4 research outputs found
Environmental Impacts of the Tennessee Valley Authority Kingston Coal Ash Spill. 2. Effect of Coal Ash on Methylmercury in Historically Contaminated River Sediments
The Tennessee Valley Authority Kingston coal ash spill
in December
2008 deposited approximately 4.1 million m<sup>3</sup> of fly ash
and bottom ash into the Emory and Clinch River system (Harriman, Tennessee,
U.S.A.). The objective of this study was to investigate the impact
of the ash on surface water and sediment quality over an eighteen
month period after the spill, with a specific focus on mercury and
methylmercury in sediments. Our results indicated that surface water
quality was not impaired with respect to total mercury concentrations.
However, in the sediments of the Emory River near the coal ash spill,
total mercury concentrations were 3- to 4-times greater than sediments
several miles upstream of the ash spill. Similarly, methylmercury
content in the Emory and Clinch River sediments near the ash spill
were slightly elevated (up to a factor of 3) at certain locations
compared to upstream sediments. Up to 2% of the total mercury in sediments
containing coal ash was present as methylmercury. Mercury isotope
composition and sediment geochemical data suggested that elevated
methylmercury concentrations occurred in regions where native sediments
were mixed with coal ash (e.g., less than 28% as coal ash in the Emory
River). This coal ash may have provided substrates (such as sulfate)
that stimulated biomethylation of mercury. The production of methylmercury
in these areas is a concern because this neurotoxic organomercury
compound can be highly bioaccumulative. Future risk assessments of
coal ash spills should consider not only the leaching potential of
mercury from the wastes but also the potential for methylmercury production
in receiving waters
Environmental Impacts of the Tennessee Valley Authority Kingston Coal Ash Spill. 1. Source Apportionment Using Mercury Stable Isotopes
Mercury stable isotope abundances were used to trace
transport
of Hg-impacted river sediment near a coal ash spill at Harriman, Tennessee,
USA. δ<sup>202</sup>Hg values for Kingston coal ash released
into the Emory River in 2008 are significantly negative (−1.78
± 0.35‰), whereas sediments of the Clinch River, into
which the Emory River flows, are contaminated by an additional Hg
source (potentially from the Y-12 complex near Oak Ridge, Tennessee)
with near-zero values (−0.23 ± 0.16‰). Nominally
uncontaminated Emory River sediments (12 miles upstream from the Emory-Clinch
confluence) have intermediate values (−1.17 ± 0.13‰)
and contain lower Hg concentrations. Emory River mile 10 sediments,
possibly impacted by an old paper mill has δ<sup>202</sup>Hg
values of −0.47 ± 0.04‰. A mixing model, using
δ<sup>202</sup>Hg values and Hg concentrations, yielded estimates
of the relative contributions of coal ash, Clinch River, and Emory
River sediments for a suite of 71 sediment samples taken over a 30
month time period from 13 locations. Emory River samples, with two
exceptions, are unaffected by Clinch River sediment, despite occasional
upstream flow from the Clinch River. As expected, Clinch River sediment
below its confluence with the Emory River are affected by Kingston
coal ash; however, the relative contribution of the coal ash varies
among sampling sites
Arsenic Speciation in Bituminous Coal Fly Ash and Transformations in Response to Redox Conditions
The
risk of the mobilization of coal ash into the environment has
highlighted the need for the assessment of the environmental behavior
of coal ash, particularly with respect to toxic trace elements such
as arsenic (As). Here, we examined As speciation in coal fly ash samples
and transformations in response to aquatic redox conditions. X-ray
absorption spectroscopy indicated that 92–97% of total As occurred
as AsÂ(V), with the remainder present as AsÂ(III). Major As-bearing
hosts in unamended ashes were glass, iron (oxyhydr)Âoxides, and calcium
arsenate. Oxic leaching resulted in immediate As mobilization to the
aqueous phase, reprecipitation of As-iron ferrihydrite, and As adsorption
to mineral surfaces. Under anoxic conditions, the (reductive) dissolution
of As-bearing phases such as iron ferrihydrite resulted in increased
dissolved As compared to oxic conditions and reprecipitation of iron
arsenate. Overall, As in coal ash is not environmentally stable and
can participate in local biogeochemical cycles
Long-Term Transformation and Fate of Manufactured Ag Nanoparticles in a Simulated Large Scale Freshwater Emergent Wetland
Transformations and long-term fate of engineered nanomaterials
must be measured in realistic complex natural systems to accurately
assess the risks that they may pose. Here, we determine the long-term
behavior of polyÂ(vinylpyrrolidone)-coated silver nanoparticles (AgNPs)
in freshwater mesocosms simulating an emergent wetland environment.
AgNPs were either applied to the water column or to the terrestrial
soils. The distribution of silver among water, solids, and biota,
and Ag speciation in soils and sediment was determined 18 months after
dosing. Most (70 wt %) of the added Ag resided in the soils and sediments,
and largely remained in the compartment in which they were dosed.
However, some movement between soil and sediment was observed. Movement
of AgNPs from terrestrial soils to sediments was more facile than
from sediments to soils, suggesting that erosion and runoff is a potential
pathway for AgNPs to enter waterways. The AgNPs in terrestrial soils
were transformed to Ag<sub>2</sub>S (∼52%), whereas AgNPs in
the subaquatic sediment were present as Ag<sub>2</sub>S (55%) and
Ag-sulfhydryl compounds (27%). Despite significant sulfidation of
the AgNPs, a fraction of the added Ag resided in the terrestrial plant
biomass (∼3 wt % for the terrestrially dosed mesocosm), and
relatively high body burdens of Ag (0.5–3.3 μg Ag/g wet
weight) were found in mosquito fish and chironomids in both mesocosms.
Thus, Ag from the NPs remained bioavailable even after partial sulfidation
and when water column total Ag concentrations are low (<0.002 mg/L)