Odd Isotope Deficits in Atmospheric Hg Measured in Lichens

• Published in: Environmental science & technology 2009-08, Vol.43 (15), p.5660-5664
• Main Authors: Carignan, Jean, Estrade, Nicolas, Sonke, Jeroen E, Donard, Olivier F.X
• Format: Article
• Language: English
• Subjects: Air Pollutants - analysis; Analytical chemistry; Animal, plant and microbial ecology; Applied ecology; Applied sciences; Atmosphere; Atmospheric chemistry; Biological and medical sciences; Characterization of Natural and Affected Environments; Chemical Sciences; Cities; Ecotoxicology, biological effects of pollution; Emissions; Environment; Environmental Monitoring - methods; Environmental Pollutants; Exact sciences and technology; France; Fundamental and applied biological sciences. Psychology; Isotopes; Lichens; Lichens - drug effects; Lichens - metabolism; Mercury; Mercury - analysis; Mercury Isotopes; Pollution; Sedimentation & deposition
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es900578v

Redox reactions govern mercury (Hg) concentrations in the atmosphere because fluxes (emissions and deposition), and residence times, are largely controlled by Hg speciation. Recent work on aquatic Hg photoreduction suggested that this reaction produces non-mass dependent fractionation (NMF) and that residual aquatic Hg(II) is characterized by positive Δ199Hg and Δ201Hg anomalies. Here, we show that atmospheric Hg accumulated in lichens is characterized by NMF with negative Δ199Hg and Δ201Hg values (−0.3 to −1‰), making the atmosphere and the aquatic environment complementary reservoirs regarding photoreduction and NMF of Hg isotopes. Because few other reactions than aquatic Hg photoreduction induce NMF, photochemical reduction appears to be a key pathway in the global Hg cycle. Based on a NMF isotope mass balance, direct anthropogenic emissions may account for only 50 ± 10% of atmospheric Hg deposition in an urban area of NE France. Furthermore, isotopic anomalies found in several polluted soils and sediments strongly suggests that an important part of Hg in these samples was affected by photoreactions and has cycled through the atmosphere before being stored in the geological environment. Thus, mercury isotopic anomalies measured in environmental samples may be used to trace and quantify the contribution of source emissions.