Mechanical Collection of Toxic Cyanobacterial Blooms and the Soil-based Treatment Strategy in China: An Opportunity or A New Challenge?

摘要

In past years, mechanical collection of bloom biomass has been employed as an emergency strategy in China and most of the harvested bloom biomass was discharged into three-level soil filtration systems (bloom biomass reduced gradually and algal broth in the 3rd level was pumped to agricultural soils as organic fertilizer) and single-level system for toxin and biomass removal. This study was conducted to test the efficiencies of the soil-based treatment technologies and to evaluate potential risks as well. Results indicated that more than 90% of algal biomass and 96% of dissolved microcystins could be restrained in the soil via the three-level system, and the efficiency was much better than that of single-level system. However, the filtered toxins were found to be transferred to soil interface, with the microcystin concentration ranged from 65 to 276 ng g-1 in the soils at the investigated soil filtration systems, and 2.12 to 6.60 ng g-1 in the agricultural soils irrigated with algal broth from above systems, respectively. Microcystin concentrations in the soil solutions ranged from 0.35 μg L-1 to 2.0 ?g L-1, showing high leaching potential of toxins into the groundwater in these regions. As a result, the detected microcystins in shallow groundwater ranged from 0.3 μg L-1 to 1.2 μg L-1 at the investigated area. Additionally, bioaccumulations of microcystins in the crops and the grass were also investigated. This study demonstrated that this practice could lead to potential public health risks, as well as the environmental and ecological risks.