A MINISCALE ALGAL TOXICITY TEST

A simple miniscale (approx. 1-2.5 ml) toxicity test procedure with the freshwater green alga Selenastrum capricornutum is described. The pro cedure fulfils the validity criteria of the ISO (International Associa tion for Standardization) standard test protocol. Practically identica l concentration-response curves were obtained with the ISO standard te st and the minitest for potassium dichromate and 3,5-dichlorophenol. T he minitest is conveniently carried out using 2.5 ml test volume in 20 ml glass scintillation vials, placed on a microplate shaker or on an ordinary shaking table, but smaller containers and test volumes (down to 1 ml) could also be used. Tissue culture treated polystyrene microp lates were found toxic to algae and thus unusable. pH control is achie ved more easily in the minitest than in larger size shake flasks due t o greater turbulence and a larger surface/volume ratio which both faci litates CO2 mass transfer. Uniform illumination of the individual unit s of a minitest setup is obtained readily due to the small area that h as to be illuminated. Using the rapidly growing green alga S. capricor nutum as test organism, it is proposed generally to reduce the standar d test duration from 3 days to 2 days (minitest as well as larger volu me tests) in order to avoid excessive biomass growth. Shortening tests to 2 days appears necessary if light intensity and temperature are ne ar the upper limits of the intervals stated in the ISO standard.