Underwater hidden microplastic hotspots: Historical ocean dumping sites

Area of Science:

• Marine pollution
• Environmental science
• Sedimentology

Background:

• Ocean dumping of terrestrial waste, including industrial wastewater and sewage sludge, occurred in South Korea's Yellow Sea (YS) and East Sea (ES) from 1988 to 2015.
• These waste materials are known sources of microplastics, posing a significant environmental threat.

Purpose of the Study:

• To investigate the spatiotemporal distribution and characteristics of microplastics in sediments from South Korean marine environments.
• To identify the primary sources and transport pathways of microplastics, particularly at historical ocean dumping sites.

Main Methods:

• Analysis of microplastic abundance and composition in surface and core sediments from the YS, South Sea (SS), and ES, including specific dumping sites (YDP and EDP).
• Age-dating of core sediments to establish historical trends of microplastic pollution.
• Utilizing a particle transportation model to understand microplastic dispersal.

Main Results:

• Ocean dumping sites (EDP and YDP) exhibited significantly higher microplastic abundances (up to 59,457 particles/kg d.w.) compared to non-dumping areas.
• Spherical polystyrene (PS) was identified as the dominant microplastic type, originating from industrial wastewater sludge and dispersed via ocean dumping and deep circulation.
• Microplastic abundance correlated with historical ocean dumping volumes, decreasing after the dumping ban in 2015.

Conclusions:

• Ocean dumping sites are confirmed hotspots for microplastic accumulation in seafloor sediments.
• Industrial wastewater sludge dumped at sea is a major source of microplastic pollution, particularly polystyrene.
• Effective waste management and cessation of ocean dumping are crucial for mitigating microplastic contamination in marine ecosystems.