Cresol / Cresylic Acid – Guide to Hazardous Air Pollutants used by the Irish Air Corps

Cresol / Cresylic Acid


Cresylic Acid spilled all over the floor of the NDT shop of ERF and indeed dribbling down the wall from the extractor fan.

CAS  1319-77-3 , 95-48-7, 108-39-4, 106-44-5

Hazard Summary

Ambient air contains low levels of cresols from automobile exhaust, power plants, and oil refineries. Acute (short-term) inhalation exposure by humans to mixed cresols results in respiratory tract irritation, with symptoms such as dryness, nasal constriction, and throat irritation.  Mixed cresols are also strong dermal irritants.

No information is available on the chronic (long-term) effects of mixed cresols in humans, while animal studies have reported effects on the blood, liver, kidney, and central nervous system (CNS), and reduced body weight, from oral and inhalation exposure to mixed cresols.

Several animal studies suggest that o-cresol, m-cresol, and p-cresol may act as tumor promotors.  EPA has classified o-cresol, m-cresol, and p-cresol as Group C, possible human carcinogens.

Please Note: The main sources of information for this fact sheet are EPA's IRIS (4), which contains information on oral chronic toxicity and the RfD, and the carcinogenic effects of cresols, and the Agency for Toxic Substances and Disease Registry's (ATSDR's) Toxicological Profile for Cresols. (1)


  • Mixed cresols are used as disinfectants, preservatives, and wood preservatives. (1)
  • o-Cresol is used as a solvent, disinfectant, and chemical intermediate. (1)
  • m-Cresol is used to produce certain herbicides, as a precursor to the pyrethroid insecticides, to produce antioxidants, and to manufacture the explosive, 2,4,6-nitro-m-cresol. (1)
  • p-Cresol is used largely in the formulation of antioxidants and in the fragrance and dye industries. (1)

Sources and Potential Exposure

  • Mixed cresols may be found in ambient air; sources are car exhaust, electrical power plants, municipal solid waste incinerators, oil refineries, and cigarettes. (1)
  • People in residential areas where homes are heated with coal, oil, or wood may be exposed to mixed cresols in the air. (1)
  • Some foods, such as tomatoes, ketchup, asparagus, cheeses, butter, bacon, and smoked foods, as well as beverages, such as red wine, raw and roasted coffee and black tea, contain mixed cresols. (1)
  • Occupational exposure to mixed cresols may also occur at workplaces where mixed cresols and/or cresol containing products are produced or used. (1)

Assessing Personal Exposure

  • Mixed cresols can be measured in the urine of exposed individuals.

Health Hazard Information

Acute Effects:

  • Acute inhalation exposure by humans to mixed cresols results in respiratory tract irritation, with symptoms such as dryness, nasal constriction, and throat irritation.  Mixed cresols are also strong dermal irritants. Ingestion of high levels of mixed cresols by humans has resulted in effects on the respiratory system, gastrointestinal system, blood, liver, kidney, and CNS. (1,2)
  • Animal studies have reported respiratory tract and eye irritation, and effects on the liver, kidney, and CNS from acute inhalation exposure to mixed cresols. (1)
  • Acute animal tests in rats have shown mixed cresols to have moderate acute toxicity, while o-cresol, m-cresol, and p-cresol have been shown to have high acute toxicity from oral exposure. (3)

Chronic Effects (Noncancer):

  • No information is available on the chronic effects of mixed cresols in humans. (1)
  • Animal studies have reported effects on the blood, liver, kidney, and CNS, as well as reduced body weight, from oral and inhalation exposure to mixed cresols. (1,5)
  • EPA has not established a Reference Concentration (RfC) or a Reference Dose (RfD) for mixed cresols. (4)
  • The California Environmental Protection Agency 3  (CalEPA) has established a chronic reference exposure level of 0.004 milligrams per cubic meter (mg/m ) for mixed cresols based on bone marrow effects in rats. The CalEPA reference exposure level is a concentration at or below which adverse health effects are not likely to occur. It is not a direct estimator of risk, but rather a reference point to gauge the potential effects. At lifetime exposures increasingly greater than the reference exposure level, the potential for adverse health effects increases. (5)
  • EPA has not established an RfC for o-, m-, or p-cresol.  (5-7)
  • The RfD for o-cresol and m-cresol is 0.05 milligrams per kilogram body weight per day (mg/kg/d) based on decreased body weights and neurotoxicity in rats. The RfD is an estimate (with uncertainty spanning
    perhaps an order of magnitude) of a daily oral exposure to the human population (including sensitive subgroups) that is likely to be without appreciable risk of deleterious noncancer effects during a lifetime. (5,6)
  • EPA has high confidence in the studies on which the RfDs are based because they provided adequate toxicological endpoints that included both general toxicity and neurotoxicity; medium confidence in the database because there are adequate supporting subchronic studies but lacking chronic toxicity and reproductive studies; and, consequently, medium confidence in the RfD. (5,6)
  • The provisional RfD for p-cresol is 0.005 mg/kg/d based on neurological and respiratory effects in rabbits. The provisional RfD is a value that has had some form of Agency review, but it does not appear on IRIS. (8)

Reproductive/Developmental Effects:

  • No information is available on the reproductive or developmental effects of mixed cresols in humans. (1)
  • Animal studies have reported developmental effects, but only at maternally toxic doses, and no reproductive effects from oral exposure to mixed cresols. (1)

Cancer Risk:

  • Only anecdotal information is available on the carcinogenic effects of mixed cresols in humans. (4-7)
  • The only available oral animal study is a 13-week study that suggested that p-cresol may act as a promotor for tumors of the forestomach. (1)
  • Several dermal animal studies have suggested that o-cresol, m-cresol, and p-cresol may act as tumor promotors. (1,4-7)
  • EPA has classified o-cresol, m-cresol, and p-cresol as Group C, possible human carcinogens. (5-7)

Physical Properties

  • Mixed cresols are colorless solids, but usually they occur as a brown liquid mixture. (1)
  • Mixed cresols have a medicinal odor; the odor thresold for m-cresol is 0.00028 parts per million (ppm). (1,9)
  • The chemical formula for cresol is C 7 H 8 O, and the molecular weight is 108.14 g/mol. (1)
  • The primary synonym for o-cresol is 2-methylphenol; m-cresol is 3-methylphenol, and p-cresol is 4-methylphenol. (5-7)
  • The vapor pressures, at 25 °C, for o-cresol, m-cresol, and p-cresol are 0.299 mm Hg, 0.138 mm Hg, and 0.11 mm Hg, respectively. (1)
  • The octanol/water partition coefficients (log K ow) for o-cresol, m-cresol, and p-cresol are 1.95, 1.96, and 1.94, respectively. (1)

Read the full EPA PDF on the above Hazardous Air Pollutant with references below.


Relavance to personnel who served in the Air Corps

  1. Cresylic Acid is  component of Ardrox 666
  2. Cresols are consitituent chemicals of turbine engine oils. e.g. Tri-cresyl phosphate which is an organophosphate.

There are likely many more chemicals used by the Air Corps that contain Benzene. If you know of some let us know in the comments section.

Safe Handling of Cresols, Xylenols & Cresylic Acids


Cresols, xylenols and cresylic acids are hazardous substances and dangerous both to people and the environment if handled improperly. Cresols, xylenols and cresylic acid products produced by Sasol Chemicals (USA) LLC are highly versatile materials and are used as intermediates in the manufacture of a wide variety of industrial products such as resins, flame retardants, antioxidants, and coatings. In these and other applications, cresylic acids can be stored, transferred, processed and disposed of safely when proper procedures and safeguards are used. 

“Cresol” refers to any of the three isomers of methylphenol (C7H8O) or combinations thereof. “Cresols” commonly refer to a mixture which is predominantly methylphenol but may also contain lesser amounts of other alkylphenols. “Xylenol” is a common name for any of the six isomers of dimethylphenol (C8H10O) or their various combinations. Material which is predominantly dimethylphenol but which also contains ethylphenols and other alkylphenols may be referred to as “Xylenols”. “Cresylic acid” is a generic term referring to various combinations of cresols, xylenols, phenol or other alkylphenols (ethylphenols, propylphenols, trimethylphenols, etc.). 

Purpose & Scope

The purpose of this document is to provide information gathered through Sasol’s long experience in the safe handling of cresylic acids. It focuses on basic and practical information about working safely with these substances. Additional references are provided and it is strongly recommended that these and others be consulted prior to working with cresylic acids. Please do not hesitate to contact your regional Sasol office if we can be of assistance in the safe storage, handling, processing and disposal of our products.


Health Hazards

The primary dangers posed in handling cresylic acids are those resulting from physical exposure. Cresylic acids are highly corrosive and contact with exposed skin or mucous membranes causes severe burns. These burns progress from an initial whitening of the exposed skin to blackishbrown necroses within 24 hours after exposure. Cresylic acids also exhibit anesthetic properties. Therefore, victims frequently misjudge the extent of their exposure when the initial burning sensation rapidly subsides. This can result in prolonged contact, causing toxic effects in addition to the corrosive damage. 

Cresylic acids are readily absorbed through the skin and mucous membranes in liquid or vapor form and act as systemic toxins for which there is no established treatment. Relatively small areas of exposure (e.g. an arm or a hand) can allow sufficient absorption to cause severe poisoning. Progressive symptoms of such poisoning include headache, dizziness, ringing in the ears, nausea, vomiting, muscular twitching, mental confusion, loss of consciousness and, possibly, death from lethal paralysis of the central nervous system. Chronic exposure can lead to loss of appetite, vomiting, nervous disorders, headaches, dizziness, fainting and dermatitis. 

The Occupational Health & Safety Administration (OSHA) has established 5ppm or 22 mg/m3 permissible exposure limits (PEL’s) for cresols on an 8-hour time-weighted average basis. OSHA guidelines also indicate that adequate personal protective equipment (PPE) should be employed to avoid skin contact with cresols. Cresylic acids are not listed as carcinogens by OSHA, the International Agency for Research on Cancer (IARC) or the National Toxicology Program (NTP).

Environmental Hazards

Cresylic acids show high acute toxicity towards both fish and aquatic invertebrates and must be prevented from entering surface or ground waters. Depending upon the specific composition, the material may be classified as a marine pollutant. Please refer to the current label and safety datasheet.

Controls for Working with Cresols

Safe storage, handling, processing and disposal of cresylic acids begin long before they ever arrive on-site. Measures necessary to ensure the health and well-being of employees, customers, the community and the  environment include the development of effective administrative and engineering controls designed to specifically address the hazards associated with cresylic acids. Personal protective equipment (PPE) is integral to safe handling and should be viewed as the last line of defense against an accidental failure of the administrative and/or engineering controls. 

Administrative Controls

Administrative controls are the foundation of any program designed for safely handling cresylic acids. Every company is unique in how they run their business and establish administrative controls. Those specifically developed for working with cresylic acids should address comprehensive process planning, thorough communication of hazards to employees and extensive training of employees on the proper implementation of all safety measures.

Personal Protective Equipment (PPE)

All personnel who work with or near cresylic acids must use adequate personal protective equipment (PPE). The extent of the potential exposure and consideration of established permissible exposure limits (PEL’s) should dictate the level of protection necessary. Personnel working with or near lab-scale quantities should always wear safety glasses with side-shields or

chemical mono-goggles, chemical-resistant or impermeable gloves, long-sleeved shirts and trousers as a minimum.

Circumstances such as elevated temperature and pressure or vacuum conditions should dictate if more substantial protection is necessary, including face shields, chemically impermeable outerwear, and breathing protection. Personnel transferring larger quantities of cresylic acids, or working in areas where a line-break could result in similar exposure, should always wear full protective equipment.

Emergency Procedures

Physical Exposure – External

The primary dangers involved in working with cresylic acids are the corrosive and toxic effects resulting from a physical exposure. Studies suggest that the severity of the exposure depends more on the magnitude of the exposed skin area than the concentration of cresylic acid. Therefore, the critical factor in dealing with an external physical exposure to cresylic acids is to minimize the extent and duration of the contact. To this end, the immediate response must be thorough flushing of the exposed areas with copious amounts of running water to remove all the cresylic acid in contact with the skin or eyes. Any contaminated clothing should be removed as quickly and carefully as possible during this process to avoid any additional skin contact.

Any exposed areas will have readily absorbed the cresylic acids and may be evidenced by a characteristic whitening of the skin. After thorough flushing with water, a solution consisting of 2 parts polyethylene glycol 400 to 1 part ethanol (PEG/EtOH) should be liberally applied to any affected skin (avoid contact with eyes), allowed to remain 15 to 30 seconds and then flushed away with fresh running water. Continue the cycling of PEG/EtOH and water for at least 15 minutes and then finish with thorough washing with soap and water. This decontamination procedure reduces the severity of the exposure, but does not completely eliminate damage to the skin or toxic effects. Medical attention should be sought as soon as possible.

Spill Containment & Clean-Up

Spill containment and cleanup of cresylic acids should only be performed by properly trained personnel employing an appropriate level of protective equipment as dictated by the extent of the spill. Small to medium spills on land should be surrounded by and absorbed onto inert clay absorbent and transferred to a disposal container. Larger land-spills should be diverted away from waterways, contained with booms, dikes or trenches, and collected in a vacuum truck. Any residual cresylic acids remaining after vacuuming should be cleaned up using the clay absorbent. All soils affected by the spill should be removed and placed in approved disposal containers.

Water spills are of particular concern due to the acute toxicity of cresylic acids to marine life. Clean up efforts should focus on containing the spill and quickly removing the cresylic acids that settle in deeper areas of the waterway. This can be aided greatly if the flow of water can be slowed or stopped. Further efforts should focus on removing as much of the dissolved cresylic acids as possible from the water using activated charcoal.

The composition and extent of any spill should be evaluated against local guidelines (ex. SARA Title III and RCRA in the U.S.) and reported to the proper agencies, if necessary. Any non disposable clean-up equipment should be thoroughly decontaminated with soap and water after use.

Source : SASOL / USA

Safe Handling of Cresols, Xylenols & Cresylic Acids


Some significant points to note about Cresylic Acid

Below is a photo taken 10 years ago in the Irish Army Air Corps NDT shop,  part of the Avionics / ERF building complex. Ardrox 666 can be seen spilled on the ground where it was free to leach through a shore onto the grass verge outside. 

  • 25% of fresh Ardrox 666 used by the Air Corps was Cresylic Acid. This percentage was higher in waste Ardrox 666 as Dichloromethane evaporated.
  • That greenish / yellow stain dripping from the extractor fan is also Ardrox 666 from the air.