Reduction of the toxin microcystin-LR with different types of sediments

Abstract

Microcystis aeruginosa blooms in water bodies, evidencing a high risk of exposure to human health due to the release of toxins, which affects water quality. Implementing physical, chemical, and microbial control methods requires an integrated understanding of cyanotoxin dynamics, especially their relationship with sediments. Consequently, sediment obtained from three stations of the Riogrande II reservoir (Antioquia, Colombia) was analyzed to determine the adsorption and removal capacity of the microcystin-LR (MC-LR). For this purpose, the sediment was subjected to different treatments to select the one with the highest MC-LR removal capacity. Furthermore, the effectiveness and stability of adsorption removal process were evaluated by analyzing mechanical processes such as aeration, sonication, and agitation. The dried sediment showed the highest reduction in toxin concentration (93%) after 24 h, followed by washed sediment (91%) and sterilized sediment (81%).On the other hand, the sediment was fractionated into silts and clays; the latter was the least effective. Finally, the fine and half silts were better adsorbents of the toxin, acting similarly over time. Initially, the utilization of sediment that has been dried by sunlight could be a complementary alternative to reinforce MC-LR control methodologies in water bodies.On the one hand, MC-LR desorption assays showed that aeration of the sediment for 30 min caused a release of up to 96% of the adsorbed compound. At the same time, the effect of sonication and agitation was less intense. However, the absorption process must be fast to avoid efficiency losses due to desorption since a high percentage of the toxin was spontaneously desorbed from the sediment in two days.