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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

Based on read across, results of dibutyl hydrogen phosphate (CAS No. 107-66-4) regarding the acute toxicity to alga (Desmodesmus subspicatus) is taken into account. The study was tested according to OECD guideline 201 ' Alga, Growth Inhibition Test'. During 72 hours exposure for dibutyl hydrogen phosphate an ErC50 of >100 mg/L was obtained and a NOEC of 50 mg/L was calculated. 

Key value for chemical safety assessment

EC50 for freshwater algae:
100 mg/L
EC10 or NOEC for freshwater algae:
50 mg/L

Additional information

For bis(2-ethylhexyl) hydrogen phosphate, there is only one study on toxicity to aquatic plants available.

In this test the algae Chlorella emersonii was exposed to bis(2-ethylhexyl) hydrogen phosphate for 72 hours. Growth was followed by measuring absorbance at 540 nm and growth curves were constructed by plotting the logarithm of the absorbance against time. The inoculum was adjusted to give an initial cell concentration corresponding to a chlorophyll concentration of 0.16 µg/cm³. The exponential growth rate was determined from the linear part of the growth curve by means of linear regression analysis. A 72h-EC50 of > 100 mg/L related to nominal concentrations was observed. A NOEC is not reported. There was no guideline stated but the test was performed in under generally accepted scientific principles. However, if exponential growth over time is given is not clear, as it is not clear, wether light adsorption correlates with cell density. The result cannot be sufficiently validated and is therefore scored to be reliable with restrictions only. Nevertheless, it can be used as a supporting study.

In order to draw a conclusion on toxicity towards aquatic plants for bis(2-ethylhexyl) hydrogen phosphate, read across with dibutyl hydrogen phosphate (CAS No. 107-66-4) is proposed and the corresponding study on the toxicity to freshwater algal species Desmodesmus subspicatus with dibutyl hydrogen phosphate is taken into account.

Dibutyl hydrogen phosphate and bis(2-ethylhexyl) hydrogen phosphate have very similar chemical structures and their main physico-chemical parameters (vapour pressure, water solubility, octanol/water partition coefficient, organic carbon partition coefficient and dissociation constant) are in the same range. Therefore a read across between this two substances to cover physico-chemical and ecotoxicological endpoints for bis(2-ethylhexyl) hydrogen phosphate seems to be justified.

More details regarding the read across justification are depicted in the annex of the Chemical Safety Report (CSR).

A study was performed to assess the adverse effects of dibutyl hydrogen phosphate on the growth rate (= rate of increase in cell density with time) of the planktonic freshwater algal species Desmodesmus subspicatus (former name: Scenedesmus subspicatus) over several generations. The study was conducted in accordance with Commission Regulation (EC) No 761/2009 amending Regulation No 440/2008, Method C.3 ‘Freshwater Alga and Cyanobacteria, Growth inhibition test’ (2009) which is equivalent to OECD Guideline for Testing of Chemicals No. 201 (2006). Exponentially growing alga cells were exposed for a period of 72 hours to a range of concentrations, nominally 3.1, 6.3, 12.5, 25, 50 and 100 mg/L of dibutyl hydrogen phosphate dissolved in dilution water. Auxiliary used to prepare the test media was a magnetic stirrer. The cell densities were measured at 24 hour intervals. Inhibition of the algal population was measured as reduction in growth rate (index r), relative to control cultures grown under identical conditions. Growth rates were also used to calculate a No Observed Effect Concentration and a Lowest Observed Effect Concentration according to Welch-t test for Inhomogeneous Variances with Bonferroni-Holm Adjustment. During 72 hours exposure for dibutyl hydrogen phosphate an ErC50 of >100 mg/L and ErC10 of 76 mg/L was measured and a NOEC of 50 mg/L was calculated. The lowest substance concentration 3.1 mg/L slightly dropped below the 80% recovery limit during the 72-hour exposure period. This is considered as not significant, because the highest determined test item concentration remained stable over the exposure time and therefore all results are expressed in terms of nominal concentrations. Effective concentrations ranged from 80.6 % to 103.0 % of nominal values at 0 hours, and from 79.6 % to 91.5 % of nominal values at 72 hours.

Based on the results, it could be shown, that bis(2-ethylhexyl) hydrogen phosphate and dibutyl hydrogen phosphate cause the inhibition on aquatic plants in the same order of magnitude.