Oral (drinking water) two-generation reproductive toxicity study of dibromoacetic acid (DBA) in rats

In a two-generation study of dibromoacetic acid (DBA), Crl SD rats (30 rats/sex/group/generation) were provided DBA in drinking water at 0 (reverse osmosis-deionized water), 50, 250, and 650 ppm (0, 4.4 to 11.6, 22.4 to 55.6, and 52.4 to 132.0 mg/kg/day, respectively; human intake approximates 0.1 microg/kg/day [0.0001 mg/kg/day]). Observations included viability, clinical signs, water and feed consumption, body and organ weights, histopathology, and reproductive parameters (mating, fertility, abortions, premature deliveries, durations of gestation, litter sizes, sex ratios and viabilities, maternal behaviors, reproductive organ weights, sperm parameters and implantation sites, sexual maturation). Histopathological evaluations were performed on at least 10 P and F1 rats/sex at 0 and 650 ppm (gross lesions, testes, intact epididymis; 10 F1 dams at 0, 250, and 650 ppm for primordial follicles). Developmental observations included implantations, pup numbers, sexes, viabilities, body weights, morphology, and reproductive performance. At 50 ppm and higher, both sexes and generations had increased absolute and relative liver and kidneys weights, and female rats in both generations had reduced absolute and relative adrenal weights; adrenal changes were probably associated with physiological changes in water balance. The livers and kidneys (10/sex/group/generation) had no histopathological changes. Other minimal effects at 50 ppm were reduced water consumption and a transient reduction in body weight. At 250 and 650 ppm, DBA reduced parental water consumption, body weight gains, body weights, feed consumption, and pup body weights. P and F1 generation male rats at 250 and 650 ppm had altered sperm production (retained step 19 spermatids in stages IX and X tubules sometimes associated with residual bodies) and some epididymal tubule changes (increased amounts of exfoliated spermatogenic cells/residual bodies in epididymal tubules, atrophy, and hypospermia), although inconsistently and at much lower incidences. Unilateral abnormalities of the epididymis (small or absent epididymis) at 650 ppm in four F1 generation male rats were considered reproductive tract malformations. The no-observable-adverse-effect level (NOAEL) and reproductive and developmental NOAELs for DBA were at least 50 ppm (4.5 to 11.6 mg/kg/day), 45,000 to 116,000 times the human adult exposure level. Reproductive and developmental effects did not occur in female rats exposed to DBA concentrations as high as 650 ppm. Based on the high multiples of human exposure required to produce effects in male rats, DBA should not be identified as a human reproductive or developmental risk.     

Oral (drinking water) developmental toxicity studies of bromodichloromethane (BDCM) in rats and rabbits

Crl:CD(SD)IGS BR VAF/Plus (Crl SD) rats and Hra(NZW) SPF rabbits were tested for potential developmental toxicity from bromodichloromethane (BDCM) provided continuously in the drinking water during gestation (gestation days [GDs] 6 to 21 in rats and GDs 6 to 29 in rabbits). Concentrations of 0, 50, 150, 450, or 900 ppm of BDCM were used for rats; 0, 15, 150, 450, or 900 ppm were used for rabbits (in dose range-finding studies, 1350 ppm was excessively maternotoxic to both species). Investigated maternal parameters included viability, clinical signs, water and feed consumption, and body weights. Maternal gross lesions, gravid uterine weights, abnormal placentas, and numbers of corpora lutea, implantation sites, live and dead fetuses, and early and late resorptions were observed at time of Caesarean sectioning (GD 21 in rats; GD 29 in rabbits). Body weights, sex ratios, and morphological abnormalities (external, soft tissue, and skeletal) were noted in the fetuses. Mean consumed doses of BDCM were calculated to be 0, 2.2, 18.4, 45.0, or 82.0 mg/kg/day for the rats, and 0, 1.4, 13.4, 35.6, or 55.3 mg/kg/day for the rabbits (approximate human intake is 0.8 microg/kg/day [0.0008 mg/kg/day] in adults). In pregnant rats, toxicologically important, statistically significant effects included reduced absolute (g/day) and relative (g/kg/day) water consumption values at > or =50 ppm (2.2 mg/kg/day) and reduced body weight gains (also when corrected for gravid uterine weight) and absolute (g/day) and relative (g/kg/day) feed consumption values at >450 ppm (45.0 mg/kg/day). These parameters were also significantly reduced at > or =450 ppm (35.6 mg/kg/day) in pregnant rabbits (significant weight loss occurred in the rabbits at 900 ppm, i.e., 55.3 mg/kg/day). Thus, the maternal no-observable-adverse-effect level (NOAEL) for BDCM was 150 ppm, i.e., 18.4 and 13.4 mg/kg/day in rats and rabbits, respectively. No adverse effects on embryofetal viability, growth, sex ratio, gross external, soft tissue, or skeletal morphology occurred at 900 ppm in rats or rabbits. Minimal delays in the ossification of forepaw phalanges and hindpaw metatarsals and phalanges occurred in rat fetuses at 900 ppm; delays were considered marginal, reversible, and associated with severely reduced maternal weight gain. Therefore, the developmental NOAEL for rats was 450 ppm (45.0 mg/kg/day), whereas in rabbits it was 900 ppm (55.3 mg/kg/day). These NOAELs are 56,250 and 69,120 times the human adult exposure level of 0.0008 mg/kg/day, respectively. Based on the results of these studies, BDCM should not be identified as a risk to development of human conceptuses.     

Biodisposition of dibromoacetic acid (DBA) and bromodichloromethane (BDCM) administered to rats and rabbits in drinking water during range-finding reproduction and developmental toxicity studies

Dibromoacetic acid (DBA) and bromodichloromethane (BDCM), by-products of chlorine disinfection of water, were provided in drinking water in range-finding reproductive/developmental toxicity studies (rats) and a developmental toxicity study (BDCM) in rabbits. Studies included absorption and biodisposition of DBA and BDCM, including passage into placentas, amniotic fluid, fetuses (rats and rabbits), or milk (rats). The DBA and BDCM range-finding reproductive/developmental toxicity studies each included 50 Sprague-Dawley rats/sex/group. DBA (0, 125, 250, 500, or 1000 ppm) or BDCM (0, 50, 150, 450, or 1350 ppm) was provided in drinking water 14 days premating through gestation and lactation (63 to 70 days). The developmental toxicity range-finding study included 25 time-mated New Zealand white rabbits/group given 0, 50, 150, 450, or 1350 ppm BDCM in drinking water on gestation days (GDs) 6 through 29. Satellite groups (6 male, 17 female rats/group/study and 4 rabbits/group) were used for bioanalytical sampling. Rats and rabbits had exposure-related reduced water consumption caused by apparent taste aversion to DBA or BDCM, especially in the parental animals at the two highest exposure levels (500 and 1000 ppm DBA; 450 and 1350 ppm BDCM). Female rats consumed slightly higher mg/kg/day doses of DBA than male rats, especially during gestation and lactation; weanling rats consumed the highest mg/kg/day doses. DBA produced detectable and quantifiable concentrations in plasma, placentas, amniotic fluid, and milk. Plasma samples confirmed that rats drink predominately during the dark; this drinking pattern, not accumulation, produced detectable plasma concentrations for 18 to 24 hours/day. No quantifiable concentrations of BDCM occurred in plasma, placentas, amniotic fluid, or milk, suggesting that BDCM is rapidly degraded or metabolized in vivo. DBA (500 and 1000 ppm, rats) and BDCM (450 and 1350 ppm, rats and rabbits) produced secondary toxicity in the parental generation by reducing water consumption, which caused severe exposure-related apparent dehydration, reduced feed intake and weight gain. Reproductive and developmental parameters were essentially unaffected (mating possibly reduced [DBA at 1000 ppm]; exposure-related decreases in body weights of pups secondary to reduced water and feed consumption [DBA at 250, 500, and 1000 ppm; BDCM at 150, 450, and 1350 ppm]). No effects on development of rabbit fetuses occurred at BDCM concentrations as high as 1350 ppm. Results from these preliminary studies, in which DBA and BDCM were provided in the drinking water at concentrations thousands of times higher than those to which humans are exposed, suggest that neither DBA nor BDCM are reproductive/developmental risks for humans.     

Reproductive toxicity of MCPA (4-chloro-2-methylphenoxyacetic acid) in the rat

The reproductive effects of the administration of 4-chloro-2-methylphenoxyacetic acid (MCPA) to rats were evaluated through two generations, from prior to mating, throughout mating, to gestation and lactation. MCPA was administered in the diet at doses of 0, 50, 150, or 450 ppm to 25 male and female immature rats (F0 parents) for 10 weeks. F0 parents were then mated to produce a first litter (F1a), retained only until weaning, and were subsequently remated to produce a second litter, F1b. Groups of male and female F1b animals were then dosed as were their parents for 10 weeks postweaning, and the breeding was repeated to produce F2a and F2b animals. The study concluded with the F2b weanlings. MCPA was administered continuously throughout the study. Only minimal, non-treatment-related observations were noted, which included rhinorrhea (in both treated and control animals in the F0 generation) and malocclusion and alopecia (in both the F0 and F1b generations). There were no consistent dose-related effects on reproductive function for parental animals of either sex in either generation. Statistically significant differences were noted in body weights and body weight gains in the 450-ppm dose group for both male and female pups in F2a and F2b. There were no treatment-related macroscopic or microscopic observations noted for any animal in this study. The no-observable-effect level (NOEL) for reproductive function in rats administered MCPA continuously for two successive generations was determined to be 450 ppm (approximately 22 mg/kg/day). The NOEL for general systemic toxicity, based on body weight effects in adult animals in the F1b generation was 150 ppm. The NOEL for effects on the offspring of the F1b generation, manifested as reduced pup weights and pup weight gains was also 150 ppm (approximately 8 mg/kg/day). Based upon the results of this study, MCPA, administered for two generations to Crl:CD(SD)BR Albino rats, is considered not to be a reproductive toxicant.     

Three-generation reproductive toxicity study of dietary bisphenol A in CD Sprague-Dawley rats.

Bisphenol A (BPA) was evaluated at concentrations of 0, 0.015, 0.3, 4.5, 75, 750, and 7500 ppm ( approximately 0.001, 0.02, 0.3, 5, 50, and 500 mg/kg/day of BPA) administered in the diet ad libitum to 30 CD((R)) Sprague-Dawley rats/sex/dose for 3 offspring generations, 1 litter/generation, through F3 adults. Adult systemic toxicity at 750 and 7500 ppm in all generations included: reduced body weights and body weight gains, reduced absolute and increased relative weanling and adult organ weights (liver, kidneys, adrenals, spleen, pituitary, and brain), and female slight/mild renal and hepatic pathology at 7500 ppm. Reproductive organ histopathology and function were unaffected. Ovarian weights as well as total pups and live pups/litter on postnatal day (PND) 0 were decreased at 7500 ppm, which exceeded the adult maximum tolerated dose (MTD). Mating, fertility, gestational indices; ovarian primordial follicle counts; estrous cyclicity; precoital interval; gestational length; offspring sex ratios; postnatal survival; nipple/areolae retention in preweanling males; epididymal sperm number, motility, morphology; daily sperm production (DSP), and efficiency of DSP were all unaffected. At 7500 ppm, vaginal patency (VP) and preputial separation (PPS) were delayed in F1, F2, and F3 offspring, associated with reduced body weights. Anogenital distance (AGD) on PND 0 was unaffected for F2 and F3 males and F3 females (F2 female AGD was increased at some doses, not at 7500 ppm, and was considered not biologically or toxicologically relevant). Adult systemic no observed adverse effect level (NOAEL) = 75 ppm (5 mg/kg/day); reproductive and postnatal NOAELs = 750 ppm (50 mg/kg/day). There were no treatment-related effects in the low-dose region (0.001-5 mg/kg/day) on any parameters and no evidence of nonmonotonic dose-response curves across generations for either sex. BPA should not be considered a selective reproductive toxicant, based on the results of this study.     

Reproductive toxicity evaluation of dietary butyl benzyl phthalate (BBP) in rats

Butyl benzyl phthalate (BBP) was administered in the diet at 0, 750, 3750, and 11,250 ppm ad libitum to 30 rats per sex per dose for two offspring generations, one litter/breeding pair/generation, through weaning of F2 litters. Adult F0 systemic toxicity and adult F1 systemic and reproductive toxicity were present at 11,250 ppm (750 mg/kg per day). At 11,250 ppm, there were reduced F1 and F2 male anogenital distance (AGD) and body weights/litter during lactation, delayed acquisition of puberty in F1 males and females, retention of nipples and areolae in F1 and F2 males, and male reproductive system malformations. At 3750 ppm (250 mg/kg per day), only reduced F1 and F2 offspring male AGD was present. There were no effects on parents or offspring at 750 ppm (50 mg/kg per day). The F1 parental systemic and reproductive toxicity no observable adverse effect level (NOAEL) was 3750 ppm. The offspring toxicity NOAEL was 3750 ppm. The offspring toxicity no observable effect level (NOEL) was 750 ppm, based on the presence of reduced AGD in F1 and F2 males at birth at 3750 ppm, but no effects on reproductive development, structures, or functions.     

Oral (gavage) two-generation (one litter per generation) reproduction study of pentachlorophenol (penta) in rats

The potential for pentachlorophenol (penta) to induce general and reproductive/developmental toxicity was evaluated in Crl Sprague-Dawley rats, employing a two-generation reproduction toxicity study. Penta was administered by gavage at doses of 0, 10, 30, and 60 mg/kg/day. In both generations, the parental animals (30/sex/group) were intubated daily for 10 weeks before cohabitation and continuing through cohabitation, gestation, and lactation periods. Intubation of the F1 generation was begun 28 days postpartum. Animals were evaluated daily for mortality and general toxicity (clinical observations, body weights and gains, feed consumption). Organ weights were recorded and histopathological evaluations were made. Specific indices of reproductive function evaluated included estrous cycles, mating and fertility, parturition, lactation, viability, and growth and development of offspring, including sexual maturation, sperm parameters, and numbers of ovarian primordial follicles. All deaths in the parental rats were unrelated to penta. Expected metabolic effects of penta, sporadic increased liver weights associated with hepatocellular centrilobular hypertrophy and vacuolation and lipofuscin pigmentation, were evident in the 10-, 30-, and 60-mg/kg/day dose group P1 and F1 animals. Toxicity, in the form of liver pathology (single cell necrosis), reduced body weights and associated reductions in organ weights, and reduced feed consumption were noted in both generations at the 30- and 60-mg/kg/day doses. Developmental toxicity associated with these doses included reduced pup weights and viability. The 60-mg/kg/day dose also resulted in delayed sexual maturation, decreased spermatid counts, small prostates and testes, decreased implantations, reduced fertility, and increased resorptions of embryos. Based on these results, it was concluded that 30 mg/kg/day is the lowest-observable-adverse-effect level (LOAEL) and 10 mg/kg/day is the no-observable-adverse-effect level (NOAEL) for both reproductive and general toxicity. These findings are consistent with results from previously conducted studies wherein reproductive/developmental toxicity was observed only at doses that also induced general toxicity. It differs from previous findings in that the NOAEL for general toxicity is two to three times higher for the more pure product than for products produced and tested previously. In addition, the results did not indicate bioaccumulation of penta. Thus, penta did not selectively affect reproduction or development of the offspring of rats at a dose of 10 mg/kg/day, a dose that is 7000 to 20,000 times higher than human exposure.     

Two-generation reproduction study and immunotoxicity screen in rats dosed with phenol via the drinking water

This study evaluated the potential reproductive toxicity of phenol in a rat two-generation reproduction study, which included additional study endpoints, such as sperm count and motility, developmental landmarks, histological evaluation of suspect target organs (liver, kidneys, spleen, and thymus), weanling reproductive organ weights, and an immunotoxicity screening plaque assay. Phenol was administered to 30 Sprague-Dawley rats/sex/group in the drinking water at concentrations of 0, 200, 1000, or 5000 ppm. Parental (P1) animals were treated for 10 weeks prior to mating, during mating, gestation, lactation, and until sacrifice. The F1 generation (P1 offspring) was treated using a similar regimen, while the F2 generation was not treated. After mating, 10 P1 males/group were evaluated using standard clinical pathology parameters and an immunotoxicity screening plaque assay. Significant reductions in water and food consumption were observed in the 5000-ppm group in both generations; corollary reductions in body weight/body weight gain were also observed. Mating performance and fertility in both generations were similar to controls, and no adverse effects on vaginal cytology or male reproductive function were observed. Vaginal opening and preputial separation were delayed in the 5000-ppm group, and were considered to be secondary to the reduction in F1 body weight. Litter survival of both generations was reduced in the 5000-ppm group. Absolute uterus and prostate weights were decreased in the F1 generation at all dose levels; however, no underlying pathology was observed and there was no functional deficit in reproductive performance. Therefore, these findings were not considered to be adverse. No evidence of immunotoxicity was noted in the 5000-ppm group. The effects noted at the high concentration were presumed to be associated with flavor aversion to phenol in the drinking water. Based on a comprehensive examination of all parameters, the no-observable-adverse-effect level (NOAEL) for reproductive toxicity of phenol administered in drinking water to rats is 1000 ppm. The corresponding daily intake of phenol for an adult rat at the NOAEL of 1000 ppm is equivalent to about 70 mg/kg/day for males and 93 mg/kg/day for females.     

Assessment of adult and neonatal reproductive parameters in Sprague-Dawley rats exposed to propylene glycol monomethyl ether vapors for two generations.

This study evaluated propylene glycol monomethyl ether (PGME) in a rat 2-generation reproduction study, which included non-traditional study end points, such as sperm count and motility, developmental landmarks, estrous cyclicity, and weanling organ weights. Groups of 30 male and 30 female Sprague-Dawley rats (6-weeks-old) were exposed to 0, 300, 1000, or 3000 ppm of PGME vapors via inhalation for 6 hours/day, 5 days/week prior to mating, and 6 hours/day, 7 days/week during mating, gestation, and lactation, for 2 generations. These concentrations corresponded to estimated oral equivalent doses of 0, 396, 1325, or 3974 mg/kg/day. At 3000 ppm, toxicity in the P1 and P2 adults was marked, as evidenced by sedation during and after exposure, and mean body weights which were as much as 21% lower than controls. This marked parental toxicity was accompanied by lengthened estrous cycles, decreased fertility, decreased ovary weights, and histologic ovarian atrophy in maternal rats. In the offspring from these dams, decreased body weights, reduced survival and litter size, slight delays in puberty onset, and histologic changes in liver and thymus in the F1 and F2 offspring were observed. The nature of the reproductive/neonatal effects and their close individual animal correlation with decreased maternal body weights suggested that these effects were secondary to general toxicity and/or nutritional stress. No such reproductive/neonatal effects were observed at 1000 ppm, a concentration which caused less marked, but significant body weight effects without sedation. There were no treatment-related effects of any kind noted at 300 ppm of PGME. Therefore, the no-observable-effect level (NOEL) for reproductive/neonatal effects was 1000 ppm, and that for parental toxicity was 300 ppm.     

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.     

One-generation reproductive toxicity study of dietary 17beta-estradiol (E2; CAS No. 50-28-2) in CD-1 (Swiss) mice

There is no information on reproductive/developmental effects in mice from dietary estrogen. Therefore, 10 adult CD-1^® mice/sex/group were administered dietary 17β-estradiol (E2) at 0, 0.005, 0.05, 0.5, 2.5, 5, 10, and 50 ppm for 2-week prebreed, mating, gestation, lactation. F1 weanlings (3/sex/litter) were necropsied and 2/sex/litter were retained, with exposure, until vaginal patency (VP) or preputial separation (PPS) and then necropsied.

Results included complete infertility at 2.5–50 ppm with normal mating indices. At 0.5 ppm (and above), F0 adult female uterus plus cervix plus vagina weights (UCVW) were increased. At 0.5 ppm: prolonged gestational length; increased F1 stillbirth index; reduced live birth index and litter size; decreased testes and epididymides weights at weaning; unaffected AGD on pnd 0 and 21; delayed PPS; increased undescended testes; unaffected prostate weight; accelerated VP; enlarged vaginas; fluid-filled uteri. At 0.05 ppm: no F0 reproductive effects, increased F1 weanling UCVW; delayed PPS. The NOEL was 0.005 ppm (1 μg/kg/day).     

Two-generation reproductive toxicity evaluation of dietary 17beta-estradiol (E2; CAS No. 50-28-2) in CD-1 (Swiss) mice.

No information exists on reproductive/developmental effects in mice exposed to dietary 17beta-estradiol (E2) over multiple generations. Therefore, under OECD Test Guideline 416 with enhancements, CD-1 mice (F0 generation, 25 mice/sex/group) were exposed to dietary E2 at 0, 0.001, 0.005, 0.05, 0.15, or 0.5 ppm ( approximately 0, 0.2, 1, 10, 30, or 100 mug E2/kg body weight/day) for 8 weeks prebreed, 2 weeks mating, approximately 3 weeks gestation, and 3 weeks lactation. At weaning, selected F1 offspring (F1 parents; 25/sex/group) and extra retained F1 males (one per litter) were exposed to the same dietary concentrations and durations as the F0 generation; study termination occurred at F2 weaning; F1/F2 weanlings (up to three per sex per litter) were necropsied with organs weighed. At 0.5 ppm, effects were increased F1/F2 perinatal loss, prolonged F0/F1 gestational length, reduced numbers of F2 (but not F1) litters/group, reduced F1/F2 litter sizes, accelerated vaginal patency (VP) and delayed preputial separation (PPS), increased uterus + cervix + vagina weights (UCVW) in F0/F1 adults and F1/F2 weanlings, and decreased testes and epididymides weights (TEW) in F1/F2 weanlings. At 0.15 ppm, effects were increased UCVW in F0/F1 adults and F1/F2 weanlings, accelerated VP, delayed PPS, and reduced TEW in F1/F2 weanlings. At 0.05 ppm, UCVW were increased in F1/F2 weanlings, and PPS was delayed only in extra retained F1 males. There were no biologically significant or treatment-related effects on F0/F1 parental body weights, feed consumption, or clinical observations, or on F0/F1 estrous cyclicity, F0/F1 andrology, or F1/F2 anogenital distance at any dose. The no observable effect level was 0.005 ppm E2 ( approximately 1 mug/kg/day). Therefore, the mouse model is sensitive to E2 by oral administration, with effects on reproductive development at doses of 10- 100 mug/kg/day.     

Reproductive and developmental toxicity in F1 Sprague-Dawley male rats exposed to di-n-butyl phthalate in utero and during lactation and determination of its NOAEL

Di-n-butyl phthalate (DBP) is one of the commonly used plasticizers in China. DBP can enter the environment and organisms through various routes and then affect reproductive and developmental processes of the organism and its descendants (mainly affecting male offspring). It is known that animals are sensitive to exposure of DBP in utero and during lactation. In the present study, pregnant rats were treated with different doses of DBP (0, 50, 250, and 500 mg/kg body weight/day) by daily gavage from GD1 to PND21. The developmental condition of F1 rats and the reproductive system of mature F1 male rats were monitored. DBP had no obvious effect on pregnant rats; however, it reduced several parameters including birth weight, number of live pups per litter, body weight gain and male anogenital distance. Severe damage to the reproductive system of mature F1 male rats included testicular atrophy, underdeveloped or absent epididymis, undescended testes, obvious decline of epididymal sperm parameters, total sperm heads per g testis, decrease of organ/body weight ratio of epididymis and prostate, and was observed in the group treated with 250 mg/kg BW/day and higher. These results showed that the male reproductive system was the main target organ of DBP exposure. The NOAEL (no observable adverse effect level) for developmental toxicity of DBP was established based on pup body weight and male reproductive lesions at 50 mg/kg BW/day. Accordingly, the RfD for human exposure to DBP through oral intake was recommended as 500 mg/kg BW/day.     

A toxicologic evaluation of 5-ethoxy-3-trichloromethyl-1,2,4-thiadiazole (ETMT)

The following studies were conducted on 3-ethoxy-3-trichloromethyl-1,2,4-thiadiazole (ETMT, Terrazole), a soil fungicide: acute oral toxicity in rats, rabbits, and dogs; acute and subchronic percutaneous toxicity in rabbits; subchronic feeding to rats and dogs; 2-year feeding to rats and dogs; and a three-generation reproduction study in rats. CD rats, albino rabbits, and mongrel and beagle dogs were employed. The acute oral toxicity values (LD₅₀ ± SD) were: rats, 1077 ± 78 mg/kg; rabbits, 779 ± 532 mg/kg; dogs > 5000 mg/kg (premedicated with morphine). The test material was added to the diet of rats at levels of 0, 78, 156, 312, 625, and 1250 ppm (subchronic study) and 0, 10, 80, and 640 ppm (chronic study and reproductive study); and to the diet of dogs at levels of 0, 100, 400, and 1600 ppm (subchronic study); and 0, 10, 100, and 1000 ppm (chronic study). Three-month feeding in rats resulted only in growth inhibition at 1250 ppm and elevated liver to body weight ratios at 625 and 1250 ppm. Dogs fed 3 months showed a decrease in spleen-to-body weight ratios at all feeding levels and a higher liver-to-body weight ratio at 1600 ppm. No consistent adverse dose-related effects were apparent in the 2-year rat feeding study. The following findings were noted only in dogs that received the 1000-ppm diet: a lesser body weight gain, increases in SAP, SGOT, serum cholinesterase, BSP retention, liver weights; cholestatic hepatosis with secondary bile nephrosis. No adverse effects were apparent at 10 or 100 ppm. In the three-generation reproduction study, no adverse effects were apparent on fertility, gestation, viability, lactation, number of stillborn, and mean number of pups born and weaned per litter. Adverse effects occurred only on the 640-ppm diet and these consisted of lower weaning weights of offspring and depressed body weight gains of parent rats.     

Two-generation reproductive toxicity study of inhaled toluene diisocyanate vapor in CD rats.

Twenty-eight 42-day-old pups/sex/group (F0) were exposed to toluene diisocyanate vapor (TDI; 80% 2,4-TDI, 20% 2,6-TDI) by inhalation at 0.0, 0.02, 0.08, or 0.3 ppm, 6 h/day, 5 days/week, for 10 weeks, then mated within groups for 3 weeks, with exposure 7 days/week during mating, gestation, and lactation. F0 maternal animals were not exposed from gestational day (gd) 20 through postnatal day (pnd) 4; maternal exposures resumed on pnd 5. Twenty-eight weanlings/sex/group continued exposure for 12 weeks (starting on pnd 28) and were bred as described above. F0 and F1 parents and ten F1 and F2 weanlings/sex/group were necropsied, and adult reproductive organs, pituitary, liver, kidneys, and upper respiratory tract (target organs) were evaluated histologically in ten/sex/group. Adult toxicity was observed in both sexes and generations at 0.08 and 0.3 ppm, including occasional reductions in body weights and weight gain, clinical signs of toxicity at 0.08 and 0.3 ppm, and histologic changes in the nasal cavities at 0.02, 0.08, and 0.3 ppm (including rhinitis, a nonspecific response to an irritating vapor, at all concentrations). There was no reproductive toxicity, reproductive organ pathology, or effect on gestation or lactation at any exposure concentration. Postnatal toxicity and reduced body weights and weight gains during lactation occurred only in F2 litters at 0.08 and 0.3 ppm. Therefore, under the conditions of this study, a no observed adverse effect level (NOAEL) was not determined for adult toxicity; the NOAEL for reproductive toxicity was at least 0.3 ppm, and the NOAEL for postnatal toxicity was 0.02 ppm.     

Two-generation reproduction study by dosing with glutaraldehyde in the drinking water of CD rats

Adult male and female CD rats (F0) were dosed with glutaraldehyde (GA; CAS number 111-30-8) in drinking water at concentrations of 0 (controls), 50, 250, or 1000 ppm for a 10-wk prebreed period and through mating, gestation, and lactation. Resultant F1 offspring, selected to be parents of the next generation, were continued on the same regime from prebreed through lactation. Twenty-eight parental animals per sex per generation for each dose group were evaluated for clinical signs, body weight (absolute and gain), and water and food consumption. The offspring were evaluated for survival and body weight to weaning. Necropsy and light microscopic examination of removed tissues were conducted in all F0 and F1 parents and in 10 offspring/sex/group/generation. Average daily consumptions of GA (as mean +/- SD) for the low, intermediate, and high concentrations were respectively 4.25 +/- 0.87, 17.50 +/- 4.16, and 69.07 +/- 14.58 mg/kg/d for F0 parental males, and 6.68 +/- 0.78, 28.28 +/- 4.09, and 98.37 +/- 11.71 mg/kg/d for F0 parental females. The corresponding values for the F1 parents were 4.53 +/- 1.02, 21.95 +/- 4.88, and 71.08 +/- 16.21 mg/kg/d for males and 6.72 +/- 0.84, 29.57 +/- 5.41, and 99.56 +/- 16.72 mg/kg/d for females. There were no effects on parental fertility and mating performance or on pup viability and litter size in any generation. No apparent treatment-related histopathology was seen in parents or offspring. Parental body weights and body weight gains were significantly reduced at 1000 ppm at a few isolated time periods, particularly during prebreed. Food consumption was significantly reduced at 1000 ppm for F0 and F1 parents during the prebreed and gestation periods, and at 250 ppm for F0 males during prebreed and gestation and F1 females during gestation and lactation. Water consumption by the F0 and F1 parents of the 250 at 1000 ppm groups was reduced throughout the prebreed period. At 1000 ppm, average litter weights were reduced over lactation d 21-28 for the F1 and F2 offspring. The no-observed-effect level (NOEL) for adult toxicity was 50 ppm and for offspring 250 ppm. There were no indications of reproductive toxicity, and the NOEL for this study was therefore > 1000 ppm.     

Chronic toxicity of di(2-ethylhexyl)phthalate in mice.

B6C3F1 mice were treated with 0, 100, 500, 1500, or 6000 ppm di(2-ethylhexyl)phthalate (DEHP) in the diet for up to 104 weeks. Blood and urine were analyzed at Weeks 26, 52, 78, and 104 from 10 animals per sex per group. Body weights and food consumption were measured weekly for the first 16 weeks, then monthly thereafter. Survival was reduced for mice receiving 6000 ppm DEHP. Overall weight gains were significantly lower for the 6000-ppm male group, but there was no difference among female groups. Food consumption was not affected by exposure. No biologically significant changes in clinical chemistry, hematology, or urinalysis were observed. After 104 weeks of exposure, kidney weights for the 500- and 1500-ppm male, and 6000-ppm male/female groups were significantly lower than for the controls. Significantly higher liver weight was seen for the 500-, 1500-, and 6000-ppm male groups and the 6000-ppm female group of mice. Testis weights for the 500-, 1500-, and 6000-ppm males were significantly lower than for the controls. Uterine weights for the 6000-ppm group were significantly lower than for the controls. All organs were examined for histopathology. The incidence of hepatocellular lesions has been reported separately (R. M. David et al., 1999. Toxicol. Sci. 50, 195-205). Tumors were observed at > or = 500-ppm dosages, where peroxisome proliferation was significantly increased. A NOEL for both tumors and peroxisome proliferation was 100 ppm. In the study presented here, bilateral hypospermia in the testes of male mice, hepatocyte pigmentation and cytoplasmic eosinophilia in the liver, and chronic progressive nephropathy of male and female mice were observed at 6000 ppm. Hypospermia and chronic progressive nephropathy were also observed at 1500 ppm, where peroxisome proliferation was 2.7-6.8-fold higher than controls. Many lesions observed in rats were not seen in mice. A dose level of 500 ppm (98.5-116.8 mg/kg/day) was identified as a no-observed-adverse-effect level (NOAEL) for noncarcinogenic effects.     

Two-Generation Reproductive Toxicity Study of Dietary Tributyl Phosphate in CD Rats

Tributyl phosphate (TBP) was tested for reproductive toxicityin rats. Thirty weanlings/sex (F0) were exposed to TBP in thediet ad libitum at 0, 200, 700, or 3000 ppm for 10 weeks andthen randomly mated within groups for 3 weeks with continuedexposure. F0 parents and 10 F1 weanlings/sex/dose were necropsied,and adult reproductive organs, urinary bladders (both sexes),kidneys (males), and livers (females) were evaluated histologically.Thirty F1 weanlings/sex/dose continued exposure for 11 weeksand were bred as described above. F1 parents and P2 weanlings,10/sex/dose, were then necropsied as described above. Adulttoxicity was observed in both sexes and generations at 700 and3000 ppm; observations included reduced body weights, weightgain and feed consumption, urinary bladder epithelial hyperplasia(both sexes), renal pelvis epithelial hyperplasia only at 3000ppm (male kidneys), and centrilobular hypertrophy (female livers).At 200 ppm, transient reductions in body weight were observedin F0 and F1 females, with urinary bladder epithelial hyperplasiain F0 males and females and in F1 males. There was no evidenceof reproductive toxicity, of reproductive organ pathology, orof effects on gestation or lactation at any dose tested. Postnataltoxicity was evidenced by consistent reductions in F1 and F2pup body weights at 3000 ppm and by occasional weight reductionsin F2 litters at 700 ppm, and was associated with maternal toxicityobserved at these doses and times. Under the conditions of thisstudy, a NOAEL was not determined for adult toxicity; the NOAELfor reproductive toxicity was at least 3000 ppm and the NOAELfor postnatal toxicity was approximately 200 ppm.     

A two-generation reproductive toxicity study of decamethylcyclopentasiloxane (D5) in rats exposed by whole-body vapor inhalation

This two-generation reproduction study assessed the reproductive hazard potential of decamethylcyclopentasiloxane (D(5)). Sprague-Dawley rats (30/sex/group) were exposed by whole-body vapor inhalation to a target concentration of 30, 70, or 160 ppm D(5) or filtered air for 6h/day. Exposures for the F(0) and F(1) generations started at least 70 days prior to mating and lasted through weaning of the respective pups on postnatal day (PND) 21. Female exposures were interrupted from gestation day (GD) 21 through PND 4 to allow for parturition and to permit continuous maternal care for the early neonates. F(2) pups were not directly exposed to D(5). There were no exposure-related mortalities, clinical signs of toxicity, or effects on body weight or food consumption. There were no treatment-related gross findings or organ weight effects at the F(0) and F(1) necropsies. Other than minimal alveolar histiocytosis in all exposed groups, there were no noteworthy microscopic findings. Reproductive parameters (number of days between pairing and mating, mating and fertility indices, gestation length, and parturition), spermatogenic parameters and ovarian primordial follicle counts and numbers of corpora lutea in the F(0) and F(1) parental animals were not significantly changed between treated and control groups. Mean live litter sizes, number of pups born, sex ratios, pup body weights, postnatal pup survival and general physical condition of offspring in each generation were not affected. The slight, but statistically significant, increase in the mean F(1) male pup AGD in the 160 ppm group was not considered to be related to treatment. Vaginal patency and balanopreputial separation were unchanged compared to controls. Thus, the No-Observed-Adverse-Effect-Level (NOAEL) for parental and reproductive toxicity was determined to be 160 ppm D(5).     

Reproductive Toxicity Evaluation of Methylethyl Ketoxime by Gavage in CD Rats

Methylethyl ketoxime (CAS No. 96-29-7; MEKO; 2-butanone oxime),an antioxidant agent used in paints, resins, and adhesives,was tested for reproductive toxicity in a two-generation studywith CD (Sprague-Dawley) rats. Thirty-eight-week-old rats/sex/group(F0) were administered MEKO in water, by gavage, at 0, 10, 100,or 200 mg/kg/day (at a dosing volume of 2 ml/kg), 5 days/weekfor 10 weeks with vaginal cytology evaluation (VCE) of F0 femalesduring the last 3 weeks of the prebreed period. Animals weremated within groups for 3 weeks with dosing during mating, gestation,and lactation for 7 days/week. F0 parents and F1 weanlings,10/sex/dose, were necropsied (after a 2-week postwean VCE inF0 females) with hematologic evaluation (including methemoglobin)and histology of adult livers, spleens, and reproductive organs.F1 weanlings, 30/sex/dose, were dosed for 11 weeks and matedas described above. Because of poor reproductive performance,not treatment related, F1 animals with no F2a litters were rebredto produce F2b litters. F1 parents and F2a weanlings, 10/sex/dose,were necropsied and evaluated as described above. Inguinal mammaryglands were examined histologically from all nonselected F1and F2 (a and b) female weanlings. Adult toxicity was observedin both generations and both sexes at all doses. Treatment-relatedparental deaths occurred at 200 mg/kg/day. At 100 and 200 mg/kg/day,parents exhibited dose-related reduced body weights and weightgains, reduced feed consumption, clinical signs of toxicity,and anemia with concomitant extramedul-lary hematopoiesis andhemosiderosis in livers and spleens (and increased spleen weights).At 10 mg/kg/day, only adult liver and spleen histologic effectswere present. There was no evidence of reproductive organ ormammary gland pathology or of reproductive or postnatal toxicityat any dose tested. There was no adult "no observable adverseeffect level" (NOAEL) established; the NOAEL for reproductiveand postnatal toxicity was at least 200 mg/kg/day for rats inthis study.