Examination of the ocean as a source for atmospheric microplastics

Abstract

Global plastic litter pollution has been increasing alongside demand since plastic products gained commercial popularity in the 1930's. Current plastic pollutant research has generally assumed that once plastics enter the ocean they are there to stay, retained permanently within the ocean currents, biota or sediment until eventual deposition on the sea floor or become washed up onto the beach. In contrast to this, we suggest it appears that some plastic particles could be leaving the sea and entering the atmosphere along with sea salt, bacteria, virus' and algae. This occurs via the process of bubble burst ejection and wave action, for example from strong wind or sea state turbulence. In this manuscript we review evidence from the existing literature which is relevant to this theory and follow this with a pilot study which analyses microplastics (MP) in sea spray. Here we show first evidence of MP particles, analysed by μRaman, in marine boundary layer air samples on the French Atlantic coast during both onshore (average of 2.9MP/m3) and offshore (average of 9.6MP/m3) winds. Notably, during sampling, the convergence of sea breeze meant our samples were dominated by sea spray, increasing our capacity to sample MPs if they were released from the sea. Our results indicate a potential for MPs to be released from the marine environment into the atmosphere by sea-spray giving a globally extrapolated figure of 136000 ton/yr blowing on shore.

Fig 1

The established SSA and organic matter ocean to atmosphere bubble burst (Fig 1A) and wave exchange (Fig 1B), and the potential micro and nano plastic exchange process mimicking these processes.

Fig 2. Sea mist and air mass MP counts for onshore and offshore wind and dense sea mist daily samples.

Fig 2A and 2C highlights days with rain using a blue outline. Days with onshore wind are presented in black, offshore wind samples are presented in green. The final sample A8a presented very low onshore wind, with sea mist annotated on the figure. Fig 2F illustrates recorded average wind speed and direction (arrows) and the maximum and minimum wind speeds (error bars). Fig 2G illustrates the onshore (ocean) sourced atmospheric MP compared to offshore (land-based) MP counts. The sample collectors, both standardised atmospheric sampling designs, are illustrated in 2h. MP types and found represented in the samples (aerosol and droplet) are presented in 2e. MP per m³ refer to the respective volume of air sampled.