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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The effect of Diurea 8 (both in isolated form and in base grease) on the growth of Pseudokirchneriella subcapitata gave EL50 (effect loading rate) values of greater than 100 mg/L WAF. Correspondingly the No Observed Effect Loading Rate (NOELR) was 100 mg/L WAF.

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Additional information

Three separate studies were conducted on the toxicity of Diurea 8 to algae. Two studies were conducted on Diurea 8 in base grease and the third on isolated Diurea 8 thickener. The results of the three studies are discussed below.

Harlan (2011)

The effect of Diurea 8 (in base grease) on the growth of Pseudokirchneriella subcapitata over a 72-Hour period gave a growth rate EL50 of 52 mg/L (95% Confidence Limits: 50 - 53 mg/L) and a yield EL50 of 36 mg/L (95% Confidence Limits: 32 – 39 mg/L). For both growth rate and yield, the No Observed Effect Loading Rate (NOELR) was 25 mg/L and the Lowest Observed Effect Loading Rate (LOELR) was 50 mg/L.

The method followed was designed to be compatible with the OECD guideline 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test". Following a preliminary range-finding test, Pseudokirchneriella subcapitata was exposed to Water Accommodated Fractions (WAFs) of Diurea 8 over a range of nominal loading rates of 6.25, 12.5, 25, 50 and 100 mg/L (three replicate flasks per concentration) for 72 hours, under constant illumination and shaking at a temperature of 24 ± 1°C. Samples of the algal populations were removed daily and cell concentrations determined for each control and treatment group, using a Coulter® Multisizer Particle Counter. Given that the toxicity cannot be attributed to a single component or a mixture of components but to Diurea 8 as a whole, the results were based on nominal loading rates only.

Harlan (2012b)

The effect of Diurea 8 (in base grease) on the growth of Pseudokirchneriella subcapitata gave EL50 (effect loading rate) values of greater than 100 mg/L WAF. Correspondingly the No Observed Effect Loading Rate (NOELR) was 100 mg/L WAF. It was considered unnecessary and unrealistic to test at loading rates in excess of 100 mg/L.

The method followed was designed to be compatible with the OECD guideline 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test". Following a preliminary range-finding test, Pseudokirchneriella subcapitata was exposed to a Water Accommodated Fraction (WAF) of Diurea 8, at a single nominal loading rate of 100 mg/L (six replicate flasks) for 72 hours, under constant illumination and shaking at a temperature of 24 ± 1°C. Samples of the algal populations were removed daily and cell concentrations determined for each control and treatment group, using a Coulter® Multisizer Particle Counter. Given that the toxicity cannot be attributed to a single component or a mixture of components but to Diurea 8 as a whole, the results were based on nominal loading rates only.

Harlan (2012a)

The effect of Diurea 8 (isolated thickener) on the growth of Pseudokirchneriella subcapitata gave EL50 (effect loading rate) values of greater than 100 mg/L WAF. Correspondingly the No Observed Effect Loading Rate was 100 mg/L WAF. It was considered unnecessary and unrealistic to test at loading rates in excess of 100 mg/L.

The method followed was designed to be compatible with the OECD guideline 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test". Following a preliminary range-finding test, Pseudokirchneriella subcapitata was exposed to a Water Accommodated Fraction (WAF) of Diurea 8, at a single nominal loading rate of 100 mg/L (six replicate flasks) for 72 hours, under constant illumination and shaking at a temperature of 24 ± 1°C. Samples of the algal populations were removed daily and cell concentrations determined for each control and treatment group, using a Coulter® Multisizer Particle Counter. Given that the toxicity cannot be attributed to a single component or a mixture of components but to Diurea 8 as a whole the results were based on nominal loading rates only.

Summary of available algae toxicity data for Diurea 8

Two separate tests were conducted on the toxicity of Diurea 8 base grease to algae. The initial test (Harlan 2011) was conducted at nominal loading rates of 6.25, 12.5, 25, 50 and 100 mg/L based on the results of a preliminary range finding study. The results gave a growth rate EL50 of 52 mg/L WAF (95% Confidence Limits: 50 - 53 mg/L WAF) and a yield EL50 of 36 mg/L WAF (95% Confidence Limits: 32 – 39 mg/L WAF) with a NOELR of 25 mg/L WAF for both growth rate and yield.

The level of toxicity observed in this first study (Harlan 2011) was contrary to what was expected for a clean base grease (i.e. simply the base oil plus Diurea 8 thickener prior to the addition of any other performance additives). There were concerns that the base grease sample supplied for this study may have contained additional performance additives. To address these concerns a fresh batch of Diurea 8 base grease was prepared and a second acute algae toxicity study was conducted (Harlan 2012b). The second study was conducted as a limit test at 100 mg/L WAF, based on the results of a preliminary range finding study. The results gave EL50 (effect loading rate) values of greater than 100 mg/L WAF for both growth rate and yield. Correspondingly the No Observed Effect Loading Rate (NOELR) was 100 mg/L WAF.

In addition there was sufficient quantity of the isolated Diurea 8 thickener to undertake a separate algal study (Harlan 2012a). This study was undertaken to provide additional ‘weight of evidence’ that the results of the first algae toxicity study (Harlan 2011) conducted on Diurea 8 in base grease were not representative. This proved to be the case as the isolated Diurea 8 thickener was found to be non-toxic to algae. On this basis it can be concluded that the second test (Harlan 2012b) with the base grease containing the Diurea 8 thickener presents a more relevant and reliable result for the toxicity to algae than the first study (Harlan 2011).

In summary, data are available which show that both the isolated Diurea 8 and Diurea 8 in base grease are not toxic to algae at nominal loading rates of up to 100 mg/L from relevant and reliable studies. These results are comparable to the observed toxicity of Diurea 8 base grease to other trophic levels and reflect the lack of toxicity expected for Diurea 8 with very low water solubility (and limited bioavailability in the grease matrix). Therefore, to maintain consistency with the form in which Diurea 8 was tested in the key acute aquatic toxicity studies identified for other trophic level organisms (fish and invertebrates), the second algae test (Harlan 2012b) on Diurea 8 base grease, conducted as a limit test at 100 mg/L WAF, has been used as the key study for this endpoint.