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

Abstract

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

Five Years Monitoring the Emergence of Unregulated Toxins in Shellfish in France (EMERGTOX 2018–2022)

“…In the context of this article, the authors define an “emerging toxin” as a toxin that is not regulated and for which there is little toxicological data available to characterize the hazard for humans; it can be a known toxin identified for the first time by a country’s monitoring network or a new derivative of a known toxin. In addition to risks linked to known marine toxic microalgae, other toxins suspected to be toxic to humans are being increasingly mentioned in the scientific literature as detected in shellfish: BMAA and freshwater cyanotoxins [ 2 , 3 , 4 ]. As filter feeders, shellfish accumulate toxins produced by harmful algal blooms (HABs), which can make them unsafe for human consumption.…”

Cyanobacteria and Macroinvertebrate Relationships in Freshwater Benthic Communities beyond Cytotoxicity

“…[ 2 , 32 , 105 , 120 , 121 ]. Interestingly, hepatopancreas seems to be the main target organ in Crustacea and Mollusca independently of cyanotoxins [ 2 , 30 , 99 , 101 , 122 , 123 , 124 , 125 ], but only occurs in muscle when toxin exposure thresholds are reached [ 30 ]. Curiously, some studies have highlighted that most cyanobacteria extracts, and even those species or strains that do not produce toxin, are more harmful than purified cyanotoxins by showing that cyanobacteria contain other toxic compounds beyond known toxins [ 2 , 31 , 90 , 123 ].…”

“…Other detoxification ways have also been proposed, such as accelerating intestinal food transit or increasing the bacterial flora that degrades cyanotoxins [ 31 , 32 ]. Although the transfer of toxins between trophic levels in relation to invertebrates is unquestionable [ 99 , 101 , 125 ], the detoxification capacity observed in freshwater invertebrates is beginning to challenge the established belief that they contribute to the biomagnification of toxins along the food chain [ 1 , 29 , 101 ]. In fact, even at high concentrations of cyanotoxins, as measured in aquatic consumers of different trophic levels, a meta-analysis based on the biomagnification factor has confirmed biodilution, and not biomagnifications, as the dominant process in aquatic food webs [ 28 , 29 ].…”

Evaluating the Application of Chitosan-Based Sorbents for the Solid-Phase Adsorption Toxin Tracking of Microcystins in Irrigation Water

“…Microcystins (MCs) remain the most frequently reported and abundant cyanotoxins [1,6], with about 246 variants having been recorded in fresh waters globally [6]. MCs are known to be hepatotoxins, but they have recently been recognized as reprotoxins and neurotoxins as well [6].…”

“…Microcystins (MCs) remain the most frequently reported and abundant cyanotoxins [1,6], with about 246 variants having been recorded in fresh waters globally [6]. MCs are known to be hepatotoxins, but they have recently been recognized as reprotoxins and neurotoxins as well [6]. Their mode of action is through the inhibition of the protein serine/threonine phosphatases (PP1 and PP2A) in cells (Roué et al, 2018) [7].…”