Abstract
BackgroundThe ubiquitous occurrence of microplastic particles in marine and aquatic ecosystems was intensively investigated in the past decade. However, we know less about the presence, fate, and input paths of microplastic in terrestrial ecosystems. A possible entry path for microplastic into terrestrial ecosystems is the agricultural application of sewage sludge and solid bio-waste as fertilizers. Microplastic contained in sewage sludge also includes polyethylene terephthalate (PET), which could originate as fiber from textile products or as a fragment from packaging products (foils, bottles, etc.). Information about microplastic content in such environmental samples is limited yet, as most of the used analytical methods are very time-consuming, regarding sample preparation and detection, require sophisticated analytical tools and eventually need high user knowledge.ResultsHere, we present a simple, specific tool for the analysis of PET microplastic particles based on alkaline extraction of PET from the environmental matrix and subsequent determination of the monomers, terephthalic acid, using liquid chromatography with UV detection (LC-UV). The applicability of the method is shown for different types of PET in several soil-related, terrestrial environmental samples, e.g., soil, sediment, compost, fermentation residues, but also sewage sludge, suspended particles from urban water management systems, and indoor dust. Recoveries for model samples are between 94.5 and 107.1%. Limit of determination and limit of quantification are absolute masses of 0.031 and 0.121 mg PET, respectively. In order to verify the measured mass contents of the environmental samples, a method comparison with thermal extraction-desorption-gas chromatography–mass spectrometry (TED-GC/MS) was conducted. Both methods deliver similar results and corroborated each other. PET mass contents in environmental samples range from values below LOQ in agriculture soil up to 57,000 mg kg−1 in dust samples.ConclusionsWe demonstrate the potential of an integral method based on chemical extraction for the determination of PET mass contents in solid environmental samples. The method was successfully applied to various matrices and may serve as an analytical tool for further investigations of PET-based microplastic in terrestrial ecosystems.
Highlights
The ubiquitous occurrence of microplastic particles in marine and aquatic ecosystems was intensively investigated in the past decade
Depending on the sewage sludge treatment process, sewage sludge shows concentration up to 34,000 particles k g−1 [14, 15], or mass content up to 12,000 mg kg−1 [16] or 3300 mg kg−1 [17]. 92% of the detected microplastic in soil aggregates from croplands in China consisted of synthetic fibers [12]
The buoyant organic phase was removed with a pipet. 10 ml of the aqueous phase was transferred to a 100 ml flask using a graduated pipette
Summary
The ubiquitous occurrence of microplastic particles in marine and aquatic ecosystems was intensively investigated in the past decade. A possible entry path for microplastic into terrestrial ecosystems is the agricultural application of sewage sludge and solid bio-waste as fertilizers. Studies investigating the occurrence of microplastic in the soil after the applications of sewage sludge resulted in concentrations between 1100 and 3500 particles kg−1 [13]. Synthetic fibers comprise 70% of polyethylene terephthalate (PET) regarding the production volume [18], and could remain up to 15 years in soils, after the application of sludge [19]. These fibers might negatively influence soil biota. Fibers might negatively affect the germination of ryegrass [21]
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