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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. Based on the presented information, toxicity to sediment organisms is not expected to be of concern.

Key value for chemical safety assessment

Additional 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. Based on the presented information, toxicity to sediment organisms is not expected to be of concern.

Discussion

Heptanoic acid, ester with 2,2-dimethyl-1,3-propanediol (CAS No. 68855-18-5) is readily biodegradable, therefore 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, Heptanoic acid, ester with 2,2-dimethyl-1,3-propanediol is not expected to bioaccumulate, due to rapid metabolism.

Distribution to the environmental compartments, intrinsic properties and fate

Since direct release of Heptanoic acid, ester with 2,2-dimethyl-1,3-propanediol to the aquatic system is not anticipated, release to the aquatic compartment might occur via sewage treatment plants only.

According to the Guidance on information requirements and chemical safety assessment, Chapter R7.b (ECHA, 2012) 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.7b, (ECHA, 2012). Our substance of concern is characterized by a log Koc value of 3.7 (KOCWIN v2.00, MCI) and is poorly water soluble (< 0.05 mg/L purified water; Frischmann, 2012) and thus will undergo the same fate as stated in the Guidance document. Furthermore, Heptanoic acid, ester with 2,2-dimethyl-1,3-propanediol is readily biodegradable (89.3% CO2 evolution in 28 days; Bouillon, 1999) and 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, 2012). Therefore, after passing through conventional STPs, exposure, of these polyol esters into the aqueous/sediment compartment are likely to be negligible.

Aquatic ecotoxicity data

Acute aquatic toxicity tests of the substance to fish and algae showed no adverse effects in the range of the water solubility of the substance (< 0.05 mg/L measured in aqua dest). Moreover, no toxicity to activated sludge organisms was observed. Also in the long-term study with Daphnia magna, no effect on reproduction was observed up to the highest tested concentration (0.0019 mg/L, measured, TWA). The obtained results indicate that Heptanoic acid, ester with 2,2-dimethyl-1,3-propanediol (CAS No. 68855-18-5) is also not likely to show toxicity to sediment organisms.

Metabolisms/Bioaccumulation

The test substance has a log Kow of > 5 (KOWWIN v1.67) 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. After absorption, 2,2-dimethyl-1,3-propanediol is expected to be enzymatically hydrolyzed by carboxylesterases Enzymatic breakdown will initially lead to the free fatty acid and the free alcohol (e. g. neopentyl 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 a low calculated BCF value of 33.76 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 NPG polyol esters. Thus, taking all information into account, the bioaccumulation of the category member Heptanoic acid, ester with 2,2-dimethyl-1,3-propanediol 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, Heptanoic acid, ester with 2,2-dimethyl-1,3-propanediol will be bioavailable to sediment organisms mainly via food and contact with suspended organic particles. After uptake by sediment species, extensive and fast biotransformation of the substance by carboxylesterases into heptanoic 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). Therefore, Heptanoic acid, ester with 2,2-dimethyl-1,3-propanediol is unlikely to pose a risk for sediment organisms, hence toxicity to sediment organisms is not expected to be of concern and thus there is no need to to investigate further the effects on sediment organisms.