## 6 Critical Discussion
Experimental inconsistencies are apparent in test circumstances, with several researchers using SCB or IDEAL-CT for fracture resistance, while others utilize indirect tensile strength or Marshall characteristics, hence complicating direct comparisons. Even when employing BMD frameworks, as evidenced by ref. [55], contradictory results between laboratory cracking indices and field cracking resistance highlight the necessity for standardized testing protocols and performance thresholds customized for plastic-modified systems. The environmental impacts of plastic-modified asphalt are far from negligible. While several LCAs [12; 13] demonstrate reduced greenhouse gas emissions, raw material consumption, and maintenance requirements compared to conventional pavements, these advantages are context-dependent. For example, environmental benefits are reduced when plastic feedstocks necessitate long-distance transportation or energy-intensive preprocessing [26]. Furthermore, recent research on MP emissions [14; 38] underscores the hazards linked to wear-induced separation, particularly in dry-processed pavements where plastics function as discrete particles. Despite the potential of encapsulation techniques and WMA technology to mitigate emissions and plastic exposure, field validation is still limited. Moreover, there is less agreement regarding permissible release rates of micro- and nano-plastics, as well as the ecotoxicological effects of long-term roadway exposure. The concern of fume and chemical emissions during production and installation represents another inadequately examined danger area. Some polymers, including LDPE and cPE, have been associated with reductions in VOCs at moderate mixing temperatures [20], but others, such as rABS, increase PAH emissions under comparable conditions [66]. Health risk assessments [38] indicate that occupational exposure to PAHs, such as benzo[a]pyrene, may present low-to-moderate health concerns, particularly under high-temperature conditions. Mitigation techniques employing additives such as activated carbon [68] and zeolite [69] demonstrate potential but have not been completely incorporated into normal practice. A critical necessity exists to develop temperature-dependent emission profiles for various plastic types and blending techniques, accompanied by occupational exposure modelling and sensor-based fume monitoring. Leaching behaviour remains a crucial yet insufficiently explored topic. Leaching tests employing realistic wear particle simulations (e.g., from Cantabro abrasion) have demonstrated a limited release of heavy metals alongside increased levels of DOC [25]. The effects are depending not only on the type of plastic but also on its interaction with bitumen, particle size, and environmental stresses, including UV radiation. Advancements in testing methods, such as the implementation of the US EPA TCLP and SPLP standard, for cross-study comparability is impeded by inconsistencies in sample preparation and ageing procedures. Moreover, the majority of leaching investigations are performed under batch circumstances, neglecting dynamic traffic loading, seasonal weathering, and pH variations, hence constraining their real-world applicability. Methodological divergence is a persistent troubling issue for the researchers and stakeholders in this field. The lack of uniform blending techniques, testing temperatures, plastic pre-treatment protocols, and dose criteria significantly impedes comparable evaluation. For example, research indicating enhancements in fatigue resistance through hybrid systems(e.g., LDPE + crumb rubber) frequently varies in plastic particle size and surface treatment, making hard to determine exactly what is causing a specific effect because there are multiple overlapping variables or changes happening at the same time. Similarly, variations in ageing settings (e.g., Rolling Thin-Film Oven Test (RTFOT) versus Pressure Ageing Vessel (PAV), or short-term versus field ageing) affect compatibility and storage stability evaluations, compromising generalizability.