Species-dependent variation in algal sensitivity to chemical compounds

Nineteen miscellaneous chemical compounds were tested on thirteen freshwater algal species grown in 250-microliter liquid cultures on plastic microtitration plates. It was demonstrated that the species-dependent variation in algal sensitivity (EC100) may reach over three orders of magnitude, the degree of variation depending on the chemical tested. No generally sensitive or generally insensitive species could be identified. An effort was made to quantify the predictive value of algal test batteries, at a given confidence level with respect to chemicals. The predictive value of small test batteries was low. Although it did increase with size it took the presence of more than nine members in the test batteries to improve the value to 0.1. This means that a nine-membered test battery might underestimate the sensitivity of the most susceptible algae by a factor of 0.1. A predictive value of 0.01 requires a three-membered test battery when accounting for 95% of the chemicals and a five-membered battery at the 99% confidence level. Implications for toxicity test strategies are discussed and it is suggested that algal test batteries, using simple test techniques, replace single unialgal cultures in routine work.