1,1,1,3,3,5,5,7,7,9,9,11,11,13,13,15,15,15-Octadecamethyloctasiloxane

607.303

607.30

209-138-8

DTXSID5060306

64.6

log Kow = 13.98 (est)

0.9078 g/cm³ @ Temp: 25 °C

-63 °C

153 °C

Index of refraction: 1.3970 at 20 °C/D

In water, 6.07X10-7 mg/L at 25 °C (est)

0.00 mmHg

Henry's Law constant = 7.10X10+3 atm-cu m/mol at 25 °C (est)

Hydroxyl radical reaction rate constant = 2.69X10-12 cu cm/molec-sec at 25 °C (est)

67.7 kJ/mol

SRP: Recycle any unused portion of the material for its approved use or return it to the manufacturer or supplier. Ultimate disposal of the chemical must consider: the material's impact on air quality; potential migration in air, soil or water; effects on animal, aquatic and plant life; and conformance with environmental and public health regulations. If it is possible or reasonable use an alternative chemical product with less inherent propensity for occupational harm/injury/toxicity or environmental contamination.

IDENTIFICATION AND USE: Octadecamethyloctasiloxane is silicon-containing chemical, which belongs to the general class of polysiloxanes. HUMAN STUDIES: There are no data available. ANIMAL STUDIES: There are no data available.

Silicone fluids', which include octadecamethyloctasiloxane, production and use as damping fluids, dielectric fluids, polishes, cosmetic and personal care additives, textile finishes, hydraulic fluids, paint additives, photocopy fuser oils, and heat-transfer oils(1) may result in their release to the environment through various waste streams(SRC).

TERRESTRIAL FATE: Based on a classification scheme(1), an estimated Koc value of 5.3X10+7(SRC), determined from a structure estimation method(2), indicates that octadecamethyloctasiloxane is expected to be immobile in soil(SRC). Volatilization of octadecamethyloctasiloxane from moist soil surfaces is expected to be an important fate process(SRC) given an estimated Henry's Law constant of 7.1X10+3 atm-cu m/mole(SRC), developed using a fragment constant estimation method(3). However, adsorption to soil is expected to attenuate volatilization(SRC). Octadecamethyloctasiloxane is not expected to volatilize from dry soil surfaces(SRC) based upon an extrapolated vapor pressure of 6.89X10-5 mm Hg at 25 °C(4). Biodegradation data in soil were not available(SRC, 2018).|AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 6.8X10+7(SRC), determined from a structure estimation method(2), indicates that octadecamethyloctasiloxane is expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is expected(3) based upon an estimated Henry's Law constant of 1.36X10+4 atm-cu m/mole(SRC), developed using a fragment constant estimation method(4). Using this Henry's Law constant and an estimation method(3), volatilization half-lives for a model river and model lake are 7 hrs and 9 days, respectively(SRC). However, volatilization from water surfaces is expected to be attenuated by adsorption to suspended solids and sediment in the water column. The estimated volatilization half-life from a model pond is 1.7X10+4 yrs if adsorption is considered(5). According to a classification scheme(6), an estimated BCF of 5(SRC), from an estimated log Kow of 13.98(2) and a regression-derived equation(2), suggests the potential for bioconcentration in aquatic organisms is low(SRC). Biodegradation data in water were not available(SRC, 2018).|ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), octadecamethyloctasiloxane, which has an extrapolated vapor pressure of 6.98X10-5 mm Hg at 25 °C(2), will exist in both the vapor and particulate phases in the ambient atmosphere. Vapor-phase octadecamethyloctasiloxane is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals(SRC); the half-life for this reaction in air is estimated to be 6 days(SRC), calculated from its rate constant of 2.7X10-12 cu cm/molecule-sec at 25 °C(SRC) that was derived using a structure estimation method(3). Particulate-phase octadecamethyloctasiloxane will be removed from the atmosphere by wet and dry deposition. Octadecamethyloctasiloxane does not contain chromophores that absorb at wavelengths >290 nm(4) and, therefore, is not expected to be susceptible to direct photolysis by sunlight(SRC).

Octadecamethyloctasiloxane is not expected to undergo hydrolysis in the environment due to the lack of functional groups that hydrolyze under environmental conditions(1). Octadecamethyloctasiloxane does not contain chromophores that absorb at wavelengths >290 nm(1) and, therefore, is not expected to be susceptible to direct photolysis by sunlight(SRC).

An estimated BCF of 5 was calculated in fish for octadecamethyloctasiloxane(SRC), using an estimated log Kow of 13.98(1) and a regression-derived equation(1). According to a classification scheme(2), this BCF suggests the potential for bioconcentration in aquatic organisms is low(SRC).

Using a structure estimation method based on molecular connectivity indices(1), the Koc of octadecamethyloctasiloxane can be estimated to be 5.3X10+8(SRC). An estimated log Koc of 7.09 (Koc 1.2X10+7) has also been reported(2). According to a classification scheme(3), these estimated Koc values suggest that octadecamethyloctasiloxane is expected to be immobile in soil(SRC).

The Henry's Law constant for octadecamethyloctasiloxane is estimated as 7.1X10+3 atm-cu m/mole(SRC) developed using a fragment constant estimation method(1). This Henry's Law constant indicates that octadecamethyloctasiloxane is expected to volatilize rapidly from water surfaces(2). Based on this Henry's Law constant, the volatilization half-life from a model river (1 m deep, flowing 1 m/sec, wind velocity of 3 m/sec)(2) is estimated as 7 hrs hours(SRC). The volatilization half-life from a model lake (1 m deep, flowing 0.05 m/sec, wind velocity of 0.5 m/sec)(2) is estimated as 10 days(SRC). Octadecamethyloctasiloxane's Henry's Law constant indicates that volatilization from moist soil surfaces may occur(SRC). However, volatilization from water surfaces is expected to be attenuated by adsorption to suspended solids and sediment in the water column. The estimated volatilization half-life from a model pond is 1.7X10+4 yrs if adsorption is considered(3). Octadecamethyloctasiloxane is not expected to volatilize from dry soil surfaces(SRC) based upon an extrapolated vapor pressure of 6.98X10-5 mm Hg(4).

Occupational exposure to octadecamethyloctasiloxane may occur through inhalation and dermal contact with this compound at workplaces where octadecamethyloctasiloxane is produced or used. The general population is not likely to be exposed to octadecamethyloctasiloxane. (SRC)|BACKGROUND: Low molecular weight siloxanes are used in industrial processes and consumer products, and their vapors have been detected in the atmospheres of the Space Shuttle and International Space Station. Therefore, the National Aeronautics and Space Administration (NASA) developed spacecraft maximum allowable concentrations (SMACs) for siloxane vapors to protect astronaut health. Since publication of these original SMACs, new studies and new risk assessment approaches have been published that warrant re-examination of the SMACs. OBJECTIVE: To reevaluate SMACs published for octamethyltrisiloxane (L3) for exposures ranging from 1 hour to 180 days, to develop a 1000-day SMAC, and to expand the applicability of those values to the family of linear siloxanes. METHODS: A literature review was conducted to identify studies conducted since the SMACs for L3 were set in 1994. The updated data were reviewed to determine the sensitive toxicity endpoints, and current risk assessment approaches and methods for dosimetric adjustments were evaluated. RESULTS: Recent data were used to update the original 1-hour, 24-hour, 30-day, and 180-day SMACs for L3, and a 1000-day SMAC was developed to protect crewmembers during future exploration beyond Earth orbit. Group SMACs for the linear siloxane family, including hexamethyldisiloxane (L2), L3, decamethyltetrasiloxane (L4), and dodecamethylpentasiloxane (L5), were set for exposures of 1-hour to 1000 days. CONCLUSION: New SMACs, based on acute pulmonary and neurotoxicity at high doses only achievable with L2 and potential liver effects following longer-term exposures to L2 and L3, were established to protect crewmembers from the adverse effects of exposure to linear siloxanes.

/SRP:/ Immediate first aid: Ensure that adequate decontamination has been carried out. If patient is not breathing, start artificial respiration, preferably with a demand valve resuscitator, bag-valve-mask device, or pocket mask, as trained. Perform CPR if necessary. Immediately flush contaminated eyes with gently flowing water. Do not induce vomiting. If vomiting occurs, lean patient forward or place on left side (head-down position, if possible) to maintain an open airway and prevent aspiration. Keep patient quiet and maintain normal body temperature. Obtain medical attention. /Poisons A and B/|/SRP:/ Basic treatment: Establish a patent airway (oropharyngeal or nasopharyngeal airway, if needed). Suction if necessary. Watch for signs of respiratory insufficiency and assist ventilations if needed. Administer oxygen by nonrebreather mask at 10 to 15 L/min. Monitor for pulmonary edema and treat if necessary ... . Monitor for shock and treat if necessary ... . Anticipate seizures and treat if necessary ... . For eye contamination, flush eyes immediately with water. Irrigate each eye continuously with 0.9% saline (NS) during transport ... . Do not use emetics. For ingestion, rinse mouth and administer 5 mL/kg up to 200 mL of water for dilution if the patient can swallow, has a strong gag reflex, and does not drool ... . Cover skin burns with dry sterile dressings after decontamination ... . /Poisons A and B/|/SRP:/ Advanced treatment: Consider orotracheal or nasotracheal intubation for airway control in the patient who is unconscious, has severe pulmonary edema, or is in severe respiratory distress. Positive-pressure ventilation techniques with a bag valve mask device may be beneficial. Consider drug therapy for pulmonary edema ... . Consider administering a beta agonist such as albuterol for severe bronchospasm ... . Monitor cardiac rhythm and treat arrhythmias as necessary ... . Start IV administration of D5W TKO /SRP: "To keep open", minimal flow rate/. Use 0.9% saline (NS) or lactated Ringer's (LR) if signs of hypovolemia are present. For hypotension with signs of hypovolemia, administer fluid cautiously. Watch for signs of fluid overload ... . Treat seizures with diazepam (Valium) or lorazepam (Ativan) ... . Use proparacaine hydrochloride to assist eye irrigation ... . /Poisons A and B/

Octasiloxane, 1,1,1,3,3,5,5,7,7,9,9,11,11,13,13,15,15,15-octadecamethyl-: ACTIVE