The presence of microplastics >500 μm in organisms is usually assessed via digestion of biological tissues and subsequent analysis of filtrates. Digestion techniques need to be able to deal with a number of different tissues, such as carapaces, scales and boney materials. In addition, an organism's GIT contains its own digestive tissues but also materials ingested for alimentation that have not been broken down by digestive fluids nor excreted yet. The focus of this study is on bivalve tissues.
Digestions of bivalve tissue are commonly performed with a range of acids, enzymes, alkalis and oxidising agents, such as H2O2, the latter relying on the additional step of density separation (see examples in Table 1). Some digestion protocols apply numerous steps, which may increase the possibility of airborne contamination entering the sample. For example, Collard performed various extraction steps on filtered gastrointestinal tracts of fish species after visual inspection. Reagents included nitric acid solution.