Glycerides, C16-22

Endpoint summary

Description of key information

No bioaccumulation of ‘glycerides, C16-22 (SDA Reporting Number: 21-001-00)’

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

‘Glycerides, C16-22 (SDA Reporting Number: 21-001-00)’ is composed mainly of triglycerides containing a glycerol backbone esterified to linear fatty acids with a carbon chain length of C16-22. The other known constituents are mono- and di-glycerides as well as fatty acids. The toxicokinetics of glycerides and fatty acids are well known as a result of their widespread use in nutritional (food and feed), cosmetic and industrial applications for example.

When taken uporally, triglycerides are split in the intestinal lumen into glycerol and fatty acids with the help of lipases and bile secretions (in a process called lipolysis), then move into the cells lining the intestines (absorptive 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. Various tissues can capture the chylomicrons, releasing the triglycerides to be used as a source of 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 from the adipose cells (fat cells), the major site of triglyceride accumulation. The fatty acids are then broken down by stepwise elimination of C2-units in the mitochondrial β-oxidation. 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).

In general, the extent of absorption of triglycerides in the gastro-intestinal system varies depending on the chain length of the fatty acids and their degree of saturation. The long-chain fatty acids are lesser absorbed than the short chain counterparts and it further decreases with increasing saturation (MacDonald, 1973; Robinson, 1973; Chen and Farese, 2002).

No experimental studies were located for absorption through thedermal 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 / triglyceride chain length (inversely proportional)

 

‘Glycerides, C16-22 (SDA Reporting Number: 21-001-00)’are poorly water soluble (< 10 mg/L), have an estimated log Kow > 20 and a molecular weight range of >500 (see Sections 1.3 and 4). As such, uptake into thestratum corneumof 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)).

Exposure via the inhalation route is not expected given the physical state(solid under environmental conditions)and low vapour pressure(< 1.33 x 10^-8Pa at 20°C)of ‘glycerides, C16-22 (SDA Reporting Number: 21-001-00)’.In many cases the substance is used in industrial applications and transported and handled in liquid form (heated). If the substance is handled in powder form, sprayed or otherwise finely dispersed in the air, the use of appropriate risk management measures (e.g. filter mask) is recommended.