The Hidden Poison: How Microplastics and Nanoplastics Threaten the Health of Aquatic Organisms Across Ecosystems

Synthetic polymer debris, particularly microplastics and nanoplastics (NPs), has emerged as a structurally persistent and biologically active stressor in aquatic systems. This chapter offers an integrative synthesis of how micro-/nanoplastics interact with aquatic organisms at molecular, cellular, and systemic levels. Beyond trophic ingestion, we examine sublethal toxicodynamics, including mitochondrial collapse, oxidative stress, neurotoxicity, immunomodulation, and reproductive disruption – effects now documented across phylogenetically diverse taxa. NPs, due to their ultrafine scale and surface reactivity, exhibit disproportionate bioavailability and organotropism, making them uniquely invasive at the intracellular level. We link mechanistic laboratory evidence with field-scale ecological data to trace bioaccumulation patterns and cascading disruptions across food webs. These particles are termed “hidden poison” by our laboratory in a recent paper because their effects are often cryptic, chronic, and cumulative – rarely lethal in isolation, yet profoundly destabilizing over time. Lacking scent, taste, or visibility, they bypass organismal defenses and regulatory frameworks alike. This silent toxicity challenges conventional paradigms of aquatic health assessment. By bridging ecotoxicology with systems biology and material science, this chapter proposes a new framework for understanding polymer-driven biological stress. We conclude with a call for predictive models that integrate particle-specific traits with ecosystem-level feedback, essential for mitigating this unresolved planetary contaminant.