Introduction
Solar-derived geomagnetic activity (GMA) has been related to biological effects in living beings, mainly in humans. Biological time series have only been sparsely associated with the 11-year sunspot cycle. Blooms of toxin-producing marine phytoplankton and the respective accumulation of biotoxins in bivalves present an unpredictable large intra- and inter-annual variability worldwide. In Portugal, high contamination of bivalves with paralytic shellfish poisoning toxins has been related previously with periods of low solar activity. The bioaccumulation of amnesic shellfish poisoning toxins (ASTs), derived from the marine diatom Pseudo-nitzschia spp., was related here with GMA.
Methods
ASTs in bivalves are monitored weekly in all production areas using liquid chromatography (HPLC) coupled with UV detection. It sometimes exceeds the regulatory limit in force in the European Union for shellfish flesh, leading to harvest bans.
Results and Discussion
Maximal monthly AST’s bioaccumulation during 1997-2024 in the Ria de Aveiro’s (NW coast) cockles (Cerastoderma edule) presented a stronger incidence in the years of highest geomagnetic activity rather than in the years of highest sunspot numbers. In other world regions, such as Galicia (Spain), Northern Ireland, Washington State (USA) and British Columbia (Canada), AST’s bioaccumulation in bivalves was most common during periods of higher GMA. During the 2006-2012 period of low GMA disturbance, toxin accumulation was low in all the time series reported from these regions.
GMA presents annual maxima during the equinoxes, and AST’s accumulation in Portugal also presented their highest maxima following the spring equinox (in April and May) and a secondary maximum following the autumnal equinox (in October). ASTs surpassed 5 mg/kg in 46% of these months when the monthly GMA index was above average (18.4 nT) but only in 18% of these months when the GMA index was below this average. ASTs also peaked during both equinox periods in other world regions, such as Galicia or Canada.