A straightforward method for microplastic extraction from organic-rich freshwater samples


The extraction of microplastics from organic-rich freshwater samples is challenging and limited information is available in the literature. This study aims at developing efficient methods for water volume reduction and organic matter removal in freshwater samples, while focusing on the reduction of the economic and environmental costs, maintaining microplastics integrity and avoiding contamination. For the water volume reduction approach, centrifuging freshwater samples (water, sediment, algae, leaves, driftwood, fish tissue) at different speeds (3500, 6000 rpm) and times (5, 10 min) showed that 3500 rpm for 5 min was efficient to settle the mineral and organic material, while preserving the polymers and showing high microplastic recovering rates (93 +/- 6%). These recovery rates were significantly higher than the traditional sieving approach (77 +/- 22%). The posterior minimal consumption of reagents resulting from the reduction of water volume helped to reduce the economic and environmental costs of the devised methodology, becoming more aligned with green chemistry principles. For biogenic organic matter removal, four digestion solutions were tested on freshwater samples, namely 10% potassium hydroxide, Fenton reagent (30% H2O2 + Fe(II)), 7% and 10% sodium hypochlorite (NaClO), under 3 periods of time (1, 6 and 15 h), at 50 degrees C. Both 7% and 10% NaClO showed the highest rates of organic matter removal (86 +/- 1% and 90 +/- 1%, respectively), after 6 h at 50 degrees C. Exposure of virgin and aged polymers (polyethylene, polypropylene, polystyrene, polyvinyl chloride, nylon, polyethylene terephthalate) to NaClO showed no weight, visual, surface structure, Fourier transform infrared spectra and carbonyl index changes, except for nylon, although not to an extent that affected its identification. This method resulted in high recovery rates of polymers (92 +/- 6%). Thus, 7% NaClO at 50 degrees C for 6 h (or overnight) may be efficiently used for microplastic analysis in organic-rich freshwater samples.



subject category

Environmental Sciences & Ecology


Monteiro, SS; Rocha-Santos, T; Prata, JC; Duarte, AC; Girao, AV; Lopes, P; Cristovao, T; da Costa, JP

our authors


This work was financially supported through national funds by Fundacao para a Ciencia e a Tecnologia, under the project MicroPlasTox (POCI-01-0145-FEDER-028740) and co-funded by FEDER, within the PT2020 Partnership Agreement and Compete 2020. Thanks are also due to FCT/MCTES for the financial support to CESAM and CICECO (UIDP/50017/2020+UIDB/50017/2020, UIDB/50011/2020+UIDP/50011/2020), through national funds. AV Girao and JP da Costa thank the received funding by national funds, through FCT, in the framework contract foreseen in article 23, of the Decree-Law 57/2016, changed by Law 57/2017. This work was funded by Portuguese Science Foundation (FCT) through scholarship PD/BD/135581/2018 under POCH funds, co-financed by the European Social Fund and yPortuguese National Funds from MEC.

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