Marine plastic pollution has become a major concern as it threatens marine life and human health. Most of the plastic that enters the ocean is either consumed by animals and/or trapped in sediments. However, there is little information on how sediment properties might be affected. In this article, we explore the impact of microplastic inclusions in marine settings by using PVC plastic chips and two soil samples as analogues. We conducted a comprehensive experimental study to investigate changes in compressibility, strength, stiffness, thermal and hydraulic conductivity, and particle migration by varying plastic content. Results show that as low as 1% of plastic content by volume can lead to irreversible consequences in sediment behavior while coarse particles display a heightened sensitivity than pure fines. As plastic content in sediment increases year-by-year, we anticipate significant repercussions in marine life, the future landscape of the seafloor and subsurface phenomena.