HIGH PRODUCTION VOLUME (HPV) CHEMICAL CHALLENGE PROGRAM 

TEST PLAN 

HEAVY FUEL OILS CATEGORY 

Submitted to the US EPA 

By 

The Petroleum HPV Testing Group

www.petroleumhpv.org

Consortium Registration # 1100997 

June 17, 2004 
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TABLE OF CONTENTS 

Plain Language Summary 3 

Description of The Heavy Fuel Oils Category 5 

Category Rationale and Test Material Description 10 

Evaluation of Existing Health Effects Data and Proposed Testing 11 

Evaluation of Existing Physicochemical and Environmental Fate Data and Proposed Testing 20 

Evaluation of Existing Ecotoxicity Data and Proposed Testing 24 

Matrix of Available Data and Proposed Testing 30 

References 31 

Appendices 

Appendix A. CAS Numbers and Descriptions of Category Members 38 

Appendix B. Links to Additional Resources 43 

Appendix C. Robust Summary (separate document) 44 

Figures 

Figure 1. Heavy Fuel Oils Process Diagram 9 

Figure 2. Refinery Stream Composition – Boiling Range vs. General Composition 10 

Tables 

Table 1. Composition of Representative Samples of the HFO Category 7 

Table 2. Ecotoxicity Data for Heavy Fuel Oil, Kerosene/Jet Fuel Oil, and Gas Oil. 26 

Table 3: Matrix of Available Data and Proposed Testing 30 
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PLAIN LANGUAGE SUMMARY 

The Heavy Fuel Oils (HFOs) category includes both finished products (residual fuels) and the primary refinery 

streams from which they are blended. Members of the heavy fuel oil category are a diverse group of 

substances encompassing hydrocarbons with a wide range of molecular weights, carbon numbers (C7 to C50) 

and boiling points (250 – 1112 °F (121 to 600 °C). In addition to petroleum hydrocarbons they contain 

heterocyclic compounds containing sulfur, nitrogen, and oxygen, and organo-metallic compounds. The residual 

fuels are low-grade fuels primarily used in industrial boilers and other direct source heating applications (e.g., 

blast furnaces) and as a principal fuel in marine applications. The finished heavy fuels (residual fuels) are 

products that consist primarily of the residuum of the refining process after virtually all of the higher-quality 

hydrocarbons have been distilled, cracked, or catalytically removed from crude oil feedstock. To produce a 

residual fuel of a specified viscosity, the high viscosity of the residual streams is reduced by adding a diluent 

(cutter stock) that is typically a lower quality distillate stream. The choice of the distillate cutter stock is itself 

variable and largely a function of availability at any given time within the refinery and the viscosity specifications 

of the product being manufactured. For instance, in refineries with catalytic cracking units, catalytically cracked 

cycle oils are common fuel diluents (CONCAWE, 1998). Because residual fuels are blended from a variety of 

different residual and distillate materials, the specifications for residual fuel oils are very general, with viscosity 

being the controlling specification. The exact blend used for a specific residual fuel is determined largely by the 

desired viscosity of the finished fuel and specifications set by ASTM (2002). As a result, the composition of 

residual fuel oils can vary widely and will depend on the refinery configuration, the crude oils being processed 

and the overall refinery demand. 

The Testing Group is proposing to perform a repeat-dose/reproductive/developmental screening study (OECD 

422) on a representative sample of a reformer residue. A representative sample of a residual fuel oil will be 

tested using the reproductive/developmental screening protocol (OECD 421). In-vitro genotoxicity assays 

(modified Ames & chromosomal aberration) will also be performed on samples of an atmospheric residue, 

atmospheric distillate, cracked distillate, reformer residue and a residual fuel oil. 

The environmental fate characteristics of the materials in this category are due in large part to the physicochemical parameters of the individual component hydrocarbons. Where physico-chemical data did not exist or 

were impractical to obtain, calculated physico-chemical and environmental data for selected constituents of 

category members has been developed using the EPIWIN©

 computer model. 

When released to the environment, the dispersion of heavy fuel oil depends upon the severity of the weathering 

elements. High-energy environments will tend to disperse substances more quickly than low energy 

environments. During weathering, low molecular weight fractions will dissolve in the water column or volatilize 

to the air, whereas intermediate fractions will float and/or spread out on water or soil where they tend to form 

emulsions or adsorb to soil and sediment particles. The viscous high molecular weight components will 

agglomerate and float or sink depending upon the density of the substance. Volatile components are not 

expected to persist in the atmosphere due to their capacity to undergo direct and/or indirect photodegradation. 

Hydrocarbons are regarded as being inherently biodegradable, and the low molecular weight fraction that 

dissolves in water will rapidly biodegrade. The limited water solubility and bioavailability of the heavy fractions 

reduces their capacity for biodegradation. These substances will biodegrade, although at a much slower rate. 

 

For the assessment of the ecotoxicity of heavy fuel oils, the category substances are considered as a single 

group, and the potential for any category member to elicit adverse effects in aquatic organisms is attributed to 

the solubility of the constituent hydrocarbons in that member. This is valid because petroleum hydrocarbons 

elicit effects through a common mode of toxicity termed nonpolar narcosis (van Wezel and Opperhuizen, 1995), 

which is produced by the soluble hydrocarbon fractions in aqueous preparations. Fuels having molecular weight 

hydrocarbons predominately higher than the solubility “cut-off” for acute toxicity show no measurable acute 

toxicity (CONCAWE 2001). The solubility cut-off varies with the hydrocarbon structure; thus, for paraffinic 

hydrocarbons the solubility cut-off occurs at about C10, while for alkylbenzenes it is about C14 (CONCAWE, 

2001). Other individual components contribute to toxicity, but as molecular weight increases, both solubility and 

toxicity decline 
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Existing aquatic toxicity data show heavy fuel oil related refinery streams to have moderate to no aquatic toxicity 

depending upon species and test substance. Algae have exhibited a greater sensitivity than fish or 

invertebrates to heavy fuel oil exposure, and different substances have produced different toxicity in the same 

species. Because substances in the Heavy Fuel Oil category include a wide range of molecular weight 

hydrocarbons, existing data may not represent the ecotoxicity of some category members based on their 

distillation and carbon number ranges. However, the Testing Group believes the combination of existing 

residual fuel oil ecotoxicity data and data on kerosene and gas oil streams sufficiently covers what would be 

expected for the ecotoxicity of all members of the heavy fuel oil category. Kerosene and gas oils are composed 

of similar hydrocarbon constituents as in heavy fuel oils and have similar molecular weights as the light 

components of category members with low initial boiling points. Therefore, because the light-end components 

of the heavy fuel category members are expected to be the most toxic components, the ecotoxicity of the 

kerosene and gas oils represent a conservative estimate of the ecotoxicity for those heavy fuel oil category 

members. No additional ecotoxicity testing of heavy fuel oil is proposed. 
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DESCRIPTION OF THE HEAVY FUEL OILS CATEGORY 

The Heavy Fuel Oils (HFOs) category includes both finished products (residual fuels) and the primary refinery 

streams from which they are blended. The residual fuels are low-grade fuels primarily used in industrial boilers 

and other direct source heating applications (e.g., blast furnaces) and as a principal fuel in marine applications. 

The residual fuels are products that consist primarily of the residuum of the refining process after virtually all of 

the higher-quality hydrocarbons have been distilled, cracked, or catalytically removed from crude oil feedstock. 

Historically, fuel oils were based on residues from the atmospheric column. However, the increasing demand 

for transportation fuels such as gasoline, kerosene and diesel has led to an increased value for the atmospheric 

residue as a feedstock for vacuum distillation and for cracking processes. As a consequence, most heavy fuel 

oils are currently based on vacuum residues and residues from thermal and catalytic cracking operations 

(CONCAWE, 1998). These high viscosity residual streams may in turn be “cut” with lower quality, lighter weight 

distillates to produce a finished residual fuel of a specified viscosity. The choice of the distillate cutter stock is 

itself variable and largely a function of availability at any given time within the refinery and the viscosity 

specifications of the fuel being manufactured. While the materials most frequently used as cutter stocks are 

included in this category, other streams may occasionally be used, e.g., kerosene and gas oils. These other 

materials are characterized in other API HPV Test Plans. The exact blend used for a specific residual fuel is 

determined largely by the desired viscosity of the finished fuel and specifications (ASTM, 2002). Some of the 

refinery streams in the category that have lower viscosities and lower polyaromatic compound (PAC) levels 

have low-volume, specialty applications such as cutter stock in cutback asphalt, synfuel binders and carbon 

electrode production. 

Members of the heavy fuel oils category are a diverse group of substances that encompass hydrocarbons with a 

wide range of molecular weights, with carbon numbers ranging from C7 to C50 and boiling points between 250 – 

1112 °F (121 to 600 °C). However, “typical” heavy fuel oils are C20-C50 with the low carbon numbers and boiling 

temperatures being associated with lighter weight “cutter” streams (CONCAWE, 1998). All the category 

members are complex mixtures, containing variable amounts of alkanes, cycloalkanes, aromatics, olefins, 

asphaltenes, and hetero-molecules containing sulfur, oxygen, nitrogen and organo-metals. Because they are 

complex mixtures composed of relatively high molecular weight compounds, the materials in this category are 

difficult to characterize in detail. Consequently, they are typically not defined by detailed compositional 

information but instead by process history, physical properties, and product use specifications (ASTM, 2003). 

Since viscosity is the controlling specification, and other limiting requirements - notably boiling point ranges - are 

unspecified, there is significant variation in the chemical composition of the resulting fuel products (Uhler, 2002; 

IARC, 1989). 

Because the process history of a refinery stream determines its chemical composition, the Testing Group 

expects that streams that have undergone similar processing will have similar physical/chemical/biologic 

properties and environmental fate and transport characteristics. The refinery streams within the heavy fuels 

category can therefore be grouped into seven subcategories based on their process histories. As shown in 

Figure 1, the major processes used to produce the refinery streams included in the heavy fuel oils category are:

Atmospheric distillation 

Heavy fuel oil related streams produced by atmospheric distillation comprise fractions of crude oil separated 

by heating (650-700 degrees °F) at atmospheric pressure. They include atmospheric distillates (heavy gas 

oils) and the heavier residual materials. The distillate HFO streams are similar to some of the refinery 

streams covered in the API HPV Gas Oils category, albeit of higher molecular weight. Some of these 

streams may be further hydrotreated or desulfurized to remove sulfur, nitrogen, and other impurities. Most 

atmospheric distillates undergo further processing in order to convert them into higher value fuels (diesel, 

kerosene). However, a portion of the heavier distillate streams may be used as blending stocks to reduce 

the viscosity of the residual streams. The residual refinery streams comprise a heterogeneous group of 

poorly defined, viscous, high boiling hydrocarbon streams that usually contain suspensions of 

resin/asphaltene complexes. These streams often have high levels of heterocyclic aromatic and naphthenic 

compounds. Varying percentages of sulfur, nitrogen, oxygen, and other elements are present as heterocyclic 

inclusions, primarily in the aromatics fraction. These residual streams often have a PAC content over 5%, 

but the content can be much higher depending on the processing the stream has undergone. As shown in 
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Figure 1, there are eight refinery streams in the heavy fuel oils category that are produced by atmospheric 

distillation (two distillate and six residual streams). See Appendix A for a more detailed description of each of 

these streams. 

Vacuum distillation 

The residuum from the atmospheric distillation unit is heated at higher temperatures to further separate 

heavier molecules. This is done under reduced pressure to prevent thermal cracking. In addition to 

producing lube oils, various vacuum distillates (vacuum gas oils) and vacuum residues are produced. Similar 

to the atmospheric distillates, some of the vacuum distillates may be hydrotreated or desulfurized to remove 

sulfur, nitrogen, and other impurities. Most vacuum distillates undergo further processing in order to convert 

them into higher value fuels (diesel, kerosene). However, a portion of the heavier vacuum distillate streams 

may be used as blending stocks to reduce the viscosity of the residual streams. The vacuum residual 

refinery streams comprise a heterogeneous group of poorly defined, viscous, high boiling hydrocarbon 

streams that usually contain suspensions of resin/asphaltene complexes. These streams often have high 

levels of heterocyclic aromatic and naphthenic compounds. Varying percentages of sulfur, nitrogen, oxygen, 

and other elements are present as heterocyclic inclusions, primarily in the aromatics fraction. These residual 

streams often have a PAC content over 5%, but the content can be much higher depending on the 

processing the stream has undergone. As shown in Figure 1, there are nine refinery streams in the heavy 

fuel oils category that are produced by vacuum distillation (seven distillate and two residual streams). See 

Appendix A for a more detailed description of each of these streams. 

Cracking 

Many of the distillate and residual streams used to blend heavy fuel oils are derived from cracking processes. 

Cracking is a process that breaks (“cracks”) the heavier, higher boiling petroleum streams produced by 

atmospheric or vacuum distillation into lighter molecular weight materials such as gasoline, diesel fuel, jet 

fuel and kerosene. Often, after cracking, streams may be hydrotreated (reduces nitrogen and aromatic 

content) or undergo desulfurization. 

There are two basic types of cracking processes, those using heat and pressure (thermal cracking) to break 

molecular bonds, and those using a catalyst (catalytic cracking) to facilitate the cracking process. Both 

thermal and catalytic cracking are used to produce refinery streams that are used for blending heavy fuel oils. 

Visbreaking, coking and steam cracking are types of thermal cracking. In visbreaking, the heavy feedstock is 

heated under pressure to crack the molecules in the stream. Coking is a severe method of thermal cracking. 

In steam cracking, the hydrocarbon stream is diluted with steam and then briefly heated (>900 °C) in a 

furnace. Light hydrocarbon feeds produce streams rich in the lighter alkenes, including ethylene, propylene 

and butadiene. Heavier hydrocarbon feeds give some of these, but also give products rich in aromatic 

hydrocarbons. Petroleum pitch, sold as a product for various applications, is a high aromatic residual 

material produced from either thermal cracking or catalytic cracking. 

Catalytic cracking and hydrocracking are two types of catalytic cracking. Catalytic cracking is similar to 

thermal cracking except a catalyst facilitates conversion of the heavier to lighter products and requires less 

severe operating conditions than thermal cracking. Catalytic cracking converts heavy paraffins to light 

paraffins and olefins, heavy naphthenes to light naphthenes and olefins, and heavy aromatics to light 

aromatics, naphthenes and olefins. As noted above, petroleum pitch is a high aromatic residual material 

from either catalytic cracking or thermal cracking. 

Hydrocracking is a combination of catalytic cracking and hydrogenation, using high pressure, high 

temperature, a catalyst, and hydrogen. It is typically used for feedstocks that are difficult to process by either 

catalytic cracking or reforming. When the feedstock has a high paraffin content, the primary function of 

hydrogen is to prevent formation of PACs. Hydrocracking converts sulfur and nitrogen compounds to 

hydrogen sulfide and ammonia. 

The Testing Group thinks the refinery streams produced by the various cracking processes can be 

considered as a single subcategory since they represent a continuum in the severity of the cracking process. 
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All the cracking processes produce refinery streams that are similar from a physical-chemical perspective, 

being differentiated from each other primarily by the ratio of their unsaturated and saturated hydrocarbon 

content. While the ratio of the saturated and aromatic hydrocarbons may vary between subcategory 

members, the saturated and aromatic hydrocarbons species that make up the subcategory members are 

similar. For instance, refinery streams that are produced by catalytic cracking (most severe) have high levels 

of aromatics. In contrast, hydrocracked (least severe) streams have relatively low amounts of aromatics, 

since hydrocracking introduces hydrogen into the cracking process that results in saturation of aromatic 

compounds. As shown in Figure 1, there are eleven refinery streams in the heavy fuel oils category that are 

produced by cracking (five distillate and six residual streams). See Appendix A for a more detailed 

description of each of these streams. 

Reforming

Catalytic reforming employs a catalyst to facilitate the structural rearrangement of hydrocarbon molecules in 

order to increase the aromatic content of a refinery stream, ultimately leading to a gasoline with a higher 

octane. During reforming, olefins are saturated to form paraffins, which are then converted to shorter 

paraffins, isoparaffins, and naphthenes. The naphthenes are converted to aromatics by dehydrogenation 

(Gary and Handwerk, 1994). As shown in Figure 1, there are two refinery streams in the heavy fuel oils 

category that are produced as residues of reforming. See Appendix A for a more detailed description of each 

of these streams. 

Residual Fuel Oils

In addition to the process streams discussed above, the heavy fuel oil category also includes two blended 

residual fuel oils. These two fuel oils are most often produced by blending any combination of the distillate and 

residual streams contained in the seven process subcategories, provided the finished fuel meets the appropriate 

product specifications. Less frequently, the residual fuels can be blended using residual streams from this 

category, but petroleum distillates (cutter stocks) covered in other API HPV Test Plans. See Appendix A for a 

more detailed description of each of these two residual fuel oils. 

Analytical data for representative materials in this category are shown in Table 1. 

Table 1. Composition of Representative Samples of the HFO Category

Endpoint Atmospheric 

Residue 

Vacuum 

Distillate 

Cracked 

Distillate 

Cracked 

Residue 

Residual Fuel 

Oil 

CAS No. 64741-45-3 64741-57-7) 64741-81-7 64741-62-4 68476-33-5 

Specific gravity 0.9698 0.9285 0.9383 1.0725 0.8491 

Refractive index 1.5132 1.515 1.5259 Too dark 1.6306 

Distillation (°F) 

IBP 531 548 411 395 340 

End point 1041 1131 831 952 1239 

Non-aromatics 32.18 40.03 49.6 41.7 55.8 

Aromatics (wt %) 67.82 59.97 50.4 58.3 44.2 

API, 1987;CONSCI 1992a,b; DataChem 1990

Composition of Heavy Fuel Oil Blending Streams

While detailed compositional information is limited, general compositional information can be inferred from a 

refinery stream’s physical properties and the type of processing it has undergone. For instance, the higher the 

boiling temperature range of a stream, the higher the molecular weight of the oil’s components, the higher the 

levels of PACs, polycycloparaffins and hetero-atoms (N, O, S, and metals) increase, and the lower the levels of 

paraffins (see Figure 2). Furthermore, since “cracking” raises the olefin and aromatic content of refinery 

streams, streams that have been “cracked” have higher olefin and aromatic hydrocarbon content than “straight 

run” streams that have undergone a limited amount of additional processing. For example, catalytically cracked 

clarified oil has been reported to contain 58% three to five ring aromatic hydrocarbons (IARC, 1989). Thus, a 
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residual fuel blended using primarily catalytically cracked or steam cracked components will have a higher PAC 

content (may approach 20%) than a fuel blended primarily of a non-cracked stream, i.e. heavy vacuum gas oil 

(CONCAWE, 1998). If on the other hand, the blending stocks are predominantly atmospheric or vacuum 

distillates or residues, the concentration of three to seven ring aromatic hydrocarbons is likely to be of the order 

of 6-8% (IARC, 1989). The types and levels of PACs found in a specific fuel will depend on the processing the 

residual portion of the fuel has undergone, and the nature of the blending stream (“cutter” stock) that is used to 

adjust the viscosity of the finished fuel. 
 Figure 1. HFO Process Diagram 

Atmospheric

Distillation 

Vacuum Distillation 

Residual Distillate

64741-62-4 64741-75-9 64741-80-6 68187-58-6 68478-17-1 68783-13-1

68410-00-4 68783-08-4 

64741-45-3 64742-78-5 68333-22-2 68476-32-4 68607-30-7 70592-79-9 

Residual Distillate Residual Distillate

Catalytic Cracking Thermal Cracking Coking Hydrocracking

64741-61-3 64741-81-7 68333-26-6 68333-27-7 70955-17-8 

64741-57-764742-59-264742-86-568955-27-170592-76-670592-77-770592-78-8

68512-62-9 70913-85-8 

Crude Oil 

Residual Fuel Oils 

68476-33-5 68553-00-4l 
Figure 2. Refinery Stream Composition – Boiling Range vs. General Composition

Cutter Stocks Heavy Fuel Oils 

Speight, 1998

Links to additional resources on refining processes and petroleum-related glossaries are presented in Appendix 

B. 

CATEGORY RATIONALE AND TEST MATERIAL DESCRIPTION 

With regard to mammalian toxicity, when analyzing the existing data, proposing testing and identifying potential 

test materials the Testing Group considered the following: 

• The HFO category consists of finished products (residual fuels) and the primary refinery streams from 

which they are blended; 

• The refinery streams in this category that are blended to produce finished heavy fuels can be grouped 

into seven subcategories according to their process history; 

• Refinery streams within a process subcategory are similar from a process and physical/chemical 

perspective, and are expected to have similar biologic, environmental fate and transport characteristics; 

• The range of toxicity of the materials in each process subcategory can be characterized by 

characterizing representative materials within each subcategory; 

• The toxicity of the finished products (Residual Fuel Oils) will fall within the range of toxicities exhibited 

by the streams blended to produce the finished fuel; 

• Because of compositional overlaps and similarities, other API HPV test programs involving gas oils, 

aromatic extracts, jet fuel/kerosene and asphalt will produce data that will assist in characterizing the 

materials in this category. 

With regard to ecotoxicity, when analyzing the existing data, the Testing Group proposes that a material’s

solubility (i.e. carbon chain length) determines the degree of ecotoxicity. This is valid and consistent with the 

current theory on the mode of toxic action for non-polar organic molecules (such as petroleum hydrocarbons) to 

aquatic organisms (Peterson, 1994; van Wezel and Opperhuizen, 1995). Thus, the category substances are 
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considered as a single group. Furthermore, the streams and products in the heavy fuel oil category are 

composed of constituent hydrocarbon compounds that also are represented in other petroleum product HPV 

categories that have substantial ecotoxicity data. Therefore, the Testing Group has employed data from other 

categories as read across to describe potential ecotoxicity for all streams and products in the heavy fuel oil 

category. 

Because the compositions of the materials in this category vary over time, it is not possible to specify in this Test 

Plan the exact chemical makeup of the test samples that will be used in the mammalian testing. Specific 

analytical data on the test samples will be developed and made available when the samples are obtained. For a 

both the process subcategories and the residual fuel, the Testing Group will attempt to select test sample(s) that 

are thought to have the highest potential toxicities. 

EVALUATION OF EXISTING HEALTH EFFECTS DATA AND PROPOSED TESTING 

General Evaluation

Reviews of this category of fuels have been published by two expert panels (CONCAWE, 1998; IARC, 1989). In 

preparing this Test Plan, the approach of the Testing Group has been to review the available toxicology studies 

and include in the robust summary a detailed description(s) of the one study or a small number of studies that 

best address each SIDS Level 1 endpoint. Other studies are cited in the appropriate “Remarks” section of the 

Robust Summary and are intended to supplement the readers’ knowledge. 

The Test Plan addresses the health effects endpoints of the category by: 

• Evaluating the toxicology database for the heavy fuel oil related refinery streams and products, 

• Using read-across information whenever possible among category members, and other API HPV 

categories, and 

• Proposing selected testing on representative samples. 

HEALTH EFFECTS

Acute Toxicity

The following acute toxicity results have been reported on representative samples of the seven heavy fuel oil 

subcategories: 

Acute Oral Toxicity LD50 value Species Observations 

Residual Fuel Oils 

(4 samples) 

5.13 - >25 ml/kgbw Rat Lethargy; grease on fur 

Process Subcategories

Atmospheric residue >5000 mg/kgbw Rat Stained coats; dark red 

areas in lung lobes 

Atmospheric distillate No studies available - - 

Vacuum residue Data on two vacuum 

residuum samples (CAS 

no. 64741-56-6, API 

samples 81-13 and 81-

14) are presented in the 

API HPV Asphalt Test 

Plan 

- - 

Vacuum distillate 

(3 samples) 

>5000 mg/kgbw Rat ↓ Activity; 

chromorhinorrhea, ↓ fecal 

output; urogenital 

staining; ↓ urine 

Cracked residue 4320♀ 5270♂ mg/kgbw Rat Mortalities; hypoactivity; 

piloerection; staining 

around mouth, nose, 
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urogenital; hair loss; 

weight loss; intestinal 

mucosa damage 

Cracked distillate >5000 mg/kgbw Rat Oral, nasal discharge; 

lethargy; abnormal 

stools; pale & mottled 

kidneys 

Reformer residue No studies available - - 

UBTL, 1988,1990b; API, 1980a-d, 1982; Mobil, 1988b,c, 1992a

Acute Dermal Toxicity LD50 value Species Observations 

Residual Fuel Oils 

(4 samples) 

>5 ml/kgbw Rabbit Erythema; slight 

congestion of liver 

Process Subcategories

Atmospheric residue >2000 mg/kgbw Rabbit Abnormal stool; dark red 

areas in lung 

Atmospheric distillate No studies available - - 

Vacuum residue Data on two vacuum 

residuum samples (CAS 

no. 64741-56-6, API 

samples 81-13 and 81-

14) are presented in the 

API HPV Asphalt Test 

Plan 

- - 

Vacuum distillate 

(4 samples) 

>2000 mg/kgbw Rabbit ↓ Food consumption; soft 

stool; ↓ fecal output 

Cracked residue >2000 mg/kgbw Rabbit No signs systemic 

toxicity; no gross findings 

Cracked distillate >2000 mg/kgbw Rabbit Erythema & edema; 

mottled kidneys 

Reformer residue No studies available - - 

API, 1980a-d, 1982; UBTL 1989a, 1992a,b

Dermal Irritation Irritation Index Species Observations 

Residual Fuel Oils 

(4 samples) 

0.27 – 1.54 Rabbit Minimal – slight irritant 

Process Subcategories

Atmospheric residue 3.5 Rabbit Moderately irritating 

Atmospheric distillate No studies available - - 

Vacuum residue 0.18 Rabbit Not irritating 

Vacuum distillate 

(4 samples) 

1.2 – 3.6 Rabbit - 

Cracked residue 0.2 Rabbit - 

Cracked distillate 5.6 Rabbit Moderately irritating 

Reformer residue No studies available - - 

UBTL, 1989d,e, 1992 d; API 1980a-d, 1982; Mobil, 1988a,b c, 1992a

Eye Irritation Irritation Indices Species Observations 

24 & 72 hr 

Residual Fuel Oils 

(4 samples) 

2.67 – 7.67 & 0 – 1.33 rinsed 

4.0 – 7.33 & 0.0 – 1.33 un-rinsed 

Rabbit Minimal – mild irritant 

Process Subcategories
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Atmospheric residue 0.0 & 0.0 un-rinsed only Rabbit Not irritating 

Atmospheric distillate No studies available - - 

Vacuum residue 5.0 & 4.7 un-rinsed 

5.7 & 4.7 rinsed 

Rabbit Un-rinsed - not irritating – 

Rinsed - minimal irritant 

Vacuum distillate 

(4 samples) 

2.0 – 10.3 & 1.7* – 3.3* Rabbit Un-rinsed only 

* 48 hr score 

Cracked residue 2.0 & 0 rinsed & un-rinsed Rabbit Minimal irritant 

Cracked distillate 5.7 & 0.0 un-rinsed 

5.3 & 0.0 rinsed 

Rabbit Un-rinsed - not irritating 

Rinsed – not irritating 

Reformer residue No studies available - - 

UBTL, 1989f,g, 1991 API, 1980a-d, 1982; Mobil, 1988a,b, c, 1992a

Sensitization Challenge Response Species Observations 

Residual Fuel Oils 

(4 samples) 

- Guinea Pig 3 samples non-sensitizer 

1 sample mild sensitizer 

Process Subcategories

Atmospheric residue 0/10 Guinea Pig Non-sensitizer 

Atmospheric distillate No studies available - - 

Vacuum residue 0/10 Guinea Pig Non-sensitizer 

Vacuum distillate 1/10 Guinea Pig Non-sensitizer 

Cracked residue 0/10 Guinea Pig Non-sensitizer 

Cracked distillate 0/10 Guinea Pig Non-sensitizer 

Reformer residue No studies available - - 

API, 1980a-d, 1984; UBTL, 1986,1989b,c; 1990c, 1992c

Summary: No additional testing is planned. Multiple acute toxicity studies have been reported on a number 

of representative samples of the heavy fuel oil refinery streams as well as on finished residual fuels. These data 

and data from the other 12 API HPV Test Plans show the acute toxicity of a wide-array of petroleum 

hydrocarbon streams is consistently low, with many oral LD50’s greater than 5 g/kg, and dermal LD50s greater 

than 2 g/kg. While no data is presented for the vacuum residue process subcategory, the Testing Group thinks 

existing acute toxicity data on two vacuum residuum samples (CAS no. 64741-56-6, API samples 81-13 and 81-

14) presented in the API HPV Asphalt Test Plan support the Group’s position that this subcategory of materials 

would have low acute toxicities. Similarly, although no data is presented for the atmospheric distillate or 

reformer residue subcategories, materials produced by these processes have been considered in other API 

HPV Test Plans that have consistently shown the acute toxicities of the materials to be low. Consequently, the 

Testing Group thinks the acute toxicities of these materials can be characterized by “Read Across” from 

materials other API HPV Test Plans. 

Repeat-Dose Toxicity

Studies of up to 13 weeks duration have been reported for representative streams in a number of the process 

subcategories within the heavy fuel oil category. In instances where there were multiple studies available for a 

subcategory, only the study of the longest duration was fully summarized in the attached Robust Summary 

(Appendix C). 

Residual Fuel Oils

Dose levels of 0.5 (496 mg), 1.0 (992 mg), or 2.5 (2480 mg) ml/kgbw/day of a heavy fuel oil (CAS no. 668476-33-

5) were applied undiluted to the skin of male and female rats (UBTL, 1987). The test material was applied 

5x/week for 4 weeks. The test material produced minimal reversible dermal irritation at all dose levels. Daily 

observations of the animals found no compound-related effects other than staining at the site of application. 

Similarly, there were no compound-related findings at necropsy other than the staining of the skin produced by 

the test article. 
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Eosinophil counts were significantly lower for the mid-dose and high-dose males. SGPT levels were 

significantly lower for the low- and high-dose females and the high-dose males. Glucose levels were 

significantly higher for the mid- and high-dose females and high-dose males. Total protein levels were 

significantly lower for the low-dose males. Hemoglobin levels were significantly lower for the high-dose males. 

Upon comparison and review of historic data, the study directors concluded the significant values obtained from 

the hematology or clinical chemistry assays were within normal limits and did not exhibit any clear dose-related 

trends. 

Relative liver weights were significantly higher for the females in all dose groups and in the high-dose males. 

With the exception of the liver/brain weight ratios in the low-dose males, liver/body weight and liver/brain weight 

ratios were significantly higher for both sexes in all dose groups. The liver weight changes were thought by the 

study directors to be compound-related. Spleen/body weight ratios were significantly higher for the low and middose females and the high-dose males. The spleen/brain weight ratios were significantly higher for the lowdose females and the high-dose males. The changes in relative spleen weights were not thought to be doserelated by the study directors. 

Microscopic examination of selected tissues from the control and high dose groups found no compound-related 

effects other than hyperkeratosis (minimal severity) at the test compound application site. 

Process Subcategories

Atmospheric Residue

Dose levels of 0.01 (9 mg), 0.25 (231 mg) or 1.0 (927.9 mg) ml/kgbw/day of an atmospheric residue (CAS 

no. 64741-45-3) were applied undiluted to the skin of male and female rats (UBTL, 1990a). The test 

material was applied 5x/week for 4 weeks. There were no clinical observations made that were considered 

to be treatment-related. The only treatment-related finding at gross necropsy was a dark staining of the 

treated skin site. There were no compound-related effects on either hematology or clinical chemistry 

values. Nor were there any treatment-related differences in body weights or organ weights or organ/body 

weight ratios. The only treatment-related histopathological findings occurred in the skin and these consisted 

of trace to mild acanthosis and trace to moderate hyperkeratosis in the high dose animals. The study 

authors concluded that there were no systemic effects at the highest dose level tested. 

Atmospheric Distillates

Dose levels of 30, 125 or 500 mg/kgbw/day of a heavy atmospheric gas oil (CAS no. 68783-08-4) were 

applied undiluted to the skin of male and female rats (Mobil, 1992c). The test material was applied 5x/week 

for 13 weeks. To assess male reproductive health, a satellite group of 10 males was administered 500 

mg/kgbw/day of the gas oil. At the end of the study the epididymides and testes from the male rats in the 

control and 125 mg/kgbw/day groups were given an in-depth histopathology examination, including 

spermatid (testes) and spermatozoa (epididymides) counts. In general, application of the test material 

produced only “slight” skin irritation. One of ten high dose males was sacrificed in extremis, the 

investigators considered the death to be treatment-related. There were treatment-related changes in a 

number of serum chemistry and hematological parameters in the rats in the mid- and high dose groups. At 

necropsy, treatment-related macroscopic findings in both sexes included increased liver size, decreased 

thymus size, thickening of the limiting ridge between the non-glandular and glandular sections of the 

stomach and enlarged and reddened lymph nodes. There were some organ weight (absolute and relative) 

differences in the 125 and 500 mg/kgbw/day groups. The histopathology examination found treatmentrelated changes only in animals in the 500 mg/kgbw/day groups. These changes included a severe 

reduction in hematopoiesis in the bone marrow; liver hypertrophy and connective tissue formation; 

increased areas of hematopoiesis, focal necrosis and individual cell death in the liver; and a reduction in the 

numbers of lymphocytes in the thymus glands. There were no treatment-related effects on any of the 

epididymal sperm or testicular spermatid parameters. The investigators concluded the no-observable-effect 

level (NOAEL) for the study was 30 mg/kgbw/day. 

Vacuum Residue

Data on repeat-dose toxicity studies in rabbits on two vacuum residuum samples (CAS no. 64741-56-6, API 

samples 81-13 and 81-14) are presented in the API HPV Asphalt Test Plan. 
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Vacuum Distillate

An undiluted heavy vacuum gas oil (CAS no. 64741-57-7) was applied to the skin of male and female rats 5 

days each week for 13 weeks (Mobil, 1988d). Dose levels were 30, 125, 500 & 2000 mg/kgbw/day. The 

unscheduled deaths of two of ten males in the high dose group were considered to be compound-related. 

Growth rates of males and females in the highest dose group were reduced compared to controls. At five 

and thirteen weeks, the 2000 mg/kgbw/day dose group had reduced erythrocytes and platelets. Similar 

reductions were also found in the 500 mg/kgbw/day females. Changes in several clinical chemistry values 

were also seen in the 2000 mg/kgbw/day dose group. In addition in females dosed with 500 mg/kgbw/day 

had reduced serum glucose levels, while in the 500 mg/kgbw/day males, cholesterol was increased. 

At gross necropsy, in the 500 and 2000 mg/kgbw/day dose groups, relative thymus weights were reduced 

while relative liver weights were increased. Histological examination revealed decreased erythropoiesis and 

fibrosis of the bone marrow in the 2000 mg/kgbw/day males. There was a reduction in thymic lymphocytes in 

both sexes in the 2000 mg/kgbw/day group. Examination of the testes of animals in the 2000 mg/kgbw/day 

dose group found no compound-related effect on sperm morphology. The investigators found the NOEL for 

both males and females was 125 mg/kgbw/day. 

Cracked Residue

Dose levels of 8, 30,125, 500 and 2000 mg/kgbw/day of a clarified slurry oil (CAS no. 64741-62-4) were 

applied undiluted to the skin of male and female rats (Cruzan et al., 1986; Mobil, 1985b). The test material 

was applied 5x/week for 13 weeks. There was an adverse, dose-related effect on mortality, with none of the 

rats in the highest dose group (2000 mg/kg/day) surviving past the second week of the study. Compoundrelated effects were observed on body weights, and several hematology and clinical chemistry parameters. 

Based on these changes, and histopathology findings, the target organs of toxicity were judged by the study 

directors to be the liver, thymus and bone marrow. The investigators concluded that none of the dose levels 

used in the study represented a no-observable-adverse- effect level (NOAEL). 

Cracked Distillate

Dose levels of 8, 30 and 125 mg/kgbw/day of a visbreaker gas oil (CAS no. 68471-81-7) were applied 

undiluted to the skin of male and female Sprague-Dawley rats (Feuston et al., 1994; Mobil, 1992b). The test 

material was applied 5x/week for 13 weeks. There were no deaths during the study. No clinical signs of 

toxicity were observed, with the exception of dose-related skin irritation. There were no compound-related 

effects on body weights or hematology and clinical chemistry values. Urinalysis found no treatment-related 

effects. At necropsy, the only treatment-related findings were effects on the skin and enlarged lymph nodes 

(the latter predominantly in the higher dose groups). Microscopic examination of the skin revealed 

thickened epidermis with parakeratosis, chronic inflammation in the subcutis, ulcers and increased mitosis in 

the epidermal basal cells. The skin changes were more severe in females than the males. Lymph nodes 

were enlarged in the high dose animals and in most instances, microscopic examination revealed nonspecific reactive hyperplasia. Epididymides and testes from the male rats in the control and 125 

mg/kgbw/day groups were given an in-depth histopathology examination, including spermatid (testes) and 

spermatozoa (epididymides) counts. Treatment with visbreaker gas oil did not cause any changes in 

testicular spermatid or epididymal spermatozoa count nor in sperm morphology. The investigators 

concluded the NOAEL in the study was > 125 mg/kgbw. 

Reformer Residue

No studies available. 

Carcinogenicity

In addition to the repeat-dose studies discussed above, several dermal carcinogenicity studies on samples of 

cracked residual streams have been reported (API, 1989; McKee et al., 1990; Smith et al., 1951). Although 

carcinogenicity is not a required endpoint of the HPV program, the Testing Group believes the results may be 

useful in evaluating the repeated-dose endpoint. A tabulation of these studies can be found in section 5.7 of the 

attached Robust Summary (Appendix C). 

Summary: The Testing Group proposes to test a representative sample of a reformer residue stream by 

the dermal route of administration using a 28-day repeated-dose/reproductive/developmental toxicity 
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screening protocol (OECD Test Guideline 422). No repeat dose information exists on the reformer residue 

streams. While no data is available for the vacuum residue process subcategory, the Testing Group thinks 

these materials can be characterized by “read across” from the data on the vacuum residue streams found in 

the API HPV Asphalt Test Plan. 

In-Vitro (Mutagenicity)

Subcategory Assay Results 

Residual Fuel Oils No studies to report - 

Process Subcategories

Atmospheric residue No studies to report - 

Atmospheric distillate No studies to report - 

Vacuum residue Mouse lymphoma - data on two 

vacuum residuum samples (CAS no. 

64741-56-6, API samples 81-13 and 

81-14) are presented in the API HPV 

Asphalt Test Plan 

Weakly positive with activation 

Vacuum distillate Modified Ames– Positive with activation 

Cytogenetic assay with Chinese 

Hamster Ovary cells 

Negative with/without activation 

Cracked residue Modified Ames Positive with/without activation 

Mouse lymphoma Positive with/without activation 

Sister chromatid exchange Positive with/without activation 

Cell transformation Negative without activation 

Positive with activation 

Unscheduled DNA synthesis Positive 

Bacterial forward mutation Negative with/without activation 

Cracked distillate No studies to report - 

Reformer residue No studies to report - 

API, 1985a,b, e, f, 1986b,c; Mobil, 1985a, 1987e

Summary: The Testing Group is proposing to perform a modified Ames and chromosomal aberration 

(OECD 473) assays on representative samples of a residual fuel oil, atmospheric residue, atmospheric 

distillate, cracked distillate and reformer residue. 

In-Vivo (Chromosomal Aberrations)

Subcategory Assay Species Results 

Residual Fuel Oils No studies to report - - 

Process Subcategories

Atmospheric residue No studies to report - - 

Atmospheric distillate No studies to report - - 

Vacuum residue Cytogenetic Assay - data 

on two vacuum residuum 

samples (CAS no. 64741-

56-6, API samples 81-13 

and 81-14) are presented in 

the API HPV Asphalt Test 

Plan 

Rat (♀, ♂) Negative at up to 3 g/kg/day by 

gavage for 5 days 

Vacuum distillate Micronucleus Rat (♀, ♂) Negative at up to 2000 

mg/kgbw/day; 5x/week for 13 weeks 

via dermal route 

Cracked residue Cytogenetic Assay Rat (♀, ♂) Negative at up to 1 g/kg/day by
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gavage for 5 days 

Sister Chromatid Exchange Mice (♀, ♂) Single IP dose - positive at 4.0 (♀, 

♂) & 2.0 (♂) g/kgbw; negative at 0.4 

g/kgbw

Unscheduled DNA 

Synthesis 

Rat (♂) Positive at 100 & 1000 mg/kgbw by 

gavage; negative at 50 mg/kgbw

Cracked distillate No studies to report - - 

Reformer residue No studies to report - - 

API, 1985c,d, e; Mobil, 1987f

Summary. No additional in-vivo testing is planned. Adequate studies exist on the vacuum distillate and 

cracked residue subcategories. The Testing Group thinks results from the API HPV Gas Oils test plan can be 

“read across” to the atmospheric distillate subcategory given the similar process history. Similarly, the Testing 

Group thinks results on vacuum residue streams from the API HPV Asphalt test plan can be “read across” to 

characterize the vacuum residue subcategory. Given the high aromatic content of the cracked distillates and 

reformer residues, the Testing Group would expect these types of materials would produce positive results in 

the Ames assays. Other materials with high PAC content (aromatic extracts) have produced negative results in 

in vivo chromosomal aberration assays. If the in vitro assays are positive, the Testing Group will consider 

additional in vivo testing. 

Reproductive/Developmental Toxicity

Residual Fuel Oils

No studies to report. 

Process Subcategories

Atmospheric Residue

In a developmental screening study, dose levels of 50, 333, & 1000 mg/kgbw/day of an atmospheric residue 

(CAS no. 64741-45-3) were applied to the skin of presumed-pregnant female rats on days 0-20 of gestation 

(UBTL, 1994). There were no deaths or treatment-related clinical effects amongst the dams. The study 

directors considered decreased body weight changes and the increase in gestation length at a dose of 

1,000 mg/kg to be signs of compound-related maternal toxicity. Signs of developmental toxicity considered 

by the study directors to be compound-related included decreased pup body weights on Lactation Days 0 

and 4 at a dose of 1,000 mg/kg. The report authors concluded that for maternal toxicity and signs of 

developmental toxicity the no-observable-adverse-effect level (NOAEL) was 333.0 mg/kgbw/day. 

Atmospheric Distillate

A developmental toxicity screening study has been reported on a heavy atmospheric gas oil (CAS no. 

68783-08-4) (Mobil, 1991). Undiluted test material was applied daily on days 0 to 19 of gestation to the 

clipped skin of resumed-pregnant female rats. Dose levels included 8, 30, 125 and 500 mg/kgbw/day. Signs 

of maternal toxicity considered by the study director to be related to administration of the test material 

included effects on body weights, body weight gain, food consumption, thymus weights (absolute & relative), 

liver weights (relative), and a number of clinical chemistry and hematological parameters. A red vaginal 

discharge (normally indicative of litter resorption) was observed in 7/11 animals in the 500 mg/kgbw/day 

group and two females dosed with 125 mg/kgbw/day. The investigators could not decide if the vaginal 

discharge was treatment-related since a similar observation had been noted in control animals. Evaluation 

of reproductive parameters in the 8 and 30 mg/kgbw found no compound-related effects. Statistically 

insignificant differences in preimplantation losses were seen in both the 125 and 500 mg/kgbw/day groups. 

There was a significant increase in the mean number/percent resorptions in the 500 mg/kgbw/day group. 

Mean fetal body weights were significantly decreased for all viable fetuses in the 500 mg/kgbw/day group 

and in the male pups of the 125 mg/kg group. There was a significant increase in incomplete ossification of 

a number of skeletal structures (nasal bones, thoracic centra, caudal centra, sternebrae, metatarsal and 

pubis) in the 125 and 500 mg/kgbw/day groups. There were no treatment-related abnormalities found in the 

soft tissues. Exposure to gas oil did not adversely affect pup survival or development. The investigators 
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concluded the no-observable-adverse -effect levels (NOAELs) for both maternal toxicity and teratogenicity 

were 30 mg/kgbw/day. 

Vacuum Residue

No studies to report. 

Vacuum Distillate

In a developmental screening study, dose levels of 30, 125, 500 and 1000 mg/kgbw/day of a heavy vacuum 

gas oil (HVGO, CAS no. 64741-57-7) were applied to the skin of presumed-pregnant female rats (Mobil, 

Undated). The test material was administered on days 0 to 19 of gestation. All animals were euthanized on 

day 20. Clinical signs of maternal toxicity considered by the study authors to be compound-related were 

seen primarily in the 1000 mg/kgbw/day dose group. In the dams, the only treatment-related findings seen at 

necropsy were lungs that had a pale appearance (500 and 1000 mg/kgbw/day) and a reduction in thymus 

size. Organ weight data confirmed that the thymus weights in the highest dose group were reduced and 

furthermore, relative liver weights were increased in the 500 and 1000 mg/kg/day animals. A number of 

reproductive parameters were affected by treatment with HVGO. Fetuses of dams in both the 500 and 1000 

mg/kgbw/day dose groups had treatment-related decreases in body weights. Upon external examination, 

one fetus in the 1000 mg/kgbw/day group was found to be edematous, pale in color, with both hind paws 

malformed. Malformations of the vertebral columns were observed in several fetuses, but only in the 500 

mg/kgbw/day group. While a variety of skeletal malformations were observed in both treated and control 

groups, the degree of malformation was more severe in the HVGO-exposed groups. Visceral malformations 

were restricted to two fetuses in the 500 mg/kgbw/day group. Of the two fetuses, one had microphthalmia 

and the other had a diaphragmatic hernia that displaced the heart from the left- to right-hand side. The 

study authors concluded the no-observable-adverse-effect levels (NOAELs) for both maternal and fetal 

toxicity were 125 mg/kgbw/day. 

Cracked Residue

A developmental toxicity screening study has been reported on a clarified slurry oil (CSO, CAS no. 64741-

62-4) (Hoberman et al., 1995). Undiluted test material was applied daily on days 0 to 19 of gestation to the 

clipped skin of resumed-pregnant female rats. Dose levels included 0.05, 1.0, 10, 50 or 250 mg/kgbw/day. 

No deaths occurred among the dams and no dam aborted or prematurely delivered a litter. Neither 

maternal toxicity nor fetal developmental effects were seen at the 0.05 mg/kgbw/day dose level. Nor were 

any fetal malformations or variations observed in the 0.05 mg/kgbw/day group. Dose-related signs of 

maternal toxicity were seen at dose levels greater than 0.05 mg/kgbw/day. The effects included decreased 

food consumption and decreased body and gravid uterine weights, and the occurrence of red vaginal 

exudates. Fetal developmental effects, as measured by number of live fetuses, total resorptions, early 

resorptions, % dead or resorbed conceptuses/litter and fetal body weights were seen at doses that were 

maternally toxic. There were no treatment-related incidences of fetal malformations. However, increased 

incidences of fetal variations that are generally interpreted as reversible delays in development associated 

with significant decreases in body weight were produced in fetuses in the 1.0, 10 and 50 mg/kgbw/day dose 

groups. These variations included moderate dilation of the renal pelvis, slight dilation of the lateral 

ventricles of the brain, bifid thoracic vertebral centrum and decreased average numbers of ossified caudal 

vertebrae, metacarpals and hindpaw phalanges. The study authors concluded the no-observable-adverseeffect levels (NOAELs) for both maternal and fetal toxicity were 0.05 mg/kgbw/day. 

To determine potential effects on gonadal function, reproductive organs and mating behavior, 0.1, 1, 10, 50 

& 250 mg/kg/day of a clarified slurry oil (CAS no. 64741-62-4) were applied dermally to male rats for 70 

days before a seven-day cohabitation period with untreated virgin female rats (Argus, 1992). Female rats 

were examined daily for viability and clinical observations, and body weights were recorded on days 0, 6 

and 14 of presumed gestation. On day 14 of presumed gestation, the female rats were sacrificed by carbon 

dioxide asphyxiation, and a gross necropsy of the thoracic and abdominal viscera was performed. The 

uterus of each rat was examined for pregnancy, number and distribution of implantations, early resorptions 

and live and dead embryos. No deaths and no skin reactions were caused by the test material. All absolute 

and relative organ weights were comparable among the six dosage groups. There were compound-related 

effects on body weights, body weight gains, and food consumption. Mating and fertility parameters were 

unaffected at any of the dose levels. There were no compound-related effects on any testicular parameter. 
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Litter averages for corpora lutea, implantations, and live embryos and resorptions did not significantly differ 

among females mated with male animals from the six dosage groups. There were no dead embryos, and 

no dam resorbed all conceptuses. The study directors concluded that the paternal no-observable-adverseeffect-level (NOAEL) was 1 mg/kg/day. The reproductive NOAEL for the male rats was >250 mg/kg/day (no 

mating, fertility or testicular parameters in the male rats were affected by the highest dosage tested). 

In a reproductive/developmental toxicity screen, female Sprague-Dawley rats were administered catalytically 

cracked clarified oil (CAS no. 64741-62-4) at dose levels of 0.05, 10, 250 mg/kg/day (UBTL, 1994). The test 

material was administered one week prior to the initiation of mating, throughout mating, and through Day 20 

of gestation. Male rats to which the females were mated were not administered test compound. Food 

consumption and body weights were recorded throughout the premating, mating and gestation periods. On 

Day 4 of lactation, each female was sacrificed and the ovaries and uterine horns examined to determine the 

number of corpora lutea and implantation sites, respectively. Litters were observed during Days 0 –4 of 

lactation for signs of toxicity and mortality. Pups were examined daily for external abnormalities. On Days 0 

and 4 of lactation, each pup was weighed and its sex was determined. On day 4 of lactation, all surviving 

pups were examined externally, sacrificed and discarded. No deaths occurred during the study. The study 

directors considered the following signs of maternal toxicity to be related to administration of the test 

material: a higher incidence of vaginal discharge at a dose of 250 mg/kg; decreased body weights, body 

weight changes, and food consumption at doses of 10 and 250 mg/kg; and decreased thymus size at a 

dose of 250 mg/kg. Signs of developmental toxicity considered to be compound-related were limited to the 

250 mg/kg dose group; none of the females in this dose level delivered a litter. The study directors 

concluded the no-observable-adverse-effect levels (NOAEL) were 0.05 mg/kg for maternal toxicity and 10 

mg/kg for signs of developmental toxicity. 

Cracked Distillate

Doses of 8, 30, 125 and 250 mg/kgbw/day of a heavy coker gas oil (CAS no. 64741-81-7) were applied daily 

to the skin of resumed-pregnant female rats in a developmental screening study (Mobil, 1987d). Animals 

were dosed on days 0-19 of gestation. All animals were euthanized on day 20. Treatment-related clinical 

observations in the dams consisted of erythema, flaking, scabbing, edema, eschar and fissuring and the 

occurrence of a red vaginal discharge. Eschar and fissuring occurred in the highest two dose groups only. 

Vaginal bleeding was seen in the groups receiving doses of 30 mg/kgbw/day and higher. There was a doserelated decrease in mean body weight gains over the course of the experiment. At necropsy, the only 

treatment-related observation in the dams was an apparent reduction in thymus size, which was noted at all 

treatment levels. Absolute thymus weights were decreased, while absolute liver weights were increased. A 

number of clinical chemistry values were affected, but only at the highest dose of 250 mg/kgbw/day. Select 

reproductive parameters were adversely affected, but only in the 125 and 250 mg/kgbw/day groups. Viable 

and non-viable fetuses from these two dose levels were observed to have signs of abnormal external 

development, including reduced (shortened) lower jaws and edema. Visceral anomalies seen in these 

same two dose groups included displacement of esophagus from a left-sided to a right-sided position and 

distension of the ureters. Malformations of the vertebral column were restricted to fetuses of dams exposed 

to the test material. Although signs of aberrant development were observed in control animals, the degree 

of the observed effects was not as severe in the control groups as the groups exposed to test material. The 

authors concluded that the no-observable-adverse-effect-level for maternal and fetal toxicity was 30 

mg/kgbw/day. 

Reformer Residue

No studies to report 

Summary: The Testing Group proposes to test a representative sample of a residual fuel oil by the 

dermal route of administration using a reproductive/developmental toxicity screening protocol 

(OECD Testing Guideline 421). The Testing Group proposes to test a representative sample of a 

reformer residue by the dermal route of administration using a 28-day repeatdose/reproductive/developmental toxicity screening protocol (OECD Test Guideline 422). The 

Testing Group thinks the existing data on refinery streams in the process subcategories allows the 

developmental toxicity of these materials to be characterized. While no data exists for the vacuum residue 

subcategory, the Testing Group believes the physical nature of these materials (very viscous) will limit the 
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bioavailability of any potentially biologically significant components. Furthermore, data is available for 

atmospheric residuum, a similar material, which because of its lower boiling point will contain higher levels 

of these potentially biologically significant components. Therefore, the Testing Group is not proposing any 

testing for this subcategory of materials. No reproductive or developmental data is available for the reformer 

residue streams. However, the Testing Group has already proposed a repeat-dose study on a reformer 

residue. The Testing Group is proposing to maximize the utility of the study by conducting a 28-day 

repeated-dose/reproductive/developmental toxicity screen (OECD Test Guideline 422). This will provide 

data not only on the repeat-dose toxicity of this subcategory of materials, but also on their reproductive/ 

developmental toxicity thereby adding to the extensive database that exists on these materials. 

While none of the developmental studies summarized in this test plan provide data on pre-mating exposure 

of males or females, the existing data adequately characterize the reproductive endpoint for these materials. 

Repeat-dose studies on samples of atmospheric distillates, vacuum distillates, and cracked distillates have 

included an in-depth histopathological examination of reproductive organs. Furthermore, studies have been 

reported on catalytically cracked clarified oil (cracked residue) in which pre-mating exposures of males or 

females were conducted. Catalytically cracked clarified oil has produced the lowest maternal no-observedadverse-effect-level (NOAEL) in the developmental screens that have been performed. The Testing Group 

expects the reproductive toxicity of the other materials in this category to be less than that of catalytically 

cracked clarified oil. 

The lack of reproductive/developmental toxicity data on a finished residual fuel suggests the need for a 

reproductive/developmental screen on a representative sample of a residual fuel. The Testing Group is 

proposing a reproductive/developmental toxicity screen (OECD Test Guideline 421) of a residual fuel in 

order to develop a complete data set on a finished product and to test its hypothesis that the toxicity of the 

finished fuel will fall within the range of the toxicities of the streams from which the fuel is blended. To that 

end, the Testing Group will select a residual fuel test sample that is well characterized with respect to the 

components from which it was blended. The goal will also be to select a residual fuel oil sample that has a 

significant portion of cracked residues since these streams appear to show the highest potential for toxicity 

within this category. 

EVALUATION OF EXISTING PHYSICO-CHEMICAL AND ENVIRONMENTAL FATE DATA AND PROPOSED 

TESTING 

The physicochemical endpoints for the EPA HPV chemical program include melting point, boiling point, vapor 

pressure, octanol/water partition coefficient (log Kow), and water solubility. Environmental fate endpoints include 

photodegradation, hydrolysis, environmental transport and distribution (fugacity), and biodegradation. Although 

some data for products in this category exist, not all of these endpoints are defined and a consensus database 

for chemicals that represent products in this category does not exist. Therefore, calculated and measured data 

have been identified and a technical discussion provided, where appropriate. The EPIWIN©

 (EPA, 2001) 

computer model, as discussed in the U.S. EPA document entitled "The Use of Structure-Activity Relationships 

(SAR) in the High Production Volume Chemicals Challenge Program" has been used to calculate physicalchemical properties of representative constituents of heavy fuel oils (EPA, 1999). 

The substances covered under this HPV testing plan are mixtures of differing compositions. Because of the 

diversity of compounds encompassing heavy fuel oils, it is not feasible to model the physicochemical endpoints 

for each potential compound. Where modeling was necessary to fulfill an endpoint, such estimates were made 

for common hydrocarbon structures (e.g., saturated, aromatic, olefinic and heterocyclic hydrocarbons) and 

range of molecular weight hydrocarbons (i.e., number of carbon atoms) known to be represented in heavy fuel 

oil mixtures. Since molecular weight and structural conformation determine in large part many of the physicochemical and fate processes, the modeled estimates for these isomeric structures are expected to represent 

potential ranges of values for all substances in the heavy fuel oil category. 
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Physico-Chemical Data

Melting Point

For complex mixtures like petroleum products, melting point may be characterized by a range of temperatures 

reflecting the melting points of the individual components. To better describe the physical phase or flow 

characteristics of petroleum products, the pour point is routinely used. The pour point is the lowest temperature 

at which movement of the test specimen is observed under prescribed conditions of the test (ASTM, 1999). 

Measured pour points ranged from –2 °C to 35 °C (CONSCI, 1992a,b; CONSCI, 1993a-d; Jokuty et al., 2002; 

NIPER, 1993a,b). Those values are consistent with the review by CONCAWE (1998), which stated pour points 

for these products are typically <30 °C. The differences in flow characteristics of heavy fuels are related to the 

composition of the crude oil from which they are produced, the variety of refining practices that result in products 

that go into heavy fuels, and the practice of adding a lighter “cutter stock” to heavy fuel oils to improve their 

flowable characteristics at low temperatures. Based on the cited data, heavy fuel oil streams and products will 

exist at ambient temperatures as dense, viscous oil. Those category members with the highest pour points will 

be characteristically solid to semi-solid substances, while those with the lowest pour points will have the greatest 

liquefaction. 

Summary: No additional testing is proposed. The pour points of various heavy fuel oils have been 

adequately measured. 

Boiling Point 

For complex petroleum mixtures, boiling points are expressed as ranges (i.e., distillation ranges) that are 

governed by the individual constituent hydrocarbons within the mixtures. Constituent molecules have individual 

boiling points, and boiling points increase as molecular weight increases. Streams within the Heavy Fuel Oil 

HPV category are highly diverse mixtures, and are produced from a variety of refining processes; processes 

including both atmospheric and vacuum distillation; therefore, the boiling ranges of the streams also would be 

expected to vary widely. Based on CAS definitions for the refining streams in this category, boiling points can 

range from 121 to 600 °C (EPA, 2004). Actual boiling ranges for any of the heavy fuel oil streams will depend 

upon source of the feedstock and the refining process. Boiling ranges reported in various literature sources 

such as material safety data sheets (Sinclair Oil Corp; Total UK Ltd., 2003; and TFMM, 2001), governmentsponsored databases (ECB, 2000; Jokuty et al., 2002), and the American Petroleum Institute (API, 1987) lend 

support to the CAS-defined boiling range. 

Summary: No additional testing is proposed. Products within this category vary with respect to their 

distillation ranges and specific ranges depend upon the hydrocarbon composition of the feedstocks from which 

they are produced. Values cited provide typical ranges for the distillation of these materials. 

Vapor Pressure

Few vapor pressure measurements are available for heavy fuel oils; therefore, the EPIWIN (EPA, 2001) 

computer model was used to estimate vapor pressures for representative components of these substances. For 

heavy fuel oil mixtures, the total vapor pressure is the sum of the partial pressures of the individual components 

(Dalton’s Law of Partial Pressures), while the partial pressure of an individual constituent is a product of the 

vapor pressure of the pure material times its mole fraction in the mixture (Raoult’s Law). Therefore, for complex 

mixtures such as heavy fuel oils, the partial pressures of individual constituents may be quite low. 

The heavy fuel oil category is composed of many different refining streams, and the vapor pressures of such 

substances will vary with the source of the crude and the refining method used. Measured values of <100 Pa 

(Total UK Ltd, 2003) and >500 Pa (ECB, 2000) for two heavy fuel oil streams reflected this variability. Vapor 

pressure estimates made using EPIWIN©

 version 3.10 (EPA, 2001) for constituent hydrocarbons representing 

paraffinic, olefinic, naphthenic, aromatic, and polar/heterocyclic components in heavy fuel streams bounded the 

measured data. Vapor pressure estimates of low molecular weight hydrocarbons (C7 – C11) of varying 

isomeric structures ranged from 7 Pa to 9 x 103

 Pa. As molecular weights increased, vapor pressure estimates 

decreased. Estimates for the high molecular weight constituents (C38 – C50) ranged from 2 x 10-7 Pa to 5 x 10-

17 Pa. The modeled data represent a potential vapor pressure range for the hydrocarbon constituents expected 

to occur in all subcategories of heavy fuel oils. 
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Summary: No additional testing is proposed. The vapor pressures of representative hydrocarbon 

constituents of heavy fuel oils have been adequately characterized. Measured data reflect the variability 

expected for substances in this category. 

Partition Coefficient

In mixtures such as the heavy fuel oils, the percent distribution of the hydrocarbon groups (i.e., paraffins, 

naphthenes, olefins, aromatics, polar/heterocyclics) and the carbon chain lengths determines in-part the 

partitioning characteristics of the mixture. Generally, hydrocarbons with fewer carbon atoms tend to have lower 

partition coefficients than those with higher carbon numbers (CONCAWE, 2001). However, due to their 

complex composition, unequivocal determination of the log Kow of the hydrocarbon mixtures cannot be made. 

Rather, partition coefficients of representative hydrocarbon types covering the range of carbon atoms found in 

substances in this category were modeled using the EPIWIN©

, version 3.10 computer model (U.S. EPA, 2001). 

The isomeric structures and numbers of carbon atoms were selected because they are representative of the 

types and molecular weights of hydrocarbon compounds found in heavy fuel oils. Therefore, the estimated 

values represent the potential range of values for partition coefficient for hydrocarbon constituents in this 

category. The estimates show log Kow values to range from 1.7 to 25. Standardized methods for measuring 

partition coefficient are analytically limited to substance up to log Kow ~4, or occasionally 5 (OECD, 1995). An 

estimation method is available for log Kow up to 6 (OECD, 1989). Based on the estimated values determined 

by EPIWIN©

, available analytical methods begin to fail for hydrocarbon compounds that contain roughly 15 to 20 

carbon atoms. The modeled data represent a potential log Kow range for the hydrocarbon constituents 

expected to occur in all subcategories of heavy fuel oils. 

Summary: No additional modeling is proposed. Partition coefficients (Kow) of 1.7 to 25 were calculated for 

representative hydrocarbon components of heavy fuel oils. 

Water Solubility 

When released to water, dissolution of the water-soluble constituents in heavy fuel oils will depend upon 

environmental factors affecting the mixing and weathering of the substance. Lower molecular weight 

components that have the highest solubilities also have appreciable vapor pressures and thus would tend to 

both dissolve and volatilize from the surface. Under controlled conditions with minimal opportunity for 

volatilization, the water solubility of heavy fuel oil no. 6 was measured to be 6.26 mg/l (Shiu et al., 1990). 

Additional supporting data gave a range of water solubilities from 0.4 to 6.3 mg/l (Suntio et al., 1986; Anderson 

et al., 1974; MacLean and Doe, 1989). Because blended fuels are composed of the refining streams from which 

they are produced, these solubility values are expected to approximate the water solubility for all substances 

within the heavy fuel oil subcategories. Specific solubility values for heavy fuels oils and the refining streams 

are dependent upon the composition of the crude oil and the refining process that it undergoes. Calculated and 

measured water solubilities differ for individual components of complex petroleum substances. At any particular 

loading rate, aqueous concentrations of each component are a function of relative volume of aqueous and 

petroleum phases, partition coefficient between phases, amount of component present and the maximum water 

solubility of each component. 

Summary: No testing modeling is proposed. Reported water solubility values for heavy fuel oils ranged 

from 0.4 to 6.3 mg/l. 

Environmental Fate Data

Photodegradation

The direct aqueous photolysis of an organic molecule occurs when it absorbs sufficient light energy to result in a 

structural transformation. Only light energy at wavelengths between 290 and 750 nm can result in 

photochemical transformations in the environment, although absorption is not always sufficient for a chemical to 

undergo photochemical degradation. Saturated and one-ring aromatic hydrocarbons do not show absorbance 

in the 290 to 800 nm range and would not be expected to be directly photo-degraded. Polyaromatic 

hydrocarbons (PAHs), on the other hand, have shown absorbance of the 290 to 800 nm range of light energy 

and are capable of being degraded by ultraviolet radiation (Fasnacht and Blough, 2002). The degree and rate 

at which these compounds photo-degrade depends upon whether conditions allow penetration of light with 
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sufficient energy to effect a change. In laboratory experiments, ultraviolet illumination of thin films of heavy fuel 

oil led to disappearance of polyaromatic compounds (Garrett et al., 1998). The loss was more pronounced for 

larger polycyclic species and the more alkylated forms of the parent hydrocarbon. This pattern of loss also was 

demonstrated in situ, where disappearance of PAHs on painted granite panels placed in an intertidal marine 

location was greatest for larger and more alkylated species (Jezequel, et al. 2003). 

Hydrocarbon components in heavy fuel oils are subject to indirect photodegradation within the tropospheric 

layer of the atmosphere. Indirect photodegradation is the reaction with photosensitized oxygen in the 

atmosphere in the form of hydroxyl radicals (OH) and other oxygen containing radicals (e.g., NO3). The 

potential to undergo indirect photodegradation estimated using the atmospheric oxidation potential (AOP) model 

subroutine (AOPWIN V1.90) in EPIWIN©

 (EPA, 2001), which calculates a chemical half-life and an overall OH 

reaction rate constant based on a 12-hour day and a given OH concentration. Atmospheric oxidation half-lives 

were calculated for the various molecular weight and isomeric structures representing constituent hydrocarbons 

(paraffins, naphthenes, olefins, aromatics, and polar/heterocyclics) in heavy fuel oils. Structures and molecular 

weights of selected constituents were chosen on the basis of carbon number as identified in the category 

substances and known hydrocarbon composition of heavy fuel oils. Therefore, the estimated values identify a 

potential AOP range for substances in the heavy fuel oil category. AOP half-lives for heavy fuel oil hydrocarbon 

constituents ranged from <0.1 day to 5.2 days. The modeled data represent a potential range of 

photodegradation half-lives for the hydrocarbon constituents expected to occur in all substances in the heavy 

fuel oil category. 

Summary: No additional modeling is proposed. Atmospheric half-lives of <0.1 to 5.2 days have been 

calculated for representative hydrocarbon components of heavy fuel oils. 

Stability in Water

Chemicals that have a potential to hydrolyze include alkyl halides, amides, carbamates, carboxylic acid esters 

and lactones, epoxides, phosphate esters, and sulfonic acid esters (Harris, 1982). Because heavy fuel oils do 

not contain significant levels of these functional groups, materials in the heavy fuel oils category are not subject 

to hydrolysis. 

Summary: Computer modeling will not be conducted for materials in the heavy fuel oils category 

because they do not undergo hydrolysis. 

Chemical Transport and Distribution in the Environment (Fugacity Modeling)

Fugacity-based multimedia modeling provides basic information on the relative distribution of chemicals 

between selected environmental compartments (e.g., air, water, soil, sediment, suspended sediment and biota). 

The US EPA has agreed that computer-modeling techniques are an appropriate approach to estimating 

chemical partitioning (fugacity is a calculated, not measured endpoint). A widely used fugacity model is the 

EQC (Equilibrium Criterion) model (Trent University, 1999). The EQC model is a Level 1 (i.e., steady state, 

equilibrium, closed system and no degradation) model that utilizes the input of basic chemical properties 

including molecular weight, vapor pressure, and water solubility to calculate distribution within a standardized 

regional environment. EPA cites the use of this model in its document “Determining the Adequacy of Existing 

Data” that was prepared as guidance for the HPV chemicals program (U.S. EPA, 1999). 

Based on the physical-chemical characteristics of component hydrocarbons in heavy fuel oils, the lower 

molecular weight components are expected to have the highest vapor pressures and water solubilities, and the 

lowest partition coefficients. These factors enhance the potential for distribution in the environment. To gain an 

understanding of the potential transport and distribution of heavy fuel oil components, the EQC model was used 

to characterize the environmental distribution of hydrocarbons having different molecular weight and isomeric 

structures. Structures and molecular weights of selected constituents were chosen on the basis of carbon 

number as identified in the category substances and known and estimated hydrocarbon composition of heavy 

fuel oils (Potter and Simmons, 1998; Quann and Jaffe, 1992; Saeger and Jaffe, 2002). Therefore, the estimated 

values identify the potential environmental distribution for component hydrocarbons in the Heavy Fuel Oil 

Category. 
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Partitioning behavior of constituent hydrocarbons of substances in the Heavy Fuel Oil Category depends largely 

on molecular weight, with smaller compounds (e.g., 7 to 12 carbon atoms) partitioning to the air or water 

according to their vapor pressure or water solubility properties. In the atmosphere they are expected to degrade 

rapidly via indirect photodegradation processes, while water soluble components are subject to biodegradation. 

Once hydrocarbons attain a size of approximately 20 carbon atoms, their low vapor pressure and water 

solubility prevent their partitioning to air or dissolving in water. Much real-world information has been gained 

from studies on heavy fuel oil spills (Fuel oil #6 or Bunker C) since this oil is carried by all cargo ships and is the 

most frequently spilled oil (Jezequel et al. 2003). When spilled on water, heavy fuel oil usually spreads into 

thick, dark colored slicks that will often breakup into discrete patches and tar balls (NOAA, 2004). Only the 

lowest molecular weight fractions would be expected to disperse into the water column, and only 5-10% of the 

material is expected to evaporate within the first few hours of a spill. The specific gravity of a particular fuel oil 

may vary from 0.95 to 1.03; thus, spilled oil can float, suspend, or sink (NOAA, 2004). Small changes in water 

density may dictate whether the oil will sink or float. With time and the effects of weathering, heavy fuel oil 

attains a tar-like consistency, and these fractions will become incorporated into soil or bottom sediments where 

they will undergo slow to moderate biodegradation. Overall, the principle routes of weathering of spilled heavy 

fuel include physical removal, dissolution, photo-oxidation, and biodegradation (Jezequel, et al. 2003). 

Summary: No further modeling is proposed. Fugacity-based computer modeling has been done for 

representative constituent hydrocarbon components of heavy fuel oils. 

Biodegradation

Extensive research on oil degradation in marine environments indicates that virtually all kinds of oil are 

susceptible to microbial oxidation. When a heavy fuel oil is spilled, shoreline microbial communities respond 

quickly to the oiling, with numbers of hydrocarbon-degrading microbes and mineralization potentials increasing 

after exposure (Leahy and Colwell, 1990). The rate of mineralization is influenced by microbial characteristics 

(e.g., species), and environmental factors such as available nutrients, oxygen, temperature and degree of 

dispersion (Mulkins-Phillips and Stewart, 1974; Rashid, 1974; Prince, 2002; Garrett, et al., 2003). In marine 

systems, degradation is most enhanced by the addition of nutrients (nitrogen and phosphorus), as these are 

considered most limiting in seawater (Richmond et al., 2001). In general, due to the high viscosity of heavy 

fuels, their tendency to slowly weather into discrete tar balls, and the eventual incorporation of those substances 

into soil/sediment can physically isolate and prevent dispersion and microbial attack (Richmond et al., 2001; 

Prince et al., 2003). However, over time, component hydrocarbons are depleted through selective 

biodegradation (Lee, et al. 2003). This structure-related trend shows hydrocarbons in order of increasing 

difficulty for biodegradation to be: 1) n-alkanes, 2) isoalkanes, 3) alkenes, 4) monoaromatic alkylbenzenes, 5) 

polyaromatic compounds, and 6) high molecular weight cycloalkanes (Bartha and Atlas, 1977; Potter and 

Simmons, 1998). Less is known about the biodegradability of polar components in oils, which are collectively 

known as asphaltenes and resins. Many of these have molecular weights of 2000 to 5000 and show little 

degradation; hence they can persistent in the environment for a long time (Prince, 2002; Prince et al., 2003). 

In standard 28-day studies, heavy fuel oils would not be expected to be readily biodegradable. In one study, 

Walker et al. (1975) measured an 11% biodegradation of Bunker C fuel oil over 28 days when incubated with a 

mixed culture of estuarine bacteria in a nutrient medium. Based on the current understanding of hydrocarbon 

biodegradability, constituents in heavy fuel oils would be expected to biodegrade over time. 

Summary: No additional testing is proposed. A technical discussion of hydrocarbon biodegradation based 

on reviews of available literature was incorporated in a robust summary format. 

EVALUATION OF EXISTING ECOTOXICITY DATA AND PROPOSED TESTING 

Various ecotoxicity studies on heavy fuel oils have been reported using different means of test substance 

exposures. These have been reviewed and reported by CONCAWE (1998). For the assessment of ecotoxicity 

of poorly water soluble mixtures of hydrocarbons as found in petroleum products, the generally accepted 

procedure is to report results expressed in terms of the "loading rate" (OECD, 2000). The loading rate is defined 

as the amount of the product that is equilibrated with the aqueous test medium, and the aqueous phase at 

equilibrium is termed the water-accommodated fraction (WAF) for the specific loading rate. Toxicological 

endpoints such as the LL50 or EL50 are used to express the loading rate of the product lethal to or produce a 

specific effect in 50% of the test organisms. Exposures may be prepared as oil-water dispersions (OWDs), 
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• 

• 

• 

where the insoluble petroleum fractions remain in the exposure solutions. This method also results in an 

expression of the concentration of the applied product (i.e., mg test substance/l), but the methodology does not 

prevent potential adverse effects to the organisms due to physical entrapment. Small species appear to be 

more susceptible than large species. Water-soluble fractions (WSFs) and their dilutions also may be reported in 

ecotoxicity studies. Ecotoxicity endpoints based on water-soluble fractions have been reported to range from 

0.9 mg/l to >4.5 milligrams total petroleum hydrocarbons (TPH)/l (MacLean and Doe, 1989; Jokuty et al., 2002). 

These preparations are expressed in terms of the measured concentrations of hydrocarbons in solution but do 

not allow the ecotoxicity of the product to be expressed in terms of the amount of that product required to 

produce a particular effect. Such results are not comparable to results obtained under WAF or OWD 

preparation methods. 

For the assessment of the ecotoxicity of heavy fuel oils, the category substances are considered as a single 

group, and the potential for any category member to elicit adverse effects in aquatic organisms is attributed to 

the solubility of the constituent hydrocarbons in that member. This is valid because petroleum hydrocarbons 

elicit effects through a common mode of toxicity termed non-polar narcosis (Peterson, 1994; van Wezel and 

Opperhuizen, 1995), which is produced by the soluble hydrocarbon fractions in aqueous preparations. Fuels 

having molecular weight hydrocarbons predominately higher than the solubility “cut-off” for acute toxicity show 

no measurable acute toxicity (CONCAWE, 2001). The solubility cut-off varies with the hydrocarbon structure; 

thus, for paraffinic hydrocarbons the solubility cut-off occurs at about C10, while for alkylbenzenes it is about 

C14 (CONCAWE, 2001). Other individual components contribute to toxicity, but as molecular weight increases, 

solubility declines, as does toxicity. 

Petroleum streams in the heavy fuel oil category generally consist of hydrocarbon molecules having 20 to 50 

carbon atoms, although some streams in this category have low-end carbon atoms from 7 to 15. Heavy fuel oils 

also may be blended with gas oils or similar low viscosity fuels to meet market specifications. This makes a 

highly heterogeneous group of petroleum substances that spans a wide range of molecular weight fractions. 

Based on distillation and carbon number ranges of the category members, existing data on heavy fuel oil 

ecotoxicity may not represent the ecotoxicity of category members that contain a relatively high proportion of 

hydrocarbons below the solubility cut-off for acute toxicity (i.e., those having hydrocarbons with low-end carbon 

numbers of 7 to 15 and low initial boiling points). In spite of the heterogeneity of the heavy fuel oil category, the 

constituents in heavy fuels are generic hydrocarbon structures (e.g., saturates, aromatics, etc.) represented in 

other petroleum HPV categories. Therefore, the Testing Group proposes to use ecotoxicity data from the 

following HPV categories to read-across to cover the lightest heavy fuel oil streams: 

Referenced data cited in the Kerosene/Jet Fuel Test Plan and robust summaries (API, 2003a), 

Referenced data cited in the Gas Oils Test Plan and robust summaries (API, 2003b), and 

Data generated from the proposed testing of select gas oils streams high in saturated and aromatic 

hydrocarbons. 

Kerosenes and jet fuels are composed of saturated and aromatic hydrocarbon compounds having structures 

and molecular weights similar to the light-end components in heavy fuel oils. Hence, the ecotoxicity of those 

substances provides conservative estimates of the ecotoxicity of the lightest heavy fuel oils. Blended heavy fuel 

oils also contain a fraction of heterocyclic compounds that show solubility and molecular weight relationships 

similar to other hydrocarbons (i.e., solubility decreases with increasing molecular weight). These compounds 

may contribute to aquatic toxicity, and their contribution is integrated in the current heavy fuel oil test data. 

When all ecotoxicity data sets are combined, the ranges of endpoint values are expected to cover the potential 

ecotoxicity of all category members of the heavy fuel oil category that contain various fractions of saturated, 

aromatic, and heterocyclic compounds. 

Robust summaries for kerosene and gas oils ecotoxicity data cited below may be found in the HPV submissions 

for Kerosenes/Jet Fuel Test Plan (API, 2003a) and Gas Oils Test Plan (API, 2003b). 

Acute Toxicity to Fish

Data for heavy fuel oils showed slight or no acute toxicity to fish when tested as either WAFs or OWDs. Shell 

(1997a,b) tested WAFs of a “light” and a “heavy” residual fuel oil (CAS No. 68476-33-5) and found the 96-hour 

LL50s for exposures to rainbow trout (Oncorhynchus mykiss) to be between 100 mg/l and 1000 mg/l for the 
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“heavy” residual fuel oil and >1000 mg/l for the “light” residual fuel oil. Mobil (1987a) obtained a 96-hour LL50 of 

>10,000 mg/l when bluegill (Lepomis macrochirus) were exposed to OWDs of No. 6 fuel oil. 

Fish LL50 values for kerosene/jet fuel tested as WAFs were between 10 mg/l and 100 mg/l (API, 2003a). LL50 

values for distillate fuels cited in the gas oil HPV test plan ranged from 3.2 to 65 mg/l (API, 2003b). 

Acute Toxicity to Aquatic Invertebrates

Data for invertebrates (Daphnia magna) showed a similar range of sensitivities as fish. In testing WAFs of the 

“light” and “heavy” residual fuels, Shell (1997c,d) found the EL50 of the “light” to be >1000 mg/l while that of the 

“heavy” to between 220 mg/l and 460 mg/l. Mobil (1987b) exposed daphnids to solutions in which oil was 

coated on the inside surface of the test vessels. Exposures done in this manner resulted in no immobilized 

daphnids at the maximum loading rate of 10,000 mg/l. 

Invertebrate EL50 values for kerosene/jet fuel tested as WAFs were ranged 1.4 mg/l to <89 mg/l (API, 2003a). 

EL50 values for distillate fuels cited in the gas oil HPV test plan ranged from 2.0 to <300 mg/l (API, 2003b). 

Toxicity to Algae

Shell (1997e,f) reported the EL50 values based on growth rate and biomass for 72-hour exposures of 

Raphidocelis subcapitata to a “light” and a “heavy” residual fuel oil. Tests were run in sealed vessels without 

headspace. For the “light” material, the ELr50 (rate-based) was concluded to lie between 100 mg/l and 300 mg/l 

while the ELb50 (biomass-based) was between 3 mg/l and 10 mg/l. This contrasted somewhat with toxicity 

endpoints for the “heavy” residual fuel oil. Those tests gave ELr50 and ELb50 values of between 30 mg/l and 

100 mg/l. Mobil (1987c) coated the surface of test flasks with No. 6 fuel oil and measured algal (R. subcapitata) 

biomass over 96 hours. Tests vessels were plugged with cotton, but otherwise allowed air exchange. Growth 

inhibition at the maximum loading rate of 10,000 mg/l was 47.5%, but the authors concluded that the ELb50 was 

>5,000 mg/l. Inhibition of 22% to 27% occurred in the lowest three test levels, and the authors suggested 

physical obstruction of light penetration may have affected cell growth. 

In 96-hour exposures using WAFs of kerosene, EL50 values ranged from 5.0 to 6.2 mg/l when based on 

inhibition of growth rate, and ranged from 5.9 mg/l to 11 mg/l when based on biomass (API, 2003a). In 72-hour 

WAF exposures, EL50 values based on growth rate and biomass fell within the range of 10 mg/l to 30 mg/l (API, 

2003a). 

Algae exposed to WAFs of distillate fuels produced 72-hour EL50 values based on growth rate that ranged from 

2.2 to <46 mg/l, while values based on algal biomass ranged from 1.8 to 25 mg/l (API, 2003b). 

The heavy fuel oil, kerosene, and gas oil ecotoxicity data described above are listed in the following Table 2. 

Together, these data encompass values that represent the potential toxicity of all members in the Heavy Fuel 

Oil HPV category. 

Table 2. Ecotoxicity Data for Heavy Fuel Oil, Kerosene/Jet Fuel Oil, and Gas Oil.

Species Material 

Exposure 

Type 

Effect / concentration 

(mg/l) Reference 

FISH

Heavy Fuel Oil 
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Rainbow trout 

(Oncorhynchus mykiss) 

Rainbow trout 

(O. mykiss) 

Bluegill 

(Lepomis macrochirus) 

CAS No. 68476-33-5 (light) 

residual fuel oil 

CAS No. 68476-33-5 

(heavy) residual fuel oil 

No. 6 fuel oil 

WAF 

WAF 

OWD 

96-h LL50 = >1000 

96-h LL50 = 100 – 1000 

96-h LL50 = >10,000 

Shell, 1997a 

Shell, 1997b 

Mobil, 1987a 

Kerosene/Jet Fuel 

Various species Various WAF 96-h LL50 = 

18 

20 

10 – 100 

25 

API, 2003a 

Gas Oil 

Various species Distillate fuels WAF 96-h LL50 = 

57 

3.2 

6.6 

57 

21 

65 

API, 2003b 

INVERTEBRATES

Heavy Fuel Oil 

Daphnia magna 

D. magna 

D. magna 

CAS No. 68476-33-5 (light) 

residual fuel oil 

CAS No. 68476-33-5 

(heavy) residual fuel oil 

No. 6 fuel oil 

WAF 

WAF 

OWD 

48-h EL50 = >1000 

48-h EL50 = 220 – 460 

48-h EL50 = >10,000 

Shell, 1997c 

Shell, 1997d 

Mobil, 1987b 

Kerosene/Jet Fuel

D. magna Various WAF 48-h EL50 = 

21 

1.4 

40 – 89 

1.9 

API, 2003a 

Gas Oil 
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D. magna Distillate fuels WAF 48-h EL50 = 

7.8 

5.3 

14 

42 

2.0 

210 

68 

13 

100 – 300 

13 

6.4 

36 

9.6 

API, 2003b 

ALGAE

Heavy Fuel Oil

Raphidocelis 

subcapitata 

R. subcapitata 

R. subcapitata 

CAS No. 68476-33-5 (light) 

residual fuel oil 

CAS No. 68476-33-5 

(heavy) residual fuel oil 

No. 6 fuel oil 

WAF 

WAF 

OWD 

96-h ELr50 = 100 – 300 

96-h ELb50 = 3 – 10 

96-h ELr50 = 30 – 100 

96-h ELb50 = 30 – 100 

96-h ELb50 = >5,000 

Shell, 1997e 

Shell, 1997f 

Mobil, 1987c 

Kerosene/Jet Fuel 

R. subcapitata Various WAF 96-h ELr50 = 

6.2 

5.0 

96-h ELb50 = 

11 

5.9 

72-h ELr50 = 

10 – 30 

72-h ELb50 = 

10 – 30 

API, 2003a 
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Heavy Fuel Oils 

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Gas Oil 

R. subcapitata Distillate fuels WAF 72-h ELr50 = 

2.9 

2.2 

78 

22 

22 – 46 

72-h ELb50 = 

1.8 

2.2 

25 

10 

10 – 22 

API, 2003b 

WAF = Water Accommodated Fraction 

OWD = Oil-Water Dispersion 

Summary. No further testing is proposed. The ecotoxicity data for heavy fuel oils combined with data for 

kerosene/jet fuel and gas oils HPV categories provides a range of ecotoxicity endpoints expected to encompass 

the ecotoxicity of all members of the heavy fuel oils HPV category. 
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MATRIX OF AVAILABLE DATA AND PROPOSED TESTING 

Table 3. Matrix of Available Data and Proposed Testing 

REFINERY Streams Subcategories Finished

Residual 

Fuels 

TEST

Atmospheric Residue Atmospheric Distillate Vacuum Residue Vacuum Distillate Cracked Residue Cracked Distillate Reformer Residue Residual Fuel Oil 

Physical/Chemical 

Properties7

Melting Point Ad 

Boiling Point Ad

Vapor Pressure Ad

Water Solubility Ad 

Partition coefficient (log Kow) Ad 

Ecotoxicity7

Algae Growth Inhibition RA9

Acute Freshwater Invertebrate RA9

Acute Freshwater Fish RA9

Environmental Fate7

Biodegradation Ad

Stability in Water NA

Photodegradation (estimate) Ad 

Transport and Distribution Ad

Mammalian Toxicity 

Acute Ad RA1 RA2 Ad Ad Ad RA3 Ad 

Repeat-dose Ad Ad Ad2 Ad Ad Ad Test5 Ad 

Reprod/Develop Ad Ad Ad Ad Ad Ad Test5 Test6

Genotoxicity, in vitro Test8 Test8 Ad Ad Ad Test8 Test8 Test8

Genotoxicity, in-vivo RA4 RA1 RA2 Ad Ad RA4 RA4 RA4

Ad = Adequate, indicates adequate existing data. 

NA = Not Applicable, the endpoint is not applicable” due to inherent physical and/or chemical properties. 

A technical discussion was developed to address such endpoints.

1

 read across from API HPV Gas Oils Test Plan 

2

 read across from API HPV Asphalt Test Plan 

3

 read across from API HPV Aromatic Extracts Test Plan Test Plan 

4

 read across from in-vitro genotoxicity assay 5

 OECD 422 repeat dose/reproductive/developmental screen 6

 OECD 421 reproductive/developmental screen 

7 For the assessment of the physical/chemical properties, ecotoxicity, and environmental fate, the 

category substances are considered as a single group, and the potential for any category member to 

elicit adverse effects in aquatic organisms is attributed to the solubility of the constituent hydrocarbons 

in that member 

8

 Modified Ames & in vitro chromosomal aberration (OECD 473). 
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API (American Petroleum Institute). 1980a. Acute toxicity tests API 78-6 #6 Heavy fuel oil (API gravity 

11.7/2.7%S. API Med. Res. Publ. 27-32814, Washington D.C. 

API (American Petroleum Institute). 1980b. Acute toxicity tests API 78-7 #6 Heavy fuel oil (API gravity 

17.1/0.8%S. API Med. Res. Publ. 27-32774, Washington D.C. 

API (American Petroleum Institute). 1980c. Acute toxicity tests API 78-8 #6 Heavy fuel oil (API gravity 

23.1/0.2%S. API Med. Res. Publ. 27-32816, Washington D.C. 

API (American Petroleum Institute). 1980d. Acute toxicity tests API 79-2 #6 Heavy fuel oil (API gravity 

5.2/1.2%S. API Med. Res. Publ. 27-32813, Washington D.C. 

API (American Petroleum Institute). 1982. Acute toxicity studies catalytically cracked clarified oil Sample 81-

15. API Med. Res. Publ. 30-31854, Washington D.C. 

API (American Petroleum Institute). 1984. Dermal sensitization study in guinea pigs closed patch technique 

Catalytic cracked clarified oil API sample 81-15. API Med. Res. Publ. 31-31417, Washington D.C. 

API (American Petroleum Institute). 1985a. CHO/HGPRT Mammalian cell forward gene mutation assay of API 

81-15. API Med. Res. Publ. 32-32118, Washington D.C. 

API (American Petroleum Institute). 1985b. Evaluation of the potential of RO-1, 81-15 and PS8-76D5-SATto 

induce unscheduled DNA synthesis in primary rat hepatocyte cultures. API Med. Res. Publ. 32-32407, 

Washington D.C. 

API (American Petroleum Institute). 1985c. Evaluation of the potential of RO-1, 81-15, and PS8-76D-SATto 

induce unscheduled DNA synthesis in the in vivo-in vitro hepatocyte DNA repair assay. API Med. Res. Publ. 

32-32406, Washington D.C. 

API (American Petroleum Institute). 1985d. In vivo sister chromatid exchange assay API 81-15, catalytically 

cracked clarified oil (CAS 64741-62-4). API Med. Res. Publ. 32-32254, Washington D.C. 

API (American Petroleum Institute). 1985e. Mutagenicity evaluation studies in the rat bone marrow cytogenetic 

assay in the mouse lymphoma forward mutation assay catalytic cracked clarified oil API sample 81-15. API 

Med. Res. Publ. 32-30534, Washington D.C. 

API (American Petroleum Institute). 1985f. Sister chromatid exchange assay in Chinese Hamster Ovary (CHO) 

cells. Catalytic cracked clarified oil; API sample 81-15 CAS 64741-62-4. API Med. Res. Publ. 32-32750, 

Washington D.C. 

API (American Petroleum Institute). 1986b. Morphological transformation of BALB/3T3 Mouse embryo cellsAPI 

81-15, Catalytically cracked clarified oil (CAS 64741-62-4). API Med. Res. Publ. 33-32638, Washington D.C. 

API (American Petroleum Institute). 1986c. Salmonella/Mammalian-microsome plate incorporationmutagenicity 

assay (Ames test). API Med. Res. Publ. 33-30599, Washington D.C. 

 

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Fuel Oil. Report No. ATX-86-0008. Salt Lake City UT. 

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Report No. ATX-88-0086, study No. 64707. Salt Lake City, UT 

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Can. J. Microbiol. 22:598-602. 
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APPENDIX A. 

CAS Numbers and Definitions of Category Members 

The CAS numbers and definitions of refinery streams, including those in the heavy fuel oils category, were 

developed in response to Section 8(b) of the Toxic Substances Control Act. This section of TSCA required 

identification and registration with the Environmental Protection Agency before July 1979 of each “chemical 

substance” being manufactured, processed, imported or distributed in commerce. Due to analytical limitations 

and known variability in refinery stream composition, identification of every specific individual molecular 

compound in every refinery process stream under all processing conditions was impossible. Recognizing these 

problems, the American Petroleum Institute (API) recommended to the EPA a list of generic names for refinery 

streams consistent with industry operations and covering all known processes used by refiners. The list, 

including generic names, CAS numbers and definition of each stream, was published by the EPA as “Addendum 

I, Generic Terms Covering Petroleum Refinery Process Streams.” 

Because of the variability inherent in the processing of petroleum materials, the definitions API developed for the 

CAS numbers are qualitative in nature, written in broad, general terms. The definitions often contain only 

ranges of values for carbon numbers, with little if any quantitative analytical information or concern for possible 

compositional overlaps. As a result, the CAS descriptions are not useful in determining the exact composition of 

any specific refinery stream. 

Residual Fuel Oils

68476-33-5 

Fuel oil, residual 

The liquid product from various refinery streams, usually residues. The composition is complex and 

varies with the source of the crude oil. 

68553-00-4 

Fuel oil, no. 6 

A distillate oil having a minimum viscosity of 900 SUS at 37.7°C (100°F) to a maximum of 9000 SUS 

at 37.7°C (100°F).

Process Subcategories

Atmospheric Residual 

64741-45-3 

Residues (petroleum), atm. Tower 

A complex residuum from the atmospheric distillation of crude oil. It consists of hydrocarbons having 

carbon numbers predominantly greater than C20 and boiling above approximately 350 °C (662°F). 

This stream is likely to contain 5 wt % or more of 4- to 6-membered condensed ring aromatic 

hydrocarbons. 

64742-78-5 

Residues (petroleum), hydrodesulfurized atmospheric 

 A complex combination of hydrocarbons obtained by treating an atmospheric tower residuum with 

hydrogen in the presence of a catalyst under conditions primarily to remove organic sulfur 

compounds. It consists of hydrocarbons having carbon numbers predominantly greater than C20 

and boiling above approximately 350°C (662°F). This stream is likely to contain 5 wt % or more of 4- 

to 6-membered condensed ring aromatic hydrocarbons. 

68333-22-2 

Residues (petroleum), atmospheric 

A complex residuum from atmospheric distillation of crude oil. It consists of hydrocarbons having 
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carbon numbers predominantly greater than C11 and boiling above approximately 200°C (392°F). 

This stream is likely to contain 5 wt.% or more of 4- to 6-membered condensed ring aromatic 

hydrocarbons. 

68607-30-7 

Residues (petroleum), topping plant, low-sulfur 

A low-sulfur complex combination of hydrocarbons produced as the residual fraction from the 

topping plant distillation of crude oil. It is the residuum after the straight-run gasoline cut, kerosene 

cut and gas oil cut have been removed. 

70592-79-9 

Residues (petroleum), atm. tower, light 

A complex residuum from the atmospheric distillation of crude oil. It consists of hydrocarbons having 

carbon numbers predominantly greater than C11 and boiling above approximately 200°C (392°F). 

This stream is likely to contain 5 wt % or more of 4- to 6-membered condensed ring aromatic 

hydrocarbons. 

68476-32-4 

Fuel oil, residues-straight-run gas oils, high-sulfur 

NONE 

Atmospheric Distillate

68410-00-4 

Distillates (petroleum), crude oil 

A complex combination of hydrocarbons produced by distillation of crude oil. It consists of 

hydrocarbons having carbon numbers predominantly in the range of C11 through C50 and boiling in 

the range of approximately 205°C to greater than 495°C (401°F to above 923°F). 

68783-08-4 

Gas oils (petroleum), heavy atmospheric 

A complex combination of hydrocarbons obtained by the distillation of crude oil. It consists of 

hydrocarbons having carbon numbers predominantly in the range of C7 through C35 and boiling in 

the range of approximately 121°C to 510°C (250°F to 950°F), 

Residual 

Vacuum Residual 

68512-62-9 

Residues (petroleum), light vacuum 

A complex residuum from the vacuum distillation of the residuum from the atmospheric distillation of 

crude oil. It consists of hydrocarbons having carbon numbers predominantly greater than C13 and 

boiling above approximately 230°C. 

70913-85-8 

Residues (petroleum), solvent-extd. vacuum distilled atm residuum 

A complex residuum produced by the solvent extraction of the vacuum distillate of the complex 

residuum from the atmospheric distillation of crude oil. 

Vacuum Distillate

64741-57-7 

Gas oils (petroleum), heavy vacuum 

A complex combination of hydrocarbons produced by the vacuum distillation of the residuum from 

atmospheric distillation of crude oil. It consists of hydrocarbons having carbon numbers 
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predominantly in the range of C20 through C50 and boiling in the range of approximately 350°C to 

600°C (662°F to 1112°F). This stream is likely to contain 5 wt. % or more of 4- to 6-membered 

condensed ring aromatic hydrocarbons. 

64742-59-2 

Gas oils (petroleum), hydrotreated vacuum 

A complex combination of hydrocarbons obtained by treating a petroleum fraction with hydrogen in 

the presence of a catalyst. It consists of hydrocarbons having carbon numbers predominantly in the 

range of C13 through C50 and boiling in the range of approximately 230°C to 600°C (446°F to 

1112°F). This stream is likely to contain 5 wt % or more of 4- to 6-membered condensed ring 

aromatic hydrocarbons. 

64742-86-5 

Gas oils (petroleum), hydrodesulfurized heavy vacuum 

A complex combination of hydrocarbons obtained from a catalytic hydrodesulfurization process. It 

consists of hydrocarbons having carbon numbers predominantly in the range of C20 through C50 

and boiling in the range of approximately 350°C to 600°C (662°F to 1112°F). This stream is likely to 

contain 5 wt. % or more of 4- to 6-membered condensed ring aromatic hydrocarbons. 

68955-27-1 

Distillates (petroleum), petroleum residues vacuum 

A complex combination of hydrocarbons produced by the vacuum distillation of the residuum from 

the atmospheric distillation of crude oil. 

70592-76-6 

Distillates (petroleum), intermediate vacuum 

A complex combination of hydrocarbons produced by the vacuum distillation of the residuum from 

atmospheric distillation of crude oil. It consists of hydrocarbons having carbon numbers 

predominantly in the range of C14 through C42 and boiling in the range of approximately 250°C to 

545°C (482°F to 1013°F). This stream is likely to contain 5 wt.% or more of 4- to 6-membered 

condensed ring aromatic 

70592-77-7 

Distillates (petroleum), light vacuum 

A complex combination of hydrocarbons produced by the vacuum distillation of the residuum from 

atmospheric distillation of crude oil. It consists of hydrocarbons having carbon numbers 

predominantly in the range of C11 through C35 and boiling in the range of approximately 250°C to 

545°C (482°F to 1013°F). 

70592-78-8 

Distillates (petroleum), vacuum 

A complex combination of hydrocarbons produced by the vacuum distillation of the residuum from 

atmospheric distillation of crude oil. It consists of hydrocarbons having carbon numbers 

predominantly in the range of C15 through C50 and boiling in the range of approximately 270°C to 

600°C (518°F to 1112°F). This stream is likely to contain 5 wt.% or more of 4- to 6-membered 

condensed ring aromatic hydrocarbons. 

Cracked Residual 

64741-62-4 

Clarified oils (petroleum), catalytic cracked (also listed in Olefins Panel Fuel Oils Category) 

A complex combination of hydrocarbons produced as the residual fraction from distillation of the 

products from a catalytic cracking process. It consists of hydrocarbons having carbon numbers 

predominantly greater than C20 and boiling above approximately 350°C (662°F). This stream is 

likely to contain 5 wt % or more of 4- to 6-membered condensed ring aromatic hydrocarbons. 
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Consortium Registration # 1100997 

64741-75-9 

Residues (petroleum), hydrocracked 

A complex combination of hydrocarbons produced as the residual fraction from distillation of the 

products of a hydrocracking process. It consists of hydrocarbons having carbon numbers 

predominantly greater than C20 and boiling above approximately 350°C (662°F). 

64741-80-6 

Residues (petroleum), thermal cracked 

A complex combination of hydrocarbons produced as the residual fraction from distillation of the 

product from a thermal cracking process. It consists predominantly of unsaturated hydrocarbons 

having carbon numbers predominantly greater than C20 and boiling above approximately 350°C 

(662°F). This stream is likely to contain 5 wt % or more of 4- to 6-membered condensed ring 

aromatic hydrocarbons. 

68187-58-6 

Pitch, petroleum, arom 

The residue from the distillation of thermal cracked or steam-cracked residuum and/or catalytic 

cracked clarified oil with a softening point from 40 degree C to 180 degree C (104 degree F to 356 

degree.F). Composed primarily of a complex combination of three or more membered condensed 

ring aromatic hydrocarbons. 

68478-17-1 

Residues (petroleum), heavy coker gas oil and vacuum gas oil 

A complex combination of hydrocarbons produced as the residual fraction from the distillation of 

heavy coker gas oil and vacuum gas oil. It predominantly consists of hydrocarbons having carbon 

numbers predominantly greater than C13 and boiling above approximately 230°C (446°F). 

68783-13-1 

Residues (petroleum) coker scrubber condensed-ring-aromatic-containing 

A very complex combination of hydrocarbons produced as the residual fraction from the distillation 

of vacuum residuum and the products from a thermal cracking process. It consists predominantly of 

hydrocarbons having carbon numbers predominantly greater than C20 and boiling above 

approximately 350°C (662°F). This stream is likely to contain 5 wt. % or more of 4- to 6-membered 

condensed ring 

Cracked Distillate 

64741-61-3 

Distillates (petroleum), heavy catalytic cracked 

A complex combination of hydrocarbons produced by the distillation of products from a catalytic 

cracking process. It consists of hydrocarbons having carbon numbers predominantly in the range of 

C15 through C35 and boiling in the range of approximately 260 °C to 500°C (500°F to 932°F). This 

stream is likely to contain 5 wt. % or more of 4- to 6-membered condensed ring aromatic 

hydrocarbons. 

64741-81-7 

Distillates (petroleum), heavy thermal cracked 

A complex combination of hydrocarbons from the distillation of the products from a thermal cracking 

process. It consists predominantly of unsaturated hydrocarbons having carbon numbers 

predominantly in the range of C15 through C36 and boiling in the range of approximately 260°C to 

480°C (500°F to 896°F). This stream is likely to contain 5 wt. % or more of 4- to 6-membered 

condensed ring aromatic hydrocarbons. 

68333-26-6 

Clarified oils (petroleum), hydrodesulfurized catalytic cracked 

A complex combination of hydrocarbons obtained by treating catalytic cracked clarified oil with 
June 17, 2004 Page 42 of 44 

Heavy Fuel Oils 

Consortium Registration # 1100997 

hydrogen to convert organic sulfur to hydrogen sulfide which is removed. It consists of 

hydrocarbons having carbon numbers predominantly greater than C20 and boiling above 

approximately 350°C (662°F). This stream is likely to contain 5 wt. % or more of 4- to 6-membered 

condensed ring aromatic hydrocarbons. 

68333-27-7 

Distillates (petroleum), hydrodesulfurized intermediate catalytic cracked 

A complex combination of hydrocarbons obtained by treating intermediate catalytic cracked 

distillates with hydrogen to convert organic sulfur to hydrogen sulfide which is removed. It consists 

of hydrocarbons having carbon numbers predominantly in the range of C11 through C30 and boiling 

in the range of approximately 205°C to 450°C (401°F to 842°F). It contains a relatively large 

proportion of tricyclic aromatic hydrocarbons. 

70955-17-8 

Aromatic hydrocarbons, C12-20 

A complex combination of hydrocarbons obtained from the distillation of biphenyl and naphthalene 

feedstocks. It consists predominantly of hydrocarbons having carbon numbers predominantly in the 

range of C12 through C20, such as alkylbenzenes, alkylnaphthalenes, indans, fluorenes, 

acenaphthalenes, phenanthrenes and anthracenes, and boiling in the range of approximately 

282.degree.C to 427.degree.C (540.degree.F to 800.degree.F). 

Reformer Residual

64741-67-9 

Residues (petroleum), catalytic reformer fractionator 

A complex combination of hydrocarbons produced as the residual fraction from distillation of the 

product from a catalytic reforming process. It consists of predominantly aromatic hydrocarbons 

having carbon numbers predominantly in the range of C10 through C25 and boiling in the range of 

approximately 160 °C to 400°C (320°F to 725°F). This stream is likely to contain 5 wt. % or more of 

4- or 6-membered condensed ring aromatic hydrocarbons. 

68478-13-7 

Residues (petroleum), catalytic reformer fractionator residue distn. 

A complex residuum from the distillation of catalytic reformer fractionator residue. It boils 

approximately above 399°C (750°F). 
June 17, 2004 Page 43 of 44 

Heavy Fuel Oils 

Consortium Registration # 1100997 

APPENDIX B. 

Links to Additional Resources 

Refining Processes: General Descriptions

http://www.chevron.com/about/learning_center/refinery 

http://www.lubrizol.com/lubetheory/default.htm 

http://www.orionrefining.com/flow.htm 

http://www.osha-slc.gov/dts/osta/otm/otm_toc.html 

http://www.shellglobalsolutions.com/base_oils/library/library.htm 

http://www.shell-lubricants.com/learningcenter/aboutoil.html 

http://www.shellus.com/welcome/history/hist_oil_main.html 

http://www.epa.gov/compliance/resources/publications/assistance/sectors/notebooks/petrefsnpt1.pdf 

http://www.mts.net/~dbrad1/base_oil.htm 

Petroleum Related Glossaries

http://www.caltex.com.au/products_glo.asp 

http://www.citgo.com/CommunityInvolvement/Classroom/Glossary.jsp 

http://www.epplp.com/gloss.html 

http://www.prod.exxon.com/exxon_productdata/lube_encyclopedia/ 

http://www.hellenic-petroleum.gr/english/glossary/gl_main.htm 

http://www.prod.exxon.com/exxon_productdata/lube_encyclopedia/ 

http://www.oilanalysis.com/dictionary 

http://www.orionrefining.com/glossary.htm 

http://www.gedolbear.com/glossary.htm

http://www.shellglobalsolutions.com/base_oils/glossary/a_g.htm 

http://www.ursa-texaco.com/English/glossary_a.html 

http://www.eia.doe.gov/pub/oil_gas/petroleum/data_publications/petroleum_marketing_annual/current/pdf/gloss

ary.pdf
June 17, 2004 Page 44 of 44 

Heavy Fuel Oils 

Consortium Registration # 1100997 

APPENDIX C. 

Robust Summary 

(Separate document)