Mercury contamination and cycling in the coastal zone

pp. 127-13

Pre-colombian mercury pollution associated with the smelting of argentiferous ores in the bolivian andes

The development of the mercury (Hg) amalgamation process in the mid-sixteenth century triggered the onset of large-scale Hg mining in both the Old and New Worlds. However, ancient Hg emissions associated with amalgamation and earlier mining efforts remain poorly constrained. Using a geochemical time-series generated from lake sediments near Cerro Rico de Potosí, once the world\u27s largest silver deposit, we demonstrate that pre-Colonial smelting of Andean silver ores generated substantial Hg emissions as early as the twelfth century. Peak sediment Hg concentrations and fluxes are associated with smelting and exceed background values by approximately 20-fold and 22-fold, respectively. The sediment inventory of this early Hg pollution more than doubles that associated with extensive amalgamation following Spanish control of the mine (1574-1900 AD). Global measurements of [Hg] from economic ores sampled world-wide indicate that the phenomenon of Hg enrichment in non-ferrous ores is widespread. The results presented here imply that indigenous smelting constitutes a previously unrecognized source of early Hg pollution, given naturally elevated [Hg] in economic silver deposits. © Royal Swedish Academy of Sciences 2010

Drivers of Surface Ocean Mercury Concentrations and Air–Sea Exchange in the West Atlantic Ocean

Accurately characterizing net evasion of elemental mercury (Hg⁰) from marine systems is essential for understanding the global biogeochemical mercury (Hg) cycle and the pool of divalent Hg (Hg^II) available for methylation. Few high resolution measurements of Hg⁰ are presently available for constraining global and regional flux estimates and for understanding drivers of spatial and temporal variability in evasion. We simultaneously measured high-resolution atmospheric and surface seawater Hg⁰ concentrations as well as the total Hg distribution during six cruises in the West Atlantic Ocean between 2008 and 2010 and examined environmental factors affecting net Hg⁰ formation and evasion. We observed the lowest fraction of Hg as Hg⁰ (7.8 ± 2.4%) in the near-coastal and shelf areas that are influenced by riverine inputs. Significantly higher %Hg⁰ observed in open ocean areas (15.8 ± 3.9%) may reflect lower dissolved organic carbon (DOC) in offshore environments, which is known to affect both the reducible Hg^II pool and redox kinetics. Calculated Hg⁰ evasion changed by more than a factor of 3 between cruises (range: 2.1 ± 0.7 to 6.8 ± 5.1 ng m^–2 h^–1), driven mainly by variability in Hg⁰ and wind speed. Our results suggest that further mechanistic understanding of the role of DOC on Hg redox kinetics in different types of marine environments is needed to explain variability in Hg⁰ concentrations and improve global estimates of air–sea exchange

Portable X-ray Fluorescence as a Rapid Determination Tool to Detect Parts per Million Levels of Ni, Zn, As, Se, and Pb in Human Toenails: A South India Case Study

Chronic exposure to inorganic pollutants adversely affects human health. Inductively coupled plasma mass spectrometry (ICP-MS) is the most common method used for trace metal(loid) analysis of human biomarkers. However, it leads to sample destruction, generation of secondary waste, and significant recurring costs. Portable X-ray fluorescence (XRF) instruments can rapidly and nondestructively determine low concentrations of metal(loid)s. In this work, we evaluated the applicability of portable XRF as a rapid method for analyzing trace metal(loid)s in toenail samples from three populations (n= 97) near the city of Chennai, India. A Passing-Bablok regression analysis of results from both methods revealed that there was no proportional bias among the two methods for nickel (measurement range ∼25 to 420 mg/kg), zinc (10 to 890 mg/kg), and lead (0.29 to 4.47 mg/kg). There was a small absolute bias between the two methods. There was a strong proportional bias (slope = 0.253, 95% CI: 0.027, 0.614) between the two methods for arsenic (below detection to 3.8 mg/kg) and for selenium when the concentrations were lower than 2 mg/kg. Limits of agreement between the two methods using Bland-Altman analysis were derived for nickel, zinc, and lead. Overall, a suitably calibrated and evaluated portable XRF shows promise in making high-throughput assessments at population scales. © 2021 American Chemical Societ

Drivers of Surface Ocean Mercury Concentrations and Air–Sea Exchange in the West Atlantic Ocean

Accurately characterizing net evasion of elemental mercury (Hg⁰) from marine systems is essential for understanding the global biogeochemical mercury (Hg) cycle and the pool of divalent Hg (Hg^II) available for methylation. Few high resolution measurements of Hg⁰ are presently available for constraining global and regional flux estimates and for understanding drivers of spatial and temporal variability in evasion. We simultaneously measured high-resolution atmospheric and surface seawater Hg⁰ concentrations as well as the total Hg distribution during six cruises in the West Atlantic Ocean between 2008 and 2010 and examined environmental factors affecting net Hg⁰ formation and evasion. We observed the lowest fraction of Hg as Hg⁰ (7.8 ± 2.4%) in the near-coastal and shelf areas that are influenced by riverine inputs. Significantly higher %Hg⁰ observed in open ocean areas (15.8 ± 3.9%) may reflect lower dissolved organic carbon (DOC) in offshore environments, which is known to affect both the reducible Hg^II pool and redox kinetics. Calculated Hg⁰ evasion changed by more than a factor of 3 between cruises (range: 2.1 ± 0.7 to 6.8 ± 5.1 ng m^–2 h^–1), driven mainly by variability in Hg⁰ and wind speed. Our results suggest that further mechanistic understanding of the role of DOC on Hg redox kinetics in different types of marine environments is needed to explain variability in Hg⁰ concentrations and improve global estimates of air–sea exchange

Above- and belowground plant mercury dynamics in a salt marsh estuary in Massachusetts, USA

<jats:p>Abstract. Estuaries are a conduit of mercury (Hg) from watersheds to the coastal ocean, and salt marshes play an important role in coastal Hg cycling. Hg cycling in upland terrestrial ecosystems has been well studied, but processes in densely vegetated salt marsh ecosystems are poorly characterized. We investigated Hg dynamics in vegetation and soils in the Plum Island Sound estuary in Massachusetts, USA, and specifically assessed the role of marsh vegetation for Hg deposition and turnover. Monthly quantitative harvesting of aboveground biomass showed strong linear seasonal increases in Hg associated with plants, with a 4-fold increase in Hg concentration and an 8-fold increase in standing Hg mass from June (3.9 ± 0.2 µg kg−1 and 0.7 ± 0.4 µg m−2, respectively) to November (16.2 ± 2.0 µg kg−1 and 5.7 ± 2.1 µg m−2, respectively). Hg did not increase further in aboveground biomass after plant senescence, indicating physiological controls of vegetation Hg uptake in salt marsh plants. Hg concentrations in live roots and live rhizomes were 11 and 2 times higher than concentrations in live aboveground biomass, respectively. Furthermore, live belowground biomass Hg pools (Hg in roots and rhizomes, 108.1 ± 83.4 µg m−2) were more than 10 times larger than peak standing aboveground Hg pools (9.0 ± 3.3 µg m−2). A ternary mixing model of measured stable Hg isotopes suggests that Hg sources in marsh aboveground tissues originate from about equal contributions of root uptake (∼ 35 %), precipitation uptake (∼ 33 %), and atmospheric gaseous elemental mercury (GEM) uptake (∼ 32 %). These results suggest a more important role of Hg transport from belowground (i.e., roots) to aboveground tissues in salt marsh vegetation than upland vegetation, where GEM uptake is generally the dominant Hg source. Roots and soils showed similar isotopic signatures, suggesting that belowground tissue Hg mostly derived from soil uptake. Annual root turnover results in large internal Hg recycling between soils and plants, estimated at 58.6 µg m−2 yr−1. An initial mass balance of Hg indicates that the salt marsh presently serves as a small net Hg sink for environmental Hg of 5.2 µg m−2 yr−1. </jats:p&gt