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Sediment toxicity

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Description of key information

The chemical safety assessment according to Annex I of Regulation (EC) No. 1907/2006 does not indicate the need to investigate further the effects on sediment organisms.

Key value for chemical safety assessment

Additional information

No experimental data evaluating the toxicity to sediment organisms is available for ethylene distearate (CAS 627-83-8). Since the substance is ready biodegradable, chronic exposure of sediment organisms is unlikely. Furthermore, the substance is not toxic to aquatic organisms up to the limit of water solubility. In addition, available data indicate, that ethylene distearate is not bioaccumlative. Based on the available information, toxicity to sediment organisms is not expected to be of concern.

 

Intrinsic properties and fate

Ethylene distearate is readily biodegradable (73% O2 consumption in 28 days; METI, 1998). According to the Guidance on information requirements and chemical safety assessment, Chapter R.7b, readily biodegradable substances can be expected to undergo rapid and ultimate degradation in most environments, including biological Sewage Treatment Plants (STPs) (ECHA, 2008). Therefore, after passing through conventional STPs, only low concentrations of these substances are likely to be (if at all) released into the environment.

 

Furthermore, the substance exhibits a log Koc value of 8.80 (MCI) and is poorly water soluble (4.24E-012 mg/L; SRC PhysProp database). The Guidance on information requirements and chemical safety assessment, Chapter R7.B (ECHA, 2008) states that once insoluble chemicals enter a standard STP, they will be extensively removed in the primary settling tank and fat trap and thus, only limited amounts will get in contact with activated sludge organisms. Nevertheless, once this contact takes place, these substances are expected to be removed from the water column to a significant degree by adsorption to sewage sludge (Guidance on information requirements and chemical safety assessment, Chapter R.7a, (ECHA, 2008)) and the rest will be extensively biodegraded (due to ready biodegradability). Thus, discharged concentrations of these substances into the aqueous/sediment compartment are likely to be negligible. Considering this one can assume that the availability of ethylene distearate in the sediment environment is generally very low, which reduces the probability of chronic exposure of sediment organisms in general.

 

Aquatic ecotoxicity data

Acute aquatic toxicity tests of the substance to fish, invertebrates, algae and microorganisms showed no adverse effects occurred in the range of the water solubility of the substance (4.24E-012 mg/L; SRC PhysProp database). The obtained results indicate that ethylene distearate is likely to show no toxicity to sediment organisms as well.

 

Metabolisms/Bioaccumulation

After absorption, ethylene distearate is expected to be enzymatically hydrolyzed by carboxylesterases yielding the corresponding alcohol and fatty acid. Ethylene distearate has a log Kow of 16.12 (KOWWIN v1.68) indicating a potential for bioaccumulation. But due to the low water solubility, rapid environmental biodegradation and metabolisation via enzymatic hydrolysis, a relevant uptake and bioaccumulation in aquatic organisms is not expected. Enzymatic breakdown will initially lead to the free fatty acid and the free glycol alcohol (e. g. ethylene glycol). From literature it is well known, that these hydrolysis products will be metabolized and excreted in fish effectively (Heymann, 1980; Lech & Bend, 1980; Lech & Melancon, 1980; Murphy & Lutenske, 1990). This is supported by low calculated BCF values of 0.893 - 41.86 L/kg ww (BCFBAF v3.01, Arnot-Gobas, including biotransformation, upper trophic). Please refer to IUCLID Section 5.3 for a detailed overview on bioaccumulation of the Glycol Esters Category members. Thus, taking all information into account, the bioaccumulation of the category member ethylene distearate is assumed to be low.

 

Conclusion

Due to its readily biodegradable nature, extensive degradation of this substance in conventional STPs will take place and only low concentrations are expected to be released (if at all) into the environment. Once present in the aquatic compartment, further biodegradation will occur and, due to the high log Kow, low water solubility and high adsorption potential, ethylene distearate will be bioavailable to sediment organisms mainly via feed and contact with suspended organic particles. After uptake by sediment species, extensive and fast biotransformation of the substance by carboxylesterases into the free fatty acid and the corresponding alcohol is expected. The supporting BCF/BAF values estimated with the BCFBAF v3.01 program, Arnot-Gobas model including biotransformation, also indicate that this substance will not be bioaccumulative (all well below 2000). Furthermore, aquatic toxicity data show that no effects occur up to the limit of water solubility. Therefore, ethylene distearate is unlikely to pose a risk for sediment organisms in general and testing is thus omitted.

 

References

ECHA. 2008a. Guidance on information requirements and chemical safety assessment – Part C: PBT assessment. European Chemicals Agency, Helsinki

 

ECHA. 2008b. Guidance on information requirements and chemical safety assessment – Chapter 7c: Endpoint specific guidance. European Chemicals Agency, Helsinki

 

Heymann, E. (1980): Carboxylesterases and amidases. In: Jakoby, W.B., Bend, J.R. & Caldwell, J., eds., Enzymatic Basis of Detoxication, 2nd Ed., New York: Academic Press, pp. 291-323.

 

Lech, J.J. & Bend, J.R. (1980): Relationship between biotransformation and the toxicity and fate of xenobiotix chemicals in fish. Environ. Health Perspec. 34, 115-131.

 

Lech, J., Melancon, M. (1980): Uptake, metabolism, and deposition of xenobiotic chemicals in fish. EPA-600 3-80-082. U.S. Environmental Protection Agency, Duluth, MN, USA.

 

Murphy, P.G., Lutenske, N.E. (1990): Bioconcentration of haloxyfop-methyl in bluegill (Lepomis macrochirus Rafinesque). Environ. Intern. 16, 219-230.