The developmental toxicity of inhaled methanol in the CD-1 mouse, with quantitative dose-response modeling for estimation of benchmark doses.

The developmental toxicity of the alternative motor vehicle fuel methanol was assessed in mice by the inhalation route. Pregnant CD-1 mice were exposed to 1,000, 2,000, 5,000, 7,500, 10,000, or 15,000 ppm methanol for 7 hr/day on days 6-15 of gestation. Sham-exposed controls were exposed to filtered air under similar conditions. Additional control groups were left in their home cages either unhandled or food-deprived for 7 hr/day to match the food deprivation experienced by the exposed mice. Dams were observed twice daily and weighed on alternate days during the exposure period. Blood methanol concentrations were determined in some mice on gestation days 6, 10, and 15. On day 17, the remaining mice were weighed and killed and the gravid uteri removed. Implantation sites, live and dead fetuses and resorptions were counted, fetuses were examined externally and weighed as a litter. Half of each litter was examined for skeletal morphology and the other half of each litter was examined for internal soft tissue anomalies. One dam died in each of the 7,500, 10,000, and 15,000 ppm methanol exposure groups, but no dose-response relationship was evident for maternal death. The sham-exposed and food-deprived controls as well as all methanol exposed dams gained less weight than did unexposed dams fed ad libitum, but methanol did not exacerbate this effect. Significant increases in the incidence of exencephaly and cleft palate were observed at 5,000 ppm and above, increased embryo/fetal death at 7,500 ppm and above (including an increasing incidence of full-litter resorptions), and reduced fetal weight at 10,000 ppm and above. A dose-related increase in cervical ribs or ossification sites lateral to the seventh cervical vertebra was significant at 2,000 ppm and above. Thus, the NOAEL for the developmental toxicity in this study was 1,000 ppm. A log-logistic dose response model was applied to the incidence data for exencephaly, cleft palate, resorption and cervical rib, and maximum likelihood estimates (MLEs) and benchmark dosages (BDs, the lower 95% confidence interval of the MLEs) corresponding to 1% and 5% added risk above background were calculated. The MLE for 5% added combined risk of having either exencephaly or cleft palate or being resorbed was 3667 ppm, and the corresponding BD was 3,078 ppm. For cervical rib, the 5% added risk values for the MLE and BD were 824 and 305 ppm, respectively. The BDs for 1% added risk were 1915 ppm for exencephaly, cleft palate or resorption, and 58 ppm for cervical rib.(ABSTRACT TRUNCATED AT 400 WORDS)

Developmental effects of methyl benzimidazolecarbamate following exposure during early pregnancy.

Methyl 2-benzimidazolecarbamate (MBC) and its parent compound benomyl are used as agricultural fungicides. Both chemicals are embryotoxic if administered during organogenesis, and benomyl is teratogenic. Based on a previous study indicating a lack of maternal effects of MBC following exposure during early pregnancy, the current experiments were designed to evaluate the effect of exposure to MBC during early pregnancy on developmental parameters of offspring. Rats were administered MBC at 0, 100, 200, 400, or 600 mg/kg/day during Days 1-8 of pregnancy and killed on Day 11 or Day 20 of gestation. On Day 11, embryos were assessed for survival rate, growth parameters, and anomalies. On Day 20, standard developmental toxicity evaluations were performed. Doses of 200 to 600 mg/kg/day MBC reduced embryonic survival by Day 11; exposure to MBC at 100 to 600 mg/kg/day reduced the number of fetuses surviving on Day 20. Evidence of developmental delay was apparent on Day 11 at all doses, and fetal weight was reduced by Day 20. MBC produced a dose-dependent increase in developmental defects seen on Day 11 and in several malformations observed on Day 20. MBC exposure during the first week of pregnancy was shown to be embryotoxic, resulting in embryonic death, growth retardation, and developmental abnormalities when evaluated on Days 11 or 20 of gestation.

Developmental toxicity of bromoxynil in mice and rats.

The developmental toxicity of the wide-spectrum herbicide bromoxynil (bromoxynil phenol; 3,5-dibromo-4-hydroxyphenyl cyanide) was evaluated in Sprague-Dawley rats and Swiss-Webster mice, and the developmental toxicity of its octanoate ester (2,6-dibromo-4-cyanophenyl octanoate) was evaluated in Sprague-Dawley rats. Animals were treated from Day 6 to Day 15 of gestation [presence of sperm or semen plug = 0 of gestation]. The doses administered were as follows: bromoxynil phenol in the mouse, 342, 114, and 38 mumol/kg/day; bromoxynil phenol and bromoxynil octanoate in the rat, 54, 18, and 6 mumol/kg/day. Some animals were killed on selected days during treatment for measurement of organ weights sensitive to stress. In mice treated with bromoxynil phenol, maternal mortality was noted at 114 and 342 mumol/kg/day, but surviving females gained weight normally. Liver to body weight ratios increased with increasing dose, but no consistent effect was seen on adrenal, thymus, or spleen weights. Fetuses of mice treated with the highest dose of bromoxynil phenol were of lower weight and had a higher incidence of supernumerary ribs than controls. In rats, bromoxynil phenol and its octanoate ester at the highest doses used caused no mortality but resulted in only transient decreases in maternal weight gain and significantly increased the liver to body weight ratio, but did not significantly alter adrenal, thymus, or spleen weight in the dams. No significant maternal effects were seen at lower doses. The highest doses of both compounds increased the incidence of supernumerary ribs in fetuses of treated rats, but did not induce other anomalies.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of dinocap on otolith development: evaluation of mouse and hamster fetuses at term.

The morphology of otoliths in CD-1 mouse and Syrian hamster fetuses exposed to the fungicide dinocap were evaluated at the end of gestation. Pregnant mice were dosed by gavage with 0, 10, 15, 30, or 60 mg/kg/day dinocap in corn oil on days 7-16 of gestation. Pregnant hamsters were dosed by the same route with 0, 50, 100, or 200 mg/kg/day on days 7-14 of gestation. At the end of gestation (day 18 in mice, day 15 in hamsters) dams were killed and all fetuses were removed and fixed overnight in 70% ethanol. Fetal heads were then removed, left in 70% ethanol for at least 3 days, and then dehydrated in a graded ethanol series and cleared with methyl salicylate. Otoliths were examined by darkfield microscopy, and each otolith was scored for morphological completeness on a scale of 0 to 3. Otolith development was complete by day 18 of gestation in control mouse fetuses. Otolith development was complete in many, but not all, of the hamster fetuses by day 15 of gestation. In the mouse, dinocap exposure inhibited fetal otolith formation in a dose-related manner, with a significant effect on total otolith score occurring at 10 mg/kg/day and above. Dinocap affected otolith formation in the hamster only at 100 mg/kg/day (200 mg/kg/day was embryolethal), concomitant with severe maternotoxicity and fetotoxicity.(ABSTRACT TRUNCATED AT 250 WORDS)