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Probabilistic Human Health Risk Assessment of Inorganic Arsenic Exposure Following the 2020 Taal Volcano Eruption, Batangas, Philippines

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Summary

This 2026 probabilistic risk assessment characterises aggregate inorganic arsenic exposure in a population affected by the January 2020 Taal volcano eruption (Batangas, Philippines). The study measured arsenic in drinking water, soil, sediment, and freshwater clams (Corbicula fluminea) and used Monte Carlo simulation (10,000 iterations) to estimate aggregate daily inorganic arsenic (iAs) dose across multiple simultaneous exposure pathways. It represents a severe geogenic contamination scenario, not a background dietary-exposure context, and is cited here for its speciation methodology and for the dominance of freshwater shellfish and rice in dietary arsenic intake.

Key numbers

  • Drinking water arsenic (As): 0.000735-0.11 mg/L (some samples exceeding WHO 0.01 mg/L guideline and Philippines national standard)
  • Freshwater clams (Corbicula fluminea): total As 5.0-6.3 mg/kg dw
  • Rice iAs range (simulated, 50% iAs fraction lower bound): 0.007-0.06 ug/g; at 90% iAs fraction upper bound: 0.02-0.12 ug/g
  • Aggregate daily iAs dose (mean): 3.0 +/- 1.4 ug/kg bw/day (lower bound) and 4.0 +/- 2.0 ug/kg bw/day (upper bound)
  • Hazard quotient (HQ): all simulated individuals well above 1 (maximum 212-286)
  • Excess cancer risk (ECR): all individuals above 10^-6; distribution centres at 10^-2 to 10
  • Dominant exposure pathway contribution: freshwater clams 26.2% of aggregate dose (lower bound); rice 30.4% (upper bound)

Methods

Measurements: drinking water and soil/sediment by ICP-MS after acid digestion; freshwater clams by wet digestion and ICP-MS. Probabilistic Monte Carlo simulation using published intake and body weight distributions; 10,000 iterations per scenario. Lower bound (LB) assumes 50% iAs of total rice As; upper bound (UB) assumes 90%. Aggregate multi-pathway exposure summed oral (ingestion of water, rice, corn, vegetables, root crops, clams) and dermal pathways.

Implications

Cited for the geogenic context demonstrating that freshwater shellfish and rice can be dominant pathways in volcanic contamination zones. The quantitative dominance of rice as a pathway (30.4% of aggregate dose) confirms the importance of rice in population-level iAs exposure even in multi-pathway contamination scenarios. The aggregate dose (mean 3.0-4.0 ug/kg bw/day) is two orders of magnitude above the EFSA BMDL05 of 0.06 ug/kg bw/day, reflecting extreme contamination rather than typical dietary exposure.

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