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Environmental and Human Health Impacts of Spreading Oil and Gas Wastewater on Roads

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Environmental and Human Health Impacts of Spreading Oil and Gas Wastewater on Roads

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Thirteen states in the United States allow the spreading of O&G wastewaters on roads for deicing or dust suppression. In this study, the potential environmental and human health impacts of this practice are evaluated. Analyses of O&G wastewaters spread on roads in the northeastern, U.S. show that these wastewaters have salt, radioactivity, and organic contaminant concentrations often many times above drinking water standards. Bioassays also indicated that these wastewaters contain organic micropollutants that affected signaling pathways consistent with xenobiotic metabolism and caused toxicity to aquatic organisms like Daphnia magna. The potential toxicity of these wastewaters is a concern as lab experiments demonstrated that nearly all of the metals from these wastewaters leach from roads after rain events, likely reaching ground and surface water. Release of a known carcinogen (e.g., radium) from roads treated with O&G wastewaters has been largely ignored. In Pennsylvania from 2008 to 2014, spreading O&G wastewater on roads released over 4 times more radium to the environment (320 millicuries) than O&G wastewater treatment facilities and 200 times more radium than spill events. Currently, state-by-state regulations do not require radium analyses prior to treating roads with O&G wastewaters. Methods for reducing the potential impacts of spreading O&G wastewaters on roads are discussed.
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Environmental and Human Health Impacts of Spreading Oil and Gas
Wastewater on Roads
T. L. Tasker,
W. D. Burgos,*
,
P. Piotrowski,
L. Castillo-Meza,
T. A. Blewett,
§
K. B. Ganow,
A. Stallworth,
P. L. M. Delompre,
§
G. G. Goss,
§
L. B. Fowler,
J. P. Vanden Heuvel,
,#
F. Dorman,
and N. R. Warner
Department of Civil and Environmental Engineering, The Pennsylvania State University, 212 Sackett Building, University Park,
Pennsylvania 16802, United States
Department of Chemistry, The Pennsylvania State University, 104 Chemistry Building, University Park, Pennsylvania 16802, United
States
§
Department of Biological Sciences, University of Alberta, 11455 Saskatchewan Drive, Edmonton, Alberta T6G 2E0, Canada
Penn State Law, The Pennsylvania State University, Lewis Katz Building, University Park, Pennsylvania 16802, United States
Department of Veterinary and Biomedical Sciences, The Pennsylvania State University, 115 Henning Building, University Park,
Pennsylvania 16802, United States
#
INDIGO Biosciences, Inc., 1981 Pine Hall Road, State College, Pennsylvania 16801, United States
Department of Biochemistry and Molecular Biology, The Pennsylvania State University,107 Althouse Lab, University Park,
Pennsylvania 16802, United States
*
SSupporting Information
ABSTRACT: Thirteen states in the United States allow the
spreading of O&G wastewaters on roads for deicing or dust
suppression. In this study, the potential environmental and human
health impacts of this practice are evaluated. Analyses of O&G
wastewaters spread on roads in the northeastern, U.S. show that
these wastewaters have salt, radioactivity, and organic contaminant
concentrations often many times above drinking water standards.
Bioassays also indicated that these wastewaters contain organic
micropollutants that aected signaling pathways consistent with
xenobiotic metabolism and caused toxicity to aquatic organisms
like Daphnia magna. The potential toxicity of these wastewaters is
a concern as lab experiments demonstrated that nearly all of the
metals from these wastewaters leach from roads after rain events,
likely reaching ground and surface water. Release of a known
carcinogen (e.g., radium) from roads treated with O&G wastewaters has been largely ignored. In Pennsylvania from 2008 to
2014, spreading O&G wastewater on roads released over 4 times more radium to the environment (320 millicuries) than O&G
wastewater treatment facilities and 200 times more radium than spill events. Currently, state-by-state regulations do not require
radium analyses prior to treating roads with O&G wastewaters. Methods for reducing the potential impacts of spreading O&G
wastewaters on roads are discussed.
INTRODUCTION
Fugitive dust emissions from unpaved roads represent a global
human and environmental health hazard. Approximately 34% of
the 6.6 million kilometers of roads in the United States (U.S.)
are unpaved and produce 47% of the annual airborne
particulate matter (<10 μm size) emissions.
1
Airborne
particulate matter from roads can contribute to chronic
respiratory and cardiovascular diseases
2
as well as vegetative
stress in local plant communities.
3
Throughout the U.S., road
managers work to alleviate these adverse human and environ-
mental health eects by spreading products on roads to
suppress dust.
There are over 190 dierent dust suppressants used to treat
unpaved roads in the U.S.
4
After application, dust suppressants
change the physical properties of the road aggregate by forming
coatings or causing particles to agglomerate together and retain
moisture. It is estimated that nearly 75% of all dust
suppressants applied to unpaved roads are chloride salts or
salt brine products that average around $0.25/L.
4
In regions
Received: February 5, 2018
Revised: April 16, 2018
Accepted: May 14, 2018
Published: May 30, 2018
Article
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where road managers have low annual budgets for road
maintenance, even $0.25/L may be too costly.
A free alternative in many states is to use wastewater from oil
and gas (O&G) wells. The high salt content of the O&G
wastewater is eective in retaining road moisture for
suppressing dust or lowering freezing points for deicing.
Here, road spreading of O&G wastewater in northwestern
Pennsylvania and northeastern Ohio was evaluated as a
demonstrative case study. Much of the unpaved road materials
in this region are from glacial till with ne particulate material
that is mobile in air and rain runo.
5
The long history of O&G
development in this region has provided opportunities for well
operators to give O&G wastewater to townships as a free dust
suppressant. In 2015, townships in northwestern Pennsylvania
spread an average of 280,000 L of O&G wastewater on their
roads,
6
equivalent to saving approximately $70,000 dollars per
township.
There are concerns with spreading O&G wastewaters on
roads. Wastewater contaminants may threaten environmental
and public health by leaching into surface or groundwater,
7
accumulating around roads,
8
modifying adjacent soil chem-
istry,
9
or migrating in air and dust. The Pennsylvania
Department of Environmental Protection (PA DEP) inves-
tigated the potential for radium, a known carcinogen, to
accumulate around roads treated with O&G wastewaters. Large
variabilities in radium concentrations measured in untreated
and treated roads led to inconclusive results. Further studies
were recommended to evaluate radionuclide concentrations in
O&G wastewaters used on roads and their transport after road
treatment.
10
O&G wastewater contaminants not retained in the road or
soils will be transported to water resources and require
signicant dilution to prevent the salinization of freshwater
resources. There are two reported cases in Ohio where
spreading O&G wastewaters on roads caused groundwater
contamination and salinization.
7,11
Salinization of freshwater
resources
12,13
is not a new issue as several studies document
increasing chloride and sodium concentrations in fresh water
resources.
14,15
Wastewater pollutants that migrate to water
resources could have toxic eects on sh, macroinvertebrates,
amphibians, and other salinity-intolerant species.
16
Therefore, it
is important to assess the extent of O&G wastewater spreading
in the U.S. and its potential impact on human and
environmental health.
The objectives of this research were to 1) identify states that
spread O&G wastewater on roads and then review their
associated regulations, 2) document the spatial and temporal
trends of spreading O&G wastewater on roads in Ohio and
Pennsylvania as demonstrative case studies, 3) determine the
chemical characteristics of O&G wastewater spread on roads,
4) evaluate the mobility of O&G wastewater contaminants after
road application and rainwater leaching, and 5) measure the
aquatic and human toxicity potential of O&G wastewaters used
on roads.
MATERIALS AND METHODS
Regulatory Review and Data Collection. Road spread-
ing and benecial reuse regulations for all 50 states were
reviewed by using the LexisNexis law database and contacting
O&G state regulators throughout the United States. Waste-
water volumes applied to roads were determined by reviewing
data on the PA DEP O&G reporting Web site
6
or digitizing
monthly spreading reports collected from Ohio and Pennsylva-
nia through public records requests. Certicate of analyses for
wastewaters applied to roads in New York and Pennsylvania
were also collected from public records requests.
Inorganic Analyses of O&G Wastewaters Spread on
Roads in Pennsylvania. O&G wastewaters were collected in
10 L high density polypropylene containers from storage tanks
in 14 townships throughout northwestern, PA that were to be
spread on roads in the summer 2017. Elemental analyses of
wastewaters were performed on a Thermo Scientic iCAP 6000
inductively coupled plasma optical emission spectrophotometer
(ICP-OES) for Na, Ca, Mg, Sr, and K, a Thermo X-Series 2
mass spectrophotometer (ICP-MS) for Ba, Fe, Pb, Cd, Cr, Cu,
and As, and a Dionex ICS-1100 ion chromatograph (IC) with
an AS18 column for Cl and Br at the Pennsylvania State
University. Before elemental analyses, samples were ltered
(0.45 μm) and diluted in 2% nitric acid or 18MΩultrapure
water (Thermo Scientic Barnstead Nanopure) to reach a
dilution factor of 2000 for Na, Ca, Mg, Sr, and K, 100 for Cl,
Br, and SO4, or 50 for all other metals. Dilutions were made on
a mass basis but were converted to volume using the specic
gravity of the O&G wastewaters. Mass interferences and matrix
complications of analyzing high salinity samples by ICP-MS or
ICP-OES were accounted for using internal spikes (Sc, In, Re,
Y) and high salinity, matrix matched standards synthesized
from High Purity Standards Inc. Calibration curves for all
analyses were veried with check standards (USGS M-220,
USGS T-227, and SRM1640a). Radioactivity was measured on
a small anode germanium detector (Canberra Instruments) at
geometries consistent with internal standards. After a 21-day
equilibration, 226Ra was measured using Bi-214 (609 keV) and
Pb-214 (295,351 keV) decay products. Direct measurement of
228Ra was performed using its 228Ac daughter at 911.16 keV.
Organic Analysis of O&G Wastewaters Used on
Roads. Organic compounds were extracted from 100 mL of
O&G wastewater sample using 3, 50 mL aliquots of
dichloromethane (DCM) per pH adjustment to pH < 2 with
H2SO4and pH > 10 with NaOH (EPA method 3510C:
Separatory Funnel LiquidLiquid extraction). Extracts were
concentrated to 1 mL using a Kuderna-Danish apparatus and
nitrogen gas blow down. Extracts were analyzed for diesel and
gas range organics using comprehensive two-dimensional gas
chromatography coupled to a time-of-ight mass spectrometer
(LECO Pegasus 4D GCxGC-TOFMS). The separation was
performed using a 100 m ×0.25 μmID×0.5 μm df RTX-
DHA-100 column in the rst dimension followed by a 1.7 m ×
0.25 μmID×0.25 μm df Rxi-17SilMS column in the second
dimension using He as carrier gas at 2.0 mL/min. The GC oven
was held at 50 °C for 0.2 min followed by a 5 °C/min ramp to
315 °C. The secondary GC oven was oset by 5 °C, while the
modulator was oset by 15 °C from the primary GC oven. A
modulation time of 3.0 s was used. The TOFMS was operated
from 50 to 550 amu at 70 eV at an acquisition frequency of
200 Hz. Diesel and gas range organics were determined using
an Alaska UST Standard (Restek, Bellefonte, PA) and TN/MS
DRO mix (Restek, Bellefonte, PA), with naphthalene-d8
(Restek, Bellefonte, PA) used as an internal standard.
Evaluating Contaminant Leachability after Spreading
O&G Wastewaters on Roads. Laboratory experiments were
conducted to determine the mobility of contaminants in O&G
wastewaters applied to road materials. In the eld, roads are
recommended to be treated with 1.6 L of O&G wastewaters
per m2which does not easily translate to a volume per mass of
road aggregate.
17
We assumed that the volume of dust
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suppressant in contact with a road aggregate would be
inuenced by the water retention capacity of the aggregate
itself. For lab experiments, O&G wastewater was applied to
road aggregate collected from Erie County, PA based on the
amount of water that the aggregate could retain. The water
retention capacity was determined to be 0.2 mL/g by mixing
100 g of aggregate (sieve < 1.18 mm) with 100 mL of water and
then measuring the amount of water that could be recovered
after ltering through a glass ber lter. Three O&G
wastewaters (PA01, PA02, and PA07; Table S5) were applied
to 100 g of the sieved road aggregate at the water retention
capacity (0.2 mL/g), dried (50 °C), and leached with 2000 mL
of synthetic rainwater (pH = 4.2) for 18 h according to the EPA
synthetic precipitation leaching procedure (SW-846 Test
Method 1312). Experiments were run in duplicate for the
three wastewaters, and leachates were tested for Cl, Br, Na, Mg,
Ca, Sr, Fe, and Pb according to the analytical methods above. A
mass balance was performed to determine the percent of the
contaminant mass that leached from the road aggregate.
A modied leaching method was used to test the mobility of
radium and organics after treating road aggregate with O&G
wastewaters. With the previous method, only 0.2 pCi/g of
radium would be applied to road aggregate from the O&G
wastewaters, making it dicult to measure the fate of radium in
the solid material. Therefore, three O&G wastewaters (PA01,
PA02, and PA03) were applied to aggregate (30 g) at higher
application volumes (0.9 mL/g) to increase the measurable
radium and organic concentrations in solid and liquid phases.
After drying at 50 °C for 4 days, the treated aggregate was
leached with 25 mL of synthetic rainwater for 18 h. The
leachate was collected, and then the solid was leached 2 more
times with 25 mL of synthetic rainwater to ensure that all
leachable contaminants were removed from the solid material
prior to analysissimilar to leaching procedures reported
elsewhere.
1820
Leached roads samples were dried at 50 °C and
analyzed for radium using gamma spectroscopy. A mass balance
was performed to determine the amount of radium that could
be retained in roads treated with O&G wastewaters. These
same experiments were repeated to determine the fate of
organic compounds after road spreading. After completing the
leaching experiment, road aggregate and leached road aggregate
were sequentially extracted 3 times for 10 min with 100 mL of a
50:50 acetone:DCM mixture using ultrasonic disruption (Omni
Sonic Ruptor 400 Ultrasonic Homogenizer) in accordance with
EPA Method 3550C. Extracts were analyzed on the LECO
Pegasus 4D GCxGC-TOFMS, and organic concentration
dierences between O&G wastewaters, untreated road
aggregates, and leached road aggregates were used for mass
balance calculations.
Multiple road spreading and runoevents were simulated in
lab experiments to better understand the fate of radium. Road
aggregate was treated with O&G wastewater (PA03), dried,
leached (same methods as previous paragraph), and measured
for 226Ra retained in the road material. This was repeated four
times to determine how much radium could accumulate in
roads treated multiple times with O&G wastewater. Radium in
O&G wastewaters that leach from the road after rain events
could also attenuate in roadside ditches or soils below the road
surface. Rain events were simulated by mixing road subgrade
and ditch material from Erie County, PA (30 g) with a 200 mL
solution of O&G wastewater diluted (5, 25, and 50 times
dilution) in synthetic rainwater. After 24 h of mixing, samples
were then centrifuged (3,000 rcf; 5 min), decanted, and rinsed
three times with 25 mL of ultrapure water (18 MΩ). Dried
samples were analyzed for 226Ra by gamma spectroscopy.
Evaluating the Potential Human Toxicity of O&G
Wastewaters Spread on Roads. Potential human toxicity of
O&G wastewaters spread on roads was evaluated using ve
commercial bioassays. The particular suite of bioassays was
selected to cover the major toxicity pathways commonly
observed in water samples,
21
including pathways for induction
to xenobiotic metabolism, specic modes of toxic action, and
induction of adaptive stress responses.
21
Bioassays with the
human aryl hydrocarbon receptor (AhR) and pregnane-X
receptor (PXR) tested for induction to xenobiotic metabolism,
while the human estrogen receptor alpha (ERα) tested for
ability to interfere with hormone action. Bioassays with the
nuclear factor erythroid 2related factor 2 (Nrf2) and nuclear
factor kappa-light-chain-enhancer of activated B cells (NFκB)
tested for oxidative signaling and inammatory stress. All
bioassays were purchased from INDIGO Biosciences (State
College, PA) and were used according to the manufacturers
protocols (Table S1). Each kit contains a luciferase reporter
gene that is specic for the human form of the signaling
proteins mentioned above. An increase in luciferase expression
is indicative of the signaling pathway.
Prior to bioassay testing, three O&G wastewater samples and
18MΩultrapure water (PA01, PA02, PA03, and Blank; all 1 L)
were extracted and concentrated in DCM as described above.
Extracts were evaporated with nitrogen gas and then
redissolved in dimethyl sulfoxide (DMSO). Extracted samples
and a reference compound (e.g., 1-methyl-6-bromoindirubin-
3-oximeMeBIO for AhR) prepared in DMSO were then
serially diluted in triplicate across a 96 well plate using the
manufacturers compound screening media (CSM). The
reference compound (included in each kit) was used as a
positive control, while a solution of 0.1% DMSO diluted in
CSM was used as a negative control. All samples were diluted in
triplicate. Dilution factors for the O&G samples were converted
to the relative enrichment factor (REF) which is calculated as
REF = DCM extraction enrichment factor/dilution factor in
bioassay.
22
Diluted samples were transferred to another 96 well
plate containing cells grown from the manufacturers cell
recovery media and incubated for 24 h at 37 °C with 5% CO2.
Following incubation, the manufacturers luciferase detection
reagent (LDR) was added to each well, and the luminescence
was quantied using a Molecular Devices microplate reader
(SpectraMax i3).
Luminescense results were normalized according to previous
studies.
23,24
Response data for reference compounds were tted
to a four parameter sigmoid loglogistic equation where the
minimum response (Mincontrol) was xed from the negative
control results. The remaining parameters such as the
maximum (Maxref) luminesence response, the reference
compound concentration causing 50% of the maximum
response, and the slope of the curve were calculated using
GraphPad Prism version 7.03 (see the Supporting Information
for more details). Thereafter, the responses of the DMSO
extraction control (Blank) and DMSO with O&G wastewaters
extractants were normalized to the response of the reference
compound as follows: % eect = (response Maxref)/(Maxref
Mincontrol). The limit of quantication (LOQ) for each
bioassay plate was calculated as 10×the standard deviation of
the%eect observed in the negative control according to
previous methods.
22
Bioanalytical equivalent concentrations
(BEQs), which normalize the eect observed in unknown
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samples to the eect of a reference compound (1-methyl-6-
bromoindirubin-3-oximeMeBIO for AhR), were calculated
for samples inducing responses above the LOQ. BEQs were
calculated using the linear-concentration eect method.
24
Normalized data from 0 to 30% eect were t to a line (y
intercept = 0), and the slope was compared to the reference
compound to calculate the BEQ as follows: BEQ =
slopeunknownsample/slopereference compound. Concentration units are
the same as the reference compound. Additional descriptions of
these bioassays are provided in the Supporting Information.
Evaluating the Potential Aquatic Toxicity of O&G
Wastewaters Spread on Roads. Toxicity studies on Daphnia
magna were used to assess the potential aquatic toxicity of
O&G wastewaters spread on roads. O&G wastewaters (PA01,
PA02, and PA03), saltwater (SW)-matched controls, and
organics extracted from the O&G wastewaters into DCM
(Organics-only controls) were serially diluted with dechlori-
nated Edmonton, Canada city water to reach REFs ranging
from 104to 101. Organic extracts in DCM were blown down
with nitrogen and suspended in DMSO prior to dilution with
the water. The SW-matched controls (Table S3) were designed
to have an ionic composition similar to the three O&G
wastewaters but with no organic compounds. Five neonate D.
magna (<24 h old) were transferred from a parental culture
into 50 mL glass beakers with the appropriate dilution of O&G
wastewater or SW-matched control and were maintained at 22
°C. Each series was run in triplicate, and mortality was recorded
at the end of the 48 h exposure according to the Organisation
for Economic Co-operation and Development (OECD)
guidelines.
25
Daphnia immobility was also assessed for O&G
wastewaters and Organics-only controls according to OECD
protocols. Immobility was determined on a binary scale and
was scored as immobile if the animal did not locomote within
15 s after gentle agitation.
26
The Toxicity Relationship Analysis
Program (TRAP) version 1.30a (EPA, Washington, DC, USA)
was used to calculate the lethal REF that would kill 50% of the
Daphnia (LC50), the eective REF that would cause 50% of the
Daphnia to be immobile (EC50), and the associated 95%
condence intervals (C.I.) for each treatment.
RESULTS AND DISCUSSION
Oil and Gas Wastewater Spreading on Roads in the
United States. At least 13 U.S. states allow the benecial use
of O&G wastes (e.g., wastewaters, sludges, oils) for road
maintenance, dust suppression, or deicing (Figure 1). To
document O&G benecial use practices, we reviewed
regulations on a state-by-state basis, documenting these
practices for 22 states (Figure 1;Table S4). States not included
in our review either had no O&G development or regulators
could not conrm their states benecial use practices. Most
states attempt to incentivize O&G developers to recycle O&G
wastewater or inject it into subsurface formations;
27
however,
the benecial use of O&G wastes on roads is permitted in 13
states (Figure 1). An additional 4 states may also allow road
spreading under state laws that permit land spreading or
benecial uses on a case-by-case basis (Figure 1).
A closer review of Pennsylvania and Ohio road spreading
data reveals that there is signicant spreading activity in these
states where millions of liters of O&G wastewater are spread
annually (Figure 2). The PA DEP and the Ohio Department of
Natural Resources (OH DNR) track road spreading by
requiring spreaders to complete monthly reports that document
O&G wastewater volumes spread on roads. More O&G
wastewater is spread on roads in Pennsylvania than Ohio.
Since 2008, an average of 35 million L/year of O&G
wastewater were spread on roads in 21 counties in
Pennsylvania, whereas 5 million L/year were spread in Ohio.
The majority of road spreading in Pennsylvania occurs in the
northwestern part of the state during April to August (Figure
2C). In 2016, there were 42 million L spread in Pennsylvania,
with 96% of this spread on roads in northwest Pennsylvania
(Figure 2). This represents approximately 6% of the total
wastewater volume (633 million L) generated from conven-
tional O&G wells in Pennsylvania.
6
The O&G wastewaters spread on Pennsylvania roads are
primarily from conventionally drilled wells. Before the increase
in high volume hydraulic fracturing (HVHF) in 2008,
Pennsylvanias O&G industry historically drilled vertical wells
into permeable sandstone reservoirs, referred to as conventional
O&G formations. In comparison, low permeability unconven-
tional O&G formations are developed using directional drilling
and HVHF. Current regulations for Colorado, New York,
Figure 1. U.S. states with regulations for spreading oil and gas (O&G)
wastewaters on roads.
Figure 2. A) Counties in Pennsylvania and Ohio that spread O&G
wastewaters on roads since 2008.
6
B) Volumes of O&G wastewater
spread on roads in PA and Ohio. C) Monthly volumes of O&G
wastewater spread in NW PA.
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Ohio, Pennsylvania, and West Virginia state that no produced
waters from formations developed with HVHF can be spread
on roads (Table S4). Conventional and unconventional O&G
wastewaters have organic and inorganic constituents that are
similar.
28
However, wastewaters from unconventional O&G
development may also include chemicals from the HVHF
process that could be potentially more toxic than the formation
specic constituents.
29
Chemical Characteristics of Oil and Gas Wastewater
Spread on Roads. O&G wastewaters spread on roads in the
northeast, U.S. (NY an PA) are chloride-rich uids with
sodium, calcium, magnesium, and strontium comprising greater
than 90% of the total cation charge equivalents (Table 1;Table
S5). Notably both the TDS and total radium concentrations are
elevated compared to the 500 mg/L TDS and 5 pCi/L radium
standards for drinking water, with median values over 293,000
mg/L and 1,230 pCi/L, respectively. Previous disposal of these
wastewaters through treatment facilities into streams raised
concerns of metal accumulation in stream sediments,
8,3032
salinity-driven toxicity impacts in receiving waterways,
33
and
increased potential for disinfection byproduct formation in
drinking water.
34
These same concerns also extend to roads
treated with O&G wastewaters.
7,8,11
Chemical characterizations of the 14 O&G wastewaters
collected for this study are consistent with formation brine from
conventional O&G formations. The Sr/Ca molar ratios and
87Sr/86Sr ratios (Table S5; Figure S1) for these 14 O&G
wastewaters indicate that they were likely sourced from Lower
Silurian or Upper Devonian age conventional O&G formations
which generally have Sr/Ca < 0.05 and 87Sr/86Sr between 0.710
and 0.715.
28
Therefore, the wastewaters currently spread on
roads in northwest PA appear to be in compliance with state
regulations that only permit road spreading with O&G
wastewaters from conventional gas formations.
Considering the chloride concentrations in the 14 O&G
wastewaters and 53 certicate of analyses (Table 1), these uids
require 730 to 1,600 times dilution to prevent drinking water
quality degradation around road spreading locations. Compar-
isons to primary and secondary standards show that TDS,
chloride, strontium, and radium are the pollutants in O&G
wastewaters that require the most dilution to reach maximum
contaminant level (MCL) concentrations for drinking water
(Table 1). Based on the data collected from the 14 O&G
wastewaters spread on roads in northwest PA, radium requires
more dilution (250450 times dilution) than every contami-
nant in the wastewater except chloride and TDS. At least six of
the 13 states with regulations for road spreading require a
certicate of analysis before O&G waste is permitted for use on
roads. However, there are no universal standards that limit the
contaminant concentrations in O&G wastewaters applied to
Table 1. Contaminants of Concern in O&G Wastewaters Spread on Roads
a
pollutant data source % reported % BDL MCL median max median DF max DF
TDS analyzed 100 0 500(+) 293,000 356,000 590 710
digitized 68 0 318,000 481,000 640 960
Cl analyzed 100 0 250(+) 183,000 211,000 730 840
digitized 87 0 185,000 389,000 740 1600
Br analyzed 100 0 1,950 2,970
digitized NR NR NR NR
Ba analyzed 100 0 2(*)4.12 22 2.06 11
digitized 30 0 2.03 490 1.01 245
Sr analyzed 100 0 10()1,270 4,310 130 430
digitized NR NR NR NR
Ra analyzed 100 0 5(*)1,230 2,270 250 450
digitized NR NR NR NR
Cr analyzed 100 93 0.1(*)0.097 0.097 0.97 0.97
digitized 19 60 0.019 0.021 0.19 0.21
Cd analyzed 100 100 0.005(*)BDL BDL
digitized 19 60 0.009 0.20 1.8 40
As analyzed 100 72 0.01(*)0.147 0.161 16 20
digitized 17 22 0.087 0.7 8.7 70
Pb analyzed 100 57 0.015(*)0.099 0.432 6.6 29
digitized 32 76 0.086 0.31 5.7 21
Cu analyzed 100 71 1.3(*)0.963 3.27 0.74 2.5
digitized 13 57 0.094 0.16 0.07 0.12
benzene analyzed NR NR 0.005(*)NR NR
digitized 36 53 0.023 0.053 4.6 11
DRO analyzed 86 0 3.41 685
digitized NR NR NR NR
GRO analyzed 86 0 7.89 25.9
digitized NR NR NR NR
a
Results are from 14 O&G wastewaters collected and analyzed from northwest PA and 53 digitized certicate of analyses from NY and PA. The
percent of the wastewater pollutants reported in digitized certicate of analyses are shown along with regulated primary(*), secondary(+), or industrial
euent()concentrations for drinking water and/or surface water. Of the values reported, the % of the results below detectable concentrations
(BDLs) are calculated. Dilution factors (DF) represent the amount of O&G wastewater dilution needed to reach the maximum contaminant levels
(MCLs) recommended for a receiving stream. DRO = diesel range organics; GRO = gas range organics; NR = not reported. All values are in mg/L
except radium (pCi/L).
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roads (Table S4). Chloride concentrations are reported in
nearly 87% of the certicates of analysis for O&G wastewaters
spread on roads in NY and PA, while radium concentrations
were never reported (Table 1).
Mobility of Oil and Gas Wastewater Contaminants
after Road Application. Exposure to pollutants in O&G
wastewaters spread on roads relates to their potential to be
transported from the road. Laboratory experiments were
conducted to determine the mobility of contaminants in
O&G wastewaters applied to road materials (Figure 3). Most
contaminants in O&G wastewater applied to roads were
leached with synthetic rainwater (chloride, bromide, sodium,
magnesium, calcium, and strontium). In contrast, a few
contaminants were retained in the road aggregate at greater
than 99% (iron and lead) after rainwater leaching. Both radium
and diesel range organics (DRO) displayed intermediate
behavior. The majority of DRO (>75%) applied to roads was
retained after rainwater leaching, while 50% of the radium was
retained.
Both sorption and mineral precipitation reactions could be
controlling the fate of iron and lead in the road aggregate.
When O&G wastewaters are applied to roads, iron likely
precipitates as iron oxides that are retained in the road material.
During leaching experiments, the pH of the synthetic rainwater
(4.2) increased to approximately 7 after interacting with the
treated road aggregate. This increase in pH would promote
precipitation of iron hydroxides. The formation of iron oxides,
which have a high sorption capacity for trace metals,
35
could
also inuence lead and radium retention in road aggregates.
Studies modeling the reactive transport of trace metals in O&G
wastewaters after spill events show that sorption and exchange
processes are important in controlling the mobility of trace
metals.
36
These modeling studies also highlight that precip-
itation reactions with hydroxide and carbonate minerals are the
primary factors controlling the fate of trace metals such as
lead.
36
Lead is known to cause physiological, biochemical, and
behavioral dysfunctions in humans.
37
Therefore, further studies
should explore how lead attenuates in road aggregate and if it is
accumulating in dust or ne particulates around roads treated
with O&G wastewaters.
O&G wastewaters used on roads also contain C6C30 diesel
range organics (DRO) that are largely retained in road
aggregates even after multiple rainwater leaching events.
Previous research showed that petroleum hydrocarbons in
O&G wastewaters can migrate to drinking water aquifers
following accidental spill events.
38
However, the majority of
DRO in O&G wastewaters applied to roads are retained
(>75%) in road aggregate after rainwater leaching (Figure 3A),
potentially limiting migration to water resources. The high
anity of DRO for road aggregate can be attributed to the low
water solubility of these C6C30 hydrocarbons.
39
Dust
originating from roads treated with O&G wastewaters could
contain adsorbed hydrocarbons, representing another exposure
pathway.
Radium in O&G wastewaters will accumulate in roads
following spreading events but likely at concentrations below
regulatory standards. Two previous studies analyzed radium
accumulation around roads spread with O&G wastewaters, but
ndings were dicult to interpret because the O&G wastewater
composition was unknown and radium concentrations in the
road aggregate were not measured immediately before and after
spreading.
8,10
Leaching experiments with three O&G waste-
waters (PA01, PA02, and PA03; Table S2) showed that
approximately 45% of the radium applied to a road aggregate
leached out after one application (Figure 3A). To test radium
accumulation in the road aggregate after multiple applications,
one O&G wastewater (PA03) was repeatedly applied to road
aggregate, dried, and leached with synthetic rainwater. Radium
concentrations in the road aggregate increased following
multiple applications but approached a maximum concentration
of 2 pCi/g after four treatments (Figure 3B).
Radium Release from Spreading O&G Wastewater on
Roads. Radium not retained in the road aggregate will run o
into ditches or underlying soils. To determine the potential
radium concentrations in soils around roads following spread-
ing and rain events, O&G wastewater was diluted with
synthetic rainwater and reacted with ditch and road subgrade
material (Figure 3C). At low dilution with rainwater (4 times
dilution), radium in the O&G wastewaters accumulated up to
34 pCi/g in the ditch and subgrade materials. As the
wastewater was diluted with more rainwater (>50 times
dilution), less radium accumulated. In all cases, radium
concentrations were below the regulatory standard of 5 pCi/g
above background for remediating land surfaces impacted by
radioactive waste materials (40 Code Federal Regulations §
Figure 3. A) Lab experiments showing the percent of contaminant
mass that was leached from road aggregate after O&G wastewater
application, drying, and leaching with synthetic rainwater. Values
below 100% indicate mass retention in the road aggregate. B) Radium
in road aggregate after multiple O&G wastewater applications and
rainwater leachings. C) Radium in ditch (red) and subgrade
(green) materials after reacting with O&G wastewater diluted with
synthetic rainwater. The red and black dotted lines represent
background radium activity in the ditch and subgrade materials,
repectively.
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192.12) or limiting materials that can be sent to landlls [(Ohio
Revised Code §3734.02 (P)(2)].
Where all the radium goes after spreading O&G wastewaters
on roads is still an unanswered question. There are numerous
processes that inuence the mobility of radium in the
environment, including salinity, pH, coprecipitation with
minerals (e.g., with barite), and sorption onto clays, oxides,
or pyrite.
40
While this study suggests that radium may not
accumulate to concentrations above regulatory standards in
areas where roads have been treated with O&G wastewaters,
further work is needed to investigate if the radium will migrate
to groundwater or accumulate in areas where mineral
precipitation or sorption processes are favorable. For instance,
radium sorption decreases as salinity increases.
40
After rain
events, radium from O&G wastewaters spread on roads could
migrate away from roads, becoming more diluted, and
potentially sorb to clay minerals in a more favorable low
salinity environment.
Spreading conventional O&G wastewaters on roads could
release more radium to the environment than any other O&G
wastewater disposal option. In Pennsylvania, more O&G
wastewater is disposed of by wastewater treatment plants
(180 million L in 2016) than road spreading (40 million L in
2016) (Figure 4). However, treated euents from these
facilities contain median radium concentrations of 14.5 pCi/
L,
41
levels that are close to the national primary drinking water
MCL of 5 pCi/L radium. In contrast, the O&G wastewaters
spread on roads in northwest Pennsylvania had a median
radium concentration of 1,230 pCi/L (Table 1;Table S5). For
estimating radium loads to the environment, the known
volumes of O&G wastewater disposed by these dierent
disposal options were multiplied by the 25th percentile,
median, and 75th percentile radium concentrations in treated
wastewaters
41
or wastewaters spread on roads (this study). In
2016, based on median radium concentrations, approximately
52 millicuries (mCi) of radium were spread on roads (Figure
4), whereas 2.6 mCi of radium were discharged through O&G
wastewater treatment facilities. Although less O&G wastewaters
is spread on roads, the release of radium could be much higher
than the release of radium from wastewater treatment facilities.
Road spreading may also release more radium to the
environment than spill events. While there is uncertainty in the
number of O&G wastewater spills and their associated
volumes,
42
we used previously published data from 2008 to
2014 to estimate the total O&G wastewater spilled from
unconventional O&G development in Pennsylvania. Only
saltwater spill volumes from owback, recycled, or produced
water were included to reduce the contributions from other
nonformation derived wastes such as hydraulic oils, fracturing
chemicals, etc. From 2008 to 2014, O&G wastewater saltwater
spill volumes were reported for 91 of the 256 incidents, with
median spill volumes of 794 L.
42
Assuming that unconventional
O&G wastewaters contain a median radium concentration of
1550 pCi/L,
28
these incidents (from 2008 to 2014) released
approximately 0.3 mCi of radium to the environment (median
spill volume ×256 spills ×radium concentration). Allowing for
various assumptions for spill size, radium released from
incidents in 20082014 ranged from 0.06 to 1.5 mCi (Table
S6). In comparison, approximately 83 mCi of radium were
discharged to rivers from O&G wastewater treatment facilities,
while 320 mCi were spread on roads during that same seven
year span. Although there has been considerable focus on spill
events and discharges of O&G wastewaters from wastewater
treatment plants into surface waters throughout the U.S.,
31
our
results demonstrate that from 2008 to 2014 road spreading may
have released over 4 times more radium to the environment
than O&G wastewater treatment facilities and potentially over
200 times more radium than spill events. In 2016, road
spreading may have released 20 times more radium than O&G
wastewater treatment facilities.
Aquatic and Human Toxicity Potential of O&G
Wastewaters Used on Roads. While radium is a known
carcinogen, organic compounds in O&G wastewaters also
exhibit potential toxicity. Organics extracted from O&G
wastewaters (PA01, PA02, and PA03) covering a range of
DRO and GRO concentrations were tested for their potential
to cause human toxicity. Mechanism and human cell-based
assays detected that organic micropollutants in these samples
could induce xenobiotic metabolism associated with the aryl
hydrocarbon receptor (AhR) (Figure 5;Figure S2). PXR
activation, which is also involved in regulating xenobiotic
metabolism, was detected in two of the three O&G wastewaters
tested (Figure S3). However, a minor response in the blank led
to uncertainty in these PXR results. Several AhR and PXR
agonists are associated with altering drug and xenobiotic
metabolism in humans and causing hepatotoxicity and liver
tumors in laboratory animals.
43,44
There were no signicant
increases in activity of bioreceptor assays targeting endocrine
disruption (ERα), oxidative stress (Nrf2), and inammation
Figure 4. A) Volumes of O&G wastewater spread on roads or
discharged through wastewater treatment plants with NPDES permits
in Pennsylvania.
6
B) Annual radium loads to the environment based
on radium euent concentrations reported for O&G wastewater
treatment facilities
41
and radium concentrations in 14 O&G
wastewaters spread on Pennsylvania roads in 2017 (this study). Blue
and red shaded regions represent loads based on the 25th75th
percentile radium concentrations. Solid and dotted lines represent
median loads.
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(NFkB) (Table S7;Figures S4S6). The absence of induction
in these other bioassays could have been the result of REFs not
high enough to generate responses or the lack of bioactive
micropollutants in the O&G wastewaters.
Induction to AhR was inuenced by the DRO and GRO
concentrations in the O&G wastewaters. BEQs for the
bioactive compounds in the samples were calculated in terms
of a reference compound known to interact strongly with the
receptor (MeBIO for AhR) (Figure 5). Steeper linear response
curves (Figure 5C) from 0 to 30% eect responses reect
higher BEQs within samples.
24
Organic compounds extracted
from PA01 had the highest BEQ value for AhR (6000 pM
MeBio). PA02 was also active toward AhR, while PA03
generated no AhR response. The BEQ values for all three
samples corresponded to their concentrations of DRO and
GRO. PA01 had the highest DRO and GRO concentrations
(684 mg/L DRO; 23.5 mg/L GRO) and induced the greatest
AhR response among the three wastewaters, while PA03 had
the lowest DRO and GRO (0.60 mg/L DRO; 8.11 mg/L
GRO) and generated no response to AhR. These data suggest
that induction to this potential human toxicity pathway could
be reduced by setting DRO and GRO concentration limits to
less than 10 mg/L for O&G wastewaters that can be applied to
roads.
The O&G wastewater samples (not extracted into DCM
solvent) were also shown to be toxic to Daphnia magna (Figure
6). Daphnia magna, the water ea, is an important aquatic
organism in freshwater ecosystems
45
and a common ecotox-
icological model organism for risk assessment and regulatory
guidelines.
25
In the current study, all three O&G wastewaters
yielded statistically similar toxicity to Daphnia magna, with LC50
values ranging between REFs of 101.89 (PA01) and 101.77
(PA02) (Figure 6A; Table S7). Lower REFs reect more toxic
samples. For PA01 and PA02, there was no dierence in
toxicity between the O&G samples and their SW-matched
Figure 5. Induction to AhR human receptor by O&G wastewaters
(PA01, PA02, and PA03). The response curve for the 1-methyl-6-
bromoindirubin-3-oxime (MeBio) reference compound is shown in
parts A) and B). The % eect curves for the O&G wastewater samples
are normalized to the minimum and maximum responses observed
from the reference compound. Linear response data from 0 to 30%
eect were used for calculating BEQs. PA01 induced the greatest
response, while PA03 generated no response (NR).
Figure 6. Acute lethal toxicity (Figure 6A) in Daphnia magna neonates
after 48 hour exposure to oil and gas wastewater samples. Daphnia
toxicity was also tested after exposure to control samples containing
salinities that matched the O&G wastewaters (Figure 6B). The %
immobile or dead D. magna were also measured after exposure to the
O&G wastewaters.
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controls. However, for PA03 the SW-matched control was
slightly less toxic (causing 50% mortality at a dilution factor of
101.75, relative to 101.89 for the O&G wastewater). We tried to
determine if this dierence in toxicity could be attributed to
organic compounds in the O&G wastewaters that were not in
the SW-matched controls. However, organic compounds
extracted and concentrated by DCM from the three O&G
wastewaters (Organics-only control) had no lethal toxicity
responses to Daphnia magna over 48 h experiments, even in
undiluted samples (Table S7). While these results suggest that
the additional toxicity observed in PA03 versus its SW-matched
control was not from the organic compounds present in PA03,
liquidliquid extractions into DCM may not have extracted
polar organic compounds or concentrations of organic
pollutants may have been too low to induce a toxic response.
Overall, these data suggest that the high salt concentrations of
the O&G wastewaters (Table 1) are the most signicant factor
for Daphnia magna toxicity, consistent with recent work
examining the toxicity of hydraulic fracturing wastewaters.
46
During these experiments it was observed that Daphnia were
physically immobile at the water surface in incubations with
O&G wastewater. As the traditional toxicity end point of
lethality does not account for physically immobile animals that
are still alive, additional experiments were performed by
measuring the eective concentrations causing immobility or
toxicity. These new eect concentrations (EC50) values were
signicantly higher than the LC50 values for the same samples.
For example, the highest EC50 occurred in PA01 at an REF of
102.79, a value much greater than the LC50 (101.95). The
physical immobility observed was likely caused by organic
compounds present in the O&G wastewater. Physical
immobility was not observed in SW-controls but was observed
in Organics-only controls (Table S7). No experiments were
performed to identify the specic organic components
responsible for the cessation of movement. However, these
results demonstrate that using lethality as an end point for
Daphnia toxicity studies may not capture the potential toxicity
implications of Daphnia becoming immobile after interacting
with organic compounds in O&G wastewater. Depending on
how the mode of action is dened, normal laboratory
assessments may underestimate the risk associated with
physical immobility from oil and gas wastewaters. Physical
immobilization will likely be a signicant mechanism for
potential toxicity to freshwater zooplankton.
47
Implications for Spreading O&G Wastewaters on
Roads. Spreading O&G wastewater on roads can harm aquatic
life and pose health risks to humans. Experiments simulating
the application of O&G wastewater to road materials followed
by leaching with synthetic rainwater demonstrated that the
majority of contaminants are not retained in the road. Despite
the presence of biologically active organic micropollutants that
could promote cancer, the high salt concentrations in O&G
wastewaters transported from the road to surface water after
rain events are likely the major potential threat to aquatic
toxicity. These wastewaters could require up to 1600 times
dilution to reach drinking water quality standards or
approximately 100 times dilution to reduce acute toxicity to
aquatic organisms.
Some contaminants such as lead, radium, and organic
micropollutants may also accumulate in roads treated with
O&G wastewaters. Future work should study roads treated with
O&G wastewaters to see how these contaminants partition into
various grain sizes in road materials. Accumulation in ne
particulate dust particles could be a potential exposure pathway
not discussed in this current study. This study showed that
radium was partially retained in the road materials, but its
concentration reached a plateau after multiple applications of
O&G wastewater. Additional radium applied to radium-
saturated road materials could be transported to surface water
or groundwater or accumulate in local soils. The release of
radium, a known carcinogen, is a potential threat to human
health. In Pennsylvania, we found that radioactivity associated
with radium released to the environment via road spreading
exceeds the radioactivity of radium released by spill events or
wastewater treatment plants. The spreading of O&G waste-
waters on roads could be a signicant contributor of inorganic
and organic micropollutants to the environment and has been
largely ignored in environmental studies on O&G development.
We propose three means to reduce the environmental
impacts associated with spreading O&G wastewaters on roads:
1) Only O&G wastewaters that have been treated at wastewater
treatment facilities should be considered for road spreading.
The high calcium, sodium, and magnesium concentrations in
O&G wastewaters are important for suppressing dust. In
addition to the high salt concentrations, these wastewaters
contain lead, radium, and organic compounds that could be
potentially toxic. Wastewater treatment facilities are not
designed to remove the high salt concentrations in O&G
wastewaters. However, they can eectively remove radium, oil
and grease, and other trace metals. 2) O&G wastewaters
approved for road spreading should contain <60 pCi/L radium
and <10 mg/L of total DRO and GRO, similar to other
industrial wastewater euent standards. No induction to
human cell receptors was observed at DRO and GRO
concentrations below 10 mg/L. In most cases, the chemical
composition of O&G wastewater intended for road spreading
must be submitted and approved before use. However,
requirements for these chemical characterizations are relatively
modest, vary widely between states, and currently do not
include radium. Having chemical standards for O&G waste-
waters that can be spread on roads could help reduce the
potential toxicity concerns associated with this practice. 3)
Aordable nontoxic dust suppressants should be developed and
used. Many of the townships in Pennsylvania that spread O&G
wastewaters on roads have low annual budgets for road
maintenance. Based on the cost of many commercial dust
suppressants, the annual township budgets would not be
enough to maintain roads and suppress dust using these
products. Solutions to this road maintenance issue could be to
use alternative products or pave roads, but this would require
substantial amounts of money that many townships do not
possess. O&G wastewaters may be a viable and cheap option
for suppressing dust, but as discussed in this study, there could
be potential human and environmental health consequences of
this practice. Some of these concerns could be mitigated by
new regulatory standards as described above or by developing
alternative low-cost products so townships can maintain their
roads without the need to use O&G wastewaters.
ASSOCIATED CONTENT
*
SSupporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.est.8b00716.
Detailed method descriptions for performing bioassay
testing; chemistry of saltwater matched controls for
Environmental Science & Technology Article
DOI: 10.1021/acs.est.8b00716
Environ. Sci. Technol. 2018, 52, 70817091
7089
Daphnia magna testing; results from human bioassays
and aquatic toxicity tests (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: wdb3@psu.edu.
ORCID
T. L. Tasker: 0000-0001-5040-7579
W. D. Burgos: 0000-0003-3269-2921
P. Piotrowski: 0000-0002-8039-7911
T. A. Blewett: 0000-0001-6834-1571
N. R. Warner: 0000-0002-6434-5118
Notes
The authors declare no competing nancial interest.
ACKNOWLEDGMENTS
The authors acknowledge the help from several anonymous
townships in northwestern, PA who provided the wastewater
and road samples. The authors also thank Zhang Cai for
assisting in data interpretation. This research was partially
supported by the United States Geological Survey 104B Grant
No. G16AP00079 to W.B. and L.F., the National Science
Foundation project CBET-1703412 to W.B., J.V., F.D. and
N.W., and the Penn State Institutes of Energy and the
Environment to N.W. and W.B.
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Rapid growth in unconventional oil and gas (UOG) has produced jobs, revenue, and energy, but also concerns over spills and environmental risks. We assessed spill data from 2005 to 2014 at 31 481 UOG wells in Colorado, New Mexico, North Dakota, and Pennsylvania. We found 2-16% of wells reported a spill each year. Median spill volumes ranged from 0.5 m(3) in Pennsylvania to 4.9 m(3) in New Mexico; the largest spills exceeded 100 m(3). Seventy-five to 94% of spills occurred within the first three years of well life when wells were drilled, completed, and had their largest production volumes. Across all four states, 50% of spills were related to storage and moving fluids via flowlines. Reporting rates varied by state, affecting spill rates and requiring extensive time and effort getting data into a usable format. Enhanced and standardized regulatory requirements for reporting spills could improve the accuracy and speed of analyses to identify and prevent spill risks and mitigate potential environmental damage. Transparency for data sharing and analysis will be increasingly important as UOG development expands. We designed an interactive spills data visualization tool ( http://snappartnership.net/groups/hydraulic-fracturing/webapp/spills.html ) to illustrate the value of having standardized, public data.