Recent studies have shown that while the recovery of MNPs >200 um size was above 65% in fish tissue, recovery was much lower for smaller MNPs. Are there any validated processing methods available that have demonstrated higher recovery for smaller MNPs?

Answer Explanations

• Yes (please explain)

  Expert 3
  FTIR analyses may be carried out using KBr pellets embedded with known quantities of microplastics. In oxidative digestion methods, one study reported about 150% recovery rates (https://www.microplasticsolution.com/post/microplastic-recovery-experiments-beads-vs-fragments). And iterative approaches have been suggested to achieve better recoveries: https://microplastics.springeropen.com/articles/10.1186/s43591-025-00115-y. 
• No

  Expert 9
  Not to my knowledge.
• No

  Expert 2
  Yes, a progress in improving recovery methods for smaller MNPs having less than 200 µm, has been reported but from what I have researched, so far, the standardized and fully validated methods are still in the stage of ongoing research. Nonetheless, recent studies and protocols have aimed to enhance recovery efficiency for these smaller particles through a combination of optimized digestion, density separation, and detection techniques. A 2021 (DOI: 10.1016/j.scitotenv.2021.152675) study reported the development of  a multi-step protocol using enzymatic digestion, membrane filtration, centrifugation, dialysis, and SDS treatment. The authors reported that  they achieved 71–110 % recovery of fluorescently labeled PVC and PS nanoparticles having sizes ranging from ~76 nm to 750 nm from fish and oyster tissue.  In 2020  another study reported a new method for microplastic extraction from fish guts assisted by chemical dissolution, (DOI: 10.1039/d0ay01277g). The authors demonstrated that the microplastic extraction proposed method was suitable for the extraction and identification of small (>20 μm) and potentially brittle microplastic. A more recent study reported in 2024 (DOI: 10.1016/j.marpolbul.2023.115726),  highlighted that using MEF for biological or liquid samples, a  80–87 % recovery for particles between 0.5–10 µm, varying by size and charge was obtained.  Although no single method has been yet universally standardized, these methods that integrate methods like enzymatic or Fenton digestion, high-density salt separation, ultrafiltration, and advanced spectroscopic detection have shown  improved recovery rates (>70%) for smaller MNPs in controlled studies. 
• No

  Expert 4
  I am not aware of any such methods and am not able to provide more detailed information. My expectation is that reovery rates are always lower for smaller particles, given some of the possibly underlying processes like sorption to all kinds of surfaces the particles get in touch with. Smaller particles are more likely to adhere more effectiently.
• Yes (please explain)

  Expert 1
  I am aware of studies reporting lower recoveries of smaller MNPs from biota.  Tanaka et al. (2023) (https://doi.org/10.1016/j.marpolbul.2023.114812) used four types of polyethylene MNPs of different sizes (27-75 μm) and densities (ρ=1.0-1.5 g/cm3) for a recovery test from the digestive tract of hermit crabs. They found that MNPs of 63-75 μm are recovered at 80-88%, but smaller MNPs (27-45 μm) showed lower recovery (48%).  
  
  Very few studies have reported MNPs in biological samples and that are needs to be explored further.
  
  The lower recoveries of small MNPs are hypothesized to be due to aggregation of particles and binding to biological tissues and / or loss in the analytical steps due to sorption to glassware.  Modifying sample preparation steps and rinsing of glassware with solvents to extract sorbed MNPs may increase the recoveries.
  
  
  
  
• No

  Expert 5
  Improvements in routine filtration/separation are needed. 
• Yes (please explain)

  Expert 6
  There will be digestion and filtration process involved in the recovery process. To have a higher recovery for smaller MNPs, smaller mesh size filter could be used, which is also like to take longer time. 
• No

  Expert 8
  Not that i know of, but I'd have to do a very detailed lit search for the recovery values.
• Expert 7
  Yes, recent studies have validated innovative processing methods that significantly improve the recovery of smaller microplastics (<200 µm) in tissue and environmental matrices. Here are two promising approaches:
  
  

  1. KBr Pellet Embedding with FTIR Imaging
  
  

  A 2025 study introduced a method using potassium bromide (KBr) pellets embedded with microplastics for method validation and quality control 
  
  

  1. Key features include:

  • High recovery rates (>95%) for small particles, including LDPE, PVC fragments, and spherical PS beads.
  • Precise particle number determination using FTIR imaging.
  • KBr is infrared-transparent and water-soluble, making it ideal for embedding and later dissolving to release particles.

  This method is particularly effective for particle-based validation and helps monitor losses during sample prep.
  
  

  2. Soda Tablet Reference Materials
  
  

  Another validated approach involves soda tablets containing known quantities of microplastics (e.g., PE, PET, PS, PVC) in the 125–355 µm range 
  
  

  2. These tablets:

  • Are used in interlaboratory comparison (ILC) studies.
  • Show recovery rates with RSDs as low as 9%, indicating good reproducibility.
  • Are more reliable than earlier gelatin capsule carriers.

  While this method is still being optimized for particles <50 µm, it represents a scalable and standardized solution for recovery testing.