Tris(2-ethylhexyl) orthoborate

Toxicity to aquatic algae and cyanobacteria

Description of key information

Exposure Pseudokirchneriella subcapitata to an analogue test item gave a 72-Hour EC50 value based on growth rate of 9.0 mg/L (95% CI = 7.8 -11 mg/L). The No Effect Concentration was 1.9 mg/L and the LOEC was considered to be 5.1 mg/L (OECD 201 and EU Method C.3).

Key value for chemical safety assessment

EC50 for freshwater algae:

9 mg/L

EC10 or NOEC for freshwater algae:

1.9 mg/L

Additional information

Introduction

A study was performed to assess the effect of the analogue test item on the growth of the green alga Pseudokirchneriella subcapitata. The method followed that described in the OECD Guidelines for Testing of Chemicals (2006) No 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test" referenced as Method C.3 of Commission Regulation (EC) No 761/2009.

Methods

Due to the low aqueous solubility and pure nature of the test item, for the purposes of the definitive test, the test medium was prepared as a slow stir saturated solution. Following preliminary range-finding tests, Pseudokirchneriella subcapitata was exposed to solutions of the test item at nominal concentrations of 1.0, 3.2, 10, 32 and 100% v/v saturated solution (three replicate flasks per concentration) for 72 hours, under constant illumination and shaking at a temperature of 24 ± 1 °C. The test item solutions were prepared by stirring an excess (100 mg/L) of test item in culture medium using a magnetic stirrer at a rate such that a dimple was formed at the water surface for 23 hours. After the stirring period, the saturated solution was allowed to stand for 1-Hour prior to the removal of any undissolved test item by filtration through a glass wool plug (first approximate 75-100 mL discarded) to produce a 100% v/v saturated solution of the test item. This saturated solution was then further diluted as necessary, to provide the remaining test groups. Samples of the algal populations were removed daily and cell concentrations determined for each control and treatment group, using a Coulter® Multisizer Particle Counter.

Results

Chemical analysis of the test preparations at 0 and 72 hours showed measured boron concentrations to range from 0.070 to 2.5 mg/L. Total Organic Carbon (TOC) analysis of test preparations at 0 and 72 hours showed measured carbon concentrations to range from less than the limit of quantification (LOQ), determined to be 1.0 mg C/L at 1.0% v/v saturated solution, through to 32 mg/L at 100% v/v saturated solution (equivalent to test item concentrations of less than the LOQ to 42 mg/L based on a test item carbon content of 75.78%). It was considered appropriate to calculate the results based on the equivalent test item concentrations obtained from TOC analysis as these results give an estimate of the total dissolved test item concentrations present.

Exposure of the test item to Pseudokirchneriella subcapitata gave a 72-Hour EC50 value based on growth rate of 9.0 mg/L (95% CI = 7.8 -11 mg/L). The No Effect Concentration was 1.9 mg/L and the LOEC was considered to be 5.1 mg/L.