Oxidizing Agents

Mathalon and Hill [92] used H202 (30%) at 55°C-65°C to digest mussel soft tissue, and although largely effective, the authors noted “flakes of debris” remained. Li et al. [98] also applied this method, but incubated samples in an oscillating incubator and then at room temperature for 24-48 h. Avio et al. [72] similarly tested alternate treatments in digesting intestinal tracts of mullet (Mugil cephalus). Avio et al. [72] identified that direct application of H202 resulted in only a 70% retrieval of spiked microplastics, with losses linked to H,0, foaming. A number of studies noted excessive foaming might obscure samples or lead to sample loss [72,78,92]. A density separation of stomach contents with hypersaline (NaCl) solution followed by digestion of isolated material with 15% H202 resulted in a much improved 95% recovery rate for spiked microplastics. Dehaut et al. [97] trialed 0.27 M K2S208 with 0.24 M NaOH in digesting biological tissues. This mixture was efficient in digesting biogenic material (<99.7% mass reduction), but the authors noted its expense and highlighted issues with crystallization of the digestive solutions and incomplete digestion causing blockages during filtration. Avio et al. [72] observed that 15% H,02 had no visible impact on PE or PS microspheres, although a slight modification to FTIR spectra was observed. Conversely, Nuelle et al. [100] identified some visual deformities to exposed plastic and quantified a 6.2% loss in size for PP and PE particles (<1 mm). K2S208 resulted in no changes in the mass or appearance in the majority of exposed polymers, but caused complete dissolution of cellulose acetate [97].

Naji et al. [109] applied the digestion method using 30% H202 to remove soft tissue of different mollusks. This was followed by filtration of the solution through 25 pm filter paper using a vacuum system.

Sodium Hypochlorite

Collard et al. [101] digested fish stomach contents, in an overnight exposure with ~3% NaClO. Filtered digestants were subsequently washed with 65% HN03 and digested in a 10:1 NaC10:HN03 solution for 5 minutes. The technique caused no visible degradation of a range of polymers (PET, PVC, PE, PP, PS, PC or PA).

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