Environmental Pollutants in the Mediterranean Sea: Recent Trends and Remediation Approaches

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.

Bioassays are defined as the measurement of toxic responses upon exposure to chemicals under controlled conditions in the laboratory using cultured organisms and represent powerful tools for the assessment of environmental quality. These biological tests were pointed out as the most common methods used to assess the environmental risk, mainly in marine ecosystems besides biomarkers and biosensors. The list of different toxicity bioassays is still increasing and a large battery of different aquatic organisms is available for the measurement of organic and inorganic chemical toxicity. The species selected for the available battery of bioassays differ taxonomically and play different roles in aquatic ecosystems. Else, they have different routes of exposure to bio-potential. Although many bioassays provide information about the overall toxicity induced, new test systems are developed and used for the determination of specific toxicity in a number of biological pathways disrupted by contaminants. Hereby, the list of bioassay tests used in aquatic ecosystems assessment is updated besides specific toxicity pathways for almost invertebrate and vertebrate aquatic species used to determine organic and inorganic pollutants effects.

In recent decades, the prevalence of plastics in the marine environment has increased and is amongst the most pervasive problems affecting the marine environment globally. Numerous studies have documented microplastic ingestion by marine species with more recent investigations focusing on the secondary impacts of microplastic ingestion on ecosystem processes. However, few studies so far have examined microplastic ingestion by mesopelagic fish which are one of the most abundant pelagic groups in the oceans and their vertical migrations are known to contribute significantly to the rapid transport of carbon and nutrients to the deep sea. Therefore, any ingestion of microplastics by mesopelagic fish may adversely affect this cycling and may aid in the transport of microplastics from surface waters to the deep-sea benthos. Microplastics are ubiquitous in the marine environment and are increasingly contaminating species in the marine ecosystem and the food chain, including food stuffs intended for human consumption. The effects of microplastics on aquatic organisms are currently the subject of intense research. Here, we provide a critical perspective on published studies of microplastic ingestion by aquatic biota. We summarize the available research on Microplastic presence, behavior, and effects on aquatic organisms monitored in the field and laboratory studies of the ecotoxicological consequences of microplastic ingestion. Finally, researchers plan further studies to learn more about how these fish are ingesting and spreading microplastics. It will be particularly interesting to see whether the fish ingest these microplastics directly as mistaken prey items, or whether they ingest them through eating prey species, which have previously ingested the microplastics. Also, there is a need to understand the mechanism of action and ecotoxicological effects of environmentally relevant concentrations of microplastics on aquatic organism health.

Plastic debris has become the main component of marine litter in the Moroccan Mediterranean due to the massive consumption of plastic and poor plastic waste management. In Morocco, plastic pollution has been a subject of increasing environmental concern in the last few years. This literature review was conducted to collect current data on plastic pollution in the Moroccan Mediterranean, considering the presence of marine debris as well as macroplastics and microplastics in different compartments. Our study shows that, until now, very few studies have been carried out and there is a lack of information, especially on the prevalence of plastic debris in the water environment, sea floor, and aquatic animals. In general, plastic is the most predominant waste on the beaches of the Moroccan Mediterranean, always contributing to more than 50% of the total composition of the waste encountered. Based on the records, tourism, recreational activities, and fishing are one of the main sources of plastic accumulation in the Moroccan Mediterranean. This was due to a lack of awareness among beach users. Awareness and behavior change is key to minimizing plastic waste on Morocco's beaches and coasts. In addition, all aspects of waste management must be improved. The beaches of the Moroccan Mediterranean have also been contaminated by microplastics. A significant positive correlation was also observed between human population density and industrial activity on microplastic abundance. Microplastic has only been found in a few commercial fish species and sea turtles, but more work will be needed in the future.

Rare earth elements (REE) have become a strategic commodity of contemporary economies due to their various uses in the technological, smart, and renewable energy industries. The boom of their uses resulted in an increased influx to the marine environment either as a result of mining or industrial discharges, or from the disposal of solid wastes, atmospheric fallout for military tests of smart weapons, and remobilization from the sediments. Although sediments are the main reservoir of REE in the marine environment, and their auspicious normalization patterns are useful geochemical tracers, it has been found that anthropogenic contributions influence REE’s natural occurrence. This indeed has raised concerns about the potential ecological impacts of REE on the marine biota and in turn on human health. The chapter gives some insights into the sources and potential ecological impacts of REE while revealing the need for future research and the knowledge gap about the REE and their ecological impacts as a group and as individual elements, as well as some potential solutions to the increased anthropogenic influx of REE to the marine environment. The potential ecological impacts of REE influx to the marine environment constitute both their bioavailability and their toxicity. Predicted ecological impacts on the marine biota may be similar to other trace metals, sharing analogous chemical characteristics. Nevertheless, whether LREE or HREE are more toxic is debatable, and their physiological and cytological effects on different organisms are still under investigation. This prompts the need for a new understanding of REE’s ecological impacts by focusing on influx rates, ecotoxicity, and mitigation of ecological impacts.