Methodological barriers for extraction and characterization of microplastics in biological matrix
Résumé
Pollution of the oceans by microplastics, defined as plastic particles of size below < 5mm by the NOAA, represent a major environmental problem worldwide. From an ecotoxicological point of view, the ingestion of microplastics by a wide range of marine organisms leading to substantial impacts on major physiological functions has been shown in several marine vertebrates and invertebrates. To date, only a few studies have investigated the levels of contamination of marine organisms collected in situ, partly due to technical difficulties in isolation and characterization of microplastics in biological samples. The crucial step is the identification of solvent(s) or chemical(s) that efficiently dissolve organic matter and biological tissues without degrading plastic polymers, and this in a time and cost effective way. Most published papers, as well as OSPAR recommendations for the development of a common monitoring protocol for plastic particles in fish and shellfish at the European level, used protocols containing nitric acid to digest the biological tissues, despite reports of substantial polyamide (also known as nylon) degradation with this solvent. In addition, testing a wide range of plastic polymers, and especially those commonly found in the marine environment (the “Big six”), is essential to proposevalidate a common protocol and avoid an underestimation of plastic contents in marine organisms after tissue digestion. In the present study, we reviewed existing approaches and we compared (i) their efficiency in digesting biological matrixes and (ii) their effects on 5 different plastic polymers. Effects on plastics were evaluated through visual inspection, weighing, Pyr-GC/MS and Raman analyses before and after digestion, while tissue digestates were filtered on 1µm-mesh fiber glass filters and observed using a binocular microscope. More research is currently ongoing in our laboratory on a wider range of plastic types (n=15 in total). The aim is to identify and proposevalidate a unique and standardized protocol that could be implemented at the international level to insure relevance and comparison of environmental studies on this topic.