Sample pretreatment to differentiate between bioconcentration and atmospheric deposition of polycyclic aromatic hydrocarbons in mosses

• Particles of different composition are deposited on roadside moss samples.
• Washing step is mandatory to study the bioconcentration of PAHs in moss tissue.
• SEM–EDS allows to check the effectiveness in the removal of particles from sample.
• High molecular weight PAHs might be efficiently bioconcentrated in moss tissue.

In this first approach a comparison using different sample pretreatment methodologies has been made to differentiate between total atmospheric deposition and bioconcentration of polycyclic aromatic hydrocarbons (PAHs) in moss samples (Brachythecium rutabulum). Samples were collected in a densely polluted urban area in Barakaldo (Biscay, Basque Country) and submitted to different cleaning procedures with the aim to remove as many deposited atmospheric particles as possible. Analysis by means of Scanning Electron Microscopy coupled to Energy Dispersive Spectroscopy (SEM–EDS) allowed to quantify the removal efficiency of each cleaning procedure and to chemically characterise particles still present in the pre-cleaned sample. Cleaning moss samples twice with deionised water in an ultrasound bath showed up as the most suitable way to remove solid particles deposited on their surface. Discerning between bioconcentration and atmospheric deposition is therefore possible after GC–MS quantitative analysis of non-washed and washed moss samples.

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