Overview
Ten small indigenous fish species (SIS) from Bangladesh’s Lower Meghna River were systematically sampled across three seasons (pre-monsoon, monsoon, post-monsoon) and ten stations to quantify total arsenic in muscle tissue and assess associated human health risks. Five of the ten species — Mystus vittatus, Glossogobius giuris, Lepidocephalichthys guntea, Neotropius atherinoides, and Apocryptes bato — exceeded the WHO safe consumption threshold of 1 mg/kg tAs in muscle tissue, at least during the pre-monsoon season. Arsenic levels in water and sediment were within non-polluting limits by standard indices, yet fish-muscle concentrations were substantially higher, demonstrating significant bioaccumulation from environmental pathways. Pre-monsoon concentrations were consistently highest across all species, followed by post-monsoon, then monsoon, with statistically significant seasonal differences (p < 0.05) but no spatial gradient across the three river zones (p > 0.05). Benthic carnivores and scaleless/fusiform species accumulated more arsenic than pelagic-benthic omnivores, indicating that morphology, habitat, and feeding behavior modulate bioaccumulation. Children were identified as the population most at risk from fish consumption in this region.
Key numbers
n = 300 fish muscle samples: 10 species × 10 stations × 3 seasons.
WHO safe consumption threshold for arsenic in fish: 1 mg/kg.
Species exceeding 1 mg/kg (pre-monsoon means):
- Apocryptes bato (Ab): mean 1.35 ± 0.20 mg/kg (pre-monsoon); range 0.99–1.67 mg/kg
- Neotropius atherinoides (Na): mean 0.97 ± 0.15 mg/kg (pre-monsoon); range 0.80–1.17 mg/kg
- Lepidocephalichthys guntea (Lg): mean 0.95 ± 0.13 mg/kg (pre-monsoon); range 0.79–1.17 mg/kg
- Mystus vittatus (Mv): mean 0.82 ± 0.16 mg/kg (pre-monsoon); range 0.53–1.03 mg/kg
- Glossogobius giuris (Gg): mean 0.92 ± 0.13 mg/kg (pre-monsoon); range 0.76–1.15 mg/kg
Note: all five exceed 1 mg/kg within their pre-monsoon range. Ab mean is above the threshold; others approach or cross it at upper range.
Species below 1 mg/kg across all seasons (selected):
- Puntius sophore (Ps): pre-monsoon mean 0.40, monsoon 0.20, post-monsoon 0.29 mg/kg
- Amblypharyngodon mola (Am): pre-monsoon mean 0.59, monsoon 0.28, post-monsoon 0.44 mg/kg
- Devario devario (Dd): pre-monsoon mean 0.70, monsoon 0.44, post-monsoon 0.60 mg/kg
- Chela cachius (Cc): pre-monsoon mean 0.61, monsoon 0.24, post-monsoon 0.42 mg/kg
- Gudusia chapra (Gc): pre-monsoon mean 0.66, monsoon 0.31, post-monsoon 0.44 mg/kg
All species showed significant seasonal variation (one-way ANOVA p = 0.0 for all), with pre-monsoon > post-monsoon > monsoon in most cases. No significant spatial variation across upper, mid, and lower river zones (p > 0.05 for all species).
Water arsenic: pre-monsoon mean 0.012 ± 0.003 mg/L (highest), monsoon mean 0.002 ± 0.0007 mg/L, post-monsoon mean 0.006 ± 0.0018 mg/L; all seasons within Bangladesh Environmental Conservation Rules limit (0.05 mg/L) and WHO drinking water guideline (0.01 mg/L is lower — pre-monsoon exceeds WHO drinking water guideline but not the national standard). Seasonal variation significant (p = 0.0); spatial variation not significant (p = 0.89).
Sediment arsenic: pre-monsoon mean 6.88 ± 0.98 mg/kg, monsoon 4.94 mg/kg, post-monsoon 5.55 mg/kg; seasonal variation significant (p = 0.0); spatial variation not significant (p = 0.5). Below the shale standard of 13 mg/kg.
LOD/LOQ: fish muscle LOD = 0.02 µg/g (20 ppb), LOQ = 0.06 µg/g (60 ppb). All fish samples above LOQ. Water LOD = 0.1 µg/L, LOQ = 0.3 µg/L. Sediment LOD = 0.5 µg/kg, LOQ = 1.5 µg/kg.
CRM recoveries: 93–106% for fish tissue (NIST SRM 2976), sediment (NIST SRM 2702), and water.
Methods
Total arsenic only; no speciation between iAs and organic As species reported. Fish muscle dissected, freeze-dried (Zirbus VaCo 2), 0.5 g aliquots digested in microwave digestion system (WX-6000) with ultrapure HNO3, analyzed by ICP-MS (PerkinElmer ELAN9000). Water: 0.45 µm membrane filtration, HNO3 acidification, ICP-MS (ELAN9000). Sediment: dried at 50°C, muffle-furnace ignition to 450°C, digestion with 50% HNO3, AAS (SHIMADZU AA-7000). QA/QC: CRM 320 (Merck), acid-cleaned labware, 10% duplicate analyses; RSD ≤ 11%. Calibration linearity R² > 0.998.
Limitation: total arsenic only — no iAs/tAs split. The WHO 1 mg/kg threshold referenced is for total arsenic in fish; the more health-relevant metric would be inorganic As fraction, which is typically 10–30% of total As in freshwater fish. Reported values therefore likely overstate inorganic-As risk. No data on cooking method effects (boiling may reduce As by ~20–35%). The 10 fish specimens per species per station is a small sample for statistical power at within-station level. Results reflect the Lower Meghna specifically, which sits in one of Bangladesh’s most arsenic-contaminated groundwater zones; these findings are not representative of freshwater fish globally.
Implications
Certification: this paper is relevant context for product categories using freshwater fish from arsenic-contaminated river basins (Bangladesh, similar groundwater-impacted regions in South/Southeast Asia). Total As in muscle tissue of certain SIS species exceeds 1 mg/kg during pre-monsoon; the absence of iAs speciation limits direct application to regulatory limits but flags these species and regions as high-risk.
Courses: the paper is a strong teaching case for the interaction between groundwater arsenic contamination, seasonal hydrology (pre-monsoon dilution vs. concentration effects), fish morphology (scaleless, benthic, fusiform body shapes concentrate more As), and food safety. The seasonal dynamic — highest risk during pre-monsoon when groundwater inputs dominate river flow — is a critical concept for sourcing-season risk management.
App: freshwater fish ingredient page should note that species from Bangladesh and similar highly arsenic-contaminated South Asian groundwater basins can carry total As well above 1 mg/kg in muscle tissue, particularly during dry seasons; speciation data are needed to compute iAs-specific risk.
Microbiome: no direct microbiome content in this paper.
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Update history
The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.
| Commit | Date | Change | Description |
|---|---|---|---|
| a8052bb | 2026-08-09 | major | 6 sections added; narrative text revised |