Assessment of mercury speciation in feathers using species-specific isotope dilution analysis

Abstract

Seabirds are considered as effective sentinels of environmental marine contamination and their feathers are extensively used as non-lethal samples for contaminant biomonitoring. This tissue represents the main route for mercury (Hg) elimination in seabirds and contains predominantly methylmercury (MeHg). In this work, we developed a robust analytical technique for precise and accurate simultaneous quantification of MeHg, inorganic Hg (iHg) and consequently total Hg (THg), in feathers by gas-chromatography (GC)-ICPMS analyses using species-specific isotope dilution technique. An optimisation of the extraction method was carried out by testing different extraction systems, reagents and spiking procedures using an internal reference feather sample. The procedure was validated for MeHg and THg concentrations with a human hair certified reference material. Microwave nitric acid extraction with spike addition before the extraction provided the best recovery and was chosen as the most appropriate species simultaneous extraction method (SSE). An additional assessment was performed by comparison of our developed extraction method and a MeHg specific extraction technique (MSE) classically used for Hg speciation studies on feathers. The developed method was applied to feather samples from a large number of seabirds from the Southern Ocean (penguins, albatrosses, petrels and skuas) to investigate the variability of Hg speciation across a large range of Hg exposure conditions and concentrations. In all cases, MeHg accounted for > 90% of THg, thus verifying the predominance of organic Hg over iHg in feathers.

Arctic climate change and pollution impact little auk foraging and fitness across a decade

“…Hence, BF collected from 2007 to 2016 were analyzed for comparison with the biological time-series. Previous studies showed that >90% of Hg in seabird feathers is methyl-Hg (Me-Hg), the most toxic form of Hg 95 . Total Hg measured in feathers is thus considered as an indicator of bird exposure to Me-Hg.…”

Mercury isotopes of key tissues document mercury metabolic processes in seabirds

“…The extraction was carried out in CEM Pyrex vessels by 1 min of warming up to 75ºC and 3 min at 75ºC with magnetic agitation to homogenise the samples. Feathers (~ 100 mg dry weight (dw)) were digested using nitric acid (HNO3•6N, INSTRA quality) with addition of isotopic enriched standard solutions before the extraction process following Renedo et al (2017). Blood and internal tissues (100-150 mg dw) were digested with 5 mL of tetramethylammonium hydroxide (25% TMAH in H2O, Sigma Aldrich).…”

“…Gradual decrease of Hg concentrations in seabird internal tissues during feather moult was identified as remobilisation of Hg body burden into growing feathers, leading to the elimination of up to 80% of the total accumulated Hg (Furness et al, 1986;Honda et al, 1986;Braune, 1987). Since relatively high Hg concentrations (almost exclusively MeHg) are usually measured in feathers (Renedo et al, 2017), the feather moult is considered as the main route for MeHg elimination in seabirds (Thompson and Furness, 1989a;Thompson et al, 1990). However, the evidence of excretion of MeHg by feathers is based simply on the balance of Hg concentrations between feathers and internal tissues, while the relative importance of the different soft tissues in the storage and distribution of Hg is not known.…”

Contrasting Spatial and Seasonal Trends of Methylmercury Exposure Pathways of Arctic Seabirds: Combination of Large-Scale Tracking and Stable Isotopic Approaches

“…Prior to Hg speciation analyses, blood and feathers (0.01−0.05 g) were digested following a previously developed method by microwave-assisted extraction (using a Discover SP-D microwave, CEM Corporation) 55,56 . We used 5 mL of tetramethylammonium (Table S1).…”