2,6-xylenol

Short-term toxicity to aquatic invertebrates

Description of key information

Selection of the key value was based on a weight-of-evidence approach, taking into account data originating from sources with different reliability and adequacy. The key value selected for the 48 h LC50 to Daphnia magna was 11 mg/L. 

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

11 mg/L

Additional information

This endpoint is addressed on a weight of evidence basis. Three experimental values are available.

 

In the first study, published in the Science of the Total Environment, the toxicity of the test material to Daphnia magna was investigated using methodology similar to the standardised guideline OECD 202 with sufficient information on methods and results to evaluate data. The study was therefore awarded a reliability score of 2 in accordance with the criteria for assessing data quality as set forth by Klimisch et al. (1997).

The main deviation from the guideline was that the IC50 was determined at 24 hours rather than the recommended 48 hours. Daphnia magna were exposed to the test material under static conditions for 24 hours.

Observations of test populations were carried out after 24 hours of exposure. Daphnids which were unable to swim within 15 seconds after stimulation by gentle agitation of the water were considered to be immobilized, even if they could still move their antennae. Percentages of immobilization (between 10 and 90 % on the basis of total number of Daphnia per concentration) were recorded and plotted as a function of concentration on log-probit paper. The points obtained were fitted to a straight line from which the IC50 was read as the abscissa of the point corresponding to 50 % immobilization. 

A range of geometrical concentrations were chosen as to include chiefly the concentrations which had given 0, 10, 90 and 100 % immobilization during the preliminary tests. A single series of geometrically spaced concentrations of test solution were used (0.1, 0.35, 1, 3.5, 10, 35, 100, and 350 mg/L). 

Under the conditions of this study, the 24 h IC50 for 2,6-Xylenol is 0.117 mmol/L with a 95 % confidence interval of 0.108 to 0.127 mmol/L. When taking the molecular weight of 2,6-xylenol (MW = 122.1644) into account, this value can be converted to 14.29 mg/L (95 % confidence interval of 13.19 to 15.51 mg/L).

 

In the second study, published by the National Institute of Technology and Evaluation (Japan) the toxicity of the test material to Daphnia magna was investigated in accordance with the standardised guideline OECD 202 under GLP conditions. The available data suggested that the study should be awarded a reliability score of 2 in accordance with the criteria for assessing data quality as set forth by Klimisch et al. (1997).

Daphnia magna were exposed to the test material for 48 h. Under the conditions of this study, the 48 h EC50 was 11 mg/L.

 

The third study, published in Chem.-Biol. Interactions, was a non-guideline, non-GLP study with little information on methodology or results. As such it was awarded a reliability score of 3 in accordance with the principles for assessing data quality as set forth by Klimisch et al. (1997).

Daphnia magna were exposed to the test material under static conditions for 4 days. The 48 h survival figures were converted to probit values which were than plotted vs. log molar concentration. 

The 48 h LC50 value was determined to be 9.2E-05 molar. When taking into account the molecular weight of the test substance, this can be converted to 11.2 mg/L.

 

A key value of 11 mg/L was selected for this endpoint. Selection of the key value took into account data originating from sources with different reliability and adequacy.