Effects of lipophilic phycotoxin okadaic acid on the early development and transcriptional expression of marine medaka Oryzias melastigma

Differential developmental effects and its potential mechanism of long-term exposure to TBBPA in two generations of marine medaka (Oryzias melastigma) during early life stages

Tetrabromobisphenol A (TBBPA), a most widely used brominated flame retardant, has been detected in worldwide aquatic environments. However, the effects and mechanisms of TBBPA at environmentally realistic levels have not been well characterized in aquatic organisms. This study aims to investigate the impact of TBBPA on developmental toxicity and endocrine system in two generations of marine medaka (Oryzias melastigma) during early life stages. The results revealed that the embryos under exposure to environmentally relevant concentrations of TBBPA (0, 5, 50, and 500 μg/L) resulted in accelerated hatching and growth development in F0 generation. Conversely, delayed hatching, decreased hatch rate, and growth inhibition were observed in the F1 generation. Moreover, TBBPA disrupted the levels of THs (thyroid hormones), GH (growth hormone), and IGF (insulin growth factor). The gene transcriptional profiling implies modified gene expressions in the HPT axis, GH/IGF axis, and endoplasmic reticulum stress. The molecular docking analysis confirmed the binding affinity of TBBPA to key endocrine-related proteins, which partially elucidates the mechanism of endocrine disruption and developmental abnormalities. Endoplasmic reticulum stress may explain the developmental differences between the two generations. This was the first study to explore the multigenerational developmental toxicity of TBBPA to marine fish, which is essential for ecological risk assessment of this emerging pollutant.

Effects of okadaic acid on Pyropia yezoensis: Evidence from growth, photosynthesis, oxidative stress and transcriptome analysis

The frequent occurrences of harmful algal blooms potentially threaten marine organisms. The phycotoxin okadaic acid (OA) has been globally detected in seawater, however, the knowledge of effects of OA on macroalgae is limited. This study investigated the effects of OA (0.01, 0.1 μM) on the growth, physiological and biochemical properties, and transcriptional expression of Pyropia yezoensis. Exposure to 0.1 μM OA for 48 h led to decreased growth, oxidative stress, and lipid peroxidation in P. yezoensis. Levels of reactive oxygen species, glutathione and malondialdehyde, and activity of catalase enzyme were increased, but activity of superoxide dismutase was decreased in P. yezoensis exposed to OA. Even at the low concentration of 0.01 μM, OA influenced the photosynthetic efficiency and stimulated the pigment levels, including phycoerythrin, phycocyanin, allophycocyanin and chlorophyll a. Analytical results of amino acids indicated that OA reduced the nutritional quality of P. yezoensis. The expression of genes involved in nitrogen metabolism was up-regulated, but the genes associated with ABC transporters and photosynthesis was down-regulated by the OA exposure, suggesting that OA may affect photosynthesis and enhance nitrogen uptake and assimilation processes. This study provides a new perspective on the chemical ecology risk of phycotoxins to marine macroalgae.

Effects of Dinoflagellate Toxins Okadaic Acid and Dinophysistoxin-1 and -2 on the Microcrustacean Artemia franciscana

Harmful algal blooms are an expanding phenomenon negatively impacting human health, socio-economic welfare, and ecosystems. Such events increase the risk of marine organisms' exposure to algal toxins with consequent ecological effects. In this frame, the objective of this study was to investigate the ecotoxicological potential of three globally distributed dinoflagellate toxins (okadaic acid, OA; dinophysistoxin-1, DTX-1; dinophysistoxin-2, DTX-2) using Artemia franciscana as a model organism of marine zooplankton. Each toxin (0.1-100 nM) was evaluated for its toxic effects in terms of cyst hatching, mortality of nauplii Instar I and adults, and biochemical responses related to oxidative stress. At the highest concentration (100 nM), these toxins significantly increased adults' mortality starting from 24 h (DTX-1), 48 h (OA), or 72 h (DTX-2) exposures, DTX-1 being the most potent one, followed by OA and DTX-2. The quantitation of oxidative stress biomarkers in adults, i.e., reactive oxygen species (ROS) production and activity of three endogenous antioxidant defense enzymes (glutathione S-transferase, superoxide dismutase, and catalase) showed that only DTX-2 significantly increased ROS production, whereas each toxin affected the antioxidant enzymes with a different activity profile. In general, the results indicate a negative impact of these toxins towards A. franciscana with potential consequences on the marine ecosystem.

Effects of microorganisms, temperature and irradiation on the stability of dissolved okadaic acid and dinophysistoxin-1 in seawater

Diarrhetic shellfish toxins (DSTs) are widespread in marine environments, posing potential threats to marine ecosystems, shellfish aquaculture, and human health. Despite their prevalence, knowledge of the stability of dissolved DSTs in seawater is still limited. This study aimed to investigate the effects of bacteria, temperature, and irradiation on the stability of dissolved okadaic acid (OA) and dinophysistoxin-1 (DTX1) in seawater. Results indicated that bacteria did not contribute to the biodegradation of OA and DTX1, while their growth was inhibited by the toxins over the 7-day experiment. During a 28-day period without irradiation at 4 °C, 20 °C, and 37 °C, no degradation of OA was observed, whereas significant degradation of DTX1 occurred, with concentrations dropping to 58%-78% of the initial concentration at the end of the experiment. Under xenon lamp irradiation at 1000 W, the concentrations of DTX1 decreased by 15%-19% in seawater after 160 min, while the concentrations of OA showed minimal change. Conversely, both OA and DTX1 underwent significant degradation under mercury lamp irradiation with an irradiation intensity-dependent pattern. Additionally, the degradation rates of OA and DTX1 increased with higher concentrations of dissolved organic matter in the range of 1.2-15 mg C L⁻1. This study enhances the understanding of DST stability in seawater under varying temperature and light conditions, highlighting the complexities involved in their degradation processes. The results of this study found that ultraviolet is an important driving environmental factor for OA and DTX1 degradation in the natural marine environment. In case of harmful algal blooms with associated phycotoxins, ultraviolet irradiation can be used as a removal method for OA and DTX1.

Spatial distribution of lipophilic shellfish toxins in seawater and sediment in the Bohai Sea and the Yellow Sea, China

Lipophilic shellfish toxins (LSTs) are widely distributed in marine environments worldwide, potentially threatening marine ecosystem health and aquaculture safety. In this study, two large-scale cruises were conducted in the Bohai Sea and the Yellow Sea, China, in spring and summer 2023 to clarify the composition, concentration, and spatial distribution of LSTs in the water columns and sediments. Results showed that okadaic acid (OA), dinophysistoxin-1 (DTX1) and/or pectenotoxin-2 (PTX2) were detected in 249 seawater samples collected in spring and summer. The concentrations of ∑LSTs in seawater were ranging of ND (not detected) -13.86, 1.60-17.03, 2.73-17.39, and 1.26-30.21 pmol L-1 in the spring surface, intermediate, bottom water columns and summer surface water layers, respectively. The detection rates of LSTs in spring and summer seawater samples were 97% and 100%, respectively. The high concentrations of ∑LSTs were mainly distributed in the north Yellow Sea and the northeast Bohai Sea in spring, and in the northeast Yellow Sea, the waters around Laizhou Bay and Rongcheng Bay in summer. Similarly, only OA, DTX1 and PTX2 were detected in the surface sediments. Overall, the concentration of ∑LSTs in the surface sediments of the northern Yellow Sea was higher than that in other regions. In sediment cores, PTX2 was mainly detected in the upper sediment samples, whereas OA and DTX1 were detected in deeper sediments, and LSTs can persist in the sediments for a long time. Overall, OA, DTX1 and PTX2 were widely distributed in the water column and surface sediments in the Bohai Sea and the Yellow Sea, China. The results of this study contribute to the understanding of spatial distribution of LSTs in seawater and sediment environmental media and provide basic information for health risk assessment of phycotoxins.

Intrinsic and extrinsic pathways of apoptosis induced by multiple antibiotics residues and ocean acidification in hemocytes of scallop Argopecten irradians irradians: An interactionist perspective

The increasing prevalence of antibiotics in seawater across global coastal areas, coupled with the ocean acidification induced by climate change, present a multifaceted challenge to marine ecosystems, particularly impacting the key physiological processes of marine organisms. Apoptosis is a critical adaptive response essential for maintaining cellular homeostasis and defending against environmental threats. In this study, bay scallops Argopecten irradians irradians were exposed to multiple antibiotics (sulfamethoxazole, tetracycline, oxytetracycline, norfloxacin, and erythromycin, each at a concentration of 1 μg/L) combined with/without acidic seawater (pH 7.6) for 35 days. The single and interactive effects of the two stressors on apoptosis and the underlying mechanisms in hemocytes of A. irradians irradians were determined through flow cytometry analysis, comet assay, oxidative stress biomarkers analysis, and transcriptome analysis. Results showed that apoptosis could be triggered by either AM exposure or OA exposure, but through different pathways. Exposure to AM leads to mitochondrial dysfunction and oxidative damage, which in turn triggers apoptosis via a series of cellular events in both intrinsic and extrinsic pathways. Conversely, while OA exposure similarly induced apoptosis, its effects are comparatively subdued and are predominantly mediated through the intrinsic pathway. Additionally, the synergistic effects of AM and OA exposure induced pronounced mitochondrial dysfunction and oxidative damages in the hemocytes of A. irradians irradians. Despite the evident cellular distress and the potential initiation of apoptotic pathways, the actual execution of apoptosis appears to be restrained, which might be attributed to an energy deficit within the hemocytes. Our findings underscore the constrained tolerance capacity of A. irradians irradians when faced with multiple environmental stressors, and shed light on the ecotoxicity of antibiotic pollution in the ocean under prospective climate change scenarios.