Environmental contamination from microplastics and synthetic chemical pollutants represents a critical threat to global ecosystems, biodiversity, and human health. Traditional end-of-pipe remediation and linear production models have proven fundamentally insufficient to mitigate this compounding planetary crisis. This review paper systematically evaluates the transformative role of green chemistry in mitigating both microplastic fragmentation and hazardous chemical pollution. By analyzing recent advancements in sustainable molecular design, biodegradable polymer engineering, benign alternative synthesis, and catalytic upcycling technologies, this paper demonstrates how the twelve principles of green chemistry can systematically dismantle toxic industrial loops. We examine current bioremediation strategies, computational toxicological models, catalyst developments, and industrial scaling challenges, providing a comprehensive, life-cycle-based framework for future research and global policy integration.