Overview
TCAS has broad experience assessing the health effects of hydrocarbons[a]
Hydrocarbons are a class of organic chemical compounds containing only hydrogen
and carbon. Although hydrocarbons all possess structural similarities, there is
a vast spectrum of compounds and each has different physical, chemical and reactive
properties. Similarly, each type of hydrocarbon can affect human health in different
ways. Hydrocarbons include a wide range of toxic compounds, some of which can cause
cancer, respiratory problems, nervous system damage and a variety of adverse health
effects.
It is not possible to provide a comprehensive overview of hydrocarbon toxicology
in this brief section; however, the following hydrocarbons represent compounds with
which TCAS has acquired extensive experience over a period of more than
34 years and which have repeatedly appeared on our radar as recurring toxic and/or
causative agents. These include benzene, benzo[a]pyrene, BTEX, dioxins and PCBs,
LNAPL, PAHs, and petroleum products.
Click on any substance to view the corresponding entry.
Click to view other types of hazardous substances.
Benzene
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Chemical structure of benzene[b]
Benzene is a solvent used extensively as a gasoline additive and in a variety of
manufacturing processes for drugs, chemicals, plastics, rubber, elastomers,
phenol and acetone. A colorless, highly flammable, volatile organic chemical, benzene
is primarily introduced to the environment through industrial processes, air emissions
from burning coal and oil, vehicle exhaust, industrial discharge, spills, gasoline
leaks and improper disposal. Benzene is moderately soluble in water, highly mobile
in soil and readily leaches into groundwater.1
Acute effects of low-level benzene exposure (700–3,000 ppm) include drowsiness,
dizziness, rapid heart rate, headaches, tremors, confusion, and unconsciousness.
Ingestion of benzene in foods or liquids can cause vomiting, irritation of the stomach,
dizziness and sleepiness. Benzene also causes dermal irritation effects including
redness and sores, as well as damage to the cornea if introduced in the eyes. Brief
exposure (5–10 minutes) to high levels in air (10,000–20,000 ppm) can be fatal.
Chronic effects of benzene exposure include rapid heart rate convulsions, disruption
of blood production, anemia and damage to bone marrow . Long-term exposure can result
in acute myeloid leukemia (AML) and damage to the immune system.2
Both the U.S. EPA
and the International Agency for Cancer Research (IARC) have determined that benzene
is carcinogenic to humans. TCAS
has extensive experience in toxicologically assessing benzene exposures and remediation
issues in residential, environmental and industrial cases in both causative and
risk assessment scenarios. Please
contact our office for additional information.
Benzo[a]pyrene
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![Benzo[a]pyrene](images/000024m.jpg)
Benzo[a]pyrene[c]
Benzo[a]pyrene is a specific type of PAH (polycyclic aromatic hydrocarbon) which
is listed as a hazardous substance under CERCLA (the Comprehensive Environmental
Response, Compensation and Liability Act). It has been identified at 524 hazardous
waste sites on the National Priorities List (NPL) and is ranked number 8 out of
275 chemicals on U.S. EPA's Priority List of Hazardous Substances. Benzo[a]pyrene
is also listed as a drinking water contaminant and is one of the 20 chemicals included
in U.S. EPA’s "Persistent Bioaccumulative and Toxic Chemical Program."3
The most common routes of exposure are oral (through contaminated
drinking water) or the consumption of certain food products (such as charred meats)
or by eating foods grown in contaminated areas (air and/or soil). Aside from natural
releases to the environment (such as forest fires), benzo[a]pyrene is released via
anthropogenic sources including stoves/furnaces burning fossil fuels (especially
wood and coal), motor vehicle exhaust, cigarettes, and various industrial combustion
processes. Dermal exposure may occur from contact with soils or materials containing
soot, tar or crude petroleum products.4
Although human epidemiological studies are inconclusive, a vast number of animal
studies have demonstrated strong associations between benzo[a]pyrene and cancers.
The most recent U.S. EPA toxicological review (in draft form as of this writing)
notes multiple indications that benzo[a]pyrene targets the protective p53 gene,
which is a transcription factor that functions as a tumor suppressor. Studies in
multiple animal species demonstrate that benzo[a]pyrene is carcinogenic at multiple
tumor sites (alimentary tract, liver, kidney, respiratory tract, pharynx, and skin)
by all routes of exposure. Consequently, U.S. EPA presently classifies benzo[a]pyrene
as a "Probable Human Carcinogen" based on sufficient evidence of carcinogenicity
in animals, whereas IARC (the International Agency for Research on Cancer) presently classifies
benzo[a]pyrene as a "Group 1 Known Human Carcinogen."5
TCAS has regularly produced toxicological assessments involving benzo[a]pyrene
contamination in residential areas, as well as individual exposures involving both
B[a]P and other polycyclic aromatic hydrocarbons (see below). We have regularly
provided expert opinions and testimony over a period of more than 34 years on behalf
of both plaintiffs and defendants. Please contact our
office for additional information.
BTEX
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BTEX fate & transport[d]
BTEX refers to a compound consisting of benzene, toluene, ethylbenzene and xylene.
These volatile aromatic compounds are most frequently found in combination in gasoline
and diesel fuel. Historically, BTEX contamination of groundwater and soil occurs
most frequently near petroleum refineries, natural gas production facilities, petrol
loading stations and sites with above- or below-ground storage tanks containing
gasoline or petroleum products.
BTEX represents a light aromatic fraction of a broader value called Total Petroleum
Hydrocarbons (TPH), which describes a broad family of hundreds
of different chemical compounds originating from crude oil. EPA provides guidelines
for calculating BTEX in which the concentrations of benzene, toluene, ethylbenzene
and total xylene are added together to obtain a value for "Total BTEX"
(xylene is treated as a separate calculation as three isomers are added together
to obtain total xylene).6
BTEX is important from a toxicological perspective because the health effects of
the most typical constituent chemicals (benzene, toluene, ethylbenzene and xylene)
have been more extensively studied than most of the heavier petroleum components
present in TPH. A number of detailed toxicological profiles have been developed
by ATSDR on individual TPH constituents. These and other studies have documented
many of the generally-recognized health effects in humans. Benzene (a recognized
carcinogen) can cause vomiting, irritation of the stomach, dizziness, sleepiness,
convulsions, rapid heart rate, coma and death. The main effect of toluene is on
the brain and nervous system. Ethylbenzene has been shown to cause damage to the
inner ear and hearing of animals. High concentrations of xylene affects the nervous
system, causing headaches, lack of muscle coordination, dizziness, confusion and
irritation of the eyes and respiratory tract.7
A scientifically credible toxicological health risk assessment involving BTEX requires
measurement and laboratory analyses of the individual hydrocarbons present in the
contaminated media. However, other constituent chemicals (such as naphthalene and
styrene) may also be present in such analyses and must be accounted for. TCAS
has extensive experience with BTEX exposures and remediation issues in residential,
environmental and industrial cases and has produced objective toxicological assessments on
behalf of both plaintiffs and defendants. Please contact our
office for additional information.
Dioxins and PCBs
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Dioxin bonding to AhR (Aryl Hydrocarbon Receptors)[e]
Of the many toxic substances confronting the expert toxicologist, dioxins are among
the most challenging. The dioxin family of compounds is vast and complex. There
are three basic sets of chlorinated compounds with intrinsically similar chemical
structures: (a) 75 polychlorinated dibenzo-p-dioxins (PCDDs), (b) 135 polychlorinated
dibenzofurans (PCDFs) and (c) 209 polychlorinated biphenyls (PCBs). Dioxins can
be produced from incomplete combustion and a variety of other sources. Although
PCBs are no longer manufactured in the United States, they were used in electrical
transformers and other commercial products and can still be found in the environment.
Although some dioxins and PCBs are relatively harmless, others can induce a wide
range of adverse health effects when only very tiny amounts are present in the blood.
TCDD [2,3,7,8-tetrachlorodibenzo-p-dioxin] is generally regarded as the most toxic.
TCDD is classified as a "Group 1 Known Human Carcinogen" by the World
Health Organization (WHO) and by the U.S. EPA.8
WHO created a set of standardized Toxic Equivalency Factors (TEFs) which
allow the toxicologist to perform dose calculations and objectively assess risk
by expressing dose in terms of TCDD potency (TCDD has a TEF of 1.0, the highest
toxicity).
It is generally believed that dioxin causes
genetic damage by activating specific gene subgroups through an AhR (Aryl Hydrocarbon
Receptor). This ultimately produces cancer through a process called "tumor
promotion" in which the descendents of a single initiated (carcinogenic) cell
survive and expand in number. A multi-site carcinogen, dioxins can induce multiple
types of cancer in different locations in the human body. This phenomenon has been
repeatedly observed in both human and animal studies.9
A scientifically credible toxicological assessment of a dioxin exposure must meet
many requirements. The body of ongoing research is vast and there are a great many
human epidemiological studies covering a wide range of potentially adverse health
effects. Additionally, there are numerous remedial and regulatory guidelines which
set precise limits for dioxins and dioxin-like compounds, some of which vary widely
by state and locale. Thus, there are many complex issues the expert toxicologist must
consider when conducting a formal dioxin exposure and corresponding risk assessment,
particularly in cases involving whole communities.
TCAS has extensive experience in toxicologically assessing dioxin exposures,
contamination and remediation issues in residential, environmental and industrial
cases in both causative and risk assessment scenarios. Our work in this field has
been voluminous and we are regularly consulted by clients seeking toxicological
opinions and assessments. Please
contact our office for additional information.
LNAPL
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LNAPL[f]
LNAPL (Light Non-Aqueous Phase Liquid) refers to a group of organic chemical substances
(often petroleum) which are relatively insoluble and less dense than water. These characteristics cause them to form a layer
at or near the surface of a water table. LNAPL can pose significant environmental and toxicological
issues with respect to both short- and long-term exposures. LNAPL analyses can involve
aspects of analytical and reconstructive chemistry as well as modeling of liquid
behavior, migration and fate. U.S. EPA provides general guidance10,11 with respect to
LNAPL analyses, health impacts and remediation of contamination.
A comprehensive toxicological risk assessment will typically include objective analyses
and determination of total petroleum hydrocarbons (TPH). Health effects from TPH
exposures depend on many factors and the compounds in different TPH fractions impact
the body in different ways. Toxicological variables include (but are not limited
to) the types of chemical compounds present in contamination, exposure dose, duration
and pathways. Some TPH compounds, particularly the smaller compounds such as benzene,
toluene, and xylene (which are present in gasoline) impact the human central nervous
system. However, human studies are lacking for the majority of TPHs and the documented
toxicity and effects of some TPH compounds are presently based largely on animal
studies. Thus, in human health risk assessments, the expert toxicologist must rely
upon animal and human epidemiological studies of TPH mixtures with respect to identifying
specific potential adverse health effects.12
Scientifically credible LNAPL analyses frequently require the combined efforts of
a qualified hydrogeologist working in concert with an analytical toxicologist. An
objective LNAPL toxicological assessment involves compositional chemistry analyses
designed to assess source and age, followed by a comprehensive health risk assessment
based on a quantitative evaluation of water ingestion, vapor intrusion and other
factors. It is highly recommended that in view of the scope of potential liabilities
associated with LNAPL, any individual, company or government agency engaged in LNAPL
litigation matters always retain an experienced expert toxicologist and hydrologist.
TCAS has performed numerous LNAPL assessments and provided objective reports
as well as expert opinions and expert witness consults for many types of LNAPL and
DNAPL contamination. This website contains a comprehensive review of LNAPL toxicology.
Please
contact our office for additional information.
PAHs
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Gulf oil clean-up worker[g]
PAHs (polycyclic aromatic hydrocarbons) have been found in at least 600 of the sites
on the U.S. EPA's National Priorities List. Found in crude oil, coal, coal tar pitch,
creosote, roofing tar and many other substances, PAHs can be found throughout the
environment in the air, water, and soil. PAHs generally occur as complex mixtures
or as part of combustion products (such as soot). Some PAHs occur naturally whereas
others are manufactured as individual compounds. As pure chemicals, PAHs generally
exist as colorless, white, or pale yellow-green solids. A few PAHs are used in medicines
and to make dyes, plastics, and pesticides.13
Although most PAHs are only slightly mutagenic, their metabolites or derivatives can
be potent mutagens. The most significant toxicological endpoint of PAH toxicity
is cancer. However, some studies have shown non-carcinogenic effects based on exposure
dose [Gupta et al. 1991]. Non-carcinogenic effects involve the pulmonary, gastrointestinal,
renal, dermatologic and respiratory systems. Increased incidences of lung, skin,
and bladder cancers are also associated with occupational exposure to PAHs.14
The most recent large-scale release of PAHs occurred in the 2010 "Deepwater
Horizon" oil release. Vast quantities of "dispersant" were applied
to floating crude oil causing PAHs in the oil to be liberated. The release of these
chemicals into the water had
pronounced adverse health effects on aquatic life in the Gulf region as well
as clean-up workers, local residents and others. Dr. Sawyer was directly involved
in
sampling and assessing the toxicological impacts of these PAH releases (litigation
continues to the present time). TCAS has extensive experience in toxicologically
assessing PAH exposures and remediation issues in both causative and risk assessment
scenarios. Please
contact our office for additional information.
Petroleum Products
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Petroleum[h]
Human health hazards with respect to petroleum products are a significant problem
for both occupationally exposed individuals and among the general population.
Petroleum products are widely used as fuels, greases, solvents and intermediates
in many branches of industry. Products derived from petroleum constitute a vast
and complex universe of substances, some of which are classified as both hazardous
and toxic. U.S. EPA maintains a comprehensive Consolidated List of Chemicals Subject
to the Emergency Planning and Community Right-To-Know Act which lists hazardous
substances and toxic chemicals subject to regulation under CERCLA.15 A long list of petroleum-derived
substances appears in ATSDR's Priority List of Hazardous Substances
including such toxic agents as benzene, polycyclic aromatic hydrocarbons (PAHs),
benzo(b)fluoranthene and many others.16
Variable
composition of individual petroleum products and limited human epidemiological studies
for some substances impose challenging complexities when producing a scientifically
credible toxicological assessment of human health risks. In some cases, contamination
may consist of a historical progression of substances released over a period of
decades. In other cases, unintentional releases (such as waste products from refineries)
can infiltrate into groundwater and soil and/or release volatile vapors. In residential
exposure scenarios, the population may not even be aware of the hazards until adverse
health effects begin to appear. In the case of consumer products, cosmetics, cleaning
and janitorial chemicals and substances that emit volatile vapors (such as certain
plastics) all possess different toxicological characteristics.
The expert toxicologist must account for all of these variables in any objective
health risk assessment relating to petroleum products. Exposure assessment involves a process
whereby the toxicologist calculates the magnitude, frequency and duration of exposure,
compiles sets of information describing exposure concentrations and intake variables,
applies the appropriate assessment methodologies and arrives at pathway-specific
exposure doses for each substance of concern. Uncertainties must also be taken into
account as some exposure events may have occurred in the distant past and may represent
a cumulative exposure dose.
Thus, petroleum-related assessments frequently fall within the realm of forensic
toxicology. TCAS has substantial experience in assessing the health hazards
associated with petroleum products and has regularly provided written reports and
expert testimony on behalf of both plaintiffs and defendants in accordance with
federal, state and local regulations. Please contact our
office for additional information.
Notes and References
- U.S. Environmental Protection Agency, "Benzene," Drinking Water Treatability Database, July, 2009.
- ATSDR, Division of Toxicology and Environmental Medicine, "Toxicological Profile for Benzene," August, 2007.
- U.S. Environmental Protection Agency, "Toxicological Review of Benzo[a]pyrene," (External Review Draft) September, 2014
- ATSDR, Division of Toxicology and Environmental Medicine, "Toxicological Profile for Polycyclic Aromatic Hydrocarbons," August, 1995.
- International Agency for Research on Cancer, "IARC Monographs: Benzo[a]pyrene," July, 2012.
- U.S. Environmental Protection Agency, "Region VIII Pretreatment Guidance on the Analysis of BTEX," August, 1999.
- ATSDR, Division of Toxicology and Environmental Medicine, "Toxicological Profile for Total Petroleum Hydrocarbons (TPH)," September, 1999.
- U.S. Environmental Protection Agency, "Supplemental guidance for assessing cancer susceptibility from early-life exposure to carcinogens," 2005
- Beischlag et al., "The aryl hydrocarbon receptor complex and the control of gene expression," Critical Reviews in Eukaryotic Gene Expression, 2008;18(3):207-50
- U.S. Environmental Protection Agency, "Light Non-Aqueous Phase Liquids (LNAPLs),"
- U.S. Environmental Protection Agency, "A Decision-Making Framework for Cleanup of Sites Impacted With Light Non-Aqueous Phase Liquid (LNAPL)"
- ATSDR, Centers for Disease Control and Prevention, "Public Health Statement for Total Petroleum Hydrocarbons (TPH)," September, 1999.
- ATSDR, Division of Toxicology and Environmental Medicine, "Toxicological Profile for Polycyclic Aromatic Hydrocarbons," August, 1995.
- ATSDR, Division of Toxicology and Environmental Medicine, "Health Effects Associated With PAH Exposure," December, 2013
- U.S. Environmental Protection Agency, "List of Chemicals Subject to the Emergency Planning and Community Right-To-Know Act," March, 2015.
- ATSDR, Division of Toxicology and Environmental Medicine, "Priority List of Hazardous Substances," February, 2016.
Images
- Montage image sources as cited below
- U.S. Environmental Protection Agency, "Benzene"
- National Coordination Office for Networking and Information Technology Research and Development, "Benzo[a]pyrene"
- U.S. Geological Survey, "BTEX," Fact Sheet FS-019-98
- National Institutes of Health, Department of Health & Human Services, "Molecular Docking of TCDD in Aryl Hydrocarbon Receptors"
- Adapted from U.S. EPA, "Understanding
Light Non-Aqueous Phase Liquid (LNAPL) Behavior in Soil"
- U.S. Fish and Wildlife Service, "PCB Marking Requirements"
- U.S. Bureau of Labor Statistics, "Petroleum Manufacturing: Beyond the Numbers"