Determination of Marine Biotoxins Contamination Level of Mussel (Perna Perna) (Linne, 1758) from the Mamelles Bay, Dakar

Abstract

This study evaluating marine biotoxins contamination level of mussel (Perna Perna) in the Mamelles Bay (Ouakam) of Dakar is the first report in Senegal. It took place over one year (from March 2018 to February 2019). Liquid chromatography with mass spectrometry (LC-MS-MS) reference method (Regulation (EC) 15/2011 of 10 January 2011) was used to quantify marine biotoxins. Okadaic acid (OA) and its esters are the most problematic of all the researched biotoxins. They are present throughout most of the year, except September and November, with an average monthly concentration of 163 µg/kg, slightly above the regulatory limit (160 µg/kg). The sanitary status of the mussel shows two peaks of contamination, the first of which occurs in the rainy season (August) and the second in the cold season (December), with values equal to 654 and 802 µg/kg respectively 4 to 5 times higher than the regulatory threshold set by Regulation (EC) No 853/2004 of 29 April 2004 supplemented by Regulation (EU) No 786/2013 amending its Annex III and Senegalese Order No 07951 of 12 May 2017. These two peaks coincide with (i) the wintering period, marked by continental land- based inputs due to rainwater runoff, but also with the temperature rise, or (ii) the cold period with the appearance of upwelling (upwelling of cold water, rich in nutrient salts). In addition to the chemical analyses carried out on the mussel, the research work on phytoplankton and the surveys of physicochemical parameters carried out on the water at the collection site show (i) the existence of toxic algae of the Dinophysis genus and Gambierdiscus, in June, i.e., one to two months before the first peak of contamination of the Perna perna by AO; (ii) also a coincidence between the appearance of these phenomena and variations in surface water temperature and salinity, which are determining factors in the appearance and development of harmful algal blooms. Concerning the other biotoxins investigated, in particular AZA and yessotoxins, it was noted that AZA was absent throughout the year, unlike yessotoxins, which were found in the flesh of Perna perna at concentrations below the regulatory limit set at 3750 µg/kg. The maximum being 51 µg/kg obtained in June, i.e., 73 times lower than the regulatory threshold. In the light of the results obtained, it appears that the periods of high contamination are the winter period and the upwelling period, which could lead to closure measures to guarantee the safety of the mussels. It would be interesting to extend the study to all other bivalve mollusks and gastropods, to carry out an inventory and quantify the toxic microalgae present in the water. To this end, the effectiveness of purification techniques would be tested