Health status assessment through an integrative biomarker approach in mussels of different ages with a different history of exposure to the Prestige oil spill

Microplastics in marine mussels, biological effects and human risk of intake: A case study in a multi-stressor environment

This study documented seasonal levels of microplastics (MPs) and biomarkers (condition index, neurotoxicity, energy, oxidative stress) in mussels (Mytilus galloprovincialis), and water physico-chemical parameters in the Douro estuary (NE Atlantic coast), and estimated the human risk of MP intake (HRI) through mussels. Mussel stress was determined through the Integrated Biomarker Response (IBR). HRI was estimated from mussel MP concentrations and consumer habits. MPs were mainly micro-fibres (72 %) with varied chemical composition. Seasonal MP means (±SEM) in mussels ranged from 0.111 ± 0.044 (spring) to 0.312 ± 0.092 MPs/g (summer). Seasonal variations of mussel stress (IBR: 1.4 spring to 9.7 summer) and MP concentrations were not related. MeO-BDEs, PBDEs, temperature, salinity and other factors likely contributed to mussel stress variation. HRI ranged from 2438 to 2650 MPs/year. Compared to the literature, MP contamination in mussels is low, as well as the human risk of MP intake through their consumption.

Variability and distribution of parasites, pathologies and their effect on wild mussels (Mytilus sp) in different environments along a wide latitudinal span in the Northern Atlantic and Arctic Oceans

Histopathological examination in mussels can provide useful information for the diagnosis of ecosystem health status. The distribution of parasites in mussels can be conditioned by several environmental factors, including mussels collecting sites or the presence/absence of other species necessary to complete the complex life cycle of certain parasites. Thus, these variables could not only govern the parasitic burden of mussels but also the presence of pathologies associated to parasitism. The aim of this study was to identify the histopathological alterations which could be indicative of a health status distress along a wide latitudinal span in the Northern Atlantic and Arctic Oceans in mussels of two size-classes sampled in clean and impacted sites. A latitudinal gradient is clearly observed in gamete developmental stages as northern and southern mussels presented different conditions at the same period. Furthermore, mussels of the same size in different latitudes presented differences in the reproductive cycle and the appearance of related pathologies, which probably meant the age of individuals was different. In addition, specific parasitic profiles ruled by latitudinal conditions and the settlement of mussels in the shore (horizontal/vertical) have been demonstrated to be significantly influential in the health condition of mussels. Furthermore, the present work provides the first histological description of Gymnophallus cf. bursicola parasite causing a considerable host response in Tromsø and Iceland plus the report of grave histopathological status that included high prevalence of granulocytomas in Scotland and Germany.

Differences in chemical contaminants bioaccumulation and ecotoxicology biomarkers in Mytilus edulis and Mytilus galloprovincialis and their hybrids

The Mytilus mussels are spread all over the world and many related species coexist in several areas and can produce hybrid offspring. Mussels have been used for decades in national and international programs to monitor chemical contamination in the environment. Differences in bioaccumulation and biotransformation abilities between species and their hybrids should be evaluated to assess the comparability of the results obtained within the international biomonitoring programs. The objective of this study was to characterize bioaccumulation abilities and biomarker responses in Mytilus edulis, Mytilus galloprovincialis and their hybrids via an in situ transplantation experimentation on their progenies. Four mussel groups (M. edulis, M. galloprovincialis and two hybrids batches) issued from genetically characterized parents were transplanted for one year in Charente Maritime (France) to ensure their exposure to identical sources of contamination. The bioaccumulation of several families of contaminants (trace metals, polycyclic aromatic hydrocarbons, polybrominated diphenyl ethers, polychlorinated biphenyls), the response of several biomarkers (DNA strand breaks level, lysosomal membrane stability, metallothionein content, acetylcholine esterase activity) and some physiological parameters (growth, mortality, gonadal development), were analyzed. Differences were observed between species, however they were contaminant-specific. Variations in contaminants levels were observed between progenies, with higher levels of Cu, PBDE, PCB in M. edulis, and higher levels of Cd, Hg, Zn in M galloprovincialis. This study demonstrated that variations in contaminant bioaccumulation and different biomarker responses exist between Mytilus species in the field. Data on species or the presence of hybrid individuals (or introgression) is an important additional parameter to add to biomonitoring programs databases.

Contrasting reproductive health of female clams Megapitaria squalida from two nearby metal-polluted sites in the Gulf of California: Potential effects of copper, lead, and cobalt

We studied the effects of chronic exposure to metals on energy reserves and reproduction in the clam Megapitaria squalida in two nearby populations exposed to different levels of pollution from mining operations in the Gulf of California, Mexico. Female M. squalida from San Lucas beach had good reproductive health status, whereas Santa Rosalia specimens consistently showed low energy reserves, massive oocyte resorption throughout the year, high frequencies of undifferentiated individuals, low proportions of ripe and spawning organisms, smaller and fewer oocytes per follicle, and significantly lower follicular areas. Ovarian levels of Co, Cu, Pb, Mn, and Zn were consistently higher in clams from Santa Rosalia. The poor reproductive health of clams inhabiting this site may be attributed to their long-term exposure to high Co, Cu, and Pb concentrations, as these have been shown to cause toxicity and reproductive impairments in other marine organisms.

Sex and sex-related differences in gamete development progression impinge on biomarker responsiveness in sentinel mussels

In marine pollution monitoring, the biomarkers recorded in sentinel organisms are influenced by natural confounding factors that may jeopardise their interpretation. Among these confounding factors, little is known about the influence of sex along the annual reproductive cycle. The present investigation aims at contributing to understand how sex and sex-related differences in gamete development progression impinge on biomarker baseline values and on biomarker responsiveness to pollution in sentinel mussels. Mussels (Mytilus galloprovincialis) were collected from a relatively clean locality and from a chronically polluted site in the Basque Coast (Bay of Biscay) in January, April, August and November. Sex and gametogenesis stages were determined for each mussel. Tissue concentration of metals and PAHs was analysed. A battery of biomarkers was investigated: cytochrome c oxidase, pyruvate kinase and phosphoenolpyruvate carboxykinase enzyme activities; levels of protein carbonyls, malondialdehyde and 4-hydroxy-2-nonenal; lysosomal enlargement and membrane stability; intracellular neutral lipid accumulation; cell type composition and thinning of the digestive gland epithelium; and survival-in-air. Sex- and reproductive stage-related differences were found in bioaccumulation and in the values and responsiveness of most of the biomarkers. However, the patterns of sex-related differences were not consistent across all biomarkers. The differences in the biomarker responses between females and males also depended on the season, reflecting the progression of the gametogenesis cycle. Thus, selecting mussels of one specific sex does not seem to be a crucial requisite to carry out biomarker-based monitoring; yet, it is highly recommended to identify sex condition and gamete developmental stage of each mussel to test for the potentially confounding effects of sex, reproductive status and sex-related variability along the reproductive cycle.

Organotropism and biomarker response in oyster Crassostrea gigas exposed to platinum in seawater

Platinum (Pt) is a technology critical element (TCE) for which biogeochemical cycles are still poorly understood. This lack of knowledge includes Pt effects on marine organisms, which proved to be able to bioconcentrate this trace element. Oysters Crassostrea gigas were exposed to stable Pt isotope spiked daily in seawater for 35 days. Seawater was renewed daily and spiked (with Pt(IV)) to three nominal Pt concentrations (50, 100, and 10,000 ng L^-1) for two replicate series. Organotropism study revealed that gills, and to a lesser extent mantle, are the key organs regarding Pt accumulation, although a time- and concentration-dependent linear increase in Pt levels occurred in all the organs investigated (i.e., digestive gland, gonads, gills, mantle, and muscle). In oysters exposed to Pt concentrations of 10,000 ng L^-1, significant biomarker impairments occurred, especially at cellular levels. They reflect altered lipofuscin and neutral lipid contents, as well as intralysosomal metal accumulation. These observations were attributed to activation of excretion/detoxification mechanisms, including Pt elimination through feces and clearly support the importance of the digestive gland in the response to direct Pt exposure. Despite relatively constant condition index, the integrative biological response (IBR) index suggests a generally decreasing health status of oysters.

Multiple-biomarker approach in the assessment of the health status of a novel sentinel mussel Brachidontes rodriguezii in a harbor area

The objective of this study is to analyze whether a combination of biomarkers at different levels of biological complexity could be used to assess the health status of a population of Brachidontes rodriguezii associated to a harbor area in Mar del Plata, Argentina. A battery of biomarkers of general stress was measured in mussels collected from impacted and non-impacted areas. This included: condition index; shell analysis; histopathological alterations; atrophy and integrity of the digestive gland tissue; changes in cell type composition of the digestive gland, and glycogen accumulation. The studied biomarkers were integrated into the Integrative Biological Response (IBR/n) index. Overall, the IBR/n indicated a higher level of stress in mussels located in the harbor area. Thus, this biomarker index is a sensitive analytical tool that could be used to classify the ecotoxicological risk in coastal sites.

Multibiomarker biomonitoring approach using three bivalve species in the Ebro Delta (Catalonia, Spain)

Bivalves have proved to be useful bioindicators for environmental pollution. In the present study, mussels (Mytilus galloprovincialis), cockles (Cerastoderma edule), and razor shells (Solen marginatus) were collected in the Ebro Delta, an extensive area devoted to rice farming and affected by pesticide pollution, from April to July, the heaviest rice field treatment period. Possible effects of pollution were assessed through biochemical markers (carboxylesterase (CE), antioxidant and neurotoxicity-related enzymes, and lipid peroxidation levels). Data on environmental variables, bivalve reproductive condition, and presence of organic pollutants, marine phycotoxins, pathogens, or histopathological conditions in bivalve's tissues were also evaluated. Although the bioaccumulated pesticides did not explain the patterns observed for biochemical responses, the obtained results point to an effect of environmental pesticide pollution on enzymatic markers, with a prominent contribution of CE to such changes. Mussels and razor shells provided a more sensitive biochemical response to pollution than cockles. Environmental variables, bivalve reproductive condition, and marine phycotoxins did not seem to have a relevant effect on the biomarkers assessed.

Assessing the health status of farmed mussels (Mytilus galloprovincialis) through histological, microbiological and biomarker analyses

The Gulf of La Spezia (northern Tyrrhenian Sea, Italy) is a commercially important area both as a shipping port and for mussel farming. Recently, there has been increased concern over environmental disturbances caused by anthropogenic activities such as ship traffic and dredging and the effects they have on the health of farmed mussels. This paper reports the results of microbiological and histological analyses, as well as of measurement of several biomarkers which were performed to assess the health status of mussels (Mytilus galloprovincialis) from four rearing sites in the Gulf of La Spezia. Mussels were collected between October 2015 and September 2016 and histological analyses (including gonadal maturation stage), as well as the presence of pathogenic bacteria (Vibrio splendidus clade, V. aestuarianus and V. harveyi), viruses (Herpes virus and ostreid Herpes virus 1) and protozoa (Marteilia spp., in the summer season only) were carried out on a monthly basis. Conversely, biomarker responses in haemocyte/haemolymph (total haemocyte count, haemocyte diameter and volume, lysozyme and lactate dehydrogenase activities in cell-free haemolymph, and micronuclei frequency) and in gills and digestive gland (cortisol-like steroids and lipid peroxidation levels), were evaluated bimonthly. Microbiological data indicated that mussels contain a reservoir of potentially pathogenic bacteria, viruses and protozoa that in certain environmental conditions may cause a weakening of the immune system of animals leading to mortality episodes. The percentage of parasites detected in the mussels was generally low (9.6% for Steinhausia mytilovum, that is 17 samples out of 177 examined females; 3.4% for Proctoeces maculatus; 0.9% for Mytilicola intestinalis and 2% for ciliated protozoa), while symbiont loads were higher (31% for Eugymnanthea inquilina and Urastoma cyprinae). Interestingly, a previously undescribed haplosporidian was detected in a single mussel sample (0.2%) and was confirmed by in situ hybridization. Cells morphologically similar to Perkinsus sp. trophozoites were observed in 0.7% of the mussels analysed; however, infection with Perkinsus spp. could neither be confirmed by ISH nor by PCR. Different pathological aspects, such as host defence responses and regressive/progressive changes were detected in the gills, digestive glands, gonads and mantle. Only one single case of disseminated neoplasia (0.2%) was observed. As for the biomarker evaluation, the MANOVA analysis revealed the statistically significant effect that the variable "sampling site" had on the biological parameter measured, thus suggesting that the multibiomarker approach was able to differentiate the rearing sites.

Mortality and histopathological effects in harbour-transplanted snails with different exposure histories

Contaminants are important stressors in the aquatic environment and may exert selective pressures on organisms. We hypothesized that snails originating from a metal-contaminated habitat (B) would have increased tolerance to harbour contaminants (e.g. metals from antifouling paints), compared to snails originating from a relatively clean habitat (A). We assessed tolerance to metals in terms of survival and histopathological alterations after 2, 4 and 8 weeks of in situ exposure in three Baltic Sea boat harbours and three reference sites. We also hypothesized that any potential tolerance to contaminants would be associated with differences in genetic diversity between the two snail populations (evaluated as mitochondrial cytochrome c oxidase subunit I, COI). The results show that snails from population A survived to a higher extent compared to population B, possibly indicating either a lack of adaptation to metals in snails B or impaired health condition due to contaminant pre-exposure or a higher resilience of snails A. Moreover, the genetic diversity of COI was low within each population and did not differ between populations. In general, 83% of all the types of histopathological alterations (e.g. lysis and necrosis of gonads and digestive gland or granulocytoma and phagocytosis in the storage tissue, among others) had a higher probability of occurrence among harbour-exposed snails compared to reference-exposed snails, regardless of snail population origin. The only significant difference in histological effects between the two populations was in the frequency of parasite infestations and shell fouling, both being larger for population A than B. Interestingly, the rate of parasite infestations was higher for males than females from population A, whereas no sexual dichotomy was observed for population B. Our results show that exposure to harbour contaminants causes both lethal and sublethal toxicity to snails, and the association between many of the toxic responses and metals substantiates that antifouling substances contribute to the observed effects, although there is a large proportion of variation in our data that remains unexplained.

Assessment of the effects of Cu and Ag in oysters Crassostrea gigas (Thunberg, 1793) using a battery of cell and tissue level biomarkers

Oysters are considered sentinel organisms in environmental water quality monitoring programs in which cell and tissue level biomarkers are reliable tools. Copper (Cu) and silver (Ag) are present in relatively high concentrations in several estuaries, potentially affecting environmental and human health. Crassostrea gigas oysters were exposed during 28 days to a range of environmentally relevant concentrations of Cu and Ag alone or in mixture. Effects were studied through cell and tissue level biomarkers approach. Results indicated: changes in the Condition Index (CI), altered digestive gland epithelium and presence of histopathological alterations in the gonad and digestive gland of exposed oysters. A time-dependent increase in lipofuscin contents in exposed oysters and an increase in intralysosomal metal accumulation in digestive cells through the experiment were also recorded. The Integrative Biological Response (IBR) Index showed that even at low exposure levels, Ag and Cu can produce alterations on oysters' health status.

Is there a direct relationship between stress biomarkers in oysters and the amount of metals in the sediments where they inhabit?

The effects exerted by metals in oysters are still a matter of debate and require more detailed studies. In this work we have investigated whether the health status of oysters are affected by the amount of metals present in the sediments of their habitat. Sediments and oysters were collected in the tidal part of the estuary of the Oka River (Basque Country), representative of other mesotidal, well mixed and short estuaries of the European Atlantic coast. The concentrations of 14 elements were determined in all the samples. Several biomarkers were also measured in the soft tissues of oysters. According to the concentrations found, the sediments were classified as non-toxic or slightly toxic. In good agreement, the histological alterations observed in oysters were not severe. Interestingly, in those sampling sites where the sediments showed relatively high metal concentrations, the metallic content in oysters was lower, and vice versa.

Seasonal and size-related variation of subcellular biomarkers in quagga mussels (Dreissena bugensis) inhabiting sites affected by moderate contamination with complex mixtures of pollutants

The size-related differences in subcellular biomarker responses were assessed in Dreissena bugensis mussels inhabiting harbours moderately affected by pollution with complex mixtures of heavy metals and polycyclic aromatic hydrocarbons (PAHs). Adult D. bugensis samples were collected from three harbours of Lake Balaton (Hungary) characterized by moderate shipping activity, and as reference site, from a highly protected remote area of the lake. Biomarkers of exposure (metallothioneins (MTs), ethoxyresorufin-o-deethylase (EROD)), oxidative stress (lipid peroxidation (LPO), DNA strand breaks (DNAsb)) and possible endocrine disruption (vitellogenin-like proteins (VTG)) were analysed in whole-tissue homogenates of differently sized groups of mussels in relation to environmental parameters and priority pollutants (heavy metals and polycyclic aromatic hydrocarbons). Integrated biomarker response (IBR) indices were calculated for biomarker responses gained through in situ measurements to signalize critical sites and to better distinguish natural tendencies from biological effects of contaminants. Biomarker responses showed close positive correlation in case of MT, EROD, LPO, and DNAsb and negative correlation with VTG levels with mussel shell length in autumn, when higher levels of biomarkers appeared, possibly due to natural lifecycle changes of animals.

Oxidative status assessment of the endemic bivalve Pinna nobilis affected by the oil spill from the sinking of the Don Pedro

Several biomarkers were determined to evaluate the effects of the Don Pedro spillage on the digestive gland of the fan mussel Pinna nobilis (Linnaeus, 1758). Two areas in the southeast of Ibiza Island (Western Mediterranean) were selected; one affected by the oil spill (Talamanca) and one did not affected (Espardell). Mussels were sampled one, six and twelve months after the accident. PAH levels were elevated in P. nobilis from the affected area one month after the accident and, although they were decreasing gradually, they were always higher than in the control area. An increase in enzyme activities, reduced glutathione and lipid peroxidation were evidenced one month after the spillage, with no changes in acetylcholinesterase. All biomarkers progressively returned to basal levels one year after the oil spill. In conclusion, the Don Pedro oil spill induced an acute situation of oxidative stress on P. nobilis that were recovered twelve months later.

Histopathological baseline levels and confounding factors in common sole (Solea solea) for marine environmental risk assessment

Liver and gonad histopathology, biometric parameters and hepatic metal bioaccumulation were assessed monthly over a one-year period in common soles from the Basque continental shelf, in order to determine baseline levels and confounding factors within biomonitoring studies. Biometric parameters and hepatic metal bioaccumulation varied according to season and gender. Accordingly, hepatic histopathological traits presented seasonal variations related to the reproductive cycle. However, the hepatic histopathological index showed that seasonality and gender were not significant confounding factors. Conversely, the gonad histopathological index was modulated by season and gender. As for organ comparison, the liver endured more severe histopathological damage than the gonad. In brief, the sampling period and gender may not affect the estimation of hepatic histopathological indices for biomonitoring purposes. Nonetheless, due to different sensitivities to environmental 'noise' variables, the sampling period and gender differentiation should be thoroughly considered for the assessment of gonad histopathology, biometrics and metal bioaccumulation.

Habitat pollution and thermal regime modify molecular stress responses to elevated temperature in freshwater mussels (Anodonta anatina: Unionidae)

Elevated temperature and pollution are common stressors in freshwater ecosystems. We study cellular stress response to acute warming in Anodonta anatina (Unionidae) from sites with different thermal regimes and pollution levels: a pristine area and an agriculturally polluted site with normal temperature regimes (F and A, respectively) and a polluted site with elevated temperature (N) from the cooling pond of an electrical power plant. Animals were exposed to different temperatures for 14 days and stress response markers were measured in gills, digestive gland and hemocytes. Mussels from site N and A had elevated background levels of lactate dehydrogenase activity indicating higher reliance on anaerobic metabolism for ATP production and/or redox maintenance. Exposure to 25°C and 30°C induced oxidative stress (indicated by elevated levels of lipid peroxidation products) in digestive gland and gills of mussels from A and F sites, while in mussels from N sites elevated oxidative stress was only apparent at 30°C. Temperature-induced changes in levels of antioxidants (superoxide dismutase, metallothioneins and glutathione) were tissue- and population-specific. Acute warming led to destabilization of lysosomal membranes and increased frequencies of nuclear lesions in mussels from F and A sites but not in their counterparts from N site. Elevated temperature led to an increase in the frequency of micronuclei in hemocytes in mussels from F and A sites at 25°C and 30°C and in mussels from N site at 30°C. The mussels from N site also demonstrated better survival at elevated temperature (30°C) than their counterparts from the F and A sites. Taken together, these data indicate that long-term acclimation and/or adaptation of A. anatina to elevated temperatures result in increased thermotolerance and alleviate stress response to moderate temperature rise. In contrast, extreme warming (30°C) is harmful to mussels from all populations indicating limit to this induced thermotolerance.