Development of efficient analytical method for microplastics in bivalves

Abstract

As marine plastic debris breaks down to microplastics in the environment, it becomes available for ingestion by a wide range of small marine organisms. Among them, filter feeding bivalves can be an important monitoring species due to high accumulation of microplastics as well as sources of human microplastic consumption. There is, however, no standardized analytical method for microplastics in bivalve species. In order to develop an adequate and efficient pretreatment method, various types of digestion solution such as enzymes (Savinase+Lipase, Stainzyme plus, and Proteinase-K), base (KOH), acid (HNO3), and hydrogen peroxide (H2O2), and density separation solution such as sodium chloride, sodium iodide (NaI), and lithium metatungstate (LMT) were compared in four species of bivalves (mussel, oyster, scallop, and clam). Digestion efficiency of biological materials and physio-chemical changes of polymeric materials were evaluated. The optimized protocol developed involves a digestion of tissue by 10% KOH solution at 40˚C for one day, followed by density separation using LMT (1.6 g/ml) solution. This method can digest over 50 g of tissue (10 individual) at one time, without any surface change of the tested polymers with the exception of alkyd. The method was also found to have high microplastic recoveries in both high density and low density polymer (100% for polyethylene, 100% for expanded polystyrene, 93±6% for polypropylene, 93±6% for nylon, and 90±14% for polyester). This method is efficient for detection and quantification of microplastic in large amount of tissue samples, providing a method to monitor microplastic contamination in marine bivalves.