Cyanobacterium Microcystis aeruginosa response to pentachlorophenol and comparison with that of the microalga Chloyella vulgaris

Pentachlorophenol (PCP) effects on a strain of the cyanobacterium Microcystis aeruginosa were investigated at laboratory scale. This is the first systematic ecotoxicity study of the effects of PCP on an aquatic cyanobacterium. The microalga Chlorella vulgaris was studied in the same conditions as the cyanobacterium, in order to compare the PCP toxicity and its removal by the species. The cells were exposed to environmental levels of PCP during 10 days, in Fraquil culture medium, at nominal concentrations from 0.01 to 1000 mu g L-1, to the cyanobacterium, and 0.01 to 5000 mu g L-1 to the microalga. Growth was assessed by area under growth curve (AUC, optical density vs time) and chlorophyll a content (chl(a)). The toxicity profiles of the two species were very different. The calculated effective concentrations EC20 and EC50 were much lower to M. aeruginosa, and its growth inhibition expressed by chl(a) was concentration-dependent while by AUC was not concentration-dependent. The cells might continue to divide even with lower levels of chl(a). The number of C. vulgaris cells decreased with the PCP concentration without major impact on the chl(a). The effect of PCP on M. aeruginosa is hormetic: every concentration studied was toxic except 1 mu g L-1, which promoted its growth. The legal limit of PCP set by the European Union for surface waters (1 mu g L-1) should be reconsidered since a toxic cyanobacteria bloom might occur. The study of the removal of PCP from the culture medium by the two species is an additional novelty of this work. M. aeruginosa could remove part of the PCP from the medium, at concentrations where toxic effects were observed, while C. vulgaris stabilized it. (C) 2014 Elsevier Ltd. All rights reserved.