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Description of key information

The key inhaled repeated dose toxicity study was a 90-day study in the rat conducted according to OECD 413 (DCC, 2013). The NOAEL was defined as 1 ppm (18.2 mg/m³), the lowest dose tested, based on hyperplasia and inflammation in the nasal tissues at 10 and 30 ppm, indicative of a mucosal irritant and therefore a local effect. The systemic NOAEL was considered to be 30 ppm (546 mg/m³) based on the absence of adverse effects in either sex up to the highest dose tested. The inhaled local LOAEC is considered to be the mid-dose, 182 mg/m³, and this is used as the starting point for calculation of the local Derived No Effect Level The key repeated dose oral  toxicity study (DCC, 2005) was a 4-week rat combined repeated dose toxicity study with the reproductive/developmental toxicity study screening test, conducted according to OECD TG 422 and with GLP compliance. A NOAEL of 1000 mg/kg bw/day, the highest dose tested, was reported in this study with the liver effects (increased absolute and/or relative liver weight in all treated groups and periportal lipidosis at all doses in females) described as “of minimal toxicologic significance” and the thyroid effects (follicular cell hypertrophy, incidence possibly treatment-related in both sexes) referred to as secondary and adaptive to the liver changes.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
NOAEL
1 000 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
546 mg/m³
Study duration:
subchronic
Species:
rat
System:
respiratory system: upper respiratory tract
Organ:
nasal cavity

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
LOAEC
182 mg/m³
Study duration:
subchronic
Species:
rat

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

Additional information

In the key inhaled OECD 413 study on D6 (DCC, 2013), the test article was administered daily, 6 hours/day for 90 days at 0, 1, 10 or 30 ppm. At the end of dosing necropsy test article-related findings were noted in the nasal tissues of both sexes and the liver of females at ≥ 10 ppm and the lungs of females at 30 ppm. Increased incidence and severity of minimal to mild subacute inflammation, mucous cell hyperplasia and epithelial cell hyperplasia of the squamous (30 ppm males only), respiratory and/or transitional epithelium were observed in the rostral-most section (level 1) of the nasal cavity. At level 2 only an increased incidence of mucous cell hyperplasia was noted. These observations were considered to be adverse and consistent with a mucosal irritant. The incidence and severity of the nasal findings did not resolve after a 28-day recovery period, with the exception of the mucous cell hyperplasia at level 2 in females. A higher incidence of alveolar macrophage accumulation at 30 ppm and higher incidences of minimal and mild periportal hepatocellular vacuolation at ≥ 10 ppm were both noted in females at the end of dosing necropsy; the incidence of these changes was not statistically significant and they were not defined as adverse. At the end of the recovery period the extent of accumulation of alveolar macrophages in the 30 ppm group was comparable to controls and the incidence of periportal hepatocellular vacuolation was only marginally higher than controls suggesting near complete recovery. There were no other findings considered to be attributable to treatment. Based on the hyperplasia and inflammation in the nasal tissues at 10 and 30 ppm the No-Observed-Adverse-Effect-Concentration (NOAEC) was stated to be 1 ppm and as the findings in the nasal tissues may be considered to be a local effect this may be considered to be the inhaled local NOAEC. The inhaled local LOAEC is considered to be the mid-dose, 182 mg/m3, and this is used as the starting point for calculation of the local Derived No Effect Level (refer to Section 5.11 for further information). Although not explicity stated, the inhaled systemic NOAEC may be considered to be 30 ppm (546 mg/m3) in this study as the only changes stated to be considered adverse were the findings in the nasal cavity.

In the key oral OECD 422 study on D6 (Dow Corning Corporation, 2005), the test article was administered in corn oil daily, seven days a week by oral gavage to 10 rats/sex/group at 0, 100, 330 or 1000 mg/kg/day for up to 45 consecutive days. All female rats in each of the treatment groups expressed hepatic lipidosis with the exception of one animal in the high dose group. The severity among dose groups was not statistically different and was not dose-responsive. Thyroid effects (follicular cell hypertrophy, incidence possibly treatment-related in both sexes) were also noted and referred to as secondary and adaptive to the liver changes.

After reviewing additional oral data on D6 (administered without a vehicle) and conducting a literature review of periportal lipidosis, it was concluded that the periportal lipidosis observed in this study was more likely an exacerbation of the diffuse fatty changes of the liver seen following oral gavage administration of corn oil or an interaction between the test substance and the corn oil vehicle.  

Key evidence to support the argument that the periportal lipidosis is attributed to the corn oil vehicle comes from an older study, where the test material is administered neat. The 1990 oral study with neat D6 (DCC, 1990) at a dose of 1500 mg/kg/day for 28-days did not identify any histological effects, including periportal lipidosis. In 2010, a review of the slides from this older 1990 study was conducted to specifically look for the periportal lipidosis and other liver effects. The review of slides in 2010 did not find any evidence of periportal lipidosis (or other histological findings) at the dose of 1500 mg/kg/day for D6 when it was administered neat via oral gavage. 

In addition, well-founded and compelling reasons not to interpret observations of hepatic lipidoses in rodents as treatment-related adverse effects when the test substance is administered by corn oil gavage were found during a review of the literature (Condie et al., 1986; Bull et al., 1986; Lowe et al., 2009; Marty et al., 2007). Several studies provide evidence that the use of corn oil (CO) as the vehicle for gavage administration of test substances may increase the incidence and severity of fatty infiltrates in liver and may alter (either exacerbate or reduce depending on species and conditions) hepato- and nephro-toxicity in rats and mice. Taken together, these studies suggest caution in interpreting fatty changes in the livers of rodents administered test substances by gavage in corn oil vehicle. In particular, hyperlipidosis that occurs without a clear dose response may be due to interactions between the test substance and the corn oil vehicle rather than to the test substance alone. 

There was also an NTP study with corn oil that demonstrated significant increases in diffuse fatty changes of the liver following oral gavage administration. This study was designed to evaluate the effects of various concentrations of various oils (safflower oil, corn oil, and tricaprylin) on the incidence and pattern of neoplasms in the F344/N rat. To evaluate corn oil as well as two other gavage vehicles for potential toxicity, corn oil, safflower oil, and tricaprylin were administered by gavage to male F344/N rats for 2 years. This NTP report focused on in the influence of corn oil as a gavage vehicle on the incidence and severity of pancreatic neoplasms, but additionally provides data on non-neoplastic changes. In a comparison of untreated controls, saline, and 2.5 ml/kg, 5 ml/kg, and 10 ml/kg corn oil in this study, NTP noted significant increases in “diffuse fatty changes” in the liver of rats receiving corn oil. The incidences for each of these groups, respectively, are: 3/50 (6%), 2/50 (4%), 19/50 (38%), 27/50 (54%), and 33/50 (66%). NTP noted the potential confounding effects of corn oil gavage in the interpretation of bioassay results.

Therefore, based on the additional oral data on neat D6 and the findings of the literature review of periportal lipidosis, it can be concluded that the periportal lipidosis observed in this study was more likely an exacerbation of the diffuse fatty changes of the liver seen following oral gavage administration of corn oil, or an interaction between the test substance and the corn oil vehicle, and not an inherent toxicity of the test material.

The OECD 422 study is selected as the key oral study, as it is the most reliable and most recent study available for repeated dose toxicity by this exposure route.


Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint:
The key oral repeat dose toxicity study was conducted according to an appropriate guideline and in compliance with GLP.

Justification for selection of repeated dose toxicity inhalation - systemic effects endpoint:
Study was conducted in accordance with an appropriate guideline and in compliance with GLP.

Justification for selection of repeated dose toxicity inhalation - local effects endpoint:
Study was conducted in accordance with an appropriate guideline and in compliance with GLP.

Repeated dose toxicity: inhalation - systemic effects (target organ) respiratory: lung; respiratory: nose

Justification for classification or non-classification

Based on the available sub-acute and sub-chronic toxicity studies for D6, there is no evidence that classification for Specific Target Organ Toxicity (STOT) is required following repeated oral or inhalation exposure according to Regulation (EC) No 1272/2008. No data are available for the dermal route.