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Determination of Total PetroleumHydrocarbon (TPH) and
PolycyclicAromatic Hydrocarbon (PAH) inSoils: A Review of
Spectroscopic andNonspectroscopic TechniquesReuben Nwomandah
Okparanma a & Abdul Mounem Mouazen aa Department of
Environmental Science and Technology, NationalSoil Resources
Institute , Cranfield University , Cranfield ,Bedfordshire ,
UKAccepted author version posted online: 07 Jan
2013.Publishedonline: 13 Mar 2013.
To cite this article: Reuben Nwomandah Okparanma & Abdul
Mounem Mouazen (2013) Determinationof Total Petroleum Hydrocarbon
(TPH) and Polycyclic Aromatic Hydrocarbon (PAH) in Soils: A
Reviewof Spectroscopic and Nonspectroscopic Techniques, Applied
Spectroscopy Reviews, 48:6, 458-486,DOI:
10.1080/05704928.2012.736048
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http://dx.doi.org/10.1080/05704928.2012.736048
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Applied Spectroscopy Reviews, 48:458486, 2013Copyright Taylor
& Francis Group, LLCISSN: 0570-4928 print / 1520-569X
onlineDOI: 10.1080/05704928.2012.736048
Determination of Total Petroleum Hydrocarbon(TPH) and Polycyclic
Aromatic Hydrocarbon (PAH)
in Soils: A Review of Spectroscopic andNonspectroscopic
Techniques
REUBEN NWOMANDAH OKPARANMAAND ABDUL MOUNEM MOUAZENDepartment of
Environmental Science and Technology, National Soil
ResourcesInstitute, Cranfield University, Cranfield, Bedfordshire,
UK
Abstract: In the analysis of petroleum hydrocarboncontaminated
soils for totalpetroleum hydrocarbons (TPHs) and polycyclic
aromatic hydrocarbons (PAHs), theroles of spectroscopic and
nonspectroscopic techniques are inseparable.
Therefore,spectroscopic techniques cannot be discussed in
isolation. In this report, spectroscopictechniques including Raman,
fluorescence, infrared, and visible and near-infrared (Vis-NIR)
spectroscopies, as well as mass spectroscopy (coupled to a gas
chromatograph)and nonspectroscopic techniques such as gravimetry,
immunoassay, and gas chro-matography with flame ionization
detection are reviewed. To bridge the perceived gapin coverage of
the quantitative applications of Vis-NIR spectroscopy in the rapid
de-termination of TPHs and PAHs in soils, a detailed review of
studies from the period19992012 are presented. This report also
highlights the strengths and limitations ofthese techniques and
evaluates their performance from the perspective of their
attributesof general applicability, namely economic portability,
operational time, accuracy, andoccupational health and safety
considerations. Overall, the fluorescence spectroscopictechnique
had the best performance (85% total score) in comparison to the
others,and the gravimetric technique performed the least (60% total
score). Method-specificsolutions geared toward performance
improvement are also suggested.
Keywords: Petroleum hydrocarbons, soil, Raman spectroscopy, IR
spectroscopy,fluorescence spectroscopy, mass spectroscopy, Vis-NIR
spectroscopy
IntroductionIn both the upstream and downstream sectors of the
oil and gas industry, available recordsshow that spillage of crude
oil and its daughter products occurs frequently due to naturaland
anthropogenic causes (1, 2). A crude oil spill on land introduces
petroleum-basedhydrocarbons (PHCs), which negatively impact soils
biological, chemical, and physicalcharacteristics. Results of
various environmental studies carried out in oil spill areas
show
Address correspondence to Abdul Mounem Mouazen, Department of
Environmental Scienceand Technology, National Soil Resources
Institute, Cranfield University, Cranfield, BedfordshireMK43 0AL,
UK. E-mail: [email protected]
458
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Petroleum HydrocarbonContaminated Soils 459
staggering levels of environmental pollution and adverse effects
on biota due to the haz-ardous nature of PHCs (310). Prior to the
remediation of the impacted media, a fullassessment of the impact
of the PHCs on the environment and/or humans is essential
toidentifying both the chemistry and the areal extent to which the
PHCs exceed local thresh-old limit values (TLV) and providing
decision support on the appropriate remedial strategyto adopt for
effective cleanup of the environmental media. The hierarchical
approach torisk assessment (1120) reflects the different types of
data handling required at each stagein the data gathering process.
Whereas tier 1 risk assessment involves, but is not limitedto, the
quantitation of the total petroleum hydrocarbons (TPHs) and
n-alkanes to establishtheir risk-based screening levels (RBSLs),
tier 2 (i.e., generic quantitative risk assessment)involves the
analysis of the proximal composition and distribution of individual
polycyclicaromatic hydrocarbon (PAH) fractions and the indicator
PAH compounds. Tier 3 involves amore detailed investigation to
determine the compound-specific biomarkers (CSBs) in
theenvironmental sample (21).
Over the years, several spectroscopic and nonspectroscopic
techniques have been de-veloped for the analysis of TPH and PAH in
soil samples; the most frequently used areimmunoassay (IMA),
general gravimetry, laboratory-based gas chromatography (GC)
withflame ionization detection (FID) or mass spectrometry (MS),
infrared (IR) spectroscopy,Raman spectroscopy, and fluorescence
spectroscopy. Recently, a couple of equally im-portant innovative
methods that have shown reasonable potential for the measurement
ofTPH and PAH in oil-contaminated soils are emerging. These include
field-portable GC-MS(22), and new-generation near-infrared analysis
with visible and near-infrared (Vis-NIR)spectroscopy (2328).
Although it was not until recently that some IMA techniques
(29,30), field-portable GC-MS systems (22), and Vis-NIR
spectroscopy (28) were used to de-tect PAHs in soil samples.
Previously, the laboratory-based GC-MS systems,
fluorescencespectroscopy, and Raman spectroscopy were used for the
analysis of PAH in environmentalsamples, but GC-MS systems are
preferred due to their relative selectivity and sensitivity(18,
3133).
It has been widely acknowledged that making informed decisions
on remediation re-quirements after an oil spill incident requires
information about hydrocarbon fractions. Italso requires that the
degree of accuracy achieved by different analytical techniques
cur-rently available meets given standards. This, of course, is a
function of sampling resolutionand cost of analysis, because these
are crucial factors for a successful evaluation of hydrocar-bon
contamination in soils. This may explain the spate of recent
efforts to evolve innovativeanalytical techniques that are believed
to be economical, rapid, less prone to creating oc-cupational
hazards, and capable of high sampling resolution for improved
contaminantmapping and refined soil remediation recommendations,
though they still complement thestandard analytical techniques.
Unfortunately, to our knowledge, there is no review at themoment on
environmental diagnostic tools for TPHs and PAHs in contaminated
soils, whichincludes the latest advancements in Vis-NIR
spectroscopic methods. Thus, there is a gapin coverage of well over
a decade since the Vis-NIR spectroscopic method was first usedby
Malley et al. (25) to measure TPHs in diesel-contaminated
field-collected soil samples.We acknowledge, no less, opinions
already expressed by analysts that this might be due toa series of
unanswered questions about the Vis-NIR spectroscopic method
concerning, forinstance, the requirements in terms of accuracy
indicators (e.g., residual prediction devia-tion and root mean
square error of prediction values) from the industry and/or
regulatoryagencies for a method to be applied in routine
applications. However, it is the authorsbelief that it may be a
worthwhile effort having recently published significant
improve-ments regarding the TPH measurement accuracies of Vis-NIR
spectroscopic methods as
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460 R. N. Okparanma and A. M. Mouazen
Table 1Summary of selected spectroscopic and nonspectroscopic
techniques for petroleum hydro-
carbon measurement
Measurement technique Detection device Measured target
Gas chromatography Flame ionizationdetector
TPH
Mass spectrometry TPH, PAH, and CSBInfrared spectroscopy IR
spectrometer TPH and PAHGeneral gravimetry Gravimetric balance
TPHImmunoassay ELISA kits TPH and PAH
ECIA kits TPH and PAHRaman spectroscopy CCD detector TPH and
PAHFluorescence
spectroscopyPolychromator/CCD
camera
TPH and PAH
Silicon-intensified targetcamera
TPH and PAH
Visible andnear-infraredspectroscopy
High-intensityprobe/mug lamp
TPH and PAH
Modified from and reprinted with permission from Weisman
(31).
well as their ability to measure relative concentrations of PAHs
in soils all documentedalongside other methods. Of course, the
importance of such information to industry and/orregulatory
agencies cannot be overemphasized. It is also believed that with
more research,a Vis-NIR-based operating field protocol for TPHs and
PAHs can be developed for routineapplications.
The objective of this article was to review the traditional
spectroscopic and nonspec-troscopic analytical techniques and
selected rapid measurement techniques (RMTs) basedon spectroscopy
for measurement of TPHs and the PAHs in contaminated soils.
Analytical Techniques for Petroleum Hydrocarbons in
SoilsAnalytical methods for petroleum hydrocarbons currently in use
are numerous and it wouldbe a Herculean task to review all of them
in one article. Therefore, this review focusedon a selected number
of the most frequently used traditional methods and
innovativetechniques including the Vis-NIR spectroscopic method to
drive home the aim of thisreport. These methods are distinguishable
by the level of analytical details they provideand their method of
application as screening techniques, conventional nonspecific
methods,and methods for detailed component analysis (34), which may
be field and/or laboratorybased. As stated earlier, there are
several field- and laboratory-based analytical methods forpetroleum
hydrocarbons currently in use but the most frequently used methods
(Table 1) areGC-FID (EPA method 8015) and GC-MS (EPA methods 8270
and 625), IR spectroscopy(EPA method 418.1), petroleum hydrocarbons
by IMA (EPA methods 4030 and 4035),and gravimetric TPH analysis
methods (EPA method 1664) (3541). Others are Ramanspectroscopy,
fluorescence spectroscopy, and Vis-NIR spectroscopy.
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Petroleum HydrocarbonContaminated Soils 461
Laboratory-Based Techniques
General Gravimetry. Gravimetric methods employ an initial cold
solvent extraction stepand a final weight-difference step. In
between there may be a further cleanup step withsilica gel to
remove biogenic material. If it does not involve a cleanup step, it
is termed anoil and grease method; if it does, it is termed a TPH
method (31). In the general gravimetricTPH method (EPA method 1664)
(41), soil samples are uniformly graded by sieving, oven-dried at
105C for 12 h, and TPH compounds are eluted with n-hexane. The
liquid extract(eluate) is contacted with silica gel to remove
biogenic polar materials and then evaporated.The residue is
retained and weighed, and the weight difference is reported as a
percentageof the total soil sample on a dry weight basis. Because
of the presence of suspendedsolids, EPA method 1664 (41) recommends
using a 0.45-m filter (31). Among the earliestmethods developed,
though obviously one of the fast declining choices (42),
gravimetricmethods have been widely used to determine TPHs in
contaminated soils (42). BeforeVillalobos et al. (42) finished
their work, gravimetric methods were described as quick
andinexpensive methods, but, in their recent study, the long time
required for complete hexaneevaporation, of not less than 60 min,
elevates the energetic costs of the overall procedure(p. 156) and
analytical losses at higher times that cause negative errors are
incurred. Thelatter limitation corroborates similar findings in
earlier studies (34, 43, 44). The extractionefficiency of
gravimetric methods, albeit poor, is greatly affected by the type
of elutingsolvent used (38, 45). Hexane has poor extraction
efficiency for higher molecular weightpetroleum compounds (31) and
low polarity, which causes the coextraction of naturalorganic
matter containing multiple polar functional groups (39, 46).
Consequently, otherchlorinated compounds like chloroform (47) as
well as toluene (48) have been used asliquid extractants. It is
well known that both chloroform and toluene have serious
healthimplications as evident in the risk phrases published in
their respective safety data sheets.Additionally, gravimetric
methods are nonspecific because they give no information aboutthe
type of hydrocarbon present (31, 42). As a result, they are not
suitable for assessing PAHcompounds. Instead, the method is best
suited for screening TPHs in very oily sludges orsamples containing
very heavy molecular-weight hydrocarbons because light
hydrocarbons(
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462 R. N. Okparanma and A. M. Mouazen
Protection Agency (EPA) as an official TPH screening method
(e.g., EPA method 418.1(38)) (34) as well as by the International
Organization for Standardization (ISO; e.g.,ISO/TR 11046 (52))
(53). But, following the ban on the use of Freon (also known as
1,1,2-trichlorotrifluoroethane, CFE) as an extracting solvent
because of its potentials to depletethe ozone layer, the use of
IR-based methods has plummeted over the years (31). Despite theban,
a handful of studies can be found in the open literature on the use
of IR-based methods(27, 50, 53). However, its use as a TPH
measurement method is no longer supported byinternational
standardization; the ISO for instance, has replaced ISO/TR
11046:1992 (52)with ISO/DIS 16703:2001 (54), which recommends the
use of GC-FID after extractionwith a halogen-free solvent (45).
ISO/DIS 16703:2001 (54) has been updated since 2004(55). In
addition to the limitations on its use, a major constraint of the
IR-based method,according to the literature (34, 56), is the
insensitivity of the technique to unsaturatedcomponents of
weathered hydrocarbons not exhibiting detectable adsorption bands
at themonitoring wavelength. Additionally, the use of standard
hydrocarbon mixtures differentfrom the contaminating oil for prior
equipment calibration invariably does not produce atrue contaminant
concentration because different hydrocarbons respond differently to
IRspectroscopy, because single hydrocarbon oil may not be suitable
as a universal calibrationstandard (34, 56). This is because the
proportion of saturated and unsaturated hydrocarbongroups varies
with each oil derivative and produces correspondingly variable IR
spec-troscopic responses (50). The nonspecificity of IR-based
methods (50) also limits theirsuitability for PAH assessments.
IR-based methods are prone to interference, both negativeand
positive biases, due to the use of dissimilar calibration standards
as the spilled oil andfrom spurious signals due to CH3 groups
associated with nonpetroleum sources (31). Asstated previously,
multivariate calibration solves the interference problem in
general. Theaccuracy of IR-based techniques is dependent on the
extraction efficiency of the extractingsolvent, which in turn is
affected by the type of solvent used (31, 50). Sample porosity
alsohas a profound influence on IR signal intensity (27).
Gas ChromatographyFlame Ionization Detection. The origin,
principles, and techniquesof chromatography have been widely
documented (57). Succinctly, chromatography is aseparation method
in which a mixture is applied as a narrow initial zone to a
stationary,porous sorbent, which causes the components to undergo
differential migration by the flowof the mobile phase, a liquid or
a gas (57). In gas chromatography, an inert carrier gas(helium,
hydrogen, or nitrogen) carries the gaseous mixture (or, if aqueous,
liquids withboiling points < 400C) to be analyzed through a
capillary column onto a detector at the endof the column (31, 57),
which allows better resolution of components in complex
mixtures.
In the GC-FID method, as-received samples are first refrigerated
at 4C until extrac-tion and dried either chemically (using a
suitable drying agent, say anhydrous sodiumsulfate) or physically
in an oven at 105C for 24 h to remove any residual moisture.
TPHcompounds in the dried samples are then extracted employing
eluting solvents (e.g., ace-tone, dichloromethane, hexane, or
pentane), and different forms of adsorbents (e.g., silicagel,
alumina, or Florisil [Fisher Scientific Ltd., Loughborough, UK])
are used for the ex-tract cleanup and fractionation into aliphatics
and aromatics (32) prior to injection intoa chromatographic column.
Sample extracts are introduced into the capillary column
byheadspace, purge-and-trap (for volatile compounds in the rage C6
to C25 or C36), or directinjection (for the less volatile
fractions) methods. As the temperature of the column isgradually
raised, TPH compounds are separated according to their boiling
points as theymigrate toward the end of the column onto the flame
ionization detector. In the detector,the high-concentration
effluent eluting the column is trapped and ionized by burning in
a
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Petroleum HydrocarbonContaminated Soils 463
hydrogenair or oxygen flame, causing the gas in the detector to
conduct electric current,and the conductivity is measured by a
DC-powered collector electrode above the flame. Theretention time
of a PAH compound prior to elution from the column is typical of
the speciesunder a set of conditions and is used to correlate the
detector response to the amount ofcompound present. The detectors
responses in a given range are then integrated to give thetotal
concentration of hydrocarbons with reference to external and/or
internal hydrocarbonstandards (31, 57).
GC-FID is mostly preferred for laboratory applications because
it provides relativeselectivity and sensitivity (18, 3133) and is
recognized by the EPA, British Standard Insti-tution (BSI), and
ISO. EPA method 8015 (35) is used to determine TPH, BS ISO
15009:2002(58) is for volatile aromatic and halogenated
hydrocarbons, and BS ISO 16703:2004 (59) isused to determine the
content of hydrocarbons in the range C10 to C40 (n-alkanes) in
solids,including soils and wastes. GC-FID is used for both
quantitative and qualitative applica-tions, including the screening
of environmental samples (6062), unraveling the type andidentity of
fresh to mildly weathered oil in environmental samples for pattern
recognitionof the petroleum hydrocarbons (18, 19), and
characterizing and resolving the profile ofunresolved complex
mixtures in petroleum-contaminated sediments (63). The
biodegra-dation rate constant of petroleum hydrocarbons in a
contaminated site is highly variableand difficult to evaluate due
to variable site conditions. However, GC-FID has been usedto
develop a simple correlation model to estimate the bioventing
degradation rate constantof gasoline in several soils without
having to conduct lengthy and expensive experiments(64). Detection
limits for GC-FID depend on the method and sample matrix with
typicalvalues of 10 mg/kg in soil (31). However, high analytical
costs and operational time (21,65), instrument calibration problems
(66), effects of sample matrix (62), and the impact ofGC operating
conditions (67) are some of the challenges of the method (see also
Table 2).
Gas ChromatographyMass Spectrometry. Over the years, a couple of
alternatives to FID(Table 1) have been developed for more detailed
analysis of a wider range of samplematrixes due to the selectivity
of FID for hydrocarbons (32). The most prominently used isthe mass
spectrometric detection (MSD) technique. MSD basically uses the
characteristicmass spectra of molecular and/or fragmented ions
produced after ion impact to identifycompounds in the sample (68).
The mass spectrometer has been described as a universaldetector
because of its versatility in the measurement of TPHs, PAHs, and
CSBs for awide variety of environmental samples (69) and is
recommended by the EPA for thedetermination of both TPHs and PAHs
(EPA methods 8270 and 625) (36, 37). The popularchoice of a mass
selective detector for most environmental analysis is due to its
specificityand discrete monitoring capabilities, particularly when
operated in the selective-ion mode(69). As part of its
wide-reaching applications, GC-MS has been used in
environmentalmonitoring programs to assess sediment quality in
terms of concentration of total PAHs (70),to investigate the amount
of PAHs in the topsoil of a tar-contaminated industrial site (71),
forthe fingerprinting analysis of some environmental sediments
containing unsaturated priorityPAHs (72), and to monitor the
bioremediation of PAH-contaminated soil through in-vesselcomposting
with fresh organic wastes (73). Despite its widespread application,
a majordrawback of the GC-MS is that it requires volatile and
thermally stable analytes; as such,only about 10% of organics are
amenable to GC-MS analysis (74). Moreover, the MSDis reported to
have a lower sensitivity than the FID, because in the impact ion
mode, therespective detectors collect and measure different
proportions of the generated molecularions (69). Quantitative
chemical analysis with laboratory-based GC-MS is
undoubtedlyexhaustive and, like GC-FID, involves lengthy and
labor-intensive extraction protocols
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Tabl
e2
Char
acte
ristic
sofs
elec
ted
petro
leum
hydr
ocar
bon
mea
sure
men
ttec
hniq
ues
Tech
niqu
eA
pplic
atio
nm
etho
dA
ppro
x.LD
L(m
g/kg)a
Estim
ated
anal
ysis
run
time
(min
)Sa
mpl
ing
type
Stre
ngth
Lim
itatio
ns
GC-
base
dLa
bora
tory
and
field
1045
2,8
80b,
c(ex
clud
ing
extr
actio
ntim
e,la
b-ba
sed
GC
cycl
etim
em
aybe
40m
in,
whe
reas
som
e
porta
ble
devic
esta
ke
