Microplastics in Marine Sediments: Effects of Microplastics and their Sorbed Environmental Pollutants on Marine Benthic Ecosystem Functions

Microplastics (MPs) are universal, yet their abundance in marine benthic sedimentary environments, and its impacts on ecosystem functions are still unknown. This research investigates the MPs accumulation across different marine locations, from the benthic sediments of the Central Arabian Sea (CAS) and Carlsberg Ridge (CR) in the North-western Indian Ocean to the macrobenthic coastal sediments of the Dunstaffnage Bay, Scotland. The study integrates multiple approaches combining localised MPs and macrobenthic assessments and controlled mesocosm experiments to identify the impacts of MPs and their sorbents on ecosystem functions.
The Indian Ocean sediments confirmed the occurrence of MPs with significant spatial distribution, exposing higher MPs concentrations in the deep-sea sediments of CAS (2464 ± 459 MPs kg-1 d.w.) compared to the CR (1704 ± 392 MPs kg-1 d.w.). µFTIR-spectroscopy confirmed polyester/PET as the major polymer source, with the presence of non-synthetic fibres identifying the risk of overestimating synthetic burdens through visual identification alone. In contrast, coastal surveys in Dunstaffnage Bay sediments revealed a pristine baseline with no detectable MPs. However, the benthic community exhibited extreme stratification, with macrofaunal diversity were highly abundant in the top 0-2 cm, indicating a high vulnerability to surface-level disruptions.
A 21-day mesocosm incubation research was conducted to investigate the impacts of primary and secondary microplastics (SecMPs) with sorbed pollutants (PAHs, PCBs), which did not cause acute mortality but triggered significant functional changes. The results showed that weathered SecMPs reduced bioirrigation efficiency by 63% and altered bioturbation rates. However, no significant differences were observed between primary virgin PVC spheres (VPVCs) and those with sorbed diesel (DPVCs), suggesting that longer duration experiments are essential to measure the impacts of sorbed pollutants. These findings indicated that the MPs pollution poses a significant, indirect, but transformative threat to the fundamental processes that sustain benthic ecosystem health.