Secretion of creosote preservative into aquatic ecosystem | Wikipedia audio article


Creosote is a category of carbonaceous chemicals
formed by the distillation of various tars and pyrolysis of plant-derived material, such
as wood or fossil fuel. They are typically used as preservatives or
antiseptics.Some creosote types were used historically as a treatment for components
of seagoing and outdoor wood structures to prevent rot (e.g., bridgework and railroad
ties, see image). Samples may be commonly found inside chimney
flues, where the coal or wood burns under variable conditions, producing soot and tarry
smoke. Creosotes are the principal chemicals responsible
for the stability, scent, and flavor characteristic of smoked meat; the name is derived from Greek,
Modern κρέας (kreas), meaning ‘meat’, and σωτήρ (sōtēr), meaning ‘preserver’.The
two main kinds recognized in industry are coal-tar creosote and wood-tar creosote. The coal-tar variety, having stronger and
more toxic properties, has chiefly been used as a preservative for wood; coal-tar creosote
was also formerly used as an escharotic, to burn malignant skin tissue, and in dentistry,
to prevent necrosis, before its carcinogenic properties became known. The wood-tar variety has been used for meat
preservation, ship treatment, and such medical purposes as an anaesthetic, antiseptic, astringent,
expectorant, and laxative, though these have mostly been replaced by modern formulations.Varieties
of creosote have also been made from both oil shale and petroleum, and are known as
oil-tar creosote when derived from oil tar, and as water-gas-tar creosote when derived
from the tar of water gas. Creosote also has been made from pre-coal
formations such as lignite, yielding lignite-tar creosote, and peat, yielding peat-tar creosote.==Creosote oils==
The term creosote has a broad range of definitions depending on the origin of the coal tar oil
and end use of the material. With respect to wood preservatives, the United
States Environmental Protection Agency (EPA) considers the term creosote to mean a pesticide
for use as a wood preservative meeting the American Wood Protection Association (AWPA)
Standards P1/P13 and P2. The AWPA Standards require that creosote “shall
be a pure coal tar product derived entirely from tar produced by the carbonization of
bituminous coal.” Currently, all creosote treated wood products—foundation
and marine piling, lumber, posts, railroad crossties, timbers, and utility poles—are
manufactured using this type of wood preservative. The manufacturing process can only be a pressure
process under the supervision of a licensed applicator certified by the State Departments
of Agriculture. No brush-on, spray, or non-pressure uses of
creosote are allowed, as specified by the EPA approved label for the use of creosote. The use of creosote according to the AWPA
Standards does not allow for mixing with other types of “creosote type” materials—such
as lignite-tar creosote, oil-tar creosote, peat-tar creosote, water-gas-tar creosote,
or wood-tar creosote. The AWPA Standard P3 does however, allow blending
of a high-boiling petroleum oil meeting the AWPA Standard P4.The information that follows
describing the other various types of creosote materials and its uses should be considered
as primarily being of only historical value. This history is important, because it traces
the origin of these different materials used during the 19th and early 20th centuries. Furthermore, it must be considered that these
other types of creosotes – lignite-tar, wood-tar, water-gas-tar, etc. – are not
currently being manufactured and have either been replaced with more economical materials,
or replaced by products that are more efficacious.For some part of their history, coal-tar creosote
and wood-tar creosote were thought to have been equivalent substances—albeit of distinct
origins—accounting for their common name; the two were determined only later to be chemically
different. All types of creosote are composed of phenol
derivatives and share some quantity of monosubstituted phenols, but these are not the only active
element of creosote. For their useful effects, coal-tar creosote
relies on the presence of naphthalenes and anthracenes, while wood-tar creosote relies
on the presence of methyl ethers of phenol. Otherwise, either type of tar would dissolve
in water. Creosote was first discovered in its wood-tar
form in 1832, by Carl Reichenbach, when he found it both in the tar and in pyroligneous
acids obtained by a dry distillation of beechwood. Because pyroligneous acid was known as an
antiseptic and meat preservative, Reichenbach conducted experiments by dipping meat in a
diluted solution of distilled creosote. He found that the meat was dried without undergoing
putrefaction and had attained a smoky flavor. This led him to reason that creosote was the
antiseptic component contained in smoke, and he further argued that the creosote he had
found in wood tar was also in coal tar, as well as amber tar and animal tar, in the same
abundance as in wood tar.Soon afterward, in 1834, Friedrich Ferdinand Runge discovered
carbolic acid in coal-tar, and Auguste Laurent obtained it from phenylhydrate, which was
soon determined to be the same compound. There was no clear view on the relationship
between carbolic acid and creosote; Runge described it as having similar caustic and
antiseptic properties, but noted that it was different, in that it was an acid and formed
salts. Nonetheless, Reichenbach argued that creosote
was also the active element, as it was in pyroligneous acid. Despite evidence to the contrary, his view
held sway with most chemists, and it became commonly accepted wisdom that creosote, carbolic
acid, and phenylhydrate were identical substances, with different degrees of purity.Carbolic
acid was soon commonly sold under the name “creosote”, and the scarcity of wood-tar creosote
in some places led chemists to believe that it was the same substance as that described
by Reichenbach. In the 1840s, Eugen Freiherr von Gorup-Besanez,
after realizing that two samples of substances labelled as creosote were different, started
a series of investigations to determine the chemical nature of carbolic acid, leading
to a conclusion that it more resembled chlorinated quinones and must have been a different, entirely
unrelated substance. Independently, there were investigations into
the chemical nature of creosote. A study by F.K. Völkel revealed that the smell of purified
creosote resembled that of guaiacol, and later studies by Heinrich Hlasiwetz identified a
substance common to guaiacum and creosote that he called creosol, and he determined
that creosote contained a mixture of creosol and guaiacol. Later investigations by Gorup-Besanez, A.E. Hoffmann, and Siegfried Marasse showed that
wood-tar creosote also contained phenols, giving it a feature in common with coal-tar
creosote.Historically, coal-tar creosote has been distinguished from what was thought of
as creosote proper—the original substance of Reichenbach’s discovery—and it has been
referred to specifically as “creosote oil”. But, because creosote from coal-tar and wood-tar
are obtained from a similar process and have some common uses, they have also been placed
in the same class of substances, with the terms “creosote” or “creosote oil” referring
to either product.===Wood-tar creosote===
Wood-tar creosote is a colourless to yellowish greasy liquid with a smoky odor, produces
a sooty flame when burned, and has a burned taste. It is non-buoyant in water, with a specific
gravity of 1.037 to 1.087, retains fluidity at a very low temperature, and boils at 205-225
°C. When transparent, it is in its purest form. Dissolution in water requires up to 200 times
the amount of water as the base creosote. The creosote is a combination of natural phenols:
primarily guaiacol and creosol (4-methylguaiacol), which will typically constitute 50% of the
oil; second in prevalence, cresol and xylenol; the rest being a combination of monophenols
and polyphenols. The simple phenols are not the only active
element in wood-tar creosote. In solution, they coagulate albumin, which
is a water-soluble protein found in meat; so they serve as a preserving agent, but also
cause denaturation. Most of the phenols in the creosote are methoxy
derivatives—they contain the methoxy group linked to the benzene nucleus (O–CH3). The high level of methyl derivates created
from the action of heat on wood (also apparent in the methyl alcohol produced through distillation)
make wood-tar creosote substantially different from coal-tar creosote. Guaiacol is a methyl ether of pyrocatechin,
while creosol is a methyl ether of methyl-pyrocatechin, the next homolog of pyrocatechin. Methyl ethers differ from simple phenols in
being less hydrophilic, caustic and poisonous. This allows meat to successfully be preserved
without tissue denaturation, and allows creosote to be used as a medical ointment. Because wood-tar creosote is used for its
guaiacol and creosol content, it is generally derived from beechwood rather than other woods,
since it distills with a higher proportion of those chemicals to other phenolics. The creosote can be obtained by distilling
the wood tar and treating the fraction heavier than water with a sodium hydroxide solution. The alkaline solution is then separated from
the insoluble oily layer, boiled in contact with air to reduce impurities, and decomposed
by diluted sulphuric acid. This produces a crude creosote, which is purified
by re-solution in alkali and re-precipitation with acid and then redistilled with the fraction
passing over between 200° and 225° constituting the purified creosote.When ferric chloride
is added to a dilute solution, it will turn green; a characteristic of ortho-oxy derivatives
of benzene. It dissolves in sulphuric acid to a red liquid,
which slowly changes to purple-violet. Shaken with hydrochloric acid in the absence
of air, it becomes red, the color changing in the presence of air to dark brown or black.In
preparation of food by smoking, guaiacol contributes mainly to the smoky taste, while the dimethyl
ether of pyrogallol, syringol, is the main chemical responsible for the smoky aroma.====Historical uses=========
Industrial=====Soon after it was discovered and recognized
as the principle of meat smoking, wood-tar creosote became used as a replacement for
the process. Several methods were used to apply the creosote. One was to dip the meat in pyroligneous acid
or a water of diluted creosote, as Reichenbach did, or brush it over with them, and within
one hour the meat would have the same quality of that of traditionally smoked preparations. Sometimes the creosote was diluted in vinegar
rather than water, as vinegar was also used as a preservative. Another was to place the meat in a closed
box, and place with it a few drops of creosote in a small bottle. Because of the volatility of the creosote,
the atmosphere was filled with a vapour containing it, and it would cover the flesh.The application
of wood tar to seagoing vessels was practiced through the 18th century and early 19th century,
before the creosote was isolated as a compound. Wood-tar creosote was found not to be as effective
in wood treatments, because it was harder to impregnate the creosote into the wood cells,
but still experiments were done, including by many governments, because it proved to
be less expensive on the market.=====Medical=====
Even before creosote as a chemical compound was discovered, it was the chief active component
of medicinal remedies in different cultures around the world. In antiquity, pitches and resins were used
commonly as medicines. Pliny mentions a variety of tar-like substances
being used as medicine, including cedria and pissinum. Cedria was the pitch and resin of the cedar
tree, being equivalent to the oil of tar and pyroligneous acid which are used in the first
stage of distilling creosote. He recommends cedria to ease the pain in a
toothache, as an injection in the ear in case of hardness of hearing, to kill parasitic
worms, as a preventative for impregnation, as a treatment for phthiriasis and porrigo,
as an antidote for the poison of the sea hare, as a liniment for elephantiasis, and as an
ointment to treat ulcers both on the skin and in the lungs. He further speaks of cedria being used as
the embalming agent for preparing mummies. Pissinum was a tar water that was made by
boiling cedria, spreading wool fleeces over the vessels to catch the steam, and then wringing
them out. The Pharmacopée de Lyon, published in 1778,
says that cedar tree oil is believed to cure vomiting and help medicate tumors and ulcers. Physicians contemporary to the discovery of
creosote recommended ointments and pills made from tar or pitch to treat skin diseases. Tar water had been used as a folk remedy since
the Middle Ages to treat affections like dyspepsia. Bishop Berkeley wrote several works on the
medical virtues of tar water, including a philosophical work in 1744 titled Siris: a
chain of philosophical reflexions and inquiries concerning the virtues of tar water, and divers
other subjects connected together and arising one from another, and a poem where he praised
its virtues. Pyroligneous acid was also used at the time
in a medicinal water called Aqua Binelli.Given this history, and the antiseptic properties
known to creosote, it became popular among physicians in the 19th century. A dilution of creosote in water was sold in
pharmacies as Aqua creosoti, as suggested by the previous use of pyroligneous acid. It was prescribed to quell the irritability
of the stomach and bowels and detoxify, treat ulcers and abscesses, neutralize bad odors,
and stimulate the mucous tissues of the mouth and throat. Creosote in general was listed as an irritant,
styptic, antiseptic, narcotic, and diuretic, and in small doses when taken internally as
a sedative and anaesthetic. It was used to treat ulcers, and as a way
to sterilize the tooth and deaden the pain in case of a tooth-ache.Creosote was suggested
as a treatment for tuberculosis by Reichenbach as soon as 1833. Following Reichenbach, it was argued for by
John Elliotson and Sir John Rose Cormack. Elliotson, inspired by the use of creosote
to arrest vomiting during an outbreak of cholera, suggested its use for tuberculosis through
inhalation. He also suggested it for epilepsy, neuralgia,
diabetes and chronic glanders. The idea of using it for tuberculosis failed
to take hold, and use of this purpose was dropped, until the idea was revived later
in 1876 by the British doctor G. Anderson Imlay, who suggested it be applied locally
in spray to the bronchial mucous membrane. This was followed up in 1877 when it was argued
for in a clinical paper by Charles Bouchard and Henri Gimbert. Germ theory had been established by Pasteur
in 1860, and Bouchard, arguing that a bacillus was responsible for the disease, sought to
rehabilitate creosote for its use as an antiseptic to treat it. He began a series of trials with Gimbert to
convince the scientific community, and claimed a promising cure rate. A number of publications in Germany confirmed
his results in the following years.Following that, that was a period of experimentation
of different techniques and chemicals using creosote in tuberculosis, which lasted until
about 1910, when radiation therapy looked to be a more promising treatment. Guaiacol, instead of a full creosote solution,
was suggested by Hermann Sahli in 1887; he argued it had the active chemical of creosote
and had the advantage of being of definite composition and of having a less unpleasant
taste and odor. A number of solutions of both creosote and
guaiacol appeared on the market, such as phosphotal and guaicophosphal, phosphites of creosote
and guaiacol; eosot and geosot, valerinates of creosote and guaicol; phosot and taphosot,
phosphate and tannophospate of creosote; and creosotal and tanosal, tannates of creosote. Creosote and eucalptus oil were also a remedy
used together, administered through a vaporizor and inhaler. Since then, more effective and safer treatments
for tuberculosis have been developed. In the 1940s, Canadian-based Eldon Boyd experimented
with guaiacol and a recent synthetic modification—glycerol guaiacolate (guaifenesin)—on animals. His data showed that both drugs were effective
in increasing secretions into the airways in laboratory animals, when high enough doses
were given.====Current uses=========
Industrial=====Wood-tar creosote is to some extent used for
wood preservation, but it is generally mixed with coal-tar creosote, since the former is
not as effective. Commercially available preparations of “liquid
smoke”, marketed to add a smoked flavour to meat and aid as a preservative, consist primarily
of creosote and other constituents of smoke. Creosote is the ingredient that gives liquid
smoke its function; guaicol lends to the taste and the creosote oils help act as the preservative. Creosote can be destroyed by treatment with
chlorine, either sodium hypochlorite, or calcium hypochlorite solutions. The phenol ring is essentially opened, and
the molecule is then subject to normal digestion and normal respiration.=====Medical=====
The guaifenesin developed by Eldon Boyd is still commonly used today as an expectorant,
sold over the counter, and usually taken by mouth to assist the bringing up of phlegm
from the airways in acute respiratory tract infections. Guaifenesin is a component of Mucinex, Robitussin
DAC, Cheratussin DAC, Robitussin AC, Cheratussin AC, Benylin, DayQuil Mucous Control, Meltus,
and Bidex 400. Seirogan is a popular Kampo medicine in Japan,
used as an anti-diarrheal, and has 133 mg wood creosote from beech, pine, maple or oak
wood per adult dose as its primary ingredient. Seirogan was first used as a gastrointestinal
medication by the Imperial Japanese Army in Russia during the Russo-Japanese War of 1904
to 1905.Creomulsion is a cough medicine in the United States, introduced in 1925, that
is still sold and contains beechwood creosote. Beechwood creosote is also found under the
name kreosotum or kreosote.===Coal-tar creosote===
Coal-tar creosote is greenish-brown liquid, with different degrees of darkness, viscosity,
and fluorescence depending on how it’s made. When freshly made, the creosote is a yellow
oil with a greenish cast and highly fluorescent; the fluorescence increased by exposure to
air and light. After settling, the oil is dark green by reflected
light and dark red by transmitted light. To the naked eye, it will generally appear
brown. The creosote (often called “creosote oil”)
consists almost wholly of aromatic hydrocarbons, with some amount of bases and acids and other
neutral oils. The flash point is 70–75 °C and burning
point is 90–100 °C, and when burned it releases a greenish smoke. The smell largely depends on the naptha content
in the creosote; if there is a high amount, it will have a naptha-like smell; otherwise
it will smell more of tar. In the process of coal-tar distillation, the
distillate is collected into four fractions; the “light oil”, which remains lighter than
water, the “middle oil” which passes over when the light oil is removed; the “heavy
oil”, which sinks; and the “anthracene oil”, which when cold is mostly solid and greasy,
of a buttery consistence. Creosote refers to the portion of coal tar
which distills as “heavy oil”, typically between 230–270 °C, also called “dead oil”; it
sinks into water but still is fairly liquid. Carbolic acid is produced in the second fraction
of distillation and is often distilled into what is referred to as “carbolic oil”. Commercial creosote will contain substances
from six groups. The two groups occur in the greatest amounts
and are the products of the distillation process—the “tar acids”, which distill below 205 °C and
consist mainly of phenols, cresols, and xylenols, including carbolic acid—and aromatic hydrocarbons,
which divide into naphthalenes, which distill approximately between 205° and 255 °C, and
constituents of an anthracene nature, which distill above 255 °C. The quantity of each
varies based on the quality of tar and temperatures used, but generally, the tar acids won’t exceed
5%, the naphthalenes will make up 15 to 50%, and the anthracenes will make up 45% to 70%. The hydrocarbons are mainly aromatic; derivatives
of benzene and related cyclic compounds such as naphthalene, anthracene, phenanthrene,
acenapthene, and fluorene. Creosotes from vertical-retort and low temperature
tars contain, in addition, some paraffinic and olefinic hydrocarbons. The tar-acid content also depends on the source
of the tar—it may be less than 3% in creosote from coke-oven tar and as high as 32% in creosote
from vertical retort tar. All of these have antiseptic properties. The tar acids are the strongest antiseptics
but have the highest degree of solubility in water and are the most volatile; so, like
with wood-tar creosote, phenols are not the most valued component, as by themselves they
would lend to being poor preservatives. In addition, creosote will contain several
products naturally occurring in coal—nitrogen-containing heterocycles, such as acridines, carbazoles,
and quinolines, referred to as the “tar bases” and generally make up about 3% of the creosote—sulfur-containing
heterocycles, generally benzothiophenes—and oxygen-containing heterocycles, dibenzofurans. Lastly, creosote will contain a small number
of aromatic amines produced by the other substances during the distillation process and likely
resulting from a combination of thermolysis and hydrogenation. The tar bases are often extracted by washing
the creosote with aqueous mineral acid, although they’re also suggested to have antiseptic
ability similar to the tar acids. Commercially used creosote is often treated
to extract the carbolic acid, naphthalene, or anthracene content. The carbolic acid or naphthalene is generally
extracted to be used in other commercial products. American produced creosote oils typically
will have low amounts of anthracene and high amounts of naphthalene, because when forcing
the distillate at a temperature that produces anthracene the soft pitch will be ruined and
only the hard pitch will remain; this ruins it for use in roofing purposes, and only leaves
a product which isn’t commercially useful.====Historical uses=========
Industrial=====The use of coal-tar creosote on a commercial
scale began in 1838, when a patent covering the use of creosote oil to treat timber was
taken out by inventor John Bethell. The “Bethell process”—or as it later became
known, the full-cell process—involves placing wood to be treated in a sealed chamber and
applying a vacuum to remove air and moisture from wood “cells”. The wood is then pressure-treated to impregnate
it with creosote or other preservative chemicals, after which vacuum is reapplied to separate
the excess treatment chemicals from the timber. Alongside the zinc chloride-based “Burnett
process”, use of creosoted wood prepared by the Bethell process became a principal way
of preserving railway timbers (most notably railway sleepers) to increase the lifespan
of the timbers, and avoiding having to regularly replace them.Besides treating wood, it was
also used for lighting and fuel. In the beginning, it was only used for lighting
needed in harbour and outdoor work, where the smoke that was produced from burning it
was of little inconvenience. By 1879, lamps had been created that ensured
a more complete combustion by using compressed air, removing the drawback of the smoke. Creosote was also processed into gas and used
for lighting that way. As a fuel, it was used to power ships at sea
and blast furnaces for different industrial needs, once it was discovered to be more efficient
than unrefined coal or wood. It was also used industrially for the softening
of hard pitch, and burned to produce lamp black. By 1890, the production of creosote in the
United Kingdom totaled approximately 29,900,000 gallons per year.In 1854, Alexander McDougall
and Angus Smith developed and patented a product called McDougall’s Powder as a sewer deodorant;
it was mainly composed from carbolic acid derived from creosote. McDougall, in 1864, experimented with his
solution to remove entozoa parasites from cattle pasturing on a sewage farm. This later led to widespread use of creosote
as a cattle wash and sheep dip. External parasites would be killed in a creosote
diluted dip, and drenching tubes would be used to administer doses to the animals’ stomachs
to kill internal parasites.Two later methods for creosoting wood were introduced after
the turn of the century, referred to as empty-cell processes, because they involve compressing
the air inside the wood so that the preservative can only coat the inner cell walls rather
than saturating the interior cell voids. This is a less effective, though usually satisfactory,
method of treating the wood, but is used because it requires less of the creosoting material. The first method, the “Rüping process” was
patented in 1902, and the second, the “Lowry process” was patented in 1906. Later in 1906, the “Allardyce process” and
“Card process” were patented to treat wood with a combination of both creosote and zinc
chloride. In 1912, it was estimated that a total of
150,000,000 gallons were produced in the United States per year.=====Medical=====
Coal-tar creosote, despite its toxicity, was used as a stimulant and escharotic, as a caustic
agent used to treat ulcers and malignancies and cauterize wounds and prevent infection
and decay. It was particularly used in dentistry to destroy
tissues and arrest necrosis.====Current uses=========
Industrial=====Coal-tar creosote is the most widely used
wood treatment today; both industrially, processed into wood using pressure methods such as “full-cell
process” or “empty-cell process”, and more commonly applied to wood through brushing. In addition to toxicity to fungi, insects,
and marine borers, it serves as a natural water repellant. It is commonly used to preserve and waterproof
cross ties, pilings, telephone poles, power line poles, marine pilings, and fence posts. Although suitable for use in preserving the
structural timbers of buildings, it is not generally used that way because it is difficult
to apply. There are also concerns about the environmental
impact of the secretion of creosote preservative into the aquatic ecosystem. Due to its carcinogenic character, the European
Union has regulated the quality of creosote for the EU market and requires that the sale
of creosote be limited to professional users. The United States Environmental Protection
Agency regulates the use of coal tar creosote as a wood preservative under the provisions
of the Federal Insecticide, Fungicide, and Rodenticide Act. Creosote is considered a restricted-use pesticide
and is only available to licensed pesticide applicators.===Oil-tar creosote===
Oil-tar creosote is derived from the tar that forms when using petroleum or shale oil in
the manufacturing of gas. The distillation of the tar from the oil occurs
at very high temperatures; around 980 °C. The tar forms at the same time as the gas,
and once processed for creosotes contains a high percentage of cyclic hydrocarbons,
a very low amount of tar acids and tar bases, and no true anthracenes have been identified. Historically, this has mainly been produced
in the United States in the Pacific coast, where petroleum has been more abundant than
coal. Limited quantities have been used industrially,
either alone, mixed with coal-tar creosote, or fortified with pentachlorophenol.===Water-gas-tar creosote===
Water-gas-tar creosote is also derived from petroleum oil or shale oil, but by a different
process; it is distilled during the production of water gas. The tar is a by-product resulting from enrichment
of water gas with gases produced by thermal decomposition of petroleum. Of the creosotes derived from oil, it is practically
the only one used for wood preservation. It has the same degree of solubility as coal-tar
creosote and is easy to impregnate into wood. Like standard oil-tar creosote, it has a low
amount of tar acids and tar bases, and has less antiseptic qualities. Petri dish tests have shown that water-gas-tar
creosote is one-sixth as anti-septically effective as that of coal-tar.===Lignite-tar creosote===
Lignite-tar creosote is produced from lignite rather than bituminous coal, and varies considerably
from coal-tar creosote. Also called “lignite oil”, it has a very high
content of tar acids, and has been used to increase the tar acids in normal creosote
when necessary. When it has been produced, its generally been
applied in mixtures with coal-tar creosote or petroleum. Its effectiveness when used alone has not
been established. In an experiment with southern yellow pine
fence posts in Mississippi, straight lignite-tar creosote was giving good results after about
27 years exposure, although not as good as the standard coal-tar creosote used in the
same situation.===Peat-tar creosote===
There have also been attempts to distill creosote from peat-tar, although mostly unsuccessful
due to the problems with winning and drying peat on an industrial scale. Peat tar by itself has in the past been used
as a wood preservative.==Health effects==
According to the Agency for Toxic Substances and Disease Registry (ATSDR), eating food
or drinking water contaminated with high levels of coal tar creosote may cause a burning in
the mouth and throat, and stomach pains. ATSDR also states that brief direct contact
with large amounts of coal tar creosote may result in a rash or severe irritation of the
skin, chemical burns of the surfaces of the eyes, convulsions and mental confusion, kidney
or liver problems, unconsciousness, and even death. Longer direct skin contact with low levels
of creosote mixtures or their vapours can result in increased light sensitivity, damage
to the cornea, and skin damage. Longer exposure to creosote vapours can cause
irritation of the respiratory tract. The International Agency for Research on Cancer
(IARC) has determined that coal tar creosote is probably carcinogenic to humans, based
on adequate animal evidence and limited human evidence. It is instructive to note that the animal
testing relied upon by IARC involved the continuous application of creosote to the shaved skin
of rodents. After weeks of creosote application, the animals
developed cancerous skin lesions and in one test, lesions of the lung. The United States Environmental Protection
Agency has stated that coal tar creosote is a probable human carcinogen based on both
human and animal studies. As a result, the Federal Occupational Safety
and Health Administration (OSHA) has set a permissible exposure limit of 0.2 milligrams
of coal tar creosote per cubic meter of air (0.2 mg/m3) in the workplace during an 8-hour
day, and the Environmental Protection Agency (EPA) requires that spills or accidental releases
into the environment of one pound (0.454 kg) or more of creosote be reported to them.There
is no unique exposure pathway of children to creosote. Children exposed to creosote will probably
experience the same health effects seen in adults exposed to creosote. It is unknown whether children differ from
adults in their susceptibility to health effects from creosote. A 2005 mortality study of creosote workers
found no evidence supporting an increased risk of cancer death, as a result of exposure
to creosote. Based on the findings of the largest mortality
study to date of workers employed in creosote wood treating plants, there is no evidence
that employment at creosote wood-treating plants or exposure to creosote-based preservatives
was associated with any significant mortality increase from either site-specific cancers
or non-malignant diseases. The study consisted of 2,179 employees at
eleven plants in the United States where wood was treated with creosote preservatives. Some workers began work in the 1940s to 1950s. The observation period of the study covered
1979- 2001. The average length of employment was 12.5
years. One third of the study subjects were employed
for over 15 years.The largest health effect of creosote is deaths caused by residential
chimney fires due to chimney tar (creosote) build-up. This is entirely unconnected with its industrial
production or use.==Build-up in chimneys==
Burning wood and fossil fuels in the absence of adequate airflow (such as in an enclosed
furnace or stove), causes incomplete combustion of the oils in the wood, which are off-gassed
as volatiles in the smoke. As the smoke rises through the chimney it
cools, causing water, carbon, and volatiles to condense on the interior surfaces of the
chimney flue. The black oily residue that builds up is referred
to as creosote, which is similar in composition to the commercial products by the same name,
but with a higher content of carbon black. Over the course of a season creosote deposits
can become several inches thick. This creates a compounding problem, because
the creosote deposits reduce the draft (airflow through the chimney) which increases the probability
that the wood fire is not getting enough air for complete combustion. Since creosote is highly combustible, a thick
accumulation creates a fire hazard. If a hot fire is built in the stove or fireplace,
and the air control left wide open, this may allow hot oxygen into the chimney where it
comes in contact with the creosote which then ignites—causing a chimney fire. Chimney fires often spread to the main building
because the chimney gets so hot that it ignites any combustible material in direct contact
with it, such as wood. The fire can also spread to the main building
from sparks emitting from the chimney and landing on combustible roof surfaces. In order to properly maintain chimneys and
heaters that burn wood or carbon-based fuels, the creosote buildup must be removed. Chimney sweeps perform this service for a
fee.==Release into environment==Even though creosote is pressurized into the
wood, the release of the chemical can be seen from many different events. During the lifetime of the marine piling,
weathering occurs from tides and water flow which slowly opens the oily outer coating
and exposes the smaller internal pores to more water flow. Frequent weathering occurs daily, but more
severe weather, such as hurricanes, can cause damage or loosening of the wooden pilings. Many pilings are either broken into pieces
from debris, or are completely washed away during these storms. When the pilings are washed away, they come
to settle on the bottom of the body of water where they reside, and then they secrete chemicals
into the water slowly over a long period of time. This long term secretion is not normally noticed
because the piling is submerged beneath the surface hidden from sight. The creosote is mostly insoluble in water,
but the lower molecular weight compounds will become soluble the longer the broken wood
is exposed to the water. In this case, some of the chemicals now become
water-soluble and further leach into the aquatic sediment while the rest of the insoluble chemicals
remain together in a tar-like substance. Another source of damage comes from wood boring
fauna such as Shipworms and Limnoria. Though creosote is used as a pesticide preservative,
studies have shown that Limnoria is resistant to wood preservative pesticides and can cause
small holes in the wood which creosote can then be secreted from.==Chemical reactions with sediment and organisms
==Once the soluble compounds from the creosote
preservative leach into the water, the compounds begin reacting with the external environment
or are consumed by organisms. The reactions vary depending on the concentration
of each compound that is released from the creosote, but major reactions are outlined
below:===Alkylation===
Alkylation occurs when a molecule replaces a hydrogen atom with an alkyl group that generally
comes from an organic molecule. Alkyl groups that are found naturally occurring
in the environment are organometallic compounds. Organometallic compounds generally contain
a methyl, ethyl, or butyl derivative which is the alkyl group that replaces the hydrogen. Other organic compounds, such as methanol,
can provide alkyl groups for alkylation. Methanol is found naturally in the environment
in small concentrations, and has been linked to the release from biological decomposition
of waste and even a byproduct of vegetation. The following reactions are alkylations of
soluble compounds found in creosote preservatives with methanol.====m-Cresol====The diagram above depicts a reaction between
m-cresol and methanol where a c-alkylation product is produced. The c-alkylation reaction means that instead
of replacing the hydrogen atom on the -OH group, the methyl group (from the methanol)
replaces the hydrogen on a carbon in the benzene ring. The products of this c-alkylation can be in
either a para- or ortho- orientation on the molecule, as seen in the diagram, and water,
which is not shown. Isomers of the dimethylphenol (DMP) compound
are the products of the para- and ortho-c-alkylation. Dimethylphenol (DMP) compound is listed as
an aquatic hazard by characteristic, and is toxic with long lasting effects.====Phenol====This diagram shows an o-alkylation between
phenol and methanol. Unlike the c-alkylation, the o-alkylation
replaces the hydrogen atom on the -OH group with the methyl group (from the methanol). The product of the o-alkylation is methoxybenzene,
better known as anisole, and water, which is not shown in the diagram. Anisole is listed as an acute hazard to aquatic
life with long term effects.===Bioaccumulation===
Bioaccumulation is the process by which an organism takes in chemicals through ingestion,
exposure, and inhalation. Bioaccumulation is broken down into bioconcentration
(uptake of chemicals from the environment) and biomagnification (increasing concentration
of chemicals as they move up the food chain). Certain species of aquatic organisms are affected
differently from the chemicals released from creosote preservatives. One of the more studied organisms is a mollusk. Mollusks attach to the wooden, marine pilings
and are in direct contact with the creosote preservatives. Many studies have been conducted using Polycyclic
aromatic hydrocarbons (PAH), which are low molecular hydrocarbons found in some creosote-based
preservatives. In a study conducted from Pensacola, Florida,
a group of native mollusks were kept in a controlled environment, and a different group
of native mollusks were kept in an environment contaminated with creosote preservatives. The mollusks in the contaminated environment
were shown to have a bioaccumulation of up to ten times the concentration of PAH than
the control species. The intake of organisms is dependent on whether
the compound is in an ionized or an un-ionized form. To determine whether the compound is ionized
or un-ionized, the pH of the surrounding environment must be compared to the pKa or acidity constant
of the compound. If the pH of the environment is lower than
the pKa, then the compound is un-ionized which means that the compound will behave as if
it is non-polar. Bioaccumulation for un-ionized compounds comes
from partitioning equilibrium between the aqueous phase and the lipids in the organism. If the pH is higher than the pKa, then the
compound is considered to be in the ionized form. The un-ionized form is favored because the
bioaccumulation is easier for the organism to intake through partitioning equilibrium. The table below shows a list of pKas from
compounds found in creosote preservatives and compares them to the average pH of seawater
(reported to be 8.1). Each of the compounds in the table above are
found in creosote preservatives, and are all in the favored un-ionized form. In another study, various species of small
fish were tested to see how the exposure time to PAH chemicals affected the fish. This study showed that an exposure time of
24–96 hours on various shrimp and fish species affected the growth, reproduction, and survival
functions of the organisms for most of the compounds tested.===Biodegradation===
Biodegradation can be seen in some studies that biodegradation accounts for the absence
of creosote preservatives on the initial surface of the sediment. In a study from Pensacola, Florida, PAHs were
not detected on the surface on the aquatic sediment, but the highest concentrations were
detected at a depth of 8-13 centimeters. A form an anaerobic biodegradation of m-cresol
was seen in a study using sulfate-reducing and nitrate-reducing enriched environments. The reduction of m-cresol in this study was
seen in under 144 hours, while additional chemical intermediates were being formed. The chemical intermediates were formed in
the presence of bicarbonate. The products included 4-hydroxy-2-methylbenzoic
acid and acetate compounds. Although the conditions were enriched with
the reducing anaerobic compounds, sulfate and nitrate reducing bacteria are commonly
found in the environment. For further information, see sulfate-reducing
bacteria. The type of anaerobic bacteria ultimately
determines the reduction of the creosote preservative compounds, while each individual compound
may only go through reduction under certain conditions. BTEX is a mixture of benzene, toluene, ethylbenzene,
and xylene, that was studied in the presence of four different anaerobic-enriched sediments. Though the compound, BTEX, is not found in
creosote preservatives, the products of creosote preservatives’ oxidation-reduction reactions
include some of these compounds. For oxidation-reduction reactions, see the
following section. In this study, it was seen that certain compounds
such as benzene were only reduced under sulfate-enriched environments, while toluene was reduced under
a variety of bacteria-enriched environments, not just sulfate. The biodegradation of a creosote preservative
in an anaerobic enrichment depends not only on the type of bacteria enriching the environment,
but also the compound that has been released from the preservative. In aerobic environments, preservative compounds
are limited in the biodegradation process by the presence of free oxygen. In an aerobic environment, free oxygen comes
from oxygen saturated sediments, sources of precipitation, and plume edges. The free oxygen allows for the compounds to
be oxidized and decomposed into new intermediate compounds. Studies have shown that when BTEX and PAH
compounds were placed in aerobic environments, the oxidation of the ring structures caused
cleavage in the aromatic ring and allowed for other functional groups to attach. When an aromatic hydrocarbon was introduced
to the molecular oxygen in experimental conditions, a dihydrodiol intermediate was formed, and
then oxidation occurred transforming the aromatic into a catechol compound. Catechol allows for cleavage of the aromatic
ring to occur, where functional groups can then add in an ortho- or meta- position.===Oxidation-reduction===
Even though many studies conduct testing under experimental or enriched conditions, oxidation-reduction
reactions are naturally occurring and allow for chemicals to go through processes such
as biodegradation, outlined above. Oxidation is defined as the loss of an electron
to another species, while reduction is the gaining of an electron from another species. As compounds go through oxidation and reduction
in sediments, the preservative compounds are altered to form new chemicals, leading to
decomposition. An example of the oxidation of p-cresol and
phenol can be seen in the figures below:====p-Cresol====This reaction shows the oxidation of p-cresol
in a sulfate-enriched environment. P-cresol was seen to be the easiest to degrade
through the sulfate-enriched environment, while m-cresol and o-cresol where inhibited. In the chart above, p-cresol was oxidized
under an anaerobic sulfate reducing condition and formed four different intermediates. After the formation of the intermediates,
the study reported further degradation of the intermediates leading to the production
of carbon dioxide and methane. The p-hydroxylbenzyl alcohol, p-hydroxylbenzaldehye,
p-hyrdoxylbenzoate, and benzoate intermediates all are produced from this oxidation and released
into the sediments. Similar results were also produced by different
studies using other forms of oxidation such as: iron-reducing organisms, Copper/Manganese
Oxide catalyst, and nitrate- reducing conditions.====Phenol====This reaction shows the oxidation of phenol
by iron and peroxide. This combination of iron, which comes from
iron oxide in the sediment, and the peroxide, commonly released by animals and plants into
the environment, is known as the Fenton Reagent. This reagent is used to oxidize phenol groups
by the use of a radical hydroxide group produced from the peroxide in the p-benzoquinone. This product of phenol’s oxidation is now
leached into the environment while other products include iron(II) and water. P-benzoquinone is listed as being a very toxic,
acute environmental hazard.==Environmental hazards=====
Sediment===In aquatic sediments, a number of reactions
can transform the chemicals released by the creosote preservatives into more dangerous
chemicals. Most creosote preservative compounds have
hazards associated with them before they are transformed. Cresol (m-, p-, and o-), phenol, guaiacol,
and xylenol (1,3,4- and 1,3,5-) all are acute aquatic hazards prior to going through chemical
reactions with the sediments. Alkylation reactions allows for the compounds
to transition into more toxic compounds with the addition of R-groups to the major compounds
found in creosote preservatives. Compounds formed through alkylation include:
3,4-dimethylphenol, 2,3-dimethylphenol, and 2,5-dimethylphenol, which are all listed as
acute environmental hazards. Biodegradation controls the rate at which
the sediment holds the chemicals, and the number of reactions that are able to take
place. The biodegradation process can take place
under many different conditions, and vary depending on the compounds that are released. Oxidation-reduction reactions allow for the
compounds to be broken down into new forms of more toxic molecules. Studies have shown oxidation-reduction reactions
of creosote preservative compounds included compounds that are listed as environmental
hazards, such as p-benzoquinone in the oxidation of phenol. Not only are the initial compounds in creosote
hazardous to the environment, but the byproducts of the chemical reactions are environmental
hazardous as well.===Other===
From the contamination of the sediment, more of the ecosystem is affected. Organisms in the sediment are now exposed
to the new chemicals. Organisms are then ingested by fish and other
aquatic animals. These animals now contain concentrations of
hazardous chemicals which were secreted from the creosote. Other issues with ecosystems include bioaccumulation. Bioaccumulation occurs when high levels of
chemicals are passed to aquatic life near the creosote pilings. Mollusks and other smaller crustaceans are
at higher risk because they are directly attached to the surface of wood pilings that are filled
with creosote preservative. Studies show that mollusks in these environments
take on high concentrations of chemical compounds which will then be transferred through the
ecosystem’s food chain. Bioaccumulation contributes to the higher
concentrations of chemicals within the organisms in the aquatic ecosystems.==Remediation of pilings==
While creosote treated wood is no longer used in the building of structures and piers, old
broken down piers still could contain these creosote preservatives. Many properties contain piers that were built
before 2008 with creosote preservatives, and now remain in the water even if they are broken
down. One simple remedy for this would be removing
the pilings after they are broken down or are no longer in use. On the coast, after storms pass through, debris
and wreckage breaks piers that are built on the water. One of the harder remedies is for pilings
that have sunk to the bottom of the water and settled on the sediment. These pilings are not visible and are harder
to detect. The pilings will then sit on the bottom and
leach chemicals out into the sediment and ecosystem. A solution to the problem of hidden pilings
could be an analytical method or technique that could be used to track creosote compounds
or byproducts in situ (the original place of contamination). If there was a technique that could be used
out in the field that could trace higher concentrations of the chemical in the sediment, then hidden
pilings could be isolated and removed from the environment. Many methods, such as gas chromatography-mass
spectroscopy (GCMS) and high performance liquid chromatography (HPLC), have been used to identify
creosote preservatives in the ground water and sediment, but most methods must be taken
back to the lab in order to be properly conducted due to the run time and size of the instrument. New studies have shown that the use of smaller,
more user friendly bio-assays are available to researchers so they can be used in the
field for faster identification of chemical compounds. A test that could identify creosote compounds
or other toxic byproducts quickly and efficiently in the field would allow researchers to remove
contaminated pilings before further damage can be done.==See also==
Pentachlorophenol Creolin==Notes

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