## 5 Environmental Aspects and Health Risks
### Leading Characteristics and Release of MPs from Plastic-Modified Asphalt Mixtures
While the use of locally sourced waste plastics can significantly reduce transportation-related emissions, quality control procedures for plastic feedstocks are essential to guarantee performance consistency and environmental safety. Contamination from food residues, non-thermoplastic materials, or toxic additives may require energy-intensive cleaning and sorting processes, offsetting environmental benefits [4; 26]. Standardized preprocessing techniques, such as shredding, washing, density separation, and melt filtration, are crucial for guaranteeing feedstock purity and performance compatibility with bitumen. Moreover, material attributes including polymer type, crystallinity, molecular weight, and additive concentration affect both preprocessing necessities and environmental consequences. For example, plastics with higher melting points may require additional thermal or chemical pre-treatment, increasing energy consumption and associated greenhouse gas emissions [26; 28]. Consequently, it is imperative to establish effective feedstock preparation and quality assurance frameworks to optimize the environmental advantages of plastic-modified asphalt pavements. PE-modified asphalt was found to offer economic and environmental advantages. Incorporating 5% PE binder can decrease bitumen consumption by nearly 1 ton per kilomet of roadway and divert roughly 1.125 million plastic bags from landfills for each kilomet [39]. The incorporation of 4% PET and rABS in asphalt binders resulted in substantial decreases in rehabilitation cycles and net present worth expenses, thus reducing the equivalent annualized cost by as much as 50% relative to traditional mixtures [84]. According to [26], the utilization of recycled PE resulted in a 12.5% decrease in pavement thickness or a 7% extension of maintenance intervals, producing net environmental advantages. In a cradle-to-grave LCA study, Ref. [13] found that plastic-modified asphalt pavements utilizing PET and HDPE through the dry method enhanced pavement longevity by 14-65%, depending on structural design and traffic conditions. Although early impacts in raw material production were greater, these were mitigated by reduced maintenance requirements and landfill diversion. However, the progressive deterioration of pavement roughness over time has resulted in heightened vehicle emissions, which may overshadow total global warming potential unless maintenance cycles are meticulously optimized. Figure 3: Environmental impact of plastic-modified asphalt: **(a)** time emissions at elevated temperatures [20; 38], **(b)** leaching of hazardous substances including heavy metals and DOC [25], and **(c)** microplastic release under mechanical and environmental stress [76]. A study compared plastic-modified mixtures produced using dry and wet methods to SBS-modified asphalt and determined that recycled plastic surpassed SBS-modified mixes in the majority of environmental parameters [13]. Wet-processed mixtures demonstrated greater environmental benefits owing to superior dispersion and performance, despite elevated initial energy requirements for processing. Similarly, Ref. [89] indicated that the combining 40% RAP with 2% PET may diminish life cycle expenses by as much as 31.8% and lessen GHG emissions by 37.6%. A study by [90] determined that wet-processed plastic pellets diminished climate change, acidification, ozone depletion, and photochemical oxidation potentials by 8.6% to 15.6%, 4.7% to 8.9%, 7.2% to 13.4%, and 4.5% to 8.6%, respectively. Additionally, Refs. [13,37] emphasized that the integration of recovered plastics into asphalt advanced circular economy objectives by redirecting substantial amounts of post-consumer plastics from landfills. Nonetheless, economic viability and ecological efficacy are significantly influenced by mixture formulation, local accessibility of plastic waste, and processing logistics [4].