Rosin, decarboxylated

Toxicity to aquatic algae and cyanobacteria

Description of key information

A study was performed to assess the effect of the test item on the growth of the green alga Raphidocelis subcapitata (formerly known as Pseudokirchneriella subcapitata).  The method followed was designed to be compatible with the OECD Guidelines for Testing of Chemicals(2011) No 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test" and Method C.3 of Commission Regulation (EC) 761/2009. Due to the low aqueous solubility and complex nature of the test item for the purposes of the study the test medium was prepared as a Water Accommodated Fraction (WAF) of the test item. Following a preliminary range-finding test, Raphidocelis subcapitata was exposed to Water Accommodated Fractions (WAFs) of the test item over a range of nominal loading rates of 10, 18, 32, 56 and 100 mg/L (three replicate flasks per concentration) for 72 hours, under constant illumination and shaking at a temperature of 24 ±1 °C.

Chemical analysis of the test preparations at 0 hours showed measured test concentrations to range from 0.019 to 0.096 mg/L.  A decline in measured test concentrations was observed after each 24 hour period in the range of less than the limit of quantification (LOQ) of the analytical method employed, determined to be 0.010 mg/L, to 0.011 mg/L at 24 hours, and to less  than the LOQ (0.010 mg/L) in all preparations at 48 and 72 hours.  Analysis of additional samples ran alongside the test but to which no algal cells were added at 0 hours showed  measured test concentrations of less than the LOQ were obtained indicating that the losses were not attributable to adsorption of the test item to the algal cells present, but more likely due to instability of the test item under the conditions of the test.

Given that toxicity cannot be attributed to any single component or a mixture of components but to the test item as a whole, in accordance with the OECD Guidance Document on Aqueous-Phase Aquatic Toxicity Testing of Difficult Test Substances (OECD, 2019), the results were based on nominal loading rates only. Exposure of Raphidocelis subcapitata to the test item gave EL₅₀values of greater than 100 mg/L loading rate WAF.  The No Observed Effect Loading Rate (NOELR) was 100 mg/L loading rate WAF.