Hoy et al. 2023 — Arsenic speciation in freshwater fish: challenges and research needs
This systematic review, published in Food Quality and Safety (Oxford University Press), synthesizes the current state of knowledge on arsenic speciation in freshwater fish, covering extraction methods, chromatographic separation, and mass spectrometry detection, while cataloguing total arsenic and inorganic arsenic (iAs) values across species and geographies from the published literature. The review establishes that freshwater fish have substantially lower total arsenic than marine fish (freshwater fish mean tAs ~0.03–0.075 mg/kg w.w. vs marine fish ~0.42–2.82 mg/kg in cited studies), but that iAs constitutes a larger fraction of tAs in freshwater fish than in marine fish because the organoarsenic species typical of marine organisms (arsenobetaine, arsenosugars) are less abundant in freshwater species. This distinction is critical: regulatory limits set on total arsenic substantially overestimate risk for marine fish (dominated by low-toxicity arsenobetaine) but may underestimate risk for freshwater fish relative to the iAs contribution. The review also documents that a large fraction of tAs in freshwater fish remains chemically unidentified.
Key numbers
From Table 2 (Total and inorganic arsenic in freshwater fish, selected highlights):
Canada (Yellowknife Bay area lakes, dry weight):
- Lake whitefish (Great Slave Lake): tAs 1.82 ± 2.00 mg/kg d.w., iAs 0.098 ± 0.035 mg/kg d.w. (n=8)
- Northern pike (Great Slave Lake): tAs 1.59 ± 0.61 mg/kg d.w., iAs 0.078 ± 0.015 mg/kg d.w. (n=9)
- Burbot liver (Great Slave Lake): tAs 4.56 ± 2.94 mg/kg d.w., iAs 0.094 ± 0.043 mg/kg d.w. (n=5)
- High-arsenic site (Lower Martin Lake): lake whitefish tAs 5.97 ± 1.46 mg/kg d.w., iAs 0.050 ± 0.025 mg/kg d.w. (n=10)
China (purchased from fishery in Changsha, wet weight):
- Crucian carp muscle: tAs 0.16 ± 0.02 mg/kg w.w. (n=14); iAs not reported for muscle
- Mandarin fish: tAs 0.13 ± 0.04 mg/kg w.w. (n=27)
- Northern snakehead: tAs 0.37 ± 0.12 mg/kg w.w. (n=25)
- Grass carp: tAs 0.12 ± 0.08 mg/kg w.w. (n=42)
France (multiple hydrographic basins, wet weight from Noël et al. 2013):
- European eel: tAs 0.026–0.647 mg/kg w.w. (n=53)
- Bream: tAs 0.029–0.331 mg/kg w.w. (n=19)
- Roach: tAs 0.027–0.255 mg/kg w.w. (n=57)
- Common carp: tAs 0.060–0.209 mg/kg w.w. (n=4)
- Tilapia: tAs 0.623–1.22 mg/kg w.w. (n=14)
Thailand (aquaculture and natural sources, wet weight from Ruangwises 2012):
- Silver barb: tAs 0.622–1.38 mg/kg w.w. (n=14); iAs 0.078–0.154 mg/kg w.w.
- Striped catfish: also reported
Germany total diet study (Hackethal et al. 2021): freshwater fish mean tAs 0.03 mg/kg — lowest of all fish categories (migratory 0.73 mg/kg; marine 2.82 mg/kg).
Key speciation finding across the literature: iAs typically represents only a small fraction of tAs in freshwater fish muscle; in many North American samples, iAs values were consistent at ~0.04–0.13 mg/kg d.w. even where tAs varied widely, indicating the unexplained arsenic fraction (tAs minus all identified species) can be large. The review explicitly notes that in arsenic-contaminated environments, iAs concentrations in freshwater fish can increase, making speciation essential rather than optional.
Methods (brief)
Systematic review; no new primary measurements. Authors at University of Alberta (Le lab) and Alberta Health reviewed extraction methods (water/methanol, sonication, enzyme treatment), HPLC-ICPMS and HPLC-ESI-MS/MS methods for speciation in freshwater fish. Table 2 compiles published tAs and iAs data by species, country, and wet vs dry weight basis from the cited literature. DOI: 10.1093/fqsafe/fyad032, published advance access 27 July 2023.
Critical speciation note for the wiki: This review explicitly documents that iAs and tAs are non-substitutable in risk assessment. Marine fish are dominated by non-toxic arsenobetaine (tAs high, iAs very low); freshwater fish have lower tAs overall but a higher iAs/tAs ratio. Applying a total arsenic limit without speciation to fish matrices systematically produces different risk pictures for marine vs freshwater species. This is direct support for the wiki’s iAs ≠ tAs rule.
Implications
Certification: Key analytical reference for HMT&C if the program addresses freshwater fish products. Documents that iAs measurement (requiring HPLC-ICPMS speciation) is necessary to correctly assess health risk in freshwater fish; tAs alone is inadequate and can both over- and under-estimate risk depending on fish type.
Courses: Excellent teaching resource on arsenic speciation in seafood. The marine vs freshwater contrast is the clearest illustration in the literature of why tAs ≠ iAs matters for regulatory and health purposes.
App: The review supports using iAs rather than tAs for freshwater fish risk scoring. Where only tAs is available for freshwater fish, apply a conservative iAs/tAs ratio (literature suggests iAs is typically <15% of tAs in non-contaminated freshwater species, but can be higher in contaminated environments).
Microbiome: Not applicable.