Diisobutyl phthalate

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Effect on fertility: via oral route

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LOAEL

125 mg/kg bw/day

Additional information

No standard one or two generation studies are available for DIBP, however results from repeated dose toxicity testing indicate adverse effects on testicular function with decreased testis weights, altered testosterone and zinc concentrations, reduced spermatogenesis and histologically apparent testicular atrophy reported in rodents. As discussed below, similar changes in the male reproductive system are apparent following pre-natal and post-natal exposure, with a LOAEL of 125 mg DIBP/kg bw/d (Saillenfait et al., 2008). Results from a continuous breeding / 2-generation study with dibutyl phthalate (NTP, 1995) revealed reduced pregnancy and fertility indices, decreased pup weights, reductions in sperm and spermatid counts and degeneration of seminiferous tubules and/or interstital cell hyperplasia.

Short description of key information:
Results of repeated dose and pre/post-natal toxicity testing indicate that diisobutyl phthalate has a potential to cause changes in the male reproductive system.

Effects on developmental toxicity

Description of key information

Results of developmental toxicity testing of diisobutyl phthalate in rodents indicates the occurence of adverse effects in the male reproductive system together with external, visceral and skeletal malformations and/or variations, generally in the absence of maternal effects.

Effect on developmental toxicity: via oral route

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LOAEL

125 mg/kg bw/day

Additional information

Several studies are available that inform on the developmental toxicity potential of DIBP.

In a near-guideline pre-natal developmental toxicity study (Saillenfait et al., 2006), an increase in resorptions and reduction in the number of live foetuses was apparent in litters from rats administered 750 mg DIBP/kg bw/d and above on GD 6-20 of pregnancy, with mean foetal body weight significantly reduced at 500 mg/kg bw/d and above. The incidence of external malformations, total visceral malformations, skeletal malformations and skeletal variations was significantly increased at 750 mg/kg bw/d and above, with visceral variations (including significantly increased incidences of unilateral or bilateral undescended testes and significantly increased transabdominal testicular migration) apparent at 500 mg/kg bw/d and above. No evidence of foetal effects was found at the 250 mg/kg bw/d, the lowest dose tested. The NOAEL for maternal toxicity in this study was 1000 mg/kg bw/d (the highest dose tested), and the NOAEL for foetal effects 250 mg/kg bw/d.

In the dose-range finding study that preceded this investigation (Saillenfait et al., 2005), a dose related reduction in foetal body weight was noted in litters from dams administered 0, 250, 500, 750 or 1000 mg DIBP/kg bw/d by gavage on GD 6-20, with a marked increase in resorptions in the 750 and 1000 mg /kg bw/d groups. Gross internal examination of the reproductive tract revealed undescended testes in 56% and 70% of the male foetuses from the 750 and 1000 mg/kg bw/d groups (no further visceral or skeletal examinations conducted). These changes occurred in the absence of apparent maternal toxicity.

The effects of pre- and post-natal exposure to DIBP have also been investigated (Saillenfait et al., 2008), with decreased anogenital distance, retention of areolas and/or nipples and underdeveloped or absent testes and/or epididymes noted in male rats from dams administered 250 mg DIBP/kg bw/d and above by gavage during days 12-21 of pregnancy and also during adult life. Delayed preputial separation, decreased testes, epididymes, seminal vesicle and prostate weights, and severe malformations (e.g. hypospadias) were noted at 500 mg/kg bw/d. Histopathological examination revealed moderate or severe degeneration of seminiferous tubules (including Sertoli cell only tubules) and oligospermia or total azoospermia in all treated male off-spring. No maternal effects were recorded (NOAEL = 1000 mg DIBP/kg bw/d), while the LOAEL for male developmental effects (degeneration of the seminiferous tubules) was 125 mg/kg bw/d.

Changes in foetal testicular testosterone production were apparent in male rats from dams given 300 mg DIBP/kg bw/d and above by gavage on GD 8-18 of pregnancy (Howdeshell et al., 2008). Maternal body weight gain was reduced, and foetal mortality increased, after administration of 600 and 900 mg/kg bw/d. These findings indicate a maternal NOAEL of 300 mg/kg bw/d and a foetal NOAEL of 100 mg/kg bw/d following oral administration of DIBP on GD 8-18 of pregnancy.

Administration of DIBP (0 or 600 mg/kg bw/d) by gavage to pregnant rats from GD 7 to GD 19-21 resulted in a statistically significant reduction in AGD in male pups (and increased AGD in female pups) together with a 10 % reduction in bodyweights of male and female foetuses (Borch et al., 2006; cited by ECHA, 2009). Testicular testosterone production and testicular testosterone content was significantly decreased in male offspring, with clustering of small Leydig cells and vacuolisation of Sertoli cells seen microscopically. Immunohistochemical techniques demonstrated reduced staining for StAR and P450scc two proteins involved in testicular steroid synthesis. Further results from this study were reported by Boberg et al. (2008; cited in ECHA, 2009) who noted that treated animals exhibited statistically significantly reduced testicular mRNA levels of SR-B1, StAR, P450c17, P450scc, Insl-3 and SF-1 mRNA whereas mRNA levels of aromatase or PBR were unaffected. Gene expression analysis revealed significantly reduced mRNA levels of PPAR-alpha in male livers and testes on GD 19 but not on GD 21. Immunohistochemical techniques showed reduced protein levels of P450c17 and PPAR-gamma in Leydig cells from treated animals on GD 19 and GD21.

Boberg, l, Metzhoff, S, Wortzinger, R, Axelstadt, M, Brokken, L, Vinggaard, AM, Dalgaard, M, and Nellemann, C (2008): Impact of diisobutyl phthalate and other PP AR agonists on steroidogenesis and plasma insulin and leptin levels in fetal rats. Toxicology, 250, 75-81

Borch, l, Axelstad, M, Vinggaard, AM and Dalgaard, M (2006): Diisobutyl phthalate has comparable anti-androgenic effects to di-n-butyl phthalate in foetal rat testis. Toxicol. Lett., 163, 183-190

Saillenfait, AM, Sabate, JP and Gallissot, F (2005): Developmental toxic effects of diisobutylphthalate administered by gavage to rats. Toxicology, 213; 231-232

Justification for classification or non-classification

Effects on fertility: the nature and severity of the findings described above are consistent with a potential to cause adverse effects on fertility. Classification Repr Cat 3, R62 / Repr 1B H360Df is appropriate.

Effects on development: the nature and severity of the findings described above are consistent with a potential to cause adverse effects on foetal development. Classification Repr Cat 2, R61 / Repr 1B H360Df is appropriate.