Comparison of Short- and Long-Term Toxicity Test Results for the Green Alga, Selenastrum capricornutum

Abstract

Algae are important components of many aquatic communities that can be sensitive to effects of aquatic pollutants. Standard algal toxicity tests quantify effects on population growth over 3 to 14 days. These population growth tests are useful for environmental hazard assessment but have limitations. These limitations include test duration, pH, nutrient and metabolite changes during toxicity testing, inability to test at the community level, potential interaction between algal media and test materials, and poor control or understanding of the effects of sample volatilization, sorption, biodegradation, photolysis, or hydrolysis on test material toxicity. These test limitations can be addressed in short-term (<4 h duration) toxicity tests. Short-term algal toxicity tests were conducted with seven pure compounds and three municipal wastewater treatment plant effluents, and the results were compared to those obtained in a standard four-day population growth test (PGT). The short-term tests involved exposure of the green alga, Selenastrum capricornutum, to test materials and quantification of effects on oxygen generation (O2) in a 30-min exposure and 14CO2 fixation in a 35 min exposure. For test materials used in this research, the short-term tests were consistently less sensitive than the PGT, with ratios of the EC50 (effective concentrations) for the CO2:PGT and the O2:PGT ranging from 1.4 to > 161. However, short-term to long-term test ratios were consistently less than 20, indicating that these tests may be appropriate systems to study effects of test material on algae without the limitations of the long-term test. Although the short-term algal test methods have their own set of limitations for environmental hazard testing, the information gained in the short-term approaches can be used to complement information gained in long-term toxicity tests. This research has demonstrated the relative sensitivities of two short-term tests.