Assessing meso-, micro-, and nanoplastic pollution in Los Angeles County estuaries.

Estuaries can behave as plastic pollution hotspots, although the dynamics of accumulation in these unique habitats are not understood. We quantified the current levels of meso-, micro-, and nanoplastic pollution in four Los Angeles County estuaries for the first time, as a function of distance from the water outlet and local population density. Fourier-transform infrared spectroscopy (FTIR) and microscope imaging revealed the presence of six types of plastic; polyethylene or polypropylene dominated the meso- and microplastic, and nanoplastics were identified as mainly polyolefin fibers. The distribution was heterogeneous throughout, although the sand between the river mouth and ocean generally contained more plastic than inland control samples. Population density did not appear to affect the abundance of plastic estuarine pollution. Other factors, such as waste treatment effluent, recreation, and river geography, may contribute to plastic deposition. A positive correlation between meso- and microplastic abundance provides insight into such mechanisms for accumulation.