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Effects on fertility

Effect on fertility: via oral route
Endpoint conclusion:
no study available
Effect on fertility: via inhalation route
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
NOAEC
2 261 mg/m³
Species:
rat
Quality of whole database:
The available key and supporting studies provide information that is adequate for the purpose of hazard assessment
Effect on fertility: via dermal route
Endpoint conclusion:
no study available
Additional information

The effect of toluene exposures on fertility was reviewed and reported in the EU RAR (2003). No additional relevant data have been found in the updated literature review.

Non-human information

Two key studies are identified.

Roberts et al (2003) conducted a combined two-generation fertility and teratogenicity inhalation study in rats. Exposure to toluene was at 0, 100, 500 or 2000 ppm 6 h/day, 7 days/week during an 80 day pre-mating period and 15 day mating period. Females were further exposed during gestation (GD 1-20) and lactation (LD 5-21). Toluene exposure did not induce adverse effects on fertility and the NOAEC for effects on fertility was 2000 ppm (7500 mg/m3), the highest dose tested.

In the study of Ono et al (1996) rats were exposed to toluene vapour at 600 and 2000 ppm for 6 h/day, and effects on their fertility were investigated. Females were exposed from 14 days before mating until day 7 of gestation. Males were exposed for a total of 90 days, including the mating period; treatment was begun 60 days before pairing, and toxicity with respect to testicular and reproductive functions was examined. Although no abnormalities were seen in mating behaviour or fertility in the males exposed to 2000 ppm decreases in the weights of the epididymides and sperm count were observed. The NOAEC for effects on male fertility was 600 ppm (2261 mg/m3).

Human information

The EU RAR (2003) concluded “In humans, no studies of effects of toluene on sperm count were found. Limited data in humans have not shown indication of effects on fertility in men or menstrual function in women”.  Consequently a value of 2261 mg/m3 from the Ono study will be taken into consideration for risk characterisation.


Short description of key information:
Although no functional effects were seen on fertility in a 2-generation study in rats lower epididymides weight and sperm count were observed at 2000 ppm (7537 mg/m3) with a NOAEC of 600 ppm (2261 mg/m3).

Justification for selection of Effect on fertility via inhalation route:
The available data indicate no functional effect on fertility in a rat 2-generation study, however epididymal weight and sperm count were decreased at 2000 ppm (7537 mg/m3)

Effects on developmental toxicity

Description of key information
Animal studies indicate that toluene is not teratogenic however there is evidence of developmental toxicity (lower birth weight, delayed vaginal opening) at exposures ≥ 1000 ppm in the presence of slight maternal toxicity; the NOAEC for developmental and maternal effects is 600 ppm (2261 mg/m3). Findings suggestive of an increased risk of late spontaneous abortions associated with exposure to toluene at levels around 88 ppm (330 mg/m3) were considered by the Commission Group of Specialised Experts in the fields of Carcinogenicity, Mutagenicity and Reprotoxicity to require confirmation, while the EU Scientific Committee on Occupational Exposure Limits SCOEL (2001) noted that abortions have not been reported upon accidental high exposure or toluene abuse by pregnant women.
Effect on developmental toxicity: via oral route
Endpoint conclusion:
no study available
Effect on developmental toxicity: via inhalation route
Endpoint conclusion:
adverse effect observed
Dose descriptor:
NOAEC
2 261 mg/m³
Species:
rat
Quality of whole database:
The available animal and human data provide information that is adequate for the purpose of hazard assessment
Effect on developmental toxicity: via dermal route
Endpoint conclusion:
no study available
Additional information

The developmental toxicity of toluene exposures was reviewed and reported in the EU RAR (2003). One additional study published after completion of the RAR has been included in this dossier.

Non-human information

Developmental toxicity has been assessed in a number of studies in several species and there is no evidence that toluene produces malformations in rats or rabbits (Roberts et al, 2007; Saillenfait et al, 2007; Klimisch et al, 1992). However, some evidence of developmental toxicity in the absence of maternal toxicity has been reported in rat inhalation studies (Thiel and Chahoud, 1997; Hass et al, 1999). Roberts and co-workers used whole body inhalation (6 h/day) in pregnant rats exposed to toluene at concentrations of 0, 250, 750, 1500 or 3000 ppm from GD6-15 (Roberts et al, 2007). Toluene induced evidence of maternal toxicity at 3000 and 1500 ppm. There were no adverse effects on implantation number, foetal viability or foetal sex distribution at caesarean section on GD20. Litter weight and mean foetal weight was reduced at 3000 ppm and mean foetal weight was lower at 1500 ppm. Instances of reduced or unossified skeletal elements occurred at the same dose levels. 

The developmental toxicity of toluene was evaluated in the Himalayan rabbit (Klimisch et al, 1992). Pregnant females were exposed to toluene by inhalation 6 h/day at concentrations of 0, 30, 100, 100, 300 or 500 ppm. Toluene was not embryotoxic, foetotoxic, or teratogenic to rabbits.

Thiel and Chahoud (1997) assessed pregnant female rats exposed to toluene via inhalation 6 h/day during gestation (days 9 -21) at concentrations of 0, 300, 600, 1000 or 1200 ppm. A detailed evaluation of physical development of offspring was conducted and included a number of reflex tests, measures of locomotor activity/co-ordination and a discrimination learning test. Maternal toluene exposures of 1200 ppm resulted in a reduced body weight gain of rat dams and offspring had lower body weight at birth and day 7 and a higher mortality until weaning. Some developmental landmarks (incisor eruption and vaginal opening) were delayed in this group and are likely to be secondary to the effect on body weight. At 1000 ppm maternal body weight gain was low and offspring had low body weight at birth and delayed vaginal opening. There were no differences in the development of reflexes, rota rod performance and locomotor activity that were attributable to treatment with toluene and no effects were found on learning ability in the operant conditioning task.

In a study of broadly similar design but using only two exposure levels, groups of pregnant female rats were exposed (gestation days 6-20) to toluene vapour at exposure concentrations of 0, 500 or 1500 ppm (Saillenfait et al., 2007). Maternal toluene exposures of 1500 ppm resulted in a significant (-40%) reduction in corrected maternal body weight gain and a non-significant increase in visceral malformations. The malformations were not fully characterised (described as "mainly diaphragmatic hernia") and affected a total of two foetuses from two litters. In contrast, maternal and foetal parameters at 500 ppm were unremarkable. The LOAEC for maternal and developmental toxicity from this was therefore 1500 ppm, and the NOAEC was 500 ppm.

Rats were exposed to 1200 ppm or 0 ppm toluene for 6 h/day from day 7 of pregnancy until day 18 post-natally (Hass et al, 1999). Developmental and neurobehavioural effects in the offspring were investigated using a test battery including assessment of functions similar to those in the OECD 426, i.e., physical development, reflex ontogeny, motor function, motor activity, sensory function, and learning and memory. The exposure did not cause maternal toxicity or decreased viability of the offspring, however pup birth weight was lower and effects were reported on water maze performance and open field activity. Evaluation of the toxicological relevance of these findings during the EU risk assessment of toluene lead the UK CA to state that there were design limitations as only one exposure level was investigated and it considered that "it is not possible to assess the presence or absence of consistent dose-response relationships". They concluded that there was "weak evidence that toluene may elicit developmental neurotoxicity, manifested as differences in water maze performance and open field activity" and that "the conclusion that toluene is a developmental neurotoxicant to be a tentative one with uncertainties remaining to be addressed". Consequently no conclusion on developmental neurotoxicity can be made on the basis of these data.

It is concluded that toluene is not teratogenic but there is evidence of developmental toxicity (lower birth weight, delayed vaginal opening) at toluene exposure concentrations ≥ 1000 ppm. There are contradicting data as to whether these concentrations are also maternally toxic. In the study of Thiel and Chahoud, maternal body weight at 1000 ppm was statistically significantly lower than concurrent control group (9%) at the end of gestation whereas there were no effects on maternal body weight at 1200 ppm in the study of Hass et al (1999). The NOAEC for developmental effects is 600 ppm (2261 mg/m3) on the basis of lower birth weight and delayed vaginal opening.

The EU RAR (2003) concluded that rat inhalation studies provide strong evidence of developmental toxicity (lower birth weight and long-lasting developmental neurotoxicity) in the absence of maternal toxicity. The effective dose levels are around or more than 1,000 ppm (3752 mg/m3). The NOAEC for lower birth weight and delayed postnatal development is set at 600 ppm (2250 mg/m3). The RAR noted that a NOAEC for developmental neurotoxicity cannot be determined from the available studies but the LOAEC for this effect is 1,200 ppm (4500 mg/m3). The RAR also reported that toluene induces similar effects in mice while data in rabbits are insufficient to evaluate the sensitivity of this species compared to rats and mice. Appendix D of the EU RAR documents that not all Member States agreed with the interpretation of the animal developmental neurotoxicity studies.

Human information

In a study designed to examine pregnancy outcomes in women occupationally exposed to toluene (Ng et al., 1992), rates of late spontaneous abortion (12-28 weeks) were compared by retrospective questionnaire in 55 women (105 pregnancies) exposed to toluene (mean 88 ppm, range 50-150 ppm: high exposure group), 31 women (68 pregnancies) working in the same factory in departments where much lower exposure to toluene occurred (range 0-25 ppm: low exposure group), and an external community control group of 190 women (444 pregnancies) attending antenatal and postnatal clinics. The study is assigned Klimisch Rel. 4 (not assignable) due to inconsistencies in its design and reporting/analysis of the results obtained (see below). The rate of late spontaneous abortion for the high exposure group was significantly higher than in the low exposure group (OR 4.80, 95% CI 1.01-22.86). The rate was also higher than for the pregnancies of women attending antenatal and postnatal clinics, but it was not stated that the current pregnancies of this group were excluded from the study which is necessary to avoid bias (the most recent pregnancy of a postnatal recruit or an antenatal attendee who was more than 28 weeks pregnant cannot be a late spontaneous abortion). Early spontaneous abortions in the first months after conception were not recorded which may have lead to misclassification, while in the maternal health clinic group there were 27 pregnancies that were neither late spontaneous abortions nor live births, but were not characterised further. Exposure information was obtained from a separate, earlier study of 41 female and 9 male workers at the same factory who performed assembly jobs in a sitting position and who were exposed to relatively steady levels of toluene emitted from glue used for bonding electronic parts (Foo et al., 1988); exposures were in a range 8.5 ppm to 262.7 ppm, with 7 measurements >150 ppm and 10 measurements <50 ppm i.e more variable than information presented by Ng et al. (1992). Furthermore, the exposure study by Foo et al (1988) did not include workers from departments from which the low exposure group was recruited. Overall therefore, this study provides weak evidence of an elevated rate of late spontaneous abortions at 88 ppm.

The findings of Ng et al. were considered by the EU RAR (2003) to suggest “an increased risk of late spontaneous abortions associated with exposure to toluene at levels around 88 ppm (range 50-150 ppm)”, although it was also noted that the study “cannot be used to establish definitively a causal relationship between late spontaneous abortions and toluene exposure or the magnitude of the LOAEL”. Nonetheless, the EU RAR (2003) concluded that exposure of pregnant women to the levels experienced by the High exposure group would raise “serious ethical concerns” based on the current evidence suggesting an increased risk for late spontaneous abortions. The results of this study were also considered by the Commission Group of Specialised Experts in the fields of Carcinogenicity, Mutagenicity and Reprotoxicity (SEG, 2000) who concluded that the findings were of concern but in need of confirmation, and corroborating evidence from experimental studies was lacking. SCOEL (2001) observed that abortions have not been reported upon accidental high exposure or toluene abuse by pregnant women (Wilkins-Haug and Gabow, 1991) and that an exposure limit of 50 ppm (192 mg/m3) would protect against potential foetotoxicity.

A review by Bukowski (2001) examined the epidemiological evidence for adverse reproductive outcomes from occupational studies that presented toluene-specific findings. Clinical investigations of the reproductive effects of toluene abuse were also examined.  The reproductive outcomes of concern in these studies were primarily spontaneous abortion (SA), congenital malformation (CM), or decreased fertility/fecundity. As these were observational research studies not controlled experiments a number of potentially important biases were identified: (1) selection bias, (2) recall bias, and (3) confounding. It was concluded that the literature reviewed cannot be used to definitively establish a causal relationship between toluene exposure and spontaneous abortion or congenital malformation or the magnitude of the lowest effect level.


Justification for selection of Effect on developmental toxicity: via inhalation route:
Animal studies indicate that toluene is not teratogenic however there is evidence of developmental toxicity (lower birth weight, delayed vaginal opening) at exposures ≥ 1000 ppm in the presence of slight maternal toxicity.

Justification for classification or non-classification

There is no evidence that toluene has any effect on fertility and does not warrant classification for reproductive toxicity.

Lower birth weight in the absence of significant maternal toxicity and weak evidence of behavioural effects (water maze and open field performance) was seen in offspring of dams exposed to toluene from day 7 of pregnancy until day 18 post-natally. Toluene is therefore classified as Category 2 (H361d) according to GHS.

Additional information