Microplastics in Aquatic Ecosystems: A Review of Ecotoxicological Effects, Exposure Pathways and Trophic Transfer Risks

Microplastics, defined as plastic particles smaller than 5 mm, have emerged as pervasive pollutants in aquatic ecosystems, posing growing ecotoxicological risks to aquatic fauna. Originating from a wide array of sources, including industrial discharge, wastewater effluents, and degradation of larger plastic debris, microplastics are now documented in marine, freshwater, and estuarine environments globally. Their small size, persistence, and ability to adsorb toxic chemicals make them a multifaceted threat. The ecotoxicological impacts of microplastics, emphasising physiological, cellular, behavioural, genotoxic, and endocrine-related effects across diverse taxa such as plankton, invertebrates, fish, amphibians, and marine vertebrates. Documented impacts include digestive obstruction, energy depletion, reproductive impairments, oxidative stress, DNA damage, and disrupted predator-prey interactions. The role of microplastics as vectors for heavy metals, pesticides, and persistent organic pollutants further compounds their toxicity, often leading to synergistic effects. Weathering and biofouling enhance their chemical reactivity and alter exposure pathways. While laboratory studies provide mechanistic insights, limitations in ecological realism and a lack of long-term or multigenerational data persist. The underrepresentation of freshwater species and nanoplastic-specific studies presents further knowledge gaps. Monitoring efforts remain hindered by inconsistent analytical methods, while regulation have only recently begun addressing microplastic-specific challenges. Current knowledge on the ecotoxicological impacts of microplastics on aquatic fauna by examining their sources, pathways, exposure mechanisms, and biological effects across different taxa. Emphasis is placed on evidence from peer-reviewed experimental and field studies to assess the scale and severity of effects. Microplastic pollution poses significant ecological risks, necessitating robust policy and mitigation strategies. Global initiatives, including the EU Single-Use Plastics Directive and UNEA’s commitment to a legally binding treaty, demonstrate growing policy attention. Public engagement, biodegradable alternatives, and integrated scientific approaches are essential components of future mitigation. Urgent need for standardised methodologies, cross-ecosystem studies, and adaptive risk assessment frameworks to address microplastic pollution holistically. Bridging experimental findings with real-world ecological complexity is key to understanding the long-term consequences for biodiversity, ecosystem services, and human health, and to informing science-based environmental policies on both national and global scales.