Ezzeddine Mahmoudi

Effect of permethrin, anthracene and mixture exposure on shell components, enzymatic activities and proteins status in the Mediterranean clam Venerupis decussata

Anthracene (ANT) and permethrin (PER) are two of the more toxic compounds reaching the marine environment. This study aimed to determine the impact of these molecules on Venerupis decussata, an economically important species cultured on the Tunisian coast. Shell structure and its possible transformation upon exposure to the two contaminants were studied by X-ray diffraction and gravimetric analyses. Results revealed a phase transition in shell composition from aragonite to calcite after PER exposure, to a mixture of PER and ANT (Mix) but not for ANT alone. Catalase (CAT), superoxide dismutase (SOD) and glutathione transferase (GST) activities were determined in digestive gland and gills after exposure to ANT, PER and Mix to assess the impact of the contamination on the oxidative status of V. decussata. Enzyme activities increased in the digestive gland after PER treatment and in the gills after ANT treatment. PER exposure significantly reduced the levels of free thiols and increased levels of carbonylated proteins in the digestive gland, as compared to controls. In contrast, ANT exposure significantly reduced free thiols and increased the number of carbonylated proteins in the gills. Mix induced additive effects as measured by both enzymatic and proteomic approaches. The present study suggests that PER has a strong effect on shell structure; that PER and ANT exposure generate compound-dependent oxidative stress in the tissues of V. decussata and that a mixture of the two compounds has synergistic effects on biochemical response.

Acute toxicity of cypermethrin on the freshwater mussel Unio gibbus

Cypermethrin is a synthetic pyrethroid insecticide used worldwide in agriculture, home pest control, food stuff protection and disease vector control. We investigate the potential of cypermethrin to induce oxidative stress and enzyme activities within the gills of freshwater mussel Unio gibbus. This study was carried out under laboratory conditions using two nominal cypermethrin concentrations C1 (100µg/L) and C2 (150µg/L) during 96h. The measured concentrations of cypermethrin using GC-MS-MS in the treatment aquariums were respectively 59.7 µg/L and 97.5µg/L. Antioxidant enzyme activities (superoxide dismutase (SOD) and catalase (CAT)) as well as H2O2, malondialdehyde (MDA) and protein carbonyl (PCO) levels were assessed. An exposure during 96h induced the SOD activity at the highest concentration. The CAT activity and H2O2 level were increased significantly (P<0.05) in gills following a dose-dependent profile. Cypermethrin also generated an increase in malondialdehyde (MDA) levels reaching the highest value at the high concentration. The considered parameters can be used as biomarkers of exposure to cypermethrin. Freshwater mussel U. gibbus can be potentially employed in biomonitoring surveys of such threatened ecosystems.

Mussel-farming effects on Mediterranean benthic nematode communities

Mussel aquaculture activities in coastal areas are growing rapidly throughout the world, inducing an increasing interest and concern for their potential impact on coastal marine environments. We have investigated the impact of organic loads due to the biodeposition of a mussel farm in a lagoonar ecosystem of the Mediterranean Sea (Bizerta lagoon, northern Tunisia) on the benthic environment. The most evident changes in the benthic habitat under the farm were a strong reduction of oxygen penetration into the bottom sediments and a large accumulation of chlorophyll a (concentrations up to 16 μg g–1), phaeopigments (concentrations up to 48 μg g–1) and total organic matter (concentrations up to 12%). Results from univariate analysis of the nematofaunal data show that the nematode abundance increased in all the stations located inside the mussel farm (I1, I2, I3) and the site I2, located in the centre of the mussel farm, was the most affected. At this site, Shannon-Wiener index H′, species richness (d), evenness (J′) and number of species (S) decreased significantly. Results from multivariate analyses of the species abundance data demonstrated that responses of nematode species to the organic matter enrichment were varied: Mesacanthion diplechma was eliminated at the most affected station (I2), whereas the abundances of Paracomesoma dubium, Terschellingia longicaudata and T. communis were significantly enhanced. Responses of free-living nematodes to mussel farm biodeposition (elimination of some species and increase or decrease of some others) could lead to food limitation for their predators that, ultimately, could alter entire communities and ecosystems. Consequently, we suggest that site-specific hydrodynamic and biogeochemical conditions should be taken into account when planning new mussel farms, and meiobenthic communities should be monitored before and after farm development to prevent excessive modifications of benthic assemblage structure.

The effects of anthracene on biochemical responses of Mediterranean mussels Mytilus galloprovincialis

ABSTRACT Mediterranean mussels Mytilus galloprovincialis is among the most widely used bioindicators, and anthracene (AN) is one of the most commonly found hydrocarbons in the aquatic environment. M. galloprovincialis were exposed to nominal concentrations of 0.05, 0.15 and 0.4 μg/L AN. Chemical analysis using high-performance liquid chromatography revealed the uptake of AN in the whole soft body and digestive gland at different amounts. After a short exposure (2, 4 and 8 days), the results revealed that AN induced malondialdehyde (MDA), glutathione (GSH) and acetylcholinesterase (AChE) activity in digestive gland. Our findings demonstrated also that AN reduced the filtration rates in a concentration-dependent manner. Increase in lipid peroxidation (MDA content) in digestive gland (p < .05) can possibly indicate that AN can cross the membrane barrier, leading to cellular membrane alteration. Decrease in GSH content following the concentration and exposure time support MDA content result. AN exposure significantly reduced AChE activity as a more sensitive biomarker in digestive gland in a time- and concentration-dependent manner. This review provides a framework for the understanding of toxicological effects of AN under an environmental point of view. It provides also original data on the distribution of AN in M. galloprovincialis, where digestive gland constitutes a valuable organ for investigating AN biotransformation and toxicity.

Environmental quality assessment of El Bibane lagoon (Tunisia) using taxonomic and functional diversity of meiofauna and nematodes

The lagoon of El Bibane (Tunisia) is a Mediterranean coastal area that is affected by an increasing human impact. Thus, an estimation of its biodiversity and an ecological quality assessment are very urgent. This study investigates the meiofaunal and nematode communities of the El Bibane lagoon both from a taxonomic and a functional point of view. Nematodes were the dominant group as is common in brackish water systems. The nematode community was made up of 62 genera in 22 families. Xyalidae, Chromadoridae and Cyatholaimidae were the richest and most abundant families. The taxonomic composition and biodiversity of nematodes were comparable to those found in other European and Mediterranean transitional areas. Both meiofauna and nematodes showed a clear subdivision between marginal and central areas. The central stations, represented by fine sediments and higher amounts of organic carbon, seemed to be characterized by low meiofaunal densities, nematode diversity and a strong dominance of 1B and 2B trophic guilds. These trends could be related not only to the grain size and organic load, but also to a possible influence of tidal currents that can transport pollutants in the central area of the lagoon coming from the adjacent coastal areas. Shannon diversity and life strategies are not always in agreement in defining the ecological quality, but an overall worse ecological quality was detected especially at S6. The results of this study are an important starting point for the future monitoring of the potential and actual human impact on the El Bibane area over time.

Neurotoxicity and oxidative stress induced by permethrin in gills of the freshwater mussel Unio ravoisieri

ABSTRACT Pyrethroids are contaminants found in the aquatic environment, and their toxicological effects on aquatic organisms have received extensive attention. However, the impact on freshwater bivalve of exposure to these chemicals is still largely unknown. Freshwater mussels Unio ravoisieri were exposed to two nominal permethrin (PM) concentrations C1 = 50 µg/L and C2 = 100 µg/L during 7 days. The measured concentrations of PM using gas chromatography (GC/ECD) in the treated aquariums were, respectively, 28.7–62.3 µg/L. Catalase (CAT), Glutathione-S-transferase (GST), and Acetylcholinesterase (AChE) activities, Glutatione (GSH) and Malondialdehyde (MDA) levels were determined in gills of U. ravoisieri. Significant increase in CAT activity by the lowest concentration and decrease by highest concentration were observed. Additionally, GST activity was increased in a concentration-dependent manner. However, statistically significant decrease in GSH levels (about 39%) was observed only at high concentration of this compound (100 µg/L). PM generated an increase in MDA levels reaching the highest value at the high concentration. AChE activity of mussel ranging from 51% inhibition at lowest concentration 50 µg/L to 89% inhibition at highest concentration 100 µg/L. The results indicated that oxidative stress and cell damage might be one of the main mechanisms of PM toxicity to freshwater mussels.

Diastereomeric and enantiomeric selective accumulation of cypermethrin in the freshwater mussel Unio gibbus and its effects on biochemical parameters.

Synthetic pyrethroids are a family of chiral pesticides with a large number of stereoisomers. Cypermethrin (CYP) is used in a variety of agricultural crops, but also has public health and veterinary uses. In this work, the freshwater mussel (Unio gibbus) was chosen to evaluate the stereoselectivity of CYP through the use of gas chromatography with mass-spectrometry. The effects of CYP on mussels were examined by measuring neurotoxicity and oxidative stress biomarkers during its uptake. The investigation was performed under laboratory conditions using nominal CYP concentrations C1=100 μg/L and C2=150 μg/L over 96 h. Preferential bioaccumulation of cis-CYP isomers was observed. Furthermore, enantiomeric characterization revealed enantioselective accumulation, most probably related to mussel metabolism. Antioxidant enzyme activities (superoxide dismutase (SOD), and catalase (CAT)), and levels of reduced glutathione (GSH) and malondialdehyde (MDA) were determined in digestive gland after 4 days of exposure. CYP significantly inhibited acetylcholine esterase activity, by 51% and 57%, respectively, in mussels treated with 100 and 150 μg/L doses. The highest and lowest CYP concentrations elicited an increase of 67 and 63%, respectively, in SOD activity compared to the controls, while CAT activity was increased by 65 and 73%. A statistically significant decrease in GSH levels (40%) was observed only with the highest CYP concentration tested (150 μg/L). In addition, lipid peroxidation was significantly higher (67%) than in controls. These results provided information on CYP-enantioselective uptake and potential biomarkers that could be effectively applied for the biomonitoring of freshwater ecosystem.

Relation entre facteurs environnementaux et densités larvaires d’Ochlerotatus caspius Pallas 1771 et Ochlerotatus detritus Haliday 1833 (Diptera: Culicidae) en Tunisie

Résumé Ochlerotatus caspius et Oc. detritus, deux espèces de moustiques fréquemment rencontrées en Tunisie, font l’objet de traitements insecticides en vue de limiter leur nuisance. Cependant, la portée de ces traitements demeure limitée compte tenu des grandes étendues de leurs biotopes larvaires et du caractère synchrone de leurs éclosions. Le but de cette étude vise à caractériser, à travers des analyses multivariées (AFC, CHA), la niche écologique de chaque espèce afin de définir des plans d’intervention plus adaptés. Nos résultats montrent que les abondances larvaires d’Oc. caspius et Oc. detritus sont principalement corrélées au couvert végétal et à la salinité des gîtes larvaires. En effet, Oc. detritus se développe abondamment dans les milieux fortement salés dominés par Sarcocornia fruticosa, alors qu’Oc. caspius est associé à une végétation plus diversifiée supportant une salinité moindre dominée par Juncus maritimus, et développant une litière végétale plus abondante.

Distribution of organic contamination of sediments from Ichkeul Lake and Bizerte Lagoon, Tunisia

Analyses of organochlorine pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and butyl tins (BuSn) were conducted on sediments from Ichkeul Lake-Bizerte Lagoon watershed (Tunisia). A total of 59 compounds (16 PAHs, 12 PCBs, 22 OCPs and 9 BuSn) were measured in 40 surface sediment samples collected during two campaigns. High concentrations of total PAHs were identified in the lagoon ranging from 122 to 19600ng·g-1. Several OCPs, including endrin, dieldrin, and lindane (Hexachlorocyclohexane or HCH or BHC) were found in high concentrations in Ichkeul Lake, ranging from 28 to 2012ngg-1. PAHs and OCPs varied seasonally, in response to the complex hydrology of the watershed. The concentrations of total PCBs ranged between 0.04 and 10.653ngg-1 and suggests low total PCBs sediment contamination, when compared to most international criteria. Total BuSn concentrations range between 67 and 526ng·g-1, which are relatively low when compared to most international criteria and ecological risk assessments. This is the first study of organic contamination in Ichkeul Lake (RAMSAR and UNESCO World Heritage site).

Effects of 2-(4-Methoxyphenyl)-5, 6-trimethylene-4H-1, 3, 2-oxathiaphosphorine-2-sulfide on biomarkers of Mediterranean clams Ruditapes decussatus.

The effects of exposure to a novel synthetic organophosphorus compound, 2-(4-Methoxyphenyl)-5, 6-trimethylene-4H-1, 3, 2-oxathiaphosphorine-2-sulfide (OMTOS) concentrations (Control=0, C1=0.01, C2=0.1, C3=1 and C4=10μg/L) were investigated in the clam Ruditapes decussatus. Vitellogenin (Vg)-like protein levels in haemolymph from males and females were investigated. Concentrations of 1μg/L and 10μg/L significantly decreased Vg levels in male haemolymph after 7 days, whereas significant variations were only found in females treated with 10μg/L. On the other hand, superoxide dismutase (SOD), catalase (CAT) and acetylcholinesterase activities (AChE) in whole soft tissue were measured after 2, 4 and 7 days of exposure to the same series of concentrations. After 2 days of exposure, 0.1, 1, and 10μg/L of OMTOS increased SOD activity significantly, but this decreased with 10μg/L after 4 and 7 days. No changes in CAT activity were observed after 2 days compared to controls. OMTOS significantly reduced AChE activity after 4 and 7 days in treated clams with the highest concentration 10μg/L, but it did not induce significant variations at the other concentrations tested. Our study demonstrates that OMTOS alters biochemical parameters in R. decussatus, even at low concentrations, and suggests differing modes of action of the contaminant. Using clams is a powerful tool to provide valuable insights into possible mechanisms of environmental toxicity of novel synthetic organic products both in non-target organisms and the marine ecosystem. Additionally, our results highlight that biomarker responses facilitate elucidation of putative mechanisms of action of OMTOS in non-target species.