5 research outputs found
Surface Water Withdrawals for Marcellus Shale Gas Development: Performance of Alternative Regulatory Approaches in the Upper Ohio River Basin
Almost
all of the water used for developing Marcellus Shale gas
is withdrawn from surface water sources. State environmental and interstate
water authorities take different approaches to managing these withdrawals.
In the Upper Ohio River Basin, which covers the western third of Pennsylvania,
the Pennsylvania Department of Environmental Protection requires that
all water sources used for development have an approved water management
plan. For surface water sources the plans stipulate the amount and
timing of withdrawals from each source as a function of annual streamflow
statistics. Neighboring regulatory authorities and some environmental
groups now favor the use of monthly streamflow statistics to establish
the conditions for water withdrawals. Our analysis indicates that,
given the state of flow measurement data in the Upper Ohio River Basin,
the annual streamflow statistics are more likely to prevent water
withdrawals during the driest times of the year when aquatic ecosystems
are most stressed, and to result in fewer and smaller occurrences
of computed low-flow ecodeficits
Modeling Nanosilver Transformations in Freshwater Sediments
Silver
nanoparticles (AgNPs), an effective antibacterial agent,
are a significant and fast-growing application of nanotechnology in
consumer goods. The toxicity of AgNPs released to surface waters during
the use or disposal of AgNP-containing products will depend on the
chemical transformations the nanoparticles undergo in the environment.
We present a simple one-dimensional diagenetic model for predicting
AgNP distribution and silver speciation in freshwater sediments. The
model is calibrated to data collected from AgNP-dosed large-scale
freshwater wetland mesocosms. The model predicts that AgNP sulfidation
will retard nanoparticle oxidation and ion release. The resultant
Ag<sub>2</sub>S-coated AgNPs are expected to persist and accumulate
in sediment downstream from sources of AgNPs. Silver speciation and
persistence in the sediment depend on the seasonally variable availability
of organic carbon and dissolved oxygen. The half-life of typical sulfidized
(85% Ag<sub>2</sub>S) AgNPs may vary from less than 10 years to over
a century depending on redox conditions. No significant difference
in silver speciation and distribution is observed between ā„50%
Ag<sub>2</sub>S and 100% Ag<sub>2</sub>S AgNPs. Formation and efflux
of toxic silver ion is reduced in eutrophic systems and maximized
in oligotrophic systems
Stream Dynamics and Chemical Transformations Control the Environmental Fate of Silver and Zinc Oxide Nanoparticles in a Watershed-Scale Model
Mathematical models are needed to
estimate environmental concentrations
of engineered nanoparticles (NPs), which enter the environment upon
the use and disposal of consumer goods and other products. We present
a spatially resolved environmental fate model for the James River
Basin, Virginia, that explores the influence of daily variation in
streamflow, sediment transport, and stream loads from point and nonpoint
sources on water column and sediment concentrations of zinc oxide
(ZnO) and silver (Ag) NPs and their reaction byproducts over 20 simulation
years. Spatial and temporal variability in sediment transport rates
led to high NP transport such that less than 6% of NP-derived metals
were retained in the river and sediments. Chemical transformations
entirely eliminated ZnO NPs and doubled Zn mobility in the stream
relative to Ag. Agricultural runoff accounted for 23% of total metal
stream loads from NPs. Average NP-derived metal concentrations in
the sediment varied spatially up to 9 orders of magnitude, highlighting
the need for high-resolution models. Overall, our results suggest
that āfirst generationā NP risk models have probably
misrepresented NP fate in freshwater rivers due to low model resolutions
and the simplification of NP chemistry and sediment transport
Time and Nanoparticle Concentration Affect the Extractability of Cu from CuO NP-Amended Soil
We assess the effect of CuO nanoparticle
(NP) concentration and
soil aging time on the extractability of Cu from a standard sandy
soil (Lufa 2.1). The soil was dosed with CuO NPs or CuĀ(NO3)Ā2 at 10
mg/kg or 100 mg/kg of total added Cu, and then extracted using either
0.01 M CaCl<sub>2</sub> or 0.005 M diethylenetriaminepentaacetic acid
(DTPA) (pH 7.6) extraction fluid at selected times over 31 days. For
the high dose of CuO NPs, the amount of DTPA-extractable Cu in soil
increased from 3 wt % immediately after mixing to 38 wt % after 31
days. In contrast, the extractability of CuĀ(NO<sub>3</sub>)<sub>2</sub> was highest initially, decreasing with time. The increase in extractability
was attributed to dissolution of CuO NPs in the soil. This was confirmed
with synchrotron X-ray absorption near edge structure measurements.
The CuO NP dissolution kinetics were modeled by a first-order dissolution
model. Our findings indicate that dissolution, concentration, and
aging time are important factors that influence Cu extractability
in CuO NP-amended soil and suggest that a time-dependent series of
extractions could be developed as a functional assay to determine
the dissolution rate constant
CuO Nanoparticle Dissolution and Toxicity to Wheat (<i>Triticum aestivum)</i> in Rhizosphere Soil
It
has been suggested, but not previously measured, that dissolution
kinetics of soluble nanoparticles such as CuO nanoparticles (NPs)
in soil affect their phytotoxicity. An added complexity is that such
dissolution is also affected by the presence of plant roots. Here,
we measured the rate of dissolution of CuO NPs in bulk soil, and in
soil in which wheat plants (<i>Triticum aestivum)</i> were
grown under two soil NP dosing conditions: (a) freshly added CuO NPs
(500 mg Cu/kg soil) and (b) CuO NPs aged for 28 d before planting.
At the end of the plant growth period (14 d), available Cu was measured
in three different soil compartments: bulk (not associated with roots),
loosely attached to roots, and rhizosphere (soil firmly attached to
roots). The labile Cu fraction increased from 17 mg/kg to 223 mg/kg
in fresh treatments and from 283 mg/kg to 305 mg/kg in aged treatments
over the growth period due to dissolution. Aging CuO NPs increased
the toxicity to <i>Triticum aestivum</i> (reduction in root
maximal length). The presence of roots in the soil had opposite and
somewhat compensatory effects on NP dissolution, as measured in rhizosphere
soil. pH increased 0.4 pH units for fresh NP treatments and 0.6 pH
units for aged NPs. This lowered CuO NP dissolution in rhizosphere
soil. Exudates from <i>T. aestivum</i> roots also increased
soluble Cu in pore water. CaCl<sub>2</sub> extractable Cu concentrations
increaed in rhizosphere soil compared to bulk soil, from 1.8 mg/kg
to 6.2 mg/kg inĀ fresh treatment and from 3.4 mg/kg to 5.4 mg/kg
inĀ aged treatments. Our study correlated CuO NP dissolution and
the resulting Cu ion exposure profile to phytotoxicity, and showed
that plant-induced changes in rhizosphere conditions should be considered
when measuring the dissolution of CuO NPs near roots