Castor oil, dehydrated

Endpoint summary

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Additional information

Glycerides

When taken up orally, triglycerides are split in the intestinal lumen into glycerol and fatty acids with the help of lipases and bile secretions, then move into the cells lining the intestines (enterocytes). The triglycerides are rebuilt in the enterocytes from their fragments and packaged together with cholesterol and proteins to form chylomicrons. These are excreted from the cells, collected by the lymph system and transported to the large vessels near the heart before entering the blood.Eventually, they bind to the membranes of hepatocytes, adipocytes or muscle fibers, where they are either stored or oxidized for energy.When the body requires fatty acids as a source of energy, the hormone glucagon signals the breakdown of the triglycerides by hormone-sensitive lipases to release free fatty acids. The fatty acids are then broken down by stepwise elimination of C2-units in the mitochondrial β-oxidation.Alternate oxidation pathways can be found in the liver (ω-oxidation) and the brain (α-oxidation) (HERA, 2002).The C2-units are esterified to acetyl-coenzyme A which directly enters the citric acid cycle where it is converted to carbon dioxide and energy (MacDonald, 1973; Robinson, 1973; Chen and Farese, 2002). The extent of absorption in the gastro-intestinal system varies depending on the chain length of the fatty acids and their degree of saturation. Generally, short-chain fatty acids are better absorbed than the long chain counterparts. Also, absorption decreases with increasing saturation (MacDonald, 1973; Robinson, 1973; Chen and Farese, 2002). Castor oil (containing ricinoleic acid) is generally well absorbed and metabolised (Paul and McKay, 1942; Ihara-Watanabe et al., 1999; CIR, 2007).In an overview by the Cosmetic Ingredient Review Panel (CIR, 1987), stearic acid (C18) was cited as being the most poorly absorbed of the common fatty acids.

 

No experimental studies were located for absorption through the dermal route. However,as per Section R.7.12.2.1 of REACH guidance document R7.C (May 2008),the extent of dermal absorption may be predicted based on physico-chemical properties, including:

-        Water solubility

-        Partition coefficient

-        Molecular weight / fatty acid chain length (inversely proportional)

 

Castor oil, dehydrated is poorly water soluble (< 5.8 mg/L), has an estimated log Pow of > 16 and a molecular weight range > 500 (see Sections 1.3 and 4). As such, uptake into the stratum corneum of skin and further transfer into the epidermis are likely to be low. A default dermal penetration value of 10% can be assumed (REACH guidance document R7.C (May 2008)).

No significant inhalatory exposure to castor oil, dehydrated is expected to occur as the substance is not volatile and has a low vapour pressure 7.43 × 10^-5Pa.

Adducts

Adducts of fatty acids, C18 and C18-unsatd., C18-hydroxy and Glycerides C18 and C18-unsatd., C18-hydoxy. Mono-, Di- and Tri-are present in castor oil, dehydrated. The toxicokinetics of these components are expected to be similar to those of the glycerides, although breakdown may be slower due to size.