Repeated inhalation or oral exposure of mice and rats to octamethylcyclotetrasiloxane produced
an increase in liver size. No gross histopathological or significant clinical chemistry effects were
observed. An increase in liver metabolizing enzymes, as well as a transient increase in the
number of normal cells (hyperplasia) followed by an increase in cell size (hypertrophy) were
determined to be the underlying causes of the liver enlargement. The biochemical
mechanisms producing these effects are highly sensitive in rodents, while similar mechanisms in
humans are insensitive. A two year combined chronic and carcinogenicity assy was conducted on
octamethylcyclotetrasiloxane. Rats were exposed by whole-body vapor inhalation 6hrs/day,
5days/week for up to 104weeks to 0, 10, 30, 150 or 700ppm of octamethylcyclotetrasiloxane. The
increase in incidence of (uterine)endometrial cell hyperplasia and uterine adenomas(benign
tumors) were observed in female rats at 700ppm. Since these effects only occurred at 700ppm, a
level that greatly exceeds typical workplace or consumer exposure, it is unlikely that industrial,
commercial or consumer uses of products containing octamethylcyclotetrasiloxane would result in
a significant risk to humans. [Octamethylcyclotetrasiloxane]
Repeated inhalation or oral exposure of mice and rats to decamethylcyclopentasiloxane produced
an increase in liver size. No gross histopathological or significant clinical chemistry effects were
observed. An increase in liver metabolizing enzymes , as well as a transient increase in the
number of normal cells (hyperplasia) followed by an increase in cell size (hypertrophy) were
determined to be the underlying causes of the liver enlargement. The biochemical mechanisms
producing these effects are highly sensitive in rodents, while similar mechanisms in humans are
insensitive. [Decamethylcyclopentasiloxane]