In situ use of bivalves and passive samplers to reveal water contamination by microcystins along a freshwater-marine continuum in France

Cyanobacteria are a potential threat to aquatic ecosystems and human health because of their ability produce cyanotoxins, such as microcystins (MCs). MCs regularly monitored in fresh waters, but rarely estuarine marine waters despite the possibility downstream export. Over period two years, we monthly analyzed intracellular (in phytoplankton) extracellular (dissolved water) at five stations along river continuum from freshwater reservoir with ongoing cyanobacterial blooms coast Brittany, France. were quantified using integrative samplers placed each site: solid phase adsorption toxin tracking (SPATT) for collecting caged mussels (Anodonta anatina Mytilus edulis) filter-feeding on MC-producing cyanobacteria. The MC transfer was demonstrated year during months sites sporadically outlet. SPATT integrated MCs, notably low environmental concentrations (0.2 µg/L) same variant profile water. mussel A. highlighted presence including below 1 µg/L. M. edulis more efficiently revealed than water samplings. Bivalves showed phytoplankton samples, differential accumulation capacities between variants species. Using or bivalves can give accurate assessment contamination level freshwater-marine continuum, which be episodic. content represents potent if considering updated French guideline values, particularly total (free protein-bound) content, highlighting necessity include cyanotoxins monitoring seafood originating areas.