Treatment Wetlands for Cyanotoxin Remediation
Harmful cyanobacterial blooms are projected to intensify, threatening surface waterdependent communities. Treatment wetlands (TWs) offer a potential cost-effective, decentralized solution for cyanotoxin remediation, a topic still underexplored. This study evaluated the performance of TWs to remove microcystin-LR (MC-LR) and cylindrospermopsin (CYN), investigating the role of substrate, plants and microorganisms within the TW system. For that mesocosms assembled with gravel, light expanded clay, biochar and sand substrates, and planted with Sparganium erectum and/or Canna indica (monocultures and polycultures) were used. Spring water spiked with 2-15 µg/L of each cyanotoxin (in a mixture) was treated in one-week cycles over 10 weeks. Cyanotoxins removal rates, substrate retention and plant accumulation were assessed, along with TW performance (organic matter and nutrients removals), plant health indicators and substrate microbiomes. All TWs achieved >96% MC-LR mass removal. CYN removal improved over time, being higher in C. indica systems (73-98 %) compared to S. erectum alone (70-91 %). Organic matter and nutrients removals remained stable across treatments and unaffected by cyanotoxinspresence in the spring water. Cyanotoxins substrate retention was higher in S. erectum TWs, but values were low in all systems (<8 %). C. indica showed higher resilience and plant stress adaptability to TW conditions treating cyanotoxins. However, no cyanotoxins were detected in the plant tissues (leaves and roots). Microbiomes shifted over time and within substrate matrices and TWs plant composition. No mlr genes for MC-LR degradation were found in the substrates, but enriched taxa included MC-LR degraders (Sphingomonas, Novosphingobium, Shinella), CYN-potential degraders (Hyphomicrobium). In the C. indica system, plant-growth promoters (Leifsonia, Terrabacter, Altererythrobacter) were enriched. Post cyanotoxin exposure enrichment of mlr-independent degraders (Sphingorhabdus, Porphyrobacter) and taxa (Ilumatobacteraceae, Roseomonas, Obscuribacteraceae) associated with harmful algal blooms suggests that novel degradation pathways need exploration. Current results highlight the C. indica planted TWs potential for cyanotoxins contaminated water remediation, as these systems showed better efficiency and adaptability, warranting pilot-scale trials to fully assess effluent quality and safe water reuse.
Harmful cyanobacterial blooms are projected to intensify, threatening surface waterdependent communities. Treatment wetlands (TWs) offer a potential cost-effective, decentralized solution for cyanotoxin remediation, a topic still underexplored. This study evaluated the performance of TWs to remove microcystin-LR (MC-LR) and cylindrospermopsin (CYN), investigating the role of substrate, plants and microorganisms within the TW system. For that mesocosms assembled with gravel, light expanded clay, biochar and sand substrates, and planted with Sparganium erectum and/or Canna indica (monocultures and polycultures) were used. Spring water spiked with 2-15 µg/L of each cyanotoxin (in a mixture) was treated in one-week cycles over 10 weeks. Cyanotoxins removal rates, substrate retention and plant accumulation were assessed, along with TW performance (organic matter and nutrients removals), plant health indicators and substrate microbiomes. All TWs achieved >96% MC-LR mass removal. CYN removal improved over time, being higher in C. indica systems (73-98 %) compared to S. erectum alone (70-91 %). Organic matter and nutrients removals remained stable across treatments and unaffected by cyanotoxinspresence in the spring water. Cyanotoxins substrate retention was higher in S. erectum TWs, but values were low in all systems (<8 %). C. indica showed higher resilience and plant stress adaptability to TW conditions treating cyanotoxins. However, no cyanotoxins were detected in the plant tissues (leaves and roots). Microbiomes shifted over time and within substrate matrices and TWs plant composition. No mlr genes for MC-LR degradation were found in the substrates, but enriched taxa included MC-LR degraders (Sphingomonas, Novosphingobium, Shinella), CYN-potential degraders (Hyphomicrobium). In the C. indica system, plant-growth promoters (Leifsonia, Terrabacter, Altererythrobacter) were enriched. Post cyanotoxin exposure enrichment of mlr-independent degraders (Sphingorhabdus, Porphyrobacter) and taxa (Ilumatobacteraceae, Roseomonas, Obscuribacteraceae) associated with harmful algal blooms suggests that novel degradation pathways need exploration. Current results highlight the C. indica planted TWs potential for cyanotoxins contaminated water remediation, as these systems showed better efficiency and adaptability, warranting pilot-scale trials to fully assess effluent quality and safe water reuse.
Interdisciplinary Center of Marine and Environment Research