Effects of Heavy Metals on the Sorption of Polycyclic Aromatic Hydrocarbons by Microcystis aeruginosa

To date, little is known about the effects of heavy metals on the sorption of organic contaminants by phytoplankton. In this study, the effects of Cu2+, Cd2+, and Ag+ on the sorption of polycyclic aromatic hydrocarbons (PAHs) by Microcystis aeruginosa were studied. Phenanthrene sorption was facilitated by low concentrations of metal salts (≤20 mmol L-1) and was significantly suppressed in the presence of 50 to 200 mmol L-1 metal salts and rebounded and exceeded the control in the presence of 500 to 5000 mmol L-1 Cu(NO3)2 and AgNO3, respectively. Although the ionic strengths of the solutions were the same, phenanthrene sorption was different in the presence of the same concentrations of Cu(NO3)2 and Cd(NO3)2 especially in the high concentration range. In the high concentration range, Ag+ was much more effective than Cu2+ and Cd2+ to increase phenanthrene sorption. In contrast to phenanthrene, sorption of both pyrene and benzo[a] pyrene increased dramatically in the presence of Cu(NO3)2. The cation-π interactions between the metal cations and PAHs facilitated the sorption of the PAHs. Sorption enhancement of the PAHs caused by the cation-π interactions increased with the softness order of the metals (Cd2+ < Cu2+ < Ag+) and the π donor strength order of the PAHs (phenanthrene < pyrene < benzo[a]pyrene). This study suggests that sorption of PAHs by cyanobacteria can be significantly altered by concentrations and properties of both heavy metals and PAHs. © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.