*3.2.1 Drugs effects*

Free-living marine nematodes from Bizerte lagoon were exposed to the penicillin G (D1: 3 mg.L−1, D2: 30 mg.L−1, D3: 300 mg.L−1, D4: 600 mg.L−1, and D5: 700 mg.L−1) in microcosm experiment for 30 days. Results showed significant differences between nematode assemblages from control assemblage and those treatments. Univariate measures, containing diversity (H'), species richness (d), equitability (J'), and a number of species (S) diminished significantly with increasing levels of antibiotic treatment. Results of multivariate analyses showed that the nematode's response was varied: *Kraspedonema octogoniata* and *Paracomesoma dubium* were eliminated at all doses tested and seemed to be sensitive species; *Oncholaimus campylocercoides* survived even the highest dose of D5, may be classified as "opportunistic" species, whereas, *Nannolaimoides decoratus* that showed a positive response at the highest concentration, seems to be "penicillin G resistant" species [12]. In terms of feeding responses, Microvores (M), Deposit feeders (DF), and Ciliate consumers (CF), most abundant in the control microcosm, were very much affected and their abundance decreased significantly in response to antibiotic contamination. Epistrate Feeders (EF) seem unaffected by the treatment but an abundance of optional Predators (FP) and exclusive Predators (Pr) showed a significant increase in dominance compared to the control [54]. In addition, the trophic index was significantly reduced in all microcosms treated whereas the trophic ratio 1B/2A appears to be insignificant [55].

The ecotoxicity of ciprofloxacin on the nematodes community was studied. Four ciprofloxacin doses [D1 (50 mg/g), D2 (100 mg/g), D3 (200 mg/g), and D4 (500 mg/g)] were applied, and responses were considered after 1 month. All univariate measures were modified significantly compared to those in the control assemblage. The non-parametric Multi-Dimensional Scaling based on species abundances (MDS) showed significant separation of the control assemblage from the treated populations. *Odontophora villoti* was reduced at all ciprofloxacin concentrations and considered "sensitive," whereas *Metoncholaimus pristiurus* was affected by moderate concentrations and was described as "opportunistic." *Paramonohystera pilosa*, whose abundance increased with antibiotic doses, appeared "resistant" [13]. The trophic structure of nematodes was modified in terms of relative abundance—the microvores (M), epigrowth feeders (EF), and ciliate consumers (CF) elevated in the control assemblage, were highly altered in response to contamination. Nevertheless, the deposit feeders (DF), optional predators (FP), and exclusive predators (Pr) showed a significant increase. In addition, ciprofloxacin leads to a significant reduction in bacterial density with the highest dose, which could explain the results obtained for the nematode trophic group's distribution [14]. The association of the twodimensional (2D) non-metric multidimensional scaling (nMDS) plots and relative functional groups abundances revealed that all biological traits were affected. Amphid shape and feeding diet were the most affected and the tail shape was the closest biological trait to the generic distribution [15].

#### *3.2.2 polycyclic aromatic hydrocarbons (PAHs) effects*

The nematofauna were exposed to four treatments of three polycyclic aromatic hydrocarbons (PAHs), including one with chrysene (150 ppb), chrysene (150 ppb) plus fluoranthene (75 ppb), chrysene (150 ppb) and phenanthrene (15 ppb), and an uncontaminated reference during 30 days. Results showed that the diversity of nematodes differed based on hydrocarbon combinations. Nematodes populations in contaminated compartments differed from those in control. *Rhabditis* sp., *Calamicrolaimus honestus*, and *Oncholaimus campylocercoides* presented in all compartments and categorized as tolerant to PAHs. *Parasphaerolaimus paradoxus*, *Encheliidae* (sp.), *Trichotheristus mirabilis*, and *Theristus pertenuis* were considered sensitive because of their presence only in control compartments [56]. *Metoncholaimus* response studies after selection showed a marked increase in activity of catalase and glutathione S-transferase, and the response was more accentuated when zinc and permethrin were administered in combination [57]. In another study, *Oncholaimus campylocercoides* were cultured and exposed for 21 days to phenanthrene and chrysene. Toxicity has been shown with high levels of PAH fluorescence at the level of the spicules, mouth, and pharynx compared to the other organs [58].

Three increasing concentrations of BaP (i.e. 100, 200, and 300 ng/l) were used in the experiment for 30 days to determine the effect on nematode structure and functional traits. The results revealed a reduction in the abundance and significant changes were observed at the community level. The nematode populations were dominated at the start of the experiment and also after being exposed to BaP by *Odontophora villoti*, explicable through the presence of well-developed chemosensory organs (i.e., amphids), which potentially increased the avoidance reaction following exposure to this hydrocarbon. Moreover, changes in the activity of catalase 'CAT', glutathione S transferase 'GST', and ethoxyresorufin-O-deethylase 'EROD' were detected in *Oncholaimus campylocercoides*, paralleled by significant reductions in CAT activity compared to controls at concentrations of 25 ng/l BaP and associated with a significant increase in GST and EROD activities [59].

#### *3.2.3 Metals effects*

The nickel effects on nematode communities were examined. Sediments were contaminated with three concentrations [(250 ppm), (550 ppm), and (900 ppm)], *Marine Free-Living Nematodes as Tools for Environmental Pollution Assessment: A Special Focus… DOI: http://dx.doi.org/10.5772/intechopen.104721*

and effects were studied after 1 month. Results showed significant differences between nematode assemblages from undisturbed controls and those from nickel treatments. Diversity and species richness indices diminished significantly with increasing nickel levels. The nematode species responses to the nickel treatments were varied: *Leptonemella aphanothecae* was removed and seemed to be sensitive species; *Daptonema normandicum*, *Neochromadora trichophora,* and *Odontophora armata* that were significantly augmented at 550 ppm appeared to be "opportunistic," whereas *Oncholaimus campylocercoides* and *Bathylaimus capacosus* that augmented at all doses used (250, 550, and 900 ppm) seemed to be "resistant" [60].

Nematodes were exposed to chromium concentrations (500 ppm, 800, and 1,300 ppm), and effects were studied after 4 weeks through an experimental microcosm. Results showed significant differences between univariate measures of control nematodes and those from treatment microcosms. *Leptonemella aphanothecae* species was eliminated at all doses tested and seemed to be sensitive; *Daptonema normandicum* and *Sabatieria longisetosa* that significantly augmented at 500 ppm appeared to be "opportunistic" at this dose, whereas the *Bathylaimus* species that augmented seemed to be "resistant" [61].

#### *3.2.4 Brominated flame retardants (BFRs) effects*

The taxonomic and trophic response of marine nematodes to polybrominated diphenyl ether (BDE-47) was examined using four concentrations [(2.5 mg.kg−1), (25 mg.kg−1), (50 mg.kg−1), and (100 mg.kg−1] after 30 days after exposure. All univariate indices were significantly affected compared to the control. After grouping nematode species according to their trophic diversity, their abundance showed differential responses. A significant separation between the control microcosm and each treatment condition was registered using the non-metric multidimensional scaling analysis and cumulative k-dominance. The analyses of trophic groups' abundance showed the control microcosm was dominated by microvores, represented by *Terschellingia*. However, when treated with the highest concentration of BDE-47, the community was occupied by the facultative predators and epigrowth feeders represented by *Metoncholaimus pristiurus* and *Paracomesoma dubium*, respectively [17]. Nasri et al [16] showed also that BDE-47 decreased nematodes and bacterial abundance. The taxonomic structures as well as the relative abundances of each functional group were modified. Nevertheless, only three of the functional traits, adult length, feeding group, and amphid shape, showed a clear difference between the control nematodes assemblages and those treated with BDE-47. A positive correlation was registered between bacteria and the functional groups [1A, Cr, and ef ], conversely, a negative correlation was recorded only with the "cla"-type tail shape.

#### *3.2.5 Microplastics (MPs) effects*

The ecotoxicity of heavy metals and polyvinyl chloride microplastics (cadmium (10 and 20 mg kg-1), polyvinyl chloride (PVC) and its modified forms; PVC-DETA (PD) and PVC-TETA (PT) (20 and 40 mg kg-1), separately and in mixtures on marine nematodes was investigated after exposure during one month. Results displayed that single treatments were toxic for free-living nematodes. The binary combinations of contaminants have a lesser toxic effect compared to their individual effects. This effect could be related to the high-capacity chelating ability of PVC and its polymers against cadmium [62].

The toxic mechanisms exerted by two lipid regulator agents, as well as their interactions with the polyvinyl chloride microplastic on marine nematodes, were examined in an experimental microcosm. Two concentrations of Atorvastatin and Simvastatin, (0.6 mg.kg−1 and 6 mg.kg−1), as well as a single dosage of polyvinyl chloride microplastics at 20 mg.kg−1, separately and their mixtures were used. Results showed a significant reduction in abundance in treatments compared to control. A significant decrease in epigrowth feeders (2A) abundance, which possesses conical (co) tails, and indistinct (id) amphideal foveas, reflected mainly in the decrease in abundance of the species *Prochromadorella longicaudata*. The exposure to microplastic affected only the omnivores-carnivores guild, while, the mixtures with drugs lead to synergic interactions that increased their toxic effects on marine nematode communities (**Table 2**) [63].
