3,3,6,6-tetramethoxy-2,7-dioxa-3,6-disilaoctane

Endpoint summary

Description of key information

Several repeated dose inhalation studies with the test material as a vapor are available and were evaluated in a weight of evidence approach:

Crofoot et al., 1993:

An acute and 14 -day repeated dose inhalation study was initiated to assess the inhalation toxicity and to determine the NOAEL of DOW CORNING® X1-6154A Additive in rats. The study consisted of both an acute and repeated dose phase. Eight groups of five rats/sex were exposed acutely for six hours to target concentrations of 0, 0.5, 1.0 and 2.0 ppm of the test material. Four groups, one from each concentration level, were sacrificed immediately following exposure. The remaining groups were scheduled to be sacrificed following a 14 -day recovery period. The repeated dose phase was scheduled to expose four grups of rats to the same target concentrations as the acute phase for six hours per day for two weeks.

The actual exposure concentrations of DOW CORNING® X1-6154A for the acute and repeated dose phases were 0.4, 0.9 and 1.9 ppm.

In the repeated dose phase, two males and two females in the 2.0 ppm group died after the second exposure to DOW CORNING® X1 -6154A Additive. All surviving rats in the 1.0 and 2.0 ppm groups were sacrificed in a moribund state before the third exposure. Rats in the 0.5 ppm group were sacrificed in a moribund state after the fourth exposure along with the corresponding control animals. Test article-related gross findings in the repeated dose phase included corneal opacity and ulceration, nasal obstruction and failure of the lungs to collapse. These gross findings were correlated with histopathologic changes observed in these tissues. Microscopic examination of tissues and organs indicated that various levels of the respiratory tract had epithelial necrosis with associated fibrinopurulent exudate, olfactory epithelium was less severely involved and squamous epithelium was spared. Chemical related toxicity was also observed in the eye and lung. A NOAEC could not be determined.

Siddiqui et al., 1997:

A 14 -day repeated dose inhalation toxicity study was conducted to investigate the inhalation toxicity of DOW CORNING® X1 -6145A Additive, chemically described as hexamethyldisilylethane (CAS no 18406 -41 -2), in rats. A previously conducted inhalation toxicity study with DOW CORNING® X1 -6145A Additive was terminated, because the target exposure concentrations were too high and caused morbitiy in rats (Crofoot et al., 1993). The purpose of the present study was to assess the repeated dose inhalation toxicity of DOW CORNING® X1 -6145A Additive and to determine the NOAEL in rats.

Four groups of ten male and ten female Fischer 344 rats were exposed to target concentrations of 0, 50, 100 and 200 ppb of the substance for six hours a day, for ten exposures over 14 days (excluding weekends). Animals were observed for treatment-related signs of toxicity, growth, and mortality. At termination of the study, rats were sacrificed and examined fro changes in organ weights, gross pathology, and histopathology.

No mortality was observed in the study. Very slight to moderate rales were observed in several animals exposed to 100 and 200 ppb. No apparent treatment-related clinical signs were observed in animals exposed to 50 ppb. Statistically significant decreases in body weights were observed in males exposed to 200 ppb on day 8, 15, and at sacrifice. Female body weights were decreased in animals exposed to 200 ppb onl day 8 only. Statistically significant increases in liver/body weight ratios were observed in males exposed to 100 and 200 ppb of the test material. Statistically significant increases in kidney/body weight ratios were observed in males exposed to 200 ppb of the test material. A statistically significant increase in liver/body weight ratio and in the adrenal/body weight ratio was observed in females exposed to 200 ppb of the test material. There were no other statistically significant differences in organ weights between test and control animals.

There were no apparent test article-related gross pathological changes in exposed animals. Test article-related changes were observed microscopically in the respiratory tract of all animals exposed to the test material. The nares, nasal cavity, and pharynx were the most common sites of test article-related changes with the larynx and trachea only infrequently affected. Squamous metaplasia and acute inflammation of the nasal cavity were the most common findings in the 200 ppb group and also occurred, with somewhat reduced incidence and severity, in many rats from the 50 and 100 ppb groups. An increased activity of mucus goble cells of the respiratory epithelium, characterized by incresaed height and prominence of goblet cells with formation of microcysts, was the most common finding in all sections of the nasal cavity from the 50 and 100 ppb groups. All lesions in the lung and other organs examined microscopically were considered agonal and spontaneous and unrelated to test article exposure.

Based on these results, a NOAEC was not established for the test material in Fischer 344 rats under the conditions of this study.

Kolesar et al., 1992:

A 14 -day vapor inhalation toxicity study was initiated in rats to assess the inhalation toxicity of DOW CORNING® X1-6154A Additive. Three groups of five male and five female Sprague-Dawley rats were to be exposed to target concentrations of 0, 3 and 10 ppm of DOW CORNING® X1 -6154A Additive for six hours/day, five days a week, for two weeks. One male rat in the 10 ppm group died during the second exposure period. After the second exposure, all surviving test animals were clinically moribund in severe respiratory distress and the study was terminated. The actual overall mean exposure concentration of DOW CORNING® X1 -6154A Additive for the test groups were 2.0 and 13.0 ppm. Clinical signs observed in the two-day period included dyspnea, lethargy and nasal and/or oral discharges. Gross pathological examination revealed nasal passage occlusion and distension of the digestive tracts of all exposed animals. Histopathology of the respiratory tract revealed severe and extensive damage to the lining of the nasal cavity, trachea and bronchi in animals exposed to the test-article. Lesions, consisting of necrosis and desquamation of respiratory tract epithelium and fibrinopurulent inflammatory exudate, were generally most severe in the most anterior level of the nasal cavity. Similar necrotizing lesions were present throughout the respiratory tree down to the level of the bronchi in most rats. Lung parenchyma was not involved with the test article-related lesions. A NOAEC could not be determined.

Discussion:

A NOAEC could not be determined in any of the available repeated dose studies. The test material exhibited severe toxicity in all of the studies, including mortality at concentrations as low as 0.5 ppm. The study by Siddiqui et al. (1997) was the only one in which mortality did not occur. None of the concentrations tested in that study 50, 100 and 200 ppb marked a NOAEC, because because adverse histopathological findings in the upper respiratory tract were observed even at the lowest concentration. Thus, the LOAEC of the test material is 50 ppb.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Link to relevant study records

Reference

Reference 1

Endpoint:

short-term repeated dose toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Remarks:

GLP-compliant non-guideline study with 14 d of exposure. Otherwise similar to guideline and reported in sufficient detail.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 412 (Subacute Inhalation Toxicity: 28-Day Study)

Deviations:

yes

Remarks:

animals were exposed for 14 days only, some parameters like clinical chemistry and hematology were not reported

GLP compliance:

yes

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

Male and female CD(R) (Sprague-Dawley) rats (weighing approximately 100-185 g and 5-8 weeks of age) were purchased from Charles River Breeding Laboratories, Kingston, New York. Upon arrival at the TOxicology Department, all rats were quarantined for one week. Approved rats were weighed and randomized into 12 controls and test groups (5/sex/group) using the Xybion ASLECT program. Groups I-VIII were employed in the acute phase and Groups IX-XII were used in the repeat dose phase of the study. After randomization, test animals were ear tagged and color coded tags (listing the rat's sex, exposure level, ear tag, file and group numbers) were placed on the outside of each cage.

The rats were housed individually in suspended stainless steel, wire mesh bottom cages were designed to be placed within the exposure chambers. After each exposure, the rats were returned to their original housing. The rats were fed certified Purina rodent chow and water ad libitum except during exposures. The rats were housed during non-exposure periods in rooms designed to be maintained at 68-73°F and 30-70 percent relative humidity. A light cycle of alternating 12 hours light and 12 hours dark was maintained.

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Details on inhalation exposure:

Exposures were conducted in 2 m3 liter stainless steel whole body exposure chambers. The chambers were operated under dynamic conditions where the chamber air was room air, which had been filtered (hepa and charcoal filters). Airflows through the chambers were kept at approximately 12-15 air changes per hour. Chamber temperature, humidity, and airflow were monitored continuously and were recorded every five minutes by the Camile(R) Data Acquisition System during the exposure periods. The test material was introduced into the chambers through special designed glass J-tubes. The test material was metered into the J-tubes with harvard Apparatus syringe pumps. Instrument air which was filtered, flowed through the J-tubes at a controlled rate. The air/vapor mixture passed into the inlet port at the top of the chambers. During the exposure periods, attempts were made to keep the actual concentrations of the test material in the chambers as constant as possible.
The duration of each exposure period was six hours after equilibration of the chamber concentration. The equilibration time, which is a function of chamber airflow, was approximately 25 minutes. The amount of test material used during the exposure period was determined by pre- and post-measuring the weight of the test material in each syringe. The exposure duration (exposure period and equilibration time), test material used and airflows through the chambers were then used to calculate nominal concentrations.
Actual chamber concentrations were measured a minimum of once an hour by a Varian(R) 3400 Gas Chromatograph (GC) equipped with a flame ionization detector. The GC was calibrated before the start of the study and one bag standard was prepared and analyzed during each exposure period.

Analytical verification of doses or concentrations:

yes

Duration of treatment / exposure:

6 h, 10x over 14 days

Frequency of treatment:

daily

Dose / conc.:

0 ppm

Dose / conc.:

0.5 ppm

Dose / conc.:

1 ppm

Dose / conc.:

2 ppm

No. of animals per sex per dose:

5

Control animals:

yes

Details on study design:

Four groups of animals were exposed for two weeks and sacrificed immediately following the last exposure.
All surviving rats were observed daily during the post-exposure period for treatment-related signs of toxicity, in particular, any evidence of respiratory, dermal, behavioral, nasal and/or ocular changes.
Individual body weights were collected prior to exposure for animals in all groups. Body weights for rats in groups V-VIII (single exposure with 14 day post-exposure observation) were scheduled to be measured on days 1, 8 and 15.
A gross pathologic examination was conducted on all rats. The brain, kidneys, lungs, liver, spleen, adrenals and ovaries or testes were dissected free of fat and weighed from rats surviving until scheduled sacrifice. The lungs were removed intact, weighed and distended to their approximate normal inspiratory volume by tracheal infusion with 10% neutral buffered formalin.
Organs or samples of organs or tissues listed below for animals in all groups were preserved in 10% neutral buffered formalin. Hematoxylin and eosin stained paraffin sections of the organs and tissues were prepared using standard histologic methods:
Adrenal (2), Nasal Cavity (4 levels), brain (3 levels), eyes (2), heart, kidneys (2), larynx, liver (3 lobes), lymph nodes (mandibular, mediastinal), lungs (5 lobes), trachea (multiple levels, cervical and bifurcation), ovaries (2), pharyns, spleen, testes (2), thymus.
Histopathological examination was performed on the tissues specified above for all male and female animals in both the acute and repeated dose phases at all exposure concentrations by consulting pathologist Dr. Robert G. Geil, D.V.M., Diplomate, American College of Veterinary Pathologists.

Statistics:

Statistical analyses were conducted on terminal body weights, organ weights and organ weight ratios where appropriate. This data was analyzed by a two-sided Welch Trend test. If a significant overall trend was detected, then all follow-up tests were one-sided and in the same direction as the overall trend. Body weights, collected during the in-life phase of the study, were statistically analyzed by the Dow Corning HBS ANOVA program. All tests were conducted at the P<=0.05 level of significance.

Mortality:

mortality observed, treatment-related

Description (incidence):

Two males and two females in the 2.0 ppm group died after a second six-hour exposure. All surviving rats in the 1.0 or 2.0 ppm groups were sacrificed in a moribund state on study day three. On study day five, all rats in the 0.5 ppm group were sacrificed in a moribund state with the corresponding control group.

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

Test article related macroscopic findings included corneal opacity and ulceration, nasal obstruction and failure of the lungs to collapse. These findings correlated with microscopic changes. All other findings which were observed during gross necropsy were considered spontaneous or agonal and not test article-related.

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Microscopic examination of tissues and organs indicated that various levels of the respiratory tract, i.e., nasal cavity, pharynx, larynx and trachea, had test-article-related epithelial necrosis with associated fibrinopurulent exudate. As with the acute phase of this study, the respiratory epithelium of the nasal cavity was most severely affected in the repeated dose phase animals; this change was most evident in rats from the 1.0 and 2.0 ppm groups. However, in contradistinction from the 0.5 ppm groups of the acute phases, rats from the 0.5 ppm group of the repeated dose phase had necrosis on the respiratory epithelium of the nasal cavity; olfactory epithelium was less severely involved and squamous epithelium was spared. As with the acute recovery phase, the eye also had test article-related effects which included desquamation, hyperplasia and keratitis of corneal epithelium. The lung had test article-related necrosis of bronchial epithelium. THere was no evidence of spontaneous diseases which would have had an effect on the validity of the study in any of the organs examined microscopically.

Dose descriptor:

NOAEC

Effect level:

< 0.5 ppm

Sex:

male/female

Basis for effect level:

gross pathology

histopathology: non-neoplastic

mortality

Critical effects observed:

yes

Lowest effective dose / conc.:

0.5 ppm

System:

other: respiratory system

Organ:

bronchi

larynx

lungs

nasal cavity

trachea

Treatment related:

yes

Test article-related macroscopic findings in the repeated dose phase included corneal opacity and ulceration, nasal obstruction and failure of the lungs to collapse. These findings correlated with microscopic changes. All other findings which were observed during gross necropsy were considered spontaneous or agonal and not test article-related.

Microscopic examination of tissues and organs indicated that various levels of the respiratory tract, i.e., nasal cavity, pharynx, larynx and trachea, had test article-related epithelial necrosis with associated fibrinopurulent exudate. As with the acute phases of this study, the respiratory epithelium of the nasal cavity was mose severely affected in the repeated dose phase animals; this change was most evident in rats from the 1.0 and 2.0 ppm groups. However, in contradistinction from the 0.5 ppm groups of the acute phases, rats from the 0.5 ppm grou pof the repeated dose phase had necrosis of respiratory epithelium of the nasal cavity; olfactory epithelium was less severely involved and squamous epithelium was spared. As with the acute recovery phase, the eye also had test article-related effects which included desquamation, hyperplasia and keratitis of corneal epithelium. THe lung had test article-related necrosis of bronchial epithelium. There was no evidence of spontaneous disease which would have had an effect on the validity of the study in any of the organs examined microscopically.

Conclusions:

The results of this study indicate that the inhalation exposure of DOW CORNING® X1-6154A Additive at the concentrations and conditions of this study roduced significant toxicologic effects in rats. This study did not establish a no-observable-effect-level for the test material.

Executive summary:

An acute and 14 -day repeated dose inhalation study was initiated to assess the inhalation toxicity and to determine the NOAEL of DOW CORNING® X1-6154A Additive in rats. The study consisted of both an acute and repeated dose phase. Eight groups of five rats/sex were exposed acutely for six hours to target concentrations of 0, 0.5, 1.0 and 2.0 ppm of the test material. Four groups, one from each concentration level, were sacrificed immediately following exposure. The remaining groups were scheduled to be sacrificed following a 14 -day recovery period. The repeated dose phase was scheduled to expose four grups of rats to the same target concentrations as the acute phase for six hours per day for two weeks.

The actual exposure concentrations of DOW CORNING® X1-6154A for the acute and repeated dose phases were 0.4, 0.9 and 1.9 ppm.

All rats in the acute phase, which were scheduled for immediate sacrifice, survived the exposure. Three rats, two male and one female, fromt the acute recovery phase died in the 2.0 ppm group. The remaining animals in this group were sacrificed in moribund state two days post-exposure. All other rats in the acute recovery phase survived to the scheduled sacrifice.

Clinical signs of toxicity which were considered treatment-related included ocular and nasal discharge, facial soiling, rough coats, soft feces, lethargy and labored breathing.

A statistically significant decrease in body weights was seen in male rats in the 0.5 and 1.0 ppm groups of the acute recovery phase.

Gross pathologic examination indicated that there were no test article-related lesions at necropsy in any of the rats from the acute phase which were sacrificed immediately after exposure. Histopathologic examination of tissues, however, indicated necrosis of respiratory epithelium of the nasal cavity in rats in the 1.0 and 2.0 ppm groups. Test article-related necrosis of the tracheal epithelium was also noted in these groups. No test article-related microscopic changes were observed in the respiratory tract or other organs examined in the 0.5 ppm group.

In the acute recovery phase, corneal opacity and a decrease in thymus size was noted in some animals in the 0.5 and 1.0 ppm groups. Several organs had test article-related effects, these included the eye and various levels of the respiratory tract. As in the acute immediate sacrifice phase of this study, necrosis of the respiratory epithelium of the nasal cavity was evident.

In the repeated dose phase, two males and two females in the 2.0 ppm group died after the second exposure to DOW CORNING® X1 -6154A Additive. All surviving rats in the 1.0 and 2.0 ppm groups were sacrificed in a moribund state before the third exposure. Rats in the 0.5 ppm group were sacrificed in a moribund state after the fourth exposure along with the corresponding control animals. Test article-related gross findings in the repeated dose phase included corneal opacity and ulceration, nasal obstruction and failure of the lungs to collapse. These gross findings were correlated with histopathologic changes observed in these tissues. Microscopic examination of tissues and organs indicated that various levels of the respiratory tract had epithelial necrosis with associated fibrinopurulent exudate, olfactory epithelium was less severely involved and squamous epithelium was spared. Chemical related toxicity was also observed in the eye and lung.

Reference 2

Endpoint:

short-term repeated dose toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 412 (Subacute Inhalation Toxicity: 28-Day Study)

Deviations:

yes

Remarks:

animals were exposed for 14 days only

GLP compliance:

yes

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

Male and female CD(R) (Sprague-Dawley) rats (weighing between 100-160 g and 5-7 weeks of age) were obtained from Charles River Breeding Laboratories, Portage, Michigan. Upon arrival at the Toxicology Department, all rats were quarantined for one wek. Approved animals were weighed and randomized into control and test groups using the Xybion ASLECT program. After randomization, test animals were ear-tagged and color coded tags (listing the animal's sex, exposure level, animal, file and group numbers) were placed on the outside of each cage.
The rats were housed individually in suspended stainless steel, wire mesh bottom cages. Before each exposure, animals were transferred into cages that were designed to be placed within the exposure chambers. After each exposure, the animals were returned to their original housing. The animals were fed certified Purina rodent chow and water ad libitum except during exposures. The rats were housed during non-exposure periods in rooms designated to be maintained at 68-73°F and 30-70% relative humidity. A light cycle of alternating 12 hours light and 12 hours dark was maintained.

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

air

Details on inhalation exposure:

Exposures were conducted in 450 liter stainless steel whole body exposure chambers. The chambers were operated under dynamic conditions where chamber air was room air, which had been filtered (HEPA and charcoal filters). The airflows through the chambers were kept at approximately 12-15 air changes per hour. Chamber temperature, humidity, and airflow were monitored continously and were recorded every five minutes by the Camile Data Acquisition System during the daily exposure period. The test material was introduced into the chambers through special designed glass J-tubes. The test material was metered into the J-tubes with FMI lab pumps. Intrument air which was filtered (Drierite) flowed through the J-tubes at a controlled rate. Glass beads and heating tape were used to help vaporize the test material. The air/vapor mixture passed into the inlet port at the top of the chambers. The exhaust air from the chambers was filtered with a hepa and charcoal filters and a water cyclone. During the exposure periods, attempts were made to keep the actual concentrations of the test material in the chambers as constant as possible.
The duration of each exposure period was six hours after equilibration of the chamber concentration. The equilibration time, which is afunction of chamber airflow, was approximately 20 min.
The amount of test material used during the exposure period was determined by pre- and post-measuring the weight of the test material in each graduated cylinder reservoir. The exposure duration (exposure period and equilibration time), test material used, and airflows through the chambers were then used to calculate nominal concentrations.
Actual chamber concentrations were measured a minimum of once an hour by a Varian(R) 4600 Gas Chromatograph (GC), which was connected to a Varian(R) 402 Microprocessor. The GC was calibtrated before the start of the study and one bag standard was prepared and analyzed during each exposure period.

Duration of treatment / exposure:

six hours/day, five days a week, for two weeks

Frequency of treatment:

daily

Dose / conc.:

0 ppm

Dose / conc.:

3 ppm (nominal)

Dose / conc.:

10 ppm (nominal)

Dose / conc.:

2 ppm (analytical)

Dose / conc.:

13 ppm (analytical)

No. of animals per sex per dose:

5

Control animals:

yes

Observations and examinations performed and frequency:

All animals were observed daily during the post-exposure period for treatment-related signs of toxicity. In particular, any evidence of respiratory, dermal, behavioral, nasal and/or ocular changes.
Individual body weights were recorded on the initial day of the study and before necropsy (terminal weight).

Sacrifice and pathology:

A gross pathological examination was conducted on all animals that died or were sacrificed at the termination of the study. The respiratory tract of the control and test-article exposed animals were collected, processed by standard techniques and examined microscopically.

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Clinical signs observed during the two-day period included dyspnea, lethargy and nasal and/or oral discharges.

Mortality:

mortality observed, treatment-related

Description (incidence):

One male animal in the high dose group died during the second exposure period. After the second exposure, all surviving exposed rats were clinically moribund in severe respiratory distress and the study was terminated. Clinical signs observed during the two-day period included dyspnea, lethargy and nasal and/or oral discharges.

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

Gross tissue damage attributable to test article exposure were observed in all exposed rats of both sexes in both the 3 and 10 ppm exposure groups. Nasal passage occlusion was evident in all exposed rats and the digestive tract of these animals were distended with gas. The lungs of these animals were not grossly abnormal in any animal.

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Histopathology of the respiratory tract revealed severe and extensive damage to the lining of the nasal cavity, trachea and bronchi in rats of both sexes exposed to the test article. The lesions, consisting of necrosis and desquamation of respiratory tract epithelium and fibrinopurulent inflammatory exudate, were generally most severe in the most anterior level of the nasal cavity. Similar necrotizing lesions were pesent throughout the respiratory tree down to the level of the bronchi in most rats. There appeared to be a lsight dose response with respect to severity between the 3 and 10 ppm levels with males tending to have more severe lesions than females within a given exposure level. Lung parenchyma was not involved with test article-related lesions.

Dose descriptor:

LOAEC

Effect level:

2 ppm

Sex:

male/female

Basis for effect level:

clinical signs

gross pathology

histopathology: non-neoplastic

mortality

Critical effects observed:

yes

Lowest effective dose / conc.:

2 ppm

System:

respiratory system: upper respiratory tract

Organ:

bronchi

nasal cavity

trachea

Treatment related:

yes

Dose response relationship:

yes

Relevant for humans:

not specified

Good agreement was observed between the actual and nominal atmospheric chamber concentrations. The overall mean concentration of DOW CORNING® X1 -6154A Additive to which the test groups were exposed were 2.0 and 13.0 ppm.

For further details on observations see section "attached bakcground material".

Conclusions:

Exposure of rats to DOW CORNING® X1 -6154A Additive at concentrations of 3 and 10 ppm (2 and 13 ppm actual concentrations) for 6 hrs/day for two days resulted in morbidity and termination of the study. Microscopic examination of the respiratory tract of animals exposed to the test-article revealed necrosis and desquamation of epithelium lining the nasal cavity, nasopharynx, trachea and bronchi, with concomitant fibrinopurulent inflammation. A NOAEC could not be determined in this study.

Executive summary:

A 14 -day vapor inhalation toxicity study was initiated in rats to assess the inhalation toxicity of DOW CORNING® X1-6154A Additive. Three groups of five male and five female Sprague-Dawley rats were to be exposed to target concentration sof 0, 3 and 10 ppm of DOW CORNING® X1 -6154A Additive for six hours/day, five days a week, for two weeks. One male rat in the 10 ppm group died during the second exposure period. After the second exposure, all surviving test animals were clinically moribund in severe respiratory distress and the study was terminated. The actual overall mean exposure concentration of DOW CORNING® X1 -6154A Additive for the test groups were 2.0 and 13.0 ppm. Clinical signs observed in the two-day period included dyspnea, lethargy and nasal and/or oral discharges. Gross pathological examination revealed nasal passage occlusion and distension of the digestive tracts of all exposed animals. Histopathology of the respiratory tract revealed severe and extensive damage to the lining of the nasal cavity, trachea and bronchi in animals exposed to the test-article. Lesions, consisting of necrosis and desquamation of respiratory tract epithelium and fibrinopurulent inflammatory exudate, were generally most severe in the most anterior level of the nasal cavity. Similar necrotizing lesions were present throughout the respiratory tree down to the level of the bronchi in most rats. Lung parenchyma was not involved with the test article-related lesions.

Reference 3

Endpoint:

short-term repeated dose toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 412 (Subacute Inhalation Toxicity: 28-Day Study)

Deviations:

yes

Remarks:

animals were exposed for 14 days only

GLP compliance:

yes

Specific details on test material used for the study:

The test material was characterized by Dow Corning's Analytical department using best available technology.
Identification: DOW CORNING® X1 -6145A Additive (1,2-Bis(trimethoxysilyl)ethane)
Lot no.: BN099001
Purity: approx. 94%.
Physical descirption: water white liquid
Stability: stable
Storage conditions: container was closed and kept away from water and moisture.

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

Male and female Fischer 344 rats weighing approximately 100-185 g and 5-8 weeks of age, were purchased from Charles River Laboratories, Kingston, New York. Upon arrival, all rats were quarantined for one week. Approved rats were weighed and randomized into control and test groups (10/sex/group) using the Xygion Pathox Aslect program. After randomization, test animals were uniquely identified with monel metal eartags and color coded tags placed on the outside of each cage listing the study number, gorup number, exposure level, ear tag number, and sex.
Animals were housed individually in suspended stainless steel, wire mesh bottom cages. Before each exposure, the animals were transferred into cages that were designed to be placed within the exposure chambers. After each exposure, the animals were returned to their oirignal housing. The rats were fed ceritfied Purina Rodent Chow and water via the automatic watering system ad libitum except during exposures. The sponsor or study director was not aware of any potential contaminants likely to be present in the diet or drinking water that would interfere with the results of this study. The rats were housed during non-exposure periods in a room maintained at 68-75°F, 40-70% relative humidity and light cylces of alternating 12 hours light and 12 hours dark. Temperature and humidity were monitored continously with a chart recorder. Animal room conditions were checked twice a day on weekdays and once a day on weekends.

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

air

Details on inhalation exposure:

Exposures were conducted in 2 m3 stainless steel whole body exposure chambers. The chambers were operated under dynamic conditions where chamber air was room air, which had been filtered (HEPA and charcoal filters): Airflow through the chambers were kept at approximately 10-15 air changes per hour. Chamber temperature, humidity, and airflow were monitored continously and were recorded every five minutes by the validated Camile Data Acquisition System. The test material for the 100 and 200 ppb groups was introduced into the chambers through special designed glass J-tubes. The test material was metered into the heated J-tubes with Harvard Apparatus syringe pumps. Intrument air which was filtered, flowed through the J-tubes at a controlled rate. The air/vapor mixture passed into the inlet port at the top of the chambers. Test material generation for the 50 ppb group was performed by preparing bag standards which were metered into the dilution air stream to produce the desired chamber concentration. During the exposure periods, attempts were made to keep the actual concentrations of the test material in the chambers as constant as possible.
The duration of each exposure period was six hours after equilibration of the chamber concentration. The equilibration time, which is afunction of chamber airflow, was approximately 25 min. The amount of test material used during the exposure period was determined by pre- and post-measuring the weight of the test material in each syringe. The exposure duration (exposure period and equilibration time), test material used, and airflows through the chambers were then used to calculate nominal concentrations for the 100 and 200 ppb groups. The actual chamber concentration was measured using an Analect Diamond FT-IR spectrometer equipped with a fixed 22 meter path length cell. The spectrometer was calibrated before the study with standards prepared in Tedlar gas sampling bags.

Duration of treatment / exposure:

6 h/d, 10 exposures over 14 days

Frequency of treatment:

once daily

Dose / conc.:

50 other: ppb

Dose / conc.:

100 other: ppb

Dose / conc.:

200 other: ppb

No. of animals per sex per dose:

10

Control animals:

yes, concurrent vehicle

Observations and examinations performed and frequency:

Animals were observed daily during the week following each exposure for test article-related signs of toxicity and mortality/morbidity. Signs evaluated included, but were not limited to, any evidence of respiratory, dermal, behavioral, nasal and/or ocular changes. Animals were observed for signs of mortality/morbidity once a day on weekends by Animal Resources personnel.

Body weight measurements: Individual body weights were collected for randomization purposes prior to exposure. Also, body weights were recorded on days 1, 8, 15 and prior to terminal necropsy.

Gross pathology and organ weight assessment: A gross pathologica examination was conducted on all rats on Study Day 15. The heart, brain, kidneys, lungs, liver, spleen, adrenals, and ovaries or testes were dissected free of fat and weighed. The lungs were removed intact, weighed, and distended to their approximate normal inspiratory volume by tracheal infusion with 10% neutral buffered formalin.

Histopathology: Samples of organs and tissues listed below for all groups with the exception of the eyes were preserved in 10% neutral buffered formalin. Eyes were preserved in Davidson's fixative. Hematoxylin and eosin stained paraffin sections of the organs and tissues were prepared using standard histologic methods. The following organs were preserved: Adrenals, nasal cavity (4 levels), brain (3 levels), eyes, heart, kidneys (2), larynx, liver (3 lobes), lymph nodes (mandibular, mediastinal), lungs (5 lobes), trachea (multiple levels, cervical and bifurcation), ovaries (2), pharynx, spleen, testes (2), thymus, nares, selected gross lesions. Histopathological examination was performed on the tissues specified from all rats from the control and 200 ppb exposure groups by consulting pathologist, Robert G. Geil, D.V.M, DACVP. Lesions were observed in the nasal tissue, trachea, and, larynx, therefore, histopathological examinations were performed on these tissues from the rats in the 50 and 100 ppb group.

Statistics:

Statistical analysis of body weights, organ weights, and organ weight ratios were conducted. Originally, the data was analyzed by two-sided Welch Trend test, however during a data review, it was noted that Animal no. C4363 had two significantly different body weights for Study Day 15 and terminal sacrifice. Both of these body weights were taken on the same day. When this error was discovered the study director elected to reanalyze the data. Because the software package with this procedure was no longer being supported, the data could not be reanalyzed with the two-sided Welch Trend test. Therefore, the biostatistician elected to analyze the data as a one-way analysis of variance using proc GLM, SAS(R) V.6.12. When the overall F test indicated significant treatment-related effects, mean response in expsed animals were compared to control using a two-tailed Dunnett's test for multiple comparisons. The probability of Type I error was set at 5% (p<0.05).

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Very slight to moderate rales were observed in several animals exposed to 100 and 200 ppb during the first week of exposure. At the termination of the study, no apparent treatment-related clinical signs were observed in any of the animals exposed to 100 and 200 ppb. No apparent treatment-related clinical signs were observed in animals exposed to 50 ppb of the test material during the study.

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Statistically significant decrease in body weights were observed in males exposed to 200 ppb of the test material on day 8, 15, and at sacrifice. Female body weights were decreased in animals exposed to 200 ppb on day 8. No significant differences between test and control body weights were observed in females on day 15.

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Statistically significant increase in liver/body weight ratios were observed in males exposed to 100 and 200 ppb of the test material. Statistically significant increase in kidney/body weight ratios were observed in males exposed to 200 ppb of the test material. In addition, a statistically significant increase was observed in the liver/body weight and adrenal/body weight ratios of females exposed to 200 ppb. The biological significance of these results are questionable because of the depression of body weights in animals exposed to 200 ppb of test article and the lack of correlation between the organ weight increases and microscopic finding. THere were no other significant organ weight differences between test and control animals.

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Test article related changes were limited to the respiratory tract organs and occurred in all rats exposed to 50, 100 and 200 ppb. The nares, nasal cavity, and pharynx were the most common sites of test article related changes with the trachea and larynx only infrequently affected. The most severe lesions in each treated rat were found in the Nasal Cavity #1 section with decreasing incidence of changes occurring in the upper levels of the nasal cavity. Squamous metaplasia and acute inflammation of the nasal cavity were the most common findings in animals exposed to 200 ppb and also occurred, with somewhat reduced incidence and severity, in many rats exposed to 50 and 100 ppb of the test article. An increased activity of mucus goblet cells of the respiratory epithelium, characterized by increased heights and prominence of goblet cells with formation of microcysts, was the most commong findings in all sections of the nasal cavity of rats exposed to 50 and 100 ppb of the test article. This was also see nin animals exposed to 200 ppb of the test article at nasal levels 2, 3 and 4. Mucous goblet cell hyperactivity also occurred in sections of pharynx in all treatment groups. Incidence and severity of nasal cavity and pharyngeal changes generally had a positive dose response relationship. Other test article related changes in the nasal cavity included erosions and ulcers of the epithelium, suppurative exudate in the lumen, chronic inflammation and hemorrhage. Test article related changes in the larynx and trachea were infrequently seen. These included saryngeal ulcers in two rats exposed to 200 ppb and one exposed to 50 ppb, suppurative laryngeal exudate in one animal exposed to 200 ppb, and chronic tracheitis in one animal exposed to 200 ppb of the test article. Epithelial desquamation, of varying severity, occurred in the nasal cavity, pharynx and trachea in similar numbers of rats exposed to 0, 50, 100, and 200 ppb of the test article. Where desquamation was unaccompanied by inflammation, as was the case in most instances, it was considered an artifact which was probably induced by handling at necropsy. All lesions in the lung and other organs examined microscopically were considered agonal or spontaneous and unrelated to test article exposure.

Dose descriptor:

LOAEC

Effect level:

50 other: ppb

Sex:

male/female

Basis for effect level:

histopathology: non-neoplastic

Critical effects observed:

yes

Lowest effective dose / conc.:

50 other: ppb

System:

respiratory system: upper respiratory tract

Organ:

larynx

nasal cavity

pharynx

trachea

Treatment related:

yes

Dose response relationship:

yes

Relevant for humans:

not specified

see section "attached background material"

Conclusions:

Test article related changes were observed microscopically in the respiratory tract of all animals exposed to DOW CORNING® X1 -6145A Additive. All lesions in the lung and other organs examined microscopically were considered agonal or spontaneous unrelated to test article exposure. Based on the results, a NOAEL was not established for DOW CORNING® X1 -6145A Additive in Fischer 344 rats under the conditions of this study.

Executive summary:

A 14 -day repeated dose inhalation toxicity study was conducted to investigate the inhalation toxicity of DOW CORNING® X1 -6145A Additive, chemically described as hexamethyldisilylethane (CAS no 18406 -41 -2), in rats. A previously conducted inhalation toxicity study with DOW CORNING® X1 -6145A Additive was terminated, because the target exposure concentrations were too high and caused morbitiy in rats (Crofoot et al., 1993). The purpose of the present study was to assess the repeated dose inhalation toxicity of DOW CORNING® X1 -6145A Additive and to determine the NOAEL in rats.

Four groups of ten male and ten female Fischer 344 rats were exposed to target concentrations of 0, 50, 100 and 200 ppb of the substance for six hours a day, for ten exposures over 14 days (excluding weekends). Animals were observed for treatment-related signs of toxicity, growth, and mortality. At termination of the study, rats were sacrificed and examined fro changes in organ weights, gross pathology, and histopathology.

No mortality was observed in the study. Very slight to moderate rales were observed in several animals exposed to 100 and 200 ppb. No apparent treatment-related clinical signs were observed in animals exposed to 50 ppb. Statistically significant decreases in body weights were observed in males exposed to 200 ppb on day 8, 15, and at sacrifice. Female body weights were decreased in animals exposed to 200 ppb onl day 8 only. Statistically significant increases in liver/body weight ratios were observed in males exposed to 100 and 200 ppb of the test material. Statistically significant increases in kidney/body weight ratios were observed in males exposed to 200 ppb of the test material. A statistically significant increase in liver/body weight ratio and in the adrenal/body weight ratio was observed in females exposed to 200 ppb of the test material. There were no other statistically significant differences in organ weights between test and control animals.

There were no apparent test article-related gross pathological changes in exposed animals. Test article-related changes were observed microscopically in the respiratory tract of all animals exposed to the test material. The nares, nasal cavity, and pharynx were the most common sites of test article-related changes with the larynx and trachea only infrequently affected. Squamous metaplasia and acute inflammation of the nasal cavity were the most common findings in the 200 ppb group and also occurred, with somewhat reduced incidence and severity, in many rats from the 50 and 100 ppb groups. An increased activity of mucus goble cells of the respiratory epithelium, characterized by incresaed height and prominence of goblet cells with formation of microcysts, was the most common finding in all sections of the nasal cavity from the 50 and 100 ppb groups. All lesions in the lung and other organs examined microscopically were considered agonal and spontaneous and unrelated to test article exposure.

Based on these results, a NOAEL was not established for the test material in Fischer 344 rats under the conditions of this study.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEC

Study duration:

subacute

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

Justification for classification or non-classification

The predominant toxic effect observed in the available repeated dose inhalation studies was local damage to the upper respiratory tract, with a LOAEC of 50 ppb (corresponding to 0.000562 mg/L). Specific toxicity to organs or tissues other than the respiratory tract was not observed. Therefore, classification for specific target organ toxicity by repeated dose exposure according to CLP is not warranted.