The use of potassium hydroxide (KOH) solution as a suitable approach to isolate plastics ingested by marine organisms

Abstract

In studies of plastic ingestion by marine wildlife, visual separation of plastic particles from gastrointestinal tracts or their dietary content can be challenging. Earlier studies have used solutions to dissolve organic materials leaving synthetic particles unaffected. However, insufficient tests have been conducted to ensure that different categories of consumer products partly degraded in the environment and/or in gastrointestinal tracts were not affected. In this study 63 synthetic materials and 11 other dietary items and non-plastic marine debris were tested. Irrespective of shape or preceding environmental history, most polymers resisted potassium hydroxide (KOH) solution, with the exceptions of cellulose acetate from cigarette filters, some biodegradable plastics and a single polyethylene sheet. Exposure of hard diet components and other marine debris showed variable results. In conclusion, the results confirm that usage of KOH solutions can be a useful approach in general quantitative studies of plastic ingestion by marine wildlife.

Quality Criteria for the Analysis of Microplastic in Biota Samples: A Critical Review

“… 63 Therefore, it is advised to apply the original protocol of Foekema et al (2013). 6 The adequacy of the 10% KOH protocol has recently been confirmed by Kühn et al (2017) 64 and Munno et al (2018). 63 However, for smaller organisms, like the soft tissue of mussels or plankton species, enzymatic methods have also been shown to provide high digestion rates with no damage to microplastic.…”

Quantifying ecological risks of aquatic micro- and nanoplastic

“…A variety of methods have been applied to isolate nano-or microplastic from the samples for plastic analyses. These include density separations with varying types and concentrations of salts, sieving, removal of organic matter with acids, bases, peroxide and enzymes (or combinations thereof) and drying or decomposing samples at different temperatures (Hermsen et al, 2017;Hidalgo-Ruz, Gutow, Thompson, & Thiel, 2012;K€ uhn et al, 2017;Lusher, Welden, Sobral, & Cole, 2017;Rocha-Santos & Duarte, 2015;Song et al, 2015;Van Cauwenberghe, Devriese, Galgani, Robbens, & Janssen, 2015). These methods differ in the extent to which particles other than plastic are removed, the likelihood of contamination of the samples with procedural plastic particles from materials used or the work space (Foekema et al, 2013;Torre, Digka, Anastasopoulou, Tsangaris, & Mytilineou, 2016), but also in the extent to which plastic particles that are present in the environmental samples are retained in the samples.…”

“…Losses of plastic particles occur during these procedures, depending on the number of extraction cycles involved and the aggressiveness of the chemicals used. Several chemicals used for sample preservation or for the digestion of tissue or organic matter, as well as high temperatures, are known to degrade specific polymer types, which thus will affect the analysis results (D€ umichen et al, 2015;K€ uhn et al, 2017;Lenz, Enders, & Gissel, 2016;Lusher et al, 2017). After clean-up of the samples, the subsequent detection of microplastic particles is usually done by visual inspection and increasingly by polymer identification techniques using reference spectra, like FTIR and Raman spectroscopy.…”

Progress towards monitoring of microlitter in Scandinavian marine environments

“…In order to reduce the amount of natural particulate matter, and extract the microlitter from natural matter to facilitate subsequent separation and/or analysis, a chemical procedure can be employed. There are currently a number of digestion protocols for different types of samples available in the literature (Kühn et al, 2017, Mintenig, 2014. Although it is not clear which methods is overall superior, some discussion towards the approaches used by the partners will be given here.…”