Algal growth inhibition test results of 425 organic chemical substances

The toxicity towards the algal species Pseudokirchneriella subcapitata of 425 organic chemical substances was tested in a growth inhibition test. Precautions were taken to prevent loss of the compounds from the water phase and the test system (closed test system, low biomass, shorter test duration, silanized glass) and to keep pH constant by applying a higher alkalinity. Chemical phase distribution was modelled taking ionization, volatilisation, and adsorption to glass and biomass into consideration. If the modelled water concentration was below 90% of the nominal concentration the calculated EC values were corrected accordingly. The model helped to identify substances, where the calculated water concentration was too uncertain. Substances covering a wide range of physical-chemical properties and different modes of action were tested. Median effect concentrations (EC50) lower than 1000 mg/L were found for 310 substances; 216 of these were in the range from 1 to 1000 mg/L and 94 substances had EC50s below 1 mg/L and should be classified as “Very toxic”. 36 substances fell in the group with EC50 > 1000 mg/L. An EC50 could not be established for 79 substances. These 425 different organic substances were tested under uniform conditions and thus considered a valuable source of information for administrators, industry, risk assessors and QSAR modellers.