The chapter reviews the ecotoxicological responses of algae to various contaminants in aquatic environments, emphasizing their significant role in maintaining aquatic ecosystems. Algae are vulnerable to environmental stressors and contaminants, which can lead to harmful algal blooms, deplete oxygen levels, and create dead zones. Key points include: 1. **Polycyclic Aromatic Hydrocarbons (PAHs)**: PAHs accumulate in food chains and ecosystems, posing a major concern for environmental health. 2. **Bisphenol A (BPA)**: BPA negatively impacts algae by inhibiting biochemical and physiological processes, with effective concentrations ranging from 1.0 mg L⁻¹ to 100 mg L⁻¹. 3. **Per- and Polyfluoroalkyl Substances (PFAS)**: Despite low levels in the environment, combined exposure to PFAS can have significant toxic effects, including growth inhibition and damage to photosynthesis. 4. **Environmental Stress**: Anthropogenic disturbances, such as pollution and land-use changes, contribute to biodiversity degradation and adverse impacts on benthic algae. 5. **Chemical, Biological, and Physical Factors**: The ecotoxicity of chemicals to algae is influenced by various factors, creating complex effects at the biological community level. 6. **Importance of Monitoring and Interventions**: The review underscores the necessity for monitoring and strategic interventions to protect the sustainability of aquatic ecosystems. The introduction highlights the increasing global pressure of chemical and micropollutant stressors on ecosystems, emphasizing the need for enhanced stress monitoring and risk assessment to address the adverse ecological impacts. The chapter also discusses the direct and indirect effects of chemicals on algae, including genotoxicity and immune function compromise, and the role of microalgae in the dispersal and bioaccumulation of toxic chemicals.The chapter reviews the ecotoxicological responses of algae to various contaminants in aquatic environments, emphasizing their significant role in maintaining aquatic ecosystems. Algae are vulnerable to environmental stressors and contaminants, which can lead to harmful algal blooms, deplete oxygen levels, and create dead zones. Key points include: 1. **Polycyclic Aromatic Hydrocarbons (PAHs)**: PAHs accumulate in food chains and ecosystems, posing a major concern for environmental health. 2. **Bisphenol A (BPA)**: BPA negatively impacts algae by inhibiting biochemical and physiological processes, with effective concentrations ranging from 1.0 mg L⁻¹ to 100 mg L⁻¹. 3. **Per- and Polyfluoroalkyl Substances (PFAS)**: Despite low levels in the environment, combined exposure to PFAS can have significant toxic effects, including growth inhibition and damage to photosynthesis. 4. **Environmental Stress**: Anthropogenic disturbances, such as pollution and land-use changes, contribute to biodiversity degradation and adverse impacts on benthic algae. 5. **Chemical, Biological, and Physical Factors**: The ecotoxicity of chemicals to algae is influenced by various factors, creating complex effects at the biological community level. 6. **Importance of Monitoring and Interventions**: The review underscores the necessity for monitoring and strategic interventions to protect the sustainability of aquatic ecosystems. The introduction highlights the increasing global pressure of chemical and micropollutant stressors on ecosystems, emphasizing the need for enhanced stress monitoring and risk assessment to address the adverse ecological impacts. The chapter also discusses the direct and indirect effects of chemicals on algae, including genotoxicity and immune function compromise, and the role of microalgae in the dispersal and bioaccumulation of toxic chemicals.