Atmospheric Deposition Of Microplastics Recorded In Icelandic Lake Sediments: Estimating Microplastic Fluxes Using Short Sediment Cores

Atmospheric transport is a major pathway for microplastics (MP) to reach remote regions, and it plays a significant role in the global distribution of MP. Processes of wet and dry deposition of atmospheric MP are not well understood, but fallouts from atmospheric MP have been previously measured in remote locations. Iceland holds a very strategic location for studying long-range transport of MP, as it is scarcely populated and is located within major oceanic currents and large-scale weather patterns, far from continental Europe and North America.

This study aims to estimate flux rates of atmospheric deposition of MP in Icelandic lakes and to improve the understanding of the atmospheric transport and deposition of MP towards the Arctic. We collected surface sediment from remote crater-like lakes (elevated, with small catchment areas and no apparent main in- or outflows) to minimize contributions from runoff and avoid local sources of MP. A total of six lakes were targeted, located in various locations around Iceland to cover a large scale of mean annual precipitation, ranging from 1000 to 5000 mm. We sampled from the central parts of ice-covered lakes, using a short coring device to preserve the water-sediment interface and prevent loss of easily suspended particles. Only the interface water and upper first centimetre of sediment were collected for the MP study, and additional short cores were retrieved to assess sediment-accumulation rates, and estimate MP flux rates for each lake. MP were extracted using a heavy liquid separation method, followed by organic matter elimination with an enzymatic purification protocol, and identified using micro-FTIR spectroscopy analyses.

As a matter of concern, every sediment sample from every lake contained microplastic particles, with significant variations between lakes. Estimated MP fluxes range from 1 MP/m²/d in Langanes, a peninsula in NE Iceland to 348 MP/m²/d in Skersli, a shield volcano in the highlands, central Iceland. Polymer types PP and PE largely dominate the pollution, and the average MP size decreased with the distance from the coastline. These results emphasize the ubiquity of MP pollution, even in a remote sub-Arctic region, and highlight that MP accumulation in lake sediments is driven by a complex interaction between precipitation, wind patterns and local topography.