Effects of metals on the uptake of polycyclic aromatic hydrocarbons by the cyanobacterium Microcystis aeruginosa

Abstract

Effects of Cu2+, Zn2+, Cd2+, and Ag+ on the uptake of phenanthrene, pyrene, and benzo[a]pyrene by Microcystis aeruginosa were investigated. A biomimic passive sampler, triolein embedded cellulose acetate membrane (TECAM) was used to help to study the related mechanisms. The facilitation effects of the metals on the uptake of the PAHs by M. aeruginosa increased with the softness order of the metals (Zn2+≈Cd2+<Cu2+<Ag+) and the π donor strength of the PAHs (phenanthrene<pyrene<benzo[a]pyrene). The cation–π interactions between Cu2+, Ag+ and the PAHs increased the freely dissolved concentrations of the PAHs, and consequently their uptake by M. aeruginosa. The increase in aromaticity of dissolved organic matter (DOM) caused by Cu2+, and Ag+ also enhanced the uptake of the PAHs. The facilitation effects of Cu2+, and Ag+ exceeded their toxic effects, uptake of the PAHs was thereby enhanced. In the presence of Zn2+, and Cd2+, no cation–π interactions between Zn2+, Cd2+ and the PAHs formed in solutions. Aromaticity of DOM was reduced, the diffusive mass transfer of the PAHs was not enhanced. Uptake of the PAHs was thereby reduced. This study suggests that uptake of PAHs by phytoplankton can be significantly influenced by the properties of both metals and PAHs, which will help to understand the fate and risks of PAHs in eutrophic waters co-contaminated with metals.