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

Abstract

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 μg 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 μg L −1 . Moreover, bioaccumulations of MCs varied between 22 and 365 μg kg −1 , and 19−222 μg 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.

Analysis of Trace Microcystins in Vegetables Using Solid-Phase Extraction Followed by High Performance Liquid Chromatography Triple-Quadrupole Mass Spectrometry

“…High levels of MCs, ranging from 2.1 to 6.6 ng/g and 1.4 to 21.3 ng/g, were detected in the cropland soil near Taihu Lake and Dianchi Lake in China, respectively. 15,16 Previous studies have shown that the morphological characteristics and the productivity of crop plants were affected when exposed to microcystins. 17,18 Furthermore, the exposure of edible crops to microcystins would cause human health risks, as terrestrial crops can take up and accumulate these compounds in the roots, stems, and leaves.…”

Heavy metal migration and risk transference associated with cyanobacterial blooms in eutrophic freshwater

“…While the mechanical harvesting and subsequent treatment effectively removed the cyanobacterial biomass, nutrients such as nitrogen and phosphorus, and non-nutrient contaminants (Chen et al, 2017), our previous research showed that the use of decomposed cyanobacterial biomass may pose a risk to human health (Fig. S1) from bioaccumulation of contaminants in irrigated row crops (Chen et al, 2012).…”

“…It is assumed that water from Lake Taihu might present a risk of heavy metal transfer from the lake into crops grown using the water from the lake for irrigation. Over the past decade, physical removal of cyanobacterial scums has occurred with the material treated on the shoreline in ponds (Shen et al, 2003a;Chen et al, 2012). While the mechanical harvesting and subsequent treatment effectively removed the cyanobacterial biomass, nutrients such as nitrogen and phosphorus, and non-nutrient contaminants (Chen et al, 2017), our previous research showed that the use of decomposed cyanobacterial biomass may pose a risk to human health (Fig.…”

“…In our previous study, we focused on the investigation how mechanical collection of cyanobacterial biomass was degraded in the artificial ponds and the risk associated with this process (Chen et al, 2012). During the blooming seasons, more than 1.5 million m 3 of concentrated blooms were collected and transported to shoreside artificial ponds or directly discharged into cropland around Lake Taihu.…”

Evaluation of the potential of anoxic biodegradation of intracellular and dissolved microcystins in lake sediments

“…Therefore, our results suggest that the biodegradation process of intracellular MCs in fresh cyanobacterial samples must occur after the release of toxins, and degradation may be considered a slow reaction. However, further treatments to remove cyanobacterial toxins were not conducted after the mechanical collection of bloom biomass, and fresh cyanobacterial biomass are usually discharged directly into croplands, irrigation canals, and forest land near the lakeshore as plant fertilizer [38]. In the future, effective further treatment methods for the removal of cyanobacterial toxins should be developed to reduce the potential risks associated with MCs release.…”