The detection of pollutant impact in marine environments: condition index, oxidative DNA damage, and their associations with metal bioaccumulation in the Sydney rock oyster Saccostrea commercialis

Exposure to multiple elements reduces the health of Saccostrea glomerata: An assessment of the Richmond River estuary, NSW, Australia

This study investigated relationships between Sydney Rock Oyster (SRO) health and element concentrations in sediments and oysters from the Richmond River estuary. Six sites were sampled between November 2019 and May 2020. Multivariate permutational analysis of variance was used to compare oyster health parameters and element concentrations between sites, wet and dry conditions, and in oyster and sediment samples. Statistical analysis revealed significant spatial differences in oyster mortality, condition index, and size. Metal concentrations in oyster flesh significantly differed from metals in sediments. Most metals in sediments were below guideline values, except for Ni at some sites. Mortality, condition index, and weight correlated negatively with individual elements in oyster flesh (P, Zn, Mg, Al, Ni). BEST statistical models included various combinations of metals in sediment and flesh. This study highlights that spatial differences in SRO health tend to be related to site-specific metal compositions in sediment and oysters.

Trophic transfer of copper decreases the condition index in Crassostrea gigas spat in concomitance with a change in the microalgal fatty acid profile and enhanced oyster energy demand

Due to new usages and sources, copper (Cu) concentrations are increasing in the Arcachon Basin, an important shellfish production area in France. In the present paper, the trophic transfer of Cu was studied between a microalga, Tetraselmis suecica, and Crassostrea gigas (Pacific oyster) spat. An experimental approach was developed to assess Cu exposure, transfer and toxicity on both phytoplankton and spat. Exposure of microalgal cultures to Cu for 7-8 days (3.1 ± 0.1, 15.7 ± 0.2 and 50.4 ± 1.0 μg Cu·L^-1 for the control, Cu15 and Cu50 conditions, respectively) led to concentrations in microalgae (28.3 ± 0.9 and 110.7 ± 11.9 mg Cu·kg dry weight^-1 for Cu15 and Cu50, respectively) close to those measured in the field. Despite Cu accumulation, the physiology of the microalgae remained poorly affected. Exposed cultures could only be discriminated from controls by a higher relative content in intracellular reactive oxygen species, and a lower relative content in lipids together with a reduced metabolic activity. By contrast, the fatty acid profile of microalgae was modified, with a particularly relevant lower content of the essential polyunsaturated fatty acid 22:6n-3 (docosahexaenoic acid [DHA]). Following 21 days of spat feeding with Cu15 and Cu50 microalgal cultures, trophic transfer of Cu was observed with a high initial Cu concentration in spat tissues. No effect was observed on oxidative stress endpoints. Cu exposure was responsible for a decrease in the spat condition index, an outcome that could be related to an insufficient DHA supply and extra energy demand as suggested by the overexpression of genes involved in energy metabolism, ATP synthesis and glycogen catabolism.

Oxidative stress induction by the invasive sponge Paraleucilla magna growing on Peyssonnelia squamaria algae

The introduction of invasive species can lead to significant adverse effects on the colonized areas. The aim of the present research was to determine if the invasive behavior of Paraleucilla magna could induce the activation of the antioxidant defences in the native red algae, Peyssonnelia squamaria. Individuals of isolated P. squamaria and individuals epiphytized by P. magna, both growing on rocky bottoms, were collected. The activity of the antioxidant enzymes - catalase, superoxide dismutase, glutathione peroxidase and glutathione reductase - and the levels of the malondialdehyde were significantly higher in the algae of the epiphytic group compared to the control group, while the detoxifying enzyme glutathione S-transferase did not show significant differences. The levels of reduced glutathione and total polyphenols were higher in the algae affected by the sponge. In conclusion, the arrival of the species P. magna induces an adaptative antioxidant response in P. squamaria determined by the use of biomarkers.

Trace metals in oysters: molecular and cellular mechanisms and ecotoxicological impacts

Oysters are important benthic bivalves in coastal and estuarine environments. They are widely farmed due to their rapid growth and taste; they are also widely applied in environmental monitoring of coastal pollution due to their accumulation of contaminants. Most importantly, oysters are among the few marine organisms that are considered to be hyper-accumulators of many toxic metals, such as cadmium, copper and zinc. As such, there is a tremendous call to study the interactions between metals and oysters, especially due to the increasing metal pollution in many coastal and estuarine waters. Over the past decades, many studies have focused on metal accumulation in oysters as well as the ecotoxicological effects of metals on oysters. In this review, we summarize the recent progress in our understanding of the molecular and cellular mechanisms of metal accumulation, sequestration and toxicity in oysters. Applications of modern technologies such as omics and nanoscale imaging have added significantly to our knowledge of metal biology in oysters. Variations between different metals also demonstrate the diversity of the interactions between oysters and metals. Despite this recent progress, however, there is a need for further study of the molecular mechanisms of metal uptake and toxicity as well as the joint effects of metal mixtures on oyster populations. Oysters have higher numbers of stress responsive genes than most animals, which may have been induced by gene duplication during the evolution of their intertidal environmental adaptations. The divergent expression of stress responsive genes may explain the different tolerances for metals among different species. These fundamental studies may eventually provide promising solutions for reducing toxic metal concentrations in oysters for safe consumption by humans. To conclude, the complexity of life history and metal chemistry of oysters coupled with emerging pollution and application of modern techniques represents an important and exciting research area in modern ecotoxicology.

Effects of increasing temperatures on biomarker responses and accumulation of hazardous substances in rope mussels (Mytilus galloprovincialis) from Bizerte lagoon

This study examined the influence of increasing temperatures in spring and summer on biochemical biomarkers in Mytilus galloprovincialis mussels sampled from Bizerte lagoon (northern Tunisia). Spatial and seasonal variations in a battery of seven biomarkers were analyzed in relation to environmental parameters (temperature, salinity, and pH), physiological status (condition and gonad indexes), stress on stress (SoS), and chemical contaminant levels (heavy metals, polycyclic aromatic hydrocarbons (PAHs), and PCBs) in digestive glands. Integrated biological response (IBR) was calculated using seven biomarkers (acetylcholinesterase (AChE), benzo[a]pyrene hydroxylase (BPH), multixenobiotic resistance (MXR), glutathione S-transferase (GST), catalase (CAT), malondialdehyde (MDA), and metallothioneins (MT). Seasonal variations in biological response were determined during a critical period between spring and summer at two sites, where chemical contamination varies by a factor of 2 for heavy metals and a factor 2.5 for PAHs. The analysis of a battery of biomarkers was combined with the measurement of physiological parameters at both sites, in order to quantify a maximum range of metabolic regulation with a temperature increase of 11 °C between May and August. According to our results, the MT, MDA, CAT, and AChE biomarkers showed the highest amplitude during the 11 °C rise, while the BPH, GST, and MXR biomarkers showed the lowest amplitude. Metabolic amplitude measured with the IBR at Menzel Abdelrahmen-the most severely contaminated station-revealed the highest metabolic stress in Bizerte lagoon in August, when temperatures were highest 29.1 °C. This high metabolic rate was quantified for each biomarker in the North African lagoon area and confirmed in August, when the highest IBR index values were obtained at the least contaminated site 2 (IBR = 9.6) and the most contaminated site 1 (IBR = 19.6). The combined effects of chemical contamination and increased salinity and temperatures in summer appear to induce a highest metabolic adaptation response and can therefore be used to determine thresholds of effectiveness and facilitate the interpretation of monitoring biomarkers. This approach, applied during substantial temperature increases at two sites with differing chemical contamination, is a first step toward determining an environmental assessment criteria (EAC) threshold in a North African lagoon.

Combined use of native and caged mussels to assess biological effects of pollution through the integrative biomarker approach

Native and caged mussels were used in combination for the monitoring of pollution biological effects through an integrative biomarker approach. Mussels (Mytilus galloprovincialis) were deployed in cages in two well-known model localities with different pollution levels in the Basque coast. After 3 weeks caged and native mussels were collected from each site and a suite of effect and exposure biomarkers (from molecular/cellular to organism level) was applied and chemical contaminants (metals, PAHs, PCBs, phthalates and nonylphenol ethoxylates) were analytically determined. Integrative biomarker indices and pollutant indices of tissues were calculated. Several biomarkers used herein responded similarly in native and caged mussels, whereas others exhibited significant differences. Overall, biomarkers in-a-suite depicted site-specific profiles useful for the diagnostic of mussel health status and therefore for ecosystem health assessment in marine pollution biomonitoring. On the other hand, biomarkers and bioaccumulation exhibited different response times, which was especially evident when comparing biomarker and pollutant indices of tissues. The suite of biomarkers was more sensitive after caging (short-term response), whereas tissue pollutant concentrations were more sensitive in native mussels (long-term response). Thus, the combination of native and caged mussels is highly recommended to monitor biological effects of pollution in mussels through the integrative biomarker approach, especially in chronically polluted sites.

Impact of remobilized contaminants in Mytilus edulis during dredging operations in a harbour area: bioaccumulation and biomarker responses

Dredging operations in harbours are recurrent to maintain accessibility and navigational depths. One of the main environmental risks of these operations is the remobilization of contaminants trapped in the sediments, rendering them more bioavailable to the biota. However, regulatory policies regarding the contamination risk of dredging chiefly apply to the disposal of dredged materials rather than the direct impact of the procedure itself. In order to assess the ecotoxicological risk of harbour dredging operations in a polluted estuary (the Tagus, W Portugal), the present study compared bioaccumulation and biomarker responses in field-deployed mussels before and after the beginning of operations, complemented by sediment characterization and risk analysis based on standardized sediment quality guidelines. The results revealed a very significant increase in genotoxicity and oxidative stress from the beginning of dredging onwards, which was accompanied by increased bioaccumulation of toxicants, especially polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). Overall, the results indicate the importance of surveying the direct impacts of these procedures on local contamination, especially considering these sediments had been previously classified as "trace contaminated", according to normative guidelines, and therefore safe for disposal. This study shows the importance of obtaining both chemical and biological data in standard monitoring procedures and that the remobilization of contaminants by dredging operations may be grossly underestimated, which calls for caution when assessing the impact of these activities even in low to moderately polluted areas.

Dietary carotenoids regulate astaxanthin content of copepods and modulate their susceptibility to UV light and copper toxicity

High irradiation and the presence of xenobiotics favor the formation of reactive oxygen species in marine environments. Organisms have developed antioxidant defenses, including the accumulation of carotenoids that must be obtained from the diet. Astaxanthin is the main carotenoid in marine crustaceans where, among other functions, it scavenges free radicals thus protecting cell compounds against oxidation. Four diets with different carotenoid composition were used to culture the meiobenthic copepod Amphiascoides atopus to assess how its astaxanthin content modulates the response to prooxidant stressors. A. atopus had the highest astaxanthin content when the carotenoid was supplied as astaxanthin esters (i.e., Haematococcus meal). Exposure to short wavelength UV light elicited a 77% to 92% decrease of the astaxanthin content of the copepod depending on the culture diet. The LC(50) values of A. atopus exposed to copper were directly related to the initial astaxanthin content. The accumulation of carotenoids may ascribe competitive advantages to certain species in areas subjected to pollution events by attenuating the detrimental effects of metals on survival, and possibly development and fecundity. Conversely, the loss of certain dietary items rich in carotenoids may be responsible for the amplification of the effects of metal exposure in consumers.

Oxidative stress in rainbow trout (Oncorhynchus mykiss) exposed to sewage treatment plant effluent

Effluents from sewage treatment plants (STPs) can be regarded as "hot spots" of discharge releasing large amounts of chemicals into the aquatic environment. Many of these compounds are toxic to organisms due to their ability to form reactive oxygen species (ROS) and cause oxidative stress. In order to investigate if STP effluents contain compounds that may cause oxidative stress, rainbow trout (Oncorhynchus mykiss) were exposed to effluent from a Swedish STP at different dilutions in a flow-through system. Antioxidant enzymes analyzed were glutathione reductase (GR), catalase (CAT) and DT-diaphorase (DTD). Catalytic activities of CYP1A (EROD) and the conjugating enzyme glutathione-S transferase (GST) were also analyzed. Results indicate that the effluent contains prooxidants since the activities of the antioxidant enzymes GR, CAT, and DTD were all elevated after 5 days of exposure. A prolonged exposure resulted in an inhibition of DT diaphorse activity, suggesting a depleted cellular ROS defence. EROD activities increased in a dose- and time-dependent manner, which suggests the presence of aryl hydrocarbon receptor (AHR) ligands such as polycyclic aromatic hydrocarbons (PAHs) in the effluent. These results indicate that STPs do not have the capacity to biodegrade harmful chemicals sufficiently to protect the aquatic environment. However, STPs are designed to remove nutrients and not persistent pollutants from the sewage and effort should be made to diminish the amount of chemicals entering the sewage in the first place.

Oxidative stress, evident in antioxidant defences and damage products, in rainbow trout caged outside a sewage treatment plant

Sewage treatment plants (STPs) are common sources of a wide variety of chemicals entering into the aquatic environment. We have investigated the effects of STP effluent on oxidative stress parameters in rainbow trout via measurements of several enzymatic antioxidants as well as the molecular antioxidant glutathione (GSH). In addition, we have measured levels of oxidative damage, i.e. protein carbonyls and lipid peroxides. Our findings indicate that STP effluent does contain prooxidants that affect fish. Oxidative damage was a more consistent indicator of exposure to prooxidants than antioxidant enzymes. Protein carbonyls and lipid peroxides were both elevated (1.3- and 1.8-fold increases, respectively) in fish caged at the STP site compared with reference site as was the amount of oxidized GSH (GSSG), which showed a 3-fold increase. Antioxidant enzymes showed no clear-cut response. Additionally, older pollutants that have been present in down stream sediment for decades had no effects on the parameters measured here.

In-situ microcosms, a tool for assessment of pesticide impacts on oyster spat (Crassostrea gigas)

Effects of the herbicide Basamaïs (bentazon) and the fungicide Opus (epoxiconazole) on oyster spat (Crassostrea gigas) were assessed using in-situ microcosms in a field experiment lasting 13 days. Six-week-old hatchery spat (mean size 1.1 mm), previously collected on PVC plates, was immersed in glass bottles filled with 200 mum filtered seawater. Bottles were maintained underwater at 6 m depth and their water content changed every other day. Growth, measured as shell area index increase, was 126 +/- 4% in the control bottles. While no growth differences were observed between control and individual pesticide treatments at 10 microg l(-1), oysters treated with a mix of 10 microg l(-1) Opus and 10 microg l(-1) Basamaïs showed a 50% growth reduction compared with the control (P < 0.0001), suggesting a synergistic effect of these contaminants. Laboratory controls in microcosms maintained in a water bath with filtered natural light, were not significantly different from in-situ microcosm controls in the field, for organic weight content or growth. This in-situ experiment in microcosms allowed us to conclude that: (1) oyster spat can achieve significant growth in bottles immersed in situ without supplementary food; (2) this microcosm system is reliable and easy to use for environmental toxicity tests with C. gigas spat; (3) such microcosm systems can also be run in a laboratory water bath instead of more technically difficult immersed field experiments; (4) the synergistic effect observed here, at a concentration simulating a peak agricultural runoff event, suggests that the impacts of pesticides could be a real threat for oysters in estuarine areas.

Assessment of environmental pollution at Balearic Islands applying oxidative stress biomarkers in the mussel Mytilus galloprovincialis

The antioxidant enzyme response of the mussel Mytilus galloprovincialis to different degree of pollution was investigated. Antioxidant enzyme activities - catalase (CAT), glutathione peroxidase (GSH-PX), glutathione reductase (GR), superoxide dismutase (SOD) - and malondialdehyde (MDA) concentration were measured in gills and digestive glands of mussels. Mussels from the same origin were transplanted along the Balearic coastal waters in eight stations characterized by a different degree of contamination and human impacts. Antioxidant enzyme activities showed an adaptive response to increase the activities in the more polluted areas. CAT, GR and SOD in gills and CAT and GR in digestive gland presented significant differences between polluted and non-polluted stations. No significant differences were observed in MDA concentration indicating that the antioxidant response is capable to avoid the lipid peroxidation. The use of biomarkers such as CAT and GR in gills and digestive glands of the mussel M. galloprovincialis is a good tool to categorize differences between polluted and non-polluted areas.

Cadmium effects on ros production and DNA damage via adrenergic receptors stimulation: role of Na+/H+ exchanger and PKC

The objective of the present study was to elucidate the events that are involved in reactive oxygen species (ROS) production and DNA damage after adrenergic receptors stimulation by cadmium, in relation to cAMP, protein kinase C (PKC) and Na+/H+ exchanger (NHE). Cadmium (50 microM) caused increased levels of ROS with a concomitant increase in DNA damage in digestive gland of Mytilus galloprovincialis. Either the use of EIPA, a NHE blocker, or calphostin C, the inhibitor of PKC, reduced cadmium effects. Cells treated with alpha1-, alpha2-, beta- and beta1- adrenergic antagonists together with cadmium reversed cadmium alone effects, while the respective adrenergic agonists, phenylephrine and isoprenaline, mimic cadmium effects. Moreover, cadmium caused an increase in the levels of cAMP in digestive gland cells that were reversed after NHE and PKC inhibition as well as in the presence of each type of adrenergic antagonist. The different sensitivity of alpha1-, alpha2-, beta-, beta1- adrenergic receptors on ROS, cAMP production and DNA damage possibly leads to the induction of two signaling pathways that may be interacting or to the presence of a compensatory pathway that acts in concert with the alpha- and beta- adrenergic receptors. In these signaling pathways PKC and NHE play significant role.

DNA strand length and EROD activity in relation to two screening measures of genotoxic exposure in Great Lakes herring gulls

We collected tissues from herring gulls (Larus argentatus) nesting within and outside of the Great Lakes basin. Genotoxin exposure was assessed as fluorescent aromatic compounds (FACs) in bile and SOS Chromotest-inducing activity in muscle extracts. We determined whether these exposures were associated with decreased erythrocyte DNA strand length and/or induction of hepatic ethoxyresorufin-O-deethylase (EROD) activity. FACs were detected in all bile samples. Most muscle extracts produced a positive or marginal SOS response in the presence of S9. SOS induction potentials were strongly associated with dietary trophic level. The median molecular length of DNA isolated from erythrocytes for 14 of 17 adult and 10 of 11 prefledgling collections was reduced compared to the modal class for their respective age group suggesting widespread DNA damage. DNA damage was greatest in gulls from Saginaw Bay, Lake Huron. Median EROD activity in both adults and prefledglings from remote locations was significantly lower than that of gulls from the lower Great Lakes and was not associated with concentrations of benzo[a]pyrene (B[a]P)-like FACs. Our results indicate Great Lakes herring gulls were exposed to genotoxins and Ah-receptor activating agents in biologically significant concentrations in the early 1990s. These agents appear to be persistent bioaccumulative compounds and/or their metabolites.

The catadromous European eel Anguilla anguilla (L.) as a model for freshwater evolutionary ecotoxicology: relationship between heavy metal bioaccumulation, condition and genetic variability

Understanding the effects of pollutants on the genome is of crucial importance to preserve the evolutionary potential of endangered natural populations. The highly vagile European eel (Anguilla anguilla L.) has suffered a dramatic decline in recruitment since two decades, urging for a better understanding of the genetic impact of pollution. Its catadromous life history constitutes a model to assess local selection of pollutants on condition and genetic variability, as juveniles recruit in European rivers without appreciable pollution load or interfering genetic background. Because of its high fat content and local benthic feeding behaviour, the feeding stage is considered extremely prone to the bioaccumulation of pollutants. We studied the relationship between heavy metal bioaccumulation, fitness (condition) and genetic variability in the European eel. The muscle tissues of 78 sub-adult eels, originating from three Belgian river basins (Scheldt, Meuse and Yser), were examined for nine heavy metal pollutants (Hg, Cd, Pb, Cu, Zn, Ni, Cr, As and Se), while in total 123 individuals were genotyped at 12 allozyme and 8 microsatellite loci. A significant negative correlation between heavy metal pollution load and condition was observed, suggesting an impact of pollution on the health of sub-adult eels. In general, we observed a reduced genetic variability in strongly polluted eels, as well as a negative correlation between level of bioaccumulation and allozymatic multi-locus heterozygosity (MLH). Microsatellite genetic variability did not show any pollution related differences, suggesting a differential response at metabolic enzymes and possibly direct overdominance of heterozygous individuals.

Relationship between two oxidative stress biomarkers, malondialdehyde and 8-oxo-7,8-dihydro-2'-deoxyguanosine, in the freshwater bivalve Unio tumidus

This study addresses the question of the relation between cellular and genomic oxidative damages in freshwater bivalves in realistic conditions of exposure in the field. Membrane and genomic oxidative damages were studied by means of lipid peroxidation and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), respectively. Malondialdehyde (MDA) was used as an indicator of lipid peroxidation. The biomarkers were measured in the digestive gland and the gills of mussels (Unio tumidus) after 7 and 21 days of exposure in four ponds of the Moselle Basin, during three field studies conducted in 1999 and 2000. Effects measured at three sites (1R, 3C and 4M) were moderate and lipid peroxidation was slightly enhanced in mussels transferred in these ponds. In contrast, an important degradation was observed at site 2V reflected by a sharp increase in MDA and 8-oxodGuo concentrations in 2000. The biomarker responses agreed with the results of physicochemical analyses that indicated a worsening of water quality at the same site. Globally, a relationship was found between MDA increase and 8-oxodGuo formation, in the digestive gland after 7 days of exposure, and later in the gills (21 days). Responses of the digestive glands and gills to the oxidative parameters appeared correlated only after 21 days of exposure. The biomarkers selected confirmed their sensitivity for appraising the water quality of hydrosystems.

Effects of sewage effluent discharge on the abundance, condition and mortality of hulafish, Trachinops taeniatus (Plesiopidae)

The effects of sewage effluent on the abundance, condition (length and reproduction) and mortality of hulafish Trachinops taeniatus were investigated at multiple outfall and control locations on the central coast of New South Wales, Australia. Underwater visual surveys found consistently fewer T. taeniatus at locations where sewage was discharged compared to control locations. The condition of T. taeniatus was investigated by comparing mean length and reproductive indices of fish from two outfall and two control locations. Fish from the largest outfall location were significantly smaller in comparison with fish from control locations. Gravid female fish from outfall locations had similar gonadosomatic indices but a significantly greater number of eggs and smaller size of eggs in comparison with fish from control locations. Mortality of T. taeniatus was investigated during 2-week, in situ, caging experiments at multiple locations and times and 80% of fish survived, although mortalities of up to 73% per cage were recorded at one sewage outfall. T. taeniatus may be a suitable environmental indicator species of sewage pollution.