New challenges of marine ecotoxicology in a global change context.

Currently, research agenda in marine ecotoxicology is facing new challenges with the emergence of newly and complex synthetized chemicals. The study of the fate and adverse effects of toxicants remains increasingly complicated with global change events. Ecotoxicology had provided for a decades, precious scientific data and knowledge but also technical and management tools for the environmental community. Regarding those, it is necessary to update methodologies dealing with these issues such as combined effect of conventional and emergent stressors and global changes. In this point of view article, we discuss one hand the new challenges of ecotoxicology in this context, and in the other hand, the need of updating agenda and methodologies currently used in monitoring programs and finally recommendations and future research needs. Among recommendations, it could be cited the necessity to perform long-term experiments, the standardization of sentinel species and taking benefit from baseline studies and omics technologies.

Microplastics mixture exposure at environmentally relevant conditions induce oxidative stress and neurotoxicity in the wedge clam Donax trunculus.

Contamination by micro and nano plastics is actually considered as a global environmental preoccupation. The quantification of microplastics in natural habitats and the characterization of their potential effects in marine wild organisms is currently of high importance. The main objective of this work was to investigate the fate and the effects of a microplastic mixture (ratio of 1: polyethylene (PE), 1: polypropylene (PP)) in the wedge clam Donax trunculus. The assimilation kinetics of microplastics particles was assessed in different organs (gills, digestive gland and flesh) using three different protocols (direct observation, H2O2, and HNO3/HCl digestion) in order to compare method's efficacity. The main biological endpoints studied were Aceylcholinesterase (AChE) inhibition as a neurotoxicity biomarker, the Catalase (CAT) enzymatic activity and the Gluthation-S-Transfereases (GSTs) activities as oxidative stress and phase II detoxification phase markers, respectively. Results showed that the H2O2 digestion method was more efficient to assess particles assimilation than the direct observation and acid digestion. In all cases no particles were detected in clam's flesh and gills were the first target organ for micro-plastics accumulation. The exposure of Donax truculus to PP/PE mixture (0.06 g/Kg of sand) induce a significant inhibition of AChE activity in both gills and digestive gland and oxidative stress in all organs studied. This study brings new results on the potential accumulation of PP and PE associated to neurotoxicity and oxidative stress of the wedge clam Donax trunculus.

Acute toxicity, uptake and accumulation kinetics of nickel in an invasive copepod species: Pseudodiaptomus marinus.

Pseudodiaptomus marinus is a marine calanoid copepod originating of the Indo-Pacific region, who has successfully colonized new areas and it was recently observed in the European side of the Mediterranean Sea as well as in the North Sea. Actually, many questions were posed about the invasive capacity of this copepod in several non-native ecosystems. In this context, the main aim of this study was to investigate the tolerance and the bioaccumulation of metallic stress in the invasive copepod P. marinus successfully maintained in mass culture at laboratory conditions since 2 years. In order to study the metallic tolerance levels of P. marinus, an emergent trace metal, the nickel, was chosen. First, lethal concentrations determination experiments were done for 24, 48, 72 and 96 h in order to calculated LC50% but also to select a relevant ecological value for the suite of experiments. Then, three types of experiments, using a single concentration of nickel (correspond the 1/3 of 96 h-LC50%) was carried in order to study the toxico-kinetics of nickel in P. marinus. Concerning lethal concentrations, we observed that P. marinus was in the same range of sensitivity compared to other calanoid copepods exposed to nickel in the same standardized experimental conditions. Results showed that the uptake of nickel in P. marinus depends from the pathways of entrance (water of food), but also that Isochrysis galbana, used as a food source, has an important bioaccumulation capacity and a rapid uptake of nickel.

Is the reproduction of Donax trunculus affected by their sites of origin contrasted by their level of contamination?

The reproductive cycle of bivalves is regulated by several natural environmental factors but exposure to chemical pollutants can also interfere and may result in advanced or delayed spawning season. To our knowledge, the gametogenic cycle of the suspension-feeder bivalve Donax trunculus has not yet been used as biomonitoring tool in ecotoxicological surveys. The aim of this study was to examine over a year physiological reproductive endpoints (sex-ratio, gametogenic and energy reserve cycles) and biological indices (condition index, allometry) in D. trunculus originating from two sites differing by their level of contamination. Specimens were collected bimonthly from November 2008 to October 2009 from a polluted site (Radès Méliane) and a comparatively reference site (Sidi Jehmi) in the Gulf of Tunis (Tunisia). Five stages were depicted by histological examination of gonads: undifferentiated, developing, mature, spawn and spent. Differences in the gametogenic cycle according to the site of origin of bivalves were observed. The spawning period began in March and was maximum in May in bivalves from both sites, but the percentage of spawning animals was higher in the polluted site vs the reference site. The spawning period was shorter in animals from the polluted site comparatively to the reference site. Energy reserves (glycogen, lipids) were higher in March and May comparatively to the other studied periods in bivalves from both sites. Lower energy reserves levels were usually observed in animals from the polluted site compared to the reference site. Seasonal variations of the condition index were associated to the reproductive and nutritive status of bivalves. Differences in allometry were depicted between bivalves from both studied sites. If we try to link allometry, energy reserves and reproduction, it can be hypothesized that for bivalves from the reference site, energy reserves are allocated to gametogenesis and length growth. For bivalves from the polluted site, energy reserves could be devoted to tolerance to chemical stress and to reproductive processes. Therefore, D. trunculus appears as a suitable sentinel species for the assessment of the ecotoxicological risk of contaminants such as endocrine disruptors.

Linking changes at sub-individual and population levels in Donax trunculus: assessment of marine stress.

Research in ecotoxicology currently focuses to fill the gap existing between sub-organismal responses (e.g. biomarkers) to toxicants and effects occurring at higher levels of biological organisation (e.g. population). The intra-sedimentary bivalve Donax trunculus commonly found in West Atlantic and Mediterranean coasts is a sentinel species useful for biomonitoring studies in sandy beaches. The objective of this work was to link responses at the infra-individual level (core biomarkers as early and sensitive tools) to supra-individual level (population for its ecological relevance). D. trunculus, originating from a polluted site (Radès Méliane) and a comparatively reference site (Sidi Jehmi) in the Gulf of Tunis (Tunisia), were collected bimonthly from November 2008 to October 2009. An increase in catalase activities was usually observed in bivalves from the polluted site compared to the reference site whereas no differences in TBARs were depicted. The anti-oxydant enzyme (catalase) could be able to prevent the deleterious effect on the lipid membranes. Usually GST activities were decreased in the polluted site. Significantly high inhibition in AChE activities in bivalves from the polluted site suggested neurotoxicity disturbances to their in situ exposure to compounds such as organophosphate and carbamates pesticides, heavy metals. Size-distribution of populations of D. trunculus from the polluted Radès Méliane site consisted of four cohorts whereas five cohorts were depicted in the comparatively reference Sidi Jehmi site. The mean total length size and the growth rate of cohorts were significantly reduced in the impacted site compared to the reference site. In conclusion, it may be suggested that disturbances in responses to chemical stress at the infra-individual level could be linked to the responses observed at the population level.

Multimarker approach analysis in common carp Cyprinus carpio sampled from three freshwater sites.

The aim of this study is to assess the response of a multimarker approach in common carp Cyprinus carpio sampled from three Tunisian dam lakes selected according to different environmental and ecological characteristics. Glutathione-S-transferase (GST) activity was analyzed in carp liver and used as a phase II detoxification enzyme, hepatic metallothionein content (MTs) was used as a metallic stress indicator, and cholinesterase activities were analyzed in muscle and brain and used as neurotoxicity biomarker. Micronucleus frequency test (MN) as a genotoxicity marker. GST and MT levels showed an increase in fish from the Bir Mcherga site and a decrease in Sidi Saâd site with respect to fish from Nebhana site. Results showed a strong inhibition of cholinesterase activities in fish from Bir Mcherga and Sidi Saâd sites compared to Nebhana site. Relatively high level of MN is reported specially in fish blood from the Bir Mcherga site.