Registration Dossier

Diss Factsheets

Administrative data

Description of key information

A GLP-study according to OECD guideline 422 with oral gavage administration of the test material to rats is available for DVB-96. Several repeated dose inhalation studies in rats and mice, equivalent to OECD guidelines 412 and 413, are available for DVB-55 and DVB-HP. No repeated dose studies via the dermal route have been conducted with the reaction mass of divinylbenzene and ethylstyrene.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion
Dose descriptor:
NOAEL
30 mg/kg bw/day

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion
Dose descriptor:
NOAEC
133 mg/m³

Additional information

Oral route: a combined repeated-dose toxicity and reproductive and developmental toxicity study (OECD 422) has been conducted using oral gavage administration of divinylbenzene (96%) to male and female rats. Rats were exposed to 0, 30, 100, 300, or 1000 mg/kg bw day. There were no deaths or moribund cases in any of the male groups. However, there was one death and one moribund case in the high-dose female group. In the high dose group, lowered skin temperatures, depilation and soiling of fur were seen for both sexes. In addition, reduced spontaneous movements and bleeding from the vagina was seen in the females. Both males and females showed reduced body weight gain and reduced food consumption at the two high dose levels. The males also showed changes in blood chemistry. High Increased relative liver weights were seen in males at 100 mg/kg, and increased absolute and relative liver weights, or tendencies towards this, were seen in the 300 mg/kg and higher groups. For females high relative weights of the kidneys were seen in the 300 mg/kg and 1000 mg/kg group. Reduced relative and absolute thymus weights, low absolute spleen weights, and a tendency towards low relative spleen weight, as well as increased relative liver, kidney, and adrenal weights were seen in the 1000 mg/kg group. No histopathological changes were observed in any of the males. In females, atrophy of both the cortex and medulla of the thymus, atrophy of the marginal zone of the spleen and degeneration / necrosis of the urinary tubules in the cortex-medulla boundary of the kidneys were seen in the high dose group. In the moribund cases central necrosis in the lobules of the liver, reduction of thymogen granules in the acinar cells of the pancreas, erosion of the glandular stomach mucosa and reduced hematopoiesis of the bone marrow were seen. The NOEL of DVB-96 based on general toxicological effects was 30 mg/kg/day for the males (due to high relative livers weights seen from the 100 mg/kg dose) and 100 mg/kg for the females (due to suppression of body weight increases and a decrease in food consumption from the 300 mg/kg dose).

Inhalation route: Several studies via the inhalation route are available for DVB-HP and DVB-55.

In a 14-day inhalation study with DVB-55, rats and mice were exposed daily to 0.25, 1.0 and 2.5 mg/l or 0.1, 0.25 and 1.0 mg/l, respectively. Rats exposed to 1.0 or 2.5 mg/l of DVB-55 exhibited very slight to slight degenerative and regenerative alterations of olfactory neuroepithelium, but no other histopathologic alterations. The nasal effects are not considered relevant for human risk assessment based on read-across data from structurally related chemicals (see below). Therefore, a NOAEC of 2.5 mg/l (470 ppm) will be taken forward for the risk characterization. Four out of ten mice died at the highest concentration (1.0 mg/l). Renal tubular degeneration and an increase in alanine aminotransferase activity accompanied by liver weight changes and microscopic centrilobular hepatocellular alterations were observed in this group. These morphologic changes in the liver and kidneys were most noticeable in those mice which died during exposure. Mice exposed to 0.25 or 1.0 mg/l of DVB-55 also exhibited very slight to slight degenerative and regenerative alterations of the olfactory neuroepithelium. The nasal effects are not considered relevant for human risk assessment. Therefore, a NOAEC of 0.25 mg/l (47 ppm) will be taken forward for the risk characterization.

In a 13-week inhalation study in rats with daily exposure to 25, 50, 100, 200 and 400 ppm of DVB-HP all rats survived to the end of the study. At the high dose levels increased weights of kidney, liver, heart & testis were observed. The increase in kidney weights in male rats is considered to be a species specific effect in male rats due to alpha-2-µ globulin mediated effects. Incidences of degeneration of the olfactory epithelium in 200 and 400 ppm rats and basal cell hyperplasia of the olfactory epithelium in rats exposed to 100 ppm or greater were significantly increased. Nasal/eye discharge was noted in 400 ppm males and 100 ppm females. In another 13-week inhalation study with mice and exposure concentrations of 12.5, 25, 50, 100 and 200 ppm of DVB-HP all high-dose males and nine females died early. Final mean body weights were significantly lower in males and females exposed to 25, 50, or 100 ppm when compared with chamber controls. Lethargy or hypoactivity was observed in the higher exposure concentration groups. Exposure to divinylbenzene was associated with necrosis of the liver and kidney in 200 ppm males and females dying early. In all exposed groups of male and female mice, there was necrosis of nasal cavity lateral walls, olfactory epithelium, and glands with resultant atrophy of olfactory epithelium and glands in females. A lower number of animals had necrotic or degenerative changes of the upper respiratory tract. However, the nasal effects observed in rats and mice after inhalation exposure to DVB-HP are not considered relevant for human risk assessment based on read-across data from structurally related chemicals (see below). Therefore, a NOAEC of 100 ppm for rats and a NOAEC of 25 ppm for mice will be taken forward for the risk characterization. In mice the only other effect observed at 25 ppm was a decrease in final body weights which can be considered secondary to the nasal irritation and general discomfort as it is not accompanied by any systemic effect at this dose level. Overall similar effects were observed in the 14-day inhalation studies with DVB-HP in rats and mice at higher dose levels resulting in a NOAEC of 100 ppm for rats and 50 ppm for mice. Based on the similarity of the effects observed in the 14-day inhalation studies with DVB-55 and DVB-HP at comparable dose levels, it can be concluded that the NOAEC from the sub-chronic studies with DVB-HP are also applicable to and sufficiently protective for exposure to DVB-55 and DVB-63.

Available information on treatment-related histopathologic nasal effects in rats and mice following exposure to DVB or styrene for 3 months or 2 years, were reviewed to determine if these effects were comparable. In mice, inhalation of DVB at 25 ppm or greater for 3 months was reported to cause necrosis of olfactory epithelium, which was not reported in mice after 3-month exposure to styrene even at 200 ppm (exception: 2 early deaths at 200 ppm styrene were reported to have manifested marked olfactory necrosis). It must be noted that DVB inhalation study was conducted in B6C3F1 mice and styrene studies were conducted with CD-1 mice and whether or not this strain difference may have contributed to this discrepancy is not clear. With the exception of some minor differences, all other nasal effects induced by DVB were comparable to those induced by styrene, although comparison to similar dose-levels could not be made (lowest doses for DVB and styrene were 12.5 and 50 ppm respectively). Comparison of the histopathologic nasal effects induced by DVB or styrene inhalation in mice for a 2-year period showed, that with the exception of suppurative inflammation in the nasal lumen of mice treated with DVB at 10 ppm or greater, other reported nasal effects also occurred with styrene exposure and thus, in general, were comparable to the spectrum of changes described for styrene induced nasal effects in mice. It is concluded from the review of available information, that the described nasal effects for rats and mice exposed to DVB, in general, were comparable to most, if not all effects described for styrene. However, the important difference noted was the occurrence of necrosis of olfactory epithelium in mice exposed to DVB for 3 months at concentrations of 25 ppm or above, an effect not described in mice following 3-month exposure to styrene even at the highest dose of 200 ppm. However, at the end of 2 years, nasal effects were largely comparable between those caused by DVB or styrene. Although, the exact reasons for this difference noted at the end of 3-months are not clear, it may be due to a higher irritancy and/or other possible olfactory metabolic effects of DVB compared to those of styrene.

Further, it has been established that rats and mice are particularly sensitive to respiratory tract toxicity following styrene exposure. Inhalation of styrene by mice results in cytotoxicity in terminal bronchioles, followed by increased incidence of bronchioloalveolar tumors, as well as degeneration and atrophy of nasal olfactory epithelium. In rats, no effects on terminal bronchioles are seen, but effects in the nasal olfactory epithelium do occur, although to a lesser degree and from higher exposure concentrations. Whole-body metabolism studies have indicated major differences in styrene metabolism between rats and mice. The major differences are 4- to 10-fold more ring-oxidation and phenylacetaldehyde pathways in mice compared to rats. The data indicate that local metabolism of styrene is responsible for cytotoxicity in the respiratory tract. Cytotoxicity is seen in tissues that are high in CYP2F P450 isoforms. These tissues have been demonstrated to produce a high ratio of R-SO compared to S-SO (at least 2.4:1). In other rat tissues the ratio is less than 1, while in mouse liver the ratio is about 1.1. Inhibition of CYP2F with 5-phenyl-1-pentyne prevents the styrene-induced cytotoxicity in mouse terminal bronchioles and nasal olfactory epithelium. RSO has been shown to be more toxic to mouse terminal bronchioles than S-SO. In addition, 4-vinylphenol (ring oxidation of styrene) has been shown to be highly toxic to mouse terminal bronchioles and is also metabolized by CYP2F. In human nasal and lung tissues, styrene metabolism to SO is below the limit of detection in nearly all samples, and the most active sample of lung was approximately 100-fold less active than mouse lung tissue. It can be concluded that styrene respiratory tract toxicity in mice and rats, including mouse lung tumors, are mediated by CYP2F-generated metabolites. The PBPK model predicts that humans do not generate sufficient levels of these metabolites in the terminal bronchioles to reach a toxic level. Therefore, the postulated mode of action for these effects indicates that respiratory tract effects in rodents are not relevant for human risk assessment.

According to the assessment presented above the nasal effects caused by inhalation exposure to DVB are comparable to the effects caused by inhalation exposure to styrene. In addition, it was shown that the major routes of DVB hepatic metabolism are comparable to styrene and it is expected that the routes of non-hepatic metabolism of DVB would also be consistent with those observed for styrene (see section 7.1.1 of IUCLID). Therefore, it is concluded that the nasal effects observed in mice and rats after inhalation exposure to DVB are not relevant for human exposure to DVB.


Repeated dose toxicity: via oral route - systemic effects (target organ) digestive: liver

Repeated dose toxicity: inhalation - systemic effects (target organ) digestive: liver; urogenital: kidneys

Justification for classification or non-classification

No classification for repeated exposure, according to Annex VI of Directive 67/548/EE,C is proposed for the reaction mass of divinylbenzene and ethylstyrene as the NOAECs from the repeated dose inhalation studies are above the threshold for classification and the only effect observed after repeated oral exposure to 100 mg/kg bw/day of DVB-HP was relative increased liver weights (without accompanying histopathology) which is considered to be an adaptive effect.