5 research outputs found
Methylmercury Cycling in High Arctic Wetland Ponds: Controls on Sedimentary Production
Methylmercury (MeHg) is a potent neurotoxin that has
been demonstrated
to biomagnify in Arctic freshwater foodwebs to levels that may be
of concern to Inuit peoples subsisting on freshwater fish, for example.
The key process initiating the bioaccumulation and biomagnification
of MeHg in foodwebs is the methylation of inorganic HgÂ(II) to form
MeHg, and ultimately how much MeHg enters foodwebs is controlled by
the production and availability of MeHg in a particular water body.
We used isotopically enriched Hg stable isotope tracers in sediment
core incubations to measure potential rates of HgÂ(II) methylation
and investigate the controls on MeHg production in High Arctic wetland
ponds in the Lake Hazen region of northern Ellesmere Island (Nunavut,
Canada). We show here that MeHg concentrations in sediments are primarily
controlled by the sediment methylation potential and the quantity
of HgÂ(II) available for methylation, but not by sediment demethylation
potential. Furthermore, MeHg concentrations in pond waters are controlled
by MeHg production in sediments, overall anaerobic microbial activity,
and photodemethylation in the water column
Determination of Monomethylmercury and Dimethylmercury in the Arctic Marine Boundary Layer
Our
understanding of the biogeochemical cycling of monomethylmercury
(MMHg) in the Arctic is incomplete because atmospheric sources and
sinks of MMHg are still unclear. We sampled air in the Canadian Arctic
marine boundary layer to quantify, for the first time, atmospheric
concentrations of methylated Hg species (both MMHg and dimethylmercury
(DMHg)), and, estimate the importance of atmospheric deposition as
a source of MMHg to Arctic land- and sea-scapes. Overall atmospheric
MMHg and DMHg concentrations (mean ± SD) were 2.9 ± 3.6
and 3.8 ± 3.1 (<i>n</i> = 37) pg m<sup>−3</sup>, respectively. Concentrations of methylated Hg species in the marine
boundary layer varied significantly among our sites, with a predominance
of MMHg over Hudson Bay (HB), and DMHg over Canadian Arctic Archipelago
(CAA) waters. We concluded that DMHg is of marine origin and that
primary production rate and sea-ice cover are major drivers of its
concentration in the Canadian Arctic marine boundary layer. Summer
wet deposition rates of atmospheric MMHg, likely to be the product
of DMHg degradation in the atmosphere, were estimated at 188 ±
117.5 ng m<sup>–2</sup> and 37 ± 21.7 ng m<sup>–2</sup> for HB and CAA, respectively, sustaining MMHg concentrations available
for biomagnification in the pelagic food web
Methylmercury Cycling in High Arctic Wetland Ponds: Sources and Sinks
The sources of methylmercury (MeHg; the toxic form of
mercury that
is biomagnified through foodwebs) to Arctic freshwater organisms have
not been clearly identified. We used a mass balance approach to quantify
MeHg production in two wetland ponds in the Lake Hazen region of northern
Ellesmere Island, NU, in the Canadian High Arctic and to evaluate
the importance of these systems as sources of MeHg to Arctic foodwebs.
We show that internal production (1.8–40 ng MeHg m<sup>–2</sup> d<sup>–1</sup>) is a much larger source of MeHg than external
inputs from direct atmospheric deposition (0.029–0.051 ng MeHg
m<sup>–2</sup> d<sup>–1</sup>), as expected. Furthermore,
MeHg cycling in these systems is dominated by HgÂ(II) methylation and
MeHg photodemethylation (2.0–33 ng MeHg m<sup>–2</sup> d<sup>–1</sup>), which is a sink for a large proportion of
the MeHg produced by HgÂ(II) methylation in these ponds. We also show
that MeHg production in the two study ponds is comparable to what
has previously been measured in numerous more southerly systems known
to be important MeHg sources, such as temperate wetlands and lakes,
demonstrating that wetland ponds in the High Arctic are important
sources of MeHg to local aquatic foodwebs
Sources of Methylmercury to Snowpacks of the Alberta Oil Sands Region: A Study of In Situ Methylation and Particulates
Snowpacks in the Alberta Oil Sands
Region (AOSR) of Canada contain
elevated loadings of methylmercury (MeHg; a neurotoxin that biomagnifies
through foodwebs) due to oil sands related activities. At sites ranging
from 0 to 134 km from the major AOSR upgrading facilities, we examined
sources of MeHg by quantifying potential rates of MeHg production
in snowpacks and melted snow using mercury stable isotope tracer experiments,
as well as quantifying concentrations of MeHg on particles in snowpacks
(pMeHg). At four sites, methylation rate constants were low in snowpacks
(<i>k</i><sub>m</sub> = 0.001–0.004 d<sup>–1</sup>) and nondetectable in melted snow, except at one site (<i>k</i><sub>m</sub> = 0.0007 d<sup>–1</sup>). The ratio of methylation
to demethylation varied between 0.3 and 1.5, suggesting that the two
processes are in balance and that in situ production is unlikely an
important net source of MeHg to AOSR snowpacks. pMeHg concentrations
increased linearly with distance from the upgraders (R<sup>2</sup> = 0.71, <i>p</i> < 0.0001); however, snowpack total
particle and pMeHg loadings decreased exponentially over this same
distance (R<sup>2</sup> = 0.49, <i>p</i> = 0.0002; R<sup>2</sup> = 0.56, <i>p</i> < 0.0001). Thus, at near-field
sites, total MeHg loadings in snowpacks were high due to high particle
loadings, even though particles originating from industrial activities
were not MeHg rich compared to those at remote sites. More research
is required to identify the industrial sources of snowpack particles
in the AOSR
Atmospheric Deposition of Mercury and Methylmercury to Landscapes and Waterbodies of the Athabasca Oil Sands Region
Atmospheric deposition of metals
originating from a variety of
sources, including bitumen upgrading facilities and blowing dusts
from landscape disturbances, is of concern in the Athabasca oil sands
region of northern Alberta, Canada. Mercury (Hg) is of particular
interest as methylmercury (MeHg), a neurotoxin which bioaccumulates
through foodwebs, can reach levels in fish and wildlife that may pose
health risks to human consumers. We used spring-time sampling of the
accumulated snowpack at sites located varying distances from the major
developments to estimate winter 2012 Hg loadings to a ∼20 000
km<sup>2</sup> area of the Athabasca oil sands region. Total Hg (THg;
all forms of Hg in a sample) loads were predominantly particulate-bound
(79 ± 12%) and increased with proximity to major developments,
reaching up to 1000 ng m<sup>–2</sup>. MeHg loads increased
in a similar fashion, reaching up to 19 ng m<sup>–2</sup> and
suggesting that oil sands developments are a direct source of MeHg
to local landscapes and water bodies. Deposition maps, created by
interpolation of measured Hg loads using geostatistical software,
demonstrated that deposition resembled a bullseye pattern on the landscape,
with areas of maximum THg and MeHg loadings located primarily between
the Muskeg and Steepbank rivers. Snowpack concentrations of THg and
MeHg were significantly correlated (<i>r</i> = 0.45–0.88, <i>p</i> < 0.01) with numerous parameters, including total suspended
solids (TSS), metals known to be emitted in high quantities from the
upgraders (vanadium, nickel, and zinc), and crustal elements (aluminum,
iron, and lanthanum), which were also elevated in this region. Our
results suggest that at snowmelt, a complex mixture of chemicals enters
aquatic ecosystems that could impact biological communities of the
oil sands region