Barium diboron tetraoxide

Toxicity to aquatic algae and cyanobacteria

Description of key information

The 72-h ErC50 and EbC50-values (72 h) were calculated to be 7.8 and 2.0 mg/L respectively based on the haemocytometer cell counts.  The NOEC for growth rate was statistically determined to be 1.1 mg/L.  The NOEC for biomass was below the lowest test concentration and therefore the EbC10 was calculated as 0.56 mg/L, this is considered to represent a conservative estimation of the NOEC.

Key value for chemical safety assessment

EC50 for freshwater algae:

7.8 mg/L

EC10 or NOEC for freshwater algae:

1.1 mg/L

Additional information

A GLP compliant OECD 201 algal inhibition test was conducted with Selenastrum capricornutum at nominal test concentrations of 0.31, 0.65, 1.3, 2.5, 5.0 and 10 mg a.i./L.

A 10 mg a.i./L primary stock solution (the highest nominal test solution) was prepared by dissolving 0.0222 g (0.0200 g as a.i.) of Busan 11-M1 in 2000 mL of AAP medium. The resultant solution was observed to be clear and colourless. Appropriate volumes (i.e., 31, 65, 130, 250 and 500 mL) of the 10 mg a.i./L primary stock solution were removed and diluted to 1000 mL with sterile AAP medium to prepare the remaining test solutions. Additional untreated AAP medium was prepared and designated as the control.

Triplicate vessels were prepared for each test concentration and control (test vessels were conditioned prior to use by rinsing with the appropriate test solution). All test vessels were fitted with stainless steel caps which permitted gas exchange. In order to estimate the impact the presence of algal biomass had on the test substance concentration, two additional replicate flasks of the 2.5 mg a.i./L (nominal) treatment level were prepared and maintained during the 72-hour test. These two flasks, which were not inoculated with algae, were composited and analysed at test termination.

The test was conducted in an environmental chamber adjusted to maintain the test conditions specified in the study protocol: a temperature of 24 ± 1 °C, continuous light intensity of 3200 to 5400 lux (300 to 500 foot candles) and a shaking table rate of 100 ± 10 rpm. Based on the experience of this laboratory, algal growth is improved at this light intensity range as compared to the intensity recommended by the OECD.

All samples were analysed for boron and barium content using Inductively Coupled Argon Plasma Spectrometry (ICP) analysis following U.S. EPA SW846 procedures. Concentrations of Busan 11-M1 present in the test solutions were calculated from the measured boron and barium concentrations by dividing the appropriate analytical result by the decimal percent of each analyte present in Busan 11-M1 (i.e., 8.7 and 57.4, respectively).

The 72-h E_rC₅₀and E_bC₅₀-values (72 h) were calculated to be 7.8 and 2.0 mg/L respectively based on the haemocytometer cell counts. 

The NOEC for growth rate was statistically determined to be 1.1 mg/L. The NOEC for biomass was below the lowest test concentration and therefore the E_bC₁₀was calculated as 0.56 mg/L, this is considered to represent a conservative estimation of the NOEC however, for REACH purposes the NOEC based on growth rate should be used for the risk assessment.