Paz-Suconota et al. 2024 — Total mercury in freshwater fish from the Pastaza River, Ecuador
This study quantified total mercury (THg) in dorsal muscle tissue of 40 fish specimens representing 13 families from two sites (Metzeras River and Pastaza River at Santa Inés) in the Amazon region of Ecuador. Carnivorous species accumulated the highest THg concentrations, with Charax sp. reaching 0.241 ± 0.018 mg kg⁻¹ and Hoplias malabaricus reaching 0.160 ± 0.033 mg kg⁻¹, while herbivorous Hypostomus sp. showed the lowest levels and the omnivore Creagrutus sp. measured 0.020 ± 0.007 mg kg⁻¹. All measured concentrations fell below the maximum permissible limits set by INEN (Ecuador), FAO/WHO, and the European Commission, and hazard quotients were below 1, indicating that consumption of these fish poses no significant risk to human health under normal consumption rates.
Key numbers
THg in muscle tissue, wet weight (mg kg⁻¹), by species:
- Charax sp. (carnivore): 0.241 ± 0.018
- Cetopsis plumbea (carnivore): 0.116 ± 0.045
- Hoplias malabaricus (carnivore, Site 1): 0.160 ± 0.033
- Hoplias malabaricus (carnivore, Site 2): 0.020 ± 0.007 (omnivore Creagrutus sp.)
- Hypostomus sp. (herbivore): lowest values in the dataset
- Overall range across all species: approximately 0.020–0.241 mg kg⁻¹
THg values treated as proxy for MeHg per USEPA convention (approximately 80% of THg in freshwater fish muscle). Daily safe consumption rate estimated at 6–199 g/day for children and 29–928 g/day for adults, depending on species.
Analytical method: Milestone DMA-80 Direct Mercury Analyzer; LOD 1.14 µg kg⁻¹; LOQ 3.80 µg kg⁻¹. Certified reference material DORM-4 (fish protein); mean recovery 92.74%, CV 2.46%.
Note: The study reports total arsenic separately; no As values for fish muscle were provided in the source. The tHg/MeHg speciation is estimated (not directly measured by HPLC speciation); the paper uses THg as a conservative MeHg proxy per USEPA guidance.
Methods (brief)
Forty fish collected by cast-net at two river sites in Palora Canton (Morona Santiago, Ecuador) in October 2023. Dorsal muscle (6 g) extracted per specimen, lyophilized, ground, and analyzed by direct mercury analyzer (DMA-80). Species classified by feeding habit (carnivore, omnivore, herbivore, detritivore). Mann-Whitney U test for site comparison; Kruskal-Wallis for feeding-habit comparison. No speciation of Hg into inorganic Hg vs. MeHg was performed; all THg treated as MeHg per USEPA convention.
Implications
Certification: Freshwater fish from Amazonian Ecuador are below international THg limits under current sampling conditions, but carnivorous top-predator species consistently accumulate the highest concentrations. HMT&C certification contexts using freshwater fish from mining-adjacent watersheds should specify trophic level and species.
Courses: Demonstrates trophic magnification of mercury in freshwater ecosystems with known upstream contamination sources (mining, agriculture); illustrates the carnivore-accumulation gradient important for consumer guidance.
App: tHg data for freshwater fish species across trophic levels; Latin America freshwater matrices.