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PBT assessment

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PBT assessment: overall result

PBT status:
the substance is not PBT / vPvB
Justification:

The PBT Assessment for Octadecanoic acid, branched and linear, “Hydrogenated monomer acid” (CAS No. 68201-37-6) is based on the criteria set out in the “Guidance on information requirements and chemical safety assessment, Chapter R.11: PBT Assessment” (ECHA, 2012).

Persistence

Only secondary source data based on the Screening-Level Hazard Characterisation of High Production Volume Chemicals (HPV) (U.S. EPA 2007) for the Category “Tall Oil Fatty Acids and Related Substances” is available for Octadecanoic acid, branched and linear. This OECD 301B biodegradation study reported 47% degradation within 28 days using activated sludge from a municipal sewage treatment plant as inoculum. Since the original report is not available and the given information is insufficient for assessment, this result cannot be taken into account. However, in accordance to Regulation (EC) No. 1907/2006 Annex XI, 1.5 1.2. Weight of evidence, there is sufficient data from several independent sources of information of monomeric fatty acids C16-18 saturated and unsaturated leading to the conclusion that this substance is readily biodegradable. Stearic acid (CAS No. 57-11-4), the saturated C18 fatty acid was tested by Bogers (1989) for ready biodegradability according to OECD 301B and GLP. At concentrations of 10 and 20 mg/L the degradation values were 72 % and 71 %, respectively at test termination (28 d). Furthermore the biodegradation of Octadec-9-enoic acid (CAS No. 112-80-1) was investigated in a GLP study according to OECD 301B (Coenen, 1991). After 28 days 93 % and 75 % of octadec-9-enoic acid was biodegraded at concentrations of 10 mg/L and 20 mg/L, respectively. The validity of this study was limited, since thevalidity criteria for the reference substance were not passed.Additionally, it can be taken into account that Isooctadecanoic acid is also highly branched and has a lower water solubility than Octadecanoic acid, branched and linear, so the bioavailability of Octadecanoic acid, branched and linear is expected to be higher than that of Isooctadecanoic acid.

Thus, Octadecanoic acid, branched and linear can be considered as readily biodegradable and does not meet the screening criterion for persistency and it is not considered to be persistent (P) or very persistent (vP).

Bioaccumulation

No tests on bioaccumulation are available for Octadecanoic acid, branched and linear, “Hydrogenated monomer acid”, nevertheless the potential for bioaccumulation is expected to be low.

First of all, Octadecanoic acid, branched and linear (CAS No. 68201-37-6) has a poor water solubility (1.1 – 2.5 mg/L) therefore one can only expect to have a very low water concentration and consequently a reduced bioavailability, thus exposure to the aquatic environment would be extremely low. This would automatically reduce the uptake of the chemical through the aquatic environment. In addition the biotic degradation of the substance would also contribute to a reduced concentration in the aquatic environment. As ECHAs R.7c Endpoint specific guidance states that readily biodegradable substances are most likely to be rapidly metabolised in organisms.

Due to the potential of these substances to absorb, one may assume that if uptake will occur, it can be attributed to the pathway of ingestion of soil or sediment. From the toxicokinetic behaviour of monomeric acids in mammals it can be assumed that unsaturated monomeric C16-C18 fatty acids are more readily absorbed than saturated fatty acids like octadecanoic and isooctadecanoic acid but less than fatty acids with shorter chain length. Fatty acids occur naturally in all aquatic organisms and are ubiquitous in the aquatic environment, where fatty acids are predominantly readily biodegraded in an aerobic environment by microorganisms. Microbial metabolism is the primary route of degradation in aquatic environment.  As nutritional energy source, fatty acids are absorbed by different uptake mechanisms in mammals depending on the chain length. Long chain fatty acids (>C12) are absorbed into the walls of the intestine villi and assembled into triglycerides, which then are transported in the blood stream via lipoprotein particles (chylomicrons). In the body, fatty acids are metabolised by various routes to provide energy. Besides this, fatty acids are stored as lipids in adipose tissue and as precursors for signalling molecules and even long chain fatty. In addition fatty acids are an integral part of the cell membranes of every living organism from bacteria and algae to higher plants. Fatty acids are known to be easily metabolised. The rate of metabolism of fatty acids was considered to vary in proportion to their water solubility (Lloyd, 1957). In case of absorption fatty acids will undergo rapid metabolism and excretion (either in the expired CO2 or as hydroxylated or conjugated metabolite in the urine in the case of cyclic fatty acids) as they feed into physiological pathways like the citric acid cycle, sugar synthesis, and lipid synthesis. As fatty acids are naturally stored in the form of triacylglycerols primarily within fat tissue until they are used for energy production (fat storage tactic), it is therefore concluded that there will be no risk to organisms from bioconcentration/biomagnification of fatty acids within the food chain.

Due to the potential of these substances to absorb, one may assume that if uptake will occur, it can be attributed to the pathway of ingestion of soil or sediment. From the toxicokinetic behaviour of monomeric acids in mammals it can be assumed that unsaturated monomeric C16-C18 fatty acids are more readily absorbed than saturated fatty acids like octadecanoic and isooctadecanoic acid but less than fatty acids with shorter chain length. Fatty acids occur naturally in all aquatic organisms and are ubiquitous in the aquatic environment, where fatty acids are predominantly readily biodegraded in an aerobic environment by microorganisms. Microbial metabolism is the primary route of degradation in aquatic environment.  As nutritional energy source, fatty acids are absorbed by different uptake mechanisms in mammals depending on the chain length. Long chain fatty acids (>C12) are absorbed into the walls of the intestine villi and assembled into triglycerides, which then are transported in the blood stream via lipoprotein particles (chylomicrons). In the body, fatty acids are metabolised by various routes to provide energy. Besides this, fatty acids are stored as lipids in adipose tissue and as precursors for signalling molecules and even long chain fatty. In addition fatty acids are an integral part of the cell membranes of every living organism from bacteria and algae to higher plants. Fatty acids are known to be easily metabolised. The rate of metabolism of fatty acids was considered to vary in proportion to their water solubility (Lloyd, 1957). In case of absorption fatty acids will undergo rapid metabolism and excretion (either in the expired CO2 or as hydroxylated or conjugated metabolite in the urine in the case of cyclic fatty acids) as they feed into physiological pathways like the citric acid cycle, sugar synthesis, and lipid synthesis. As fatty acids are naturally stored in the form of triacylglycerols primarily within fat tissue until they are used for energy production (fat storage tactic), it is therefore concluded that there will be no risk to organisms from bioconcentration/biomagnification of fatty acids within the food chain. Hence Octadecanoic acid does not pose a risk to organisms in regard to bioaccumulation/biomagnification. Although the range of logKow values given suggests that the dimerised fatty acids may be expected to have tendency of a higher bioaccumulation, this only indicates intrinsic potential of the substance, but not of its behaviour in the environment. For instance, one must consider the biodegradation of the substance, and also its degradation within living organism, for example, metabolism. One should keep in mind that the fat storage strategy evolved as adaption in an environment where food supply was uncertain. Furthermore, as fatty acids are the end products of carbohydrate metabolism in living organisms muscle tissues, an evaluation of anthropogenic distribution of fatty acids based on the natural concentrations determined in the organs and tissues of aquatic organisms may be over estimated or not relevant.

In conclusion, Octadecanoic acid, branched and linear (CAS No. 68201-37) does not pose a risk to organisms in regard to bioaccumulation/biomagnification. Bioconcentration of fatty acids is generally below the level of concern. Hence, no classification to chronic hazardous to environment needs to be assigned.

Toxicity 

Long-term toxicity testing with Daphnia magna with the read-across substance Fatty acids, C16-18 and C18-unsaturated, branched and linear, “Monomer acid” (CAS No. 68955-98-6 ) resulted in a NOEC of ≥ 5 mg/L for Fatty acids, C16-18 and C18-unsaturated, branched and linear, “Monomer acid” (OECD 211). Moreover, the test substance is not classified according to Directive 67/548/EEC and Regulation (EC) No. 1272/2008 (2nd ATP). Thus, the criteria set out in Annex XIII of Regulation (EC) No. 1907/2006 are not met and the test substance is not considered to meet the T criterion.

References:

Lloyd, L. E. and Crampton, E. W. (1957). The relation between certain characteristics of fats and oils and their apparent digestibility by young pigs, young guinea-pigs and pups. J. Anita. Sci. 16:377.