Microplastics distribution in bottom sediments of the Baltic Sea Proper.

An abundance of microplastics particles (0.2-5 mm, MPs) in bottom sediments is analyzed based on 53 samples (3 to 215 m deep) obtained in 8 cruises of research vessels across the Baltic Sea Proper in March-October 2015-2016. MPs content varied between stations from 103 up to 10,179 items kg d.w., with the bulk mean of 863 ± 1371 items kg d.w., showing a statistically significant increase with water depth. As many as 74.5% of MPs are of fibrous shape, followed by films (19.8%) and fragments (5.7%). The distributions of fibres, fragments, films, and different types of natural bottom sediments are significantly different, highlighting the specific behaviour of each of these kinds of bottom deposits. A statistically significant correlation between water depth and fibres content is found. Based on the analysis of oceanographic factors and sedimentological principles, an erosion/transition/accumulation pattern for fibres in the Baltic Sea Proper is outlined. Fibres can be considered as a specific type of "synthetic sediment", while principles of distribution of other MPs are not yet certain.