Field study of metal concentrations and biomarker responses in resident oysters of an estuarine system in southern Brazil.

Pollutant exposure is considered an important factor responsible for the decline in marine biodiversity of Latin American coastal ecosystems. This threat has been detected in an estuarine system in southern Brazil, which prompted an investigation into the long-term biological effects of a chronic metal contamination on resident oysters from the Laguna Estuarine System (LES). Here, we present the species- and size-specific variations of biomarker responses (catalase, glucose-6-phosphate dehydrogenase, glutathione S-transferase, and protein carbonylation) in the gills and digestive gland of Crassostrea gigas and Crassostrea gasar. In parallel, concentrations of eight metals (Al, Cd, Cr, Cu, Fe, Mn, Pb, Zn) in soft tissues were measured. Our analyses revealed that the metal levels exhibited decreasing order in both species: Zn > Fe > Al > Cu > Mn > Cd. Except for Cu and Al, metal concentrations did not differ between oyster species. Biomarker results highlighted that C. gasar presented higher antioxidant responses, whereas C. gigas showed increased biotransformation upon exposure to LES pollutants, which varied according to the tissue. However, C. gasar showed a significant higher content of protein carbonylation but was not related to metals. In our research approach, the observation of metals presence and biomarkers-related responses are considered biologically relevant from an ecotoxicological perspective and serve as a baseline for future pollution studies in estuaries of Latin America. Finally, we recommend adopting a suite of biomarkers in both C. gasar and C. gigas, regardless their size and weight, as sentinel organisms in future regional biomonitoring studies in southern Brazil.

Integrated biomarker responses in oysters Crassostrea gasar as an approach for assessing aquatic pollution of a Brazilian estuary.

The Laguna Estuarine System (LES), southern Brazil, suffers impacts from anthropogenic activities, releasing contaminants into the ecosystem. This study evaluated changes in biochemical and molecular biomarkers and contaminants concentrations in oysters Crassostrea gasar transplanted and kept for 1.5 and 7 days at three potentially contaminated sites (S1, S2, and S3) at LES. Metals varied spatiotemporally; S1 exhibited higher Ag and Pb concentrations, whereas Cd was present in S3. S2 was a transition site, impacted by Ag, Pb, or Cd, depending on the period. Organic contaminants concentrations were higher before transplantation, resulting in the downregulation of biotransformation genes transcripts levels. Phase II-related genes transcripts and metals showed positive correlations. Decreased levels of HSP90-like transcripts and antioxidant enzymes activity were related to increased pollutant loads. Integrated biomarker response index (IBR) analysis showed S1 and S3 as the most impacted sites after 1.5 and 7 days, respectively. Regardless of the scenario, LES contaminants pose a significant threat to aquatic biota.

Short-term spatiotemporal biomarker changes in oysters transplanted to an anthropized estuary in Southern Brazil.

Estuarine ecosystems are increasingly being affected by pollution caused by anthropogenic activities. In this study, Crassostrea gasar oysters were transplanted and maintained for seven days at three sites (S1, S2, and S3) in the Laguna Estuarine System (LES)-situated in southern Brazil-that has been exposed to multiple anthropic stresses. On the basis of the concentrations of metal and organic pollutants in oysters, we identified marked spatial variations in pollutant levels, with S3 showing the highest concentration of Ag, Fe, Ni, Zn, and total polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and linear alkylbenzenes (LABs), followed by S2 and S1. Along with the concentrations of pollutants, a set of biomarkers was analyzed. Oysters maintained at S3 showed enhanced protective defenses in gills, as observed by the increased levels of superoxide dismutase (SOD-like) and heat shock protein 90 (HSP90-like) transcripts and catalase (CAT) activity, concomitant with reduced lipid peroxidation (MDA) levels. Decreased antioxidant activities together with increased MDA levels are indicative of the digestive gland being more susceptible to pollutant-induced oxidative damage. Oysters transplanted into LES showed lower levels of cytochrome P450 transcripts (CYP356A1-like and CYP2AU1), and decreased glutathione S-transferase (GST) enzyme activity, suggesting lower biotransformation capacity. By integrating information regarding the concentration of metal and organic pollutants with that of molecular as well as biochemical biomarkers, our study provides novel insights into pollutant exposure and the potential biological impacts of such exposure on estuarine organisms in southern Brazil.

Metal bioaccumulation, oxidative stress and antioxidant responses in oysters Crassostrea gasar transplanted to an estuary in southern Brazil.

The present study assessed the spatial and temporal variations on metal bioaccumulation and biochemical biomarker responses in oysters Crassostrea gasar transplanted to two different sites (S1 and S2) at the Laguna Estuarine System (LES), southern Brazil, over a 45-days period. A multi-biomarker approach was used, including the evaluation of lipid peroxidation (MDA) levels, and antioxidant defense enzymes (CAT, GPx, GR and G6PDH) and phase II biotransformation enzyme (GST) in the gills and digestive gland of oysters in combination with the quantification of Al, Cd, Cu, Pb, Fe, Ni and Zn in both tissues. The exposed oysters bioaccumulated metals, especially Al, Cd and Zn in gills and digestive gland, with most prominent biomarker responses in the gills. Results showed that GPx, GR and G6PDH enzymes offered an increased and coordinated response possibly against metal (Zn, Ni, Cd and Cu) contamination in gills. GST was inversely correlated to Cd levels, being its activity significantly lowered over the 45-d exposure periods at S2. On contrary, in digestive gland GST was slightly positively correlated to Cd, revealing a compensatory mechanism between tissues to protect oysters' cells against oxidative damages, since MDA levels also decreased. CAT also appeared to be involved in the cellular protection against oxidative stress, being increased in gills. However, CAT was negatively correlated to Al levels, which might suggest a possible inhibitory effect of this metal in the gills of C. gasar. Differences between tissues were evident by the Integrative Biomarker Responses version 2 (IBRv2) indexes, which showed different pattern between tissues when studying the sites and exposure periods separately. This study provided evidence for the effectiveness of using a multi-biomarker approach in oyster C. gasar to monitor estuarine metal pollution.

Evidence of oxidative stress in wild freshwater mussels (Lasmigona costata) exposed to urban-derived contaminants.

The physiological effect of complex mixtures of anthropogenic contaminants on aquatic organisms is not well understood. This study employed a suite of sub-cellular biomarkers and general health measurements to assess the effect of urban-derived contaminants on wild freshwater mussels. Adult Lasmigona costata were collected from four sites in the Grand River (ON, Canada) that receive incremental amounts of municipal wastewater effluents and road runoff. Biomarkers of metal exposure, oxidative stress, and general health were examined in the gills of wild mussels. Concentrations of nine metals as well as the metal-binding protein, metallothionein (MT), were significantly higher (p<0.05) in mussels living downstream of the urban area. For example the concentrations of Pb, Cr and Zn were five-fold, and Ag more than 20 fold higher in mussels collected downstream of 11 municipal wastewater treatment plants and four cities compared to levels in upstream mussels. Downstream mussels showed evidence of oxidative stress, such that lipid peroxidation (LPO) (as thiobarbiturate reactive substances) was significantly elevated and the antioxidant capacity against peroxyl radicals (ACAP) was significantly decreased (p<0.01) in downstream mussels compared to upstream mussels. Regarding general health indicators, although gill lipid concentrations were similar across sites, protein concentration was significantly (p<0.001) higher in mussels collected from the upstream reference site compared to all downstream sites. The trends observed indicate that there are physiological effects in mussels associated with chronic exposure to complex urban inputs and that some biomarkers respond to municipal wastewater effluent and road runoff exposure in a cumulative manner. The observed oxidative stress response (ACAP) along with the elevation in MT, suggest that even though the defense mechanisms in the chronically exposed mussels have been activated, there is still an excess of reactive oxygen species that result in oxidative damage. The physiological effects of exposure reported in this study correspond with previously reported whole-organism impacts and declines in freshwater mussel populations in the urban-impacted region of this watershed.

Mortality, bioaccumulation and physiological responses in juvenile freshwater mussels (Lampsilis siliquoidea) chronically exposed to copper.

Several studies have indicated that the early life stages of freshwater mussels are among the most sensitive aquatic organisms to inorganic chemicals, including copper. However, little is known about the toxic mode of action and sub-lethal effects of copper exposure in this group of imperiled animals. In this study, the physiological effects of long-term copper exposure (survival, growth, copper bioaccumulation, whole-body ion content, oxygen consumption, filtration rate, ATPase activities, and biomarkers of oxidative stress) were evaluated in juvenile (6 month old) mussels (Lampsilis siliquoidea). The mussels' recovery capacity and their ability to withstand further acute copper challenge were also evaluated in secondary experiments following the 28 day exposure by assessing survival, copper bioaccumulation and whole-body ion content. Mussels chronically exposed to 2 and 12 µg Cu/L showed significantly higher mortality than those held under control conditions (mortality 20.9, 69.9 and 12.5%, respectively), indicating that juvenile L. siliquoidea is underprotected by the U.S. Environmental Protection Agency (USEPA) biotic ligand model (BLM)-derived chronic water quality criteria (WQC) (2.18 µg Cu/L) and the hardness-derived USEPA WQC (12.16 µg Cu/L). Soft tissue copper burden increased equally for both copper exposures, suggesting that chronic toxicity is not associated with copper bioaccumulation. Several physiological disturbances were also observed during chronic copper exposure. Most relevant was a decrease in whole-body sodium content paralleled by an inhibition of Na(+) K(+)-ATPase activity, indicating a metal-induced ionoregulatory disturbance. Filtration and oxygen consumption rates were also affected. Redox parameters (reactive oxygen production, antioxidant capacity against peroxyl radicals, glutathione-S-transferase (GST) activity, and glutathione (GSH) concentration) did not show clear responses, but membrane damage as lipid peroxidation (LPO) was observed in both copper exposures. Mussels previously held in control conditions or pre-exposed to 2 µg dissolved Cu/L were able to maintain their ionic homeostasis and did not experience mortality after the 4-d recovery period. In contrast, those previously exposed to 12 µg dissolved Cu/L exhibited 50% mortality indicating that they had already reached a 'point of no return'. Pre-exposure to copper did not influence mussel response to the copper challenge test. As observed for the chronic exposure, mortality of mussels held in the absence of copper and submitted to the challenge test was also associated with an ionoregulatory disturbance. These results indicate that ionoregulatory disruption in freshwater mussels chronically exposed to copper is the main mechanism of toxicity and that redox parameters do not appear to be useful as indicators of sub-lethal copper toxicity in these animals.