Biomarker responses to sewage pollution in freshwater mussels (Diplodon chilensis) transplanted to a Patagonian river

Integrated biomarker response in Mytilus chilensis exposed to untreated urban discharges along the coast of Ushuaia Bay (Beagle Channel, Argentina)

The short-term effects of coastal untreated effluents from Ushuaia Bay, Beagle Channel, on the biochemical and physiological biomarkers of Mytilus chilensis were assessed. An integrated biomarker response (IBR) index was calculated as a helpful tool to represent the general stress of the experimental organisms. Cultured mussels were exposed during 96 h to three coastal sites impacted by sewage effluents. At the beginning (T₀) and every 24 h, mussels were subsampled from each site and different biochemical and physiological biomarkers were determined. There was no mortality registered in the experiments during the 96 h. However, biochemical and physiological biomarkers presented significant variations. Lipid peroxidation mean levels in mussels decreased in mantle and increased in digestive gland with respect to T₀ in almost all cases. Acetylcholinesterase activity was inhibited in all sites, reaching a maximal decrease of 35% with respect to T₀. Catalase remained stable and glutathione-S-transferase was activated. Oxygen consumption and ammonia excretion rates increased in organisms from two sites and, consequently, O:N ratio decreased, denoting a symptom of stress. IBR values showed the existence of different stress levels between exposed and unexposed mussels. These results exhibited an alteration of the general metabolism of mussels exposed for a short period of time to untreated coastal wastewater, suggesting the use of these organisms as early indicators of changes in the environmental quality of coastal waters of Ushuaia Bay.

In situ experiment to evaluate biochemical responses in the freshwater mussel Diplodon chilensis under anthropogenic eutrophication conditions

An in-situ experiment was performed to study metabolic responses of the freshwater mussel Diplodon chilensis to water contaminated by leachates from an open dump and cattle activity, in order to analyze both the effects of those contaminants on aquatic environments and the potential use of a native bivalve to evaluate the effects of anthropic influence and eutrophication. Bivalves from a reference site were cage-transplanted to a control site (site A) and to a temporal water pond (site B) over 30 and 60 periods. Water quality analyses revealed that the site B was affected by anthropogenic influence. Mussel's hemocytes from site B showed 50% lower reactive oxygen species production and 130% higher lysosomal membrane stability in the site B mussels. In addition, no oxidative stress was evident in gills, despite the elevated copper and iron concentrations recorded in the site B water samples (Cu_B = 0.3350 ± 0.0636 mg. L^-1vs. Cu_A = 0.0045 ± 0.0007 mg. L^-1; Fe_B = 3.8650 ± 0.4031 mg. L^-1vs. Fe_A = 0.0365 ± 0.0049 mg. L^-1). In contrast, the adductor muscle accumulated more Fe (~10-20-fold) than the gills and showed signs of oxidative stress, e.g. superoxide dismutase activity and TBARS levels were increased by 10% were 34%, respectively, in the site B compared with the site A after 60 days of exposure. Additionally, the adductor muscle showed signs of anaerobic metabolism activation. Cu is accumulated in gills from both sites' individuals, at 60 days, in concordance with the increase in the activity of the cu-containing enzyme cytochrome-c-oxidase. There was a reduction in the overall condition and digestive gland index in bivalves exposed at site B, associated with diminished levels of lipid and protein contents. Metal-pollution and eutrophication affects D. chilensis metabolism and is associated to tissue-specific exposure, anaerobic metabolism and general energetic condition depletion.

Testing biomarker feasibility: a case study of Laeonereis culveri (Nereididae, Annelida) exposed to sewage contamination in a subtropical estuary

The feasibility of biomarkers to accurately detect pollution in estuaries and coastal areas appears to be overestimated in the scientific literature, and is likely stemming from a bias towards publishing only positive results. Herein, we test the applicability of antioxidant capacity and lipid peroxidation to detect potential in situ sewage impacts on a subtropical estuary. We experimentally assessed variation in malondialdehyde (MDA, an indicator of lipid peroxidation) and total antioxidant capacity against peroxyl radicals (ACAP) through transplantations of the worm Laeonereis culveri from control to sewage-polluted areas. Variations in biomarkers were more related to natural environmental variability and small-scale heterogeneity among areas than to experimental exposure to sewage. Use of oxidative stress biomarkers is promising but further experimental work under real-life conditions is necessary to further validate and establish their accuracy and feasibility for practical purposes.

Thiol oxidation of hemolymph proteins in oysters Crassostrea brasiliana as markers of oxidative damage induced by urban sewage exposure

Urban sewage is a concerning issue worldwide, threatening both wildlife and human health. The present study investigated protein oxidation in mangrove oysters (Crassostrea brasiliana) exposed to seawater from Balneário Camboriú, an important tourist destination in Brazil that is affected by urban sewage. Oysters were exposed for 24 h to seawater collected close to the Camboriú River (CAM1) or 1 km away (CAM2). Seawater from an aquaculture laboratory was used as a reference. Local sewage input was marked by higher levels of coliforms, nitrogen, and phosphorus in seawater, as well as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), linear alkylbenzenes (LABs), and fecal steroid in sediments at CAM1. Exposure of oysters to CAM1 caused marked bioaccumulation of LABs and decreased PAH and PCB concentrations after exposure to both CAM1 and CAM2. Protein thiol oxidation in gills, digestive gland, and hemolymph was evaluated. Lower levels of reduced protein thiols were detected in hemolymph from CAM1, and actin, segon, and dominin were identified as targets of protein thiol oxidation. Dominin susceptibility to oxidation was confirmed in vitro by exposure to peroxides and hypochlorous acid, and 2 cysteine residues were identified as potential sites of oxidation. Overall, these data indicate that urban sewage contamination in local waters has a toxic potential and that protein thiol oxidation in hemolymph could be a useful biomarker of oxidative stress in bivalves exposed to contaminants. Environ Toxicol Chem 2017;36:1833-1845. © 2016 SETAC.

Modulating effects of orally supplied Euglena gracilis on the physiological responses of the freshwater mussel Diplodon chilensis, exposed to sewage water pollution in a Patagonian river (Argentina)

In order to test if orally supplied Euglena sp. cells modulate the physiological status of bivalves during bioremediation procedures, we evaluated the effect of Euglena gracilis diet on the immune response, oxidative balance and metabolic condition of Diplodon chilensis exposed to sewage water pollution. Mussels were fed for 90 days with E. gracilis (EG) or Scenedesmus vacuolatus (SV, control diet), and then exposed for 10 days at three sites along the Pocahullo river basin: 1) an unpolluted site, upstream of the city (control, C); 2) upstream (UpS) and 3) downstream (DoS) from the main tertiary-treated sewage discharge, in the city of San Martín de los Andes, Northwest Patagonia, Argentina. Our results show that the total hemocyte number decreases while pollution load increases along the river course for both, EG and SV mussels. Phagocytic activity is higher in EG mussels than in SV ones under all conditions. Reactive oxygen species (ROS) production in hemocytes increases with the increase in the pollution load, being significantly higher for EG mussels than for SV ones at DoS; no changes are observed for total oxyradical scavenging capacity (TOSC). Hemocytes' viability is increased for E. gracilis diet at C and remains unchanged in this group of mussels when exposed at the polluted sites. Lysosomal membrane stability is higher in EG mussels than in SV ones for all conditions, although it is decreased at polluted sites compared with that at C. Antioxidant (catalase) and detoxifying (gluthatione S-transferase) defenses are generally lower in gills and digestive gland of EG mussels than in SV ones. Lipid peroxidation (TBARS) is evident in gills of EG mussels at C, and in digestive gland of the same group, at all the sites. Gill mass factor (GF) is affected by the E. gracilis diet; it is increased at C and decreased at polluted sites when compared with that of SV ones. Digestive gland mass factor (DGF) is higher in EG mussels than in SV ones. In D. chilensis, continuous and long term feeding with E. gracilis cells favors immune response and reduces the damage caused by sewage pollution exposure on hemocytes. Nevertheless, diet and transplantation procedures may produce negative effects on the oxidative balance of gills and digestive gland and should be taken into account for bioremediation strategies.

Assessment of biomarkers for contaminants of emerging concern on aquatic organisms downstream of a municipal wastewater discharge

Contaminants of emerging concern (CECs), including pharmaceuticals, personal care products and estrogens, are detected in wastewater treatment plant (WWTP) discharges. However, analytical monitoring of wastewater and surface water does not indicate whether CECs are affecting the organisms downstream. In this study, fathead minnows (Pimephales promelas) and freshwater mussels Pyganodon grandis Say, 1829 (synonym: Anodonta grandis Say, 1829) were caged for 4 weeks in the North Saskatchewan River, upstream and downstream of the discharge from the WWTP that serves the Edmonton, AB, Canada. Passive samplers deployed indicated that concentrations of pharmaceuticals, personal care products, an estrogen (estrone) and an androgen (androstenedione) were elevated at sites downstream of the WWTP discharge. Several biomarkers of exposure were significantly altered in the tissues of caged fathead minnows and freshwater mussels relative to the upstream reference sites. Biomarkers altered in fish included induction of CYP3A metabolism, an increase in vitellogenin (Vtg) gene expression in male minnows, elevated ratios of oxidized to total glutathione (i.e. GSSG/TGSH), and an increase in the activity of antioxidant enzymes (i.e. glutathione reductase, glutathione-S-transferase). In mussels, there were no significant changes in biomarkers of oxidative stress and the levels of Vtg-like proteins were reduced, not elevated, indicating a generalized stress response. Immune function was altered in mussels, as indicated by elevated lysosomal activity per hemocyte in P. grandis caged closest to the wastewater discharge. This immune response may be due to exposure to bacterial pathogens in the wastewater. Multivariate analysis indicated a response to the CECs Carbamazepine (CBZ) and Trimethoprim (TPM). Overall, these data indicate that there is a 1 km zone of impact for aquatic organisms downstream of WWTP discharge. However, multiple stressors in municipal wastewater make measurement and interpretation of impact of CECs difficult since water temperature, conductivity and bacteria are also inducing biomarker responses in both fish and mussels.

The mussel caging approach in assessing biological effects of wastewater treatment plant discharges in the Gulf of Finland (Baltic Sea)

Biological effects of wastewater treatment plant (WWTP) effluents were investigated in Baltic mussels (Mytilus trossulus) caged for one month 800m and 1100m from the WWTP discharge site and at a reference site 4km away. Significant antioxidant, genotoxic and lysosomal responses were observed close to the point of the WWTP discharge. Passive samplers (POCIS) attached to the cages indicated markedly higher water concentrations of various pharmaceuticals at the two most impacted sites. Modeling the dispersal of a hypothetical passive tracer compound from the WWTP discharge site revealed differing frequencies and timing of the exposure periods at different caging sites. The study demonstrated for the first time the effectiveness of the mussel caging approach in combination with passive samplers and the application of passive tracer modeling to examine the true exposure patterns at point source sites such as WWTP pipe discharges in the Baltic Sea.

Long-term feeding with Euglena gracilis cells modulates immune responses, oxidative balance and metabolic condition in Diplodon chilensis (Mollusca, Bivalvia, Hyriidae) exposed to living Escherichia coli

We evaluated the modulating effect of long-term feeding with lyophilized Euglena gracilis cells on immune response, oxidative balance and metabolic condition of the freshwater mussel Diplodon chilensis. Mussels, previously fed with Scenedesmus vacuolatus (SV) or E. gracilis (EG) for 90 days, were challenged with an environmentally relevant concentration of Escherichia coli in water for 5 days, under feeding or starvation conditions. EG diet increased overall phagocytic activity and tissue hemocyte accumulation (gill and mantle), and favored hemocyte viability upon E. coli challenge. Tissular hemocyte accumulation, and humoral bacteriolytic activity and protein content were similarly stimulated by EG and E. coli, with no further effect when both stimuli were combined. Both, E. coli challenge and EG diet reduced gill bacteriolytic activity with respect to nonchallenged SV mussels, while no effect was observed in challenged EG mussels. Gill and digestive gland protein contents, along with digestive gland bacteriolytic activity were higher in EG than in SV mussels. Both SV and EG mussels showed increased gill mass upon E. coli challenge, while digestive gland mass was increased by bacterial challenge only in SV mussels. Bacterial challenge produced no effect on humoral reactive oxygen species levels of both groups. Total oxyradical scavenging capacity levels was reduced in challenged SV mussels but remained unaffected in EG ones. In general, EG diet decreased glutathione S-transferase and catalase activities in gill and digestive gland, compared with SV diet; but increased enzyme activity was evident in challenged mussels of both groups. Gill and digestive gland lipid peroxidation levels were higher in EG than in SV mussels but E. coli challenge had stronger effect on SV mussels. Adductor muscle RNA:DNA ratio was higher in EG mussels than in SV ones, and increased upon E. coli challenge in mussels of both groups. E. gracilis can be suggested as a nutritional and protective diet complement suitable for filtering bivalves. However, our results obtained from starved mussels show that starvation periods after supplying this diet should be avoided, since these could revert part of the acquired benefits and/or exacerbate detrimental effects.