Liu et al. 2023 — Arsenic species transformation in seafood during in vitro digestion
Liu and colleagues at Ocean University of China investigated whether organic arsenic species in seafood are converted to inorganic arsenic (iAs) during the digestive process, using an established in vitro digestion model (BARGE UBM). Their central finding is that organic arsenic forms — arsenocholine (AsC), dimethylarsinate (DMA), arsenobetaine (AsB), and monomethylarsonate (MMA) — can all be converted to As(V) during digestion at rates and extents that depend primarily on pH, digestion time, and the composition of digestion fluids. Importantly, free radicals generated during digestion appear to be the main oxidative mechanism driving the transformation. This has direct implications for arsenic risk assessment in seafood: the bioavailable iAs fraction upon absorption may be substantially higher than suggested by pre-digestion speciation analysis of the food matrix.
Key numbers
- As(V) in digested crab: 17.12 ± 1.76 µg/g (approximately 2–3-fold higher than pre-digestion iAs levels)
- As(V) in digested scallop: 138.69 ± 7.53 µg/g (approximately 2–3-fold higher than pre-digestion)
- Inorganic As not detected in digested fish samples (turbot, flounder) even though some organic species were present
- Organic As conversion rate: AsC > MMA > DMA ≈ AsB in terms of susceptibility to transformation
- Arsenocholine appeared to convert directly to MMA without the DMA intermediate (unlike arsenobetaine, which does not show this pathway)
- pH identified as the most important modulating factor; acidic gastric phase promotes free radical formation and oxidation
- Conversion was partial and species-specific; AsB showed the lowest conversion rate
Methods (brief)
In vitro digestion using the BARGE UBM (Unified Bio-accessibility Research Group) method. Seafood types: crab, scallop, turbot, flounder. As speciation by HPLC-ICP-MS. Individual organic As standards (AsC, DMA, AsB, MMA) spiked into digestion media to isolate transformation mechanisms. Free radical involvement confirmed by radical scavenger experiments. Ocean University of China, Qingdao; Food Safety Laboratory affiliation.
Implications
Certification: Complicates the use of pre-digestion iAs measurements as the sole risk metric for seafood-containing products. Bioavailable iAs in the gut may be substantially higher than detected in raw food analysis. Relevant when evaluating seafood-containing product certifications.
Courses: Illustrates why speciation analysis of food alone may underestimate iAs bioavailability from seafood; digestion-phase transformation is a critical risk factor.
App: For seafood ingredients, the app should note the gap between food-matrix iAs and potentially elevated post-digestion iAs. Crab and scallop warrant particular attention given the 2–3x amplification observed.