Are iron ore microparticles toxic for the European clam Ruditapes decussatus? Response elements from biomarker activities and in silico modeling.

Inevitably, high concentrations of iron, the most widely produced ore globally, can be found in aquatic environments. To assess the toxicity of iron on aquatic organisms, Ruditapes decussatus specimens were subjected to microparticles derived from two types of iron ore (hematite and magnetite) at four different concentrations (0.5, 1, 1.5, and 5 g/L). The findings revealed that both types of iron ore were absorbed by clams in a concentration-dependent manner. Biomarkers analysis demonstrated significant and organ-specific impacts on the health of the clams caused by these microparticles, which was further supported by computational analyses on bioavailability. Within seven days of exposure, changes were observed in the activities of several enzymes, including catalase, acetylcholinesterase, and glutathione S-transferases, as well as in the rate of lipid peroxidation in both the digestive gland and gills. This study provides an environmental perspective on the toxicological effects of iron ore microparticles.

Developmental exposure to the A6-pesticide causes changes in tyrosine hydroxylase gene expression, neurochemistry, and locomotors behavior in larval zebrafish.

Purpose: In recent years, the increase in the biopesticides synthesis for alternative agricultural uses has required their impacts study. Among these compounds, several of them are known to exert endocrinedisrupting (EDs) effects causing deregulation of physiological functions affecting cell signaling pathways involved in neural cell differentiation leading to developmental neurotoxicity. The objective of our study was to determine the impact of the biopesticide A6 structurally related to estrogenic EDs on zebrafish larvae, to define its toxicity, the mechanisms responsible, and to monitor the locomotors activity at nanomolar concentrations (0. 0.5, 5 and 50 nM).Materials and methods: Using imaging analysis tools, immunohistochemistry, quantitative PCR, and an automated behavior recording system (Zebrabox) we were able to assess these effects.Results: We have shown through its blue fluorescence properties that it accumulates in different parts of the body such as the intestine, adipose tissue, muscles, yolk sac and head. A6 also disrupted swimming behavior by affecting the expression of tyrosine hydroxylase (TH) in dopaminergic neurons.Conclusions: In conclusion, our study provided a mechanistic understanding of the A6 neurotoxic effect which could be the result of its binding to the estrogen receptor.

Acute toxicity and biomarker responses in Gammarus locusta amphipods exposed to copper, cadmium, and the organochlorine insecticide dieldrin.

The toxicity of copper, cadmium, and dieldrin in adult Gammarus locusta (a marine amphipod) is currently unclear. Thus, G. locusta from the North Lake of Tunis were subjected to acute toxicity tests to assess LC50s at 48-96 h and to biomarker response tests through the assessment of catalase and acetylcholinesterase activities and malondialdehyde levels. The present study demonstrated the abilities of a chlorinated hydrocarbon pesticide (dieldrin) induce to oxidative stress and neurotoxicity. The comparison of metal toxicity showed that G. locusta was more sensitive to cadmium than copper. The three stressors caused significant inductions of all three biomarkers in a concentration-dependent manner. Catalase induction was dependent on exposure duration for all pollutants, while only copper led to increased malondialdehyde with longer exposure times. Catalase induction and malondialdehyde increase appeared to be sex dependent for all three pollutants. The neurotoxic effects of the pollutants were concentration dependent according to inhibition of acetylcholinesterase activity. In conclusion, catalase, malondialdehyde, and acetylcholinesterase are efficient biomarkers of copper, cadmium, and dieldrin in G. locusta.

Ecotoxicity of polybrominated diphenyl ether (BDE-47) on a meiobenthic community with special emphasis on nematodes: Taxonomic and trophic diversity assessment.

The response taxonomic and trophic of meiobenthic organisms, especially marine nematodes to polybrominated diphenyl ether (BDE-47) was studied using a community from Bizerte lagoon (Nord-East Tunisia). Four concentrations of BDE-47 [D1 (2.5 µg/kg dw), D2 (25 µg/kg dw), D3 (50 µg/kg dw), and D4 (100 µg/kg dw)] were applied, and responses were determined 30 days after exposure. Species abundance and all univariate indices were significantly affected in all treated microcosms compared to the control. The non-parametric cluster based on species abundance separated the nematode population into two groups: control + all treated microcosms. After grouping nematode species according to their trophic diversity, their abundance showed differential responses. The non-metric multi-dimensional scaling analysis and cumulative k-dominance based on the abundance of trophic groups abundances reflected significant separation between the control microcosm and each treatment condition. The correspondence analysis 2D plot generated from nematode species and trophic groups abundance showed the control microcosm was dominated by microvores, represented by two species of Terschellingia. However, when treated with the highest concentration of BDE-47, the community was occupied by the resistant trophic groups of facultative predators and epigrowth feeders represented by Metoncholaimus pristiurus and Paracomesoma dubium, respectively.

Using meiobenthic taxa, nematofauna biological traits, and bacterial abundance to assess the effects of the polybrominated diphenyl ethers compound: Case study of tetrabromo diphenyl ether BDE-47.

Trophic web structuring in aquatic sediments is dependent on the biological interactions between metazoans and microbial communities. The presence of pollutants in these biotas can therefore impact the meiofauna structure via the modification of the microbial communities. The current study examined in a laboratory bioassay the response of meiobenthic communities, particularly marine nematode taxa from the Bizerte Lagoon to the effect of the most detected polybrominated diphenyl ether in this aquatic environment, BDE-47. Four doses [D1 (2.5 ppb Dry weight (DW)), D2 (25 ppb DW), D3 (50 ppb DW), and D4 (100 ppb DW)] were gradually applied and sediment microcosms were incubated for 30 days in the presence or absence of meiofauna. Our results show that BDE-47-enriched sediments decreased the meiofaunal taxa and bacterial abundance. A lower taxonomic diversity of the nematodes' general structure was observed with all doses used. The numerical analysis of the two dimensional (2D) non-metric multidimensional scaling (nMDS) plots and the evolution of the relative abundances of each functional group of nematode genus assemblages revealed that the abundance of all biological traits was modified. Nevertheless, only three of the functional traits, adult length, feeding group, and amphid shape, showed a clear difference between the control and the treated microcosms. The similarity percentage analysis (SIMPER) revealed that the average dissimilarity between nematode genera communities and biological traits increased with BDE-47-enriched sediments. The nMDS second-stage ordination of inter-matrix rank correlations for matrices including genera and biological traits showed that the amphid shape was the functional trait closest to the generic distribution. Finally, the Principal Component Analysis (PCA) for the nematode biological traits and bacteria indicated a positive correlation of these microbes with the functional groups [1A, Cr, and ef], and a negative correlation only with the "cla"-type tail shape.

Ethinylestradiol (EE2) residues from birth control pills impair nervous system development and swimming behavior of zebrafish larvae.

The ubiquitous use of ethinylestradiol (EE2), an active constituent of birth control preparations, results in continuous release of this synthetic estrogen to surface waters. Many studies document the untoward effects of EE2 on the endocrine system of aquatic organisms. Effects of environmental EE2 on the nervous system are still poorly documented. We studied effects of pico- to nanomolar concentrations of EE2 on early nervous system development of zebrafish larvae. EE2 disrupted axonal nerve regeneration and hair cell regeneration up to 50%. Gene expression in larval brain tissues showed significantly upregulated expression of target genes, such as estrogen and progesterone receptors, and aromatase B. In contrast, downregulation of the tyrosine hydroxylase, involved in the synthesis of neurotransmitters, occurred concomitant with diminution of proliferating cells. Overall, the size of exposed fish larvae decreased by 25% and their swimming behavior was modified compared to non-treated larvae. EE2 interferes with nervous system development, both centrally and peripherally, with negative effects on regeneration and swimming behavior. Survival of fish and other aquatic species may be at risk in chronically EE2-contaminated environments.

The individual and combined effects of cadmium, polyvinyl chloride (PVC) microplastics and their polyalkylamines modified forms on meiobenthic features in a microcosm.

A microcosm experiment was carried out to study the ecotoxicity and interactions between heavy metals and polyvinyl chloride microplastics. Fifteen treatments were tested and results were examined after one month. In details, this work aims to study the ecotoxicological effects of cadmium (10 and 20 mg kg-1 Dry Weight DW), polyvinyl chloride (PVC) and its modified forms; PVC-DETA (PD) and PVC-TETA (PT) (20 and 40 mg kg-1 DW), separately and in mixtures, on meiofauna from Bizerte lagoon (NE Tunisia) with focus on nematode features. The results obtained showed that individual treatments were toxic for meiofauna and particularly for free-living nematodes. No clear trends characterized the numerical responses but significant reductions were observed for diversity indices. Moreover, 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.

Neurotoxicity of a Biopesticide Analog on Zebrafish Larvae at Nanomolar Concentrations.

Despite the ever-increasing role of pesticides in modern agriculture, their deleterious effects are still underexplored. Here we examine the effect of A6, a pesticide derived from the naturally-occurring α-terthienyl, and structurally related to the endocrine disrupting pesticides anilinopyrimidines, on living zebrafish larvae. We show that both A6 and an anilinopyrimidine, cyprodinyl, decrease larval survival and affect central neurons at micromolar concentrations. Focusing on a superficial and easily observable sensory system, the lateral line system, we found that defects in axonal and sensory cell regeneration can be observed at much lower doses, in the nanomolar range. We also show that A6 accumulates preferentially in lateral line neurons and hair cells. We examined whether A6 affects the expression of putative target genes, and found that genes involved in apoptosis/cell proliferation are down-regulated, as well as genes reflecting estrogen receptor activation, consistent with previous reports that anilinopyrimidines act as endocrine disruptors. On the other hand, canonical targets of endocrine signaling are not affected, suggesting that the neurotoxic effect of A6 may be due to the binding of this compound to a recently identified, neuron-specific estrogen receptor.

Do trace metals (chromium, copper, and nickel) influence toxicity of diesel fuel for free-living marine nematodes?

The objective of this study was to test the hypotheses that (1) free-living marine nematodes respond in a differential way to diesel fuel if it is combined with three trace metals (chromium, copper, and nickel) used as smoke suppressants and that (2) the magnitude of toxicity of diesel fuel differs according to the level of trace metal mixture added. Nematodes from Sidi Salem beach (Tunisia) were subjected separately for 30 days to three doses of diesel fuel and three others of a trace metals mixture. Simultaneously, low-dose diesel was combined with three amounts of a trace metal mixture. Results from univariate and multivariate methods of data evaluation generally support our initial hypothesis that nematode assemblages exhibit various characteristic changes when exposed to different types of disturbances; the low dose of diesel fuel, discernibly non-toxic alone, became toxic when trace metals were added. For all types of treatments, biological disturbance caused severe specific changes in assemblage structure. For diesel fuel-treated microcosms, Marylynnia bellula and Chromaspirinia pontica were the best positive indicative species; their remarkable presence in given ecosystem may predict unsafe seafood. The powerful toxicity of the combination between diesel fuel and trace metals was expressed with only negative bioindicators, namely Trichotheristus mirabilis, Pomponema multipapillatum, Ditlevsenella murmanica, Desmodora longiseta, and Bathylaimus capacosus. Assemblages with high abundances of these species should be an index of healthy seafood. When nematodes were exposed to only trace metals, their response looks special with a distinction of a different list of indicative species; the high presence of seven species (T. mirabilis, P. multipapillatum, Leptonemella aphanothecae, D. murmanica, Viscosia cobbi, Gammanema conicauda, and Viscosia glabra) could indicate a good quality of seafood and that of another species (Oncholaimellus mediterraneus) appeared an index of the opposite situation.