3a,4,7,7a-tetrahydro-4,7-methanoindene

Endpoint summary

Description of key information

In an OECD 408 guideline study, rats dosed with 100 mg/kg/day DCPD had sporadic tremors and clonic convulsions. The NOAEL was concluded to be 30 mg/kg/day.

In non-guideline oral and an inhalation studies, exposure to dicyclopentadiene resulted in nephrotoxicity (alterations in renal function and kidney morphology) in male rats only and characteristic of hyaline droplet nephropathy, which is not relevant for human risk assessment. Other changes which were seen in male rats in all groups (including controls) were characteristic of chronic glomerulonephropathy. Mortality was seen in rats dosed with 100 mg/kg/day orally and in mice exposed to 51 ppm by inhalation. Apart from the effects on the kidney (in male rats only), there were few histopathological changes. Single cell necrosis in the liver and fatty changes in the adrenal glands were seen in the oral rat study only. The subchronic NOAEC in rats for DCPD is 107 mg/m3.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

4 mg/kg bw/day

Study duration:

subacute

Species:

rat

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

27.6 mg/m³

Study duration:

subchronic

Species:

mouse

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEC

27.6 mg/m³

Study duration:

subchronic

Species:

mouse

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Mode of Action Analysis / Human Relevance Framework

n/a

Additional information

Non human Information

Oral 

In an OECD 408 test guideline study rats were dosed orally with 10, 30 and 100 mg/kg/day DCPD. In the 100 mg/kg/day dose group male animals from Week 8 and female animals from Week 10 had sporadic tremors but all animals returned to normal before the next dosing. Three affected males also had clonic convulsions lasting two to five minutes during Week 10 or 12 of dosing. There were no other significant effects of DCPD on other endpoints examined under OECD 408 test guideline study. The No Observed Adverse Effect Level (NOAEL) was defined as 30 mg/kg/day for DCPD due to the severity of clinical signs at 100 mg/kg/day.

Another key study is considered to be a combined repeat dose toxicity study with reproduction/developmental toxicity screening (JETOC, 1998a). Systemic toxicityat 100 mg/kg/day was indicated by the mortality of two female rats and, decreased food consumption and bodyweight gain in both males and females. Pathological changes in the liver (single cell necrosis, males only) and adrenals (increase in fatty droplets, males and females). Similar changes were seen in the adrenals of some male rats dosed at 20 mg/kg/day. Male rat specific kidney pathology (hyaline droplet formation and basophilic changes in the tubular epithelium of the kidney) was observed in males in all dose groups. These findings are not relevant for human risk assessment.

The no effect level for systemic toxicity was therefore considered to be 20 mg/kg/day for females and 4 mg/kg/day for male rats (based on the adrenal effects at higher dose levels).

In the supporting study(Litton Bionetics, 1980),dicyclopentadiene was administered by incorporation into the diet at concentrations of 100, 300 and 1000 ppm to male and female beagle dogs for 13 weeks. No significant toxicity was seen at any dose level. Minor indications of intestinal distress (vomiting and soft stools) seen at the highest dose (1000 ppm) were considered to be of no toxicological significance.The NOAEL of dicyclopentadiene was therefore considered to be 1000 ppm (25 mg/kg/day) to beagle dogs following 13 week dietary administration.

Inhalation

Key studies were conducted in Fischer 344 rats and B6C3F1 mice (Bushy Run, 1982). Vapour generation was carefully controlled and analysed to ensure that no cyclopentadiene was formed during vapour generation. Animals were exposed (whole body) to vapours of 0, 1, 5 or 50 ppm dicyclopentadiene, 6 hr/day, 5 days/week for 13 weeks, followed by a 13-week recovery period. Animals were killed following completion of exposure at 2, 6, or 13 weeks and at post exposure weeks 4 or 13. 

There was no mortality in any of the rats butapproximately 20% of the mice (both sexes) of the 51 ppm exposure group died during the exposure period.

In rats exposed to 51 ppm, relative liver weights were significantly increased in males.

The kidney effects seen only in male rats exposed to dicyclopentadiene were reported by Bevan et al (1992) to be characteristic of alpha2u-nephropathy, which is considered to be of no relevance to human risk assessment.

The rat study indicates an overall low degree of systemic toxicity following sub-chronic inhalation exposure of dicyclopentadiene at exposure levels up to 51 ppm. As concluded by Bevan et al. (1992), increased liver weights in the absence of histopathologic changes were not considered to be an adverse effect. Excluding the male, rat-specific hyaline droplet nephropathy seen at 5.1 and 51 ppm during the exposure period, the no observed adverse effect concentration (NOAEC) in this study is therefore considered to be 51 ppm (276 mg/m3) for both male and female rats.Since approximately 20% of the mice (both sexes) of the 51 ppm exposure group died during the exposure period, the NOAEC is concluded to be 5.1 ppm (27.6 mg/m³) for male and female mice.

In the supporting studies by Kinkead et al (1971), rats were exposed (whole body) for 7 hours/day, 5 days/week for 89 days to vapours of 0, 107, 190, and 399 mg/m3, dogs were exposed to 0.00, 8.9, 23.5 and 32.5 ppm DCPD. One female rat exposed to 19.7 ppm had a 5 minute convulsion after 45 days exposure (the only potentially treatment-related effect at this concentration). No convulsions were observed among the 35.2 ppm rats. One female rat given 73.8 ppm had convulsions for about 5 min immediately after the exposure on day 19. No additional signs attributable to exposure were observed for the remainder of the study. At 32.5 ppm, BUN and acid phosphatases values were slightly elevated in the dogs at the end of 20 days, while the alkaline phosphatase values were elevated only after 85 days. At 23.5 ppm, SGOT and acid phosphatase values were elevated at 20 days. No effects were recorded at 8.9 ppm. Small decrease in neutrophil levels were recorded after 85 days of exposure to 23.5 ppm DCPD. There were no dose-dependent pathological changes.The results indicate that the subchronic NOAEC of DCPD was 19.7 (107 mg/m3) for rats and 23.6 ppm (125 mg/m3) for dogs.

Human studies

In studies in human volunteers to ascertain the odour threshold of dicyclopentadiene vapour for man and to determine the human sensory response (Kinkead et al, 1981), some inadvertent exposure to dicyclopentadiene vapour occurred during the 5 month investigation period. Three workers experienced transitory headaches during the first 2 months, but not during the last 3 months.

Justification for selection of repeated dose toxicity inhalation - systemic effects endpoint:
Mortality in male and female mice at 276 mg/m3 was associated with pulmonary congestion resulting from chronic irritation of the lung.

Justification for selection of repeated dose toxicity inhalation - local effects endpoint:
Mortality in male and female mice at 276 mg/m3 was associated with pulmonary congestion resulting from chronic irritation of the lung.

Repeated dose toxicity: via oral route - systemic effects (target organ)glandular: adrenal gland

Justification for classification or non-classification

Dicyclopentadiene is classified as STOT RE Exp. 2 H373 for repeat dose toxicity under CLP due to the tremors and convulsions seen in the OECD 408 study at 100 mg/kg/day dose level in males and females.

However, while some effects were seen in repeat dose studies, these are believed to be due to chronic irritation of the lungs and gastrointestinal tract with secondary stress-related effects rather specific target organ toxicity. DCPD is irritating; therefore it is biologically plausible that the mortality is mostly attributable to respiratory and gastric irritation effects rather than systemic effects. Liver and thyroid effects seen in the rat oral studies were not considered sufficient to warrant classification.

Repeated exposure inhalation studies in rodents show mortality at levels that would be predicted by their LC50s, and appears related to respiratory irritation/portal-of-entry effects. The original Bushy Run 90-day study showed mortality in the mice at 276 mg/m³. The LC50 in mice is about half that of rats, which might be expected for a respiratory irritant (higher ventilation rate in the mouse). This justification for non-classification for the repeat dose toxicity (mortality in mice) is supported by the existing acute inhalation classification (Acute Category 2, H330).