Developing plastic litter density maps along the Danube riverbank near Novi Sad, Serbia

Plastic accumulation along riverbanks is a significant environmental issue, with rivers acting as major carriers of plastic debris entering marine ecosystems. Large plastic items such as bottles and bags degrade in the environment, ultimately breaking down into microplastics (MPs). Investigating the relationship between environmental conditions and plastic degradation is crucial for developing strategies to mitigate the impact of MPs pollution in freshwater ecosystems. To better understand the composition and sources of plastic waste along the Danube riverbank near the city of Novi Sad, a drone imaging study was conducted to detect and map litter, whereby plastic waste was sampled by an adjusted Clean River protocol [1]. The remote litter monitoring was performed using UAS/drone data and a dedicated machine learning platform for detecting beached litter, the Coastal Marine Litter Observatory (cmlo.scidrones.com) [2]. Fourier-transform infrared (FTIR) spectroscopy was used to analyse the collected samples to identify the most common polymers found. The litter density maps show varying degrees of plastic pollution, from zero plastic items detected upstream of Novi Sad, to moderate plastic presence downstream of the city. Plastic bottles, caps, cups and bags were the most prevalent types of plastic waste, all collected across various riverbank locations. The distribution reflects both direct disposal and waste carried by the river. Other plastic waste found included disposable lighters, cigarette packs, electronic cigarettes, flip-flops and nets, indicating pollution from multiple sources. FTIR spectroscopy revealed that plastic bottles and cups were predominantly made of polyethylene terephthalate (PET), a polymer widely used in beverage and food packaging. PET was also identified in flexible packaging materials, such as cracker wrappers, and in components of electronic cigarettes. Plastic caps were primarily composed of polyethylene (PE). Plastic bags were mainly made of PE, often enriched with industrial pigments. Polyurethane (PU), a polymer often used in shoe production, was found in flip-flops and other footwear fragments. Polypropylene (PP) is widely used in packaging, and was found in cigarette boxes and chocolate wrappers. Polyamide (PA) was detected in plastic nets, likely associated with fishing or industrial activities, indicating the presence of specialized polymers in the wastes detected [1]. These initial observations do not necessarily show correlation of pollution relative to upstream vs. downstream locations and proximity to the city, since visit frequency and any possible cleaning activities were not taken into account. The variety of polymers identified highlights the complexity of plastic pollution in river environments. While PET and PE were the most prevalent materials, the presence of other polymers such as PU, PP, and PA demonstrates the diverse nature of the pollution load. These findings suggest that consumer packaging, especially related to food and beverages, is a major contributor to plastic waste in the Danube, while specialized products like footwear and fishing materials also play significant roles.