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EC number: 216-600-2 | CAS number: 1623-05-8
The repeat dose and reproductive and developmental toxicity potential of the test article was evaluated when administered by whole body inhalation to male and female Sprague Dawley rats for 28 days. The potential for the test article to affect male and female reproductive performance such as gonadal function, mating behavior and conception through day 13 of postnatal life was evaluated followed by a 14 -day recovery period. The study was conducted in compliance with OECD GLP (1997). The test was conducted according to OECD Guideline 422 (2016).The test substance was administered as a 6-hour, whole-body inhalation exposure daily to 3 groups of male and female Crl:CD(SD) rats. The low- and mid-exposure groups (Groups 2–3) each consisted of 10 rats/sex and the high-exposure group (Group 4) consisted of 15 rats/sex. Target exposure levels were 300, 1000, and 4000 parts per million (ppm). A concurrent control group of 15 rats/sex was exposed to humidified, filtered air on a comparable regimen. Overall mean exposure concentrations were 300, 1004, and 4034 ppm for the 300, 1000, and 4000 ppm groups, respectively. Males and females were approximately 10 weeks of age at the beginning of test substance exposure. Males were exposed to the test substance for 14 days prior to mating. Males continued to be exposed throughout the mating period through 1 day prior to euthanasia for a total of 28 days. Females were exposed to the test substance for 14 days prior to pairing and were exposed through Gestation Day 20. Exposure was suspended from Gestation Day 21 through Lactation Day 4 to avoid potential confounding effects on nesting and nursing behavior caused by separation of dams from their litters. Exposure of the F0 females with evidence of mating was re-initiated on Lactation Day 5 for females that delivered and continued through the day prior to euthanasia (Lactation Day 13) for a total of 50–53 days; females that failed to deliver were exposed through the day prior to euthanasia (Post-Mating day 25) for a total of 35–38 days. The extra 5 males and 5 females in the control and high-exposure groups that were not used for mating were exposed beginning on Study Day 0; following 28 days of exposure for males and 49 days of exposure for females, these animals were assigned to a 15-day nonexposure recovery period.
All animals were observed twice daily for mortality and moribundity. Clinical observations, body weights, and food consumption were recorded at appropriate intervals. FOB and motor activity data were recorded for 5 males/group on Study Day 27 and for 5 females/group on Lactation Day 13. All F0 females selected for pairing were allowed to deliver and rear their pups until Lactation Day 14. F1 clinical observations, body weights, and sexes were recorded at appropriate intervals and anogenital distance was recorded on PND 1. To reduce variability among the litters, 8 pups/litter, 4 pups/sex when possible, were randomly selected on PND 4; blood samples for possible thyroid hormone analysis were collected from the culled pups (1/sex/litter). All F1 male pups were evaluated for areolae/nipple anlagen on PND 13. Remaining F1 pups were euthanized on PND 13; blood samples for thyroid hormone analysis were collected and selected organs were weighed from 1 pup/sex/litter. Clinical pathology evaluations (hematology, coagulation, and serum chemistry) were performed on 5 F0 animals/sex/group at the primary necropsy and 5 animals/sex in the control and high-exposure groups at the recovery necropsy. Blood samples for thyroid hormone analysis were collected from F0 males and females at the primary necropsy; only male samples were analyzed. F0 males were euthanized following completion of the mating period or 15-day recovery period and F0 females were euthanized on Lactation Day 14 for females that delivered, Post-Mating Day 25 for females that failed to deliver, or following the 15-day recovery period. Complete necropsies were conducted on all F0 animals, and selected organs were weighed. Selected tissues were examined microscopically from all F0 animals in the control and high-exposure groups at the primary necropsy. In addition, the kidneys and nasal level II were identified as potential target tissues in males and were examined from all males in all groups at the primary and recovery necropsies.
There was no test substance-related mortality noted at any exposure level. One F0 female in the 300 ppm group was found dead on Lactation Day 0; this death was attributed to dystocia and was considered unrelated to test substance exposure. In addition, 1 male in the 4000 ppm group was found dead on the day of the recovery necropsy; the cause of death was undetermined due to the lack of necropsy findings or relevant histopathological changes and therefore was not attributed to test substance exposure. All other F0 and F1 males and females survived to the scheduled necropsies. Test substance-related red material around the nose was noted for F0 males and females in the 1000 and 4000 ppm groups approximately 1 hour following exposure generally throughout the exposure period. This clinical observation generally did not persist to the daily examinations on the following day and was; therefore, not considered adverse. A test substance-related lower mean body weight gain was noted for F0 males in the 4000 ppm group compared to the control group for the overall exposure period (Study Days 0–27) due to a lower mean body weight gain in this group during the first week of exposure. However, mean absolute body weights in the 4000 ppm group F0 males were similar to the control group throughout the study. Therefore, the lower mean body weight gains observed in this group were not considered adverse. Mean body weights and body weight gains in the 4000 ppm group F0 males were similar to the control group during the recovery period. Mean body weights and body weight gains in the 4000 ppm group F0 females were unaffected by test substance exposure during the premating, gestation, and lactation periods. Mean body weights in the 4000 ppm group F0 females were similar to the control group throughout the recovery period. Mean body weights and body weight gains in the 300 and 1000 ppm group F0 males and females and mean food consumption in all test substance-exposed groups were unaffected by test substance exposure throughout the study. Mean F0 male and female mating and fertility indices, F0 male copulation indices, and F0 female conception indices in the 300, 1000, and 4000 ppm groups were unaffected by test substance exposure. The mean number of days between pairing and coitus, gestation length, and the process of parturition were unaffected by test substance exposure. There were no test substance-related effects noted on mean estrous cycle lengths or the mean numbers of implantation sites and unaccounted-for sites in F0 females at any exposure level. No test substance-related effects were noted during the FOB or motor activity evaluations at any exposure level in the F0 generation. There were no test substance-related gross necropsy observations or alterations in clinical pathology parameters (hematology, coagulation, and serum chemistry) were noted for F0 males and females at any exposure level during the primary and recovery evaluations. Mean serum T4 levels in the F0 males were unaffected by test substance exposure. Test substance-related higher mean absolute and relative (to final body and/or brain weight) lung weights were noted for F0 males and females in the 4000 ppm group at the primary necropsy. There were no microscopic correlates for the higher lung weights and the values were generally within the Charles River Ashland historical control data ranges; therefore, the higher mean lung weights were not considered adverse. Mean lung weights in the 4000 ppm F0 males and females were similar to the control group at the recovery necropsy, indicative of complete recovery. At the primary necropsy, lower incidences of tubular basophilia and higher incidences of chronic progressive nephropathy (CPN) were observed in the 4000 ppm group F0 males. As tubular basophilia is the precursor change to the common background finding and spontaneously developing CPN, these incidences demonstrated a non-adverse test article-induced exacerbation in the development of CPN. 1 In addition, CPN and tubular basophilia in the control group males tended to be unilateral while CPN was predominantly bilateral in the 4000 ppm group. In nasal level II, higher incidences of mixed cell inflammation were seen in the 4000 ppm group F0 males at the primary necropsy. The distribution of the inflammation was most commonly associated with the transitional epithelium and in this study the inflammation likely represented non-adverse local irritation directly attributed to test article inhalation. At the recovery necropsy, test article-related CPN persisted in the 4000 ppm group F0 males which was expected considering the progressive nature of this spontaneously developing degenerative condition while, nasal inflammation was observed in a single male indicative of a complete recovery. There were no test substance-related histologic changes noted for F0 males in the 300 and 1000 ppm groups or F0 females at any exposure level. Mean numbers of F1 pups born, live litter size, percentage of males at birth, postnatal survival, the general physical condition of the F1 pups, pup body weights and body weight gains, anogenital distance, and areolae/nipple anlagen counts (males only) in the 300, 1000, and 4000 ppm groups were unaffected by parental test substance exposure. Necropsy findings for F1 pups that died were not suggestive of any association with maternal administration of the test substance. There were no test substance-related changes in mean serum T4 levels or mean thyroid/parathyroid weights in F1 males and females on PND 13.
Based on the results of the study, the No Observed Adverse Effect Concentration for the test article is 43.89 mg/L (4034 ppm).
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