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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 C22, mainly saturated but also unsaturated C16' and C18'. 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.
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.
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.
The vapour pressure of category members is very low. Valid calculated values are below 1 mPa at 20 °C.
Partition coefficient log Pow exceeds 3 for all category members. The positive correlation with the overall number of CH2 units is observed.
All fatty acid glycerides in the category are characterized with a very low water solubility (< 1mg/L).
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
The physico-chemical properties of the substances SALATRIM 23CA, SALATRIM 234CA and SALATRIM 234CS are not available. 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-% shot-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 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 Pow > 6. The melting point ranges from 16 °C to 71 °C, depending on triglyceride composition.
The physico-chemical properties of MCT (medium chain trigylcerides) are also not available. The above mentioned points apply also to MCT, due to the variable composition the determination of physico-chemical properties are difficult. With regard to the chain length (C6 to C12) the water solubility ia assumed to be < 1 mg/L and the log Pow > 6 (in comparison to CAS-No. 73398-61-5, glycerides, mixed decanoyl and octanoyl).

Environmental fate and pathways
All substances in the category are readily biodegradable. Because of very low water solubility, they do not hydrolyse in environmental conditions and their bioaccumulation potential is low. As the vapour pressure is also low, they will not evaporate into the air phase from water.

Ecotoxicity
Acute and chronic study results show that toxicity of fatty acid glycerides for mammals and 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 acid glycerides are not harmful in any aspects, what is confirmed by available studies of acute oral toxicity (inhalation and dermal routes are considered non-relevant), skin and eye irritation, skin sensitization, repeated dose toxicity, mutagenicity and reproductive toxicity.