eRUDE OIL

1. ehemical and Physical Data

1.1 SYDoDyms and trade Dames

Chem. Abstr. Services Reg. No.: 8002-05-9

Chem. Abstr. Name: Petroleum
IUPAC Systematic Name:-
Synonyms: Naphtha; petrol; rock oil; Seneca oil

1.2 Description

Crude oil is a product of the remains of prehistoric plants and animaIs, buried in the
primaeval mud of swamps, lakes and oceans. Over the centuries, layers of mud and organic
debris were subjected to enormous pressures and high temperatures, and a petroleum-
saturated rock was formed.
Fourelements must be present for oil to accumu1ate in commercially useful quantities:
source rock, reservoir rock, trap and seaL. These elements allow the crude oil to remain
underground and available in large quantities. A source rock is usually sedimentary rock
rich in organic matter. The crude oil created by the decayed matter migrates from the source
rock to a reservoir rock. The reservoir röck contains many tiny pores that store the oiL. A
trap, either stratigraphie layers of impermeable rock or structural traps, prevents the oil
from migrating from the reservoir rock. An impermeable 1ayer, or seal, prevents the oil from
'rising through or around the trap to the surface (American Petroleum Institute, 1984).
Crude oil has been defined as a 'highly complex mixture of paraffnic, cycloparaffinic
(naphthenic) and aromatic hydrocarbons, containing low percentages of sulfur and trace
amounts of nitrogen and oxygen compounds' (Hawley, i 981). Crude oils are often classified
on the basis of chemical composition, according to the proportion of hydrocarbon
constituents. Paraffinic crude oils are ri
ch in straight-chain and branched paraffin
hydrocarbons, whereas naphthenic crude oils contaiD mainly naphthenic and aromatic
hydrocarbons. The composition and classification of Many crude oIls are obtained by ring
analysis and by determination of the other constituents (Sachanen, 1950). Crude oil
constituents are further described in section 1.3.

-119-
120 IARC MONOGRAPHS VOLUME 45

Crude oils may also be classified by geological source, as arising from productive sands,
sandstones and limestones. The fractional and chemical compositions of crude oil from the
same producing sand are usually very similar, even if they are drawn from fairly distant
pools. However, sorne oilfields that are close together may produce quite different crude oils
from the same stratum or from different oil-bearing sands. For instance, in East Texas,
USA, W oodbine sand produces almost identical crude oils in different fields (specifie
y, 0.825-0.835; sulfur content, 0.25-0.40%); and crude oils from other Woodbine
gravit

de oil. ln
oilfields close to the East Texas field differ only slightly from the East Texas cru

contrast, crude oils produced from the New and Old Grozny fields in the USSR are quite
different, despite being only ten miles (16 km) from each other; New Grozny crude oil is
highly paraffinic, whereas Old Grozny crude oil is highly naphthenic or asphaltic
(Sachanen, 1950).
A similar phenomenon is found among different oil-bearing sands ofthe same pool. The
Old Grozny field yields at least three different types of crude oil from its 16 producing sands,
while Pennsylvania fields commonly produce similar types of crude oil in a range of
different producing sands and the New Grozny field produces almost identical crude oils
from 24 producing sands (Sachanen, 1950).

There is no clear-cut relationship between the chemical composition of crude oils and
their geological age or origin. A commonly accepted generalization for US crude oils is that
those that are geologically old are paraffin- and mixed-based, while those that are
geologically new are naphthenic or asphaltic. Oilfields in other countries, however, are
different: in Poland, crude oils that are geologically new are asphaltic, naphthenic and
paraffinic. ln practice, crude oils are often identified by the oilfield alone (Sachanen, 1950).
Crude oils are also referred to as light, medium (intermediate) or heavy, depending on
their density. A light cru de oil generally has an APl (American Petroleum Institute) gravit
y
(see section 1.3) greater than 40 (specific gravit y, -(0.82), a medium crude oil between 15 and
40 (specific gravit y, 0.82-0.97) and a heavy crude oil less than 15 (specifie gravit y, )-0.97).
Crude oils are designated in industry according to their suitability for use in various
products. Thus, a crude oil may be referred to as a 'gasoline crude', a 'wax crude', a 'lube
crude', an 'asphalt crude', and so forth.

1.3 Chemical composition and physical properties

Crude oils are complex mixtures of a vast number of individual chemical compounds.
Each crude oil is a unique mixture, not matched exactly in composition or properties by any
other sample of crude oil. Two typical crude oils, for example, have been characterized by
the American Petroleum Institute as shown in Figure 1. Although the mid-points of their
respective boiling ranges are similar, they differ considerably in other physical properties,
hydrocarbon composition and distribution and sulfur content.
The bulk of the compounds present in crude oils are hydrocarbons (Speight, 1980).
Crude oils generally contain the classes of hydrocarbons and other compounds described
below (Cuddington & Lowther, 1977).
 CRUDE OIL 121

Fig. i. Characteristics of two sam

pies of crude oU

CRUDE C (0.2% SULFUR)

100

80

~ 60
w
::
~
..
o;: 40

20

50 180 290 370 580

TEMPERATURE (OC)

CRUDE D (2.5% SULFUR)

100

80

60
~
w
::
~
..
40
o
;:
20

o
50 180 290 370 580
TEMPERATURE (OC)

(a) Hydrocarbon compounds

(i) Alkanes (paraffins)
Alkanes are straight-chain normal alkanes and branched iso-alkanes with the genera1
formula CnH2n+2. The major paraffinic components of most crude oils are in the range Ci to
C35 (Speight, 1980), although smaller quantities of alkanes up to C60 or higher may be
present. Crude oils vary widely in alkane content (Dickey, 1981). The ratio of n-alkanes to
isoalkanes is shown in Table 1 for one crude oil sample (Ponca). The ratio ranges from a
minimum of 1.7 for heptanes to a maximum of 6.9 for octanes (Speight, 1980). A
Pennsylvania crude oil sample had n-alkane:isoalkane ratios of i .3, i. 7 and 1.5 for pentanes,
122 IARC MONOGRAPHS VOLUME 45

Table 1. Alkanes isolated from a crude oil samplea

Compound Vol. % n-Alkane:isoalkane

C6 2.2
n- Hexane 1.8
2-Methylpentane 0.4
3- Methylpentane 0.3
2,2-Dimethylbutane 0.04
2,3-Dimethylbutane 0.08
C7 1.
n-Heptane 2.3
3-Methylhexane 0.5
3-Ethylpentane 0.05
2- Methylhexane 0.7
2,3-Dimethylpentane 0.1
Cg 6.9
n-Octane 1.9
2,2- Dimethylhexane 0.01
2,3-Dimethylhexane 0.06
2,4- Dimethylhexane 0.06
2,5-Dimethylhexane 0.06
3,3- Dimethylhexane 0.03
2- Meth yl-3-ethylpentane 0.04
2,2,3- Trimethylpentane 0.004
2,3,3- Trimethylpentane 0.006
2,3,4- Trimethylpentane 0.005
~ 2.6
n-Nonane 1.8
2- Methyloctane 0.4
3-Methyloctane 0.1
4-Methyloctane 0.1
2,3-Dimethylheptane 0.05
2,6- Dimethylheptane 0.05
Higher alkanes
n- Decane 1.8
n-Undecane 1.
n-Dodecane l.
aprom Speight (1980); a Ponca crude oïl

hexanes and heptanes, respectively (Tiratsoo, 1951). Alkenes are not generally found in
crude oils (Speight, 1980).

(ii) Cycloalkanes (naphthenes)

Cycloalkanes (or cycloparaffins), also called naphthenes in the petroleum industry, are
saturated hydrocarbons containing structures with carbon atoms linked in a ring. The
cycloalkane composition in crude oil worldwide typically varies from 30% to 60% (see also
 CRUDE OIL 123

Table 3). The predominant monocycloalkanes in crude oïl are in the cyclopentane series,
having five carbon atoms in the ring, and in the cyclohexanes, having a six-membered ring.
The most predominant monocycloalkanes and their composition ranges in crude oïl are
shown in Table 2 (Bestougeff, 1967). ln the higher boilng fractions, such as lubricating oils,
cycloalkanes with two or more rings are common, and structures containing up to ten rings
have been reported. These polycyclic structures are usually composed of fused five- and
six-membered rings (Table 2; Mair, 1964).

Table 2. Predominant cycloalkanes isolated from crude oUa

Cycloalkane Carbon atom % in crude oil

number
Min Max %

M onocycloalkanesb

Methylcyclopentane C6 o.ii 2.35

Cyclohexane C6 0.08 lA
Methylcyclohexane ~ 0.25 2.8
trans- 1 ,2-Dimethylcyclopentane ~ 0.05 1.2
cis- 1,3- Dimethylcyclopentane ~ 0.04 1.0
cis- 1,3- Dimethylcyclohexane Cg 0.9
cis- 1 ,2-Dimethylcyclohexane Cg 0.6
1,1,3- Trimethylcyclohexane ~ 0.7

Polycycloalkanesc
Methylbicyclo(2.2.1 )heptane Cg 0.001
cis- Bicyclo(3.3 .O)octane Cg 0.06
Bicyclo(3.2. 1 )octane Cg 0.008
trans-Decahydronaphthalene Cio 0.2
Tncyclo(3.3.1. 13.7)decane Cio 0.004
cis-Decahydronaphthalene Cio 0.01

°Reference crude oH from Amencan Petroleum Institute

bFrom Bestougeff (1967)
cFrom Mair (1964)

(iii) Aromatic hydrocarbons

The Most common aromatic compounds in crude oils are benzene (see IARC, 1982,
1987a), benzene derivatives (e.g., alkylbenzenes) and fused benzene ring compounds. The
concentration of benzene in crude oH has been reported to range between 0.01 % and i %
(Bestougeff, 1967). Table 3 shows the overall composition of three crude oil samples,
including the major classes of aromatic hydrocarbons, and Table 4 gives the levels of seven
,specife polycyclic aromatics in two of these samples (National Research Council, 1985).
124 lARe MONOGRAPHS VOLUME 45

Table 3. Composition and physical characteristics of three crude

oilsa

CharacterIstic or component Crude oil

Prudhoe South Kuwait

Bay LouIsiana

APl gravit y (20°C; °API) 27.8 34.5 31.4

Sulfur (wt %) 0.94 0.25 2.44
Nitrogen (wt %) 0.23 0.69 0.14
Nickel (ppm; mg/ kg) 10 2.2 7.7
Vanadium (ppm; mg/ kg) 20 1.9 28.0
Naphtha fractionb (wt %) 23.2 18.6 22.7
Alkanes 12.5 8.8 16.2
Cycloalkanes 7.4 7.7 4.1
Aromatic hydrocarbons 3.2 2.1 2.4
Benzenes 0.3c 0.2 0.1
Toluene 0.6 0.4 0.4
Cg aromatics 0.5 0.7 0.8
C; aromatics 0.06 0.5 0.6
Cio aromatIcs 0.2 0.3
CIl aromatIcs 0.1 0.1
Indans 0.1
High-boiling fractiond (wt %) 76.8 81.4 77.3
Saturates 14.4e 56.3 34.0
n-Alkanes 5.s! 5.2 4.7
Cu 0.12 0.06 0.12
Cii 0.25 0.24 0.28
C\3 0.42 0.41 0.38
Cl4 0.50 0.56 0.44
C1S 0.44 0.54 0.43
Cl6 0.50 0.58 0.45
Cn 0.51 0.59 0.41
Cl8 0.47 0.40 0.35
Cl9 0.43 0.38 0.33
Cio 0.37 0.28 0.25
Cii 0.32 0.20 0.20
Cii 0.24 0.15 0.17
CiJ 0.21 0.16 0.15
Ci4 0.20 0.13 0.12
Cis 0.17 0.12 0.10
Ci6 0.15 0.09 0.09
Ci7 0.10 0.06 0.06
Cis 0.09 0.05 0.06
~
CJO
0.08
0.08
0.05
0.04
0.05
0.07
CJi 0.08 0.04 0.06
CJ2 plus 0.07 0 0.06
 CRU DE OIL 125

Table 3 (contd)

Characteristic or component Crude oil

Prudhoe South Kuwait

Bay Louisiana

Isoalkanes 14.0 13.2

l-ring cycloalkanes 9.9 12.4 6.2
2-ring cycloalkanes 7.7 9.4 4.5
3-ring cycloalkanes 5.5 6.8 3.3
4-ring cycloalkanes 5.4 4.8 1.8
5-ring cycloalkanes 3.2 0.4
6-ring cycloalkanes i.
Aromatic hydrocarbons (wt %) 25.0 16.5 21.9
Benzenes 7.0 3.9 4.8
Indans and tetralins 2.4 2.2
Dinaphthenobenzenes 2.9 2.0
Naphthalenes 9.9 1. 0.7
Acenapthenes 1.4 0.9
Phenanthrenes 3.1 0.9 0.3
Acenaphthalenes 2.8 1.5
Pyrenes 1.
Chrysenes 0.2
Benzothiophenes 1. 0.5 5.4
Dibenzothiophenes 1. 0.4 3.3
Indanothiophenes 0.6
Polar materiaig (wt %) 2.9 8.4 17.9
Insolublesh 1.2 0.2 3.5

aThese analyses represent values for one typical crude oil from each of the three geographical
regions; variations in composition can be expected for oils produced from different formations
or fields within each region. From National Research Council (1985)
bFraction boiling from 20 to 205°C
CReported for fraction boilng from 20 to 1500C

dFraction boilng above 2050C

eReported for fraction boilng above 2200C

¡Prudhoe Bay crude oïl weathered two weeks to duplicate fractional distilation equivalent to
approximately 205°C n-alkane percentages from gas chromatography over the range C11-C32
plus

gClay-gel separation according to ASTM method D-2007 using pentane on unweathered

sample
hpentane-insoluble materials according to ASTM method D-893
-, not measured
126 IARC MONOGRAPHS VOLUME 45

Table 4. Concentrations of individual polynuclear

aromatic hydrocarbons in crude oil (10-6 g/ g oil)a

Compound South Louisiana Kuwaiti

crude oil crude oil

Pyrene 4.3 4.5

Fluoranthene 6.2 2.9
Benzl a )anthracene 3. i 2.3
Chrysene 23 6.9
Triphenylene 13 2.8
Benzo(a)pyrene 1.2 2.8
Benzo( e )pyrene 3.3 0.5

aFrom National Research Council (1985)

(b) Nonhydrocarbon compounds

(i) Sulfur compounds
Crude oils vary widely in sulfur content, which can range from ':0. 1 % to 10% by weight.
The following types of sulfur compounds have been identified in crude oIls: thiols
(mercaptans), sulfides, disulfides and thiophenes (Costantinides & Arich, 1967).
ln the lower distilation range up to about 150°C, the most abundant sulfur compounds
are thiols. ln the 150-250°C distilation range, the most abundant compounds are
thiocyclo-, thiobicyclo- and thiotricycloalkanes and thiophenes. These sulfur compounds
are replaced, in turn, by benzothiophenes and more complex ring structures in the higher
distilation ranges (Costantinides & Arich, 1967).

(ii) Nitrogen compounds

The nitrogen content of crude oils ranges from trace amounts to 0.9% by weight. The
bulk of the nitrogen in fractions that boil below about 200°C is basic nitrogen. The basic
nitrogen compounds often found in crude oils include pyridines and quinolines, e.g.,
3-methylpyridine and quinoline, while nonbasic nitrogen compounds include pyrroles,
indoles and carbazoles, e.g., carbazole, and amides (Costantinides & Arich, 1967).

(iii) Oxygen compounds

The oxygen content of crude oils ranges from 0.06% to 0.4% by weight, the majority of
components being alkane and cycloalkane (naphthenic) acids. Other minor components
include ketones and phenols (Costantinides & Arich, 1967). The oxygen content of crude
oils increases with boiling range, so that more oxygen-containing compounds are found in
distilates that boil above 400°C.
(iv) Metal-containing compounds
Traces of many metallc compounds can be found in crude oils. Nickel (see IARC, 1976,
1 987b) and vanadium compounds have been identified in crude oils at levels ranging from a
 CRUDE OIL 127

few parts per milion to 200 ppm (mg/ kg) nickel and up to 1200 ppm (mg/ kg) vanadium.
These metals occur primarily as complexes (porphyrins; Costantinides & Arich, 1967)
which are stable and can be distiled at temperatures above 5000C.
Table 5 is a compilation of some other trace elements reported in crude oil and their
typical concentrations either in crude oil or in crude oil ash (Magee et al., i 973; Valkovic,
1978). Most of these elements occur naturally in crude oil as a result of their presence in the
rock formation or in salt-water deposits from which the crude oB was drawn, although some

Table 5. Elements in crude oUa

Element Concentration (ppm)

Calcium 500-50 OOOb

Aluminium 200-20 OOOb
Magnesium 200- 10 OOOb
Titanium lOO-500b
Strontium lOO-IOOb
Barium 20-500b
Potassium 4.9
Sodium 2.9--20.3
Chlorine 1.5-39.3
Iron 1-125
Molybdenum .c1-lO
Tin .c1-2.2
Zinc 0.67-62.9
Lead 0.17-0.31
Fluorine 0.14-1.
Copper 0.13-6.3
Bromine 0.072-1.3
Manganese 0.05-11.4
Selenium 0.03-1.4
Antimony 0.03-0.15
Mercury 0.02-30
Rubidium 0.015 (average)
Gallium 0.01-0.30
Rhenium .c0.005-2.5
Gold 0.00 (average)
Cobalt 0.003-13.5
Arsenic 0.002-0.66
Europium 0.001 (average)
Caesium 0.000
Cadmium 0.003-0.027
Scandium 0.003-0.008
Chromium 0.0023-0.64
Uranium 0.0004-0.014
aprom Magee et al. (1973); Valkovic (1978)
bAsh
128 IARC MONOGRAPHS VOLUME 45

may also be introduced during the process of driling, pumping, preparing and transporting
crude oil to a refinery.

(v) Miscellaneous contaminants

Crude oil, as it emerges from the well-head, is typically a heterogeneous mixture of
solids, liquids and gases, including, in addition to the constituents described above, sand
and other sediments, water and water vapour, salts and acid gases such as hydrogen sulfide
and carbon dioxide. These contaminants are at least partially separated from the crude oil in
surface treatment at the well-head (see p. 132) to prepare it for transportation to the refinery
(Baker et aL., 1986a).
Crude oils are not analysed routinely for their content ofvarious classes ofhydrocarbons
and nonhydrocarbons; rather, they are usually characterized by their physical properties
(specifie gravit
y or density, viscosity) and their sulfur content. Crude oils are also
characterized in pilot-scale distilations by the volume or weight percentage in various
boiling-point ranges ('straight-run fractions').
One of the most important physical properties of crude oil is its specifie gravit
y -the
ratio of the density of oil to the density of water, both taken at the same temperature and
pressure. From the specifie gravit y, the ratio of aromatic (high density) to saturated (low
density) hydrocarbons in crude oil samples may be estimated. An alternative expression for
specifie gravit y, developed for petroleum applications, is:

141.5
Degrees APl (0 APl) = - 13 1.5.

specifie gravit y at 16°C

The specifie gravities of petroleum usually range from about 0.8 (45.3° APl) for the lighter
crude oils to over 1.0 (100 APl) for the heavier asphaltic crude oH (Dickey, 1981).
al
Crude oil is also characterized by its viscosity. Viscosity is expressed in Saybolt univers

seconds (S US) at 38°C. This value is determined by the time it takes for 60 cm3 of crude oil to
flow by gravit y through an orifice in a calibrated viscometer (Dickey, 1981). Viscosity may
also be expressed in centipoises.
Sulfur content is the third important property of crude oil because of its effect on the
refining process (in poisoning catalysts) and the malodorous and toxic properties of
hydrogen sulfide and other sulfur compounds. Table 6 gives the APl gravit
y, sulfur content
and viscosity of several crude oils.
Table 7 summarizes the composition of crude oils throughout the world, based on
analysis by the US Department of Energy of 800 crude oil samples from 691 major oilfields
in the USA (Coleman et al., 1978) and on analysis by the US Bureau of Mines of the
Department of the Interior of 169 sam pIes of crude oH from 122 fields in 27 countries outside
the USA (Ferrero & Nichols, 1972).
 CRU DE OIL 129

Table 6. Characteristics of sorne typical crude oìlsa

Name, area Specifie Sulfur Viscosity

gravit y content (S US at
(OAPI) (%) 38°C)

Smackover, AR, USA 20.5 2.30 270

Kern River, CA, USA 10.7 1.3 6000+
Kettleman, CA, USA 37.5 0.32
London, IL, USA 38.8 0.26 45
Rodessa, LA, USA 42.8 0.28
Oklahoma City, OK, USA 37.3 0.11
Bradford, PA, USA 42.4 0.09 40
East TX, USA 38.4 0.33 40
Leduc, Alberta, Canada 40.4 0.29 37.8
Boscan, Venezuela 9.5 5.25
Poza Rica, Mexico 30.7 1.67 67.9
La Rosa, Venezuela 25.3 1.6
Kirkuk, Iraq 36.6 1.93 42
Abqaiq, Saudi Arabia 36.5 1.6
Seria, Brunei, Malaysia 36.0 0.05

aFrom Dickey (1981)

Table 7. Sumrnary of worldwide crude oil compositions and characteristicsa

Geographical region Volume % in crude oil General characteristics (wt %)

Light gasoline Kerosene and Sulfur Carbon residueb

and naphtha gas oil

Africa
Maximum 48.9 43.0 2.06 10.8
Minimum 2.4 19.5 0.05 0.1
Average 24.2 28.9 0.50 2.5
(n = 47 (35))

Asia (Far East)

Maximum 37.1 4l. 0.28 8.6
Minimum 4.5 18.0 0.10 0.3
Average 16.9 26.0 0.15 3.3
(n = 7 (6))
Asia (Middle East)
Maximum 35.6 28.8 3.91 6.9
Minimum 12.1 8.8 0.62 1.3
Average 26.9 23.7 2.08 4.0
(n = 44 (34))
130 IARC MONOGRAPHS VOLUME 45

Table 7 (contd)

Geographical region Volume % in crude oil General characteristics (wt %)

Light gasoline Kerosene and Sulfur Carbon residueb

and naphtha gas oil

Australia
Maximum 50.6 56.3 0.44 3.9
Minimum 12.8 24.6 0.02 0.2
Average 37.2 33.9 0.10 0.7
(n = 9 (8))
Caribbean
Maximum 30.9 30.7 3.26 6.3
Minimum 0.6 20.6 0.88 2.6
Average 16.3 25.2 1.92 4.1
(n = 8 (3))
Europe
Maximum 26.0 46.5 4.34 9.7
Minimum 2.9 14.2 0.14 0.3
Average 14.7 23.6 1.6 4.4
(n=8(8)
North America (USA)
Maximum 84.5 68.6 5.1 14.0
Minimum 0.4 9.7 0.01 0.0
Average 27.7 28.3 0.7 2.6
(n = 800 (691))

North America (Canada)

Maximum 36.1 28.3 3.38 11.0
Minimum 6.3 20.2 0.11 1.2
Average 26.7 24.1 1. 3.6
(n = 10 (7))

South America
Maximum 43.5 40.1 5.54 8.4
Minimum 1.9 14.3 0.09 0.02
Average 18.9 23.9 1.34 4.4
(n = 36 (26))

aFrom Ferrero & Nichols (1972) and Coleman et al. (l 978). A verages are simple namerical (unweighted) averages ofthe data
for the various oilfields in the region, where n is the number of samples and (J the number of oilfields used to calculate the
average and establish the range.
b% of carbon residue, after thermie treatment, determined by the method of Conradson
 CRUDE OIL 131

2. Production, Use, Occurrence and Analysis

2.1 Production and use

(a) Production

Crude oil production is the process of raising well fluids to the surface and preparing
them for further processing at the refinery. Since 1972, about 60 millon barrels of crude oil
have been produced each day worldwide, mostly in areas of sparse population or oflimited
industrial development (Anderson, 1984; American Petroleum Institute, 1987a; British
Petroleum Company, 1988). Crude oH production begins with preparation of a well,
followed by the application of a variety of natural and artificial lift mechanisms to bring the
oil to the surface. There it is treated superficially to prepare it for transport to the refinery by
tanker or barge, by pipeline, or by truck or rail (Baker et al., 1986a).
W orldwide, about 500 000 workers are employed in oil exploration and production
(International Labour Office, 1986).

(i) Preparing the weil

The production operation begins after the well has been driled and has been evaluated
as being economically favourable for production. Pipe or casing is inserted into the well
bore in a concentric series to prevent contamination by fresh water, loss of circulation,
sloughing or charging of shallow sands with abnormal pressures (American Petroleum
Institute, 1983). The first such casing placed into a well is the conductor pipe, which may be
pile driven or cemented into place and may extend to a depth of 150-1500 m.
The conductor pipe and all other casings are attached at the surface to the casing head
(American Petroleum Institute, 1983). Surface casing is inserted through the conductor pipe
and deeper into the well to prevent underground formations of fresh water from becoming
contaminated with well fluids and to provide a mechanism for controllng the flow of fluid
from the well.

(ii) Pumping the crude

Once the well has been completed, oil begins to flow up the well as a result of the inherent
reservoir energy, which is manifested by an oil dis placement process involving water, gasor
a combination ofboth. Reservoir drive mechanisms - the processes by which the reservoir
energy dis places the crude oil- include dissolved-gas drive, gas-cap drive, water drive and
combination drive (Baker et al., 1986a; Gray, 1986). Natural drive mechanisms may, at
sorne point in the economic life of the well, lose their inherent energy and the well wil
require a mechanical force to draw the oH from the reservoir. The common methods of
artificial lift are surface pumping, submersible pumping and gas lift (Baker et al., 1986a;
Gray, 1986).
The natural and artificial lift mechanisms provide a means of raising reservoir fluids
capable of flowing into the well bore. However, fractures, channels and perforations
through which the fluids flow often become blocked and diminish the production capacity
 132 IARC MONOGRAPHS VOLUME 45

of a weIL. These passages may be cleared and new ones created by using reservoir stimulation
techniques such as acidizing and hydraulic fracturing (Baker et aL., 1986a).
Acidizing is the process of treating the formation - limestone or dolomite - with
hydrochloric, acetic or hydrofluoric acid. Additives such as corrosion inhibitors, surface
active agents, sequestering agents and antisludge agents are mixed with the acids to prevent
acid attack on tubing and casing, to help disperse the acid in the formation, to prevent
precipitation of ferric iron during acidizing and to prevent formation of insoluble sludge
(Giuliano, 1981; Baker et al., 1986a).
Hydraulic fracturing is used extensively and successfully on formations composed of
sandstone. A fluid, such as water charged with nitrogen, is pumped under high pressure at
high rates into the well to create deep penetrating fractures in the reservoir. Charging the
water with nitrogen facilitates the flow ofwater back out of the well (Giuliano, 1981; Baker
et al., 1986a).

(Hi) Surface treatment

When the crude oil has been brought to the surface, the final production step is to reduce
it to the form in which it wil be sent to the refinery for processing. Contaminants such as
sediment and water are removed, and volatile components are separated and treated by the
use of separators (Giuliano, 1981; Baker et al., 1986a; Gray, 1986).
Natural gases must be treated to remove water vapour and acid gases such as carbon
dioxide and hydrogen sulfide. Water vapour may be removed by bubbling the gas through a
solid or liquid desiccant; the acid gases may also be removed from a natural gas stream by
adsorption or absorption with an appropriate liquid or solid desiccant. This process of
removing acid gases from a natural gas stream is commonly referred to as sweetening (Baker
et al., 1986a).

(iv) Transportation and storage

The primary means of transporting crude oil are tankers and pipelines; trucks and
railways fulfil much smaller yet significant roles. Barges are used to transport oil on inland
waterways and to off-load large tankers.
Modern tankers carry over two-thirds of all crude oil produced to modern industrial
societies (Baker et al., 1986b). Oil can be loaded onto tankers either from onshore facilties
after transport from inland fields or from offshore platforms. The single-point (or single-
buoy) mooring system is a common method for loading tankers. Oil is pumped from an
offshore or onshore facilty through a pipeline on the ocean bed to a marine riser which is
suspended at the surface by a large mooring buoy. The oil is passed from the pipeline into a
flexible hose connected to the riser, through the riser to a floating base and from there to the
ship (Giuliano, 1981).

An individual oil field may contain several hundred wells. Flow lines connect individual
wells in an oil field to field storage tanks and transport oil to a central location for treatment,
testing and measurement. Following treatment, oil is transported from a central tank
battery by intermediate 'gathering' lines which, like the flow lines, generally range from 5 to
30 cm in diameter (Giuliano, 1981; Baker et al., 1986b).
 CRU DE OIL 133

Pumps at a pump station move the oil into and through a pipeline. A gathering station in
or close to an oil field receives oil from producers' tanks via a pipeline gathering system and
moves it on to a trunk-line station located on the main 'trunk' line. Trunk lines are
large-diameter (up to 120 cm) pipelines that carry oil over long distances to refineries,
central storage or ports. Booster pump stations are placed along the trunk line as necessary
to compensate for loss of pressure as the oil is moved through the line (Giuliano, 1981; Baker
et al., 1986b).
Tank farms may be located along pipelines, where oil can be temporarily side-tracked
from transit for holding, sorting, measuring or rerouting. A tank farm may function as a
receiving station for oil that is to be moved into the pipeline transportation system. Pipelines
from a tank farm converge at a station manifold which can split, merge or reroute the flow of
oil as needed (Baker et al., 1986b). Highly viscous crude oil can be heated and transported
via an insulated pipeline, along which reheating stations may be employed (Watkins, 1977).
Deposits accumulate on the inside wall of a pipe during the course of operations. Sorne
crude oils deposit substantial coatings of wax on cooling; salts and other foreign mate
rials
may also build up. To c1ean the pipeline and remove deposits, 'pigs' equipped with scrapers
and brushes are run through it periodically, entering and leaving via locks or pig traps, so
that the line can continue to operate under pressure (Anderson, 1984).
Crude oil is also transported by truck, especially from new fields where pipeline
gathering lines have not been built. However, motor carrier transport represents only a
small fraction of US domestic transportation of crude oil, accounting for less than 0.3% of
that total in 1982. An even smaller percentage (0.05% in 1982) of domestic crude oil
transportation is by raiL. Rail tank cars are used to move crude oil from ocean tankers or
waterways to small inland refineries (Baker et al., 1986b).

(v) Production volumes

World crude oil production from 1947 to 1986 is shown in Table 8 by geographical
region. Over the past 40 years, production has increased more than seven fold, from 3000
milion barrels to 22 000 millon barrels per year. Table 9 gives production data for the 20
countries that produced the most crude oil in 1976 and 1986.
ln 1986, proven worldwide reserves of crude oil were estimated to be 700000 milion
barrels (Table 10).

(b) Use

The direct use of raw crude oil was reported as far back as 3000 BC. Crude oil seeping to
the earth's surface was collected and used in ancient times by the Chinese, Babylonians,
Assyrians and other early civilizations. With only rudimentary methods of discovery and
extraction, these early peoples often located crude oil by observing natural gas escaping
from the earth's crust with the petroleum liquid. They used this natural resource for its four
principal components - oH, grease, asphalt and wax. The source of the crude oil and its
composition determined the petroleum products for which it was useful. Among the early
uses of the unrefined natural product were fuel for oil lamps, heating fuel, bitumens mixed
with fibre, sand, etc. for buildings, roads and dams, medicinal oils (e.g., Seneca oil), paints,
134 IARC MONOGRAPHS VOLUME 45

Table 8. World crude oil production, 1947-86 (milions of barrels per

year)a

Geographical region 1947 1956 1966 1976 1987

Canada and USA 1865 2789 3348 3465 4312

Latina America 574 1 128 1670 1625 2409
Western Europe 13 73 144 312 1 531
Middle East 306 1261 3408 8 116 4787
Africa 9 13 1030 2135 1907
Asia and Australasia 25 146 256 923 1 230
Centrally planned economiesb 231 715 2 165 4616 5796
Total world 3023 6125 12021 21 192 21 972

°From American Petroleum Institute (1 987a), not including natural gas liquids; British
Petroleum Company (1988), for 1987 data only, which include natural gas liquids which
typically comprise -7% of total world crude oil production (6.86-7.47%,1981-86)
b Albania, Bulgaria, China, Cuba, Czechoslovakia, Democratie Kampuchea, the Democratie
People's Republic of Korea, the German Democratie Republic, Hungary, the Lao People's
Democratie Republic, Mongolia, Poland, Romania, the USSR, Viet Nam and Yugoslavia

Table 9. World crude oil production (thousands of barrels per year): 20 leading regionsa

1976 1986

Region Production Region Production

i. USSR 3 839 800 i. USSR 4 584 000

2. USA 3 553 300 2. USA 3 741 300
3. Saudia Arabia 3111600 3. Saudia Arabia 1 879 800
4. Iran (Islamic Republic of) 2160 800 4. Mexico 1 003 800
5. Iraq 881 500 5. United Kingdom 972 700
6. Venezuela 866 900 6. China 960 000
7. Nigeria 753 700 7. Iran (Islamic Republic of) 695300
8. Kuwait 717 200 8. Venezuela 673 400
9. Libyan Arab Jamahiriya 704 500 9. Canada 671 600
10. China 611 400 10. Iraq 637 000
1 i.Canada 585 800 1 i. Nigeria 534 700
12. United Arab Emirates (Abu Dhabi) 582 200 12. Indonesia 511 000
13. Indonesia 549 300 13. Kuwait 456 300
14. Aigeria 392 400 14. United Arab Emirates (Abu Dhabi) 397 900
15. Mexico 319400 15. Aigeria 386 900
16. Qatar 180 700 16. Libyan Arab Jamihiriya 381 400
17. Neutral zoné 169 700 17. Norway 332 200
18. Argentina 142400 18. Egypt 304 800
19. Oman 133200 19. Brazil 217200
20. Egypt 118 60 20. Oman 204 40
QFrom British Petroleum Company (1986, 1988); includes natural gas liquids
bOf the Middle East
 CRUDE OIL 135

Table 10. Proven reserves at end 1987a

Region Proven reserves

Thousand million Share of total (%)

barrels

North America 41. 4.6

Latin America 114.3 12.9
Western Europe 22.4 2.5
Middle East 564.8 63.0
Africa 55.2 6.1
Asia and Australasia 19.5 2.1
Centrally planned economiesb 79.2 8.8
Total world 896.5

QEstimated quantities of crude oil demonstrated with reasonable certainty by geological and
engineering data to be recoverable from known reservoirs under existing economic and
operating conditions. From British Petroleum Company (1988)
bSee footnote b to Table 8.

waterproofing wicker and mats, adhesives for inlay work, insecticides and rodenticides, and
tool manufacture. Historical uses in Europe include lubricants for axles, lamp oil,
preservatives for wood used in shipbuilding, and other applications in navigation (Cross,
1983).
During the twentieth century, crude oil has become one of the world's most important
natural raw materials. Commercial quantities are extracted from all large land masses,
except Antarctica and Greenland, as well as from the earth beneath major bodies of water.
The petroleum or crude oil thus obtained is a major source of the world's energy and the
main feedstock for the petrochemical industry (Considine, 1974).
According to the American Petroleum Institute (1984), the use of oil refinery products as
feed stocks for the petrochemical industry has resulted in more than 3000 petrochemical
intermediates and products. Hoffman (1982) has published a useful table of 'Petroleum
Products, Their Uses and Compositions'.
Because crude oil varies markedly in composition and properties and, therefore, lacks
consistency and reproducibilty, it is no longer used directly in consumer applications, even
as fueL. Today, virtually all recovered crude oil is sent to a refinery for processing into
products or intermediates.
A significant and growing amount of the world's elemental sulfur is also recovered as a
by-product of sour crude oil. Refineries process more sour crude oils under stricter pollution
controls, with the result that the production of recovered sulfur has increased in recent years
(West, 1983). The Oit and Gas Journal Data Book (Anon., 1987) lists three countries as
producers of sulfur derived from crude oil, reporting production levels in tonnes per day at
1 January 1986 of 120 in Brazil, 51 in Hungary and 121.4 in the USA.
 136 IARC MONOGRAPHS VOLUME 45

Demand for refined petroleum products by geographical region during the past two
decades is shown in Table 11. Consumption of petroleum products by group (gasoline,
middle distillates, fuel oil, others) is given in Table 4 of the monograph on occupational
exposures in petroleum refining.

Table i i. Estimated world demand for refined petroleum

products by region (milions of barrels per year)a

Region 1966 1976 1986

Canada and USA 4850 7029 6210

Latin America 824 1 375 1 655
Western Europe 3051 4922 4508
Middle East 300 620 785
Africa 213 393 617
Asia 1248 2921 3 176
Centrally planned economiesb 1765 3916 4920
Total world 12251 21 176 21 871

aFrom American Petroleum InstItute (l987a) for 1966 and 1976; adapted from
British Petroleum Company (1988) for 1986
bSee footnote b to Table 8.

(c) Regulatory status and guidelines

Occupational exposure limits have been established or recommended for various

petroleum fractions, as well as for many of the individual substances found in crude oiL
However, for crude oil itself, no exposure limit has been set.
Several national laws and multinational agreements have been established to prevent
pollution of the seas and other environments by oil (Reitze, 1972; Myhre, 1980; Duck, 1983).

2.2 Occurrence

(a) Naturaloccurrence
Crude oil is a naturally occurring complex mixture which is found in subsurface deposits
in most regions of the world.

(b) Occupational exposure

Since crude oH is a complex liquid, there is potential occupational exposure to a va

ri et
y
of substances: various hydrocarbons and other organic compounds, dissolved gases and
metal compounds. Exposure is possible in all operations involving the product, inc1uding
 CRUDE OIL 137

driling, pumping and treating steps; transport by pipeline, ships or rail cars; storage and
refinery processing (Suess et al., 1985).
The primary route of exposure is through skin contact. However, sorne sour crude oils
contain high concentrations of hydrogen sulfide, and control of exposures, particularly
during sampling and maintenance operations, is criticaL. Some known carcinogens, such as
benzene, certain polycyclic aromatic compounds and nickel and arsenic compounds, are
commonly found in crude oils. Certain crude oil condensates can contain up to 15 vol %
benzene.
Other airborne contaminants identified in operations involving crude oil are mercaptans
and gaseous and volatile hydrocarbons. Explosive concentrations of air
borne hydro-
carbons and lethal levels of hydrogen sulfide can be found at the weIl head and in
compartments and confined spaces (Duck, 1983). No data were available to quantify
occupational exposure levels to crude oil components.

(c) Environmental exposure

A recent estimate of the total input of petroleum into the marine environment from aIl
sources is 1.7-8.8 milion tonnes per year, witha best estimate of3.2 milion tonnes per year.
Table 12 presents the approximate annual input of petroleum hydrocarbons into the oceans
from various man-made and natural sources (Koons, 1984).
The total amount of oil produced in Nigeria between 1980 and 1983 was approximately
350 millon m3 (370 milion tonnes), averaging 88 millon m3 (93 millon tonnes) per year and
generating an average of 13 milion m3 of waste water per year. The average concentration of
oil dissolved in the water ranged from 11.2 to 53.9 mgjl (total range, 0.9-96.7 mgj 1;
Ibiebele, 1986).

ln a study of estuarine and seawater samples from three Australian bodies of water, it
was found that a probable source of aromatic hydrocarbons in the dissolved and particulate
phases from the estuarine samples was crude oiL. Other probable sources included refined
petroleum products, including lubricating oil and residual fuel oil, and distilates, inc1uding
gasoline and diesel fuel (Smith & Maher, 1984).
ln a study of petroleum residues in the waters of the Shatt al-Arab River in the northwest
region of the Arabian Gulf, DouAbu1 (1984) found that average total hydrocarbon
concentrations ranged from 2.7 to 86.7 ¡.gj 1 Kuwaiti crude oil equivalents. The highest
concentrations were found at sites that were near port areas. These results were within the
range of values reported for comparable areas in other parts of the world (UK marine
waters, 24.0-74.0 p,gj 1; Canadian marine waters, 1.0-90.0 p,gj 1; Corella river, 2.2-200 ¡.gj 1;
Halifax harbour, 1.2-71.7 ¡.gjl).
ln a similar study of seasonal variations in oil residues in the waters of the Shatt al-Arab
River in Iraq, DouAbul and AI-Saad (1985) found that concentrations varied between 1.7 to
35.4 ¡.gj 1 Kuwaiti crude oil equivalents. The results suggested that petroleum hydrocarbons
found in the river originated from diverse sources. Hydrocarbon concentrations were
highest in winter (averaging 17.4 p,gjl) and lowest in summer (averaging 3.1 ¡.gjl).
138 IARC MONOGRAPHS VOLUME 45

Table 12. Petroleum hydrocarbons in the marine environmenta

Source Input rate (millon tonnes/ year)

Estimate Probable range

Natural sources
Marine seepage 0.2 0.02-2.0
Sediment erosion 0.5 0.005--.5
Offshore production 0.05 0.04--.06
Transportation
Tanker operations 0.7 0.4- 1.5
Dry docking 0.03 0.02--.05
Marine terminais 0.02 0.01--.03
Bilge and fuel oils 0.3 0.2--.6
Tanker accidents 0.4 0.3--.4
Non-tanker accidents 0.02 0.02--.04
Atmospheric deposition 0.3 0.05--.5
Waste-water, mn-off and ocean dumping
Municipal wastes 0.7 0.4-1.5
Refineries 0.1 0.06-0.6
Non-refining indus trial wastes 0.2 0.1--.3
Urban run-off 0.12 0.01--.2
River run-off 0.04 0.01--.5
Ocean dumping 0.02 0.005--.02
Total 3.7 1.-8.8
QProm Koons (1984)

Table 13 lists some accidental releases of crude oil that have been reported in the recent
past.

2.3 Analysis

Because of the extreme complexity of the composition of petroleum and petroleum

products, no single analytical method can be used to measure all the components in an
environmental sample. For example, methods suitable for sampling and analysis of the
volatile paraffinic (alkanes) hydrocarbon components are not directly applicable to the high
molecular weight aromatic and polar fractions or to metals. Moreover, because petroleum is
a complex and labile mixture, the composition of a sample released into the environment
begins to change almost immediately. Fractionation and separation of components begins
to take place by evaporation (or condensation), dissolution (e.g., of more polar components
into water) and adsorption/ absorption (e.g., into soils, sediments or biological tissues).
Chemical, photochemical and biochemical reactions occur, leading to further selective
changes and the appearance of degradation products and metabolites.
 CRUDE OIL 139

Table 13. Major accidental releases of crude oil in the recent past

Place Date Type Quantity Reference

UK 1967 Wreck of Torrey 91 00 tonnes Anon. (1973)

Canyon tanker
Santa Barbara, January 1969- Ocean platform leak Il 290- Il 2 900 Foster et al.
CA, USA October 1969 tonnes (78 00- (1971)
780 00 barre1s)
La Coruña, May 1976 Persian Gulf crude 90 00-91 00 Gundlach &
Spain oil from grounding tonnes Hayes (1977)
of Urquio/a tanker

Brittany coast, March 1978 Light Arabian and 200 00 tonnes Berne &
France Iranian oil from Bodennec (1984)
wreck of Amoco Cadiz
tanker
Arabian Gulf February 1983 Two damaged Iranian 400 barrels per Sadiq & Zaidi
oH wells day (1984)
Cape Town, August 1983 Light crude oH from 145 00- 172 00 Moldan et al.
South Mnca wreck of Casti/o de tonnes (1985)
Bel/ver tanker
Claymont, DE, September 1985 Wreck of Grand Eag/e 435 00 gallons Miler & Ott
USA tanker (1 65000 Il (1986)

The problem of identification and quantification of petroleum released into the

environment is further complicated by the fact that many petroleum components are
ubiquitous and may arise from other sources such as the incomplete combustion of fossil
fuels or biogenesis.
For these reasons, a number of analytical techniques have been applied in environmental
analyses of petroleum, ranging from low-resolution, relatively nonspecific techniques, such
as extraction/ gravimetry and infrared spectrometry, to high-resolution, specifie techniques
involving capilary gas chromatography, high-pressure liquid chromatography and mass
spectrometry (National Research Council, 1985). The choice of a method in any particular
case depends on several factors, including the objective ofthe study, the medium (air, water,
soil, sediment), what is known about the sample(s) and practical considerations such as cost,
time restrictions and availabilty of equipment.
A number of reviews have been published on the environmental analysis of crude oÏl
(e.g., Egan et al., 1979; National Research Council, 1985; US Environmental Protection
Agency, 1986; American Petroleum Institute, 1987b).
 140 IARC MONOGRAPHS VOLUME 45
3. Biological Data Relevant to the Evaluation of
earcinogenic Risk to Humans

3.1 Carcinogenicity studies in animaIs

Skin application!
Mouse: Groups of25 male and 25 female outbred albino mice(stock unspecified), 10-12
weeks of age, received twice weekly skin applications of 0.2 ml of one of three crude oils:
from Kuwait (paraffinic-asphaltic base), Lagunillasj Venezuela (naphthenic) and Oklahoma
(unspecified) or laboratory distiled fractions of the oils (obtained by fractionation using
vacuum and steam in an apparatus selected to preclude cracking) or residues for 52 weeks. A
similar experiment, using the same samples and numbers of mice of different strains was
carried out in another laboratory. Skin from the treated area of aU mice that survived 12
weeks of treatment was prepared for histology. Surviving animaIs were kiled at week 52
(survival rate and effective number of animaIs unspecified). ln 18 groups each of 50 mice in
laboratory l, the skin tumour yield per group varied between 0 and 5; that in laboratory 2
varied between 0 and 2 (tumour type unspecified). With the crude oils and residues, only two
tumours developed among mi ce treated with Kuwaiti crude oil and one among mice treated
with its residue (Hieger & W oodhouse, 1952). (The W orking Group noted the lack of
information on untreated controls, lack ofhistological classification and the short duration
of the study.)
A group of 30 mice (age, sex and strain unspecified) received thrice-weekly skin
applications of crude oil (natural Saratov; 28% methane, 68% naphthenes (cycloalkanes),
4% aromatic hydrocarbons, 2.86% paraffins (alkanes), 0.34% sulfur (quantity unspecified))
for six months, followed by twice weekly applications for life. All mice died within 13
months; the first death occurred after 40 treatments (94 days) and the last after 142
treatments (393 days). Hyperkeratosis was observed at the site of treatment in 13 of 23
animaIs of which the skin was examined histologically, and three mice developed
papilomas within 147, 149 and 154 days, respectively (Antonov & Lints, 1960). (The
W orking Group noted the smaU number of animaIs, the lack of controls and absence of
experimental detail, and the short duration of the experiment.)
Three groups of 30 mice (sex, age and strain unspecified) received twice weekly skin
applications (not otherwise specified) of crude oils (quantities unspecified) of different
origins (Bitkovsk, Gozhansk and Kokhanovsk) containing different amounts of paraffins,
sulfur and tar, for ten months. No squamous-cell tumour was observed, but an
angiosarcoma of the skin developed in two mice treated with the Bitkovsk and Gozhansk
crude oils (Shapiro & Getmanets, 1962). (The Working Group noted the absence of
experimental detail and the short duration of treatment.)

lThe Working Group was aware of studies by skin painting in progress in mice using three distilate fractions of a high-nitrogen
crude oÏl (IARC, 1986).
 CRUDE OIL 141

Groups of ten male and ten female C3H/ Bdf mice (age unspecified) received twice
weekly applications on shaved skin of 3, 6, 12 or 25 mg crude oil (Wilmington, CA;
benzo(a)pyrene content, 1 ¡.g/ g) in 70% cyc1ohexane: acetone (final volume, 50 ¡.l) for 30
weeks and were observed for a further 20 weeks. A group of50 mice received applications of
vehicle only. No skin tumour was observed in either treated or control animaIs (Holland et
al., 1979). (The W orking Group noted the small number of animaIs and the short duration
of treatment.)
Groups of 15 male and 15 female C3H/ Bdfmice(age unspecified) received thrice weekly
applications on shaved skin of 25 mg of a composite petroleum sample (Wilmington, CA,
USA (20%); South Swan Hils, Alberta, Canada (20%); Prudhoe Bay, AK, USA (20%);
Gach Sach, Iran (20%); Louisiana-Mississippi, USA, Sweet (10%); Arabian Light (10%);
polycyclic aromatic hydrocarbon content, 2.6%; benzo(a)pyrene content, 1 ¡.g/ g) in 70%
cyclohexane:30% acetone (final volume, 50 ¡.l) for 22 weeks, followed by a 22-week
observation period. A group of 25 males and 25 females received the vehicle only. None of
the animaIs developed skin tumours (Holland et al., 1979). (The Working Group noted the
small number of animaIs and short duration of treatment.
Groups of25 male and 25 female C3 H / Bdf mice (age unspecified) received thrice weekly
applications on shaved skin of 0,0.08,0.3, 0.4 or 2.0 mg of the sa me composite petroleum
samples as described above for 24 months. A group of 25 males and 25 females served as
vehicle controls. Among mice treated with the highest dose, four skin carcinomas developed
(8%), with an average latency of 658 (:1 22) days. No tumour was observed among mice
treated with lower doses or with the solvent only (Holland et al., 1979). (The W orking
Group noted the low doses tested.)
Groups of 20 male C3H mice (age unspecified) were treated on the clipped dorsal skin
with 50 ¡.l of a crude oil sample of Texan origin (benzo(a)pyrene content, 0.002%) or 50 ¡.l of
an asphaltic type (benzo(a)pyrene content, 0.0005%) two to three times per week (duration
not specified). No skin tumour developed in the animaIs. Benzo( a )pyrene (0.005% and 0.2%
in toluene) produced high numbers of skin papilomas (6/50 and 3/30) and carcinomas
(1/50 and 27/30; Bingham & Barkley, 1979). (The W orking Group noted the small number
of animaIs and the lack of experimental details.)
Groups of 25 male and 25 female C3 H / Bdf mice, ten weeks of age, received thrice weekly
applications on shaved skin of 0.08, 0.3, 0.4 or 2.0 mg of a natural composite petroleum
sample (Wilmington, CA, USA (10%); South Swan Hils, Alberta, Canada (20%); Prudhoe
Bay, AK, USA (20%); Gach Sach, Iran (20%); Louisiana-Mississippi, USA, Sweet (10%);
Arabian Light (20%)) in 70% acetone:30% cyclohexane (final volume, 50 ¡.l) for 24 months.
The numbers of animaIs that died in the respective groups were 15, 11, 14 and 10. No skin
tumour developed in the mice. Further groups of25 males and 25 females treated with 0.006,
0.03 or 0.15 mg benzo(a)pyrene per week developed skin tumours at the application site:
low-dose, 43/50; mid-dose, 49/50; high-dose, 48/50. No skin tumour was observed among
solvent-treated mice (Holland et al., 1981). (The W orking Group noted the low doses of the
petroleum mixture tested.)
Groups of 50 C3H mice (sex and age unspecified) received twice weekly skin applications
of 50 mg crude oil from either Kuwait (paraffinic with high sulfur content) or southern
 142 IARC MONOGRAPHS VOLUME 45

Louisiana, USA (naphthenic with low sulfur content), for 80 weeks and were observed for a
further 40 weeks. Of the Kuwaiti oil-treated animaIs, 38% developed squamous-cell
tumours (histo10gical type not specified) with an average tumour latency of 64 weeks; of the
Louisiana oil-treated mice, 20% had skin tumours with an average tumour latency of 69
weeks. ln a similar ex periment conducted separately, a group of 20 mice received skin
applications of southern Louisiana crU(le oil; tumour incidence was also 20%, but average
tumour latency was 86 weeks. ln an experiment conducted in another laboratory, 40 C3H
mice (sex and age unspecified) received thrice weekly applications of 5 mg southern
Louisiana crude oil (as described above) in a 30:70% cyclohexane:acetone mixture on the
skin for 78 weeks and were observed for an additional 22 weeks. Skin tumours
(histologically unspecified) developed in 92% of animaIs with an average tumour latency of
67 weeks (Coomes & Hazer, 1984). (The Working Group noted the lack of appropriate
controls and of histological characterization of the tumours.)
Groups of 50 male C3Hj HeJ mice, eight weeks of age, received twice weekly
applications of 50 mg of one of two undiluted sam pIes of crude oils ('C', predominantly
naphthenic; 'D', predominantly paraffinic with a high sulfur content) or distiled fractions of
the oils with boiling ranges corresponding to various refinery streams (petroleum ether, 0- i;
naphthas or gasoline components, C-2 and D-2; kerosene, C-3 and D-3; gas oil, C-4 and
D-4; heavy oils, C-5 and D-5; and residual, C-6 and D-6) on clipped interscapular skin for 18
months. One group of mi ce received no treatment on the clipped skin and another treated
with toluene only on the clipped skin served as negative controls; a further group treated
with 0.05 or 0.15% benzo(a)pyrene in toluene on clipped skin served as positive controk
Total polycyclic aromatic hydrocarbon and benzo(a)pyrene contents, when determined,
and details of the experiments are summarized in Table 14 (effective number of animaIs
unspecified). Fractions D-1 and C-6 produced no tumour and fractions D-4 and D.,6
produced one carcinoma and one papiloma, respectively. AH other sam
pIes produced
numerous tumours, the most potent being the C-5 and D-5 fractions (boiling range,
371 -577°C). Both crude oils induced tumours; however, the paraffinic sample (D) produced
more tumours with slightly shorter arithmetic average time to appearance of the first
tumour in weeks than the naphthenic (C) sample (56% and 64 weeks versus 30% and 69
weeks; Lewis, 1983; Lewis et al., 1984; Cragg et al., 1985). (The W orking Group noted that
the authors were not the original investigators of the study.)
Rabbit: A group of 30 male rabbits (from different stocks) (age unspecified) received
twice weekly applications of 0.3 ml of crude oils from Kuwait (paraffinic-asphaltic),
Lagunilasj Venezuela (naphthenic) or Oklahoma, USA (unspecified), on six different areas
(-3 cm2) of shaved skin for 52 weeks. Another group of 75 male rabbits received twice
weekly applications of 0.3 ml of laboratory distiled fractions (obtained by fractionation
using vacuum and steam in an apparatus selected to preclude cracking) or residues of the
same crude oils on seven different areas of shaved skin for 52 weeks. A similar experiment
using the same samples and equal numbers of animaIs of different stocks was carried out in
another laboratory (2). Surviving animaIs were kiled at 52 weeks. Treatment with
Oklahoma crude oil resulted in the development of two skin tumours in laboratory 20
Twenty-one, 34 and six skin tumours were induced by the fractions in laboratory 1 and 13,
 CRUDE OIL 143

Table 14. Carcinogenic activity of cru de oil sam pies and their fractionsa

Crude sample Distilation Average % M ice Ratio of Total Bapd

rangé (0C) latency with skin malignant: PAHC (ppm)
(weeks) tumours benign (ppm)

No treatment 0
Toluene 97 2 0/1
Naphthenic
C OP-?577 69 30 2.3 1.2
C-2 OP-I77 85 21 0.3 10-4
C-3 177-288 70 30 0.8
C-4 288-371 85 34 1.6 48 0.1
C-5 371-577 50 81 2.9 137 6.5
C-6 ?577 ? 1 ioe 0
Paraffinic
0 OP-?577 64 56 2.2 2.8
0-1 OP-49 ? 1 ioe 0
0-2 49- 1 77 85 25 4.5 10-4
0-3 177-288 62 15 1.0
0-4 288-371 40 3 1/0 1. -=0.1
D-5 371-577 34 91 9.3 62 1.9
0-6 -:577 70 2 0/1
0.05% BaP 46 74 2.1
0.15% BaP 29 97 6.2

aFrom Cragg et al. (1985)

bOp, overpoint; similar to initial boilng-point
Cpolycyclic aromatic hydrocarbons
dBenzo( a Jpyrene

eFrom Levis (1983)

12 and 12 by the fractions and residues in laboratory 2 by the Kuwaiti, Lagunilas and
Oklahoma oils, respectively. The heavy fraction of each crude oil was the most active
(Hieger & W oodhouse, 1952). (The W orking Group noted the lack of information on
controls and the lack of histological classification.)
A group of eight rabbits (sex, strain and age unspecified) received thrice weekly
applications of crude oil (natural Saratov; 28% methane, 68% naphthenes, 4% aromatic
hydrocarbons, 2.86% paraffins, 0.34% sulfur) (quantity unspecified) on the entire internaI
surface of one ear for six months followed by twice weekly applications for life. The first ,
periment. Six
death occurred at 25 months and the last at 31 months from the start of the ex

rabbits that were studied microscopically had all developed papilomas at the application
site; the first tumour appeared 14 months after the start of the experiment (Antonov & Lints,
1960). (The W orking Group noted the small number of animaIs and the lack of controls and
the uncertainty about the cause of death.)
 144 IARC MONOGRAPHS VOLUME 45

Five groups of six rab bits (sex, strain and age unspecified) received thrice weekly skin
applications (not otherwise specified) of crude oils (quantity unspecified) of different origin
(Bitkovsk, Gozhansk, Kokhanovsk, Romashkinsk and Radchenkovsk) with different
paraffin, sulfur and tar contents for 10- 1 7 months. Papilomas developed in all groups
(survival, effective number of animaIs and number of tumours unspecified) (Shapiro &
Getmanets, 1962). (The Working Group noted the lack of experimental details.)

(a) Experimental systems

Absorption, distribution, excretion and metabolism

No data were available to the W orking Group on the absorption, distribution, excretion
and metabolism of crude oil in laboratory animaIs.
Toxicokinetic studies have been reported in non-laboratory mammals, birds and
aquatic organisms (Engelhardt et al., 1977; Lee, 1977; Lawler et al., 1978a,b; Gay et al.,
1980; Engelhardt, 1981; Neff & Anderson, 1981; Oritsland et al., 1981).
Toxic effects
Oral administration of Prudhoe Bay crude oil (5.0 mIl kg bw daily for two days) to male
Charles River CD- 1 mice resulted in increases in liver weight, hepatic proteins, RN A,
glycogen, total lipids, cholesterol, triglycerides and phospholipids (Khan et al., 1987a).
Epidermal ornithine decarboxylase was induced following application of Prudhoe Bay
crude oil to the backs of female Charles River CD- 1 mice; a maximal induction of over 60
fold was seen 6 h after application of 50 ¡.I. Concurrently, epidermal putrescine levels were
elevated 4.7 fold over those in controls. Intraperitoneal administration of the crude oil led to
an increase (15-20 fold, maximal activity 12 h following administration of 4 mIl
kg bw) in
hepatic ornithine decarboxylase activity but to a 45% decrease in the renal enzyme activity.
Hepatic putrescine levels were elevated 34 fold over those in controls (Rahimtula et al.,
1987).
Application of Kuwaiti crude oil (0-200 ¡.g) to the skin of male Sprague-Dawley rats
increased dermal benzo(a)pyrene 3-hydroxylase by 15 fold and diphenyloxazole hydroxy-
lase by six fold (Rahimtula et al., 1984).
Platelets isolated from male Sprague-Dawley rats 24 h after oral treatment with a
Prudhoe Bay crude oil showed a substantial inhibition of aggregation induced by adenosine
diphosphate, arachidonic acid or epinephrine (Chaudhury et al., 1987a). Inhibition of
aggregation was effected with as little as 0.1 ml crude oill kg bw (Chaudhury et al., 1987b).
Aggregation was also inhibited by aliphatic, heterocyclic and aromatic fractions of the
crude oil (Chaudhury et al., 1987a).
Alteration in cellular calcium sequestration has been postulated to be a primary
mechanism in initiating irreversible cell damage. Administration of 5 mIl kg bw Prudhoe
Bay crude oil intraperitoneally or orally daily for two days to male Sprague-Dawley rats
that were sacrificed 24 h later resulted in an abrupt drop in Hver mitochondrial and
micros omal adenosine triphosphate-dependent calcium uptake. ln-vitro incubation of
either mitochondria or microsomes with dimethyl sulfoxide (DMSO) extracts ofthe crude
 CRU DE OIL 145

oil resulted in a concentration-dependent inhibition of calcium influx. The release of

calcium from calcium-loaded mitochondria and micros
ornes was also observed in the
presence of the crude oil extract. At concentrations which affect calcium sequestration, the
crude oil extract produced swelling of mitochondria. Microsomal adenosine triphosphatase
activity in the presence or absence of calcium was unaffected by the cru
de oiL. The results
indicate that increased permeability of the mitochondrial and micros
omal membranes to
calcium is a contributing factor in the inhibition of calcium uptake by Prudhoe Bay crude oil
(Khan et al., 1986).
Administration of a single oral dose (5- 10 mIl kg bw) of Prudhoe Bay crude oil to
pregnant Sprague-Dawley rats resulted in induction in maternaI hepatic microsomal cyto-
chrome P450 levels and various monooxygenases in a dose-dependent manner after 24 h.
Maximal induction of glutathione S-transferase, uridine 5'-diphospho (UDP) glucuronyl-
transferase and DT -diaphorase (N AD H, NAD PH q uinone oxido reductase) activities were
observed 72 h after administration of the crude oil (Khan et al., 1987b).
Many studies on the toxic effects of crude oil in non-laboratory mammals, birds, and
aquatic organisms have been reported and reviewed (Rice et al., 1977; Engelhardt, 1984;
Holmes, 1984; Engelhardt, 1985; Leighton et al., 1985; Payne et al., 1987).

EJfects on reproduction and prenatal toxicity

The effects of petroleum and petroleum products on reproduction have been reviewed
(Schreiner, 1984).
Prudhoe Bay crude oil was administered orally to pregnant Sprague-Dawley rats as a
single dose (5 mIl kg bw) on various gestation days (3, 6, IL, 15 or 17), as a single variable
dose (2-10 mIl kg bw) on gestation day 6, or as daily doses (1 or 2 mIl kg bw) on days 6- 1 7 of
pregnancy. Administration during the earlier stages of pregnancy (day 3, 6 or 11)
significantly increased the number of resorptions and decreased fetal weight and length. No
adverse effect was observed following administration on gestation day 15 or 17. Multiple
exposure to crude oil also caused a significant reduction in maternaI body weight (Khan et
aL., 1987 c). (The W orking Group noted that no information on gross external abnormalities
was reported and that the embryotoxic effects might have been a consequence of maternaI
toxicity.)
Both placental and fetal hepatic enzyme systems were induced on gestation day 18
following treatment of pregnant Sprague-Dawley rats with a single 5 ml/ kg bw dose of
Prudhoe Bay crude oH on gestation days 11, 15 or 17. Liver micros
omal P450 levels,
benzo(a)pyrene hydroxylase and ethoxyresorufin O-deethylase activities were increased
two, two to three and 10-12 fold, respectively in 18-day-old fetuses. Similar trends were
noticed in the placenta. Activities of phase II enzymes such as glutathione S-transferase,
UDP glucuronyltransferase and DT-diaphorase were also significantly elevated (Khan et
al., 1987b).
Several studies have demonstrated pronounced effects of crude oil on the reproductive
capacity ofbirds (decreased hatchabilty, deformed bils, incomplete ossification, incomplete
feather formation, gross structural abnormalities, dead embryos) after application on the
shell surface or after oral administration (Grau et al., 1977; Albers, 1978; Holmes et al.,
146 IARC MONOGRAPHS VOLUME 45

1978; Hoffman, 1978, 1979a,b; Lee et al., 1986; Walters et al., 1987). (The Working Group
noted that the avian system is a sensitive model for embryotoxic effects; results should be
interpreted with caution with respect to possible effects in mammalian systems.)
Genetic and related effects
A large number of studies have been reported on the mutagenicity of crude oil and its
fractions to Salmonella typhimurium (Table 15). Crude oil did not induce mutagenicity in
any of the studies reported, either in the presence or absence of an exogenous metabolic
system. Some neutral/ aromatic (including polycyclic aromatic) fractions of crude oil were
mutagenic in the presence of an exogenous metabolic system.
Aromatic fractions (one to three rings and four rings and more) of Prudhoe Bay crude oil
caused a significant increase in the frequency of sister chromatid exchange in cultured
Chinese hamster ovary ce lis only in the presence of an exogenous metabolic system; no
increase in the frequency of chromos omal aberrations was observed (Ellenton & Hallett,
1981). Wilmington crude oil did not increase the number of sister chromatid exchanges in
human lymphocytes in vitro in the presence of an exogenous metabolic system (Lockard et
al., 1982).
Intraperitoneal administration of Wilmington crude oil (five doses of 1 or 2.1 g/ kg bw)
did not induce sperm abnormalities in B6C3Fd Hap mice, and micronuclei were not
induced in bone marrow of outbred Swiss male mice given 6. 1 g/ kg bw intraperitoneally; an
increase in the number of sister chromatid exchanges in bone-marrow ce Ils of male outbred
Swiss mice was observed at 7.2 g/ kg bw intraperitoneally, but not at 1.8 or 3.6 g/ kg
(Lockard et al., 1982).

(b) Humans
Absorption, distribution, excretion and metabolism
No data were available to the Working Group.
Toxic effects
A labourer who had aspirated crude oil developed aspiration pneumonia and hepatic
and renal toxicity, from which he recovered completely (Wojdat & Winnicki, 1964).
Adverse skin effects including dryness, pigmentation, hyperkeratosis, pigmented plane
warts and eczematous reactions have been observed among petroleum field workers In
contact with crude oH (Mierzecki, 1965; Dzhafarov, 1970; Gusein-Zade, 1982). ln one study
in the USSR, a higher prevalence of skin effects was noted among transport workers in
crude oH production than among petroleum field workers (Gusein-Zade, 1982). Skin
diseases (hyperkeratosis and follcular lesions) were 1.5-2.5 times more frequent in
petroleum field workers than in control groups (Chernov et al., 1970).
Effects on reproduction and prenatal toxicity
No data were available to the W orking Group.
Genetic and related effects
No data were available to the W orking Group.
 CRUDE OIL 147

Table 15. Mutagenicity of crude oilsa and their fractions iD Salmonella typhimurium

Crude oil source Crude sample, Test strain Results Test method Reference
fraction or reported
specifed extract
-S9 +S9

Lo uisiana- Mississippi Neutral fraction TA98 NTb + Plate Epier et al.

sweet crude
(1978)
Composite crude Neutral fraction TA98 NT +
Arabian crude T AI535 Plate Petnll et aL.
TAI537 (1980)
T AI538
TA98
T AlOO
Extract (mechani- TA1535 Plate
cal shaking with T AI537
DMSO) TA1538
TA98
TAlOO
Prudhoe Bay crude Aliphatic fraction TAI535 Plate Ellenton &
TAI537 Hallett
T AI538 (1981)
TA98
TAlOO
Aromatic fraction T AI535 Plate
(1 - 3-ring P AH~ TAI537
T AI538
TA98
T AlOO +
Aromatic fraction T AI535
~-ring P AH) T AI537
T AI538
TA98
TAlOO +
Wilmi~on, CA, crude Polyaromatic sub- TA98 NT + Plate Guerin et al.
(5301) fraction of neutral
(1981)
Recluse (5305) fraction NT +
Louisiana-Mississippi NT +
sweet crude (5101)
South Swan Hils, Alberta, NT +
Canada, crude (5106)
Gach Saran Iran crude NT
(5104)
Prudhoe Bay, Alaska, NT
crude (5105)
Arabian light crude NT
(5102) NT
Composite (5107) NT
Prudhoe Bay crude Acid-base solvent l'A98 Plate Pelroy et al.
extraction (1981)
148 IARC MONOGRAPHS VOLUME 45

Table 15 (contd)

Crude oil source Crude sample, Test strain Results Test method Reference
fraction or reported
specified extract
-S9 +S9

Wilmington crude TA98 Plate Lockard et

T AlOO Plate aL. (1982)
US Gulf Coast Crude sample TAI535 _e _e S pot and MacGregor
Crude C (naphthenic) and 5 distilled T Al537 plate et aL. (1982)
fractions (differ- T Al538
ent boiling ranges) TA98
Crude 0 Crude sample and TA100
(paraffinic) 6 distilled
fractions (differ-
ent boiling ranges)

Petroleum crude Dewaxed TA98 NT Plate Ma et aL.

CRM3 Suspended in NT (1983)
Tween 80
DMSO slurry NT
Prudhoe Bay crude TA98 Plate Sheppard
Acid fraction + + et aL.

Basic fraction ? (1983)

Neutral fraction +
Crude C (naphthenic) Distíled TA98 NT + Plate Carver et aL.
TA 100 NT + at high (1984)
Aromatic fraction TA98 NT + amounts of
TAlOO NT + S9
Kuwaiti crude T Al535 S pot and Vander-
TA1538 plate meulen et
TA98 aL. (1985)
T A100
Saran Gach crude T A1535 S pot and
TA1538 plate
TA98
TAlOO
Kuwaiti crude Hexane Not speci- Spot and
10% benzene- fied plate
hexane
50% benzene-
hexane
Acetone + +

aDimethyl sulfoxide (DMSO) extracts, unless otherwise specified

bNT, not tested
Cpolycyc1ic aromatic hydrocarbon
dRepository number
eData for each fraction tested in different strains not reported
 CRU DE OIL 149

3.3 Epidemiological studies and case reports of carcinogenicIty to humans

(a) Cohort study

A large retfOspective cohort mortality study of US petroleum producing and pipeline

workers was reported by Divine and Barron (1987). To be included in the study, men had to
have been employed for at least six months at a producing or pipeline location and to have
worked at some time during the period 1946-80. Vital status was ascertained for 97.8% of
the cohort, which comprised 11 098 white men; death certificates were obtained for aU but
3.4% of the deceased. Complete occupational histories were available from company
records. Standardized mortality ratios (SMRs) were calculated in comparison with rates for
US white males, and mortality was studied by length of employment, latency, whether
producing or pipeline workers, and selected job categories. The SMR for aU causes of death
was significantly 10W (1886 observed; SMR, 0.63; 95% confidence interval (CI), 0.61 -0.66),
as was that for all cancers (393 observed; SMR, 0.68; 95% CI, 0.61-0.75). There was a
significant excess of thyroid cancer among men employed as pumper-gaugers in petroleum
production, but this was based on four cases only. A significant deficit of lung cancer (l09
observed; SMR, 0.61; 95% CI, 0.50-0.73) was found among producing and pipeline
workers, and no death from testicular cancer was observed although 3.2 were expected.

(b) Case-control studies

(i) Lung cancer

ln an attempt to explain an excess of lung cancer cases observed in a cluster of parishes in
Louisiana, USA, Gottlieb et al. (1979) conducted a case-control study, the design ofwhich is
described in the monograph on occupational exposures in petroleum refining (p. 102). An
elevated risk for lung cancer was observed among black men aged over 53 years who had
been employed in petroleum exploration and production (odds ratio, 1.6; 95% CI, 1.0-2.6).
By logistic analysis, the ratio associated with crude oil exploration and driling was three
fold among persons over the age of 62 in parishes with petroleum or paper industries. (The
W or king Group noted that, since information used in this study was extracted directly froID
death certificates and since no account was taken of cigarette smoking, caution should be
applied in interpreting the results.)
Gottlieb (1980) reanalysed the risk of lung cancer in relation to work in the petroleum
mining and refining industry in the men included in the previous study. A group of200 men
with lung cancer and i 70 control men who had worked in petroleum mining (125 cases, i 12
controls) and refining(75 cases, 58 controls) were identified. The odds ratio for lungcancer
associated with employment in the petroleum industry (mining and refining combined) was
estimated at 1.2 (95% CI, 1.1- 1.4). For we1ders, operators, boiler makers and painters, and
oil-field workers taken as a group (mining and refining combined), the odds ratio was 2.3
(95% CI, 1.4-3.9). (The W orking Group noted that information on exposure was extracted
directly from death certificates; that no information on cigarette smoking was available;
that cases were older than controls, which, in itself, may explain the difference observed; and
that mining and refining occupations were combined.)
150 IARC MONOGRAPHS VOLUME 45

(ii) Testicular cancer

Mils et al. (1984) studied 347 hospital patients with histologically confirmed germ-cell
tumour of the testis in the USA and matched them by age, sex, race and residence with 347
hospital controls, most of whom had tumours other than cancer of the testis. The
ascertainment period was from 1 January 1977 to 31 August 1980. Occupational histories
were extracted from medical records; when the type of industry was not apparent in the
record, this was ascertained from the employer. An excess risk for testicular cancer was
observed among petroleum and natural gas extraction workers (odds ratio, 2.3; 95% CI,
1.0-5.1). (The Working Group noted that information was obtained only on current
occupation.)
Sewell et al. (1986) conducted a population-based study in New Mexico, USA, in which
cases were identified at the New Mexico Tumor Registry. ln order to be included in the
study, the cases had to have had histologically confirmed testicular cancer registered in
1966-84, to have been 15 years old or more at the time of diagnosis and to have died of the
disease. Controls consisted of persons who had died, from other cancers, matched by age,
year of diagnosis, race and sex. A total of 81 cases and 311 controls was identified. The
source of occupational data was either death certificates (99%) or information on file at the
tumour registry (1 %). No excess risk for testicular cancer was 0 bserved among petroleum
and gas workers (odds ratio, 0.57; 95% Ci, 0.16-2.0). The authors noted the limited power
of the study, that an association might have been obscured by the restriction to fatal cases
and that information on exposure was limited.

(iii) Multiple sites

ln a large case-control study of cancer at many sites conducted in Montreal, Canada,
which is described in detail in the monograph on gasoline, p. 185, an association was seen
between exposure to crude oil and rectal cancer (five cases; adjusted odds ratio 3.7; 90% Ci,
1.3-10.6) and squamous-cell lung cancer (seven cases; adjusted odds ratio, 3.5; 90% CI,
1.5-8.2) (Siemiatycki et aL., 1987). It was indicated, however, that these associations might
only be apparent since they are based on very small numbers. The authors suggested that
one of the main groups exposed to crude oil, namely seamen, would probably have had life
styles very different from those of the rest of the study population.

4. Summary of Data Reported and Evaluation

4.1 Exposure data

Crude oil, which may be broadly characterized as paraffinic or naphthenic, is a complex

mixture of alkanes, cycloalkanes and aromatic hydrocarbons containing low percentages of
sulfur, nitrogen and oxygen compounds and trace quantities of many other elements.
W orldwide, about 500 000 workers are employed in crude oil exploration and production.
Occupational exposures during driling, pumping and transportation of crude oil, including
maintenance of equipment used for these processes, may involve inhalation of volatile
 CRUDE OIL 151

compounds, including hydrocarbons and hydrogen sulfide. Skin contact with crude oils,
which contain polycyc1ic aromatic compounds, may also occur during these operations.
Accidental releases of crude oH into the aquatic environment are also potential sources of
human exposure.

4.2 Experimental datai

Samples of crude oil from single sources and composite blends were tested for
carcinogenicity by skin application in ten experiments in mice. Four sam
pIes of crude oH
from single sources produced benign and malignant or unspecified skin tumours in two
experiments. ln one experiment, a composite sam
pIe produced a low incidence of skin
carcinomas; in a similar experiment using the same treatment regimen but a blend of slightly
different compositíon, no skin tumour was observed. The conduct and/ or reporting of the
results of six other experiments in mice were inadequate for evaluation.
fractions oftwo crude oil samples distiled under laboratory
Skin application to mice of

conditions and corresponding to various refinery streams produced skin tumours.

One sam pIe of crude oil produced skin papilomas in rab
bits in one ex periment. Two
other experiments were inadequate for evaluation.

4.3 Human data

ln a retrospective cohort mortality study of a large group of male employees in

petroleum producing and pipeline operations, mortality from all types of cancer was low,
except from thyroid cancer. There was a significant deficit oflung cancer and no death from
testicular cancer.
ln a population-based case-control study, an elevated risk for lung cancer was observed
among older men who had been employed in petroleum exploration and production.
Reanalysis of the risk for lung cancer among men who had worked in the petroleum mining
and refining industry showed an elevated risk for lung cancer among we1ders, operators,
boiler makers, painters and oil-field workers taken as a group; no data were available on
smoking habits.
ln one of two case-control studies, an excess risk for testicular cancer was observed
among petroleum and natural gas extraction workers. No such excess was found in the other
study.
ln a case-control study of cancer at many sites, an association was observed between
exposure to crude oH and rectal and squamous-cell lung cancer. However, the association
was based on small numbers and may have been confounded by life style factors.

lSubsequent to the meeting, the Secretariat became aware of a study in which skin tumours were reported in mice after application
to the skin of East Wilmington crude oil (Clark et al., 1988).
152 IARC MONOGRAPHS VOLUME 45
4.4 Other relevant data

Crude oil induces dermal xenobiotic metabolizing enzymes and ornithine decarboxylase
after skin application in mice.

ln single studies of mice treated in vivo, crudeoil induced an increase in the number of
sister chromatid exchanges at the highest dose tested but did not induce micronuclei in
bone-marrow cells or sperm abnormalities. Crude oil did not increase the number of sister
chromatid exchanges in cultured human lymphocytes. Aromatic fractions of crude oil
induced sister chromatid exchange, but not chromosomal aberrations, in cultured
mammalian cells. Crude oil ex tracts did not induce mutation in bacteria; when fractionated,
neutral fractions of crude oil, which contain aromatic or polycyclic aromatic compounds,
generally had mutagenic activity in bacteria. (See Appendix 1.)

4.5 Evaluationl

There is inadequate evidence for the carcinogenicity in humans of crude oiL.

There is limited evidence for the carcinogenicity in experimental animaIs of crude oiL.
Overall evaluation
Crude oil is not classifiable as ta ils carcinogenicity ta humans (Group 3).

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TX
American Petroleum Institute (1984) Facts About Oil, Washington DC, pp. 8-9
American Petroleum Institute (1987a) Basic Petroleum Data Book: Petroleurn Industry Statistics,
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American Petroleum Institute (1987b) Manual of Sampling and Analytical Methodsfor Petroleum
Hydrocarbons in Groundwater and Soil (APl Publ. No. 4449), Washington DC
Anderson, R.O. (1984) Fundarnentals of the Petroleurn Industry, Norman, OK, University of
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Anon. (1973) Oil spils: how se rio us a problem? J. Water Pollut. Control, 45, 583-585
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Antonov, A. M. & Lints, A.M. (1960) The blastomogenic action of natural Saratov oil. Probl. Oncol.,
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lFor definitions of the italicized terms, see Preamble, pp. 25-28.

 CRUDE OIL 153

Berne, S. & Bodennec, G. (1984) Evaluation of hydrocarbons after the Tanio oil spill - a comparison
with the Amoco Cadiz accident. Ambio, 13, 109-114
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