Comparison of total atmospheric microplastic deposition on a peri-urban and an agricultural site in the Paris region

Although the topic of microplastic pollution has been a source of increasing scientific interest since 2004, some environments are less studied and less understood than other. In particular, microplastics in the atmospheric compartment have only been studied for a few years.

Here, the literature on microplastics in the atmospheric compartment is reviewed. Upon studying published articles up to December 2020, two main categories of sampling strategies were distinguished. Articles either indirectly studied the atmospheric compartment through collection of deposited particles, or directly sampled air using vacuum pumping methods. While general sampling strategies remained the same, analysing methods was more variable.

In the following study, total atmospheric fallout was monitored on two sampling sites in the Paris region. In total, three monitoring campaigns were conducted, each lasting 4 to 6 months. Total atmospheric fallout sampling was collected using passive samplers. Each sampler consisted in a 0.3 m² metal funnel held in place in a wooden crate, and connected to a glass bottle. Samples were collected over periods ranging from 3 to 10 days. After collection, samples underwent a treatment process consisting of a density-based separation followed by a Fenton treatment. Samples were then placed on an anodisc filter and characterized using an automated µFTIR mapping analysis with a Nicolet iN10 by Thermo Scientific. Microplastics could be identified down to a size of 25 µm, cutoff point determined by the µFTIR detectors.  Finally, results were analysed using the open access software for Systematic Identification of MicroPlastics in the Environment (siMPle) developed at the Aalborg university, Denmark and the Alfred Wagner Institute in Helgoland, Germany.

Preliminary results from the total atmospheric fallout monitoring campaigns showed orders of magnitudes of a few dozen particles deposited per square meter per day (p/m²/d). Results from samples collected in a peri-urban sampling site showed deposition rates of 14.3 to 47.1 p/m²/d, while results from a rural sampling site showed deposition rates of 4.3 to 18.9 p/m²/d. While a dozen different polymers were identified, the majority of particles were polypropylene, followed by polyethylene and polystyrene. As of yet, results between sites remain to be assessed. The results will also be compared with the frequency and intensity of rain events to assess the effect of precipitations on atmospheric deposition. In particular, several samples were collected during dry spells. The deposition rates on these samples may be compared to the deposition rate during single rain events or longer precipitation periods.