Cardoso et al. 2023 — Seasonal mercury in three Portuguese estuaries and seafood health risk
This study characterises seasonal variability in total mercury (tHg) contamination across three distinct Portuguese estuarine systems (Ria de Aveiro, Tagus estuary, Ria Formosa), measuring tHg in water, primary producers, and macrobenthos including edible bivalves. The study evaluates both human health risk from bivalve consumption and environmental risk. Ria de Aveiro and Tagus estuary reflect historical industrial mercury contamination from chlor-alkali plants; Ria Formosa represents a less industrialised southern system. The study finds that tHg concentrations in surface waters were higher in Ria de Aveiro and Tagus than in Ria Formosa, with particular concern in Ria de Aveiro during autumn where Hg levels approached approximately 100 µg/L. For edible species, tHg concentrations in bivalves were below 0.5 µg/g wet weight across all systems, representing no human health risk under standard consumption scenarios. An environmental risk quotient greater than 0.1 (moderate risk) was observed in Ria de Aveiro during autumn, indicating ecosystem-level concern even where human health risk is low.
Key numbers
tHg in edible bivalves: less than 0.5 µg/g wet weight across all three estuaries. EU regulatory limit for mercury in bivalves is 0.5 µg/g wet weight (EC 1881/2006). Ria de Aveiro autumn surface water tHg approximately 100 µg/L, above European quality standards. Hazard quotient (HQ) below 1 for bivalve consumption, indicating non-carcinogenic risk within acceptable range. Environmental risk quotient greater than 0.1 in Ria de Aveiro autumn (moderate risk). Mercury quantified in water by CV-AFS with detection limit 1.6 ng/L; in biota by thermal decomposition atomic absorption spectrometry (LECO AMA-254), detection limit 0.01 ng. For human health risk calculations, 90 percent of tHg in bivalves was assumed to be MeHg, consistent with literature for bivalve matrices.
Methods (brief)
Seasonal sampling over one year at three estuaries. Water collected at low tide for tHg by CV-AFS. Macrobenthos and macroalgae collected by core and hand, processed by freeze-drying, then analysed by thermal decomposition atomic absorption spectrometry. CRMs used: ERM CD200 (plants) and TORT-3 (fauna). Human health risk assessed via hazard quotient approach with EDI compared to US-EPA RfD of 0.1 µg/g wet weight. Environmental risk assessed via species sensitivity distribution. Limitation: tHg measured rather than speciated (no separate MeHg measurement); the 90% MeHg assumption introduces uncertainty.
Implications
Certification: Relevant to seafood certification context, particularly shellfish and bivalves from European Atlantic coast origins. Documents that bivalves from historically contaminated Portuguese estuaries remain below 0.5 µg/g EU limit, though environmental risk persists.
Courses: Useful case study demonstrating the distinction between human health risk and environmental risk thresholds, and the role of historical industrial contamination in legacy mercury burden.
App: Supports the bivalves/shellfish ingredient-level tHg profile; values below EU limits at these Portuguese sites but site context matters.
Microbiome: Not addressed.