Abstract
Cyanobacterial proliferations display rapid spatiotemporal variations that can interfere in the assessment of water contamination levels by microcystins (MC), and make necessary the use of integrative tools. This study evaluates the pertinence of bivalves Anodonta anatina and Dreissena polymorpha as bioindicators of the presence of MC-producing cyanobacteria in water. Ingested MC accumulates into two fractions in bivalve tissues—the cellular free and the protein-bound fractions—both forming the total MC fraction. Mussels were exposed to the cyanobacteria Planktothrix agardhii at densities producing an equivalent of 1, 10 and 100 µg/L of intracellular MC, with the evaluation of: (i) cyanobacterial cells and MC daily intake by mussels, (ii) free and total MC kinetics in whole individuals (using all the tissues) or only in the digestive gland, during and after the exposure, (iii) bioaccumulation factors. For each species, the kinetics of the two accumulation fractions were compared to evaluate which one best reflect levels and dynamics of MC-producing cyanobacteria in water. Results showed that the dynamic of free MC in bivalve tissues better highlight the dynamic of intracellular MC in water. Using whole D. polymorpha may be appropriate to reveal and discriminate the water contamination levels above densities of cyanobacteria producing 1 µg MC/L. Digestive glands of A. anatina appeared more sensitive to reveal low environmental concentration, but without direct correlation with levels of water contamination. Further experimentations in situ are necessary to confirm those results in order to propose the use of freshwater bivalves for a biomonitoring of MC-producing cyanobacteria in fresh waters.
Highlights
Cyanobacterial proliferations often occur in reservoirs used for the supply of drinking water or recreational activities
D. polymorpha ingested the filamentous MC-producing P. agardhii continuously for 21 days when exposed to densities producing an equivalent to 10 and 100 μg MC/L (Figure 1B)
We studied which MC analysis, the free or the total fraction, in mussels’ tissues is more suitable to monitor MC-producing cyanobacteria. Both species were exposed to a MC-producing strain of P. agardhii for 21 days followed by 21 days of depuration, and kinetics of free and total MC were studied in their tissues
Summary
Cyanobacterial proliferations often occur in reservoirs used for the supply of drinking water or recreational activities. As some species are able to synthetize harmful toxic compounds, cyanobacterial blooms represent a significant risk to ecosystems and human health [1,2,3]. Those proliferations are expected to be enhanced by eutrophication [2] and global warming [4]. The hepatotoxins microcystins (MC) are the most frequently produced toxins by cyanobacteria [5]. MC are mainly intracellular during cyanobacterial proliferations, with less than 30% of the total.
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