Separation and Identification of Microplastics in Digestive System of Bivalves

Abstract

Abstract A pretreatment method was established for separating microplastics from digestive system of bivalve sample. Qualitative and quantitative analysis of microplastics was carried out by micro-Fourier transformed infrared (μ-FT-IR) spectroscope and Stereo microscope. The method was applied to analyze the microplastics in the digestive system in Chlamys farreri and Mytilus galloprovincialis. The results showed that the digestion system of using 10% KOH had high digestion efficiency. With this digestion system, the recoveries of polypropylene (PP), polyethylene (PE), polystyrene (PS) and polyvinyl chloride (PVC) ranged from 96.7% to 98.6%, with relative standard deviation (RSD, n = 3) of ≤ 3.19%. We collected Chlamys farreri from local markets (n = 50) and Mytilus galloprovincialis from both local markets (n = 50) and wild environments (n = 15) in Qingdao, China. The results showed that microplastics were found in over 80% of the individuals purchased from the market and 40% of the wild collected individuals. The average abundance of microplastics in Chlamys farreri purchased from different markets varied between 5.2 and 19.4 items/individual or between 3.2 and 7.1 items g−1 (wet weight of digestive system), while in Mytilus galloprovincialis, the numbers varied between 1.9 and 9.6 items/individual or between 2.0 and 12.8 items g−1. Farmed mussels (Mytilus galloprovincialis) contained more microplastics (average 1.9 items per individual, 3.17 items g−1) than wild mussels (average 0.53 items individual, 2.0 items g−1). Three shapes of microplastics, including fibers, fragments and granules were separated from the samples above. Among which, fibrous microplastics, being the most dominant ones, took up 84.11% of total microplastics. The average size of fibrous microplastics ((0.66 ± 0.70) mm) was larger than that of the other two shapes of microplastics. The number of microplastics decreased with increasing microplastic sizes. Microplastics of less than 500 μm coming from different markets were in the range of 26% to 84%. And it was found that the most common polymer component in the samples was cellophane (CP), followed by polypropylene (PP). The method has some advantages such as simplicity, high efficiency, and low damage to the microplastics in the sample, and can be used to detect and analyze microplastics in seafood.