Facilitating microplastic quantification through the introduction of a cellulose dissolution step prior to oxidation: Proof-of-concept and demonstration using diverse samples from the Inner Oslofjord, Norway

• Published in: Marine environmental research Vol. 161; p. 105080
• Main Authors: Olsen, Linn Merethe Brekke, Knutsen, Heidi, Mahat, Sabnam, Wade, Emma Jane, Arp, Hans Peter H.
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 01.10.2020; Elsevier BV
• Subjects: acid treatment; alkali treatment; Cellulose; Cellulosic materials; Cellulosic resins; Chitin; Digestion; Dissolution; Dissolving; enzymatic treatment; Hydrogen peroxide; Lines; Microplastic; Microplastics; Norway; nylon; Ocean floor; Organic matter; Oxidation; Plankton; Polymers; sand; Sediments; Sodium hydroxide; Thiourea; Urea; Water treatment; Water treatment plants; Norway; Oxidation; Plankton; Microplastic; Sediments; Cellulosic materials
• ISSN: 0141-1136; 1879-0291; 1879-0291
• DOI: 10.1016/j.marenvres.2020.105080

Identifying and quantifying microplastic in marine samples can be facilitated by removing natural organic matter (NOM). Cellulosic material, like chitin, however, are a type of NOM that is resistant to chemical digestion, and difficult to eliminate from samples. To address this, a two-step digestion method was developed to remove or reduce cellulosic materials in diverse marine media. This method was applied to reference microplastics, reference cellulosic materials, and diverse marine samples from the Inner Oslofjord Norway. This included plankton, seabed sediments near a water treatment plant and driftline sand. The method was developed and tested for plastic particles >45 μm. The first-step was to pre-dissolve cellulosic materials using a mixture of urea:thiourea:NaOH. This was followed by an oxidative digestion step, here using H2O2 and NaOH. Most reference plastics were unaffected, except minor effects for PET and nylon. After sufficient repetitions, cellulosic materials in both reference and marine samples were largely removed. This method was compared to other digestion methods used for microplastic quantification, including single-step oxidation, alkaline treatment, acid treatment and enzymatic treatment. The results indicate that the pre-dissolution step greatly facilitates NOM and cellulosic material digestion for the purpose of microplastic quantification. [Display omitted] •Removal of natural organic matter (NOM) is enhanced through cellulose dissolution.•An efficient cellulose dissolution step for microplastic (MP) analysis is presented.•This method is compared with acidic, alkaline, oxidation and enzymatic digestions.•MP were quantified plankton, sediments, and driftline sand from the Inner Oslofjord.•Suggestions for further method optimization are presented.