Analysis of organophosphate hydraulic fluids in U.S. Air Force base soils

Article abstract of DOI:10.1007/s002449900466

Tri-aryl and tri-alkyl organophosphates (TAPs) have been used extensively as flame-retardant hydraulic fluids and fluid additives in commercial and military aircraft. Up to 80% of the consumption of these fluids has been estimated to be lost to unrecovere

Full text of DOI:10.1007/s002449900466

Arch. Environ. Contam. Toxicol. 36, 235–241 (1999)
A R C H I V E S O F
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999 Springer-Verlag New York Inc.
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Analysis of Organophosphate Hydraulic Fluids in U.S. Air Force Base Soils
M. D. David, J. N. Seiber
Center for Environmental Sciences and Engineering and Department of Environmental and Resource Sciences, University of Nevada,
Reno, Nevada 89557, USA
Received: 22 July 1998/Accepted: 4 November 1998
Abstract. Tri-aryl and tri-alkyl organophosphates (TAPs) have
been used extensively as flame-retardant hydraulic fluids and
fluid additives in commercial and military aircraft. Up to 80%
of the consumption of these fluids has been estimated to be lost
to unrecovered leakage. Tri-aryl phosphate components of these
fluids are resistant to volatilization and solubilization in water,
thus, their primary environmental fate pathway is sorption to
soils. Environmental audits of military air bases generally do
not include quantification of these compounds in soils. We have
determined the presence and extent of TAP contamination in
soil samples from several U.S. Air Force bases. Soils were
collected, extracted, and analyzed using GC/FPD and GC/MS.
Tricresyl phosphate was the most frequently found TAP in soil,
ranging from 0.02 to 130 ppm. Other TAPs in soils included
triphenyl phosphate and isopropylated triphenyl phosphate.
Observations are made regarding the distribution, typical
concentrations, persistence, and need for further testing of
TAPs in soils at military installations. Additionally, GC and
mass spectral data for these TAPs are presented, along with
methods for their extraction, sample clean-up, and quantifica-
tion.
Toxic Substances Control Act (TSCA), to request more data
from the manufacturers in the early 1980s (Federal Register
1983). In 1992, rules were proposed by EPA requiring testing,
reporting, and record keeping by manufacturers of aryl phos-
phate base stocks (Federal Register 1992).
Measurements of environmental residues of TAPs from
hydraulic fluid release are sparse, although industrial TAPs
have been reported in pine needles (Aston et al. 1996), surface
waters (Ishikawa et al. 1985; Paxeus 1996), and in fish,
sediment, and biota (Muir et al. 1981; LeBel et al. 1989). Some
estimates have been made of the total amount of tri-aryl
phosphates used for flame-retardant hydraulic fluids (including
aviation and other applications) and the percentage of that use
which is ultimately released and unrecovered. Up to 80% of the
TAP hydraulic fluid consumption in the late 1970s (12 million
kg in 1977) was for replacement of losses due to unrecovered
leakage (Federal Register 1983; Muir 1984).
Localized fate of TAPs is dictated by their physical proper-
ties. Tri-aryl TAPs have water solubilities in the range of
Ϫ6
Ϫ8
0
.36–2.2 mg/L, low vapor pressures (10 –10 atm), very low
Ϫ6
Ϫ8
3
Henry’s Law constants (10 –10 atm m /mol) (Muir 1984;
Boethling and Cooper 1985), and high calculated sorption
coefficients (est. Koc 8,000–18,000) (Lyman et al. 1990). Water
concentrations of TAPs due to releases are expected to be low,
with accumulation occurring in the sediments. Bioaccumula-
tion could also occur. Reported bioconcentration factors for the
tri-aryl phosphate esters studied here are in the range of
570–1,420 in whole fish (Muir et al. 1983).
Tri-alkyl/aryl phosphate esters (TAPs) are widely used as
flame-retardant plasticizers and functional fluids such as hydrau-
lic fluids and additives to brake and transmission fluids (Federal
Register 1983; Muir 1984; Boethling and Cooper 1985; Syra-
cuse Research Corp. 1988; Carlsson et al. 1997; Seiber et al.
Triphenylphosphate (TPP) is acutely toxic to fish, up to
10–100 times more toxic than other tri-aryl phosphate esters
found in hydraulic fluids such as isopropylphenyldiphenylphos-
phate (IPDP) (Mayer et al. 1981). The potential hazard posed
by TAPs in soils at reported concentrations (100 ppm) (David
and Seiber 1996) is difficult to assess with the current body of
toxicity data.
Although environmental contamination of U.S. military
bases is being actively studied, there is no protocol for the
sampling and determination of TAPs. As decommissioned
military bases are being transferred to civilian uses, environmen-
tal levels of these compounds need to be assessed in order to
determine exposure and risks for humans and wildlife. We
describe here the distribution and concentration of TAPs in soil
resulting from their use in hydraulic fluids at U.S. Air Force
bases. The types of TAPs present and their concentrations and
1
998). Because of their flame retardancy, stability, and other
physical properties, TAPs have been extensively used in
aviation hydraulic fluids. Fluids in military aircraft use TAPs
primarily as antiwear additives at 1–3% levels (S. Flannagan,
personal communication 1997).
The total production volume of TAPs, including those used
for hydraulic fluids, fluid additives, and plasticizers, exceeded
4
1
3
5 million kg during the peak production years of the late
970s. In the early 1990s, total production was in the range of
0 million kg per year (Federal Register 1992). These figures
and the relative lack of environmental data prompted the EPA,
under the authority of the Interagency Testing Committee of the
Correspondence to: M. D. David

2
36
M. D. David and J. N. Seiber
locations in the soil of the bases are presented. Additionally,
analytical methods for the extraction, clean-up, identification,
and quantification of these TAPs were developed appropriate
for contaminated soils.
from different unidentified sites, were labeled AFB 1, 2, and 3. Field
sampling was accomplished at three current or former USAF air fields
as described below. All samples taken from these sites consisted of
2
5
00–1,000 g collected by combining triplicate subsamples of a 1 m
area at the described location. Zero background levels were established
with blank samples taken during the sampling events.
Mather AFB in Rancho Cordova, Sacramento County, CA, was
sampled on September 9, 1994. Mather AFB has subsequently been
decommissioned and now supports multiple uses, including serving as
a private airport. When active, MatherAFB was used by a variety ofAir
Force cargo and refueling aircraft. Soil samples were taken at two sites,
defined by an environmental audit of the Mather base as sites 15 and
Materials and Methods
Chemicals
All solvents were HPLC-grade (Fisher Scientific). Pure TAP standards
included triphenylphosphate (TPP, Aldrich, 99ϩ%), tri-m-cresylphos-
phate (TmCP, Pfaltz and Bauer, 93%), tri-p-cresylphosphate (TpCP,
Pfaltz and Bauer), tri-o-cresylphosphate (ToCP, ICN Biomedicals), and
tributylphosphate (TBP, Aldrich, 99%). Synthesis of tri-p-isopropyl-
phenylphosphate used the reagents p-isopropylphenol (Pfaltz and
6
9. Site 15 included a ditch that received surface drainage from the
entire base and the outflow from the hangar area, washpads, and service
areas of the base through a concrete culvert. Site 69 was a munitions
disposal site.
Stead AFB, located in Stead, Washoe County, NV, was sampled on
September 20, 1994. Although the Stead AFB was closed to military
use in the 1950s, it is still active for some private use, including
seasonally heavy traffic of private and vintage aircraft. A soil sample
was taken from a drainage ditch just outside the hangar area.
Beale AFB near Grass Valley, Nevada County, CA, was sampled on
April 24, 1996. Beale is an active base that, until 1989, housed SR-71
reconnaissance aircraft. At the time of sampling, the only military
aircraft being flown from Beale was the U2 reconnaissance aircraft.
Soil samples were taken from sites 1, 5, and 11, as defined by an
internal Beale site survey. Site 1 is a drainage ditch approximately 225
m west of the runway that drains runoff from the flightline areas and
runway surfaces. Samples were taken in the drainage ditch from the
sandy lining of the culvert just below the outflow (soil 1A), from the
soil lining the ditch about 20 m downstream from the outflow (soil 1B),
and from sediment near the bank, which was displaced from the ditch
during dredging of the channel in 1991 (soil 1C). Site 5 is the drainage
area between the old SR-71 hangars and the runways. Four soil samples
were taken and labeled soils 5A, B, C, and D. Site 11 is the soil-lined
drainage near the aircraft ground equipment (AGE) maintenance area.
Two soil samples were taken of the sediment just at the water surface
level of this grass covered drainage, and labeled soils 11A and 11B.
Bauer, 98%), phosphorus oxychloride (POCl , Aldrich, 99%), and
triethylamine (TEA, Acros, 99%).
3
Samples of three flame-retardant hydraulic fluids were obtained for
spectral analysis. The first was FMC’s (Princeton, NJ) Kronitex-100.
The second was a sample of a military fluid, MIL-H-83282, obtained
from the stock supplies of Beale Air Force Base, the only active
military installation from which soil samples were taken. The third
fluid was a sample of Hy-Jet from Chevron (Richmond, CA).
TAP Hydraulic Fluids
The MIL-H-83282 fluid was primarily poly-alpha-olefin with only
1
–2% TAP esters. A sample was prepared for analysis by the following
florisil clean-up method, which was developed for clean-up of soil
extracts: florisil (7–8 g activated at 110°C for at least 5 h) was
transferred to a glass clean-up column of 1–2 cm ID topped with clean
sand. The florisil was packed under vacuum and soaked with hexane.
The sample in hexane was transferred onto the column and was
immediately followed by the first elution of 100 ml 10% ethyl ether in
hexane. The first 90–100 ml of this elution, containing most of the
poly-olefin fluid, was collected and disposed. TAP analytes were then
eluted with 100 ml of 17% methanol in ethyl ether, which was reduced
to Ͻ2 ml and adjusted to 2.0 ml in methanol. The Hy-Jet and
Kronitex-100 samples were diluted in ethyl acetate and analyzed by
GC/FPD and GC/MS. Identification of TAP components was accom-
plished by comparison of GC retention times with known standards and
GC-MS analysis.
Sample Preparation
Samples were stored under ambient conditions during transport and
processed within 48 h of their collection. Soil samples were air-dried
over a period of 12–18 h and sieved through a USGS standard sieve
(
#18). Extractions of 10–60 g were accomplished using Soxhlet
extractors for 5–7 h (approximate cycle time ϭ one every 10 min) with
75 ml ethyl acetate. The extraction solvent was exchanged for hexane
1
TAP Synthesis
and adjusted using nitrogen evaporation to 2 ml. The florisil clean-up
method described previously for industrial fluid samples was then
applied to the soil extracts.
Because standards were not readily available for isopropylated triphe-
nylphosphate, one isomer was synthesized using a synthetic approach
in general use for the production of TAP esters (Muir 1984). Phospho-
rus oxychloride (1.5 g) and 4-isopropylphenol (4.2 g) were combined
in 50 ml toluene in the presence of excess TEA. The solution was
refluxed for 5 h, then washed 3 times with 1.0 N aqueous NaOH,
deionized water (3ϫ) and dilute acid (3ϫ 0.1 M HCl). The washed
solution containing tri-p-isopropylphenylphosphate was filtered over
sodium sulfate and diluted in toluene for analysis by GC-MS.
Analysis
Quantification of TAPs in soil extracts was accomplished by GC/FPD
peak heights. TAPs for which standards were obtained (i.e., TPP and
TCP isomers) were quantified based on standard curves for the
individual compounds. Quantification of isopropylated triphenylphos-
phate (IPTPP) in soils was based on standard curves developed with the
Hy-Jet fluid.
All hydraulic fluids and soil extracts were analyzed using a
Hewlett-Packard model 5890 series II gas chromatograph equipped
with a flame photometric (FPD, P mode) detector. GC temperature was
programmed from an initial temperature of 165°C for 1 min, ramped to
245°C at 10°C/min, with a final time of 9–15 min. Two columns were
Soil Samples
Three TAP-contaminated soil samples were obtained from the U.S. Air
Force Armstrong Laboratory Occupational and Environmental Health
Directorate, Brooks Air Force Base, TX. The three samples, originating

Analysis of Organophosphate Hydraulic Fluids in Soils
237
Fig. 1. GC/MS SIM chromatogram of Hy-Jet fluid containing IPTPP: RIC and 368, 410, 452, and 494 ions displayed
used: a 30-m 0.32 mm ID DB-5 of 1.0 µm film thickness and a 30-m
.53 mm ID RTX-1 of 0.25 µm film thickness. Both columns were used
time extended by 5 min. The carrier gas was helium with flow rate of 1
ml/min.
0
with a carrier gas of helium at 3 ml/min.
Mass spectral analyses of selected soil extracts, TAP standards, and
hydraulic fluids were obtained using a Finnigan MAT ssQ-710
quadrupole mass spectrometer interfaced with a Varian 3400 GC. MS
of the synthetic tri-p-isopropylphenylphosphate was obtained on a
Hewlett-Packard 5989A with a 5890 II GC. Both instruments were
operated in electron impact mode at 70 eV with a molecular scan range
of 50–600 AMU and a 5-min solvent delay. Both GCs were equipped
with similar 30-m DB-5 columns of 0.25 µm film thickness and 0.25
mm ID GC temperature profiles were similar to the program described
previously, with the temperature ramp slowed to 5°C/min and the final
Results and Discussion
Comparison of retention times of peaks present in the initial
chromatograms of the hydraulic fluids with TAP standards was
used to identify the main TAP components of FMC’s Kronitex-
1
00 and the MIL-H-83282. Kronitex-100 is primarily TCP
fluid, containing a mixture of four TCP isomers: tri-m-
cresylphosphate, bis-m,p-cresylphosphate, bis-p,m-cresylphos-

2
38
M. D. David and J. N. Seiber
Fig. 2. Mass spectral fragmentation patterns of isoproplyated triphe-
nylphosphate
Fig. 3. Comparison of mass spectra of tricresylphosphate (A) and
isopropylphenyldiphenylphosphate (B)
Table 1. Spectral and chromatographic data of hydraulic fluids
Mass. Spec. Ions (m/z)
GC RT Number of
which corresponded to P-containing compounds in the GC/FPD
analysis, had parent ion peaks of m/z 368, 410, 452, and 494.
The consistent difference of 42 mass units between the peaks
suggested C3H7, or propyl substituents. In the literature, an
industrial mixture of isopropylated triphenyl phosphate (IPTPP)
is described, with isopropyl substituents of TPP present in zero
to five units (Syracuse Research Corp. 1988).
In SIM (single ion monitoring) mode set for the formula
weights of 0–5 isopropyl substituents of TPP, the elution of at
least 34 components of this mixture was observed. Figure 1
shows the SIM chromatograms for the ions m/z 368, 410, 452,
and 494 (n ϭ 1–4 isopropyl substituents, respectively), along
with the reconstructed total ion chromatogram (RIC). As
expected, the higher molecular weight components elute later.
Compounds with 1–2 isopropyl groups are the more prevalent
peaks in the mixture. Fragmentation patterns of the components
of this mixture correspond to losses from the parent compound
of mono- or diisopropyl phenyl groups. Figure 2 shows
proposed structures of significant fragments.
a
Hydraulic Fluid
Hy-Jet (IPTPP)
Parent Fragments
(min)
Isomers
368 118, 251, 353
23–25
3
410
452
494
118, 251, 293, or 24.5–37 11
45, 160
118, 251, 335, 437, 28–44 11ϩ
1
and/or 145, 160
118, 251, 335, and
45, 160
35–50 9ϩ
1
Kronitex (TCP)
Tri-p-isopropyl
phenylphosphate
368
452
165, 261
437
24–27
38
4
1
b
251, 335
a
GC retention time, in minutes, from total ion chromatograph
Synthesized product
b
phate, and tri-p-cresylphosphate. The same isomers of TCP
were present at a level of about 2% in the MIL-H-83282 fluid.
The neurotoxic ortho isomer of TCP was absent in both of these
fluids.
Chromatograms of the Hy-Jet commercial product revealed
its primary composition (65%) as TBP. Preliminary analysis of
spectra from the GC/MS of Hy-Jet revealed that the most
significant later eluting peaks of the total ion chromatograph,
The number of isomers for each molecular weight can be
determined from the SIM data. The three isomers of MW ϭ 368
represent isopropylphenyldiphenylphosphate, with a single iso-
propyl group in either the ortho, meta, or para position on one of
the three phenyl groups. The 11 isomers of MW ϭ 410
represent either two singly substituted isopropyl phenyls, which

Analysis of Organophosphate Hydraulic Fluids in Soils
239
Fig. 4. Comparison of GC/FPD chromato-
grams of (A) Mather AFB soil extract (soil
1
5C) and (B) TCP-containing hydraulic
fluid (Kronitex) and TBP, TPP, and ToCP
standards
can each be either o, m, or p (six possible isomers), or a single
disubstituted phenyl, which could be five possible different
isomers (o,o, m,m, m,p, o,p, or o,m) for a total of 11.
One of the most prevalent compounds in the IPTPP mixture,
the mono-substituted isopropylphenyldiphenylphosphate, has
the same molecular weight as TCP (368) and similar GC
retention patterns. Distinguishing between the two can be
accomplished by observation of MS fragmentation patterns
(Figure 3). While both show a strong parent ion peak at m/z ϭ
368, the fragmentation patterns are distinctive, thus allowing
ready differentiation in unknown environmental samples.
From the numbers of isomers present in the industrial Hy-Jet
fluid, it is apparent that the ortho-isopropylated component is
included in the mixture (i.e., if it were not, there would be only
five possible isomers of IPTPP with MW ϭ 410, while 11
isomers are observed). Although certain o-alkylated derivatives
of triphenyl phosphate, including tri-o-cresyl phosphate, are
potent delayed neurotoxicants (Eto 1974), the ortho-isopropyl
isomer is apparently not of sufficient toxicological concern to
be eliminated from the mixture.
OPs in AFB Soils
A similar mass spectral analysis was accomplished with the
TCP-based Kronitex fluid. Identifications of the four significant
isomers present in the fluid were made by matching of GC
retention times with individual isomer standards. Table 1
summarizes the important mass spectral data from the analysis
of both the Hy-Jet and the Kronitex TAP based hydraulic fluids,
including approximate GC retention time, the parent ions, and
the significant EI/MS fragments. GC retention times listed are
from GC/MS analyses under the conditions previously de-
scribed. Mass spectral analysis of the synthesized tri-p-
isopropylphenylphosphate demonstrated fragmentation pat-
terns consistent with those observed for the components of the
Hy-Jet fluid.
Identification and quantification of the TAPs present in soil
extracts was accomplished, when possible, by matching reten-
tion times with TAP peaks present in the flame-retardant
hydraulic fluids. Figure 4 shows a comparison of a GC/FPD
chromatogram of an extract of Mather AFB site 15 soil to the
TCP-based fluid Kronitex. Figure 5 compares a GC/FPD
chromatogram of an extraction of the Stead soil sample to that
of Hy-Jet. Because of the matching retention times and the
similarities of pattern of elution of these TAP-containing peaks,
identification of the type of fluid responsible for the contamina-
tion was relatively straightforward. GC/MS analysis of the
Stead soil extract confirmed the presence of the mixed IPTPP
components of Hy-Jet in the soil. Low levels of TCP and

2
40
M. D. David and J. N. Seiber
Fig. 5. Comparison of GC/FPD chromatograms of
(A) Stead AFB soil extract and (B) TBP and IPTPP-
containing hydraulic fluid (Hy-Jet)
Table 2. Spectral and chromatographic data of selected
Table 3. Concentrations of OPs in Air Force base soil samples,
AFB soil extracts
in ppm (µg/g)
Mass. Spec. Ions (m/z)
Soil
Sample
Total
TPP TCP
Total
IPTPP
AFB Soil
Extract
GC RT Number of OP
Site Description
a
Parent Fragments
(min)
Isomers
Identified
AFB 1
AFB 2
AFB 3
Stead #1
Unknown
Received from
USAF
2
6
5
—
2
—
—
—
—
103
130
28
—
9
0.10
0.03
—
—
—
5.8
—
—
—
0.90
2.0
Stead
368 118, 251
21
1
3
3
1
3
IPTPP
4
4
4
10
52
94
118, 251, 293 24–27
118, 251, 335 28–33
145, 160
251
Hangar drainage
36
21–25
23–35 11
24–27 4
Mather 15C Flightline, hangar drainage
Beale 11A 368
10
Beale 1B 368
IPTPP
TCP
Beale 1B
Beale 5D
Beale 11A
Beale 11B
Flightline, hangar drainage
SR-71 hangar drainage
AGE drainage
AGE drainagea
4
251
165
a
—
—
a
GC Retention Time from Total Ion Chromatograph
a
AGE ϭ aircraft ground equipment maintenance area
IPTPPs in Beale AFB soils were identified using GC/MS in
single ion monitoring mode, selecting for m/z 368, 251, and
presence of IPTPP in soils. Quantification of the TAPs present
in soil samples are in Table 3.
165.
The location and types of TAP residues found in AFB soils
leads to some general conclusions. The TAP compound found
in the soil that is most directly related to use of military aircraft
is TCP. TCP contamination was found in soil at Mather, which
was inactive at the time of sampling, and at Beale in soil 1C,
which was from soil displaced from the drainage and exposed
for 4 to 5 years. These residues suggest that TCP is particularly
recalcitrant. Because TCP is in military hydraulic fluids at
1–2% levels, its presence in the soil may be a marker of
additional non-TAP hydrocarbon contamination. IPTPP soil
The GC/MS analyses of selected AFB soil extracts is in Ta-
ble 2. Differentiation between TCP and IPTPP was accom-
plished by comparing the fragmentation patterns of the com-
pounds with MW ϭ 368. The presence of IPTPP was also
supported by the presence of larger isomers, those with
molecular weights of 410, 452, and 494. Although not all
isomers of IPTPP present in the industrial isomer were present
in detectable levels in the soil extracts, the GC retention time
patterns and fragmentation data provide further evidence of the

Analysis of Organophosphate Hydraulic Fluids in Soils
241
contamination is more likely the result of fluid leakage from
commercial and private aircraft rather than from military jets.
Civilian airports and aircraft facilities may also be contami-
nated with IPTPP. More extensive sampling of military and
municipal airports is needed in order to reveal the extent of
contamination and persistence of these compounds in soil.
Eto M (1974) Organophosphorus pesticides: organic and biological
chemistry. CRC Press, Cleveland, OH
Federal Register (1983) Aryl phosphates: response to the interagency
testing committee. Vol. 48, no. 251, 57452-57460
Federal Register (1992) Aryl phosphate base stocks: proposed test rule
including reporting and recordkeeping requirements. Vol. 57, no.
1
2, 2138–2158
Ishikawa S, Taketomi M, Shinohara R (1985) Determination of trialkyl
and triaryl phosphates in Environmental Samples. Water Res
Acknowledgments. This work was funded in part by grants from the
Department of Energy, Nevada Operations Office (J. Seiber and G.
Miller, PI) and the United StatesAir Force Office of Scientific Research
1
9:119–125
LeBel GL, Williams DT, Berard D (1989) Triaryl/alkyl phosphate
residues in human adipose autopsy samples from six Ontario
municipalities. Bull Environ Contam Toxicol 43:225–230
Lyman WJ, Reehl WF, Rosenblatt DH (1990) Handbook of chemical
property estimation methods. ACS Publications, Washington, DC
Mayer FL, Adams WJ, Finley MT, Michael PR, Mehrle PM, Saeger
VW (1981) Phosphate ester hydraulic fluids: an aquatic assessment
of pydrauls 50E and 115E. In: Branson DR, Dickson KL (eds)
Aquatic toxicology and hazard assessment: fourth conference.
ASTM STP 737, American Society for Testing and Materials,
Philadelphia, PA, p 103
(Barry Wilson, University of California, Davis, PI). The authors would
also like to thank Tom Thomas at Brooks Air Force Base and U.S. Air
Force and civilian personnel at Mather and Beale Air Force bases for
their assistance in obtaining soil samples.
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