A comparison of new and conventional methods for isolating microplastics ingested by fish

In recent years an increasing number of techniques have been developed to detect microplastics ingested by biota. In this study we propose a new simple and rapid method of microplastics extraction in comparison with methods commonly used. The new procedure consists of: fish gastrointestinal tract extraction; organic matter digestion with a mixture of HNO3 5% and H2O215%; vacuum pump filtration through a fiber glass membrane; microplastics identification under stereomicroscope. Six types of polymers (nylon, polypropylene, polyethylene, polystyrene, polyvinylchloride, polyethylene terephthalate) were analyzed before and after the inclusion in different mixtures of H2O2 and HNO3 in order to compare the potential plastic degradation among the tested solutions. Changes in plastic items surface, colors and shape were evaluated with imaging software for microscopy (ZEN 2011 SP1) and processing software (ImageJ), before and after the treatments. The Fourier Transformed Infra-Red Spectrometry analyses (FT-IR) were used to evaluate the integrity of polymers structure. An homogenized pool, including gastro intestinal tissue and contents (from the esophagus to the cloacae), of 30 Scomber japonicus (Houttuyn, 1782), was subdivided in aliquots of around 9 grams each. The proposed procedure for biological material removing (adding 10 ml of H2O2 15% and HNO3 5% solution for one gram of tissue at 40 °C) was compared with two common methods, one using an oxidant agent as H2O2 15% at 50 °C, the other a strong base as KOH 10% at 60 °C . Samples were processed using 10 aliquots for each protocol. The results showed an efficiency over 95% on digested biological materials for the proposed procedure. Our results are comparable with those obtained using KOH protocol but with a clearer filtering membrane and an higher efficiency with respect to H2O2 15% alone.