7 research outputs found
Colloid Mobilization in a Fractured Soil during Dry–Wet Cycles: Role of Drying Duration and Flow Path Permeability
In
subsurface soils, colloids are mobilized by infiltrating rainwater,
but the source of colloids and the process by which colloids are generated
between rainfalls are not clear. We examined the effect of drying
duration and the spatial variation of soil permeability on the mobilization
of <i>in situ</i> colloids in intact soil cores (fractured
and heavily weathered saprolite) during dry–wet cycles. Measuring
water flux at multiple sampling ports at the core base, we found that
water drained through flow paths of different permeability. The duration
of antecedent drying cycles affected the amount of mobilized colloids,
particularly in high-flux ports that received water from soil regions
with a large number of macro- and mesopores. In these ports, the amount
of mobilized colloids increased with increased drying duration up
to 2.5 days. For drying durations greater than 2.5 days, the amount
of mobilized colloids decreased. In contrast, increasing drying duration
had a limited effect on colloid mobilization in low-flux ports, which
presumably received water from soil regions with fewer macro- and
mesopores. On the basis of these results, we attribute this dependence
of colloid mobilization upon drying duration to colloid generation
from dry pore walls and distribution of colloids in flow paths, which
appear to be sensitive to the moisture content of soil after drying
and flow path permeability. The results are useful for improving the
understanding of colloid mobilization during fluctuating weather conditions
Effects of Iron on Optical Properties of Dissolved Organic Matter
Iron
is a source of interference in the spectroscopic analysis
of dissolved organic matter (DOM); however, its effects on commonly
employed ultraviolet and visible (UV–vis) light adsorption
and fluorescence measurements are poorly defined. Here, we describe
the effects of ironÂ(II) and ironÂ(III) on the UV–vis absorption
and fluorescence of solutions containing two DOM fractions and two
surface water samples. In each case, regardless of DOM composition,
UV–vis absorption increased linearly with increasing ironÂ(III).
Correction factors were derived using ironÂ(III) absorption coefficients
determined at wavelengths commonly used to characterize DOM. IronÂ(III)
addition increased specific UV absorbances (SUVA) and decreased the
absorption ratios (<i>E</i><sub>2</sub>:<i>E</i><sub>3</sub>) and spectral slope ratios (<i>S</i><sub>R</sub>) of DOM samples. Both ironÂ(II) and ironÂ(III) quenched DOM fluorescence
at pH 6.7. The degree and region of fluorescence quenching varied
with the iron:DOC concentration ratio, DOM composition, and pH. Regions
of the fluorescence spectra associated with greater DOM conjugation
were more susceptible to iron quenching, and DOM fluorescence indices
were sensitive to the presence of both forms of iron. Analyses of
the excitation–emission matrices using a 7- and 13-component
parallel factor analysis (PARAFAC) model showed low PARAFAC sensitivity
to iron addition
A Framework for Identifying Organic Compounds of Concern in Hydraulic Fracturing Fluids Based on Their Mobility and Persistence in Groundwater
We developed a screening framework
for identifying organic components
of hydraulic fracturing fluid with increased probability of exposure
via groundwater based on mobility, persistence, toxicity, and frequency
of use. Of 996 organic fracturing fluid compounds identified by the
U.S. Environmental Protection Agency and FracFocus for four states,
data were available to perform an initial screening of 659 compounds
for sufficient mobility and persistence to reach a water well under
fast and slow groundwater transport scenarios. For the fast transport
scenario, 15 compounds identified on at least 50 FracFocus reports
were predicted to have an elevated exposure potential, which was defined
as ≥10% of the initial concentration remaining at a transport
distance of 94 m, the average setback distance in the United States.
Of these 15 compounds, two were identified on >20% of FracFocus
reports
(naphthalene and 2-butoxyethanol), four were compounds identified
on >5% of reports, and three had health-based standards
Fate of 4-Nonylphenol and 17β-Estradiol in the Redwood River of Minnesota
The majority of previous research investigating the fate of endocrine-disrupting
compounds has focused on single processes generally in controlled
laboratory experiments, and limited studies have directly evaluated
their fate and transport in rivers. This study evaluated the fate
and transport of 4-nonylphenol, 17β-estradiol, and estrone in
a 10-km reach of the Redwood River in southwestern Minnesota. The
same parcel of water was sampled as it moved downstream, integrating
chemical transformation and hydrologic processes. The conservative
tracer bromide was used to track the parcel of water being sampled,
and the change in mass of the target compounds relative to bromide
was determined at two locations downstream from a wastewater treatment
plant effluent outfall. In-stream attenuation coefficients (<i>k</i><sub>stream</sub>) were calculated by assuming first-order
kinetics (negative values correspond to attenuation, whereas positive
values indicate production). Attenuation of 17β-estradiol (<i>k</i><sub>stream</sub> = −3.2 ± 1.0 day<sup>–1</sup>) was attributed primarily due to sorption and biodegradation by
the stream biofilm and bed sediments. Estrone (<i>k</i><sub>stream</sub> = 0.6 ± 0.8 day<sup>–1</sup>) and 4-nonylphenol
(<i>k</i><sub>stream</sub> = 1.4 ± 1.9 day<sup>–1</sup>) were produced in the evaluated 10-km reach, likely due to biochemical
transformation from parent compounds (17β-estradiol, 4-nonylphenolpolyethoxylates,
and 4-nonyphenolpolyethoxycarboxylates). Despite attenuation, these
compounds were transported kilometers downstream, and thus additive
concentrations from multiple sources and transformation of parent
compounds into degradates having estrogenic activity can explain their
environmental persistence and widespread observations of biological
disruption in surface waters
Inhibition of Biodegradation of Hydraulic Fracturing Compounds by Glutaraldehyde: Groundwater Column and Microcosm Experiments
The
rapid expansion of unconventional oil and gas development has
raised concerns about the potential contamination of aquifers; however,
the groundwater fate and transport of hydraulic fracturing fluid compounds
and mixtures remains a significant data gap. Degradation kinetics
of five hydraulic fracturing compounds (2-propanol, ethylene glycol,
propargyl alcohol, 2-butoxyethanol, and 2-ethylhexanol) in the absence
and presence of the biocide glutaraldehyde were investigated under
a range of redox conditions using sediment-groundwater microcosms
and flow-through columns. Microcosms were used to elucidate biodegradation
inhibition at varying glutaraldehyde concentrations. In the absence
of glutaraldehyde, half-lives ranged from 13 d to >93 d. Accurate
mass spectrometry indicated that a trimer was the dominant aqueous-phase
glutaraldehyde species. Microbial inhibition was observed at glutaraldehyde
trimer concentrations as low as 5 mg L<sup>–1</sup>, which
demonstrated that the trimer retained some biocidal activity. For
most of the compounds, biodegradation rates slowed with increasing
glutaraldehyde concentrations. For many of the compounds, degradation
was faster in the columns than the microcosms. Four compounds (2-propanol,
ethylene glycol, propargyl alcohol, and 2-butoxyethanol) were found
to be both mobile and persistent in groundwater under a range of redox
conditions. The glutaraldehyde trimer and 2-ethylhexanol were more
rapidly degraded, particularly under oxic conditions
In-Stream Attenuation of Neuro-Active Pharmaceuticals and Their Metabolites
In-stream
attenuation was determined for 14 neuro-active pharmaceuticals
and associated metabolites. Lagrangian sampling, which follows a parcel
of water as it moves downstream, was used to link hydrological and
chemical transformation processes. Wastewater loading of neuro-active
compounds varied considerably over a span of several hours, and thus
a sampling regime was used to verify that the Lagrangian parcel was
being sampled and a mechanism was developed to correct measured concentrations
if it was not. In-stream attenuation over the 5.4-km evaluated reach
could be modeled as pseudo-first-order decay for 11 of the 14 evaluated
neuro-active pharmaceutical compounds, illustrating the capacity of
streams to reduce conveyance of neuro-active compounds downstream.
Fluoxetine and <i>N</i>-desmethyl citalopram were the most
rapidly attenuated compounds (<i>t</i><sub>1/2</sub> = 3.6
± 0.3 h, 4.0 ± 0.2 h, respectively). Lamotrigine, 10,11,-dihydro-10,11,-dihydroxy-carbamazepine,
and carbamazepine were the most persistent (<i>t</i><sub>1/2</sub> = 12 ± 2.0 h, 12 ± 2.6 h, 21 ± 4.5 h, respectively).
Parent compounds (e.g., buproprion, carbamazepine, lamotrigine) generally
were more persistent relative to their metabolites. Several compounds
(citalopram, venlafaxine, <i>O</i>-desmethyl-venlafaxine)
were not attenuated. It was postulated that the primary mechanism
of removal for these compounds was interaction with bed sediments
and stream biofilms, based on measured concentrations in stream biofilms
and a column experiment using stream sediments
Spatial Dependence of Reduced Sulfur in Everglades Dissolved Organic Matter Controlled by Sulfate Enrichment
Sulfate inputs to the Florida Everglades
stimulate sulfidic conditions
in freshwater wetland sediments that affect ecological and biogeochemical
processes. An unexplored implication of sulfate enrichment is alteration
of the content and speciation of sulfur in dissolved organic matter
(DOM), which influences the reactivity of DOM with trace metals. Here,
we describe the vertical and lateral spatial dependence of sulfur
chemistry in the hydrophobic organic acid fraction of DOM from unimpacted
and sulfate-impacted Everglades wetlands using X-ray absorption spectroscopy
and ultrahigh-resolution mass spectrometry. Spatial variation in DOM
sulfur content and speciation reflects the degree of sulfate enrichment
and resulting sulfide concentrations in sediment pore waters. Sulfur
is incorporated into DOM predominantly as highly reduced species in
sulfidic pore waters. Sulfur-enriched DOM in sediment pore waters
exchanges with overlying surface waters and the sulfur likely undergoes
oxidative transformations in the water column. Across all wetland
sites and depths, the total sulfur content of DOM correlated with
the relative abundance of highly reduced sulfur functionality. The
results identify sulfate input as a primary determinant on DOM sulfur
chemistry to be considered in the context of wetland restoration and
sulfur and trace metal cycling