A mass-balance model to assess arsenic exposure from multiple wells in Bangladesh

Overview

Using a mass-balance model applied to the Health Effects of Arsenic Longitudinal Study (HEALS) cohort of 11,197 participants in Araihazar, Bangladesh, Huhmann and colleagues show that participants on average obtain 60–75% of their drinking water from their primary household well and 25–40% from other wells, correcting a systematic underestimate in prior exposure assessments that relied solely on the primary well. Their new rice arsenic measurements (n=814 samples from 410 HEALS households) indicate that rice rather than drinking water is the largest As exposure source for participants whose primary wells contain 50 µg/L or less of As.

Key numbers

HEALS cohort: 11,197 participants, Araihazar, Bangladesh, baseline 2000–2002. Linear regression of urinary As on primary-well As: slope 0.69 ± 0.01, intercept 68 ± 2. Primary well As: study area mean 95 µg/L. Mass-balance model estimates fraction of drinking water from primary well: fp = 0.50 ± 0.08 (using local rice As estimate); fraction from other wells: ~0.18 ± 0.08; fraction from food and cellular respiration accounts for the remainder. Estimated daily As intake from rice: 96 µg/day (local rice estimate) or 64 µg/day (previously published El-Masri estimate). Rice arsenic (total As, ICP-MS or HPLC-ICP-MS): uncooked rice mean 244 ± 150 µg/kg, cooked rice mean 235 ± 180 µg/kg (n=408 uncooked, 406 cooked). Range: 50–1,200 µg/kg total As. Certified reference standard SRM 1568b: measured 312±10 µg/kg (ICP-MS) and 325±18 µg/kg (HPLC-ICP-MS) against certified 285±14 µg/kg.

Methods (brief)

Well-water As measured by blanket survey (2000–2002) across 25 km² study area. Urinary As collected at baseline. Rice samples collected 2016 from subset of 410 HEALS households; microwave digestion followed by ICP-MS (total As) or HPLC-ICP-MS (speciated As). The paper reports total As only for rice; speciation not differentiated in the reported rice values. Study design is observational cohort; mass-balance model uses linear regression.

Implications

Certification: Rice As values (50–1,200 µg/kg tAs, mean ~240 µg/kg) from Bangladeshi households represent a high-contamination scenario; relevant to the app model for populations with high rice consumption and for HMT&C threshold context in international markets. The finding that rice displaces drinking water as the dominant As source at lower well-water concentrations is relevant to aggregate dietary exposure modeling.

Courses: Illustrates that single-source exposure assessment systematically underestimates As burden; important for teaching exposure pathway complexity.

App: Bangladesh rice samples provide distributional data for a high-tAs rice scenario; mean 240 µg/kg and range 50–1,200 µg/kg (total As). iAs/tAs ratio not directly reported; do not assume these values represent iAs alone.

Wiki pages updated on ingest

• Arsenic
• Rice

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