Development of Optimal Digesting Conditions for Microplastic Analysis in Dried Seaweed Gracilaria fisheri

Abstract

Currently, research on the accumulation of microplastics (MPs) in the marine food web is being highlighted. An accurate and reliable digestion method to extract and isolate MPs from complex food matrices has seldom been validated. This study aimed to compare the efficacy of MP isolation among enzymatic-, oxidative-, and the combination of two digestion methods on red seaweed, Gracilaria fisheri. The dried seaweed sample was digested using three different methods under various conditions using enzymes (cellulase and protease), 30% H2O2, and a combination of enzymes and 30% H2O2. The method possessing the best digestion efficiency and polymer recovery rate of MPs was selected, and its effect on spiked plastic polymer integrity was analyzed by Raman spectroscopy. As a result, the enzymatic method rendered moderate digestion efficiency (59.3–63.7%) and high polymer recovery rate (94.7–98.9%). The oxidative method using 30% H2O2 showed high digestion efficiency (93.0–96.3%) and high polymer recovery rate (>98%). The combination method was the most effective method in terms of digestion efficiency, polymer recovery rate, and expenditure of digestion time. The method also showed no chemical changes in the spiked plastic polymers (PE, PP, PS, PVC, and PET) after the digestion process. All the spiked plastic polymers were identifiable using Raman spectroscopy.

Are Microplastics a Macro Issue? A Review on the Sources of Contamination, Analytical Challenges and Impact on Human Health of Microplastics in Food

“…DE). However, only two studies [10,58] reported achieved the digestion efficiency necessary. In the case of meat samples, only one study by Habib et al (2022) [32] proposed an analytical approach, but the effects of combining KOH with high temperature (i.e., 75 • C) have not been investigated.…”

“…However, due to the size limitations of the techniques, the qualification of smaller microplastics (<20 µm) using µ-FTIR should be reassessed (see Section 4). µ-FTIR >20 µm 0.39-7.02 mm PE, PP [20] µ-ATR-FTIR >7 µm 65-2500 µm LDPE, HDPE [21] µ-ATR-FTIR >7 µm 300-5000 µm PP, PE, PET, PS [22] µ-Raman >0.45 µm 5 to >1000 µm Rayon, PP, PES, PE [23] µ-ATR-FTIR >7 µm 23.2 µm-3.9 mm PA, PU [24] µ-FTIR >20 µm 45-100 µm HDPE, PP, PET, PS, PA [25] µ-FTIR >20 µm 3.8 µm-5.2 mm CP, PS, PA, PAR [26] SEM-EDX N/A 100-500 µm PE [27] µ-FTIR >20 µm 30 µm-3.5 mm PET, PP, PE [28] µ-FTIR >20 µm N/A PET [29] µ-FTIR >20 µm <300 µm PVC, PET, PTFE, HDPE, Nylon, ABS [30] µ-FTIR >20 µm 15.6-1151.1 µm PE [32] µ-FTIR >20 µm 5-20 µm PS, PP, PE [34] µ-Raman >0.45 µm <5 µm PET [35] µ-ATR-FTIR >7 µm N/A PES, PET, PS [42] µ-Raman >0.45 µm 1.2-10 µm PE, PET, PC [43] µ-FTIR >20 µm 0.06-0.11 mm PE, PP, PS, Nylon [44] µ-FTIR >20 µm 0.2-22 mm PE, PP [46] µ-Raman >0.45 µm 15-1175 µm PS [47] SEM/EDX N/A 100-1000 µm PET, PE [50] µ-Raman >0.45 µm <300 µm PE, PP, PET [54] µ-FTIR >20 µm 520 nm-270 µm Nylon, PET [56] µ-FTIR >20 µm 453-3885 µm Nylon, PP, HDPE [60] µ-Raman >0.45 µm N/A PE, PP, PS, PVC, PET [58] µ-Raman >0.45 µm 0.1-3 mm PA, PET, PAS [63] µ-ATR-FTIR >7 µm 24-1670 µm PES, ABS, EPM, nylon-6, CP, and viscose [51] µ-FTIR >20 µm <100 µm to 5000 µm PP, PE [52] µ-FTIR >20 µm 50-500 µm PVC, LDPE, PS, PP [57] µ-FTIR >20 µm 20-150 µm PE, PP, PS [61] µ-Raman >0.45 µm Abbreviations: Polyolefin, PO; Ethylene-propylene copolymer, EPM.…”

“…Furthermore, the absence (except for n = 2 papers) of digestive efficiencies poses a challenge in comparing the results, as well as the use of different times/temperatures which does not allow us to select which analytical approach might be the best. The temperatures used differ among studies, when the same reagent was used (i.e., H 2 O 2 , 30 • C for 24 h, 45 • C for 72 h, 60 • C for 36 h) [12,58,60]. Temperature affects the course of digestion [74].…”

Overviewing the Ground Reality of Microplastic Effects on Seafoods, Including Fish, Shrimps and Crabs: Future Research Directions

“…Prihandari et al [ 105 ] optimized a method for digesting MPs to analyze MPs in dried Gracilaria fisheri seaweed. The authors employed digestive methods, such as cellulase-based enzymatic and H 2 O 2 -based oxidative methods, and a combination of enzymatic and oxidative digestion methods for the analysis of MPs from the dried samples of edible red seaweed, Gracilaria fisheri .…”