Barquero et al. 2024 — Mercury and methylmercury in largemouth bass from Almadén, Spain
This study reports the highest total and methylmercury concentrations ever documented in Micropterus salmoides from a heavily mercury-contaminated watershed downstream of the world’s most historically productive mercury mine. THg in muscle ranged from 0.47 to 7.61 mg kg⁻¹ (wet weight), with methylmercury representing 79.7–92.1% of THg across the seven sampling sites. These values substantially exceed EU maximum limits for fish (0.5 mg kg⁻¹ for most species; 1.0 mg kg⁻¹ for certain predatory species) at all but the most downstream sites. The Se/Hg molar ratio and HBV_Se index indicated low risk for most fish except small/young specimens from the most contaminated site. Other potentially toxic elements (As, Pb, Sb, Zn, Cu) showed no concerning values despite the area being heavily populated with decommissioned polymetallic mines.
Key numbers
THg in muscle, wet weight (mg kg⁻¹): range 0.47–7.61 across all seven sites; highest at El Entredicho open pit lake, decreasing steadily downstream.
MeHg as % of THg: 79.7–92.1% at all sites.
Se in muscle, wet weight (mg kg⁻¹): <2.5 to 11.4.
As, Pb, Sb values: “show no concerning values” per authors; specific values are in supplementary materials. The abstract characterizes them as below concern levels relative to regulatory benchmarks.
Analytical methods: THg by atomic absorption spectrometry (Leco AMA 254 or equivalent); MeHg by cold vapor atomic fluorescence spectrometry (CVAFS) after distillation; other PTEs by ICP-MS. Speciation confirmed: MeHg is directly measured, not estimated from THg.
Note: Sb (antimony) is reported among the PTEs analyzed and found at non-concerning levels. This study is notable for the tHg/MeHg speciation methodology and the extreme concentrations documented, which represent the highest reported values for this species globally.
Methods (brief)
Fish collected by angling along a 34 km transect of the Valdeazogues River at seven sites, from the isolated El Entredicho open pit lake through progressively downstream sites to the mouth. Dorsal muscle sampled per specimen. THg by AAS; MeHg by distillation and CVAFS. PTEs (As, Pb, Sb, Zn, Cu, Se) by ICP-MS. Se/Hg molar ratio and HBV_Se index calculated per Ralston and Raymond framework.
Implications
Certification: This study demonstrates extreme MeHg bioaccumulation in piscivorous freshwater fish from mining-adjacent environments; confirms that MeHg constitutes 80–92% of THg in top-predator freshwater species, supporting conservative THg-as-MeHg assumptions in risk assessments.
Courses: Canonical example of mercury biomagnification in a historically contaminated watershed; demonstrates the Se-Hg antagonism framework and HBV_Se index for risk assessment.
App: tHg and MeHg data for freshwater predatory fish from mining-contaminated European waterway. Sb data shows non-concerning levels from mining-adjacent fish.
Microbiome: Extreme methylmercury concentrations in a top predator species in a human food chain context.