Life cycle environmental assessment of marine debris and post-consumer waste plastics into asphalt pavements

This study evaluates locally adapted recycling strategies for marine derelict fishing gear (DFG) and post-consumer waste (PCW) plastics in Hawaiʻi using a life cycle assessment (LCA) framework. . Comparative cradle-to-gate LCAs were conducted to assess the environmental impacts of managing marine derelict fishing gear and post-consumer waste plastics through mechanical recycling and incorporation into asphalt pavements compared to incineration at Honolulu’s local waste-to-energy facility. Global warming potential (GWP), human carcinogenic toxicity, and additional environmental impact categories were evaluated using the TRACI 2.1 method. The results show that local mechanical recycling substantially reduces environmental impacts across all impact categories compared to mainland processing, and reduces GWP compared to incineration. For DFG nets, on-island recycling reduced GWP by approximately 75 % relative to mainland processing (about 1,500 vs. 6,080 kg CO 2 -eq. per metric ton) and resulted in the lowest carcinogenic impacts (5.27x10 -7 CTUh). Incineration exhibited high GWP (about 2,910 kg CO 2 -eq. per metric ton) and elevated carcinogenic emissions compared to locally recycled DFG. This trend is largely driven by material loss during combustion. PCW plastics consistently showed higher impacts than DFG nets, particularly for carcinogens, due to diesel-based electricity use during processing. Sensitivity analysis further demonstrated that substituting recycled HDPE for virgin styrene-butadiene-styrene (SBS) in asphalt binders can reduce GWP by up to 12.6 %, whereas adding recycled polymers without replacing virgin modifiers increases overall impacts. These findings highlight the importance of local processing and true material substitution in advancing circular economy strategies for plastic waste management in island contexts. • Mechanical recycling of plastics is a better option than incineration • Trade-offs exist: HDPE net recycling raises respiratory impacts but lowers GWP • Local processing is key to lowering environmental impacts in all impact categories • Adding recycled polymer to SBS asphalt raises GWP; partial SBS swap cuts it • Recycling impacts may drop as cleaner energy powers transport and processing