# An Exploratory Review of Microplastic Pollution, Associated Microbiomes and Pathogens in Water
## 4 Conclusions and Perspectives  
The reviewed literature confirms that microplastics (MPs) are ubiquitous in aquatic environments, detected in both marine and freshwater ecosystems on a global scale. The reported concentrations in surface waters typically range from a few particles per cubic meter in offshore marine regions to several thousand particles per cubic meter in river mouths and semi-enclosed coastal areas. Freshwater systems, such as lakes and estuaries influenced by urban or agricultural runoff, often exhibit higher contamination levels. Studies have also shown that MP abundance is positively correlated with proximity to anthropogenic sources such as wastewater discharges, aquaculture zones, and densely populated river basins. A growing body of evidence highlights a strong positive correlation between the abundance of microplastics and the proximity to anthropogenic sources. Urban centres, industrial zones, and agricultural catchments contribute significantly to MP loads via multiple pathways, including wastewater effluent, stormwater runoff, untreated sewage, and effluent from aquaculture and food processing facilities. For instance, river mouths and estuarine systems receiving untreated or partially treated municipal wastewater often show the highest MP concentrations, especially where population density and infrastructure stress are high. Additionally, aquaculture farms and agricultural drainage have been identified as point sources of plastic debris, particularly fibres, films, and fragments from feed bags, nets, and agrochemical packaging. These human-driven inputs not only increase the environmental burden of MPs but also enhance the potential for microbial colonization and ARG dissemination. Therefore, the spatial distribution of MPs is not random but reflects the intensity and nature of local human activities, reinforcing the need for source-targeted mitigation strategies. Among the polymer types, polyethylene (PE) and polypropylene (PP) are the most frequently identified microplastics in aquatic environments. These low-density polymers dominate due to their widespread use in packaging, textiles, and consumer goods. Other common types include polystyrene (PS), polyethylene terephthalate (PET), and polyvinyl chloride (PVC). The buoyancy and surface properties of these polymers influence their vertical distribution in the water column and their potential to be colonized by microbial biofilms. The capacity of MPs to serve as a novel habitat--the plastigsphere--has ecological and public health implications. Biofilms developing on MPs often differ in composition from surrounding planktonic communities, favouring both opportunistic and potentially pathogenic taxa such as _Vibrio, Pseudomonas, Aeromonas_, and _Corynebacterium variable_. Furthermore, MPs facilitate the horizontal transfer of antibiotic resistance genes (ARGs) within these biofilms, including clinically important genes such as _sul1_, _tetA_, _ermF_, and ESBLs (_blaCTX-M_, _blaTEM_). This process is enhanced by co-selective pressures from sorbed pollutants, including antibiotics and heavy metals. The variability in sampling protocols and analytical methods across studies highlights the need for methodological standardization to enable robust comparisons of MP levels and microbial associations across regions and timeframes. In particular, consistent metrics for reporting MP concentration (e.g., particles per m\({}^{3}\) or gram of sediment), size classification, and polymer identification are crucial. From the perspective of the One Health framework, which recognizes the interconnectedness of human, animal, and ecosystem health, microplastics must be viewed not only as persistent physical pollutants but also as biological vectors. Their ability to transport pathogens and ARGs across hydrological networks can facilitate the emergence and dissemination of waterborne diseases and antimicrobial resistance.