Diisononyl adipate

Sediment toxicity

Description of key information

DINA is unlikely to pose a risk for sediment organisms

Additional information

Long-term toxicity

No toxicity investigating the long-term toxicity of Diisononyl adipate (CAS 33703-08-1, DINA) to sediment organisms is available. However, since DINA is readily biodegradable and does not bioaccumulate, chronic exposure of sediment organisms is unlikely.

 

Acute toxicity

Since no study assessing the short-term toxicity of DINA to sediment organisms is available, in accordance to Regulation (EC) No. 1907/2006 Annex XI, 1.5 Grouping of substances, a read-across to structurally very similar Bis(2-ethylhexyl) adipate (CAS 103-23-1, DEHA) was conducted. The read across is justified due to the similarity of structure and functional groups and accordingly similar physico-chemical properties which result in similar environmental behavior and fate (see table below).

 

Substance	Diisononyl adipate (DINA)	Bis(2-ethylhexyl) adipate (DEHA)
CAS number	33703-08-1	103-23-1
Structure	see attachment	see attachment
Molecular formula	C24H46O4	C22H42O4
Molecular weight	398.63 g/mole	370.58 g/mole
PC parameter
Water solubility	RA to 103-23-1	0.0032 mg/L (EU A.6)
Partition coefficient	9.54 (OECD 117)	8.94 (OECD 117)
Vapour pressure	0.00000002 hPa at 20 °C (calculation)	0.0000003 hPa at 20 °C (calculation)
Environmental fate
Biodegradability	> 90% in 28 days (OECD 301F)	>90% in 28 days (OECD 301F)
Adsorption [log KOC]	5.15 (calculation)	4.56 (calculation)
Hydrolysis	not relevant
Ecotoxicology
Short-term toxicity to fish [96h-LC50]	No toxicity within the limit of water solubility	No toxicity within the limit of water solubility
Long-term toxicity to aquatic invertebrates [NOEC]	-	-
Short-term toxicity to aquatic invertebrates [48h-EC50]	No toxicity within the limit of water solubility	No toxicity within the limit of water solubility
Long-term toxicity to aquatic invertebrates [21d-NOEC]	RA from 103 -23 -1	No toxicity within the limit of water solubility
Short-term toxicity to algae [72h-EC50]	No toxicity within the limit of water solubility	No toxicity within the limit of water solubility
Long-term toxicity to algae [72h-NOEC/EC10]	No toxicity within the limit of water solubility	No toxicity within the limit of water solubility
Toxicity to microorganisms [NOEC]	The inhibition of the degradation activity of activated sludge is not anticipated when DINA is introduced in appropriate low concentrations.	The inhibition of the degradation activity of activated sludge is not anticipated when DEHA is introduced in appropriate low concentrations.

 

The study was performed according to ASTM guideline E729-80 (Standard practice for conducting acute toxicity test with fishes, macroinvertebrates and amphibians adopted in 1980) under GLP conditions. Chironomus riparius, Gammarus fasciatus and Asellus spec. were used as test organisms. Analytically verified test concentrations between 0.087 and 0.73 mg/L were applied using acetone as vehicle. Throughout the exposure period a clear, colorless oily film was observed on the surface of the two highest treatment levels (0.73 and 0.38 mg/L) indicating that the solubility in medium is lower. Due to the presence of the surface film of undissolved test material, the retention chambers were placed into the test solutions at test initiation and not removed during biological observations. This procedure prevented direct exposure of the organisms to undissolved test material. Following 96 hours of exposure to the highest treatment level (0.73 mg/L), mortality of 0 and 10% was observed among the exposed amphipods and isopods, respectively. Mortality of 5 to 35% was observed among the exposed midge larvae at all treatment levels and the controls. Since midge larvae are benthic organisms which are generally found burrowed in sediment, the mortalities observed during this study were determined to be a response to the exposure conditions (i.e., absence of sediment) and not related to the toxicity of the substance. The 96h-LC50 value for all tested species is determined to be > 0.73 mg/L.

Based on this data DEHA is considered to be not acutely harmful to sediment dwelling organisms up to solubility of the substance in water. Based on the mentioned structural similarities between the source and the target substance resulting in a similar efate and ecotoxicological profile this can also considered to be true for Diisononyl adipate (CAS 33703-08-1). 

 

Intrinsic properties and fate

DINA is readily biodegradable (> 90% in 28 days, BASF 1985). 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 2012a). Therefore, after passing through conventional STPs, only low concentrations of the substance is likely to be (if at all) released into the environment. Furthermore, the substance has a log Koc value of 5.15 and low water solubility. The Guidance on information requirements and chemical safety assessment, Chapter R7.b (ECHA 2012a) 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 2012b)) and the rest will be extensively biodegraded (due to ready biodegradability). Considering this one can assume that the availability of DINA in the sediment environment is generally very low, which reduces the probability of chronic exposure of sediment organisms in general.

   

Bioaccumulation

DINA is not expected to be bioaccumulative. If present in the aquatic compartment, biodegradation will occur and, depending on their log Pow, water solubility and adsorption potential, DINA (and its metabolites) will be bioavailable to aquatic organisms such as fish mainly via water or on the other hand via feed and contact with suspended organic particles.
If taken up by living organisms, aliphatic esters such as DINA and DEHA will be initially metabolized via enzymatic hydrolysis to the respective dicarboxylic acid and alcohol components as would dietary fats (e.g., Linfield 1984, Lehninger 1970, Mattson and Volpenhein 1972). The hydrolysis is catalyzed by carboxylesterases and esterases (e.g., Heymann 1980). Carboxylesterase activity has also been reported from a wide variety of tissues in invertebrates and fishes (e.g., Barron et al. 1999, Wheelock et al. 2008). In fish, the high catalytic activity, low substrate specificity and wide distribution of the enzymes in conjunction with a high tissue content lead to a rapid biotransformation of aliphatic esters, which significantly reduces its bioaccumulation potential (Lech and Melancon 1980, Lech and Bend 1980). Isononanol (DINA), 2-ethylhexanol (DEHA) and adipic acid are the expected hydrolysis products from the enzymatic reaction catalyzed by carboxylesterase. These metabolites exhibit no potential for bioaccumulation (BCF < 80, BCFBAF v3.01 calculation): The metabolism of alcohols has been extensively reviewed in the literature (e.g., see Rizzo et al. 1987, Hargrove et al. 2004). The free alcohols can either be esterified to form wax esters (which are similar to triglycerides) or they can be transformed to fatty acids in a two-step enzymatic process catalyzed by alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). The alcohol is used by these organisms as their main source of energy throughout all the different life stages (early development, growth, reproduction, etc.). Adipic acid does not have the potential to accumulate in adipose tissue due to their low log Pow. The key study reports a BCF value of 27, which clearly indicate that rapid metabolism takes place even when log Pow values are above the trigger value of 3. Supporting BCF/BAF values, estimated using EPISuite and Catalogic models, confirm the experimental result (all well below 2000).
The information above provides strong evidence supporting the statement that rapid metabolism and low bioaccumulation potential can be expected for DINA and its metabolites.

 

Conclusion

Since the substance is readily biodegradable, 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. DINA will be bioavailable to sediment organisms mainly via feed and contact with suspended organic particles. The key study reports a BCF value of 27, which clearly indicate that rapid metabolism takes place even when log Pow values are above the trigger value of 3. Supporting BCF/BAF values, estimated using EPISuite and Catalogic models, confirm the experimental result (all well below 2000). Furthermore, aquatic toxicity data (including sediment organisms) show that no effects occur up to the limit of water solubility. Therefore, DINA is unlikely to pose a risk for sediment organisms in general and long-term testing is thus omitted.