The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings were not evaluated in accordance with the levels of evidence for reproductive or developmental criteria established by NTP in March 2009. The findings and conclusions for this study should not be construed to represent the views of NTP or the U.S. Government.
Di-N-hexylphthalate (DHP) was tested using the standard RACB protocol in both sexes of Swiss CD-1 mice. Data on food and water consumptions, body weights, and clinical signs collected in the Task 1 dose-range-finding study, were used to set doses for the continuous breeding part of the study at 0.0, 0.3, 0.6, and 1.2% in feed. Food consumption was not altered by the presence of DHP. These concentrations yielded calculated consumption estimates of nearly equal to 0.38, 0.80, and 1.67 g DHP/kg/day.
In the continuous breeding phase, there were no live pups at the high dose and 1 litter of 4 pups at the middle dose. At the low dose, there was a significant reduction in the mean number of litters per pair (3.4, vs. 4.9 for the controls). Also at the low dose, the number of live pups/litter was reduced from 12.3 (controls) to 3.4, the proportion born alive was reduced by 14%. Pup weight adjusted for litter size was unchanged. These effects occurred in the absence of an effect on post-partum dam body weights.
These significant reproductive effects prompted the determination of the affected sex in the Task 3 crossover mating trial using the control and 1.2% DHP-treated mice. Each group had 17-20 pairs of mice. The mating index (proportion of pairs showing copulatory plugs) in groups with 2 control partners, with a DHP-treated male, or a DHP-treated female, was 90%, 56%, and 88%, showing that the treated females were cycling and could be receptive, and that mating capability was reduced in the group of treated males . However, no treated females bore any litters, and only 1 of 18 treated males sired a litter. Effectively, both sexes were infertile at this level of DHP exposure.
After the litters from the crossover were examined and discarded, the F0 adults from the control and 1.2% DHP groups were killed and necropsied. Body weight in the high dose males was 10% less than controls, and absolute testis weight was 70% less. Body-weight-adjusted liver weights were increased by 34%, and adjusted weights of kidney, epididymis, and seminal vesicles were reduced by 9, 23, and 18%, respectively. Body weight of DHP-exposed F0 females was 6% less than controls, while adjusted weights of liver was increased by 32% and adjusted kidney weights were decreased by 6%. Not surprisingly, epididymal sperm concentration was reduced by 93%, and motility was reduced by 80%. Morphologic abnormalities were unchanged.
There were insufficient animals from any DHP-treated group to provide F1 mice for an evaluation of the second generation.
These data clearly demonstrate that DHP is a reproductive toxicant in mice. The relative sensitivity of the liver and the reproductive system cannot be judged from these data, but the reproductive effects occured in the absence of large changes (at the top dose) or any changes (low and middle doses) in body weight.