the males, casts were not seen in controls; however, one control female had also bilateral minimal casts.

Examination of the organ weight data, clinical chemistry and urine analysis together with the histopathology observations indicate that there was no adverse effect on the male kidney in the Mid dose group. Similarly, the data on the Low dose males suggest that there were no effects therefore no additional histopathological evaluation was performed. The 1000 ppm Low dose level was considered to be a no-observed-adverse-effect–level for d-Phenothrin in terms of the histopathology.

In conclusion, under the conditions of this study based on the potentially treatment-related findings noted at 3000 and 10000 ppm, the NOAEL of d-Phenothrin administered in the diet to Wistar rats for 90 consecutive days is considered to be 1000 ppm, equivalent to approximately 67 and 84 mg/kg bw/day achieved dose levels in males and females, respectively, with a mean achieved dose for males and females combined of approximately 75 mg/kg bw/day.