Centre for Food Safety 2019 — Organotin compounds in aquatic products, Hong Kong
This 2019 government risk assessment report from Hong Kong’s Centre for Food Safety (CFS) measured four organotin compounds (OTC) — tributyltin (TBT), dibutyltin (DBT), di-n-octyltin (DOT), and triphenyltin (TPT) — in 341 samples of fish, crustaceans, and molluscs collected from local markets in 2017–2018, finding detection in 60% of samples with TPT as the dominant compound. Dietary exposures for both average (0.020 mcg/kg bw/day as Sn) and high (0.057 mcg/kg bw/day as Sn) consumers were below the EFSA group TDI of 0.1 mcg/kg bw/day (expressed as Sn), representing 20% and 57% of the TDI respectively, and the CFS concluded no adverse health outcome was likely.
Important note on metals classification: The analytes in this paper are organotin compounds (TBT, DBT, DOT, TPT), not inorganic tin. Organotin species are distinct from total tin (Sn) in toxicological profile, environmental behavior, and regulatory framework. These compounds enter aquatic food chains primarily through antifouling paints on ships and from agricultural pesticide use; they are endocrine disruptors at very low concentrations (1 ng/L in water for TBT and TPT imposex effects) and are not addressed by the HMTc analyte vocabulary. They are included here under metals: [Sn] for routing purposes because they are tin-organic compounds, but the synthesis page for tin/organotin must not conflate inorganic Sn with OTC toxicology.
Key numbers
All concentrations expressed as mcg/kg (equivalent to µg/kg = ppb) as Sn unless otherwise noted.
Detection rates across all 341 samples:
- Any OTC: 60% (205/341)
- TPT: 53% (180/341) — dominant compound
- TBT: 21% (73/341)
- DBT: 13% (45/341)
- DOT: 2% (8/341)
Total OTC level range: below LOD to 490 mcg/kg as Sn (lower bound, LB)
Mean total OTC by food group (LB):
- Fish: 24 mcg/kg as Sn (highest)
- Molluscs: 15 mcg/kg as Sn
- Crustaceans: 14 mcg/kg as Sn
Maximum individual OTC levels (LB):
- TPT: 1400 mcg/kg (480 mcg/kg as Sn) — detected in mangrove snapper (mean 450 mcg/kg; range 41–1400 mcg/kg), giant grouper (mean 220 mcg/kg; range 11–1400 mcg/kg), sea bass (mean 140 mcg/kg), golden thread (mean 130 mcg/kg), tuna (mean 130 mcg/kg)
- TBT: 60 mcg/kg (24 mcg/kg as Sn) — maximum in Chinese noodle fish
- DBT: 8.8 mcg/kg (4.5 mcg/kg as Sn) — maximum in Chinese noodle fish
- DOT: 2.6 mcg/kg (0.89 mcg/kg as Sn)
Mean TPT by group:
- Fish: LB/UB 69 mcg/kg (23 mcg/kg as Sn)
- Molluscs: LB/UB 43 mcg/kg (15 mcg/kg as Sn)
- Crustaceans: LB 41 mcg/kg, UB 42 mcg/kg (14 mcg/kg as Sn)
Dietary exposure (consumers only, LB; body weight 61.13 kg):
- Average consumer: 0.020 mcg/kg bw/day as Sn (20% of EFSA TDI)
- High consumer (90th percentile): 0.057 mcg/kg bw/day as Sn (57% of EFSA TDI)
- Fish was the major contributor: 88% of dietary OTC exposure (0.018 mcg/kg bw/day)
EFSA group TDI: 0.1 mcg/kg bw/day as Sn (equivalent to 0.25 mcg/kg bw/day as TBTO) for the group of TBT, DBT, TPT, and DOT combined, based on NOAEL for immunotoxicity of 0.025 mg/kg bw/day (as TBTO) in rats, safety factor of 100 (EFSA 2004).
Methods (brief)
Samples collected October 2017 to June 2018 from local Hong Kong retail markets. Edible portions analyzed as consumed (some steamed, sashimi analyzed as purchased). Analysis by gas chromatography–inductively coupled plasma mass spectrometry (GC-ICP-MS). Internal standard: tripentyltin. Extraction with acidified methanol, cleanup through Florisil SPE, ethylation prior to analysis. LOD: 0.25 mcg/kg as Sn; LOQ: 1.0 mcg/kg as Sn. Non-detects treated by lower bound (LB, replaced with zero) and upper bound (UB, replaced with LOD) bracketing. Dietary exposure estimated using Hong Kong Population-Based Food Consumption Survey 2005–2007.
Implications
Certification: Organotin compounds are not currently in the HMTc 10-analyte vocabulary, but TPT contamination at levels up to 1400 mcg/kg in some predatory fish species (mangrove snapper, giant grouper) is a meaningful food safety signal. If HMTc expands scope to seafood categories, OTC should be considered alongside the standard analyte set. The regulatory landscape for OTC in food is sparse — Codex has no limit; the EFSA TDI is the primary health-based benchmark.
Courses: This report provides a clear case study in environmental contaminant bioaccumulation: TPT concentrations in predatory/demersal fish far exceed those in filter feeders, illustrating biomagnification. The contrast between 57% of HBGV for high consumers (concerning) and 20% for average consumers (low concern) illustrates how consumption frequency and species selection drive exposure.
App: For the ingredient-risk estimator, the relevant signal is that predatory and coastal fish carry substantially higher OTC loads than freshwater or cold-water species. Species-level differentiation is more meaningful than aggregate seafood categories for organotin exposure. Salmon, grass carp, eel, grey mullet, cod, sole, turbot had no detectable TBT; tuna, sea bass, mangrove snapper, giant grouper, and rabbitfish had high TPT.