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.
Tricresyl phosphate (TCP) is a mixture of isomers of ortho, meta, or para cresols. TCP is used industrially as a plasticizer, flame retardant, and a solvent. This mixture was tested for its effects on reproduction and fertility in CD-1 mice using the RACB protocol. In rats and other species, TCP (and the most toxic isomer ToCP) is neurotoxic. Data from a two week dose-range-finding study (Task 1) were used to set exposure concentrations for the Task 2 continuous cohabitation study at 0.05, 0.1, and 0.2% in feed. Based on Task 2 feed consumption and body weight data, these concentrations produced estimated daily dosages of nearly equal to 62.5, 125, and 250 mg/kg.
In the F 0 generation, the high dose females showed moderate signs of hindlimb weakness towards the end of the study, and post-partum dams weights at this dose were reduced by 10-15%, beginning with the second litter. Males were unaffected, and no F0 mice died during the study.
TCP exposure produced the greatest effects in the high dose group, which showed a 66% reduction in the number of litters/pair, and a 71% reduction in number of live pups/litter. Only 11% of the pups were born alive, they weighed nearly equal to 23% less than their controls, adjusted for litter size, and the cumulative time to deliver each litter was increased, starting with the second litter. Only 1 high dose pair delivered a fourth litter, and no pair produced five litters. The only effects in the middle dose group were a 5% reduction in adjusted pup body weight and an increase in delivery intervals, starting with the first litter.
The last litter was nursed by the dam until weaning, and consumed the same diet as their parents from weaning until mating at pnd nearly equal to 74. While there were no live pups at the high dose, the middle dose pups weighed nearly equal to 16% less than controls on pnd 0 and 4, though the subsequent differences in weight were no significant thereafter. Postnatal mortality was not significantly increased by TCP exposure.
The significant reproductive effects seen in Task 2 prompted a determination of the affected sex, using the high dose and control groups, after the weaning of the last litter. At this Task 3 crossover mating, fewer litters were derived from either treated males or treated females; both sexes were affected. While control x control litters averaged nearly equal to 9 live pups, litters from treated males averaged nearly equal to 5 pups, and from treated females averaged fewer than 1 live pup/litter.
The control and high dose F0 TCP mice were killed and necropsied after the delivery of the Task 3 litters. High dose male body weight was nearly equal to 6% lower than controls, while testis weight was nearly equal to 19% less. Relative liver, and kidney, weights were nearly equal to 11% increased, compared to controls. Treated males also had 71% fewer sperm, only 30% were motile (compared to the control value of 70%), and had almost twice as many abnormally-shaped sperm. High dose female terminal body weight was reduced by nearly equal to 17%, while relative liver weight was increased nearly equal to 15%. Estrous cyclicity was not evaluated.
For the F1 cohabitation at nearly equal to pnd 74, only control, low, and middle dose animals were available. Only 70% of middle dose pairs delivered a litter, compared to 95% of controls. Those litters were smaller than controls (9 pups vs 11 pups), and adjusted live pups weight was reduced by 6%, a statistically insignificant change.
After delivery, examination, and removal of the F2 litters, the F1 adults were killed and necropsied. Male terminal body weights were unchanged, as were all other weights except liver, which was increased by 8% in the middle dose group. Interestingly, the % motile sperm was reduced in both exposed groups, from a control value of 72%, to 47% and 40% in the low and middle dose groups, respectively. Sperm abnormalities were slightly increased in the low dose group. Female terminal body weight was reduced in both treatment groups, by 6% and 8%, respectively, although adjusted organ weights were not affected. Estrous cycle length was not evaluated.
These data showed that TCP induced infertility at the high dose (0.2% in feed). The reduced fertility at the middle dose (0.1% in feed) was evident in both generations, while the reductions in % motile sperm was evident in both the low and middle dose groups of second generation mice. These effects occurred in the presence of no change, or only minor changes, in body weight.
NTIS # PB86167277