A higher tier flow-through toxicity test with the green alga Selenastrum capricornutum

A flow-through test system for the assessment of the toxicity of substances to the green alga Selenastrum capricornutum was developed. The dosing of a test substance commenced, once the growth of the algae was in a steady state, i.e. when the dilution rate was equal to the growth rate. The growth rate and hence the effect of the test substance was determined indirectly by the estimation of cell number under consideration of inflow volume over time. The ease of manipulation of the exposure regime via digitally controlled pumps makes this flow-through system also suitable for testing substances under realistic exposure conditions or in combination with their metabolites. In this study the degradation of a herbicide and its metabolites was simulated. The substance with an ErC50 (72 h) of 1.3 microg/l under static conditions (OECD, 1984) was tested in the developed flow-through system. The simulated degradation at an initial dose of 3 microg/l of the herbicide had no effect on algal growth, whereas under static test conditions, an NOErC of 0.28 microg/l was determined. The lowest concentration at which effects were observed was a continuous dose of 6 microg/l.