Dimethyl itaconate

Toxicity to aquatic plants other than algae

Description of key information

Slightly acute toxic, EC50 calculated on the basis of changes in the logarithms of frond numbers (95 % CL: 37-55 mg/L); EC10 calculated on the basis of changes in the logarithms of dry weight over time (expressed per day), ACR 3.0

Key value for chemical safety assessment

EC50 for freshwater plants:

45 mg/L

EC10 or NOEC for freshwater plants:

15 mg/L

Additional information

The primary producer ecotoxicity of the submission item Dimethyl itaconate (CAS 617-52-7) to aquatic higher plants (Lemna minor) was measured in a GLP-compliant study (Vryenhoef 2014, Harlan Laboratories Report no. 41301815) using the “Lemna sp. Growth Inhibition test” compliant with the OECD TG 221 (2006) protocol. The validity criteria were met and the experiment can be considered relevant and adequate for the endpoint. Therefore it is deemed conclusive and was rated „reliable without restrictions“, i.e. “Klimisch 1” according to the scale of Klimisch et al. (1997).

Three colonies of the test organisms (lesser duckweed) with a total number of 10 fronds per vessel were in three replicates during 7 days exposed to nominal test item concentrations of 1.0, 3.2, 10, 32 and 100 mg/L (spacing factor 3.125 to 3.2) and a control. No vehicle was used. Test item concentrations in duplicate samples, pooled from the three replicates, were determined by gas chromatography mass spectrometry (GC-MS) using an external standard. Geometric mean of the concentrations measured at Day 0 and test end = Day 7 were 0.78 (0.836 & 0.733), 2.4 (2.43 & 2.34), 8.2 (8.11 & 8.21), 31 (29.8 & 32.) and 96 (92.4 & 99.5) mg/L. These concentrations correspond to 78, 75, 82, 97 and 96 % of nominal, respectively, and were used as basis for results. The effect parameters followed were the number of fronds in each control and treatment group recorded by manual counting on days 0, 2, 5 and 7 along with observations on plant development (frond size, appearance, root length and number of colonies present). Additionally the biomass in terms of the dry weight of the fronds in each control and treatment group was determined on day 7. At the start of the test six replicate samples of fronds identical to those used to inoculate the test vessels were taken and the dry weight determined. At the end of the test dry weight of colonies from each control and test vessel was determined by blotting the colonies dry and drying at 60 °C to constant weight.

The NOEC and the LOEC for all effect parameters were 8.2 and 31 mg/L, respectively, which gives an MATC (geometric mean of NOEC and LOEC) of 16 mg/L. The threshold levels calculated for 10, 20 and 50 % effect were determined as follows:

Response Variable	Measurement Variable	EC50 [mg/L]	95 % Confidence Limits [%]	EC20 [mg/L]	EC10 [mg/L]
Average Specific Growth Rate	Frond Number	45	37-55	24	17
	Dry Weight	54	Not calculable	24	15
Yield	Frond Number	29	23-37	14	9.5
	Dry Weight	27	21-34	13	8.8

As in agreement with the test guideline the use of average specific growth rate for estimating toxicity is considered scientifically preferred, the overall toxicity threshold levels should be based on these endpoints. According to the ECHA R.10 (2008, p 11) guidance on Characterisation of dose [concentration]-response for environment EC10 for a long-term tests, as obtained using an appropriate statistical method (i.e. regression analysis) should be used preferentially over the NOEC. Therefore the establishment of threshold levels on the basis this study should consider the lowest EC10 and EC50 based on growth rate for the short- and long-term effect assessment, which are 15 and 45 mg/L, respectively.

In conclusion the relevant endpoints for risk assessment from this study are the ErC10 (dry weight) 15 mg/L for long-term effects, while for short-term effects the ErC50 (frond number) of 45 mg/L with the 95 % CL 37-55 mg/L should be used. This places the submission item in the „slightly toxic“ acute toxicity class according to the scheme of (U.S. EPA 1994, p 10). The acute-to-chronic-ratio (ACR) is thus 3.0 indicating a low steepness of the dose-effect curve. A slight percental decrease of the test item was only in the low test concentrations important, which suggest absorption and biodegradation of the test organisms or adsorption to their biomass rather than photolysis or hydrolysis as causation.

• ECHA R.10: European Chemicals Agency (2008). Guidance on information requirements and chemical safety assessment. Chapter R.10: Characterisation of dose [concentration]-response for environment. Guidance for the implementation of REACH. Self-published, Helsinki, Finland, in May. 238 p.
• Klimisch HJ, Andreae M, Tillmann U (1997). A Systematic Approach for Evaluating the Quality of Experimental Toxicological and Ecotoxicological Data. DOI 10.1006/rtph.1996.1076 PMID 9056496 Regul Toxicol Pharmacol 25:1-5.
• U.S. EPA United States Environmental Protection Agency (1994). Pesticide Reregistration Rejection Rate Analysis, Ecological Effects. Self-published EPA, Office of Prevention, Pesticides and Toxic Substances (OPPTS), Washington, DC, U.S.A., document number 738-R-94-035. 188 p.