**1. Introduction**

Emerging contaminants (ECs), including drugs, polycyclic aromatic hydrocarbons (PAHs), metals, pesticides, brominated flame retardants (BFRs), and microplastics (MPs), resulting from the rise of industrial production and anthropogenic activities around lagoon ecosystems are transported toward the water column and adsorbed on sediments particles [1]. Coastal lagoons are considered to be distinct systems

rather than adjoining ones [2]. As interfaces between land and sea, they exhibit high primary and secondary productions that promote the development of extensive fisheries and aquaculture [3]. As semi-enclosed systems, coastal lagoons are strongly influenced by freshwater input [4] and are usually impacted by agricultural, industrial, and tourism activities [5]. These unique features allow lagoon waters to acquire significantly different characteristics compared to the nearby seawater, which leads to greater diversity in the biological communities in these ecosystems. In Tunisia, the Bizerte and Ghar El Melh lagoons are exposed to several contaminants resulting from different activities, such as agriculture, urbanization, and industrialization [6].

Free-living marine nematodes sheltering the marine sediment matrices can accumulate these chemicals and then transfer them to higher trophic levels through the food chain causing widespread contamination of the trophic chain [7]. These species constitute the dominant meiobenthic group in marine areas. They are characterized by their high abundance (up to 20 million individuals per m<sup>2</sup> ) [8] and species richness (approx. 8000 species) [9], their ubiquity and holobenthic lifestyle [10], and their small size (1–5 mm in average length), which make them easily manipulated in laboratory studies [11]. Nematodes have also high fecundity and metabolic rates and their short generation time, less than a year [12], which allow fast experimental outcomes (e.g., a month) laboratory assays based on the rapid responses to pollutants [13–17].

The objective of this chapter is to describe previous studies and to show the ecological risks of emerging contaminants in two different Tunisian lagoon ecosystems " Bizerte and Ghar El Melh lagoons" by focusing on the responses of benthic meiofauna more particularly marine nematodes to experimental various environmental pollutants exposure.
