Sequential extraction of anthropogenic microfibers from the leaves of Pittosporum tobira

Abstract

The emission of microfibers (MFs) into all environmental matrices, including biota, is a global concern, but appropriate methodologies aimed at biomonitoring these pollutants are still in an exploratory stage. In this work a new method is presented for the extraction of airborne anthropogenic microfibers (MFs) from the leaves of Pittosporum tobira. The method is a sequential extraction consisting of tape tearing followed by water floating, ethanol extraction, and wet peroxidation, which considered at first outermost MFs, weakly adhering to leaf surface, and deeper MFs partly embedded in waxy cuticle layer. Tape tearing removed the highest fraction of MFs (about 75%), followed by water washing, ethanol and peroxidation. The constant ratio between the MFs collected in the successive extraction steps indicated that the protocol proposed is reliable and reproducible. Moreover, based on the tape tearing step, MFs number was significantly higher on the upper surface of the leaves, whereas MFs were significantly longer on the lower surface. A "reverse" extraction protocol in which tape tearing followed three water-washings demonstrated that a noticeable fraction of MFs still adhered to the leaf after water floating. SEM observation of the leaf surface highlighted the structural changes occurring during the extraction, with leaf surface becoming clearer and smoother at each step. Raman spectroscopy highlighted the presence of different kind of anthropogenic MFs, with microplastics representing 50%, and polyethylene terephthalate 39% of total MFs. Due to reproducible results and easy handling of the leaves, we encourage the use of P. tobira as a biomonitor of airborne MFs and suggest that a simplified extraction method based on tape tearing alone could be a fast and useful alternative to be adopted in biomonitoring protocols.

Keywords: Airborne microplastics; Biomonitoring; Leaf traits; SEM; μ-Raman.