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Toxicity to aquatic algae and cyanobacteria

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The growth inhibition of P5524 (which contains 99.9% DEC) to Pseudokirchneriella subapitata (reported as Selenastrum capricornutum) was determined in a 72 h static GLP algae growth inhibition test (Bell, 1995). The test design was based on the OECD 203 guideline and the EU method C.3.The study was performed under GLP and according the guideline. From 48 to 72 hours, the control cultures showed only limited or even negative growth rates. Consequently, the growth of the 3 replicates of the control cultures did not fulfil the CV- section-by section growth rate as outlined in the updated OECD 201 guideline (2006). The other two quality criteria (CV Average specific growth rate and Increase >16 times) were fulfilled. For hour 0, analytical dose verification confirmed that the 100 mg/L test solution was correctly dosed (recovery > 90%). Analytical verification at hour 0 was not able to verify the nominal concentrations for test solutions with 46 mg/L or less. For these concentrations a recovery of about 40 % was obtained (except nominal 1 mg/L where 75.1 % recovery was found). The rational for this discrepancy was not reported. All results are expressed in terms of nominal concentration. Measured concentrations could not be thoroughly verified due to difficulties with the analytical method.

Based on these shortcomings (mainly for not meeting the validity criterion for the section-by section growth rate , this study is considered to have a Klimisch 3 score.


The nominal test concentrations were Control (0), 1.0, 2.2, 4.6, 10, 22, 46, and 100 mg test item/L. Three control replicates and 3 replicates from each test solution were set up. Dose verification analysis was performed but was not able to verify correct dosing. In order to determine the growth of the cultures, the cells were counted electronically. The test was started with about 12000 cells/mL. The cell density was determined at 24, 48 and 72 hours. As outlined above, the growth of the control cultures has not fulfilled the validity criteria from OECD 201 (2006). The 72 -hour ErC50 is 59 mg/L based on nominal concentrations.


Since this study is a Klimisch 3 study, the results are considered to be not relevant for the assessment of the substance.