# Chemical composition of microplastics floating on the Mediterranean Sea surface

Maialen Palazot, Mikaël Kedzierski, Lata Soccalingame, Stéphane Bruzaud

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Maialen Palazot, Mikaël Kedzierski, Lata Soccalingame, Stéphane Bruzaud. Chemical composition of microplastics floating on the Mediterranean Sea surface. Monitoring of Mediterranean coastal areas: problems and measurement techniques, Jun 2022, Livorno, Italy. http://05208649

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<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# CHEMICAL COMPOSITION OF MICROPLASTICS FLOATING ON THE MEDITERRANEAN SEA SURFACE

M. Palazot*¹, L. Soccalingame¹, M. Kedzierski¹, S. Bruzaud¹

¹ Université Bretagne Sud, IRDL, UMR CNRS 6027, 56321 Lorient, France | *corresponding author maialen.palazot@univ-ubs.fr

## CONTEXT OF THE STUDY

The TARA Mediterranean expedition (2014) aimed to assess the spatial distribution and abundance of floating plastics in the Mediterranean Sea, and study the interactions of plastics with plankton and biodiversity in general.

Among the 14 partner laboratories, the IRDL objective was:

* Characterize the chemical nature of microplastics as a function of particle size and concentration.

<figure><img src="image_2.png" /><figcaption>Plastic
chemistry</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>Physical
oceanography</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>Marine biology</figcaption></figure>

## MATERIALS AND METHODS

### FIELD SAMPLINGS

<figure><img src="image_5.png" /></figure>

124 surface samplings
333-µm mesh size manta net

<figure><img src="image_6.png" /></figure>

54 samples analyzed in this study
> 25,000 microplastics

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /></figure>

<figure><img src="image_9.png" /></figure>

### SAMPLE PROCESSING

<figure><img src="image_10.png" /><figcaption>Wet sieving by size class</figcaption></figure>

<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /></figure>

[5-2 mm], [2-1 mm],
[1-0.5 mm], [0.5-0.315 mm]

<figure><img src="image_13.png" /><figcaption>Storage in 96-well plates</figcaption></figure>

<figure><img src="image_14.png" /></figure>

Microplastics sorted by
size class and named
with a **unique identifier**

### CHEMICAL IDENTIFICATION BY INFRARED SPECTROSCOPY (ATR-FTIR)

<caption>Random draw</caption>

N particles collected
>25,000

<figure><img src="image_15.png" /></figure>

n particles analyzed
~4,700

<figure><img src="image_16.png" /></figure>

Analyze a **statistically representative proportion** of the total population of microplastics collected [1]

<figure><img src="image_17.png" /><figcaption>Automated identification with
Poseidon software</figcaption></figure>

POSEIDON: Plastic
pOllutionS ExtractIon,
DetectIon and aNalysis

<figure><img src="image_18.png" /></figure>

Open-source, developed
with R i386 3.1.2

* Automated identification of FTIR spectra of microplastics

* Fast identification based on machine learning

## RESULTS AND DISCUSSION

<figure><img src="image_19.png" /></figure>

Proportions of the different chemical
natures according to the size range of the
collected particles (±Interval of confidence).

PE: polyethylene, PP: polypropylene, PS: polystyrene.
Statistically significant variations (*) of the chemical
nature were evidenced depending on the size range
studied.

<figure><img src="image_20.png" /></figure>

<figure><img src="image_21.png" /></figure>

Synthesis map of the sources, drift, concentration and composition of MPs in the Mediterranean Sea.
Data on concentrations and drifts of MPs are based on numerical modelling [2]. The data on chemical types
are taken from the current study and various other publications (see [1]). BF: Before flooding; AF: After flooding

Chemical aging, organic fouling and inorganic fouling lead to changes in the spectra of PE microplastics collected at sea:

<figure><img src="image_22.png" /></figure>

Infrared spectra of pristine PE, weathered PE and a PE microplastic from the Tara mission (TM0048A3).
The band between 1100 cm⁻¹ and 1045 cm⁻¹ could reflect the presence of diatoms on the surface of TM0048A3.

FTIR spectra could be
used to determine the
nature of the
plastisphere present on
the surface of plastics.

<figure><img src="image_23.png" /></figure>

SEM photograph of the surface of the sample TM0048A3.

Diatoms are clearly visible.

## CONCLUSION

* A certain **homogeneity of the chemical nature** in the Mediterranean was observed during the sampling period, with **local discrepancies**.

<figure><img src="image_24.png" /></figure>

<figure><img src="image_25.png" /></figure>

* Statistical methods and automated spectra identification are essential to reduce the amount of work required for microplastics analysis.

## PERSPECTIVES

* More targeted geographic sampling and temporal monitoring are necessary.

* FTIR spectra could give precious information on the nature of the plastisphere (eg. diatoms on PE).

* A **fouling index (FI)** could be calculated to monitor the intensity of fouling on the surface of microplastics.

NEW

$$FI = \frac{I_{1040-1020}}{I_{1480-1460}}$$

<footnote>[1] Kedzierski, M., Palazot, M., Soccalingame, L., Falcou-Préfol, M., Gorsky, G., Galgani, F., Bruzaud, S., Pedrotti, M.L. (2022). Chemical composition of microplastics floating on the surface of the Mediterranean Sea. Mar. Pollut. Bull. 174, 113284.</footnote>

<footnote>[2] Liubartseva, S., Coppini, G., Lecci, R., Clementi, E. (2018). Tracking plastics in the Mediterranean: 2D lagrangian model. Mar. Pollut. Bull. 129, 151-162.</footnote>