Prometryn

Neurotoxicity

Description of key information

- Oral: no neurotoxic effects observed, male/female, rate, acute, OECD 424, Herberth 2012a

- Oral: no neurotoxic effects observed, male/female, rate, sub-chronic, OECD 424, Herberth 2012b

Key value for chemical safety assessment

Effect on neurotoxicity: via oral route

Link to relevant study records

Reference

Reference 1

Endpoint:

neurotoxicity: acute oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Study initiation: 01 November 2011; end: 16 January 2012

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 424 (Neurotoxicity Study in Rodents)

Version / remarks:

1997

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Species:

rat

Strain:

other: Crl:CD(SD)

Sex:

male/female

Details on test animals or test system and environmental conditions:

Source: Charles River Laboratories Inc., Raleigh, North Carolina, USA
Age: 31 days old at receipt, about 7 weeks at dosing
Weight: 184 to 250 g (males), 151 to 210 g (females)
Acclimation: 13 days
Housing: 2 - 3 animals per sex were housed per cage for about six days during acclimation, thereafter animals were housed individually in stainless steel, wire-mesh cages suspended above cage board
Diet: basal Certified Rodent LabDiet 5002 supplied by PMI Nutrition Internaltional LLC ad libitum
Water: Reverse osmosis treated tap water ad libitum
Temperature: 21.5 ºC to 21.9 ºC
Humidity: 43.6% to 54.1%
Lighting: 12 hours light to 12 hours darkness cycle

Route of administration:

oral: gavage

Vehicle:

CMC (carboxymethyl cellulose)

Remarks:

0.5% in distilled water

Details on exposure:

The vehicle suspension was mixed daily throughout the preparation, sampling and dose administration procedures. Dosing formulations were prepared daily as single formulations for each dose level, and stored at room temperature, protected from light before use. The substance formulations were stirred continuously throughout the preparation, sample and administration procedures. The dose volume was 5 mL/kg bw.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

A gas chromatography method using flame ionization detection was used for the determination of test substance concentrations in aqueous formulations containing 0.5% (w/v) carboxymethylcellulose. The measured concentrations were within 90 to 110% of nominal concentrations. Furthermore, the criteria for homogeneity were met as the relative standard deviation of analysed concentrations per test group was <5%.

Duration of treatment / exposure:

Single oral administration followed by an observation period of 14 days

Frequency of treatment:

One single administration

Dose / conc.:

150 mg/kg bw/day (nominal)

Dose / conc.:

500 mg/kg bw/day (nominal)

Dose / conc.:

1 500 mg/kg bw/day (nominal)

No. of animals per sex per dose:

10 per sex per dose

Control animals:

yes, concurrent vehicle

Details on study design:

The animals judged suitable for assignment to the study were selected for use in a computerized randomization procedure. A printout containing the animal numbers, corresponding body weights, and individual group assignments was generated based on body weight stratification in a block design. The animals were assigned to groups according to the printout. Individual body weights at randomization were within ± 20% of the mean for each sex. Each group (Groups 1-4) consisted of 10 males and 10 females. These animals were then randomized into 4 study replicates to allow for the reasonable conduct of the functional observational battery assessment and ambulatory locomotor activity counts.

Observations and clinical examinations performed and frequency:

All animals were observed twice daily for mortality and moribundity. Clinical examinations were performed one daily on all animals. Individual body weights were recorded one week before dosing, on the day of dosing and on days 1, 2, 3, 7, 14 and 15. Individual food consumption was recorded regularly throughout the study period.

Neurobehavioural examinations performed and frequency:

Functional observational battery assessments were recorded for all animals before the dose administration, at the time of peak effects (circa five hours post-dosing) and on study days 7 and 14. This included home cage observations, handling observations, open field observations, sensory observations, neuromuscular examinations and physiological examinations. Locomotor activity was assessed for all animals before the dose administration, at the time of peak effects and on study days 7 and 14. Locomotor activity was measured automatically using a personal computer-controlled system that utilises a series of infrared photobeams surrounding an amber plastic, rectangular cage to quantify motor activity of each animal.

Sacrifice and (histo)pathology:

All animals were sacrificed at the scheduled date of necropsy. Five animals per sex and dose group were deeply anesthesised by intraperitoneal injection of sodium pentobarbital. Each animal was perfused in situ with a 4% paraformaldehyde/0.1 M phosphate buffered solution. The central and peripheral nervous system tissues were dissected and preserved. Fixed brain weight and brain dimensions were recorded. Any observable gross changes and abnormal colouration or lesions of the brain and spinal cord were recorded. Microscopic neuropathological examinations were performed on a range of tissues.

Positive control:

Not applicable

Statistics:

Analyses were conducted using two-tailed tests (except as noted otherwise) for minimum significance levels of 1% and 5%, comparing each test substance-treated group to the control group by sex. Body weight, body weight change, food consumption, continuous FOB, and brain weight and measurement data were analyzed using a parametric one-way ANOVA (Snedecor and Cochran, 1980). If the ANOVA resulted in significant (p<0.05) intergroup variance, Dunnett's test (Dunnett, 1964) was used to compare the test substance-treated groups to the control group. FOB parameters with scalar or descriptive data and non-graded histopathologic findings were analyzed using Fisher’s Exact Test (Steel and Torrie, 1980). Statistical analysis of graded histopathologic findings was not conducted on this study due to the absence of multiple severities (i.e., those findings with more than 2 distinct severities including none/not remarkable).

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Treatment related clinical findings of decreased defecation were noted for the 1500 mg/kg males and females, primarily during the first few days following dosing. Although the incidence was low, the observations of small feces for the 1500 mg/kg males and females may be treatment related. Other clinical findings noted in the test substance-treated groups, including hair loss, scabbing, and red material on various body surfaces, occurred infrequently, at similar frequencies in the control group, and/or in a manner that was not dose-related.

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Mean body weight losses (up to 7 g/day) were noted for the 1500 mg/kg males and females during study days 0-3; differences from controls were generally statistically significant. As a result, mean absolute body weights for the 1500 mg/kg males and females were lower (up to 9.6% and 13.2%, respectively) than the control group on study days 2 and 3; these differences were statistically significant on study day 3 for males and on study days 2 and 3 for females. During study days 3-7, mean body weight gains were statistically significantly higher, and similar mean body weight gains were noted during study days 7-15. Therefore, mean body weight gains for the 1500 ppm males and females were similar to controls over the entire treatment period (study days 0-15), and mean absolute body weights were similar to the control group by study day 15.
Statistically significant mean body weight losses were noted for the 500 mg/kg males and females during study days 0-1. For the remainder of the treatment period, mean body weight gains for these animals were similar to the control group, and mean absolute body weights were not affected.
Mean body weights and body weight gains for the 150 mg/kg males and females were unaffected by prometryn administration.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

During study days 0-3 for the 1500 mg/kg males and females, mean food consumption was statistically significantly lower compared to controls; this decrease in food consumption corresponded to the mean body weight losses noted for these animals during this period. Subsequently, statistically significantly higher mean food consumption was noted for these females during study days 3-7, which corresponded to the increased mean body weight gain observed during this period. Mean food consumption in this group was similar to the control group for the remainder of the treatment period.
Statistically significantly lower mean food consumption was noted for the 500 mg/kg males during study days 0-1; this decrease corresponded to the mean body weight loss noted for these males during this period. Mean food consumption was similar to control throughout the remainder of the treatment period. No statistically significant differences in food consumption were observed for the 500 mg/kg females, although the mean food consumption for this group was slightly lower than control during study days 0-1.
Mean food consumption for the 150 mg/kg males and females was similar to controls throughout the treatment period (study days 0-14).

Behaviour (functional findings):

effects observed, treatment-related

Description (incidence and severity):

Home cage parameters were unaffected by test substance administration. On study day 7, there was a statistically significantly higher number of the 1500 mg/kg females with fecal pellets compared to control females. However, because there was no evidence of effects on defecation during the daily clinical observations, these differences were considered biological variation and unrelated to test substance administration. There were no other statistically significant differences for the test substance-treated males and females when compared to controls at the time of peak effect on study day 0 and on study days 7 and 14. No effects on handling, open field, sensory, neuromuscular, or physiological parameters were observed.
The decreased mean total and ambulatory LMA were statistically significant at the 0-10 min interval on study day 0 for the 500 mg/kg (ambulatory only) and 1500 mg/kg males and 500 mg/kg and 1500 mg/kg females.
No treatment-related effects on mean total and ambulatory LMA counts on study day 0 were observed for the 150 mg/kg males and females. No other substance related effects were noted on LMA patterns on study day 0. The statistically significantly higher mean total counts at 31-40 minutes and 51-60 minutes and mean ambulatory counts at 31-40 minutes, 41-50 minutes, and 51-60 minutes noted for the 1500 mg/kg males on study day 0 are not attributed to treatment since the differences were primarily attributed to single males and/or the mean values were similar to historical control values.
The effects of substance administration on LMA on study day 0 were transient, likely a reflection of the transient generalized systemic toxicity. No prometryn-related changes in mean total and ambulatory LMA counts were noted on study days 7 and 14. While statistically significantly lower mean total LMA counts were noted for the 1500 mg/kg females at 0-10 minutes on study day 14, this decrease was not attributed to treatment since the total activity levels during this interval were similar to pretest levels for this group.
No remarkable shifts in the pattern of habituation occurred in any of the test substancetreated groups when the animals were evaluated on study days 0, 7, and 14.

Gross pathological findings:

no effects observed

Description (incidence and severity):

Brain weights and measurements were unaffected by administration of the substance.

Neuropathological findings:

no effects observed

Description (incidence and severity):

No test substance-related microscopic lesions were observed in any of the central or
peripheral nervous system tissues examined from 5 animals/sex in the 1500 mg/kg group. There were instances of axonal degeneration in the peripheral nerves and in the spinal nerve roots. This axonal degeneration was of minimal severity, typically with only a single ‘digestion chamber’, and consistent with incidental alterations. Minimal axonal degeneration in the peripheral nerves and spinal nerve roots is a common background lesion in animals of this species, strain, and age (Eisenbrandt et al., 1990).

Key result

Dose descriptor:

NOEL

Effect level:

1 500 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

neuropathology

Key result

Dose descriptor:

NOEL

Effect level:

150 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: neurotoxicity, lower mean total and/or ambulatory locomotor activity counts

Key result

Dose descriptor:

NOAEL

Effect level:

500 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

Key result

Critical effects observed:

no

Conclusions:

Following a single oral administration of test substance, the NOAEL was 500 mg/kg bw based on reductions in mean absolute body weight and the NOEL for neurotoxicity was 150 mg/kg bw in female and male Crl:CD(SD) rats.

Executive summary:

The acute neurotoxicity of the substance to female and male rats following a single oral administration by gavage was studied under GLP to OECD TG 424. Groups of ten female and ten male Crl:CD(SD) rats, aged about 7 weeks at dosing, received one single administration of the test substance in suspensions of 0.5% carboxy-methylcellulose in distilled water at a dose volume of 5 mL/kg bw at nominal doses of 150, 500 or 1500 mg/kg bw. Control animals received the same volume of the vehicle without test substance. Animals were then observed for a period of 14 days, and functional observational battery assessments and measurements of the total and ambulatory locomotor activity were carried out regularly throughout the study period. No mortalities or clinical signs were observed. Mean body weight losses with corresponding recuctions in mean food consumption were noted for the animals treated at 1500 mg/kg bw over the first three days of the study, resulting in lower body weights on study days 2 and 3. Mean body weight losses were also noted for both sexes at 500 mg/kg bw on study days 0 to 1, but mean body weights were unaffected. Exposure to the substance cause reductions in mean total and/or ambulatory motor activity counts for males and females in the 500 and 1500 mg/kg bw groups during the 0-10 minute intervals at the time of peak effect (about 5 hours after administration) on the day of dosing. No other effects were noted on motor activity or on functional observation battery parameters. Furthermore, no effects on brain weights, brain dimensions or neuropathological lesions were apparent. The NOEL for neurotoxicity of the substance to female and male rats was found to be 150 mg/kg bw and the overall NOAEL was found to be 500 mg/kg bw, following a single oral administration of the substance by oral gavage.

Reference 2

Endpoint:

neurotoxicity: sub-chronic oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Study initiation: 14 November 2011; end: 26 April 2012

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 424 (Neurotoxicity Study in Rodents)

Version / remarks:

1997

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Species:

rat

Strain:

other: Crl:CD(SD)

Sex:

male/female

Details on test animals or test system and environmental conditions:

Source: Charles River Laboratories Inc, Raleigh, North Carolina, USA
Age: about six weeks at the initiation of treatment
Weight: 181 to 247 g (males), 147 to 197 g (females)
Acclimation: 13 days
Housing: animals were housed 2 to 3 per cage and sex for 3 days after arrival, then individually in stainless steel, wire-mesh cages suspended above cage board
Diet: Certified Rodent LabDiet 5002 supplied by PMI Nutrition International LLC ad libitum
Water: reverse osmosis treated tap water ad libitum
Temperature: 21.2 °C to 21.9 °C
Humidity: 39.9% to 52.0%
Lighting: 12 hour light to 12 hour darkness cycle
Air changes: at least 10 air changes per hour

Route of administration:

oral: feed

Vehicle:

unchanged (no vehicle)

Details on exposure:

PMI Nutrition International, LLC Certified Rodent LabDiet 5002 was used in the preparation of the control and test diets. Diets containing the test substance were prepared using an appropriate blender. Test diets were prepared approximately weekly, placed in labeled plastic storage bags, and stored at room temperature until use.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

A validated gas chromatography method using flame ionization detection for the determination of substance concentration in diet admix formulations containing rodent feed and test substance ranging in concentration from 400 to 6000 ppm was extended in this study for the determination of substance concentration in formulations as low as 250 ppm. Assessment of test substance stability following 13 days of room temperature storage at a target concentration of 250 ppm met the protocol-specified criteria for stability, i.e., the post-storage concentration was not <90% of the pre-storage value. The analyzed formulations used for dose administration met the protocol-specified acceptance criteria for concentration acceptability, i.e., the analyzed concentration was 90% to 110% of the target concentration with RSD ≤5%. No test substance was detected in the analyzed basal diet provided to the control groups.

Duration of treatment / exposure:

13 weeks

Frequency of treatment:

Daily, continuous exposure via diet

Dose / conc.:

250 ppm

Remarks:

Females only

Dose / conc.:

500 ppm

Remarks:

Females and males

Dose / conc.:

1 000 ppm

Remarks:

Females and males

Dose / conc.:

2 000 ppm

Remarks:

Males only

No. of animals per sex per dose:

12 per sex per dose

Control animals:

yes, plain diet

Details on study design:

The animals judged suitable for assignment to the study were selected for use in a computerized randomization procedure. A printout containing the animal numbers, corresponding body weights, and individual group assignments was generated based on body weight stratification into a block design. The animals were then arranged into groups according to the printout. Individual body weights at randomization were within ± 20% of the mean for each sex. Each group (Groups 1-4) consisted of 12 males and 12 females. These animals were then randomized into 4 study replicates to allow for the reasonable conduct of the FOB and LMA assessments. Each dose group and sex was equally represented within each study replicate.

Observations and clinical examinations performed and frequency:

All animals were observed twice daily for mortality and moribundity. Detailed physical examinations were recorded weekly. Individual body weights and food consumption were recorded weekly. Ophthalmic examinations were conducted on all animals prior to the initiation of treatment and near the end of the treatment period.

Neurobehavioural examinations performed and frequency:

Functional observational battery assessments were recorded for all animals one week before start of exposure and during study weeks 1, 3, 7 and 12. The examinations included home cage, handling, open field, sensory, neuromuscular and physiological observations. Furthermore, locomotor activity was assessed for all animals before initiation of exposure and during weeks 1, 3, 7 and 12. LMA, recorded after the completion of the FOB, was measured automatically using a personal computer-controlled system that utilizes a series of infrared photobeams surrounding an amber plastic, rectangular cage to quantify the motor activity of each animal. Four-sided black plastic enclosures were used to surround the transparent plastic boxes and decrease the potential for distraction from extraneous environmental stimuli or activity by biologists or adjacent animals. The black enclosures rested on top of the photobeam frame and did not interfere with the path of the beams. The LMA assessment was performed in a sound-attenuated room equipped with a white-noise generator set to operate at 70 ± 10 dB.

Sacrifice and (histo)pathology:

At the termination of the study (study week 13), 5 randomly selected rats/sex/group were deeply anesthetized by an intraperitoneal injection of sodium pentobarbital and then perfused in situ with a 4.0% paraformaldehyde/0.1M phosphate buffer solution. The central and peripheral nervous system tissues were dissected and preserved. Fixed brain weight and brain dimensions (length [excluding olfactory bulbs] and width) were recorded. Any observable gross changes, abnormal coloration, or lesions of the brain and spinal cord were recorded. After successful perfusion of the selected rats, all remaining (nonselected) rats were euthanized by carbon dioxide inhalation and discarded without macroscopic examination. Detailed microscopic neuropathological examinations were performed on various tissues of the nervous system of the selected animals.

Positive control:

Not applicable

Statistics:

See any other information on materials and methods

Clinical signs:

effects observed, non-treatment-related

Description (incidence and severity):

There were no test substance-related clinical findings observed in any group. Clinical findings observed in the test substance-exposed groups, included hair loss and scabbing on various body surfaces, were observed in the control group with similar frequency or in a limited number of animals and therefore, not considered test substance-related.

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

A general trend of decreased mean body weight gains in the 1000 and 2000 ppm males were observed throughout the first 6 weeks of the study. These differences were statistically significant during study days 7-14 and 35-42 for the 1000 ppm males and study days 0-7, 7-14, 21-28, and 35-42 for the 2000 ppm group. Consequently, this resulted in statistically significantly lower mean body weight gains for the entire study period (study days 0-91) in the 1000 and 2000 ppm males. In addition, mean absolute body weights in these groups were up to 11.3% and 14.1%, respectively, lower than the control group; differences in mean body weight were statistically significant during study days 14-91. Mean body weights and body weight gains for males in the 500 ppm group and females at all dose levels were unaffected by test substance administration.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Mean food consumption, evaluated as g/animal/day, for males in the 1000 and 2000 ppm groups was generally lower than the control group throughout the study (study days 0-91), corresponding to the reduced mean body weight gains in these groups observed during the first 6 weeks of treatment. Differences from the control group were generally statistically significant. Mean food consumption for males in the 500 ppm group and females at all dose levels was unaffected by test substance administration.

Ophthalmological findings:

no effects observed

Behaviour (functional findings):

no effects observed

Description (incidence and severity):

As part of the physiological observations, a statistically significant decrease in mean body weights for males in the 1000 and 2000 ppm groups was noted during the study week 3, 7, and 12 evaluations. The effects on mean body weight correlated with test substance-related effects during the weekly body weight evaluations. There were no test substance-related effects on mean catalepsy or body temperature for males and females at any test substance concentration. The other parameters of the functional observation battery, including home cage, handling, open field, sensory and neuromuscular parameters, were unaffected by treatment with the substance in the diet over a period of 13 weeks.
Locomotor activity patterns (mean total and ambulatory motor activity counts) were unaffected by test diet consumption. There were no statistically significant differences between the control and test substance-treated groups when values obtained from the 6 subintervals (0-10 minutes, 11-20 minutes, 21-30 minutes, 31-40 minutes, 41-50 minutes, and 51-60 minutes) and the overall 60-minute test session were evaluated during study weeks 1, 3, 7, and 12, except for statistically significant (linear trend) increased mean overall ambulatory counts during the study week 12 evaluation for males in the 2000 ppm group. However, this finding was not attributed to treatment as there were no effects on total counts, and no shifts were observed in the pattern of habituation. No remarkable shifts in the pattern of habituation occurred in any of the test substance-treated groups when the animals were evaluated on study weeks 1, 3, 7, and 12.

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

Brain weights and measurements were unaffected by administration of prometryn at any dose level.

Gross pathological findings:

no effects observed

Description (incidence and severity):

There were no macroscopic findings observed in the brain or spinal cord of males and females at any dose level. There was a statistically significant lower brain width (14.67 mm) in the 1000 ppm group females when compared to the control group. However, this lower mean width value fell within the historical control database, where mean brain width ranged from 14.2 to 15.2 mm. In addition, there were no correlating clinical signs, other changes in brain measurements, or microscopic findings. Therefore, the lower brain width in the 1000 ppm group females was considered spurious and within biological variability.

Neuropathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

No test substance-related microscopic lesions were observed in any of the central or peripheral nervous system tissues examined from 5 animals/sex in the 2000 ppm group males or 1000 ppm group females. All findings observed were consistent with normal background lesions in clinically normal rats of the age and strain used in this study, considered spontaneous and incidental in nature, and unrelated to test substance administration. Dark neurons were present in control and treated animals. These dark neurons were considered a common artifact due to fixation of neurons (Kherani, 2008).

Key result

Dose descriptor:

NOEL

Effect level:

1 000 ppm

Based on:

test mat.

Sex:

female

Basis for effect level:

other: Neurotoxicity

Remarks on result:

other: Equivalent to 79 mg/kg bw/day

Key result

Dose descriptor:

NOEL

Effect level:

2 000 ppm

Based on:

test mat.

Sex:

male

Basis for effect level:

other: Neurotoxicity

Remarks on result:

other: Equivalent to 135 mg/kg bw/day

Key result

Dose descriptor:

NOEL

Effect level:

500 ppm

Based on:

test mat.

Sex:

male

Basis for effect level:

other: Systemic toxicity

Remarks on result:

other: Equivalent to 33 mg/kg bw/day. The NOEL for systemic toxicity in female rats was 1000 ppm, equivalent to 79 mg/kg bw/day.

Key result

Critical effects observed:

no

The average doses over the period of 13 weeks were 19, 40 and 79 mg/kg bw/day for females receiving diet containing 250, 500 or 1000 ppm. The average doses over the period of 13 weeks were 33, 67 and 135 mg/kg bw/day for males receiving diet containing 500, 1000 ppm or 2000 ppm. 

Conclusions:

Following dietary exposure over a period of 13 weeks, the NOEL for neurotoxicity was 1000 ppm (79 mg/kg bw/day) in female rats and 2000 ppm (135 mg/kg bw/day) in male rats.

Executive summary:

The potential neurotoxic effects of the substance when administered continuously in the diet to rats for 13 weeks was studied under GLP to OECD TG 424. The substance was mixed into the rodent diet and offered on a continuous basis for approximately 13 weeks to female and male Crl:CD(SD) rats in at concentrations of 500, 1000, and 2000 ppm
for males and 250, 500, and 1000 ppm for females. A concurrent control group was offered the basal diet on a comparable regimen. Animals were approximately 6 weeks old at the initiation of test diet administration. Each group consisted of 12 rats/sex. Mean test substance consumption for males in the 500, 1000, and 2000 ppm groups was 33, 67, and 135 mg/kg/day, respectively, over the entire study (study days 0-91). Mean test substance consumption for females in the 250, 500, and 1000 ppm groups was 19, 40, and 79 mg/kg/day, respectively, over the entire study.
All animals survived to the scheduled necropsy. No prometryn-related clinical findings were noted during the weekly observations.
Findings attributed to treatment with prometryn were limited to statistically significant decreases in mean body weight gain, with corresponding reductions in mean food consumption, for the 1000 and 2000 ppm males. Overall (study days 0-91) mean body weight gain for the 1000 and 2000 ppm males was 16.8% and 20.9% lower than control,
respectively. At the end of treatment (study day 91), the mean absolute body weight for the 1000 and 2000 ppm males was 11.3% and 14.1% lower than control, respectively. Mean absolute body weights, body weight gains, and food consumption for males in the 500 ppm group and females at all dose levels were unaffected by exposure to the substance.
FOB parameters, including home cage, handling, open field, sensory, neuromuscular, and physiological parameters, were unaffected by prometryn exposure. There were no test substance-related effects on mean total and ambulatory LMA counts for males and females at any dose level. No remarkable shifts in the pattern of habituation occurred in any of the test substance-treated groups during the evaluation periods of study weeks 1, 3, 7, and 12. There were no substance-related ophthalmologic changes or macroscopic/microscopic findings. There were no effects on brain weights or brain measurements at any substance concentration.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Effect on neurotoxicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Effect on neurotoxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

The acute neurotoxicity of the substance to rats was studied by administering a single oral dose of 0, 150, 500, and 1500 mg/kg by gavage, respectively, in an aqueous suspension of 0.5% carboxyl-methylcellulose. Body weight losses with corresponding reductions in food consumption, lower absolute body weights and decreased defecation were observed at 1500 mg/kg. A transient body weight loss over the day following dosing was also evident at 500 mg/kg. Males and females in the 500 and 1500 mg/kg groups showed decreased locomotor activity. There were no other treatment-related findings including histopathology examination of the nervous system tissues. As the locomotor activity effects were transient and only observed at the first days, they were likely associated with generalized systemic toxicity and not considered to be due to a neurotoxic potential of the test substance. The NOEL for neurotoxic effects was set at 1500 mg/kg. The NOAEL for systemic toxicity was 500 mg/kg.

In a sub-chronic neurotoxicity study in rats, continuous administration of the substance in the diet at levels of 0, 500, 1000, and 2000 ppm in males (dietary equivalent to 0, 33, 67 and 135 mg/kg bw/day), 0, 250, 500, and 1000 ppm in females (dietary equivalent to 0, 19, 40, 79 mg/kg bw/day) over a period of 13 weeks did not induce signs of neurotoxicity. Findings attributed to treatment were limited to statistically significant decreases in mean body weight gain, with corresponding reductions in mean food consumption, for the 1000 and 2000 ppm males. No treatment related effects were observed in females. The NOEL for sub-chronic neurotoxicity of the test substance was considered to be 135 and 79 mg/kg/day for males and females, respectively. The NOAEL for systemic toxicity was 33 mg/kg/day for males and 79 mg/kg/day for females.

Justification for classification or non-classification

Based on the available information, classification for neurotoxic effects is not warranted according to EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation No. (EC)1272/2008.