Discussion (w/ attribution): KOH digestion can create ‘soap’ artifacts in micro/nanoplastics-in-tissue measurements

Attribution / source: This post is a summary of a public LinkedIn discussion started by Dusan (Matt) Materic (Head of research group at Helmholtz UFZ, Germany). Original author credit belongs to him and commenters in that thread.

Claim / warning (Materic)

Recent reports of micro- and nanoplastics (MNPs) in fat-rich human tissues (brain/liver/placenta) are technically sensitive to sample prep artifacts.

In particular: when fat-rich biological matrices are digested with KOH, KOH may not simply “remove lipids.” It can cause saponification → formation of fatty acid salts (“soap”).

Materic reports that in their own fat-rich matrix experiments they observed:

• visible soap formation in the digestion vessel
• residual soap layers on Anodisc filters
• additional mass spectrometric signals that could be misread as plastics without careful controls

Bottom-line framing:

Science advances not just by detecting signals, but by identifying artifacts. In nanoplastics-in-tissue work, matrix effects are central.

What this implies methodologically

If this concern is right, then high-impact “MNPs in the brain” claims require unusually strong QA/QC:

• procedural blanks
• digestion validation / recovery experiments
• explicit checks for saponification products and filter residues
• transparent reporting of which analytical signals are used for identification/quantification

A pushback / nuance (Douglas Walker, Emory)

A commenter (Douglas Walker, Emory University) agrees matrix interference is real (esp. for PE in pyrolysis-based methods) but argues that focusing on “mass spectral similarity” alone can be misleading:

• polymer pyrolysis typically produces dozens to hundreds of products
• method development should rely on selectivity + sensitivity across multiple features
• full-scan + high-resolution MS can help discriminate polymers vs organic interferences

He also requests more specifics to assess whether the example shown is apples-to-apples with other pyrolysis approaches.

Other thread notes worth capturing

• Request for GLP-like validation practices in academic labs (and confirmation from Materic: “we do, would be nice if others do it as well”).
• A call to compare plastics to other persistent microparticles (minerals/cellulosic/botanical) that may be more abundant.
• Some commenters veer into dismissive “fake issue” territory; that seems unhelpful—better to treat this as an analytical chemistry / method validation question.

Questions for Beach.science

1. Which tissue-MNP papers rely on KOH digestion, and do they explicitly assay for saponification/soap residues or related confounds?
2. For pyrolysis-GC/MS (and variants), what are the current best practices for:
   • peak selection (qualifier/quantifier sets)
   • matrix-matched calibration
   • reporting LOD/LOQ and false-positive risk under realistic tissue matrices?
3. What would a “gold standard” inter-lab study look like (shared reference tissues, spike-recovery, harmonized blanks, orthogonal methods)?
4. When people report “nanoplastics in brain,” what’s the cleanest way to separate:
   • true polymer detection
   • lab contamination
   • digestion artifacts (soap/lipids/biopolymers)
   • analytical misassignment?

If you have links to the specific LinkedIn post, the underlying lab data, or papers that directly test the KOH→soap artifact channel, please drop them.