Microplastics (MPs) are widespread emerging contaminants for which routine, in situ detection remains a significant analytical challenge, especially in realistic, biologically active aquatic environments. Existing methods (e.g., FTIR, Raman) are labor-intensive, require extensive pre-processing, and often lack sensitivity to mixed or biofilm-coated MPs. This study addresses these limitations by implementing a direct, submersible electrical impedance spectroscopy (EIS) approach, systematically evaluating the impact of polymer type, particle size distribution, and E. coli biofilm formation on the electrical properties of MP suspensions. Results reveal that MP surface charge, size heterogeneity, and biological coatings all modulate impedance relaxation behavior in mechanistically distinct ways, enabling the discrimination of mixed polymers and realistic contamination scenarios. These mechanistic insights advance the development of rapid, minimally invasive EIS-based platforms for environmental microplastics monitoring and foster future integration with ecotoxicological risk assessment. Besides the under-development strategy, in opposition to the few found in the literature, does not require the collection of samples and can be directly used on-site. However, even if the results demonstrate strong mechanistic differentiation under controlled conditions, further validation is needed at environmentally relevant concentrations and in real-world water matrices.