Use of metallothioneins as biomarkers for environmental quality assessment in the Gulf of Gabès (Tunisia)

Biomarkers for monitoring heavy metal pollution in the Anzali Wetland

This research aims to investigate biochemical activities of Phragmites australis, as a biomarker of heavy metals including Cr, Ni, V, Zn and Co. In order to determine and analyze biochemical parameters including flavonoids, Non-Protein Thiols (NPTs), chlorophyll a and b and total chlorophyll pigments in the roots, stems and leaves of P. australis, sediment and plant samples were collected from 7 stations in the Anzali wetland. Based on the obtained results, there were positive and significant correlation coefficients among the concentrations of the heavy metals in the sediments with non-protein thiols and flavonoids, also negative and significant correlation coefficients were found between the heavy metal contents and the total chlorophyll in the leaves in all the sampling stations. Therefore, it can be concluded that these parameters are appropriate biomarkers to evaluate the heavy metal pollution in the sediments of the aquatic ecosystem.

The Mediterranean limpet Patella caerulea (Gastropoda, Mollusca) to assess marine ecotoxicological risk: a case study of Tunisian coasts contaminated by metals

Participants in the coastal socio-economy of the Mediterranean Sea, such as industries, aquaculture, urban populations, conglomerates, and tourists, create intense anthropogenic pressures on marine ecosystems (such as the release of trace metals). This raises concerns about their impact on the surrounding environment and on marine organisms, including those collected for human consumption. This study introduces the possibility of using Patella caerulea (Linnaeus 1758), indigenous to the Mediterranean Sea, as a biosentinel of marine pollution. This study proposes coupling environmental (bioaccumulation) and toxicological (redox homeostasis) measures of bioavailability with genetic variability (COI mtDNA) assessments. Concentrations of six trace metals (cadmium, copper, iron, lead, nickel, and zinc) were measured in surface seawater and in P. caerulea individuals collected from four coastal stations on the Tunisian coast where different levels of metal contamination have occurred. The quantified biomarkers involved the determination of antioxidant defense enzymes, catalase (CAT), glutathione peroxidase (GPX), superoxide dismutase (SOD), and the measurement of lipid peroxidation indicated by malondialdehyde (MDA) levels. Our study identified critical levels of metal contamination among locations in the Gulf of Gabes. Concomitantly, the induction of antioxidant biomarkers (especially SOD and GPX) was observed, highlighting the potential of P. caerulea to acclimate to stressful pollution conditions. Molecular analysis of COI (mtDNA) revealed low discrimination between the four P. caerulea populations, highlighting the role of marine currents in the Mediterranean Sea in the dispersal and passive transportation of limpet larvae, allowing an exchange of individuals among physically separated, P. caerulea populations.

Ecdysis as an auxiliary route for the removal of heavy metals in crustaceans: an experimental analysis with fiddler crabs (Minuca burgersi)

We assessed fiddler crabs' (Minuca burgersi) ability to secrete metallic contaminants through ecdysis under controlled conditions. We fed them with contaminated food with different copper (Cu) and lead (Pb) amounts and measured their concentration in the released and renewed exuviae. We found a significant reduction in the average concentrations of Cu and Pb in the released and renewed exuviae-eliminating the exoskeleton in the ecdysis process helps in the metal detoxification mechanism of these animals. A portion of the concentration of metals is retained in the crustaceans' exuvia, and thus, they can be used to analyze bioaccumulation in ecosystems. Our results also reinforce the need for attention to the contamination characterization in crustaceans before and after ecdysis to avoid underestimation effects.

Metal and metallothionein levels in zooplankton in relation to environmental exposure: spatial and temporal variability (Saronikos Gulf, Greece)

Metal and metallothionein (MT) in mixed zooplankton were investigated as means of monitoring metal availability regarding environmental exposure. Spatial and temporal variability of Cd, Cu, Ni, Zn, Fe, Mn and Pb in zooplankton and seawater were studied in Saronikos Gulf (Aegean Sea, Eastern Mediterranean), once every second month during an annual cycle (2011-2012). Particulate organic carbon and chlorophyll α were also measured in seawater samples. Median zooplankton metal concentrations were 0.65, 32.4, 7.1, 864, 1420, 40.2 and 26.8 μg g^-1 dw for Cd, Cu, Ni, Zn, Fe, Mn and Pb, respectively, and 109 μg g^-1 ww for MTs. Metal levels in zooplankton and MTs were higher at sites influenced by human-derived pressures. Additionally, metal concentrations in pelagic fish flesh from the Greek MED-POL data base were used for bioconcentration and biomagnification factors calculation. Bioconcentration from water to zooplankton was higher than metal transfer from either seston to zooplankton or zooplankton to fish.

Uptake and detoxification of trace metals in estuarine crabs: insights into the role of metallothioneins

The detoxification process of trace metals in the estuarine burrowing crab Neohelice granulata, after previously being exposed to anthropogenic pressures in the field, is described for the first time. The objectives of this study were (a) to assess the metal content (Cd, Cu, Pb, Zn, Mn, Ni, Cr, Fe) in the sediments and the uptake of these elements in the hepatopancreas of N. granulata; (b) to quantify trace metal concentrations in the hepatopancreas before and after the detoxification experiment; and (c) to relate this information to metallothionein (MT) induction or reversibility. The detoxification assay was performed for 25 days with artificial seawater under controlled conditions in a culture chamber. The results showed higher uptake and bioaccumulation of Zn and Cu from the sediments, and the hepatopancreas exhibited increased levels of Zn and lower concentrations of the rest of the metals and MTs after the assay, mainly Fe and Mn that were significantly lower. We conclude that trace metals could be translocated to and accumulated in the hepatopancreas, the main metabolic organ, and then eliminated under controlled conditions with corresponding reversibility of MTs. Graphical abstract.

Metallothionein Induced Time Dependent Histomorphometric Analysis of Clarias gariepinus Exposed to Cadmium

Cadmium (Cd), an extremely toxic heavy metal is extensively used in modern era because of its constructive chemical and physical properties. Recently Cd contamination was estimated in India's major cities fresh water ecosystem, which may have firm impact on human health. Hence, this study was aimed to detect the time dependent effect of cadmium in fresh water fish C. gariepinus, a bioindicator species of water pollution. In a controlled environment, fishes were exposed to cadmium for different duration and analyzed for Cd accumulation. Cd induced toxicity was assessed by estimating metallothionein biomarker protein of heavy metal toxicity and histomorphometric changes in liver and kidney. Our results revealed that fish exposed to Cd induced apoptosis in fish tissues via induction of caspases and in contrast the metallothionein was also increased consistently with different doses of Cd exposure. Hence we conclude Cd induced structural damages to fishes are attributed to induction of caspases and estimating MT level in tissues can be effective biomarker to analyze the effect of acute environmental exposure to Cd.

Responses of primary cultured haemocytes derived from the marine gastropod Haliotis tuberculata to an industrial effluent exposure

This study assessed the responses of primary cultured haemocytes from the marine gastropod Haliotis tuberculata exposed to the increasing concentrations of industrial effluent (0, 0.5, 1, 10, 15 and 20%) discharged into the Tunisian coastal area. Analyses showed the presence of metals such as cadmium (Cd), chromium (Cr), copper (Cu), manganese (Mn), zinc (Zn), nickel (Ni) and lead (Pb) in the effluent. The effects of this mixture of pollutants on abalone haemocyte parameters were reflected by a significant decrease of cell viability, phagocytotic activity and reactive oxygen species (ROS) production as well as morphological and lysosomal membrane alterations. Thus, these results indicated that our primary culture system represents a suitable in vitro model for monitoring of anthropogenic contaminants in aquatic environments.

Antioxidant and detoxification responses of oysters Crassostrea hongkongensis in a multimetal-contaminated estuary

The contaminated oysters discovered in the Pearl River Estuary (Guangdong province, China) contained high levels of metals in their tissues, especially Cu and Zn, indicating that this large and densely urbanized estuary in Southern China suffers from serious metal pollution. The present study aimed to investigate the impacts of multimetal pollution in the Pearl River Estuary on oyster antioxidant and detoxification systems. The responses of various biochemical biomarkers in the ecologically important oyster Crassostrea hongkongensis collected from 7 sites in the Pearl River Estuary were quantified. Significant correlations were demonstrated between the accumulation of Cu and Zn and oxidative stress (lipid peroxidation) and oxidative stress defenses (catalase, glutathione peroxidase) in the oyster gills. Significant correlations between the accumulation of Cd and Cu and detoxification (glutathione and glutathione transferase) in the gills were also documented. Interestingly, metallothionein concentrations were positively correlated with Cd, but negatively correlated with Cu, Ni, and Zn concentrations in the gills. These measurements indicated that Cu in the Pearl River Estuary induced various biochemical responses in the oysters and influenced the susceptibility of oysters to environmental stress. The present study has provided the first evidence of antioxidant and detoxification responses in native contaminated oysters from a field environment seriously contaminated by metals. Coupling biomarkers with tissue metal concentration measurements was a promising approach to identify the metals causing biological impacts in a multimetal-contaminated estuary. Environ Toxicol Chem 2016;35:2798-2805. © 2016 SETAC.

How does the metallothionein induction in bivalves meet the criteria for biomarkers of metal exposure?

Metallothionein (MT) concentrations in the whole soft tissue or in a particular tissue of bivalves have widely been used in ecotoxicological studies and biomonitoring programmes. This approach is based on the reported results on the enhancement of MT induction in bivalves in response to metal exposure. The validity of using MT induction as a biomarker is briefly assessed in the present study. The sensitivity of MT induction in these organisms is questionable due to the high basal MT level as well as the high natural variability related to the effects of a number of biotic and abiotic factors, which are not well described yet. Moreover, the relationship between exposure to metals, the toxic effects of that exposure, and the appearance of MT in soft tissue, is not well characterized. A variety of factors may influence the appearance and distribution of MT: 1) the uneven distribution of metals in particular portions of the soft tissue and in particular subcellular compartments; 2) pre-exposure to metals, perhaps at non-toxic levels; 3) metal-metal competition and metal-protein interactions; and 4) tissue-specific induction, functions, and isoforms of MT. Therefore, attention is required when using MT induction in bivalves for assessment of metal exposure or consequent toxic effects. The MT concentration can be a reliable indicator only when it is considered in relation with metal uptake kinetics and subcellular partitioning while specifying the isoform of MT synthesised and considering various confounding factors. The kinetic turnover of MT may provide useful information on metal exposure and biological effects since it covers both the synthesis and breakdown of MT as well as the chemical species of metals accumulated and MT.

Analysis of a population of magnetotactic bacteria of the Gulf of Gabès, Tunisia

The occurrence of magnetotactic bacteria (MTB) on a Tunisian marine coast exposed to heavy metals pollution (Sfax, Gulf of Gabès, Mediterranean Sea) was investigated. The MTB population of this Southern Mediterranean coast was compared to the MTB populations previously investigated on the French Northern Mediterranean coast. A dominant MTB coccus morphotype was observed by microscopy analysis. By pyrosequencing technology, the analysis of the 16S ribosomal RNA (rDNA) revealed as much as 33 operational taxonomic sequence units (OTUs) close to sequences of MTB accessible in the databases. The majority were close to MTB sequences of the "Med group" of α-Proteobacteria. Among them, a dominant OTU_001 (99 % of the MTB sequences) affiliated within the Magnetococcales order was highlighted. Investigating the capacities of this novel bacterium to be used in bioremediation and/or depollution processes could be envisaged.

Time changes in biomarker responses in two species of oyster transplanted into a metal contaminated estuary

The Jiulong Estuary in Southern China suffers from serious metal pollution, leading to the appearance of 'colored' oysters in this estuary. In this study, two species of oysters Crassostrea hongkongensis and Crassostrea angulata were transplanted to three sites in the Jiulong Estuary over a two-month period. The time-series changes of various biomarkers were measured, coupled with simultaneous quantification of metal bioaccumulation (Ag, Cd, Cr, Cu, Ni and Zn). Cu and Zn accumulation increased linearly and reached up to 2% and 1.5% dry tissue weight by the end of exposure. Negative correlations between the tissue Cu or Zn accumulation and catalase or superoxide dismutase activities strongly indicated that Cu and Zn in 'colored' oysters induced the adjustments of oyster antioxidant systems. Metallothionein (MT) detoxification was insufficient for sequestering all the absorbed metals and its concentrations in the oysters were suppressed following an initial increase, primarily due to the high metal accumulation in the tissues. Interestingly, gradual recoveries of lysosomal membrane stability after the initial strong inhibitions were observed in both oysters. We also documented an increasing 'watering' of oyster tissues presumably as a result of rupturing of tissue cells under metal stress. This study demonstrated the complexity of biomarker responses under field condition, therefore the time changes of biomarker responses to metals need to be considered in evaluating the biological impacts of metal pollution on estuarine organisms.

Transcriptional response of stress-regulated genes to industrial effluent exposure in the cockle Cerastoderma glaucum

This study assessed the responses of molecular biomarkers and heavy metal levels in Cerastoderma glaucum exposed for 1 week to two industrial effluents (1%) discharged into the Tunisian coastal area, F1 and F2, produced by different units of production of a phosphate treatment plant. A significant uptake of metals (Cd, Cu, Zn, and Ni) was observed in exposed cockles compared to controls, with an uptake higher for F1 than for F2. A decrease in LT50 (stress on stress test) was also observed after an exposure to the effluent F1. Treatments resulted in different patterns of messenger RNA (mRNA) expression of the different genes tested in this report. Gene transcription monitoring performed on seven genes potentially involved in the tolerance to metal exposure showed that for both exposures, mechanisms are rapidly and synchronically settled down to prevent damage to cellular components, by (1) handling and exporting out metal ions through the up-regulation of ATP-binding cassette xenobiotic transporter (ABCB1) and metallothionein (MT), (2) increasing the mRNA expression of antioxidant enzymes (catalase (CAT), superoxide dismutases, CuZnSOD and MnSOD), (3) protecting and/or repairing proteins through the expression of heat shock protein 70 (HSP70) mRNAs, and (4) increasing ATP production (through the up-regulation of cytochrome c oxidase 1 (CO1)) to provide energy for cells to tolerate stress exposure. The tools developed may be useful both for future control strategies and for the use of the cockle C. glaucum as a sentinel species.

Cadmium accumulation and metallothionein biosynthesis in cadmium-treated freshwater mussel Anodonta woodiana

This study investigated the distribution of cadmium (Cd) and the protein level of metallothionein (MT) and examined the relationship of Cd accumulation and the MT concentration in different tissues of freshwater mussel Anodonta woodiana following Cd treatment. The mussels were exposed to Cd (4.21, 8.43, 16.86, 33.72 and 67.45 mg L-1) for 24, 48, 72 and 96 h, respectively. After Cd treatment, the gills, mantle, foot, visceral mass and digestive gland tissues were collected for analysis. We found that, in the controls, Cd distributed in all tissues in the concentration order of gills>mantle>foot>visceral mass>digestive gland. Upon Cd treatment, Cd concentration significantly increased in all tissues. The highest Cd accumulation was found in the digestive gland, which was 0.142 mg g-1 (P<0.05). MT levels in the gills and mantle of the mussels increased significantly (P<0.05), which were in positive correlation with Cd accumulation in the tissues (P<0.05). In conclusion, our results demonstrated a correlation between Cd accumulation and MT up-regulation in gills and mantle of the mussels after Cd treatment. It is suggested that the protein level of MT in gills and mantle of Anodonta woodiana is a good biomarker for Cd contamination.

Effects of food limitation on 9 metal concentrations in liver and polycyclic aromatic hydrocarbon metabolites in bile of juvenile turbot (Scophthalmus maximus) previously exposed to contaminated sediments

A 2-step experimental design was employed in the present study on juvenile turbot (Scophthalmus maximus): 1) juveniles were exposed for 26 d to 2 contaminated sediments and a reference one, and 2) they were transferred in clean seawater with clean sediment for 35 d, feeding fish once a day, twice a week, or once a week. Fish exposed to contaminated sediments presented a significant increase of hepatic Cd, Cu, and Pb concentrations compared with the reference condition after the 26-d exposure. Higher fluorescence signals of polycyclic aromatic hydrocarbon (PAH) metabolites were found in bile from turbot exposed to contaminated sediments for 26 d compared with reference. These signals returned to values similar to reference fish after depuration whatever the food quantity. The metal bioaccumulation of Cd, Cu, and Pb was no longer observed after 35-d depuration with once-a-day feeding but was still found with restricted feeding conditions. Results on reference fish also showed significantly higher concentrations of most metals analyzed in fish fed twice a week and once a week compared with fish fed once a day. These results could be related to a decrease of fish hepatosomatic index with food limitation and, thus, a dilution effect on metal concentrations. The present study clearly demonstrates that changes in feeding status have significant effects on metal concentrations in fish and no observed effect on PAH metabolites.