The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings may not have been peer reviewed and were not evaluated in accordance with the levels of evidence criteria established by NTP in March 2009. For more information, see the Explanation of Levels of Evidence for Developmental Toxicity. The findings and conclusions for this study should not be construed to represent the views of NTP or the U.S. Government.
Benzophenone occurs naturally in some fruits, and is used commercially as a perfumery and flavoring ingredient. This study was performed due to the potential for human exposure and the lack of pertinent developmental toxicity data.
Dose selection was based on a screening study in which New Zealand White rabbits were treated by gavage with benzophenone (0, 25, 50, 75, 100 or 125 mg/kg body weight/day) on gestational days 6 through 29 (NTP, 2004). Maternal toxicity was found at all doses, and groups treated with ≥75 mg/kg/day were terminated early due to excessive maternal toxicity or early delivery of litters. No significant developmental toxicity was found at doses up to 50 mg/kg/day.
In this study, benzophenone (5, 25 or 45 mg/kg/day) or its vehicle (0.5% ethylcellulose) was administered to naturally mated female NZW rabbits by gavage on gd 6 through 29. The dose volume was 3 ml/kg. Twenty-four timed-mated rabbits were assigned to each group (12/group/replicate). Dams were monitored at regular intervals throughout gestation for clinical signs, feed consumption, and body weight. At necropsy on gd 30, the following were recorded: maternal clinical condition; body, liver, paired kidney and gravid uterine weights; pregnancy status; and number of corpora lutea. In the gravid uterus, the numbers of resorbed, dead, or live fetuses were recorded. All live fetuses were weighed, sexed, and examined for external, visceral, and skeletal morphological anomalies. Approximately one-half of the fetuses were decapitated, heads were decalcified in Bouin's solution, and internal head structures were examined in free-hand sections.
There were no maternal deaths in the control or low-dose group. At 25 mg/kg/day, two does were found dead (one on gd 24 and the other on gd 30). At 45 mg/kg/day, four does died (gd 26-28) and one doe was terminated in extremis (gd 29). There were no spontaneous abortions or early deliveries in the control or low-dose group. At 25 mg/kg/day, one doe aborted (gd 24) and two delivered early (gd 29). At 45 mg/kg/day, seven does delivered early (gd 27-30). In addition, two does in each of the mid and high dose groups were removed due to dosing errors or animal husbandry deviations. Thus, the total number of confirmed pregnant does evaluated at necropsy was 24, 21, 17 and 10 for the control through high-dose groups, respectively. The confirmed pregnancy rate at termination was 88-100% per group.
Maternal body weight showed decreasing trends on gd 24, 27, 29 and 30. Significant decreases were noted at 25 mg/kg/day on gd 29 and at 45 mg/kg/day on gd 27, 29 and 30. Maternal body weight change was decreased at 25 mg/kg/day (gd 27 to 29,29 to 30 and 6 to 29) and at 45 mg/kg/day (gd 21 to 24, 24 to 27, 27 to 29, 6 to 29, 3 to 30, 0 to 30 and for corrected gestational weight gain). Gravid uterine weight, maternal liver and paired kidney weights (absolute or relative) were not affected at any dose.
Maternal relative feed consumption (g/kg/day) was affected at the mid and high doses of benzophenone. At 25 mg/kg/day, feed consumption was significantly reduced from gd 21 to 24 (Replicate II, only) and from gd 24 to 27. At 45 mg/kg/day, maternal relative feed consumption was significantly reduced for the following measurement periods: gd 15 to 18 (Replicate I, only), 18 to 21, 21 to 24, 24 to 27, and 27 to 29. For the treatment period as a whole, only a decreasing trend was noted for maternal relative feed consumption.
Average fetal body weight per litter exhibited decreasing dose-response trends (males, females and both sexes combined). At the high dose, significant reductions were noted for male fetal body weight (81% of control weight), female fetal body weight (85% of control weight) and both sexes (83% of control weight). Benzophenone had no adverse effect on prenatal viability or incidences of fetal morphological anomalies among litters evaluated on gd 30.
In summary, benzophenone was administered to timed-pregnant NZW rabbits by gavage on gd 6 through 29. The maternal toxicity no observed adverse effect level was 5 mg/kg/day. The lowest observed adverse effect level for maternal toxicity was 25 mg/kg/day based on reduced maternal body weight and weight change, as well as dose-related incidences of maternal mortality and early termination of pregnancy (i.e., abortion or early delivery). The developmental toxicity NOAEL was 25 mg/kg/day, and the NOAEL was 45 mg/kg/day based on reduced fetal body weight.