A new approach for routine quantification of microplastics using Nile Red and automated software (MP-VAT)

Microplastics are widespread contaminants in the environment. However, most identification protocols rely on long and subjective visual counting, which could be improved using staining dyes. Thus, the objective of this work is to identify the best staining dye protocol and create an objective and qu...

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Bibliographic Details
Published in:The Science of the total environment 2019-11, Vol.690, p.1277-1283
Main Authors: Prata, Joana C., Reis, Vanessa, Matos, João T.V., da Costa, João P., Duarte, Armando C., Rocha-Santos, Teresa
Format: Article
Language:English
Subjects:
Infrared spectra
Nanoplastics
Nile Red
Small microplastics
Staining dyes
Textile fibers
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Summary:Microplastics are widespread contaminants in the environment. However, most identification protocols rely on long and subjective visual counting, which could be improved using staining dyes. Thus, the objective of this work is to identify the best staining dye protocol and create an objective and quick automated counting software for microplastics. Tests were conducted to identify the most appropriate of eight staining dye solutions and of six wavelengths for virgin and weathered synthetic polymers, textile fibers, natural organic matter and filters. Nile Red produced the best results (without interfering in infrared spectra) rendering microplastics fluorescent at 254 nm, but with limited number of fluorescent polymers, and at 470 nm (with orange filter), with fluorescence of plastics as well as natural organic matter (requiring a digestion step). Next, a script was developed in ImageJ for the automatic quantification and characterization in shape (fiber, fragment, particle) and size of fluorescent microplastics, the Microplastics Visual Analysis Tool (MP-VAT). MP-VAT was evaluated, producing recovery rates in the range of 89.0–111.1% in spiked filters under 470 nm. Furthermore, this package is accompanied by a script that sets a scale from a known filter diameter, MP-SCALE, and a script that allows user threshold setting, MP-ACT. [Display omitted] •Nile Red was the best of eight dyes for staining microplastics.•Wavelengths of 254 and 470 nm produce the best results for Nile Red.•MP-VAT was developed for automatic quantification of fluorescent microplastics.•MP-VAT quantifies and characterizes microplastics based on shape and size.•Recovery rates of 89.0 to 111.1% deem MP-VAT accurate for microplastic quantification.
ISSN:0048-9697
1879-1026
DOI:10.1016/j.scitotenv.2019.07.060