Automated measurement of lysosomal structure alterations in oocytes of mussels exposed to petroleum hydrocarbons

Biomarker responsiveness in Norwegian Sea mussels, Mytilus edulis, exposed at low temperatures to aqueous fractions of crude oil alone and combined with dispersant

Biological effects of aqueous fractions of a crude oil, alone or in combination with dispersant, were investigated in mussels, Mytilus edulis, exposed at three temperatures (5, 10 and 15 °C). Polycyclic aromatic hydrocarbons (PAHs) tissue concentrations were determined, together with genotoxicity, oxidative stress and general stress biomarkers and the Integrated Biological Response (IBR) index. The bioaccumulation of individual PAHs varied depending on the exposure temperature, with relevant bioaccumulation of phenantrene and fluoranthene at 5 °C and heavier (e.g. 5-rings) PAHs at 15 °C. The values and response profiles of each particular biomarker varied with exposure time, concentration of the oil aqueous fraction and dispersant addition, as well as with exposure temperature. Indeed, PAH bioaccumulation and biomarker responsiveness exhibited specific recognizable patterns in mussels exposed at low temperatures. Thus, genotoxicity was recorded early and transient at 5 °C and delayed but unremitting at 10-15 °C. Catalase activity presented a temperature-dependent response profile similar to the genotoxicity biomarker; however, glutathione-S-transferase responsiveness was more intricate. Lysosomal membrane stability in digestive cells decreased more markedly at 5 °C than at higher temperatures and the histological appearance of the digestive gland tissue was temperature-specific, which was interpreted as the combined effects of PAH toxicity and cold stress. It can be concluded that the profile and level of the biological effects are definitely different at low temperatures naturally occurring in the Arctic/Subarctic region (e.g. 5 °C) than at higher temperatures closer to the thermal optimum of this species (10-15 °C).

Effects of microplastics alone or with sorbed oil compounds from the water accommodated fraction of a North Sea crude oil on marine mussels (Mytilus galloprovincialis)

Microplastics (MPs) can adsorb persistent organic pollutants such as oil hydrocarbons and may facilitate their transfer to organisms (Trojan horse effect). The aim of this study was to examine the effects of a 21 day dietary exposure to polystyrene MPs of 4.5 μm at 1000 particles/mL, alone and with sorbed oil compounds from the water accommodated fraction (WAF) of a naphthenic North Sea crude oil at two dilutions (25 % and 100 %), on marine mussels. An additional group of mussels was exposed to 25 % WAF for comparison. PAHs were accumulated in mussels exposed to WAF but not in those exposed to MPs with sorbed oil compounds from WAF (MPs-WAF), partly due to the low concentration of PAHs in the studied crude oil. Exposure to MPs or to WAF alone altered the activity of enzymes involved in aerobic (isocitrate dehydrogenase) and biotransformation metabolism (glutathione S-transferase). Prevalence of oocyte atresia and volume density of basophilic cells were higher and absorption efficiency lower in mussels exposed to MPs and to WAF than in controls. After 21 days MPs caused DNA damage (Comet assay) in mussel hemocytes. In conclusion, a Trojan horse effect was not observed but both MPs and oil WAF caused an array of deleterious effects on marine mussels at different levels of biological organization.

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.

Biological responses and toxicopathic effects elicited in Solea senegalensis juveniles by waterborne exposure to benzo[a]pyrene

Polycyclic aromatic hydrocarbons (PAHs) are priority contaminants in coastal and estuarine ecosystems under anthropogenic pressure. Although PAHs tend to accumulate in the sediment, toxicity for benthic flat fish such as soles may be caused by PAHs released from the sediment to the water column. Within this context, the present investigation aims at recognizing toxicopathic effects elicited after waterborne exposure to benzo[a]pyrene B[a]P, a model individual PAH compound, in juvenile Solea senegalensis. Sole juveniles were exposed to various concentrations of waterborne B[a]P for 3 and 7 days. Brain, liver, gills and gonad were the target tissues selected to determine biochemical and lysosomal biomarkers, and histopathology. Biological responses and toxicopathic effects were consistent with B[a]P concentration and exposure time. From day 3, hepatic catalase inhibition indicated potential oxidative effects of B[a]P. At day 7, contaminant exposure produced hepatic glutathione-S-transferase induction at low concentrations and inhibition at higher levels, evidencing a bell-shaped response. A clear gradient in lysosomal membrane destabilisation was observed in relation with B[a]P concentrations. Histopathological lesions were more frequent at day 7 and at higher contaminant levels. It seems that environmentally relevant waterborne concentrations of B[a]P (1000 ng/l) would suffice to cause toxicopathic effects on sole juveniles in relatively short exposure times. In agreement, the Integrative Biological Response index (IBR/n) indicated a dose-dependent decline in health condition upon exposure to B[a]P (IBR/n_HighB[a]P > IBR/n_MidB[a]P > IBR/n_LowB[a]P > IBR/n_DMSO > IBR/n_Control). Overall, changes in antioxidant enzymes activity, lysosomal biomarkers and gill and liver histopathology are responsive early-warning signs of health disturbance in sole juveniles exposed to waterborne PAHs.

Sub-chronic effects of AgNPs and AuNPs on Gammarus fossarum (Crustacea Amphipoda): From molecular to behavioural responses

The aim of the present study was the assessment of the sub-chronic effects of silver (AgNPs) and gold nanoparticles (AuNPs) of 40 nm primary size either stabilised with citrate (CIT) or coated with polyethylene glycol (PEG) on the freshwater invertebrate Gammarus fossarum. Silver nitrate (AgNO₃) was used as a positive control in order to study the contribution of silver ions potentially released from AgNPs on the observed effects. A multibiomarker approach was used to assess the long-term effects of AgNPs and AuNPs 40 nm on molecular, cellular, physiological and behavioural responses of G. fossarum. Specimen of G. fossarum were exposed for 15 days to 0.5 and 5 µgL^-1 of CIT and PEG AgNPs and AuNPs 40 nm in the presence of food. A significant uptake of both Ag and Au was observed in exposed animals but was under the toxic threshold leading to mortality of G. fossarum. Silver nanoparticles (CIT-AgNPs and PEG-AgNPs 40 nm) led to an up-regulation of Na⁺K⁺ATPase gene expression. An up-regulation of Catalse and Chitinase gene expressions due to exposure to PEG-AgNPs 40 nm was also observed. Gold nanoparticles (CIT and PEG-AuNPs 40 nm) led to an increase of CuZnSOD gene expression. Furthermore, both AgNPs and AuNPs led to a more developed digestive lysosomal system indicating a general stress response in G. fossarum. Both AgNPs and AuNPs 40 nm significantly affected locomotor activity of G. fossarum while no effects were observed on haemolymphatic ions and ventilation.

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.

Biological responses and toxicopathic effects elicited in Solea senegalensis juveniles on exposure to contaminated sediments under laboratory conditions

Whole-sediment toxicity assays contribute to elucidating the intricate association between the presence of contaminants in sediments and their toxicopathic effects in benthic fish. In the present study, Solea senegalensis juveniles were exposed under laboratory conditions to contaminated whole-sediments for 7 and 28 days. Sediments were obtained from a low to moderately polluted estuary, a highly polluted harbour and from the mixture of both field-collected sediments. Biometry data were recorded. Liver, brain, gills, and gonads were dissected out and processed to determine markers of oxidative stress, neurotoxicity and lysosomal biomarkers, and histopathology. Analyses of sediment granulometry and chemical profiles indicated different degrees of toxicity and suggested a distinct release of pollutants from each sediment in relation with their physicochemical properties. Interestingly, biological responses were in agreement with contaminant levels reported in source sediments. The most distinct toxicopathic effects were detected upon exposure to the harbour's sediment and particularly on day 28. Overall, enhanced hepatic glutathione-S-transferase activity and lysosomal enlargement were detected in all experimental groups, demonstrating a toxic effect from all sediments whilst catalase inhibition, lysosomal membrane destabilisation, changes in lysosomal content and liver histopathology were most pronounced in soles exposed to the harbour's sediment. The Integrative Biomarker Response index (IBR/n) evidenced that exposure to the three sediments caused an impact of diverse magnitude in sole health (IBR/n_Harbour > IBR/n_Mixture > IBR/n_Estuary). The magnitude of biological responses essentially depended on the presence of contaminants in source sediments, which seemed to be altered by the conditions imposed by whole-sediment toxicity assays.

Current issues confounding the rapid toxicological assessment of oil spills

Oil spills of varying magnitude occur every year, each presenting a unique challenge to the local ecosystem. The complex, changeable nature of oil makes standardised risk assessment difficult. Our review of the state of science regarding oil's unique complexity; biological impact of oil spills and use of rapid assessment tools, including commercial toxicity kits and bioassays, allows us to explore the current issues preventing effective, rapid risk assessment of oils. We found that despite the advantages to monitoring programmes of using well validated standardised tests, which investigate impacts across trophic levels at environmentally relevant concentrations, only a small percentage of the available tests are specialised for use within the marine environment, or validated for the assessment of crude oil toxicity. We discuss the use of rapid tests at low trophic levels in addition to relevant sublethal toxicity assays to allow the characterisation of oil, dispersant and oil and dispersant mixture toxicity. We identify novel, passive dosing techniques as a practical and reproducible means of improving the accuracy and maintenance of nominal concentrations. Future work should explore the possibility of linking this tiered testing system with ecosystem models to allow the prediction and risk assessment of the entire ecosystem.

Food-type may jeopardize biomarker interpretation in mussels used in aquatic toxicological experimentation

To assess the influence of food type on biomarkers, mussels (Mytilus galloprovincialis) were maintained under laboratory conditions and fed using 4 different microalgae diets ad libitum for 1 week: (a) Isochrysis galbana; (b) Tetraselmis chuii; (c) a mixture of I. galbana and T. chuii; and (d) a commercial food (Microalgae Composed Diet, Acuinuga). Different microalgae were shown to present different distribution and fate in the midgut. I. galbana (≈4 μm Ø) readily reached digestive cells to be intracellularly digested. T. chuii (≈10 μm Ø and hardly digestible) was retained in stomach and digestive ducts for long times and extracellularly digested. Based on these findings, it appeared likely that the presence of large amounts of microalgal enzymes and metabolites might interfere with biochemical determinations of mussel's biomarkers and/or that the diet-induced alterations of mussels' digestion could modulate lysosomal and tissue-level biomarkers. To test these hypotheses, a battery of common biochemical, cytological and tissue-level biomarkers were determined in the gills (including activities of pyruvate kinase, phosphoenolpyruvate carboxykinase and cytochrome c oxidase) and the digestive gland of the mussels (including protein, lipid, free glucose and glycogen total content, lysosomal structural changes and membrane stability, intracellular accumulation of neutral lipids and lipofuscins, changes in cell type composition and epithelial thinning, as well as altered tissue integrity). The type of food was concluded to be a major factor influencing biomarkers in short-term experiments though not all the microalgae affected biomarkers and their responsiveness in the same way. T. chuii seemed to alter the nutritional status, oxidative stress and digestion processes, thus interfering with a variety of biomarkers. On the other hand, the massive presence of I. galbana within digestive cells hampered the measurement of cytochemical biomarkers and rendered less reliable the results of biochemical biomarkers (as these could be attributed to both the mussel and the microalgae). Research to optimize dietary food type, composition, regime and rations for toxicological experimentation is urgently needed. Meanwhile, a detailed description of the food type and feeding conditions should be always provided when reporting aquatic toxicological experiments with mussels, as a necessary prerequisite to compare and interpret the biological responses elicited by pollutants.

The influence of short-term experimental fasting on biomarker responsiveness in oil WAF exposed mussels

Mussels are widely used in toxicological experimentation; however, experimental setups are not standardized yet. Although there is evidence of changes in biomarker values during food digestion and depending on the mussel nutritive status, the mode of feeding differs among toxicological experiments. Typically, mussels are fed with different diets in different long-term experiments, while fasting is the most common approach for short-term studies. Consequently, comparisons among experiments and reliable interpretations of biomarker results are often unfeasible. The present investigation aimed at determining the influence of fasting (against feeding with Isochrysis galbana) on biomarkers and their responsiveness in mussels exposed for 96 h to the water accommodated fraction (WAF) of a heavy fuel oil (0%, 6.25%, 12.5% and 25% WAF in sea water). PAH tissue levels in digestive gland and a battery of biomarkers were compared. WAF exposure led to decrease of cytochrome-C-oxidase activity, modulated glutathione-S-transferase activity, augmented lipid peroxidation, inhibited acetyl cholinesterase (AChE) activity, and led to lysosomal enlargement (Vv_LYS and S/V_LYS) and membrane destabilisation, lipofuscin accumulation, and histopathological alterations (Vv_BAS, MLR/MET and CTD ratio) in the digestive gland epithelium; and were integrated as IBR/n (biological response index). Overall, no significant changes were recorded in AChE activity, S/V_LYS and CTD ratio in any experimental treatment, while all the other biomarkers showed significant changes depending on the fasting/feeding condition, the exposure to WAF and/or their interaction. As a result, the integrated biomarker index IBR/n was higher at increasing WAF exposure levels both in fasted and fed mussels albeit the response was more marked in the latter. The response profiles were qualitatively similar between fasted and fed mussels but quantitatively more pronounced in fed mussels, especially upon exposure to the highest concentration (25% WAF). Therefore, it is highly recommended that mussels are also supplied with food during short-term, like during long-term toxicological experiments. This practice would avoid the interference of fasting with biological responses elicited by the tested chemicals and allow for reliable comparison with data obtained in long-term experiments and monitoring programmes.

Effects of dietary Pb and Cd and their combination on lysosomal and tissue-level biomarkers and histopathology in digestive gland of the land snail, Cantareus apertus (Born, 1778)

The present study was aimed at determining cell and tissue-level biomarkers and histopathological alterations in the green garden snail, Cantareus apertus (Born, 1778), exposed to different nominal dietary concentrations of Pb (25, 100 and 2500 mg Pb/kg), Cd (5, 10 and 100 mg Cd/kg) and their combination (25 mg Pb + 5 mg Cd/Kg, 100 mg Pb + 10 mg Cd/kg and 2500 mg Pb + 100 mg Cd/ kg) for 1 and 8 weeks. Lead and Cd exerted histopathological effects on the digestive gland in a dose-dependent manner and related to lysosomal and tissue-level biomarkers. The biological responses observed included digestive cell vacuolisation and numerical atrophy, calcium cell hydropic degeneration, excretory cell hypertrophy, inflammatory responses, blood vessel congestion, and disruption of the blood vessel wall and the interstitial connective tissue. Lysosomal enlargement and transient intracellular accumulation of neutral lipids and lipofuscins were also observed, together with alterations in the cell type composition and thinning of the digestive gland epithelium and with diverticular distortion. This response profile fits well with the biological effects reported after metal exposure in gastropods from other regions, as well as with data obtained in parallel studies dealing with metal bioaccumulation and intralysosomal accumulation, mortality, feeding, growth, oxidative stress and neurotoxicity exerted elicited by Pb, Cd and their mixture in green garden snails under the present experimental conditions. Consequently, C. apertus seems to be a suitable model species for the biomarker-based assessment of the biological effects of Pb and Cd, alone or in combinations, thus providing a challenging opportunity to advance in identifying suitable sentinel species for metal pollution biomonitoring and ecosystem health assessment in soil ecosystems in Northern Africa.

Chronic environmental stress enhances tolerance to seasonal gradual warming in marine mussels

In global climate change scenarios, seawater warming acts in concert with multiple stress sources, which may enhance the susceptibility of marine biota to thermal stress. Here, the responsiveness to seasonal gradual warming was investigated in temperate mussels from a chronically stressed population in comparison with a healthy one. Stressed and healthy mussels were subjected to gradual temperature elevation for 8 days (1°C per day; fall: 16–24°C, winter: 12–20°C, summer: 20–28°C) and kept at elevated temperature for 3 weeks. Healthy mussels experienced thermal stress and entered the time-limited survival period in the fall, became acclimated in winter and exhibited sublethal damage in summer. In stressed mussels, thermal stress and subsequent health deterioration were elicited in the fall but no transition into the critical period of time-limited survival was observed. Stressed mussels did not become acclimated to 20°C in winter, when they experienced low-to-moderate thermal stress, and did not experience sublethal damage at 28°C in summer, showing instead signs of metabolic rate depression. Overall, although the thermal threshold was lowered in chronically stressed mussels, they exhibited enhanced tolerance to seasonal gradual warming, especially in summer. These results challenge current assumptions on the susceptibility of marine biota to the interactive effects of seawater warming and pollution.

Effect of mussel reproductive status on biomarker responses to PAHs: Implications for large-scale monitoring programs

Biomarkers are useful tools to assess biological effects of pollutants and have been extensively used in monitoring programs to determine ecosystem health. In these programs, a wide range of environmental conditions are covered and sometimes, obtained data are difficult to interpret because of natural variables are affecting biomarker responses. Among these variables, musseĺs reproductive status has been considered one of the most changing variables between sites in a monitoring survey. Thus, the main aim of this work was to identify the effect that mussel reproductive status has on biomarker responses. For that purpose, mussels sampled at two periods in the reproductive cycle (reproductive and resting stages) were conditioned to the same laboratory conditions and exposed to fluoranthene (FLU) for three weeks. Studied biomarkers covering a wide range of organism responses were included: bioaccumulation, physiological rates (clearance rate -CR-, absorption efficiency -AE-, respiration rate -RR- and their integration in the scope for growth -SFG-), antioxidant enzyme activities (superoxide-dismutase -SOD-, catalase -CAT-, glutathione reductase -GR-, glutathione peroxidase -GPx-, glutathione-S-tranferase -GST-) and biochemical damage responses (lipid membrane peroxidation -LPO-). The results obtained evidenced that the levels of the biomarkers studied (RR, SOD, CAT and GPx) were higher at reproductive than at resting stage. On the other hand, the effect of toxicant was observed in SFG, CAT and GPx but this effect was only detected during the resting period. Moreover, there was a deterioration of mussel gonadal tissue with FLU exposure during reproductive stage. FLU accumulation in mussel tissues was also dependent of the reproductive status with higher internal concentrations during resting than reproductive period. In conclusion, there was a strong effect of reproductive status on studied biomarkers which seems to mask the effect of FLU at reproductive stage. The present study evidences the need to include the measurement of mussel biological status in marine pollution monitoring programs for a correct interpretation of biomarker data.

Biomonitoring of a polluted coastal area (Bay of Muggia, Northern Adriatic Sea): A five-year study using transplanted mussels

The subcellular effects of pollution were evaluated using two lysosomal biomarkers in mussels, Mytilus galloprovincialis, deployed periodically over a period of 5 years in a harbour area in the Bay of Muggia (Gulf of Trieste, North Adriatic Sea) that is strongly influenced by anthropogenic activities. Mussels were collected from a clean marine farm and analysed (sample T0). A sub-sample was transplanted to the harbour site (sample M) and analysed after about 12 weeks. An additional sub-sample was relocated within the farm as a control and was also tested at the end of the 12-week period (sample T1). The transplantation procedures were repeated twice yearly for 5 consecutive years, starting in 2009. Two well-established lysosomal biomarkers, i.e. lysosomal membrane stability and lipofuscin accumulation, were evaluated in hepatopancreas cells. The body condition index and mortality rate were also assessed. Moreover, various pollutants were determined in both mussel flesh, for a better comprehension of the biological response, and sediments, for a general characterization of the study area. As a whole, the applied biomarkers were found to be appropriate for determining the responses of mussels to environmental pollutant loads over time. Variations in lysosomal membrane stability and lipofuscin content were mostly related to total PAHs and metals respectively. Our results confirm the usefulness of active biomonitoring in evaluating pollution trends in marine coastal areas and in particular the value of lysosomal biomarkers as a rapid screening tool for highlighting pollutant effects at least at organism level.

Lysosomal responses to heat-shock of seasonal temperature extremes in Cd-exposed mussels

The present study was aimed at determining the effect of temperature extremes on lysosomal biomarkers in mussels exposed to a model toxic pollutant (Cd) at different seasons. For this purpose, temperature was elevated 10°C (from 12°C to 22°C in winter and from 18°C to 28°C in summer) for a period of 6h (heat-shock) in control and Cd-exposed mussels, and then returned back to initial one. Lysosomal membrane stability and lysosomal structural changes in digestive gland were investigated. In winter, heat-shock reduced the labilisation period (LP) of the lysosomal membrane, especially in Cd-exposed mussels, and provoked transient lysosomal enlargement. LP values recovered after the heat-shock cessation but lysosomal enlargement prevailed in both experimental groups. In summer, heat-shock induced remarkable reduction in LP and lysosomal enlargement (more markedly in Cd-exposed mussels), which recovered within 3 days. Besides, whilst heat-shock effects on LP were practically identical for Cd-exposed mussels in winter and summer, the effects were longer-lasting in summer than in winter for control mussels. Thus, lysosomal responsiveness after heat-shock was higher in summer than in winter but recovery was faster as well, and therefore the consequences of the heat shock seem to be more decisive in winter. In contrast, inter-season differences were attenuated in the presence of Cd. Consequently, mussels seem to be better prepared in summer than in winter to stand short periods of abrupt temperature change; this is, however, compromised when mussels are exposed to pollutants such as Cd.

Season-dependent effects of elevated temperature on stress biomarkers, energy metabolism and gamete development in mussels

In coastal areas, sessile species can be severely affected by thermal stress associated to climate change. Presently, the effect of elevated temperature on metabolic, cellular and tissue-level responses of mussels was determined to assess whether the responses vary seasonally with seawater temperature and reproductive stage. Mussels were collected in fall, winter and summer, and (a) maintained at 16, 12, and 20 °C respectively or (b) subject to gradual temperature elevation for 8 days (+1 °C per day; from 16 to 24 °C in fall, from 12 to 20 °C in winter and from 20 to 28 °C in summer) and further maintained at 24 °C (fall), 20 °C (winter) and 28 °C (summer) for the following 6 days. Temperature elevation induced membrane destabilization, lysosomal enlargement, and reduced the aerobic scope in fall and summer whereas in winter no significant changes were found. Changes at tissue-level were only evident at 28 °C. Gamete development was impaired irrespective of season. Since the threshold of negative effects of warming was close to ambient temperatures in summer (24 °C or above) studied mussel populations would be vulnerable to the global climate change.

Multibiomarker assessment of cerium dioxide nanoparticle (nCeO2) sublethal effects on two freshwater invertebrates, Dreissena polymorpha and Gammarus roeseli

Cerium nanoparticles (nCeO2) are widely used in everyday products, as fuel and paint additives. Meanwhile, very few studies on nCeO2 sublethal effects on aquatic organisms are available. We tried to fill this knowledge gap by investigating short-term effects of nCeO2 at environmentally realistic concentrations on two freshwater invertebrates; the amphipod Gammarus roeseli and the bivalve Dreissena polymorpha, using an integrated multibiomarker approach to detect early adverse effects of nCeO2 on organism biology. Differences in the behaviour of the organisms and of nanoparticles in the water column led to differential nCeO2 bioaccumulations, G. roeseli accumulating more cerium than D. polymorpha. Exposure to nCeO2 led to decreases in the size of the lysosomal system, catalase activity and lipoperoxidation in mussel digestive glands that could result from nCeO2 antioxidant properties, but also negatively impacted haemolymph ion concentrations. At the same time, no strong adverse effects of nCeO2 could be observed on G. roeseli. Further experiments will be necessary to confirm the absence of severe nCeO2 adverse effects in long-term environmentally realistic conditions.

Towards a better understanding of biomarker response in field survey: a case study in eight populations of zebra mussels

In order to provide reliable information about responsiveness of biomarkers during environmental monitoring, there is a need to improve the understanding of inter-population differences. The present study focused on eight populations of zebra mussels and aimed to describe how variable are biomarkers in different sampling locations. Biomarkers were investigated and summarised through the Integrated Biomarker Response (IBR index). Inter-site differences in IBR index were analysed through comparisons with morphological data, proteomic profiles and genetic background of the studied populations. We found that the IBR index was a good tool to inform about the status of sites. It revealed higher stress in more polluted sites than in cleaner ones. It was neither correlated to proteomic profiles nor to genetic background, suggesting a stronger influence of environment than genes. Meanwhile, morphological traits were related to both environment and genetic background influence. Together these results attest the benefit of using biological tools to better illustrate the status of a population and highlight the need of consider inter-population difference in their baselines.

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

A battery of cell and tissue-level biomarkers was applied in mussels of 6 size-classes collected from Galicia and the Basque coast in summer 2007 in an attempt to examine the health status of individuals affected as adults (mature before 2003), affected during their developmental or juvenile stages (2003-2004 offspring), or not directly affected by the Prestige oil spill (POS) exposure (presumably 2005-2006 offspring). This battery of biomarkers was akin to those formerly applied on mussels of 3.5-4.5 cm shell length for which there exist biomarker reference values in the studied geographical areas. The cause-effect relationship between biological responses and the different history of exposure to POS fuel oil was intricate for different reasons: (a) growth rate was dissimilar in mussels of the two studied localities and much lower than expected, (b) a chronological basis could not be directly associated to POS events (all mussels except the smallest from Galicia had been subjected to the direct POS impact at one or another stage of their life-cycle); and (c) some biomarkers and histopathology seemingly depended on size/age irrespectively of the locality and the POS chronology. As a whole, the present study gives a very useful set of reference values of biomarkers obtained for Mytilus galloprovincialis of different size-classes. Finally, it is recommended that Mussel Watch programmes should be designed by standardising the age of the sentinel mussels rather than their size, especially if the programme covers large or diverse geographical areas, if long-term trends are relevant or if significant pollution effects on growth are expected.

Lysosomal and tissue-level biomarkers in mussels cross-transplanted among four estuaries with different pollution levels

A 3-4 wk cross-transplantation experiment was carried out in order to investigate the sensitivity, rapidity, durability and reversibility of lysosomal and tissue-level biomarkers in the digestive gland of mussels. Four localities in the Basque coast with different levels of chemical pollution and environmental stress were selected. Lysosomal membrane stability (LP) and lysosomal structural changes (VvL; S/VL; NvL) and changes in cell-type composition in digestive gland epithelium (VvBAS) were investigated to determine short (2d) and mid-term (3-4 wk) responses after cross-transplantation. Mussels from Txatxarramendi presented VvBAS<0.1 μm(3)/μm(3) (unstressed) whilst VvBAS>0.12 μm(3)/μm(3) was recorded in mussels from Plentzia (moderate stress) and VvBAS>0.2 μm(3)/μm(3) in Arriluze and Muskiz (high stress). Accordingly, LP<10 min (high stress) was recorded in mussels from Muskiz and Arriluze and LP~15 min (low-to-moderate stress) in those from Plentzia and Txatxarramendi. According to the VvL, S/VL and NvL data, a certain lysosomal enlargement was envisaged in mussels from Arriluze in comparison with those from Txatxarramendi and Plentzia. Mussels from Muskiz exhibited a peculiar endo-lysosomal system made of abundant tiny lysosomes (low VvL and high S/VL and NvL values). Lysosomal and tissue-level biomarkers were responsive after 2d cross-transplantation between the reference and the polluted localities, which indicated that these biomarkers were quickly induced and, to a large extent, reversible. Moreover, the tissue-level biomarker values were maintained during the entire period (3-4 wk) of cross-transplantation, which evidenced the durability of the responsiveness. In contrast, comparisons in the mid-term were unfeasible for lysosomal biomarkers as these exhibited a seasonal winter attenuation resulting from low food availability and low temperatures. In conclusion, lysosomal enlargement and membrane stability and changes in cell-type composition were sensitive, rapid and reversible responses to changes in environmental stress whilst durability of the response could not be demonstrated for lysosomal responses by interferences with the seasonal variability.

Marine ecosystem health status assessment through integrative biomarker indices: a comparative study after the Prestige oil spill "Mussel Watch"

Five integrative biomarker indices are compared: Bioeffects Assessment Index (BAI), Health Status Index (HSI), integrated biological response (IBR), ecosystem health condition chart (EHCC) and Integrative Biomarker Index (IBI). They were calculated on the basis of selected biomarker data collected in the framework of the Prestige oil spill (POS) Mussel Watch monitoring (2003-2006) carried out in Galicia and the Bay of Biscay. According to the BAI, the health status of mussels was severely affected by POS and signals of recovery were evidenced in Galicia after April-04 and in Biscay Bay after April-05. The HSI (computed by an expert system) revealed high levels of environmental stress in 2003 and a recovery trend from April-04 to April-05. In July-05, the health status of mussels worsened but in October-05 and April-06 healthy condition was again recorded in almost all localities. IBR/n and IBI indicated that mussel health was severely affected in 2003 and improved from 2004 onwards. EHCC reflected a deleterious environmental condition in 2003 and a recovery trend after April-04, although a healthy ecosystem condition was not achieved in April-06 yet. Whereas BAI and HSI provide a basic indication of the ecosystem health status, star plots accompanying IBR/n and IBI provide complementary information concerning the mechanisms of biological response to environmental insult. Overall, although the integrative indices based on biomarkers show different sensitivity, resolution and informative output, all of them provide coherent information, useful to simplify the interpretation of biological effects of pollution in marine pollution monitoring. Each others' advantages, disadvantages and applicability for ecosystem health assessment are discussed.

Effects of organic pollutants on Eobania vermiculata measured with five biomarkers

In the present study, the effect of organic pollution on land snails Eobania vermiculata was investigated. Five pollution biomarkers (neutral red retention assay, morphometry of lysosomes and neutral lipids, acetylcholinesterase activity and metallothioneins content), were applied on tissues of the land snails. The results showed intense differentiations between the snails treated with organic pollutants and the control ones, as indicated by the results obtained. Statistically significant correlations among the results obtained emphasize the usefulness of these biomarkers.

Cross-effects of nickel contamination and parasitism on zebra mussel physiology

Aquatic organisms are exposed to pollution which may make them more susceptible to infections and diseases. The present investigation evaluated effects of nickel contamination and parasitism (ciliates Ophryoglena spp. and intracellular bacteria Rickettsiales-like organisms), alone and in combination, on biological responses of the zebra mussel Dreissena polymorpha, and also the infestation abilities of parasites, under laboratory controlled conditions. Results showed that after 48 h, more organisms were infected in nickel-exposed groups, which could be related to weakening of their immune system. Acting separately, nickel contamination and infections were already stressful conditions; however, their combined action caused stronger biological responses in zebra mussels. Our data, therefore, confirm that the parasitism in D. polymorpha represents a potential confounding factor in ecotoxicological studies that involve this bivalve.

Early defense responses in the freshwater bivalve Corbicula fluminea exposed to copper and cadmium: Transcriptional and histochemical studies

The aim of the present study was to measure the early effects of copper (10 and 50 μg L(-1)), cadmium (2, 10, and 50 μg L(-1)) and mixtures of these metals in the freshwater bivalve Corbicula fluminea exposed for 12 h in laboratory. Transcription levels of superoxide dismutase (SOD), catalase (CAT), selenium-dependent glutathione peroxidase (Se-GPx), pi-class glutathione S-transferase (pi-GST), metallothionein (MT) in digestive gland and gills, and response of lysosomal system and neutral lipids in digestive gland were determined after the exposure period. Results showed that lysosomal system, neutral lipids content, and mRNA levels were modified, suggesting their early response against oxidative stress and their important role in cell integrity. The integrated biomarker response was calculated and showed that the effects of the combinations of Cu and Cd on the biomarker responses are additive. MT and pi-GST mRNA expression correspond to the largest ranges of response. As efficient biomarkers should have an early warning capacity, SOD, CAT, Se-GPx, pi-GST, MT transcripts levels, lysosomal system, and neutral lipids could be used as biomarkers of metal contamination in the aquatic environment.

Effects of chronic exposure to dispersed oil on selected reproductive processes in adult blue mussels (Mytilus edulis) and the consequences for the early life stages of their larvae

Mussels (Mytilus edulis) were continuously exposed to dispersed crude oil (0.015-0.25mg/l) for 7 months covering the whole gamete development cycle. After 1 month exposure to 0.25 mg oil/l, the level of alkali-labile phosphates (ALP) and the volume density of atretic oocytes in female gonads were higher than those in the gonads of control females, indicating that oil affected the level of vitellogenin-like proteins and gamete development. Spawning of mussels was induced after 7 months oil exposure. Parental oil exposure did not affect subsequent fertilization success in clean seawater but this was reduced in 0.25 mg oil/l. Parental exposure to 0.25 mg oil/l caused both slow development and a higher percentage of abnormalities in D-shell larvae 2 days post-fertilization; reduced growth 7 days post-fertilization. These effects were greatly enhanced when larval stages were maintained at 0.25 mg oil/l. Similar studies are warranted for risk assessment prognosis.

Introduction of the land snail Eobania vermiculata as a bioindicator organism of terrestrial pollution using a battery of biomarkers

The present study aimed to enrich the group of sentinel organisms of terrestrial pollution biomonitoring, by investigating the efficacy of the land snail Eobania vermiculata. For this reason, a package of biomarkers was performed on land snails E. vermiculata collected from polluted areas in the field or treated with heavy metals in the laboratory. The biomarkers used were neutral red lysosomal retention assay of the haemocytes, acetylcholinesterase activity in the digestive gland and the haemolymph, and metallothionein content of the digestive gland. Moreover, the morphometric changes in the lysosomal system and the morphometric alterations of the neutral lipids were also investigated. In addition, the content of cadmium, lead and copper was evaluated in the digestive gland of the snails. The results revealed appreciable alterations in the biomarker values both in field- and laboratory-conditions, accompanied by significant correlations among the biomarkers. Therefore, this exploratory study suggests the utility of E. vermiculata as a sentinel organism for biomonitoring the biologic impact of terrestrial pollution, and supports the package's efficacy of the selected biomarkers.

Application of a battery of biomarkers in mussel digestive gland to assess long-term effects of the Prestige oil spill in Galicia and the Bay of Biscay: lysosomal responses

In order to assess the long-term lysosomal responses to the Prestige oil spill (POS), mussels, Mytilus galloprovincialis, were collected in 22 localities from Galicia and the Bay of Biscay (North Iberian peninsula) in July, and September 2003, April, July, and October 2004-2005 and April 2006. Lysosomal membrane stability (labilisation period, LP) and lysosomal structural changes (lysosomal volume density, Vv(L) and lysosomal surface-to-volume ratio, S/V(L)) were measured as general stress biomarkers. The most remarkable long-term effects after the POS were drastic changes in lysosomal size (lysosomal enlargement) and membrane stability (extremely low LP values) up to April-04. Later on, a recovery trend was envisaged all along the studied area after July-04, albeit membrane stability continued to be below 20 min throughout the studied period up to April-06, which indicates a "distress-to-moderate-stress" condition. Lysosomal Response Index (LRI) revealed that environmental stress was more marked in Galicia than in the Bay of Biscay, mainly in the first sampling year, although a "moderate-to-high-stress" condition persisted until July-05. Overall, although lysosomal size returned to reference values, membrane stability was not fully recovered indicating a stress situation throughout the studied period.

Spatial and temporal variations of biological responses to environmental pollution in the freshwater zebra mussel

The validation of a suite of cellular biomarkers for biomonitoring studies necessitates a good knowledge of the meaning of these early responses to environmental stress in terms of individual health. This requires confirmation (i) of linkages between the cellular and higher levels of the biological organisation, (ii) of temporal persistence of the stress symptoms and (iii) of their reversibility after a return to more favourable conditions. Besides, (iv) the sensitivity of the biomarker suite towards subtle variations of environmental contamination has to be assessed. With this aim, field experiments were performed on deployed freshwater zebra mussels (Dreissena polymorpha) in the vicinity of the confluence of a small heavily anthropized stream with a larger river. We examined the persistence of the responses over a 90-day period and their reversibility after a depuration-transplantation. A second experiment was conducted later by adding a study site at an increased distance from the confluence. Decreased digestive lysosomal volume and neutral lipid contents, and lipofuscin accumulation preceded effects on the mussels' condition. The following experiment confirmed that the cellular biomarkers were more sensitive than both individual endpoints to reflect the effects of subtler variations of environmental contamination. Integration of the results with multivariate analysis and the Integrated Biomarker Response tended to confirm the relevance of the biomarker suite.

Interactions between parasitism and biological responses in zebra mussels (Dreissena polymorpha): Importance in ecotoxicological studies

Given that virtually all organisms are hosts for parasites, the investigation of the combined effects of contamination and parasitism is important in the framework of aquatic bioindication procedures. To assess the impact of such multistresses at the host cellular level, we sampled parasitized zebra mussel (Dreissena polymorpha) populations from two sites in northeast France that presented different levels of contamination. Experimental groups were formed based on parasite species and host gender and tested by histochemistry and automated image analysis for biological responses, such as structural changes of the lysosomal system and neutral lipid accumulation. Infected organisms displayed smaller and more numerous lysosomes compared with uninfected congeners, and infection further elevated the effect of the chemical contamination on this biomarker. In contrast, co-infection of females with selected parasites did produce inverse results, i.e. a more developed lysosomal system and neutral lipid depletion. Our data, therefore, suggest that parasitism in zebra mussels represents a potential confounding factor in ecotoxicological studies and must be taken into account in environmental risk assessment studies.

Changes in cell-type composition in digestive gland of slugs and its influence in biomarkers following transplantation between a relatively unpolluted and a chronically metal-polluted site

Changes in cell-type composition (CCTC) is a general phenomenon that takes place in the digestive gland epithelium of stressed molluscs. The aim of the present work was to determine whether CCTC is a reversible process in the digestive gland of sentinel slugs chronically exposed to metal pollution and how CCTC affects metal accumulation parameters and different cell and tissue biomarkers of exposure and effect. Slugs (Arion ater) from an abandoned zinc mine were transferred to a relatively unpolluted site and the other way around for 3, 10 and 28 d. The volume density of black silver deposits (Vv(BSD)) after autometallography, and metallothionein (MT) levels were used as biomarkers of exposure to metals and CCTC and lysosomal responses were selected as effect biomarkers. Results indicated that slugs were sensitive to recent metal pollution; however, slugs chronically exposed to metals presented some characteristic features and were less responsive to pollution cessation without signs of CCTC reversal.

Reproductive toxicity of the water accommodated fraction (WAF) of crude oil in the polychaetes Arenicola marina (L.) and Nereis virens (Sars)

Accidental pollution incidents are common in the marine environment and are often caused by oil-related activities. Here the potential of such an incident to disrupt reproduction in two polychaete species is investigated, using an environmentally relevant preparation of weathered Forties crude oil, i.e. the water accommodated fraction (WAF). Oocytes were collected and exposed to three concentrations of WAF for 1h prior to the addition of sperm, so that fertilization took place under exposure conditions. Fertilization success was significantly reduced in both species by an exposure to WAF concentrations equivalent to 0.38 mgL(-1) PAHs, to just 26.8% in Arenicola marina compared to 76% in Nereis virens. The effects of WAF exposure on fertilization were greatly enhanced at lower sperm concentrations in N. virens, with a complete lack of fertilization reactions observed at sperm concentrations of 10(3)sperm per mL. We therefore suggest a mechanism of toxicity related to sperm swimming behaviour, resulting in reduced sperm:egg collision rates. WAF was found to reduce post-fertilization development rates and have teratogenic effects on early embryonic stages in both species, which exhibited abnormal cleavage patterns and high levels of fluctuating asymmetry. These results illustrate how the presence of crude oil in its soluble form in seawater at the time of a spawning event for either A. marina or N. virens could impact on fertilization success with implications for the fertilization ecology of these free spawning marine invertebrates.

Immunological and cytotoxicological responses of the Asian clam,Corbicula fluminea(M.), experimentally exposed to cadmium

Bivalve molluscs, as filter-feeding organisms, are known to accumulate metals that can produce deleterious effects on organisms. The phagocytic activity of haemocytes and lysosomal alterations in the digestive gland cells were measured in the freshwater Asian clam exposed to cadmium, in order to assess the possible use of immunocompetence and lysosomal responses as biomarkers of freshwater quality. Clams were exposed in the laboratory to nominal concentrations of 3, 10, 21.4, 46.5 and 100 microg 1(-1) of cadmium and sampled after 7, 15 and 30 days of exposure. The results show a decrease of phagocytic activity after only 7 days of exposure to 10 microg 1(-1) of cadmium. This response was also observed as the exposure time was increased. Lysosomes in the digestive cells increased in size and number after 7 days of exposure as cadmium concentration increased. After 30 days of exposure, a decrease in size and number indicated a change in the response to the metal from concentrations of 46.5 microg 1(-1) of cadmium. A dose and time response both in phagocytic activity of haemocytes and lysosomal structure demonstrated a possible use of these biomarkers in freshwater biomonitoring.

Is the freshwater gammarid, Dikerogammarus villosus, a suitable sentinel species for the implementation of histochemical biomarkers?

In order to enlarge the range of potential sentinel species for the implementation of a multiple biomarker approach, spatial and monthly morphological variations of four cellular compartments and contents were assessed during two years in the hepatopancreatic caeca of the freshwater gammarid, Dikerogammarus villosus (Crustacea, Amphipoda), using histochemistry coupled to image analysis. Among the three study sites, the second one, located in a reservoir receiving the overheated and copper-contaminated waters of a nuclear power plant, was the most anthropised. During this passive biomonitoring survey, unsaturated neutral lipids were more abundant, the surface densities of the lysosomal and peroxisomal systems were, respectively less and more important, and lipofuscin granules tended to accumulate in the amphipods from the second site compared to both others. Nonetheless, in this context, the present cellular biomarker suite, analysed through an integrative approach, was not powerful enough to highlight spatial heterogeneity significantly. This may partly result from particularities in the patterns of metal accumulation and copper physiological requirements of amphipods (haemocyanin synthesis). Nevertheless, we think that the use of this Ponto-Caspian non-indigenous species in biomonitoring surveys deserves further investigation, owing to its current position in freshwater and brackish European ecosystems, considering both biomass and functioning. Cellular responses could be studied in parallel with endpoints at other levels of the biological organization to compose a more powerful biomarker suite. Furthermore, comparing biological responses to environmental stress in this invasive species and less competitive autochthonous gammarids could be of great interest.

Assessment of biological effects of environmental pollution along the NW Mediterranean Sea using red mullets as sentinel organisms

A biomonitoring program was carried out in spring and autumn in three pollution hot-spots and sensitive areas of the NW Mediterranean Sea using red mullets (Mullus barbatus) as sentinel organisms and a battery of biomarkers together with gonad histology. In fish from anthropogenic impacted areas (Fos-sur-mer, Cortiou, Arenzano, Delta of Ebro) lysosomal membrane destabilization occurred indicating disturbed health. There were no significant differences in metallothionein (MT) levels among stations. Peroxisomal acyl-CoA oxidase (AOX) activity was highest in fish from Cortiou. Both MT levels and AOX activities were significantly correlated with gamete development. Prevalence of melanomacrophage centers were high in Cortiou in all samplings and in Fos-sur-mer in September samplings. In conclusion, the application of a battery of biomarkers in red mullets provided relevant data for the assessment of environmental pollution in the NW Mediterranean Sea but also showed the difficulties of using native fish as sentinels. For future studies caging strategies are recommended.

Assessment of biological effects of environmental pollution along the NW Mediterranean Sea using mussels as sentinel organisms

With the aim of assessing the biological effects of pollution along three gradients of pollution in the NW Mediterranean Sea, a biomonitoring survey was implemented using a battery of biomarkers (lysosomal membrane stability, lysosomal structural changes, metallothionein (MT) induction and peroxisome proliferation) in mussels over a period of two years as part of the EU-funded BEEP project. Mussels from the most impacted zones (Fos, Genova and Barcelona harbours) showed enlarged lysosomes accompanied by reduced labilisation period of lysosomal membranes, indicating disturbed health. MT levels did not reveal significant differences between stations and were significantly correlated with gonad index, suggesting that they were influenced by gamete development. Peroxisomal acyl-CoA oxidase (AOX) activity was significantly inhibited in polluted stations possibly due to interactions among mixtures of pollutants. In conclusion, the application of a battery of effect and exposure biomarkers provided relevant data for the assessment of biological effects of environmental pollution along the NW Mediterranean Sea.

Towards a validation of a cellular biomarker suite in native and transplanted zebra mussels: a 2-year integrative field study of seasonal and pollution-induced variations

Two of the questions raised in the validation process of biomarkers are their relevance in the identification and discrimination of environmental perturbations, and the influence of seasonal factors on these biological endpoints. Determining the advantages and restrictions associated with the use of native or transplanted animals and comparing their responses is also needed. To obtain this information, a 2-year integrative field study was conducted in the vicinity of a nuclear power plant in northeastern France. A station was located in the reservoir receiving the cooling waters of the plant, and two other sites were studied 2 km upstream and 5 km downstream from the reservoir's discharge in the Moselle river. Elevated temperatures, copper contamination and a 1.4-fold-concentration factor of dissolved salts affected water quality of the reservoir. Native and transplanted zebra mussels (Dreissena polymorpha) were collected monthly and their digestive glands were processed for histochemical determinations of the lysosomal and peroxisomal systems and of the lipofuscin and neutral lipid contents. The responses were quantified using automated image analysis and stereology. Apart from neutral lipid contents, there were no systematic seasonal patterns in mussel populations or from 1 year to another. Principal Component Analyses showed a general higher discrimination potential of biological responses in transplanted organisms compared to native ones. They also pointed out the relationships between the cellular and physiological markers and abiotic factors. The present multiple biomarker integrative approach in transplanted D. polymorpha brings promising elements in their validation process as relevant biomonitoring tools.

Freshwater molluscs from volcanic areas as model organisms to assess adaptation to metal chronic pollution

Cellular biomarkers of exposure and biological effects were measured in digestive gland of snails (Physa acuta) sampled in sites with and without active volcanism in São Miguel Island (Azores). Metal content in digestive cell lysosomes was determined by image analysis after autometallography (AMG) as volume density of autometallographed black silver deposits (Vv(BSD)). Lysosomal structural changes (lysosomal volume, surface and numerical densities - Vv(LYS,) Sv(LYS) and Nv(LYS-), and surface-to-volume ratio - S/V(LYS)-) were quantified by image analysis, after demonstration of beta-glucuronidase activity, on digestive gland cryotome sections. Additional chemical analyses (atomic absorption spectrophotometry) were done in the digestive gland of snails. The highest metal concentrations were found in snails from the active volcanic site, which agreed with high intralysomal Vv(BSD). Digestive cell lysosomes in snails inhabiting sites with active volcanism resembled a typical stress situation (enlarged and less numerous lysosomes). In conclusion, the biomarkers used in this work can be applied to detect changes in metal bioavailability due to chronic exposure to metals (volcanism), in combination with chemical analyses.

Biomarkers in mussels from a copper site gradient (Visnes, Norway): an integrated biochemical, histochemical and histological study

In the present work, mussels (Mytilus edulis) were transplanted into a copper (Cu) gradient in Visnes (Norway) for a period of 3 weeks during November 2003. Sites 1 and 2 showed similar low levels of Cu, site 3 had intermediate Cu levels and site 4 was the most polluted with Cu as confirmed by AAS of digestive gland tissue. Values of lysosomal membrane labilization period were significantly lower at sites 3 and 4 compared to sites 1 and 2. The volume density and size of lysosomes was significantly decreased at site 4. The volume density of neutral lipids was also significantly lower at site 4 compared with the rest of sites. The volume density of lipofuscins showed significantly higher values at sites 2 and 3 compared to the reference site 1. Similar results were obtained regarding bioavailable metal levels measured by autometallography. All together, results are indicative of exocytosis of metal-containing lysosomes and lipofuscins to the digestive tubule lumen in mussels from site 4. In fact, autometallographic metal deposits were detected in digestive tubule lumen, brown cells and stomach in site 4 mussels. In agreement, there was a loss of digestive cells in mussels from site 4 (atrophy of the digestive epithelium) and cell type replacement (diminished volume density of digestive cells and increased volume density of basophilic cells). In conclusion, selected biomarkers indicated that mussels transplanted to sites closest to the Cu mine showed significant differences in metal accumulation pattern and in organization of the digestive gland tissue. Finally, female mussels closest to the Cu mine showed advanced gametogenesis with higher gonad index and vitellogenin-like protein levels than mussels at sites 1 and 2.

Effects of tributyltin and 17β-estradiol on immune and lysosomal systems of the Asian clam Corbicula fluminea (M.)

Freshwater clams Corbicula fluminea were experimentally exposed to a range of tributyltin (TBT) (50, 250 and 500ng Sn/L) and 17β-estradiol (20, 200, 2000ng/L) for 30 days. After 15 and 30 days, phagocytosis activity of haemocytes and lysosomal structural changes in the digestive cells were assayed. 17β-Estradiol exerted a higher inhibition on phagocytosis than tributyltin. This would suggest the existence of estrogen receptors, influencing the immune function. The stereological parameters measured for lysosomal structural changes in animals exposed to tributyltin varied as observed in other studies. Tributyltin is then depurated as other contaminants via digestive cell lysosomal compartment. This experiment emphasized a possible approach on the influence of endocrine disrupting compounds on a hermaphroditic species for environmental surveys.

Field application of a set of cellular biomarkers in the digestive gland of the freshwater snail Radix peregra (Gastropoda, Pulmonata)

An active biomonitoring study was performed in the vicinity of two pulp and paper mill effluents (PPMEs) released in two different streams in northeastern France. Freshwater gastropods, Radix peregra (=Lymnaea peregra or Lymnaea pereger), were transplanted for 0, 3, 14 and 21 days at two to three sites located upstream and downstream from the mill discharge points in both rivers. Lysosomal and peroxisomal systems, as well as lipofuscin and neutral lipids, were tested using histochemical methods on cryostat sections of digestive gland tissues, and stereological data were obtained by image analysis. Evidence of structural changes in the lysosomal system was found in animals exposed to both effluents, comprising general stress responses such as enlarged and more numerous lysosomes; and also possible specific pluri-phasic effects. Modifications of the lysosomal and cytoplasmic contents of lipid-related materials were also described, namely enhanced lipofuscin deposit and neutral lipid depletion. The peroxisomal proliferation in exposed snails seems to show its implication in oxidative stress detoxication, without preventing higher lipoperoxidation, as indicated by the increased amounts of digestive lipofuscin. Structural changes of the lysosomal and peroxisomal systems, digestive lipofuscin and neutral lipid contents have potential for use as early cellular biomarkers in Radix peregra exposed to environmental stressors, which deserve further investigations.

Cell and tissue biomarkers in mussel, and histopathology in hake and anchovy from Bay of Biscay after the Prestige oil spill (Monitoring Campaign 2003)

In order to assess the biological effects of the Prestige oil spill (POS), mussels (Mytilus galloprovincialis), European hake (Merluccius merluccius) and European anchovy (Engraulis encrasicolus) were sampled between April and September 2003 in various geographical areas of Bay of Biscay: Galicia, Central Cantabrian and East Cantabrian. In mussels, several cell and tissue biomarkers were measured: peroxisome proliferation as induction of acyl-CoA oxidase (AOX) activity, lysosomal responses as changes in the structure (lysosomal volume density, V(V(L)), surface-to-volume ratio, S/V(L), and numerical density, N(V(L))) and in membrane stability (labilization period, LP), cell type replacement as relative proportion of basophilic cells (volume density of basophilic cells, V(V(BAS))) in digestive gland epithelium, and changes in the morphology of digestive alveoli as mean luminal radius to mean epithelial thickness (MLR/MET). Additionally, flesh condition index (FCI) and gonad index (GI) were measured as supporting parameters. In hake and anchovy, liver histopathology was examined to determine the prevalence of parasites, melanomacrophage centers, non-specific lesions (inflammatory changes, atrophy, necrosis, apoptosis), early non-neoplastic toxicopathic lesions (i.e., hepatocellular nuclear polymorphism), foci of cellular alteration, benign and malignant neoplasms. In mussels, AOX induction was noticeable in April except in Galicia. LP values were low in all the geographical areas studied, indicating disturbed health, especially in Galicia. Alike, lysosomal enlargement was observed in most stations as shown by the extremely low S/V(L) values. V(V(BAS)) and MLR/MET values were markedly high. Overall, employed biomarkers detected exposure to toxic chemicals and disturbed health in mussels from Bay of Biscay, with impact decreasing from April to September. Although hepatocellular nuclear polymorphism and nematode parasitization in fish liver were remarkably prominent in some areas, they cannot be hitherto related to POS, since we lack historical data to determine whether the prevalences found were normal or significantly raised after POS.

Comparison of cytochemical procedures to estimate lysosomal biomarkers in mussel digestive cells

Enlargement and membrane destabilisation in digestive cell lysosomes of mussels are biomarkers of pollution effect. Cytochemical methods are currently applied to determine lysosomal membrane stability (LMS) and lysosomal structural changes (LSC). LMS, determined after grading N-acetyl-beta-hexosaminidase activity on cryotome sections of digestive gland, is measured as labilisation period (LP). LSC, determined after image analysis of cryotome sections where beta-glucuronidase activity is revealed, are measured as lysosomal volume (Vv), surface (Sv), numerical (Nv) densities and surface-to-volume ratio (S/V). Both methods have now been compared in a field study. Mussels were collected from Biscay Bay (Plentzia, reference; Muskiz, moderately polluted) and North Aegean Sea (Olympiada, reference; Limani, heavily polluted). Higher Vv and Sv and lower S/V and LP were recorded in polluted sites than in reference sites. Significant correlations with LP were found for Vv and S/V. The cost/effectiveness and environmental significance of both methods are discussed.

Cellular biomarkers of exposure and biological effect in hepatocytes of turbot (Scophthalmus maximus) exposed to Cd, Cu and Zn and after depuration

Cellular biomarkers of exposure and biological effects were measured in hepatocytes of turbot exposed to either Cd, Cu or Zn at concentrations of 1 and 10 mg/l seawater for 7 days and after depuration for 14 days. Metal content in hepatocyte lysosomes was determined by image analysis after autometallography (AMG) as volume density of autometallographed black silver deposits (Vv(BSD)). Metallothionein (MT) levels were quantified on liver sections by microdensitometry after immunohistochemical staining with a polyclonal anti cod-MT antibody (MT-OD), and in the cytosolic fraction of hepatocytes by difference pulse polarography (MT-DPP). Lysosomal structural changes (lysosomal volume, surface and numerical densities--Vv(LYS), Sv(LYS) and Nv(LYS-), and surface-to-volume ratio S/V(Lys)) were quantified by image analysis after demonstration of beta-glucuronidase activity on liver cryotome sections. Vacuolisation produced by metal-exposure in hepatocytes was quantified by stereology as volume density of vacuoles (Vv(VAC)). Exposure time and metal concentrations significantly affected Vv(BSD) in lysosomes, MT levels and the degree of vacuolisation after 1 h and 1 day exposure to the three metals. The highest Vv(BSD), MT and Vv(VAC) values were recorded after 7 days exposure in all cases. MT-OD and MT-DPP were significantly correlated with Vv(BSD). Vv(LYS) in hepatocytes increased significantly after exposure to the metals. Exposure biomarkers returned to control values after depuration with the exception of those turbots that had been exposed to 10 mg Cd/l. Alike, Vv(LYS) and Sv(lys) (Cu exposure) and Nv(LYS) (Cd and Zn exposures) returned to control values after depuration. It has been therefore demonstrated that the biomarkers used are reversible and return towards control levels once metal exposure ceases. Overall, it is concluded that Vv(BSD), MT-levels and lysosomal responses are valuable biomarkers to assess metal exposure and its effects in turbot, although in quantitative terms the biomarker response varied between metals.

Lysosomal responses in the digestive gland of the freshwater mussel, Dreissena polymorpha, experimentally exposed to cadmium

In order to examine the possible use of lysosomal response as a biomarker of freshwater quality, structural changes of lysosomes were measured by image analysis in the digestive gland of the zebra mussel, Dreissena polymorpha, exposed in laboratory conditions to cadmium. Mussels were exposed to the metal (10 and 200 microg/L) for 3 weeks and randomly collected after 7 and 21 days. At each treatment day, digestive tissues were excised and beta-glucuronidase activity was revealed in cryotome sections. Four stereological parameters were calculated: lysosomal volume density, lysosomal surface density, lysosomal surface to volume ratio, and lysosomal numerical density. The changes observed in this study reflected a general activation of the lysosomal system, including an increase in both the number and the size of lysosomes in the digestive gland cells of mussels exposed to cadmium. The digestive lysosomal response in zebra mussels was related to exposure time and to metal concentration, demonstrating the potential of this biomarker in freshwater biomonitoring.

Lysosomal enlargement in digestive cells of mussels exposed to cadmium, benzo[a]pyrene and their combination

Digestive cell lysosomes in mussels are known to respond to individual organic chemicals and metals after experimental exposure under laboratory conditions but reports dealing with the response to mixtures of pollutants are scarce. The aim of the present investigation was to compare the lysosomal responses elicited by exposure to a model organic chemical compound (benzo(a)pyrene, B[a]P), a model toxic metal (Cd) and their combination (B[a]P+Cd) under controlled laboratory conditions. Dimethylsulfoxide (DMSO) was used as vehicle to dissolve organic chemicals into seawater. Control mussels were either kept untreated in clean seawater or treated with DMSO. Digestive glands were excised on Day 21. beta-Glucuronidase activity was demonstrated in 8 mum cryotome sections. Lysosomal volume, surface and numerical densities (Vv, Sv and Nv), and surface-to-volume ratio (S/V) were quantified by image analysis. Lysosomal enlargement was evident in digestive cells of mussels exposed to either Cd, B[a]P or B[a]P+Cd. Such enlargement was more marked after exposure to B[a]P+Cd than to B[a]P, but did not reach the levels recorded after Cd exposure. It seems therefore that the presence of B[a]P reduced to some extent the effects of Cd on digestive cell lysosomes in mussels.

The application of histo-cytopathological biomarkers in marine pollution monitoring: a review

During the past two decades, a variety of histopathological alterations in fish and bivalves have been developed and used as biomarkers in pollution monitoring. Some of these have been successfully adopted in major national monitoring programmes, while others, although show promise, are still in the experimental stage. This paper critically reviews the scientific basis, cause and effect relationship, reliability, advantages and limitations of 14 histo-cytopathological biomarkers. The usefulness and practical application of each biomarker have been evaluated against a number of objective criteria including: ecological relevance, sensitivity, specificity, dose-response relationship, confounding factors, technical difficulties and cost-effectiveness.

Acute and acclimated digestive responses of the cockle Cerastoderma edule (L.) to changes in the food quality and quantity. II. Enzymatic, cellular and tissular responses of the digestive gland

Cockles Cerastoderma edule were fed two different concentrations of two diets with different qualities which were achieved by mixing different proportions of ashed silt particles with cells of the microalgae Tetraselmis suecica. After 3 days (acute response) and 11 days (acclimated response) of exposure to the diets, we analysed the digestive activity of the digestive gland using cyto-histological and enzymatic techniques. We measured (i) the volumetric fraction of digestive and basophilic cells in digestive tubules, (ii) the diverticular radius and the thickness of digestive epithelia, (iii) the stereological parameters characterizing the lysosomal system and, (iv) dry weight, soluble protein content and specific and total amylase, cellulase, laminarinase, and protease activities of the digestive gland. In the conditions of the present study, specific cellulase and laminarinase activities in the digestive gland of cockles were correlated with the volumetric fraction of basophilic cells (r=0.672 and 0.642, respectively), whereas the specific protease was highly correlated (r=0.866) with lysosomal volume density. The implications of these correlations are discussed in relation to the feeding and absorptive parameters reported in the preceding publication. In the acute response, adjustments of the synthesis of constituents of the lysosomal/proteolytic system of the digestive cells seemed to be the only mechanism operating at the digestive level to respond to the changes in food availability. Lysosomal volume density increased with rising ingestion rate of organic matter, however, the occurrence of a limit in this short-term tissular response would account for the recorded trade-off between absorption efficiency and ingestion rate with different food qualities. With regard to acclimation, food quality determined the nature of the response of the digestive gland. With low quality diets, a time-dependent capability of the digestive gland for intensifying lysosomal/proteolytic production explains the increase of food absorption rates that result from higher filtration and ingestion rates. With high quality food, digestive acclimation differed with food particle concentration: with low rations, in spite of constant morphometrical and stereological parameters, the significant changes in the absorptive balance of biochemical components suggests the existence of an increased production of lysosomes that promotes an accelerated turn-over rate of the digestive epithelia. With high food concentrations, this response was coupled with increased activities of cellulase and laminarinase enzymes, probably as a consequence of higher rates of enzyme secretions from basophilic cells.