Octamethylcyclotetrasiloxane

Bioaccumulation: terrestrial

Description of key information

Exhibits a lower potential for bioaccumulation.

Additional information

Assessment of bioaccumulation is typically limited to water-breathing aquatic organisms e.g. fish, however, it is important to consider bioaccumulation in air-breathing organisms (non-aquatic organisms) such as marine and terrestrial mammals and birds. It has been demonstrated that the bioaccumulation behaviour of neutral hydrophobic organic substances in air-breathing organisms is often related to the octanol–air partition coefficient (K_OA) of the substance (Kelly et al, 2007). Substances with low octanol–air partition coefficients can be exhaled quickly and hence exhibit a lower potential for bioaccumulation.

 

A 2017 study (Domoradzki et al., 2017a) found that, in rats, following oral administration D4 exhibited a rapid uptake and distribution, and was then quickly depurated via exhalation and excretion of metabolites. A supporting study (Dow Corning Corporation 1998a), showed extensive biotransformation of D4 in female Fisher 344 rats following oral administration. The rapid rate of depuration of D4 via exhalation and biotransformation indicates that D4 does not have a potential for biomagnification in air-breathing organisms or terrestrial food webs. Based on concentrations of D4 in two samples of herring (Clupea harengus) and three blubber samples from drowned grey seals (Halichoergus grypus) from the Baltic Sea, Kierkegaard et al., 2013 concluded that D4 did not biomagnify in grey seals because of rapid metabolism and pulmonary elimination.

The bioaccumulation of D4 in the body is unlikely, due to the effective elimination through metabolism and exhalation (Plotzke et al. (2000), (Andersen et al., 2008). In addition, the results suggest a dose-dependency in the kinetics of D4 that is likely related to a combination of factors, such as saturation of uptake/transport mechanisms and nonlinear storage and metabolism. It is also well demonstrated that D4 is readily absorbed and reaches systemic circulation rapidly following exposure (Dobrev et al., 2008). The results also indicate that D4 is unlikely to bioaccumulate in the fat, even though it is lipophilic, primarily due to three excretion mechanisms: ready clearance as water soluble metabolites from the tissues via the urine; exhalation of parent D4; and to a lesser extent, excretion of parent D4 in the feces.

 

References:

 

Andersen ME, Reddy MB, Plotzke KP. 2008. Are highly lipophilic volatile compounds expected to bioaccumulate with repeated exposures? Toxicol Lett 179:85–92.

 

Kelly BC, Ikonomou MG, Blair JD, Morin AE, Gobas FAPC. 2007. Food web-specific biomagnification of persistent organic pollutants. Science 317:236–239.

Kierkegaard A. ; Bignert A. ; McLacklan M. 2013. Cyclic volatiles methylsiloxanes in fish from the Baltic Sea. Chemosphere 93 :774-448.

 

Varaprath S, McMahon JM, Plotzke KP. 2003. Metabolites of hexamethyldisiloxane and decamethylcyclopentasiloxane in Fischer 344 rat urine: A comparison of a linear and a cyclic siloxane. Drug Metabol Dispos 31:206–214.