Arsenic toxicity: A heart-breaking saga of a freshwater mollusc

Toxic effects of four emerging pollutants on cardiac performance and associated physiological parameters of the thick-shell mussel (Mytilus coruscus)

Robust cardiac performance is critical for the health and even survival of an animal; however, it is sensitive to environmental stressors. At present, little is known about the cardiotoxicity of emerging pollutants to bivalve mollusks. Thus, in this study, the cardiotoxic effects of four emergent pollutants, carbamazepine (CBZ), bisphenol A (BPA), tetrabromobisphenol A (TBBPA), and tris(2-chloroethyl) phosphate (TCEP), on the thick-shell mussel, Mytilus coruscus, were evaluated by heartbeat monitoring and histological examinations. In addition, the impacts of these pollutants on parameters that closely related to cardiac function including neurotransmitters, calcium homeostasis, energy supply, and oxidative status were assessed. Our results demonstrated that 28-day exposure of the thick-shell mussel to these pollutants resulted in evident heart tissue lesions (indicated by hemocyte infiltration and myocardial fibrosis) and disruptions of cardiac performance (characterized by bradyrhythmia and arrhythmia). In addition to obstructing neurotransmitters and calcium homeostasis, exposure to pollutants also led to constrained energy supply and induced oxidative stress in mussel hearts. These findings indicate that although do differ somehow in their effects, these four pollutants may exert cardiotoxic impacts on mussels, which could pose severe threats to this important species and therefore deserves more attention.

Monitoring metallothionein-like protein concentrations and cholinesterase activity in tropical cup oysters as biomarkers of exposure to metals and pesticides in the southern Caribbean, Colombia

Metallothionein-like protein concentrations (MT) and three functionally defined fractions of cholinesterase activity (ChE) were quantified in gill and digestive gland homogenates of tropical cup oysters from 5 nearshore locations in the Colombian Caribbean and correlated with sediment and tissue metal (9 metals) and pesticide (22 organophosphates, OPs, and 20 organochlorines-OCPs), as well as water physical-chemical parameters (salinity, pH, temperature, and dissolved oxygen). Tissue and sediment pesticide concentrations were below detection limits in all samples, whereas sediment and tissue metal concentrations exceeded environmental thresholds at several locations. Tissue MT and ChE biomarkers varied by a factor of 5-6 between locations. Inhibition of cholinesterase activity was negligible for all 5 sites, despite spatial-temporal variation in ChE activity, consistent with below-detection OP concentrations. Tissue MT and ChE biomarkers correlated with tissue and metal sediment concentrations, yet, statistically significant covariance between biomarkers and water chemistry parameters was also observed, indicating that both, metal concentrations and physical-chemical variables, are likely to be responsible for generating the observed spatial-temporal variations in biomarker patterns.

Effects of acute arsenic exposure in two different populations of Hyalella curvispina amphipods from North Patagonia Argentina

Arsenic (As) is a toxic metalloid present in high levels in diverse regions of Argentina. The aim of this study was to determine acute As-mediated toxicity in two different populations of autochthonous Hyalella curvispina amphipods from a reference site (LB) and an agricultural one (FO) within North Patagonia Argentina. Previously, both populations exhibited significant differences in pesticide susceptibility. Lab assays were performed to determine acute lethal concentrations, as well as some biochemical parameters. Lethal concentration (LC₅₀) values obtained after 48 and 96 hr As exposure were not significantly different between these populations, although FO amphipods appeared slightly less susceptible. LC₅₀-48 hr values were 3.33 and 3.92 mg/L As, while LC₅₀-96 hr values were 1.76 and 2.14 mg/L As for LB and FO amphipods. The no observed effect concentration (NOEC) values were 0.5 mg/L As. Cholinesterase (ChE) activity was significantly diminished by As acute exposure (0.5-1.5 mg/L As), indicative of a significant neurotoxic action for this metalloid in both amphipod populations. Activities of catalase (CAT) and glutathione S-transferase (GST) and levels of reduced glutathione (GSH) were differentially altered following As exposure. CAT activity was increased after 96 hr As exposure. GST activity and GSH levels were significantly elevated followed by either a decrease or a return to control values after 96 hr treatment. However, additional studies are necessary to understand the mechanisms underlying the As-mediated oxidative effects in H. curvispina. Our findings suggest that measurement of ChE activity in H. curvispina amphipods might serve as a useful biomarker of As exposure and effect.

Comparing the concentrations of heavy metals on two bivalve species in Santos Bay, Brazil: Subsidies to understanding the assimilation dynamic of bivalve contaminants

Contaminant substances consist of chemical elements that present the potential to adversely impact the ecology of the environment, thus representing a threat to local fauna and flora. In this context, heavy metals are critical agents that, depending on the nature and level, are potentially toxic to living organisms. In order to evaluate the bioaccumulation of heavy metals in the Santos estuary and to determine the potential influence of salinity gradient on the heavy metal bioconcentration, the present study measured the concentrations of As, Cd, Pb, Cu, Cr, Fe, Ni, and Zn in two bivalve species (Crassostrea rhizophorae and Perna Perna) sampled at different sites of Santos Bay, in the southeastern region of Brazil. Throughout the study, the "sentinel species" used were effective in bioaccumulating contaminants. In oysters, based on the Brazilian legislation, critical limits were exceeded for As, Zn, Cu, and Cr. In the case of mussels, on the other hand, only for As, Zn, and Cr, the critical limits were overcome. In the present study, obtained data suggested salinity as a determinant parameter in As incorporation processes of bivalve mollusks. PRACTITIONER POINTS: The present study presents important results for the development of environmental management policies in estuarine environments. The present study points out differences between different organisms as biomonitors, providing subsidies for the decision of an effective biomonitoring program. The present study discusses values of contaminants as a danger to public health in Santos Bay, which can be extrapolated to other similar environments around the world.

Quantification of the inflammatory responses to pro-and anti-inflammatory agents in Manila clam, Ruditapes philippinarum

Inflammation is a form of innate immune response of living organisms to harmful stimuli. In marine bivalves, inflammation is a common defense mechanism. Several studies have investigated the morphological features of inflammation in bivalves, such as hemocyte infiltration. However, the molecular and biochemical responses associated with inflammation in marine bivalves remain unexplored. Here, we investigated changes in nitric oxide (NO) levels, cyclooxygenase 2 (COX-2) activity, and allograft inflammatory factor-1 (AIF-1) gene expression levels in hemolymph samples collected from Manila clam (Ruditapes philippinarum) exposed to pro- and anti-inflammatory substances. These included the pro-inflammatory agent lipopolysaccharide (LPS), and the nonsteroidal anti-inflammatory drugs (NSAIDs) ibuprofen and diclofenac, all widely used in vertebrates. Our study showed that NO levels, COX-2 activity, and AIF-1 expression increased in response to the treatments with LPS and decreased in response to the treatments with NSAIDs in a concentration-dependent manner. These results suggest that the mechanism of inflammatory responses in bivalves is very similar to that of vertebrates, and we propose that inflammatory responses can be quantified using these techniques and used to determine the physiological status of marine bivalves exposed to biotic or abiotic stresses.

Cell to organ: physiological, immunotoxic and oxidative stress responses of Lamellidens marginalis to inorganic arsenite

The emerging pollutants in diverse habitats have created a need for basic research towards profiling the structural and functional parameters ranging from cell to organs in a diversity of species, thus enabling realistic analyses of the risks imposed by the environmental stressors. In the present study, the circulating haemocytes and digestive gland of an edible bivalve mollusc from eastern India, Lamellidens marginalis, were investigated for morphological and functional attributes under the challenge of inorganic arsenite-an up-coming threat to the natural freshwater reserves of the Indo-Gangetic flood plains. The molluscs were exposed to three sublethal concentrations of sodium arsenite under controlled laboratory conditions for a maximum time span of thirty days. The toxic exposure caused significant alteration in the haemocytometric profile. It inhibited the activities of phosphatases, transaminases and acetylcholinesterase which are iconic for assessment of the physiological homoeostasis in the haemocytes and digestive tissue. At both cellular and tissue level, immune surveillance was compromised through inhibited generation of nitric oxide, phenoloxidase and superoxide anions. Moreover, exposure to sodium arsenite promoted xenometabolic and oxidative stress in both haemocytes and digestive gland by reducing the activity of glutathione S-transferase and catalase. It inflicted inflammatory damage and promoted neplasia in the digestive tissue as evident from the histopathological observations. The findings would be crucial to gauge the impending threats from inorganic arsenite exposure to the freshwater invertebrates. Further, it creates an avenue to speculate a new model for arsenic biomonitoring.