Environmental Toxicology: Principles and Pathways

Environmental toxicology examines the adverse effects of chemical, physical, and biological agents on living organisms and the ecosystems that sustain them. This chapter provides an integrated account of the discipline’s foundational principles, experimental methods, and risk-assessment frameworks, drawing on a literature survey of 3,696 peer-reviewed publications spanning six decades of research. It begins with the historical development of the field and its core conceptual vocabulary, then develops the mechanistic basis of toxicant action at cellular and molecular levels, with particular attention to oxidative stress, mitochondrial dysfunction, epigenetic reprogramming, and ferroptosis. Experimental model systems are reviewed systematically, from classical aquatic invertebrates and teleost fish to advanced in vitro platforms, including three-dimensional organoids, organ-on-a-chip microdevices, and omics approaches such as transcriptomics, metabolomics, and phosphoproteomics. The chapter also addresses ecological risk assessment, dose - response relationships, the debated hormesis hypothesis, mixture toxicology, and the challenges posed by persistent organic pollutants, heavy metals, pharmaceuticals, and microplastics. A dedicated section examines interactions between climate change and environmental chemistry, showing how changes in temperature, pH, and hydrological regimes can alter exposure to and toxicity of chemical stressors. The chapter concludes by considering the growing role of artificial intelligence and machine learning in toxicity prediction and risk management, positioning environmental toxicology at the interface of molecular biology, ecology, data science, and environmental policy.