A NOVEL METHODOLOGY TOWARDS ACCURATE AND AUTOMATIC

MICROPLASTICS IDENTIFICATION FROM THE AQUATIC ENVIRONMENT

V. Morgado(1)(2), C. Palma(1), R.J.N. Bettencourt da Silva(2)

(1) Instituto Hidrográfico, Rua das Trinas, 49, 1249-093 Lisboa, Portugal (vanessa.morgado@hidrografico.pt)

(2) Centro de Química Estrututal, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal

BACKGROUND

Statistics point that more than 60 % of the global

composition of marine litter is plastic and about 1.15

to 2.41 million tons of plastic are dumped into oceans

every year from rivers [1,2].

Microplastics are any synthetic solid particle or

polymeric matrix, with (ir)regular shape and with size

ranging from 1 µm to 5 mm, of either primary or

secondary manufacturing origin, which are insoluble in

water [3].

Microplastics are characterised according to their

physical and chemical properties and can be identified

from collected infrared spectrum. This spectrum is

unique for a specific plastic type, working as a

molecular fingerprint. The interpretation of the infrared

spectra can be very complex and time-consuming.

PROBLEM

ADDITIVES &

CONTAMINANTS

INGESTION

BIO

AC

CU

MU

LA

TIO

N

SAMPLING AREA

Mondego river estuaryPortugal

AUTOMATIC METHODOLOGY FOR POLYMER IDENTIFICATION

0

50

100

150

600110016002100260031003600

R (%)

Wavenumber, �̃� (cm-1)

PP Reference

or+

1. Collection of µ-FTIR spectra

PA+ PC+ PE + PS+ PTFE

2. Match determination by different algorithms:

› (Un)weighted Pearson, Spearman or Alternative CC

› Original, First or Second Derivative of Signal

NEGATIVE CASES | non-PP Particles:

0

50

100

R (%)

0

10

20

30

600110016002100260031003600

Wavenumber, �̃� (cm-1)

POSITIVE CASES | PP Particles

NEGATIVE CASESPOSTIVE CASES

3. Simulation of Match

distribution:

› Bootstrap method

4. Estimation of Distribution parameters:

P5»P from Positive Cases

P95»N from Negative Cases

5. Estimation of Validation parameters: FP & LR(+)

POSITIVE CASES

NEGATIVE CASES

P95»N P5»P

+

FP > 5 %

FP < 5 %

P5»P < P95»N

P5»P > P95»N

or

PA: Polyacrilamide

PC: Polycarbonate

PE: Polyethylene

PP: Polypropylene

PS: Polystyrene

PTFE: Polytetrafluoroethylene

Note: P5»P is associated to a TP of 95 %

LR(+) > 19FP < 5 %P5»P > P95»N6. Decision on method validity

PP identification methodsMatch type

P5»P P95»N FP (%) LR(+)Signal type Algorithm

1st derivative

ComplementarUnweighted

Spearman

0.317 0.153 0.0023 41337Original 0.316 0.163 0.0032 30157Inverse 0.321 0.188 0.0091 10487Original Unweighted

Pearson

0.209 0.112 0.14 660Complementar 0.209 0.112 0.14 660

Original Unweighted

Alternative

0.209 0.112 0.14 656Complementar 0.209 0.112 0.14 656

InverseWeighted

Spearman

0.533 0.418 0.18 5372nd derivative Inverse 0.500 0.426 0.31 3081st derivative Original 0.398 0.325 0.93 102

P95»N: 95th percentile of negative cases

P5»P: 5th percentile of positive cases

TP: True postive result rate

FP: False positive result rate

LR: Likelihood ratio«Since the methodology satisfies quality

requirements appropriate to its purpose,

it is considered valid.»

Minimum Match = P5»P = 0.317

References: V. Morgado, C. Palma, R.J.N. Bettencourt da Silva, Microplastics identification by Infrared

spectroscopy – Evaluation of identification criteria and uncertainty by the Bootstrap method, Talanta (In press,

2020). DOI: 10.1016/j.talanta.2020.121814.

[1] Alfred-Wegener-Institut, Litterbase, Online Portal for Marine Litter. Available at: https://litterbase.awi.de/.

[2] Lebreton, L., van der µZwet, J., Damsteeg, J., Slat, B., Andrady, A., Reisser, J. (2017). River plastic

emissions to the world’s oceans. Nature Communications, 8, 15611. [3] Frias, J., and Nash, R. (2019).

Microplastics: Finding a consensus on the definition. Marine Pollution Bulletin, 138, 145-147. [4] Gomes, G.B.,

Morgado, V., Palma, C. (2020). Preliminary Data on Polymer Type Identification from Estuarine Environmental

Samples. En: Cocca, M., Pace, E.D., Errico, M.E., Gentile, G., Montarsolo, A., Mossotti, R., Avella, M. (eds.)

Proceedings of the 2nd International Conference on Microplastic Pollution in the Mediterranean Sea. Springer,

Switzerland, 170-174. Background Photo credits: grupo-interacao.com.

Funding: This work was supported by Universidade de Lisboa through a PhD Scholarship 2018, the Operational

Program Mar2020 through project “AQUIMAR – Caracterização geral de áreas aquícolas para estabelecimento

de culturas marinhas” (MAR2020 nº MAR-02.01.01-FEAMP-0107) and Fundacão para a Ciência e Tecnologia

(FCT) through projects UIDB/00100/2020 and UIDP/00100/2020.