Bivalve haemocyte adhesion, aggregation and phagocytosis: A tool to reckon arsenic induced threats to freshwater ecosystem

Acetylcholinesterase and dopamine inhibition suppress the filtration rate, burrowing behaviours, and immunological responses induced by bisphenol A in the hemocytes and gills of date mussels, Lithophaga lithophaga

Bisphenol A (BPA), a common industrial chemical with estrogenic activity, has recently gained attention due to its well-documented negative effects on humans and other organisms in the environment. The potential immunotoxicity and neurotoxicity of BPA remain poorly understood in marine invertebrate species. Therefore, the impacts of exposure to BPA on a series of behaviours, immune responses, oxidative stress, neural biomarkers, histology, and the ultrastructure of gills were investigated in the date mussel, Lithophaga lithophaga. After 28 days of exposure to 0.25, 1, 2, and 5 µg/L BPA, hemolymphs from controls and exposed date mussels were collected, and the effects of BPA on immunological parameters were evaluated. Moreover, oxidative stress and neurochemical levels were measured in the gills of L. lithophaga. BPA reduced filtration rates and burrowing behaviour, whereas a 2 µg/L BPA resulted in an insignificant increase after 24 h. The exposure of date mussels to BPA significantly increased total hemocyte counts, a significant reduction in the diameter and phagocytosis of hemocytes, as well as gill lysozyme level. BPA increased lipid peroxidation levels and SOD activity in gills exposed to 2 and 5 µg/L BPA, but decreased GSH levels and SOD activity in 0.25 and 1 µg/L BPA-treated date mussels. Dose-dependent dynamics were observed in the inhibition of acetylcholinesterase activity and dopamine levels. Histological and scanning electron microscope examination revealed cilia erosion, necrosis, inflammation, and hyperplasia formation in the gills. Overall, our findings suggest a relationship between BPA exposure and changes in the measured immune parameters, oxidative stress, and neurochemical disturbances, which may be factored into the mechanisms underlying BPA toxicity in marine molluscs, providing a scientific foundation for marine BPA risk assessment and indicating immunosuppression in BPA-exposed date mussels.

Exposure to microplastics renders immunity of the thick-shell mussel more vulnerable to diarrhetic shellfish toxin-producing harmful algae

Despite both microplastics (MPs) and harmful algae blooms (HABs) may pose a severe threat to the immunity of marine bivalves, the toxification mechanism underlying is far from being fully understood. In addition, owing to the prevalence and sudden occurrence characteristics of MPs and HABs, respectively, bivalves with MP-exposure experience may face acute challenge of harmful algae under realistic scenarios. However, little is known about the impacts and underlying mechanisms of MP-exposure experience on the susceptibility of immunity to HABs in bivalve mollusks. Taking polystyrene MPs and diarrhetic shellfish toxin-producing Prorocentrum lima as representatives, the impacts of MP-exposure on immunity vulnerability to HABs were investigated in the thick-shell mussel, Mytilus coruscus. Our results revealed evident immunotoxicity of MPs and P. lima to the mussel, as evidenced by significantly impaired total count, phagocytic activity, and cell viability of haemocytes, which may result from the induction of oxidative stress, aggravation of haemocyte apoptosis, and shortage in cellular energy supply. Moreover, marked disruptions of immunity, antioxidant system, apoptosis regulation, and metabolism upon MPs and P. lima exposure were illustrated by gene expression and comparative metabolomic analyses. Furthermore, the mussels that experienced MP-exposure were shown to be more vulnerable to P. lima, indicated by greater degree of deleterious effects on abovementioned parameters detected. In general, our findings emphasize the threat of MPs and HABs to bivalve species, which deserves close attention and more investigation.

Immunotoxicity of pentachlorophenol to a marine bivalve species and potential toxification mechanisms underpinning

The ubiquitous presence of pentachlorophenol (PCP) in ocean environments threatens marine organisms. However, its effects on immunity of marine invertebrates at environmentally realistic levels are still largely unknown. In this study, the immunotoxicity of PCP to a representative bivalve species was evaluated. In addition, its impacts on metabolism, energy supply, detoxification, and oxidative stress status were also analysed by physiological examination as well as comparative transcriptomic and metabolomic analyses to reveal potential mechanisms underpinning. Results illustrated that the immunity of blood clams was evidently hampered upon PCP exposure. Additionally, significant alterations in energy metabolism were detected in PCP-exposed clams. Meanwhile, the expressions of key detoxification genes and the in vivo contents (or activity) of key detoxification enzymes were markedly altered. Exposure to PCP also triggered significant elevations in intracellular ROS and MDA whereas evident suppression of haemocyte viability. The abovementioned findings were further supported by transcriptomic and metabolomic analyses. Our results suggest that PCP may hamper the immunity of the blood clam by (i) constraining the cellular energy supply through disrupting metabolism; and (ii) damaging haemocytes through inducing oxidative stress. Considering the high similarity of immunity among species, many marine invertebrates may be threatened by PCP, which deserves more attention.

Effects of microplastics on physiological performance of marine bivalves, potential impacts, and enlightening the future based on a comparative study

This review aims to explore the effects of microplastics and their corresponding additives on the physiological performances of marine bivalves together with their related genes. We identified gaps based on studies that were conducted on other organisms, and we conducted a comparative study on similar and relevant aspects for exploring future potential areas of study and interest. Microplastics are widely dispersed in all forms of media (solid, liquid, and gas). Exposure to an organism (including humans) is inevitable. However, impacts depend on the concentration of exposure, location of a biomarker being observed, and treatment involved. Different shapes, colors, and polymer types are reported and the transfer of microplastics along the food chain are recorded. The impacts of microplastics intensify when coupled with other chemicals or additives (referred to as xenobiotics) in a treated group. Thus, the degree of inhibition or enhancement of a physiological response magnifies when a coexposure of microplastic and a xenobiotic occurs. Microplastics have been observed to reduce immune system functionality by reducing hemocytes count, distorting oxidative system, respiration, and increasing energy consumption in bivalves due to physiological modulations that result from ingestion of microplastics or their additives. We found knowledge gaps and suggested future research directions to fully understand the impact of microplastics and their additives on marine bivalves.