The high levels of environmental pollutants like heavy metals and microplastics have prompted researchers to invent new remediation strategies, which might be accompanied by drawbacks, including the risk of secondary pollution, being costly, and inefficient. So, the aim of this study is the reduction of these environmental pollutants by the application of nanoparticle-producing bacteria. For this purpose, from 22 screened bacterial isolates of the Caspian Sea, the isolate (N1.5.2) was used to produce ZnO NPs, which were characterized by techniques like FTIR, XRD, Raman, SEM, EDX, UV-vis spectroscopy, Zeta potential, and DLS. Subsequently, different protocols of bacterial nanoparticle production (using supernatant, extract, biomass, and dilution) were compared by UV-vis spectroscopy. Then, the produced nanoparticles were applied to polystyrene microplastics to degrade them. This process was monitored by SEM and FTIR. The selected bacterial isolate (N1.5.2) was identified and its phylogenetic tree of life was depicted. The results of the blast illustrated 100% similarity of N1.5.2 to Bacillus cereus. The produced ZnO NPs peaked at 360 nm in their UV-vis spectrum. They showed a crystalline structure in the zincite phase and dispersed in the range of 171–262 nm in an aqueous environment with a PDI of 0.444 and zeta potential of -5.60 meV. Moreover, the comparative study between different production protocols has shown that ZnO nanoparticles produced by bacterial extract have higher UV-vis peak values. Furthermore, the photocatalytic activity of ZnO NPs and microplastic degradation has been proved by SEM and FTIR.

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