Piperazine

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

Treatment through the reproductive cycle of the rat for two successive generations with Piperazine Dihydrochloride at dose levels of 5000 ppm and above resulted in dose-related effects on the adults. Dose levels of 12000 ppm and above resulted in a dose-related reduction in litter size. The effects seen on adults and offspring were enhanced in the second generation. The no effect level for effects on the reproduction parameters evaluated was 5000 ppm.

The dietary level of 5000 ppm resulted in a mean intake of piperazine base of 204 mg/kg bw/day for P0 males and 290 mg/kg bw/day for P1 males. For P0 females the mean intake of piperazine base was at least 222 mg/kg bw/day, and for P1 females 277 mg/kg bw/day, as individual food intake values were higher during gestation and 2-4 times higher during lactation. The lowest level of 204 mg/kg bw/day was taken as overall NOAEL.  

Effect on fertility: via oral route

Dose descriptor:

NOAEL

204 mg/kg bw/day

Study duration:

subchronic

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

For reproductive effects, a NOAEL of 204 mg/kg/day was established with decreased litter size as the main effect.

In the EU RAR (2005) the following was stated on this study:

With respect to effects on reproduction, 5,000 ppm (125 mg/kg/day piperazine base) can be considered as a NOAEL, with 12,000 ppm (300 mg/kg/day) as a LOAEL for this study, with effects mainly on fertility (i.e., reduced pregnancy index and decreased number of implantation sites, although litter losses in F2 may indicate post implantation losses as well). The lack of effects in the rat developmental toxicity study (Ridgway, 1987b) could be considered to support that effects on fertility are the main effect of piperazine on reproduction in rats. It is possible that the delayed sexual development could be related to the decreased growth (body weights decreased as from week 2 and onwards), as it is therefore not considered of toxicological significance. Relative to the elicitation of toxic effects in the mother animals, there was no reduction of body weight increase in F0 females given 300 mg/kg/day. For the F1 females, the body weight gain during gestation was 44%, as compared to 49% for controls. However, their body weights before gestation were 9% lower than the controls. Based on the significantly decreased body weight gain at 300 mg/kg/day in F0 and F1 males and in F1 females, the NOAEL for the adult animals is estimated to be 125 mg/kg/day of piperazine base. Except for the sex organs and the pituitary, histopathological data from other organs are lacking.

It should be noted that in the EU RAR the following dose levels were estimated based on an assumptions of BW and food intake; however, food intake and chemical intake information has been provided in the report:

5000 ppm = 250 mg/kg bw piperazine dihydrochloride = 125 mg/kg piperazine base

12000 ppm = 600 mg/kg bw piperazine dihydrochloride = 300 mg/kg piperazine base

25000 ppm = 1250 mg/kg bw piperazine dihydrochloride = 625 mg/kg piperazine base

Also the recalculation from piperazine dihydrochloride (MW 159.05) to piperazine (MW 86.136) is equal to 0.54 and not 0.5.

The dietary level of 5000 ppm resulted in a mean intake of piperazine base of 204 mg/kg bw/day for P0 males and 290 mg/kg bw/day for P1 males. For P0 females the mean intake of piperazine base was at least 222 mg/kg bw/day, and for P1 females 277 mg/kg bw/day, as individual food intake values were higher during gestation and 2-4 times higher during lactation.  

Effects on developmental toxicity

Description of key information

At 210 mg/kg, piperazine base was highly embryotoxic and also demonstrated teratogenicity in the rabbit upon oral gavage (Ridgway 1987a). Post-implantation loss was high, fetal weights were reduced and there was a slight retardation of ossification. In addition, 23% of the fetuses exhibited major abnormalities as compared with 1.7% in controls. There was also an increased incidence of poorly ossified hindlimbs probably related to the maternal toxicity. At 94 as well as at 42 mg/kg piperazine base post-implantation loss, foetal weights, extent of ossification, and foetal sex ratios were unaffected by the treatment. Also, there was no significant increase in foetal abnormalities at the two lowest dose levels. Overall, the effects observed at 210 mg/kg/day piperazine base are considered to be secondary to maternal toxicity. Thus, in rabbits, such effects may be elicited at a dose level that is also toxic to the mother animal. The maternal NOAEL was 42 mg/kg/day piperazine base.

Piperazine did not appear to be teratogenic in the rat via oral gavage, the NOAEL for developmental toxicity was >= 2100 mg/kg bw. In two supporting oral gavage studies studies piperazine did not show developmental toxicity in rats and mice; NOAELs were >= 542 mg/kg bw.

Effect on developmental toxicity: via oral route

Endpoint conclusion:

adverse effect observed

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Toxicity to reproduction: other studies

Additional information

In the EU RAR (2005) the following was stated:

Developmental toxicity:

At 210 mg/kg, piperazine base was highly embryotoxic and also demonstrated teratogenicity. [....] Although specific and rare abnormalities, they have also been observed in food-deprivation studies in rabbits (Clarke, 1986). Thus, they can be considered to be secondary to the maternal toxicity. There was also an increased incidence of poorly ossified hindlimbs (epiphyses; 86% versus 40% variants in controls, and astragalus; 5.7% versus 0%

of minor cases in controls) probably related to the maternal toxicity. At 94 as well as at 42 mg/kg piperazine base post-implantation loss, foetal weights, extent of ossification, and foetal sex ratios were unaffected by the treatment. Also, there was no significant increase in foetal abnormalities at the two lowest dose levels. Overall, the effects observed at 210 mg/kg/day piperazine base are considered to be secondary to maternal toxicity.

In summary, piperazine does not to appear to be teratogenic in the rat. In rabbits, such effects may be elicited at a dose level that is also toxic to the mother animal. The maternal LOAEL is 94 mg/kg/day, and the NOAEL 42 mg/kg/day piperazine base.

Mode of Action Analysis / Human Relevance Framework

According to EU RAR (2005):

The lack of effects in the rat developmental toxicity study (Ridgway, 1987b) could be considered to support that effects on fertility (i.e., reduced pregnancy index and decreased number of implantation sites; litter losses in F2 may indicate post implantation losses as well) are the main effect of piperazine on reporduction in rats (Wood, 1995).

It is possible that the delayed sexual development could be related to the decreased growth (body weights decreased as from week 2 and onwards), as it is therefore not considered of toxicological significance.

Justification for classification or non-classification

Piperazine has officially been classified as Reprotoxic cat. 2 (H361fd).

The lack of effects in the rat developmental toxicity study (Ridgway, 1987b) could be considered to support that effects on fertility are the main effect of piperazine on reproduction in rats as observed in the 2 -gen study (Wood, 1995); this would warrant a classification as reproductive toxicant cat. 2.

Developmental effects have been observed in rabbits but in the presence of overt maternal toxicity, and in view of the absence of developmental toxicity in rats and mice, classification as developmental toxicant cat. 2 would be warranted.