Glycerides, tall-oil mono-, di-, and tri-

Categories

Category name:

Fatty Acid Glycerides

Justifications and discussions

Category definition:

This category comprises mono-, di-, and tri-esters of carboxylic acids with glycerol. The carbon chain length of the fatty acids ranges from C7 to C20, mainly saturated but also unsaturated C16' and C18' as well as C22'. In one case, there is an additional functional group (OH) attached ti the alkyl chain, what does not eliminate this substance from the category because of similarities in properties and mode of action.

Category description:

The category applies to all systemic and local mammalian toxicity endpoints as well as ecotoxic and environmental fate endpoints (biodegradation).

Category rationale:

The Fatty Acid Glycerides category contains mono-, di- and tri-esters of glycerol and linear saturated and unsaturated carboxylic acids (fatty acids). Structural similarities of the category substances are reflected in similar physico-chemical properties and mode of action. Fatty acid glycerides have a common metabolic fate that involves stepwise hydrolysis to the carboxylic acid and glycerol. They feed into physiological pathways like the citric acid cycle, sugar synthesis and lipid synthesis. Fatty acid glycerides constitute a large part of the fat content within human diet. Their participation in normal physiological properties renders fatty acid glycerides inherently harmless. Furthermore, structurally similar Glycerides (C10-18) are listed in Annex IV of REACH regulation 1907/2006 amended by Commission regulation 987/2008 (exemptions from the obligation of register in accordance with article 2(7)(b).

Physico-chemical properties
Acyl glycerides in the category are mono-, di- and tri-esters of glycerol and fatty acids. Depending on the degree of esterification, alkyl chain length and saturation, the substances in the category are under ambient conditions solids or liquids.
Melting point
The melting temperature is in the range from -39 °C to -4 °C for liquids and between 35 and 94 °C for solids. The lower the degree of esterification and the shorter the chain, the lower the melting point. Additionally, unsaturated components are characterized with lower melting points than saturated ones.
Boiling point
According to Blake et al. (J. Chem. Eng. Data, 1961, 6, 87-98), esters of long chain acids with β hydrogen atoms in the alcohol moiety (i.e. alcohols with C3, e.g. propanol) decompose in the range between 262 and 283 °C. Since for longer chains the boiling temperature is higher, esters of fatty acids esterified with alcohols ≥ C3 and having a molecular weight exceeding 300 amu have a boiling point > 300 °C and decompose before boiling.
Density
The densities of the substances vary in the range 910-970 mg/cm3.
Vapour pressure
The vapour pressure of category members is very low. Valid calculated values are below 0.001 Pa at 20 °C.
Octanol-water partition coefficient
Partition coefficient log Kow exceeds 3 for all category members. The positive correlation with the overall number of CH2 units is observed.
Water solubility
Very low water solubility (< 1mg/L) characterizes all Fatty Acids Glycerides in the category.
The physico-chemical properties of the substance CAS: 8001-78-3 (Castor oil, hydrogenated), which contains hydroxyl group in position 12, are in line with observed trends.
SALATRIM is the name for a group of substances (SALATRIM = Short- and long-chain acyl triglyceride molecules). SALATRIM is prepared by interesterification of triacetin, tripropionin, or tributyrin, or their mixtures with either hydrogenated canola, soybean, cottonseed, or sunflower oil. Triglycerides with three short-chain fatty acids are removed in the process. SALATRIM triglyceride molecules typically contain 30-67 mol-% short-chain fatty acids (SCFA) and 33-70 mol-% long-chain fatty acids (LCFA); stearic acid is the predominant LCFA. (http://www.fao.org/docrep/w6355e/w6355e0w.htm). Due to their variable compositions the exact determination of physico-chemical properties of SALATRIM is very difficult. With regard to the source material triacetin and the properties of C18-monoglycerides (e.g. CAS-No. 31566-31-1), the prediction of water solubility is assumed to be < 1 mg/L and the log Kow > 6. The melting point ranges from 16 °C to 71 °C, depending on triglyceride composition.
The above mentioned points apply also to MCT, due to the variable composition the exact determination of physico-chemical properties is difficult. With regard to the chain length (C6 to C12) the water solubility is assumed to be < 1 mg/L and the log Kow > 6 (in comparison to CAS-No. 73398-61-5, glycerides, mixed decanoyl and octanoyl).
The physico-chemical properties of both, MCT and SALATRIM were judged to have sufficient similarity to the other members of the Fatty Acids Glycerides category.
Environmental fate and pathways
All substances in the category are readily biodegradable. Because of their very low water solubility, hydrolysis is not a relevant degradation pathway in the environment. Due to the metabolic fate of the category members in organisms, bioaccumulation in animal tissue is non-hazardous. As the vapour pressure is low, they do not evaporate into the air phase from water.
Ecotoxicity
Acute and chronic study results show that toxicity of Fatty Acids Glycerides for aquatic organisms is negligible (no effect up to the water solubility limit for fish, daphnia and algae). Their metabolites fatty acids and glycerol feed into such physiological pathways as citric acid cycle, sugar synthesis and lipid synthesis. Furthermore, mono- and diglycerides have an amphiphilic character and can contribute to biological membranes or act as emulsifiers. Thus, they are naturally present in living organisms, stored e.g. in fatty tissues, and can be used as energy source for these organisms.

Human toxicity
The participation in normal physiological properties renders fatty acid glycerides inherently harmlos they share the same metabolic fate of acyl glycerides.
Typical dietary lipids from vegetable oils, termed long-chain triacylglycerols (LCT) are degraded by salivary, intestinal and pancreatic lipases into two fatty acids and a monoacyl glycerol. Medium-chain triacylglycerols (MCT) are degraded by the same enzymes into three fatty acids and the simple glycerol backbone. Medium-chain fatty acids (MCFA) are readily absorbed from the small intestine directly into the bloodstream and transported to the liver for hepatic metabolism. Long-chain fatty acids (LCFA) are incorporated into chylomicrons and enter the lymphatic system. MCFA are readily broken down to carbon dioxide and two carbon fragments, while LCFA are re-esterified to triacylglycerols and either metabolized for energy or stored in adipose tissue.
Fatty Acids Glycerides are not harmful in any aspects, what is confirmed by available studies of acute toxicity, skin and eye irritation, skin sensitization, oral repeated dose toxicity, genotoxicty and reproduction toxicity.