Microplastics are small plastic particles that are less than 5mm in size and can be found in various shapes such as fibers, fragments, and spheres. They enter the marine environment through various sources, including the breakdown of larger plastic debris, microbeads in personal care products, and synthetic fibers from textiles. Microplastics have been found in various marine organisms, from plankton to large mammals, and can cause a range of negative impacts on their health. The effects of microplastics on marine organisms can be broadly categorized into physical and chemical impacts.1. Physical impacts:a Ingestion: Marine organisms can accidentally ingest microplastics while feeding, mistaking them for food particles. This can lead to blockages in the digestive system, reduced nutrient absorption, and a false sense of satiation, which can ultimately result in malnutrition, starvation, and death.b Entanglement: Microplastic fibers can entangle marine organisms, causing physical injury, restricted movement, and impaired feeding and reproduction. This can lead to reduced growth, reproductive failure, and increased vulnerability to predation.2. Chemical impacts:a Leaching of additives: Microplastics often contain various additives, such as plasticizers, flame retardants, and UV stabilizers. When ingested by marine organisms, these additives can leach out and cause toxic effects, including endocrine disruption, neurotoxicity, and genotoxicity.b Sorption of environmental contaminants: Microplastics can adsorb various environmental contaminants, such as persistent organic pollutants POPs and heavy metals, from the surrounding water. When ingested by marine organisms, these contaminants can bioaccumulate and biomagnify up the food chain, leading to toxic effects in higher trophic levels.c Microbial colonization: Microplastics can serve as a substrate for the colonization of various microorganisms, including potentially pathogenic bacteria and invasive species. When ingested by marine organisms, these microorganisms can cause infections and disrupt the host's microbiome, leading to negative health effects.The specific mechanisms by which microplastics affect the health of marine organisms depend on the type of microplastic, its size, shape, and chemical composition, as well as the species and life stage of the organism. For example, smaller microplastics are more likely to be ingested by smaller organisms, such as zooplankton, while larger microplastics may pose a greater risk to filter-feeding organisms, such as bivalves and whales. Similarly, microplastics with a higher surface area-to-volume ratio, such as fibers and irregularly shaped particles, are more likely to adsorb contaminants and facilitate the transfer of toxic substances to marine organisms.In conclusion, microplastics pose a significant threat to the health of marine organisms through various physical and chemical mechanisms. Further research is needed to better understand the specific impacts of different types of microplastics on different marine species and to develop effective strategies for mitigating the negative effects of microplastic pollution on marine ecosystems.