Does water column stratification influence the vertical distribution of microplastics?

Area of Science:

• Marine pollution
• Environmental science
• Oceanography

Background:

• Microplastic (MP) pollution is a pervasive global issue affecting all marine environments.
• Limited data exists on the sub-surface abundance and vertical distribution of microplastics.
• Water column stratification may influence microplastic distribution due to density differences.

Purpose of the Study:

• To investigate the vertical distribution of microplastics in the Kattegat/Skagerrak.
• To assess the relationship between microplastic abundance and water column structure.
• To identify dominant microplastic polymer types and sizes at different depths.

Main Methods:

• Water samples were collected from various depths at nine sites using plastic-free pump-filter devices.
• CTD measurements determined water column stratification and pycnocline depth.
• Microplastic concentrations, polymer types, sizes, and densities were analyzed.

Main Results:

• Microplastic concentrations ranged from 13 to 157 MP m⁻³ across all depths, with no significant difference between surface, mid, and deep waters.
• Polyester, polypropylene, polyethylene, and polystyrene were the dominant polymers.
• Approximately 94% of microplastics were between 11-300 μm, with 68% being high-density polymers.

Conclusions:

• Microplastics are ubiquitous throughout the marine water column in the Kattegat/Skagerrak.
• Water density and stratification did not significantly impact the vertical distribution of microplastics in this study.
• Findings highlight the widespread presence of microplastics, irrespective of water mass density variations.