ABSTRACT
As a new type of pollutants,microplastics (small pieces of plastic with the longest dimension less than 5 mm) are bringing wide concerns by policy makers and researchers. The impact of microplastics on marine life is closely related to human health. Bivalves, as filter feeding creatures, can easily ingest microplastics in their feeding process. The microplastics in these bivalves can easily enter the human body through the food chain. In this study,a bivalve sample pretreatment method was established for separating the microplastics in their digestive system. Qualitative and quantitative analysis of microplastics was carried out by micro-Fourier transformed infrared spectroscope (μ-FT-IR) and Stereo microscope. By comparing the digestion systems of using 10% KOH and 30% H2O2, respectively, it was found that the digestion system using 10% KOH had better digestion efficiency. The recoveries of polypropylene (PP),polyethylene (PE), polystyrene (PS) and polyvinyl chloride (PVC) ranged from 96.7% to 98.6%, with RSD of less than 3.2%. Therefore, 10% KOH was used to digest organic tissue for separating the microplastics from the bivalves'digestive system. With this digestion system,the microplastics in Chlamys farreri from local markets and Mytilus galloprovincialis from both local markets and wild environments in Qingdao were separated and analyzed. The results showed that microplastics were found in over 80% of the individuals purchased from the market and 40% in the collected wild individuals. The average abundance of microplastics in Chlamys farreri purchased from different markets varied from 5.2 to 19.4 items/individual and 3.2-7.1 items/g, while in Mytilus galloprovincialis, the numbers varied from 1.9 to 9.6 items/individual and 2.0-12.8 items/g. Farmed mussels contained more microplastics (average 1. 9 items/individual, 3. 17 items/g) than wild mussels (average 0.53 items/individual, 2.0 items/g). There were various colors of microplastics. The detected microplastics came from three shapes: fibers, fragments and granules. Fibrous microplastics, being the most dominant ones,accounted for 84.11%. 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%. There was great spatial difference in the size of microplastics. The polymer composition of the microplastic was identified by μ-FT-IR. And it was found that the most common polymer component sin the samples were cellophane(CP),followed by polypropylene(PP). In the farmed mussels,PP was the most abundant component. The results showed that the abundance and types of microplastics in cultured or wild bivalves were closely related to their growing environment.