Soil-Based Treatments of Mechanically Collected Cyanobacterial Blooms from Lake Taihu: Efficiencies and Potential Risks

In China, mechanical collection of cyanoblooms followed by soil-based treatments has been widely used as emergency strategies in many eutrophicated freshwaters. This study was to evaluate both efficiencies and potential risks of typical soil-based technologies. Results from this study indicated that over 90% of cyanobacterial biomass and 96% of dissolved microcystins (MCs) could be restrained in soils via three-level systems, which were much better than single-level systems. High concentrations of MCs, ranged from 65 to 276 ng g(-1) and from 2.12 to 6.6 ng g(-1), were found in soils around treatment systems and croplands, respectively. In the soil solutions, MCs ranged from 0.35 to 2.0 mu g L-1, showing a potentially high leaching risk. In the samples from shallow groundwater near the treatment systems, MC concentrations were detected as high as 1.2 mu g L-1. Moreover, bioaccumulations of MCs varied between 22 and 365 mu g kg(-1), and 19-222 mu g kg(-1) were found in 13 kinds of crops and 7 kinds of wild grass, respectively. Our results indicated for the first time that current soil-based technologies were effective but could pose potential environmental, ecological, and public health risks. Further improvements of these technologies were also proposed based on our findings.