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Long-term toxicity to aquatic invertebrates

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Description of key information

No valid tests on long-term toxicity of DITA to aquatic invertebrates are available. A testing proposal is entered.


To ensure environmental safety of DITA as long as no adequate data on long-term toxicity is available, we performed an environmental safety assessment using the NOEC value of 1.64 µg/L obtained in the invalid OECD 211 test in terms of a worst-case approach.

Key value for chemical safety assessment

Additional information

The available long-term toxicity study towards aquatic invertebrates for DITA (Simon, 2016) was conducted by using the column elution method for test medium preparation. Daphnids were exposed to a steady state column eluate in form of the 100% eluate and 10 % eluate for a period of 21 days in a semi-static test design. No significant differences between the control group and the test groups were found for the following endpoints: Mobility, age at first reproduction, length and intrinsic rate. In the undiluted eluate, a ~27% reduction of mean cumulative offspring per surviving daphnids after 21 days were seen, whereas the exposure to the 10%-dilution of the eluate resulted in no significant effects for this endpoint, as well. The concentrations measured in both, the undiluted eluate and the 10%- eluate tests solution varied considerably and showed to be far above the reported and experimentally determined (e.g. Kotthoff, 2016) water solubility for DITA of ~0.7 µg/L. Hence, micelle formation or other processes causing the inhibition cannot be excluded. Consequently, this study is considered to be invalid (see study and testing proposal) and a testing proposal for a new study using a more appropriate test solution preparation technique (developed in an extensive research project) is entered in the dossier.


Several studies for structurally similar read across substances support the assumption that the observed effects in the existing OECD 211 test are not related to intrinsic toxicity of the substance and that no toxicity within the range of water solubility is to be expected:


There are three long-term toxicity tests with aquatic invertebrates available on the read-across substance bis(2-ethylhexyl) adipate (CAS 103-23-1; DEHA) and one study on the read-across substance diisotridecyl dodecanedioate (CAS 84731-63-5), which show no toxicity in the range of water solubility. All of these substances, DEHA, DITA and diisotridecyl dodecanedioate, are dialkylesters of dicarboxylic acids, either adipic acid (1,6-hexanedioic acid) or 1,12-dodecandioic acid. Both dicarboxylic acids are linear and have even-numbered carbon chains. The alcohol component of all three substances has branched alkyl groups (C8 or C13).


DEHA


In a valid 21 day reproduction test according to OECD test guideline 202 (1984, part 2), the water flea Daphnia magna was exposed to three different concentrations of bis-(2-ethylhexyl) adipate (nominal concentrations 0.5, 1.0, and 2.0 mg/L, measured concentrations 0.19, 0.39, and 0.77 mg/L). To solubilise the test substance, a vehicle was used (1g/L MARLOWET R 40). During the test, no effects were observed. Based on the reproduction rate, a NOEC of >= 0.77 mg/L was determined (Huels AG, 1996a). This is considered a valid proof of the absence of long-term aquatic toxicity of bis(2-ethylhexyl) adipate to invertebrates in the range of water solubility. This result is confirmed in another study performed by Robillard et al. (2008) (key study). A chronic Daphnia magna limit test was conducted at an average exposure concentration of 4.4 μg/L (measured water solubility = 5.5 µg/L) in laboratory diluent water to avoid insoluble test material and physical entrapment. One hundred percent of the DEHA-treated organisms survived compared to 90% survival in both the controls and solvent controls. Mean neonate reproduction was 152, 137, and 148 and mean dry weight per surviving female was 0.804, 0.779, and 0.742 mg in the treatment, control and solvent control, respectively. No adverse effects were observed. In the third study (Felder et al. (1986), not conducted according to a current guideline and GLP), which is the only one with DEHA detailed discussed in the Substance Evaluation Draft Decision, a significantly reduced yield of young per adult per day at mean measured exposure levels of 0.087 and 0.18 mg/L were found. A MATC (maximum acceptable toxicant concentration) for long-term toxicity to Daphnia magna was calculated to be between 0.024 and 0.052 mg/L based on statistical analyses of adult mean length, survival and young per adult per reproduction day. The geometric mean of the LOEC and NOEC was 0.035 mg/L, which is approximately ten-fold above the solubility limit of bis(2-ethylhexyl) adipate. Acetone was used as a solvent in this study. No adverse effects to survival growth or reproduction were observed even at levels five times the water solubility of DEHA. Effects were reported at concentrations significantly higher than the water solubility of DEHA (0.005 mg/L). Under such conditions it is likely that the observed effects have been caused by physical entrapment rather than chemical interactions (Rhodes et al. 1995). Furthermore, information provided in the results section of the publication is rather scarce. Neither raw data nor details about the extent of impairment daphnids had to face at a given concentration are given, and no information about a dose-response relationship is included. In our opinion also the study of Felder et al. (1986) with the NOEC of 0.024 mg/L shows that no toxicity occurred within the range of water solubility of 0.005-0.0032 mg/L. The lowest measured water solubility value of DEHA is lower than the NOEC. The study supports the fact that there was no toxicity in the range of water solubility. Therefore, this value cannot be used for the PNEC-derivation.


 


Diisotridecyl dodecanedioate


In addition to the presented long-term toxicity studies with Daphnia magna performed with DEHA, a recently (2013) conducted long-term toxicity test with Daphnia magna (OECD 211) on the read-across substance diisotridecyl dodecanedioate is available. The GLP study was performed under semi-static conditions using DMF as a solvent (key study). In the Substance Evaluation Draft Decision it is discussed by the MSCA that the study cannot be considered valid due to uncertainties in the preparation of samples which resulted in declining of 99 % of the test substance in 48 h to below the LOQ. We would like to defend the study and attached a letter with the complete rationale of the responsible test institute Harlan. "The decline in measured test concentrations in the inoculated test samples was due to adsorption of the test item to the algal cells that were present. In the Daphnia magna Reproduction Test, algal cells are added to the test solutions in order to provide a food source for the daphnids, it is therefore considered that the decline in measured concentrations over each test media renewal period in this test was due to adsorption of the test item to the algal cells and not due to instability and / or volatility. As the test item was adsorbed to the algal cells that the daphnids ingest as a food source it can be considered that the daphnids were exposed to the test item over the period of each test media renewal" (please see attached the complete wording of the rationale). Furthermore, based on the structure of diisotridecyl dodecanedioate it is expected that this substance is even more water insoluble than DITA (< 0.001 mg/L). The analytics for such water insoluble UVCB-substances are very difficult. The measured concentrations in this study were extremely low. Therefore, it is not unlikely that the measured concentrations were inconsistent in such a sensitive study. Analysis of the freshly prepared 100 % v/v solution preparation on days 0, 5, 12, 19 showed measured concentrations ranging from less than the LOQ (assessed as 0.00027 mg/L) to 0.0024 mg/L. Analyses of the old or expired media on days 2, 7, 14, 21 showed measured concentrations ranging from less than the limit of quantification to 0.00093 mg/L. Given to the apparent decline in measured concentration between each period of media renewal, it was considered justifiable to base the results on the mean measured test concentrations of the test media to give a "worst case" analysis of the data. The No Observed Effect Concentration based on the mean measured concentration of the test media was equal to 0.00063 mg/L respectively. The mean measured concentration of 0.00063 mg/L was estimated for the 100 % v/v solution. We provide additional information including a better justification for the choice of test solution preparation used for the diisotridecyl dodecanoate test (Harlan 2013), and why it would achieve saturation for a low solubility UVCB (please see attachment “issue1_OECD211comments2_diisotridecyldodecanoate_studyno41202662.pdf"). In the study of Robillard et al. (2008) the water solubility of 5.5 (± 0.22) μg/L for di(2- ethylhexyl) adipate (DEHA) was measured using the slow-stir method which is in the Registrants’ scientific opinion, one of the most suitable methods for substances with a very low water solubility. Compared to DEHA, the water solubility of DITA and of diisotridecyl dodecanoate can be expected to be lower because of longer C-chains. Therefore, the higher measured water solubility values for DITA and diisotridecyl dodecanoate must be interpreted with caution, since they were determined with the ASTM-E1148 Standard Test Method, a comparably less sensitive method. In general, the determination of a definite value for the water solubility of UVCB substances poses a very complex problem and is by far more complicated than the determination for single substances (monoconstituents). This study shows like the DEHA-studies no toxic effects at the limit of water solubility.


 


Together, based on the available data for DITA and the supporting information, a conclusion on chronic toxicity of DITA to aquatic invertebrates cannot be drawn. Therefore, a proposal to perform a new test using a more appropriate test solution preparation technique is entered in the dossier.


To ensure environmental safety of DITA as long as no adequate data on long-term toxicity is available, we performed an environmental safety assessment using the NOEC value of 1.64 µg/L obtained in the invalid OECD 211 test in terms of a worst-case approach.