关键词: 模式鱼类, 生物标志物, 放射生态学, 毒理效应, 生态风险评估

Abstract:

Nuclear energy has emerged as a critical source of clean energy, playing an important role in global efforts to reduce carbon emissions and combat climate change. Nuclear power plants will be operational in 32 countries until 2024, contributing significantly to global low-carbon energy. However, the rapid expansion of nuclear power has raised concerns regarding the environmental impact of radionuclides released from these facilities, particularly in aquatic ecosystems. The discharge of radioactive wastewater from nuclear power plants can affect the water quality, biodiversity, and ecosystem health. Consequently, researchers are increasingly focusing on evaluating the ecological effects of nuclear power. In the early stages of aquatic ecological impact assessment, studies have primarily focused on measuring chemical and physical parameters such as the concentration of radionuclides, pH levels, temperature, and dissolved oxygen. These parameters provide valuable information about the extent of pollution and physicochemical conditions of water. However, these studies have failed to directly reflect the biological effects of pollutants on aquatic organisms. Recognizing this limitation, researchers have begun to incorporate biological indicators into their ecological assessments. Biomarkers are measurable indicators of biological responses to environmental stressors, and play a crucial role in assessing the impact of radionuclides. These biomarkers can be molecular, cellular, tissue-based, or physiological parameters such as gene expression, protein concentrations, enzyme activities, and metabolic changes. Biomarkers offer a more comprehensive understanding of the ecological impact of pollutants by directly measuring the responses of living organisms to environmental stressors. This shift marks a significant advancement in ecological risk assessment, enabling scientists to more accurately evaluate the health of aquatic ecosystems. Aquatic ecosystems are home to diverse organisms ranging from microscopic plankton to large fish species. Owing of their complexity, researchers often rely on model organisms for laboratory studies. Model organisms are non-human species that have been extensively studied due to their genetic similarity to humans, well-characterized biology, and sensitivity to environmental changes. These organisms help us understand the effects of pollutants on broader ecosystems. Among the various model organisms used in aquatic research, fish are particularly important due to their ecological significance and sensitivity to environmental stressors. Model fish such as zebrafish (Danio rerio) and medaka (Oryzias latipes) have been widely employed in toxicological and ecological studies to assess the impact of pollutants, including radionuclides. Biomarkers for model fish can be categorized into three levels: molecular, cellular/tissue, and individual/population. Each level provides unique insights into the effects of radionuclides on aquatic organisms. Molecular biomarkers, particularly those related to oxidative stress, DNA damage, and gene expression, have been studied extensively in zebrafish and medaka. Reactive oxygen species (ROS) levels increase significantly under radiation exposure, leading to cellular damage. Studies have shown that exposure to tritiated water (HTO) or gamma radiation results in elevated ROS levels and increased apoptosis in zebrafish embryos. Additionally, radiation-induced changes in hormone levels (melatonin) and enzyme activity (catalase) were observed. DNA damage, which includes a strand breaks and mutations, is a critical biomarker. Studies have demonstrated that even low-dose radiation can cause significant genetic alterations in fishes. For example, exposure to gamma radiation induced DNA damage and altered gene expression in zebrafish embryos. Specific genes related to muscle contraction and eye opacity were also affected. Cellular/tissue biomarkers provide insights into structural and functional changes in fish tissues following radiation exposure. For example, gamma radiation has been shown to cause developmental abnormalities in zebrafish brain cells, including disorganized neuronal arrangement, cytoplasmic condensation, and mitochondrial damage. In medaka, radiation exposure leads to erythrocyte abnormalities such as cell deformation and apoptosis. Histopathological studies have also revealed radiation-induced damage in various organs including the liver, spleen, and muscles. For instance, acute gamma radiation exposure in zebrafish larvae results in increased yolk sac area, vacuolization in the liver, and structural damage to muscle tissues. These findings underscore the importance of cellular and histopathological biomarkers for assessing the toxic effects of radiation on aquatic organisms. Individual/population biomarkers can be used to evaluate an entire population. Biomarkers such as bioconcentration factors (BCF), reproductive behavior, and population dynamics are crucial for understanding the long-term ecological impacts of radionuclides. Studies have shown that radiation can reduce fecundity, alter sex ratios, and affect the survival rates of fish populations. For instance, chronic exposure to low-dose radiation has been linked to decreased egg production and altered swimming behavior in zebrafish. Furthermore, other studies have revealed that radiation-induced genetic changes can be passed down to offspring. The use of model fish biomarkers is a powerful tool for assessing the ecological impacts of nuclear power on aquatic ecosystems. Molecular and cellular biomarkers are particularly useful for the early detection of pollution due to their rapid response times and high sensitivity. However, these biomarkers often lack ecological relevance as they do not directly reflect the health of individual organisms or populations. To address this limitation, researchers have increasingly focused on individual/population biomarkers related to reproductive success, growth, and behavior, which provide a more comprehensive understanding of the ecological impacts of radiation. By integrating molecular, cellular, and population level biomarkers, researchers can gain a comprehensive understanding of the effects of radionuclides on aquatic life. Moreover, long-term monitoring of these biomarkers can help assess ecosystem recovery following radiological contamination. For instance, researchers investigating the biological communities surrounding the Chernobyl disaster have found that organisms remain suppressed and the functionality of the ecosystem has not yet fully recovered. Despite the significant progress in the use of model fish biomarkers, several challenges remain in the field of radiological ecology. A major challenge is the lack of studies on population-level effects, as most studies focus on individual organisms under controlled laboratory conditions. Additionally, the temporal variations in the biomarkers are unclear, particularly the changes following long-term exposure. Furthermore, complex interactions between radionuclides and other environmental pollutants further complicate risk assessments. Future studies should address the existing knowledge gaps, integrate laboratory findings with field studies, and improve data reliability. Future research should develop predictive models for ecological risk assessment and establish standardized monitoring protocols for radiological contaminants. Ultimately, these efforts will contribute to more accurate ecological risk assessments and inform strategies for the sustainable management of nuclear power and protection of aquatic ecosystems.

Key words: model fish, biomarkers, radioecology, toxicological effects, ecological risk assessment