Fatty acids, C16-18 and C18-unsatd., Me esters

Categories

Category name:

Fatty Acids Methyl Esters

Justifications and discussions

Category definition:

Fatty Acids Methyl Esters

Category description:

From C8 to C24 saturated and unsaturated and their mixtures

Category rationale:

STRUCTURAL SIMILARITY AND PHYSICO-CHEMICAL PROPERTIES
The substances used as Biodiesel differ from each other only for the fatty acid methyl ester (FAME) chain length(s) and for the presence or absence of a double bond in the FAME chain.
Physico-chemical properties are correlated to the fatty acid length of the chemicals, with increased boiling and melting points, and decreasing relative density and vapour pressure
In addition, the lipophilicity increases with the number of –CH2 in the chain length (decreasing water solubility and increasing octanol/water partition coefficient). The exception is related to the presence of double bonds; for example the physicochemical properties of C18:1 methyl ester are between those of C16:0 and C18:0.
The relationship between all these parameters is linear, as expected for a homologue series of chemicals. Prediction could be made on the mistures, based on their fatty length composition

BIOAVALABILITY
The biological behaviour of these chemicals has both been studied and predicted with QSAR models It is quite homogeneous. There are no large differences in bioavailability and distribution coefficients, and the variability of the parameter values has shown changes consistently with chain length variation.

TOXICOLOGY
Some toxicological endpoints have been evaluated for the homologue series using OECD QSAR Toolbox database.
For most of the evaluated endpoints , these chemicals always return the same value, demonstrating the regularity of their biological response. It seems that neither the fatty acid chain length neither the presence of a double bond in the chain , affects the biological behaviour of the variability is comprised between C14 and C22 and if there is only one unsaturation.
The only discrepancy is in the area of skin irritation. Esters of long-chain fatty acids are always negative (from C18 onward), while esters of short-chain fatty acids are always slightly positive (up to C10). It seems that in the intermediate zone (C10-C16), the uncertainty of the toolbox is too high to return an acceptable result.
In addition, the actual toxicological measured parameters also show consistency across the different carbon chain lengths.

TOXICOCINETIC
Fatty acid methyl esters are metabolised as other dietary fats. Higher molecular weight aliphatic esters are readily hydrolysed to the corresponding alcohol (methanol) and acid and then generally oxidised to carbon dioxide and water. During digestion, they are hydrolysed to the free fatty acids for absorption from the intestine into the blood stream aided by lipase enzymes and bile salts. Once formed the free fatty acid is metabolised by known oxidative processes or they are reconstituted into glyceride esters and stored in the fat depots in the body.
The effect of methanol coming from an hydrolysation process in the stomach, is already well known (there is extensive literature information on other methyl esters in support of this) and does not raising a concern, as the total amount quantity is quite low.
The free fatty acids are widely present in nature and are referenced in Annex V as being exempted from the REACH registration provisions.