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Effect of initial cell density on the bioavailability and toxicity of copper in microalgal bioassays
Author(s) -
Franklin Natasha M.,
Stauber Jennifer L.,
Apte Simon C.,
Lim Richard P.
Publication year - 2002
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1002/etc.5620210409
Subject(s) - selenastrum , toxicity , bioavailability , copper toxicity , environmental chemistry , copper , bioassay , chlorophyceae , biotic ligand model , ecotoxicology , chlorella , chlorophyta , algae , genetic algorithm , biology , chemistry , botany , ecology , organic chemistry , bioinformatics
Algal toxicity tests based on growth inhibition over 72 h have been extensively used to assess the toxicity of contaminants in natural waters. However, these laboratory tests use high cell densities compared to those found in aquatic systems in order to obtain a measurable algal response. The high cell densities and test duration can result in changes in chemical speciation, bioavailability, and toxicity of contaminants throughout the test. With the recent application of flow cytometry to ecotoxicology, it is now possible to use lower initial cell densities to minimize chemical speciation changes. The speciation and toxicity of copper in static bioassays with the tropical freshwater alga Chlorella sp. and the temperate species Selenastrum capricornutum (Pseudokirchneriella subcapitata ) were investigated at a range of initial cell densities (10 2 ‐10 5 cells/ml). Copper toxicity decreased with increasing initial cell density. Copper concentrations required to inhibit growth (cell division) rate by 50% (72‐h median effective concentration [EC50]) increased from 4.6 to 16 μg/L for Chlorella sp. and from 6.6 to 17 μg/L for S. capricornutum as the initial cell density increased from 10 2 to 10 5 cells/ml. Measurements of anodic stripping voltammetry—labile, extracellular, and intracellular copper confirmed that at higher initial cell densities, less copper was bound to the cells, resulting in less copper uptake and lower toxicity. Chemical measurements indicated that reduced copper toxicity was due primarily to depletion of dissolved copper in solution, with solution speciation changes due to algal exudates and pH playing a minor role. These findings suggest that standard static laboratory bioassays using 10 4 to 10 5 algal cells/ml may seriously underestimate metal toxicity in natural waters.