Developmental toxicity assessment of arsenic acid in mice and rabbits.

To evaluate potential effects of exposure to inorganic arsenic throughout major organogenesis, CD-1 mice and New Zealand White rabbits were gavaged with arsenic acid dosages of 0, 7.5, 24, or 48 mg/kg/d on gestation days (GD) 6 through 15 (mice) or 0, 0.19, 0.75, or 3.0 mg/kg/d on GD 6 through 18 (rabbits) and examined at sacrifice (GD 18, mice; GD 29, rabbits) for evidence of toxicity. Two high-dose mice died, and survivors at the high and intermediate doses had decreased weight gains. High-dose-group fetal weights were decreased; no significant decreases in fetal weight or increases in prenatal mortality were seen at other dosages. Similar incidences of malformations occurred in all groups of mice, including controls. At the high dose in rabbits, seven does died or became moribund, and prenatal mortality was increased; surviving does had signs of toxicity, including decreased body weight. Does given lower doses appeared unaffected. Fetal weights were unaffected by treatment, and there were no effects at other doses. These data revealed an absence of dose-related effects in both species at arsenic exposures that were not maternally toxic. In mice, 7.5 mg/kg/d was the maternal No-Observed-Adverse-Effect-Level (NOAEL); the developmental toxicity NOAEL, while less well defined, was judged to be 7.5 mg/kg/d. In rabbits, 0.75 mg/kg/d was the NOAEL for both maternal and developmental toxicity.

Subchronic and developmental toxicity studies of n-butyl propionate vapor in rats.

Two inhalation studies were conducted to evaluate the possible subchronic and developmental toxic effects of n-butyl propionate. In the subchronic study, Sprague-Dawley rats (15/sex/group) were exposed to 0, 250, 750, or 1500 ppm vapor for 6 h/d, 5 d/wk for 13 wk. Five of the rats per sex per group were held after the final exposure for an 8-wk recovery period. Standard parameters of subchronic toxicity were measured throughout the study, and at the end of exposure and recovery periods, necropsies were performed, organs weighed, and tissues processed for microscopic examination. Exposure did not produce marked treatment-related deaths or adversely affect clinical signs, hematology, clinical chemistries, organ weights, or the histology of major visceral organs. The only systemic toxic effects were significant decreases in body weight, body weight gain, and feed consumption that occurred in 1500 ppm group rats. Morphologic changes were limited to the nasal cavity as evidenced by a concentration-related increased incidence and severity of olfactory epithelium degeneration in rats of the 750 and 1500 ppm groups. These degenerative microscopic alterations were primarily confined to the olfactory epithelium within the dorsal portion of the medial meatus, with lesser involvement of the olfactory mucosae overlying the tips of some of the adjacent ethmoturbinates. Both the systemic and nasal cavity effects appeared reversible after exposure ceased. In the developmental toxicity study, pregnant Sprague-Dawley rats (24/group) were exposed to 0, 500, 1000, or 2000 ppm vapor for 6 h/d on gestation d 6-15 and sacrificed on gestation d 20. All treatment-group dams exhibited significant reductions in body weight, body weight gain, and feed consumption. Gestational parameters were equivalent across all groups and there were no treatment-related developmental or teratogenic effects. The no-observed-adverse effects levels (NOAELs) determined for nbutyl propionate were 250 ppm for subchronic toxicity (based on the olfactory epithelium degeneration) and 22000 ppm for developmental toxicity (no developmental effects at top dose tested). Under the conditions of this study, a NOAEL was not determined for maternal toxicity.

Developmental toxicity evaluation of a scrubbing solution used in petroleum refineries.

The developmental toxicity potential of a scrubbing solution used extensively in petroleum refineries to remove CO2 from hydrogen gas streams was evaluated via inhalation. Pregnant female CD (Sprague-Dawley) rats were exposed to aerosols of a "used" scrubbing solution at 0.05, 0.1, 0.2, or 0.3 mg/l for 6 h/d on d 6-19 of pregnancy. Control animals were exposed to filtered air under the same exposure conditions. Dams were sacrificed on d 20 of pregnancy and a laparohysterectomy was performed. The mass median aerodynamic diameter of the aerosol revealed that all particles ranged from 1.6 to 2.8 microm, with geometric standard deviations between 2.0 and 2.3 microm. The overall pregnancy rate was high (>95%) and equivalent across all groups. All pregnant dams had live litters, and 22-24 litters were examined in each group. Treatment-related clinical signs consisted of rales, observed at all exposure levels, and gasping noted only at the 0.3 mg/l exposure level. The occurrence of rales was presumably a localized effect on the respiratory tract and likely due to the irritating properties of the scrubbing solution. Maternal toxicity was exhibited in the 0.3 mg/l group, including reduced body weight, weight gain, and food consumption and one possible treatment-related death on gestation d 17. At scheduled necropsy, there were no treatment-related gross pathological observations and no statistically significant reproductive and developmental effects. The incidences of fetuses with skeletal variations involving the sternum were clustered in two litters at the highest exposure level with atypically low term fetal body weights. Under the conditions of this investigation, potassium carbonate scrubbing solution is not a selective developmental toxicant.

Two-generation reproductive toxicity study of resorcinol administered via drinking water to Crl:CD(SD) Rats.

The potential adverse effects of resorcinol, delivered via drinking water at 0, 120, 360, 1000, and 3000 mg/L (palatability limit), were assessed in a regulatory guideline compliant two-generation reproduction study in Crl:CD(SD) rats. Expanded end points of thyroid gland (TG) function were added because of clinical case reports indicating human TG toxicity. Average daily resorcinol intake (mg/kg) at the 3000 mg/L concentration was 233 in F0 and F1 males, whereas in females it was 304 (premating/gestation) and 660 (lactation). No resorcinol ingestion-related clinical signs of toxicity were observed. Furthermore, neither gross morphologic anomalies nor effects on reproductive function or thyroid hormone levels were detectable. Body weight reductions occurred in 3000 mg/L F0 and F1 animals and were more pronounced in males. However, there was no evidence of either cumulative toxicity in the second generation or of enhanced sensitivity to resorcinol in pregnant/lactating females. Water intake was lower in 3000 mg/L rats of both generations and intermittently, to a lesser extent, at 1000 mg/L; however, concurrent feed intake and utilization were unaffected. Decreased TG follicular colloid content (conventional histopathology; confirmed by quantitative stereomicroscopy) in the 3000 mg/L F0 males was attributed to resorcinol but not considered adverse. The 3000 mg/L intake level appeared to have caused an adaptive thyroid response to a new homeostatic level with no adverse physiological consequences in either males (the more susceptible gender) or females. There were no differences in TG histology in F0 rats of either sex at 1000 mg/L. Thus, resorcinol intake at maximum palatability via a route and mode relevant to potential human exposures via contaminated drinking water at presently unknown environmental concentrations caused no detectable adverse effects on any reproduction or TG end points. The 3000 mg/L resorcinol exposure level was the no-observed-adverse-effect level (NOAEL) for parental systemic and offspring toxicity, while 1000 mg/L was the no-observed-effect level (NOEL).

Two-generation reproductive toxicity study of inhaled acrylonitrile vapors in Crl:CD(SD) rats.

To assess the effects of acrylonitrile (AN) exposure on reproduction, Sprague-Dawley rats (25/sex/group) were exposed to vapor atmospheres of AN via whole-body inhalation at concentrations of 0, 5, 15, 45 (two offspring generations) and 90 ppm (one offspring generation), 6 h daily, 1 litter/generation, through F2 weanlings on postnatal day 28. After approximately 3 weeks of direct exposure following weaning, exposure of the F1 animals at 90 ppm was terminated due to excessive systemic toxicity in the males. There were no exposure-related mortalities in adult animals, no functional effects on reproduction or effects on reproductive organs, and no evidence of cumulative toxicity or of enhanced toxicity in pregnant and lactating dams or in developing animals. Adult systemic toxicity was limited to body weight and/or food consumption deficits in both sexes and generations (greater in males) at 45 and 90 ppm and increased liver weights in the 90 ppm F0 males and females and 45 ppm F1 males. Neonatal toxicity was expressed by F1 offspring weight decrements at 90 ppm. Clinical signs of local irritation during and immediately following exposure were observed at 90 ppm. Microscopic lesions of the rostral nasal epithelium, representing local site-of-contact irritation, were observed in some animals at 5 to 45 ppm. The no-observed-adverse-effect level (NOAEL) for reproductive toxicity over two generations and neonatal toxicity of AN administered to rats via whole-body inhalation was 45 ppm. The NOAEL for reproduction was 90 ppm for the first generation. The NOAEL for parental systemic toxicity was 15 ppm.

Teratogenic assessment of 2,4-dichlorophenol in Fischer 344 rats.

The potential maternal, embryotoxic, and teratogenic parameters of 2,4-dichlorophenol (2,4-DCP) were evaluated in Fischer 344 rats following oral administration in corn oil on Days 6 through 15 of gestation. Dose levels were 0, 200, 375, and 750 mg/kg/day. Females were sacrificed on Gestation Day 20 and cesarean sections performed. The fetuses were weighed, sexed, measured for crown-rump length, and examined for external malformations. A skeletal examination was conducted on one-half of the fetuses after staining with alizarin red S. The remaining fetuses were fixed in Bouin's solution and examined for visceral anomalies and developmental variations. Maternal body weight gain inhibition occurred in all 2,4-dichlorophenol-treated groups during the treatment period. Four treatment-related deaths occurred in the 750 mg/kg/day group. Additional indicators of maternal toxicity included urogenital staining of the fur at all levels tested, and an increased incidence of hair loss and respiratory rales at the 750 mg/kg/day level. Fetal examinations did not reveal differences in the incidence of external, visceral, or skeletal fetal malformations in any treatment group, when compared with the control group. A slight increase in early embryonic death occurred in the high-dose group only. Fetal weights were lower in the high-dose group than in the control group. Variations in skeletal structure were expressed among fetuses exposed to 750 mg/kg/day during organogenesis. These included delayed ossification of sternal elements and vertebral arches. The reduced fetal weights, intrauterine survival, and retarded ossification may represent a slight degree of embryotoxicity or fetotoxicity in this group. The test material was not teratogenic at any dose level.

Safety assessment of DHA-rich microalgae from Schizochytrium sp.

Schizochytrium sp. (DRM) contains oil rich in highly unsaturated fatty acids (PUFAs). Docosahexaenoic acid (DHA) is the most abundant PUFA component of the oil (approx. 35% w/w). DHA-rich extracted oil from Schizochytrium sp. is intended for use as a nutritional ingredient in foods. As part of a comprehensive safety assessment program, the developmental toxicity of DRM was assessed in Sprague-Dawley derived rats [25/group, provided DRM in the diet at 0.6, 6, and 30% on gestation days (GD) 6-15] and in New Zealand White (NZW) rabbits (22/group, dosed with DRM at levels of 180, 600, and 1800 mg/kg/day by oral gavage on GD 6-19). Fish oil was used as a negative control at dose levels to provide an equivalent amount of fat to that received by the high-dose DRM rabbits. Maternal food consumption, body weights, and clinical signs were recorded at regular intervals throughout these studies. Animals were sacrificed on GD 20 (rats) and GD 29 (rabbits) and examined for implant status, fetal weight, sex, and morphologic development. No clinical signs of toxicity were observed. Maternal exposure to DRM during organogenesis did not adversely affect the frequency of postimplantation loss, mean fetal body weight/litter, or external, visceral, or skeletal malformations in either the rat or the rabbit. In the rats, neither maternal nor developmental toxicity was observed at any dietary concentration of DRM. Thus, 22 g/ kg/day(1) of DRM administered in the feed to pregnant rats during organogenesis was the NOEL (no-observed-effect level) for both maternal and developmental toxicity. In rabbits, no maternal toxicity was expressed at DRM dose levels of 180 and 600 mg/kg/day. As a possible consequence of the high-fat content of the fish oil and DRM, reductions in food consumption and body weight gain and a slight increase in abortions occurred in the fish oil control and 1800 mg/kg/day DRM groups. Developmental toxicity was not observed at any DRM dose level. Based on the results of this study, the NOEL for maternal toxicity of DRM was 600 mg/kg/day, and the NOEL for developmental toxicity was 1800 mg/kg/day in NZW rabbits.

Comparative effects of single intraperitoneal or oral doses of sodium arsenate or arsenic trioxide during in utero development.

Numerous studies have suggested that single-day intraperitoneal (IP) injection of inorganic arsenic results in failure of neural tube closure and other malformations in rats, hamsters, and mice. Most of these studies involved treatment of limited numbers of animals with maternally toxic doses of arsenic (generally As(V)), without defining a dose-response relationship. In the present Good Laboratory Practice-compliant study, sodium arsenate (As(V)) was administered IP and arsenic trioxide (As(III)) was administered either IP or orally (by gavage) on gestational day 9 to groups of 25 mated Crl:CD(R)(SD)BR rats. Only at dose levels that caused severe maternal toxicity, including lethality, did IP injection of arsenic trioxide produce neural tube and ocular defects; oral administration of higher doses of arsenic trioxide caused some maternal deaths but no treatment-related fetal malformations. In contrast, IP injection of similar amounts of sodium arsenate (based on the molar amount of arsenic) caused mild maternal toxicity but a large increase in malformations, including neural tube, eye, and jaw defects. In summary, neural tube and craniofacial defects were observed after IP injection of both As(V) and As(III); however, no increase in malformations was seen following oral administration of As(III), even at maternally lethal doses. These results demonstrate that the frequently cited association between prenatal exposure to inorganic arsenic and malformations in laboratory animals is dependent on a route of administration that is not appropriate for human risk assessment.

Inhalation two-generation reproductive toxicity study of methyl isobutyl ketone in rats.

To evaluate whether methyl isobutyl ketone (MIBK) affects reproductive performance, a two-generation reproduction study was conducted. MIBK was administered to 30 Sprague-Dawley rats/sex/group via whole-body inhalation at concentrations of 0, 500, 1000, or 2000 ppm, 6 h daily, for 70 days prior to mating. F(0) and F(1) females were exposed from mating through gestation day 20 and from postnatal day 5; F(2) litters were maintained through postnatal day 21. No treatment-related mortality of adult animals occurred. There was a dose-related increase in adult animals with no or a decreased response to a sound stimulus at 1000 and 2000 ppm; however, no adverse clinical signs occurred 1 h after exposure, suggesting this was a transient sedative effect. Clinical signs of central nervous system (CNS) depression in the pups were observed and one F(1) pup died after initial exposure to 2000 ppm on postnatal day 22; subsequently exposure was delayed until postnatal day 28. Decreased body weight gain and slight decreased food consumption were observed during the first 2 weeks of exposure in both generations at 2000 ppm. There were no adverse effects on male and female reproductive function or landmarks of sexual maturation. Increased F(0) and F(1) liver weights with associated centrilobular hypertrophy occurred in rats at 2000 ppm, indicative of an adaptive response. Increased male kidney weights at all exposure concentrations, associated with hyaline droplets, were indicative of male rat-specific nephropathy. Other than acute sedative effects, the no-observed-adverse-effect level (NOAEL) for parental systemic effects (excluding male rat kidney) was 1000 ppm, based on transient decreased body weight and food consumption; for reproductive effects, 2000 ppm, the highest concentration tested; and for neonatal toxicity, 1000 ppm (based on acute CNS depressive effects).