Correction to: Letter to the editor regarding "safety of safety evaluation of pesticides: developmental neurotoxicity of chlorpyrifos and chlorpyrifos-methyl" by Mie et al. (environmental health. 2018. 17:77).

Following publication of the original article.

Postnatal ovary development in the rat: morphologic study and correlation of morphology to neuroendocrine parameters.

Histopathologic examination of the immature ovary is a required end point on juvenile toxicity studies and female pubertal and thyroid function assays. To aid in this evaluation and interpretation of the immature ovary, the characteristic histologic features of rat ovary through the developmental periods are described. These histologic features are correlated with published changes in neuroendocrine profiles as the hypothalamic-pituitary-gonadal axis matures. During the neonatal stage (postnatal day [PND] 0-7), ovarian follicle development is independent of pituitary gonadotropins (luteinizing hormone [LH] or follicle-stimulating hormone [FSH]), and follicles remain preantral. Antral development of "atypical" follicles occurs in the early infantile period (PND 8-14) when the ovary becomes responsive to pituitary gonadotropins. In the late infantile period (PND 15-20), the zona pellucida appears, the hilus forms, and antral follicles mature by losing their "atypical" appearance. The juvenile stage (PND 21-32) is the stage when atresia of medullary follicles occurs corresponding to a nadir in FSH levels. In the peripubertal period (PND 33-37), atresia subsides as FSH levels rebound, and LH begins its bimodal surge pattern leading to ovulation. This report will provide pathologists with baseline morphologic and endocrinologic information to aid in identification and interpretation of xenobiotic effects in the ovary of the prepubertal rat.

Postnatal development of the testis in the rat: morphologic study and correlation of morphology to neuroendocrine parameters.

Histopathologic examination of the testis from juvenile rats is often necessary to characterize the safety of new drugs for pediatric use and is a required end point in male pubertal development and thyroid function assays. To aid in evaluation and interpretation of the immature testis, the characteristic histologic features of the developing rat testis throughout postnatal development are described and correlated with published neuroendocrine parameter changes. During the neonatal period (postnatal day [PND] 3-7), seminiferous tubules contained gonocytes and mitotically active immature Sertoli cells. Profound proliferation of spermatogonia and continued Sertoli cell proliferation occurred in the early infantile period (PND 8-14). The spermatogonia reached maximum density forming double-layered rosettes with Sertoli cells in the late infantile period (PND 15-20). Leptotene/zygotene spermatocytes appeared centrally as tubular lumina developed, and individual tubules segregated into stages. The juvenile period (PND 21-32) featured a dramatic increase in number and size of pachytene spermatocytes with the formation of round spermatids and loss of "infantile" rosette architecture. In the peri-pubertal period (PND 32-55), stage VII tubules containing step 19 spermatids were visible by PND 46. The presented baseline morphologic and endocrinologic information will help pathologists distinguish delayed development from xenobiotic effects, determine pathogenesis when confronted with nonspecific findings, and identify sensitive time points for targeted study design.

Key lessons from performance of the U.S. EPA Endocrine Disruptor Screening Program (EDSP) Tier 1 male and female pubertal assays.

The male and female pubertal assays, which are included in the U.S. Environmental Protection Agency's (EPA) Endocrine Disruptor Screening Program (EDSP) Tier 1 battery, can detect endocrine-active compounds operating by various modes of action. This article uses the collective experience of three laboratories to provide information on pubertal assay conduct, interlaboratory reproducibility, endpoint redundancy, and data interpretation. The various criteria used to select the maximum tolerated dose are described. A comparison of historical control data across laboratories confirmed reasonably good interlaboratory reproducibility. With a reliance on apical endpoints, interpretation of pubertal assay effects as specifically endocrine-mediated or secondary to other systemic effects can be problematic and mode of action may be difficult to discern. Across 21-23 data sets, relative liver weight, a nonspecific endocrine endpoint, was the most commonly affected endpoint in male and female assays. For endocrine endpoints, patterns of effects were generally seen; rarely was an endocrine-sensitive endpoint affected in isolation. In males, most frequently missed EPA-established performance criteria included mean weights for kidney and thyroid, and the coefficient of variation for age and body weight at preputial separation, seminal vesicle weight, and final body weight. In females, the frequently missed EPA-established performance criteria included mean adrenal weight and mean age at vaginal opening. To ensure specificity for endocrine effects, the pubertal assays should be interpreted using a weight-of-evidence approach as part of the entire EDSP battery. Based on the frequency with which certain performance criteria were missed, an EPA review of these criteria is warranted.

An oral developmental neurotoxicity study of decabromodiphenyl ether (DecaBDE) in rats.

BACKGROUND: Decabromodiphenyl ether (DecaBDE; CASRN 1163-19-5) is a flame retardant used in a variety of manufactured products. A single oral dose of 20.1 mg/kg administered to mice on postnatal day 3 has been reported to alter motor activity at 2, 4, and 6 months of age. METHODS: To further evaluate these results, a developmental neurotoxicity study was conducted in the most commonly used species for studies of this type, the rat, according to international validated testing guidelines and Good Laboratory Practice Standards. DecaBDE was administered orally via gavage in corn oil to dams from gestation day 6 to weaning at doses of 0, 1, 10, 100, or 1,000 mg/kg/day. Standard measures of growth, development, and neurological endpoints were evaluated in the offspring. Motor activity was assessed at 2 months of age. Additional motor activity assessments were conducted at 4 and 6 months of age. Neuropathology and morphometry evaluations of the offspring were performed at weaning and adulthood. RESULTS: No treatment-related neurobehavioral changes were observed in detailed clinical observations, startle response, or learning and memory tests. No test substance-related changes were noted in motor activity assessments performed at 2, 4, or 6 months of age. Finally, no treatment-related neuropathological or morphometric alterations were found. CONCLUSIONS: Under the conditions of this study, the no-observed-adverse-effect level for developmental neurotoxicity of DecaBDE was 1,000 mg/kg/day, the highest dose tested.

Toxicological evaluation of the ketogenic ester bis hexanoyl (R)-1,3-butanediol: Subchronic toxicity in Sprague Dawley rats.

Bis-hexanoyl (R)-1,3-butanediol (BH-BD) is novel ketone ester undergoing development as a food ingredient to achieve nutritional ketosis in humans. Male and female Crl:CD(SD) rats were administered BH-BD twice daily at 9000, 12,000 or 15,000 mg/kg/day, by oral gavage in a 90-day toxicity study with 28-day recovery period; and an interim 28-day phase. Test substance-related early deaths occurred in four females at 15,000 mg/kg/day. A dose-dependent increase in acute transient postdose (1-3 h) observations of incoordination at ≥12,000 mg/kg/day and decreased activity at all dose levels were noted in both sexes. Postdose observations were likely associated with peak ketonemia and were considered adverse at 15,000 mg/kg/day. These daily observations decreased over the study without any persistent effects, as determined during weekly pre-dose observations. Adverse histopathological changes included ulceration/erosion in non-glandular stomach at ≥ 12,000 mg/k/day and in glandular stomach at 15,000 mg/kg/day. These histopathological findings were not noted after 28-days of recovery. Due to unlikely human relevance of the rat non-glandular stomach effects for BH-BD and test substance-related mortality at 15,000 mg/kg/day, the no-observed-adverse-effect level (NOAEL) for subchronic toxicity of BH-BD was determined to be 12,000 mg/kg/day.

Effects of dose, administration route, and/or vehicle on decabromodiphenyl ether concentrations in plasma of maternal, fetal, and neonatal rats and in milk of maternal rats.

The effects of route and vehicle on blood and milk levels of decabromodiphenyl ether (DecaBDE; CASRN 1163-19-5) were investigated in the rat to assist in the design and conduct of a developmental neurotoxicity study. Blood plasma and/or milk concentrations were determined in dams, fetuses, and/or nursing pups after repeated DecaBDE administration by gavage throughout gestation or gestation and lactation using corn oil (CO) or soyaphospholipon/Lutrol F 127-water (SPL) as the vehicle. The impact of vehicle on plasma levels was also investigated in pups derived from naive dams after a single postnatal dose. This study reports for the first time fetal and neonatal plasma concentrations concurrent with those of maternal plasma and/or milk. Higher concentrations of DecaBDE were achieved in plasma and in milk with CO than with SPL. Furthermore, pups derived from dams treated with only SPL were lower in body weight, compared with those from dams treated with either CO, CO and DecaBDE, or SPL and DecaBDE. The study further shows that exposure to DecaBDE is relatively consistent across the dose range of 100 to 1000 mg/(kg · day) when administered in CO.

The nonclinical fertility study design for pharmaceuticals.

Assessment of potential developmental and reproductive toxicity of human pharmaceuticals is currently guided by the ICH S5(R2) document, "Detection of Toxicity to Reproduction for Medicinal Products and Toxicity to Male Fertility." Studies that assess a candidate drug's effect on fertility are generally conducted in rats. The evolution of, and ultimate harmonization of, fertility study designs are reviewed, and specific elements of an acceptable design, as well as the recommendations for presentation of data, are described in detail. Additionally, the timing of nonclinical fertility studies in relation to clinical studies that enroll men and women of reproductive potential is reviewed. Possible strategies for combining fertility assessment with other study designs are also presented. This article provides testing laboratories, sponsors, and regulatory agencies with a comparison of current methods and designs, with the aim of providing a common understanding of the critical design features.

Embryo-fetal developmental toxicity study design for pharmaceuticals.

Assessment of potential developmental and reproductive toxicity of human pharmaceuticals is currently guided by the International Conference on Harmonization (ICH) S5(R2) document (available at http://www.ich.org). The studies that assess developmental hazard are generally conducted in rodents and rabbits. Based on the authors' collective experience, adequate designs (including range-finding studies) and the presentation of data for these studies are described in detail. In addition, the suggested initiation and then total duration of these studies in relation to clinical studies that enroll women of childbearing potential are described. Optional parameters that may be included in the studies are discussed, as are study designs that combine assessments of fertility and developmental toxicity. New methods that may replace or enhance current procedures are outlined. The details described herein will assist all laboratories performing these studies, individuals who need to plan for the studies, and regulatory agencies that ultimately review these studies.

Juvenile animal toxicity study designs to support pediatric drug development.

The objective of juvenile animal toxicity studies of pharmaceuticals is to obtain safety data, including information on the potential for adverse effects on postnatal growth and development. Studies in juvenile animals may assist in identifying postnatal developmental toxicities or other adverse effects that are not adequately assessed in the routine toxicity evaluations and that cannot be safely or adequately measured in pediatric clinical trials. Unlike the traditional reproductive and developmental toxicology studies that have been discussed in the accompanying reports, the design requirements for toxicity studies in juvenile animals are not explicitly defined in regulatory guidance. However, studies in juvenile animals can be useful in providing safety information necessary to enable pediatric clinical trials in pediatric patients or when there are special concerns for toxicities that cannot be safely or adequately measured in clinical trials. These juvenile animal toxicity studies are designed on a case-by-case basis. General design considerations and examples of study designs for assessment of juvenile animal toxicity are discussed.

Submarine exposure guideline recommendations for carbon dioxide based on the prenatal developmental effects of exposure in rats.

BACKGROUND: To protect crewmember health, the U.S. Navy sets exposure limits for more than 200 components of submarine atmospheres. The addition of females to nuclear submarines required a reevaluation of these exposure limits, originally established for all-male crews. In the case of carbon dioxide (CO2 ), the only available data suitable for deriving an exposure limit were from a 2010 study sponsored by the British Royal Navy that reported a debatable interpretation casting doubt on whether current U.S. Navy exposure limits served to protect fetal developmental health. METHODS: About 120 time-mated female Sprague-Dawley rats (Crl: CD[SD]) were exposed to CO2 at levels of 1.5%, 2.0%, 2.5%, and 3.0% from gestation days 6 to 20. Dams were euthanized and fetuses were examined. RESULTS: Findings with implications for exposure limits for CO2 during pregnancy were an increased mean litter proportion of early resorptions and a lower mean litter proportion of viable fetuses in the 3.0% CO2 group. CONCLUSION: The results yield a No Observed Adverse Effect Level (NOAEL) of 2.5% and a Lowest Observed Adverse Effect Level (LOAEL) of 3.0%. The results reasonably allow a point of departure of 2.5% CO2 for deriving an exposure recommendation. An interspecies uncertainty factor was applied to derive a recommended 90-day continuous exposure limit (CEL) of 0.8% for CO2 . As reproductive endpoints that are developmental in nature must be assumed to result from a single exposure at a critical point during gestation, it is further recommended that the 24-hr emergency exposure limit (EEL) also be 0.8%.

An oral two-generation reproductive toxicity study of S-111-S-WB in rats.

S-111-S-WB (CAS No. 72968-38-8), a mixture of perfluoro fatty acid ammonium salts, was administered daily via oral gavage to 30 Crl:CD(SD) rats/sex/group at 0.025, 0.125 and 0.6mg/(kgday) over two generations to assess potential reproductive toxicity. Reproductive performance, mean litter size, pup survival and pup weights were unaffected. Lower mean body weights were observed in 0.6mg/(kgday) group F(0) and F(1) males. Higher liver weights, correlating to hepatocellular hypertrophy in the 0.6mg/kg group, were noted for parental males in the 0.125 and 0.6mg/(kgday) groups, parental females in the 0.6mg/(kgday) group and F(1) pups in the 0.125 and 0.6mg/(kgday) groups. Higher kidney weights, correlating to renal tubule hypertrophy in the 0.6mg/kg group, were observed for parental males and females in the 0.125 and 0.6mg/(kgday) groups. Systemic exposure (measured only in females) to total S-111-S-WB was proportional to dose following 9 weeks of daily administration on the gestation day 19. Total S-111-S-WB concentration in the serum of male and female pups was 1.2-1.4-fold higher than in the dams 2h following administration to the dams on lactation day 13. A dosage level of 0.6mg/(kgday) was considered to be the no-observed-adverse-effect level (NOAEL) for reproductive function. A dosage level of less than 0.025mg/(kgday) was considered to be the NOAEL for F(0) and F(1) parental systemic toxicity based on microscopic hepatic findings in the males of all test article groups, and a dosage level of 0.025mg/(kgday) was considered to be the NOAEL for neonatal toxicity based on higher liver weights in the F(1) and F(2) pups at 0.125mg/(kgday) and higher.

Effects of dietary diacylglycerol oil on embryo/fetal development in rats.

Diacylglycerol (DAG) oil is an edible oil with similar taste and usability characteristics as conventional edible oil. Recent studies suggest that use of DAG oil may be helpful in the prevention and management of obesity. This study evaluated the potential maternal and fetal effects of DAG oil, following exposure to pregnant rats, during the critical period of major organogenesis. DAG oil was administered via gavage to four groups of mated female Crl:CD(SD)IGS BR rats (25/group) once daily from gestation day 6 through 17, at dose levels of 0, 1.25, 2.5 or 5.0 ml/kg/day (0, 1160, 2320 and 4630 mg/kg/day) with total volume made to 5 ml/kg/day with triacylglycerol (corn) oil. No mortality or treatment-related clinical or internal findings were noted in any of the groups. Compared to animals in control group, mean maternal body weights, body weight gains, net body weights, net body weight gains, gravid uterine weights, and food consumption were not affected by DAG oil administration. Similarly, intrauterine growth and survival were not affected by DAG oil administration. No DAG oil-related fetal malformations or developmental variations were noted. A maternal maximum tolerated dose for DAG oil was not achieved in this study. Based on the results of this study, a dose level of 5.0 ml/kg (4630 mg/kg/day) was considered as no-observed-adverse-effect level (NOAEL) for both maternal and developmental toxicity.

Safety assessment of dietary diacylglycerol oil: a two-generation reproductive toxicity study in rats.

Diacylglycerol (DAG) oil is a novel edible oil with similar taste and usability characteristics as conventional edible oils. Recent studies suggest that DAG oil may be helpful in the prevention and management of obesity. The objective of the present two-generation study was to evaluate potential adverse effects of DAG oil on reproductive processes. DAG oil was administered via gavage to rats (30/sex/group) for at least 70 days prior to mating, at dose levels of 0, 1.25, 2.5 or 5.0 ml/kg/day (0, 1160, 2320 and 4630 mg/kg/day). An additional group received a triacylglycerol (TAG) oil with a similar fatty acid composition to DAG oil. The rats were treated throughout the mating, gestation and lactation periods. Administration of DAG or TAG oil did not reveal any toxicologically significant effects on reproductive performance (mating, fertility and copulation/conception indices). DAG oil did not affect mean gestation lengths, the process of parturition, spermatogenic parameters, organ weights, histopathologic findings, mean numbers of pups born, implantation sites and unaccounted sites. F1 and F2 pup viability, live litter sizes, body weights, mean age of attainment of balanopreputial separation and vaginal patency were similar to those in the control group. Based on the results of this study, a dose level of 5.0 ml/kg (4630 mg/kg/day) was considered as the no-observed-adverse-effect level for reproductive and systemic toxicity, and neonatal toxicity.

Effects of the opioid analgesic oxymorphone hydrochloride on reproductive function in male and female rats.

BACKGROUND: Endogenous opioids seem to regulate hypothalamic gonadotropin release in both males and females, as evidenced by the effects of opioid agonists and antagonists on LHRH release and reproductive hormone levels. The effects of long-term oral administration of opioid analgesics on reproductive function have not been well characterized. METHODS: The reproductive effects of oxymorphone, a potent opioid agonist, were investigated in male and female Crl:CD(SD) IGS BR rats at oral doses of 0, 5, 10, and 25 mg/kg/day (25 animals/sex/group). Males were treated for approximately 9 weeks (mated after 4 weeks of dosing). Females were treated for 14 days before mating, and through Gestation Day (GD) 7. Estrous cycling was evaluated during the premating period. On GD15, pregnancy status and the numbers of corpora lutea, implantation sites, live and dead embryos were determined. Epididymal and testicular sperm counts and epididymal sperm motility and morphology were evaluated in males. RESULTS: Two males given 25 mg/kg/day died. Behavioral changes and deficits in body weight gain occurred at all doses. There were no effects of oxymorphone on reproductive function or sperm parameters in males. The estrous cycle was prolonged in females given 25 mg/kg/day (mean of 5.3 vs. 4.3 days in controls). A small, but consistent decrease in the numbers of corpora lutea (with associated decreases in implantation sites and embryos) occurred in females given > or =10 mg/kg/day. There were no effects on mating or fertility in females. CONCLUSIONS: Oxymorphone seems to partially inhibit ovulation in female rats, with no significant effects on male reproductive outcome.

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).

A two-generation reproductive toxicity study of octamethylcyclotetrasiloxane (D4) in rats exposed by whole-body vapor inhalation.

This study evaluated the potential toxicity of whole-body vapor inhalation of octamethylcyclotetrasiloxane (D(4)) on reproductive capabilities in exposed F(0) and F(1) parental animals and the potential effects on neonatal survival, growth, and development of the F(1) and F(2) offspring. F(0) male and female Sprague-Dawley rats (30/sex/group) were exposed to D(4) vapor at concentrations of 0, 70, 300, 500 or 700 ppm 6h per day for at least 70 consecutive days prior to mating and lasted through weaning of the pups on postnatal day (PND) 21. Female exposures were suspended from gestation day (GD) 21 through PND 4 to allow for parturition and permit continuous maternal care for the early neonates. Starting on PND 22, F(1) weanlings were exposed to D(4) as described for the F(0) generation. The F(2) pups were not directly exposed to D(4). F(0) animals were mated once to produce the F(1) generation; F(1) parental animals were mated twice to produce two F(2) litters. In addition, the F(1) males were mated with unexposed females. Prolonged estrous cycles, decreased mating and fertility indices were observed in the F(1) generation exposed to D(4) for the first and second matings. Significant reductions in the mean number of pups born and mean live litter size were observed in the 500 and 700 ppm groups for both the F(0) and F(1) generations. Implantation sites were also reduced at 700 ppm for both F(0) and F(1) generations. No adverse effects were observed at any exposure level on anogenital distance, vaginal patency and preputial separation. No adverse effects were seen on male functional reproductive parameters, spermatogenic endpoints, microscopic evaluation of male reproductive tissue, or when the D(4)-exposed F(1) males were mated with the unexposed females, demonstrating that the reproductive toxicity observed was due to D(4) exposure to the females. Based on the lack of effect on reproduction when the D(4)-exposed males were mated to näive females, the NOAEL for male reproductive toxicity was considered to be 700 ppm. Based on the statistically significant effects on fertility and litter size, NOAEL for female reproductive toxicity was considered to be 300 ppm. The findings observed in this study are consistent with suppression or delaying of LH surge as well as acceleration of the onset of female reproductive senescence in the rat. While analogous pathways control ovulation in both rats and humans, there are significant differences in the mechanism for timing and release of LH and resulting changes in the control of ovulation and mating behavior between the two species. If D(4) delays rather than causes a prolonged suppression or ablation of the LH surge, the reproductive mode of action of D(4) would not likely be relevant for humans.

An inhalation reproductive toxicity study of octamethylcyclotetrasiloxane (D4) in female rats using multiple and single day exposure regimens.

Octamethylcyclotetrasiloxane (D(4)) has been shown to have effects on the female rat reproductive cycle. This study evaluated the phase of the female rat reproductive cycle affected by D(4) using a study design that allowed the complete female reproductive cycle, as well as phases of the cycle, from pre-mating through gestation, to be evaluated. Rats were exposed via whole body vapor inhalation up to 700 ppm D(4) during the overall phase (28 days prior to mating through gestation day (GD) 19), the ovarian phase (31-3 days prior to mating), the fertilization phase (3 days prior to the start of mating through gestation day 3), and the implantation phase (GD 2-GD 5) of the reproductive cycle. D(4) was associated with decreases in implantation sites and litter size in the overall and fertilization phases, but not in the ovarian or implantation phases. In order to further define the sensitive period for D(4) exposure, additional groups of rats were exposed on single days. A single 6h exposure to D(4) on the day prior to mating resulted in a significant reduction in fertility. These data indicate that there is a very narrow window, around the time of ovulation and fertilization, for D(4) to exert effects on the reproductive cycle of the female rat. Subsequent research, reported elsewhere, has elucidated the mode of action and assessed its potential relevance to humans.

An assessment of the potential developmental and reproductive toxicity of di-isoheptyl phthalate in rodents.

Di-isoheptyl phthalate (DIHP) is a branched, phthalate ester with seven carbon alkyl side chains. Since structurally similar phthalates have been shown to produce developmental and/or reproductive effects in rodents, the potential for DIHP to produce developmental and reproductive toxicity was assessed. In a developmental toxicity study, female rats were given DIHP by oral gavage on gestational days 6-20. There were significant reductions in uterine weight, increased resorptions and reduced fetal weight in the high dose (750 mg/kg) group. Fetal examination revealed malformations and variations of both the skeletal system and the viscera including ectopic testes. The intermediate dose, 300 mg/(kg/day), was a no effect level in this study. In a two-generation reproductive toxicity study, DIHP was given in the diet at 1000, 4500 and 8000 ppm. In the 8000 ppm group of the first (F1) generation, anogenital distance was reduced, time to balanopreputial separation was increased, there was a significant increase in thoracic nipples and testicular abnormalities, and weights of testes and accessory reproductive organs were significantly reduced. Testicular sperm counts and daily sperm production were significantly reduced. Fertility was also significantly reduced in the 8000 ppm group. In the second (F2) generation offspring, anogenital distance was significantly reduced and there was evidence of reduced weight gain during lactation in both the 4500 and 8000 ppm groups. The overall no effect level (NOEL) in the reproductive toxicity study was in the range of 64-168 mg/(kg/day) (gestation-lactation periods). By comparison, estimated average human exposures in the general population are <1 microg/(kg/day).