Protocol for microplastic pollution monitoring in freshwater ecosystems: Towards a high-throughput sample processing - MICROPLASTREAM

Abstract

Robust and reproducible quantification of microplastic pollution in freshwater ecosystems requires the processing of a large amount of samples collected in varying environmental conditions. Such samples are characterized by a high amount of organic matter compared to microplastics and are highly variable in terms of the quantity and the composition of matrices, requiring a standardized analytical protocol for sample treatment and analysis. However, two important and time-consuming steps for microplastic recovery are the elimination of organic matter and microscopic inspection of samples. Here, we developed and validated a protocol, targeting particles with length ranging from 700 µm to 5 mm, that includes a double-step digestion of organic matter, consisting of incubation with potassium hydroxide followed by hydrogen peroxide solutions, and two stereomicroscopic analyses. In addition, we developed several technical improvements allowing reducing the time needed to process samples, such as the design of an adapted filter-cap to improve the content transfer. The absence of physical and chemical alterations in the investigated microplastic pellets and the average reduction of 65.8% (± 9.59 SD) of organic matter in real samples demonstrated that our protocol is fit for purpose. We recommend a second stereomicroscopic analysis to avoid underestimating microplastic concentration and particle size distribution biased towards larger particles. When used for a large-scale monitoring of microplastic pollution, this protocol resulted in an estimated time of 38 h for one person for the treatment of a batch of 24 samples, allowing a higher throughput sample processing and reproducible quantification. • Protocol customization towards high-throughput sample processing • Double step digestion to improve organic matter elimination • Importance of stereomicroscopic analysis for microplastic recovery

Microplastics in mangroves and coral reef ecosystems: a review

“…The important drivers causing microplastics pollution in the Garonne River was urbanisation, which introduced microplastics into such large streams, and hydrological parameters were majorly affecting their temporal distribution within the stream (de Carvalho et al 2021). During tourism and transportation by shipping, plastics wastes containing microplastics are being disposed of by human activities into open water sources and deterioration by external forces, such as weathering, climatic conditions lead to increasing concentrations within the coastal and marine environment.…”

“…During sample preparation, pre-treatment by digestion using acids, alkalis or enzymes are some of the preferred methods, when dealing with environmental samples, and a single or multistep digestion processes may remove any organic or inorganic constituents, if present. Chemical digestion using 10% w/w Potassium hydroxide (KOH) for 8 h at 60 °C and wet peroxidation using 30% w/w of hydrogen peroxide (H 2 O 2 ) for 16 h are commonly conducted to remove the organic contents in water samples (de Carvalho et al 2021).…”

“…To provide improved detection of microplastics, a combination of microscopic techniques, such as Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) with other detection systems like Energy Dispersive X-Ray Spectroscopy, were developed to provide a better understanding of the chemical composition, as well as its elemental analysis (Silva et al 2018). Stereomicroscopy, an advanced optical microscopic technique was then developed to detect three-dimensional structures of different sized microscopic particles present in samples along with their colour diversity (de Carvalho et al 2021).…”