Adsorption of Microcystin LR and LW on Suspended Particulate Matter (SPM) at Different pH

The occurrence of microcystins (MC) during aquatic blooms of cyanobacteria in eutrophicated freshwater body has increasingly become an environmental and health concern worldwide. An experimental study was conducted to investigate the adsorption of two common variants of microcystins, MCLR and MCLW, onto SPM at different pH values. The results showed that most microcystins spiked into an SPM solution with the concentration of 0.25g/l was adsorbed onto solids at pH3 (>95%) and 7 (>85%). At pH13, the proportion of adsorbed microcystin decreased to 8–29% for MCLR and 38–47% for MCLW. The adsorption of MCLR and MCLW onto SPM fitted well with S type of Freundlich isotherm except for pH3 at which L type of Freundlich isotherm was suitable for MCLW. At pH3 and 7, linear isotherm was also able to describe the adsorption of MCLR and MCLW. The adsorption of MCLR and MCLW decreased significantly with the elevated pH, which is consistent with the pH-dependent hydrophobicity.