Uptake and depuration of anatoxin-a by the mussel Mytilus galloprovincialis (Lamarck, 1819) under laboratory conditions
Introduction
Cyanobacterial blooms have been increasing with eutrophication of freshwater systems all over the world. The main concern about these events is related to the production of cyanotoxins that are lethal for aquatic and terrestrial organisms.
There are several types of cyanobacterial toxins: neurotoxins, hepatotoxins, cytotoxins and irritant and gastrointestinal toxins (Chorus, 2001, Codd et al., 2005). These toxins have been responsible for several human and animal poisoning, some of them with a fatal outcome (Falconer, 2005). Neurocyanotoxins comprise anatoxin-a, homoanatoxin-a and anatoxin-a(s). Anatoxin-a(s) is a potent organophosphate firstly found to be produced by a Canadian cyanobacterial strain. Presently, few reports of this toxin have been registered in United States and Denmark (Matsunaga et al., 1989, Henriksen et al., 1997, Monserrat et al., 2001). Homoanatoxin-a is a chemical homologue of anatoxin-a that was detected in France, New Zealand and Ireland (Furey et al., 2003, Cadel-Six et al., 2007, Wood et al., 2007), and anatoxin-a, the object of our study, was the first cyanotoxin to be chemically characterized (Devlin et al., 1977). It is an alkaloid and a potent neurotoxin (mice LD50 of 250 μg kg−1 i.p. (Rogers et al., 2005)), which can be produced by several cyanobacterial genera: Anabaena, Aphanizomenon, Microcystis, Planktothrix, Raphidiopsis, Arthrospira, Cylindrospermum, Phormidium and Oscillatoria (Park et al., 1993, Bumke-Vogt et al., 1999, Namikoshi et al., 2003, Viaggiu et al., 2004, Ballot et al., 2005, Gugger et al., 2005, Araós et al., 2005).
As it happens with some other cyanotoxins, anatoxin-a has been reported mainly in fresh waters but also in brackish waters (Mazur and Plinski, 2003). Although this toxin is very potent, it has received less scientific attention compared to other cyanotoxins such as microcystins and cylindrospermopsin. These have already caused serious human intoxications, including deaths, in Brazil (Carmichael et al., 2001, Byth, 1980). The lack of toxicological studies with anatoxin-a is probably due to its chemical characteristics which make it very unstable and labile in the water and therefore difficult to detect (Stevens and Krieger, 1991). Because no chronic effects have been associated with anatoxin-a, human health aspects associated with this toxin have been disregarded. Nevertheless, some animal fatalities have occurred, stressing the need to investigate anatoxin-a effects on aquatic organisms and communities. In recent study, we found that anatoxin-a may be bioaccumulated by carps in significant levels (0.768 μg of anatoxin-a per gram of dry weight of carp) (Osswald et al., 2007). Whether this may have an impact in aquatic food webs is not yet known.
In this experiment, we wanted to study the accumulation and depuration of anatoxin-a by Mytilus galloprovincialis, a very widespread mussel in estuarine and coastal waters and recognized worldwide as a bioindicator (e.g. Mussel Watch programs) (Izquierdo et al., 2003, Catsiki and Florou, 2006). This mussel is an important component of estuarine and marine food webs and because it is a sessile filter feeder, it may be exposed to high density of cyanobacteria and their toxins. Several studies with cyanotoxins have shown that bivalves are able to accumulate cyanotoxins, like microcystin-LR (Vasconcelos, 1995, Pires et al., 2004), paralytic shellfish toxins (Pereira et al., 2004), nodularin (Karlsson et al., 2003) and cylindrospermopsin (Saker et al., 2004). This later toxin is also an alkaloid like anatoxin-a but it is very stable. As far as we know there is no scientific literature about the effects of anatoxin-a in mussels. It is important to know the biological effects and the distribution of anatoxin-a in M. galloprovincialis. On the other side we should also consider the risk of human intoxications due to the consumption of bivalves contaminated with anatoxin-a. Dinoflagelates and diatoms are not the only toxin producers in estuarine and marine environments, so health authorities should also be aware of cyanobacteria. In this work, we studied the accumulation and depuration of anatoxin-a by M. galloprovincialis mimicking a bloom (105 cells ml−1) of an anatoxin-a producing Anabaena sp. strain.
Section snippets
Material and methods
M. galloprovincialis was exposed to live cells of an Anabaena sp. toxic strain (ANA 37) producer of anatoxin-a in an aquarium during 15 days (accumulation phase). A depuration period of 15 days followed, with the mussels without ANA 37 suspension (depuration phase).
Results
The mussels showed no significant behavioural alterations during the two phases of the experiment, except that pseudo faeces production decreased markedly during the last 8 days of the experiment. This was expected since the last 15 days corresponded to depuration phase (Phase II) when there was no cyanobacteria supplied to the aquarium. At the tested cell density, no deaths were observed during the 30 days of the experiment and there was no evidence of any adverse effects on M.
Discussion
No death occurred during the accumulation and depuration experiments, showing that mussels are very resistant to anatoxin-a and are good toxin vectors, as it was shown in previous experiments using other cyanotoxins (Vasconcelos, 1995, Amorim and Vasconcelos, 1999).
The fact that 100% of the cells were filtered by the mussels every day demonstrates that probably the mussels could have filtered more cyanobacteria and probably would have accumulated higher concentration of anatoxin-a, if a higher
Conclusions
At ecologically relevant density of an anatoxin-a producing cyanobacteria (105 cell ml−1), M. galloprovincialis did not show any behaviour alteration and no deaths were registered. Because clearance rates were always near 100%, this mussel is probably able to filter higher cell densities and thus to accumulate higher amounts of anatoxin-a. The maximum value of anatoxin-a accumulated by M. galloprovincialis (6.6 ng per gram of dry weight) was lower than reports for other toxins. Half of the toxin
Acknowledgements
Kaarina Sivonen (Department of Applied Chemistry and Microbiology, University of Helsinki), for supplying ANA 37 strain.
Portuguese Foundation for Science and Technology (FCT): Portuguese and European programme POCTI 2010, for the Ph.D. fellowships (SFRH/BD/9345/2002 and SFRH/BI/15841/2005) to Joana Osswald.
Xunta de Galicia Project, Ref: PGIDIT02PXIB30101PR.
Spanish Ministry of Science and Technology (MCYT) Project, Ref: BQU2002-00083. Sandra Rellán wants to thank the Doctoral Fellowship, Ref:
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2021, Environmental ResearchCitation Excerpt :When testing the ability of the rainbow trout (Oncorhynchus mykiss) to bioconcentrate ATX-a by balneation in water containing dissolved ATX-a up to 5 mg.L−1, no significant difference between bioconcentration factors (BCF) of ATX-a in juvenile subjects exposed to different doses of the toxin for 96 h was observed: in fact, ATX-a accumulates in fish body with BCF ranging from 30 to 47 (Osswald et al., 2011). The exposure of the mussel Mytilus galloprovincialis to cultures of ATX-a-producing CB for 15 days revealed very low assimilation rates, despite the great capacity of this bivalve to bioaccumulate different toxicants, such as heavy metals, drug residues or even MCs (Vasconcelos, 1995; Osswald et al., 2008). Moreover, only one day after being placed in a CB-free environment, mussels presented no detectable ATX-a in their tissues.
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