Abstract
Intensive freshwater aquaculture in the Mekong Delta of Vietnam has expanded rapidly, raising concerns regarding environmental contamination and the bioaccumulation of toxic heavy metals in sympatric wild fish populations. This study evaluated the concentrations and organ-specific partitioning of five heavy metals—cadmium (Cd), lead (Pb), total arsenic (As), mercury (Hg), and chromium (Cr)—in four ecologically and commercially important wild teleost species (Channa striata, Anabas testudineus, Oreochromis niloticus, and Pangasius bocourti) sampled across aquaculture-dense waterways in An Giang, Dong Thap, and Can Tho provinces. Heavy metal concentrations were quantified using inductively coupled plasma mass spectrometry (ICP-MS) following microwave-assisted acid digestion. Trophic position and feeding guild significantly influenced accumulation patterns, with the carnivorous predator C. striata exhibiting the highest hepatic and muscular concentrations of Hg (0.28 ± 0.04 mg/kg wet weight) and As (0.74 ± 0.11 mg/kg wet weight). Across all species, metal bioaccumulation followed a clear organotropism hierarchy: liver > gills > muscle tissue. Cadmium and lead concentrations in hepatic tissues frequently exceeded international safety baseline thresholds, reflecting chronic sub-lethal environmental exposure associated with aquaculture feed residues and agricultural runoff. Health risk assessment revealed that while Target Hazard Quotients (THQ) for human consumption of muscle tissue remained below the critical threshold of 1.0, the cumulative Hazard Index (HI) approached unity in downstream receiving waters. These findings underscore significant physiological and ecotoxicological burdens in wild ichthyofauna, highlighting the urgent need for integrated watershed management, veterinary environmental surveillance, and stringent effluent standards to safeguard aquatic biodiversity and food chain biosecurity within the Mekong River basin.
