Biotoxins in the Mediterranean Sea: Lebanon as a Case Study

Marine biotoxins are naturally occurring chemicals produced by toxic algae. They can be found in seawater and can accumulate in various marine organisms, such as commercial seafood. When contaminated seafood is consumed, these biotoxins can cause poisoning in humans, with varying health consequences depending on the type and amount of toxins. The proliferation of biotoxin-producing algae in the marine environment has dire socio-economic and environmental consequences due to the contamination of water and seafood. Due to the number of factors related to human pressures and climate change impacts, the frequency of marine biotoxins’ occurrence is increasing significantly globally, and in regional seas such as the Mediterranean Sea. In this chapter, we highlight Lebanon in the Eastern Mediterranean Sea, where marine biotoxins were recently studied. The results show for the first time the presence of lipophilic toxins and cyclic imines in marine biota, with values for okadaic acid, dinophysistoxin 1 and 2, pectenotoxin 1 and 2, yessotoxins and azaspiracids below the detection limit (LOD). Levels above LOD were detected for domoic acid (DA), gymnodimine (GYMb), and spirolides (SPXs) in some species/areas. Maximum levels of DA, GYM, and SPXs (3.88 mg DA kg-1, 102.9 µg GYM kg-1, 15.07 µg SPX kg-1) were found in the spiny oyster (Spondylus spinosus) in agreement with the occurrence of Pseudo-nitzchia spp, Gymndinium spp, and Alexandrium spp. DA was below the EU limit but above the lowest observed adverse effect level (0.9 μg g-1) for neurotoxicity in humans and below the acute reference dose (30 µg kg-1 body weight), both established by EFSA. Considering the lowest lethal dose (LD50) after administration of GYM and SPXs to mice, it is unlikely that there is a health risk due to exposure to these toxins from seafood consumption in Lebanon. Nevertheless, the chronic toxicity of DA, GYMs, and SPXs remains unclear, and the effects of repeated consumption of contaminated seafood need to be investigated. Because biotoxins have been detected in bivalves and commercial species, as well as other organisms in the marine trophic chain, it is evident that species other than bivalves should be monitored, and the spiny oyster (S. spinosus) may play the role of a sentinel species in biotoxin studies. A regular monitoring program is needed to provide reliable, accurate estimates of bloom toxicity and to investigate their potential impact on marine species and human health in Lebanon.