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.

Dail Éireann Written Answers 26/09/17 – Department of Defence – Protected Disclosures

Aengus Ó Snodaigh (Dublin South Central, Sinn Fein)

548. To ask the Taoiseach and Minister for Defence if he has acted on the information relayed to him by a whistleblower that specifically named the Defence Forces official who allegedly ordered the destruction of health and safety documents; and if he will make a statement on the matter. [40485/17]

Paul Kehoe (Wexford, Fine Gael)

As I have previously indicated to the House, this matter was raised with me in correspondence where certain allegations were made that the documents had been destroyed. The correspondence in question was also addressed to the Chief of Staff and to the Deputy. I requested a report from the Chief of Staff on the actions taken on foot of the accusation.

He has informed me that the officer named met with the General Officer Commanding the Air Corps. The officer concerned has refuted the allegations made and it should further be noted that documents referred to were not military documents, nor did they carry any military security classification.


Can we suggest that Minister Kehoe and the Chief of Staff meet with the NCO who was ordered to destroy the Health & Safety documents to hear his testimony first hand.

Can we also suggest that the Minister & Chief of Staff meet with the Health & Safety officer who commissioned the reports to determine his recollection of the contents of the Tech Stores Air Quality Report & the Ramp Carbon Monoxide report.

Perhaps they might also ask the Health & Safety officer why the adverse findings in the 1995 ERF report and the recommendations in the 1997 Forbairt report were not communicated to lower ranks and why the recommendations for PPE and chemical training were not acted upon for 20 years.


Dáil Éireann Written Answers 26/09/17 – Department of Defence – Chemical Exposure Report

Aengus Ó Snodaigh (Dublin South Central, Sinn Fein)

547. To ask the Taoiseach and Minister for Defence if he will waive legal privilege and publish the Chemical Exposure Report 1994-2005 in the public interest and in the interest of transparency. [40484/17]

Paul Kehoe (Wexford, Fine Gael)

The report referenced by the Deputy was prepared in the context of ongoing legal proceedings. As the release of the report could adversely impact on those proceedings, I will not be releasing the report.


Minister Paul Kehoe must note that there are many personnel who have not taken legal action but whose lives are being regularly threatened by illness flare-ups of pneumonia type illness, hypokalaemia & other incapacitating occurrences such as stroke like symptoms that are currently defying diagnosis

Being able to provide firm evidence of unprotected toxic chemical exposure through dangerous work practices, to treating doctors & consultants, may assist these medical personnel successfully diagnose & treat our colleagues.

The State Claims Agency, who is advising the Minister and his department, does not give a damn whether serving or former personnel live or die and furthermore they couldn’t give two hoots about Minister Kehoe’s political career.

Minister Kehoe needs to be fully aware that not releasing this document will cost lives.


Dáil Éireann Written Answers 20/09/17 – Department of Defence – Defence Forces Properties

Aengus Ó Snodaigh (Dublin South Central, Sinn Fein)

810. To ask the Taoiseach and Minister for Defence if his attention has been drawn to the fact that dangerous chemicals such as ardrox 666 were disposed of for the Air Corps by a company that collected and disposed of all such highly toxic, corrosive and carcinogenic chemicals; and if the amount of chemicals purchased corresponds with the amount sent for safe disposal by the company engaged by the Air Corps to carry out such work in the past 20 years. [39259/17]

Aengus Ó Snodaigh (Dublin South Central, Sinn Fein)

811. To ask the Taoiseach and Minister for Defence if his attention has been drawn to the fact that dangerous chemicals were over the years in a systematic fashion leeched into the soil on lands at Casement Aerodrome, Baldonnel; if soil and or ground water samples have been taken on the 600 acre site at Baldonnel during the past 20 years; if so, the results of those tests; the action taken to prevent this practice; if decontamination of the soil occurred; and if such practice has now ended. [39260/17]

Paul Kehoe (Wexford, Fine Gael)

I propose to take Questions Nos. 810 and 811 together. As this matter pertains to litigation which is ongoing, it would be inappropriate for me to comment at this time.

Skin Cancer in Irish Air Corps personnel – Basal Cell Carcinoma

Photo of BCC on the leg of a former Air Corps employee who worked daily with Ardrox 666. This person also has cancerous growths on his arm & scalp.

Basal Cell Carcinoma’s are abnormal, uncontrolled growths or lesions that arise in the skin’s basal cells, which line the deepest layer of the epidermis (the outermost layer of the skin). BCCs often look like open sores, red patches, pink growths, shiny bumps, or scars and are usually caused by a combination of cumulative and intense, occasional sun exposure.

Both long-term sun exposure over your lifetime and occasional extended, intense exposure (typically leading to sunburn) combine to cause damage that can lead to BCC. Almost all BCCs occur on parts of the body excessively exposed to the sun — especially the face, ears, neck, scalp, shoulders, and back.

On rare occasions, however, tumors develop on unexposed areas. In a few cases, contact with arsenic, exposure to radiation, open sores that resist healing, chronic inflammatory skin conditions, and complications of burns, scars, infections, vaccinations, or even tattoos are contributing factors.

It is not possible to pinpoint a precise, single cause for a specific tumor, especially one found on a sun-protected area of the body or in an extremely young individual.

Skin cancer (non-melanoma)
Causes grouped by strength of evidence
Strong  Good  Limited 
arsenic aromatic amines acrylamide
benzo(a)pyrene arsenical pesticides vinyl chloride
coal tars benz(a)anthracene
ionizing radiation creosotes
mineral oils dibenz(a,h)anthracene
shale oils dimethyl benzanthracene
UV radiation ethylene oxide

We are aware of a number of current & former Air Corps technicians who have developed Basal Cell Carcinoma. It is interesting to note that there is good evidence to link creosotes with Basal Cell Carcinoma. Creosotes are a component chemical of Ardrox 666.

However, Basal Cell Carcinoma is a very common cancer and so the occurrence may not be unusual.

Key point as with almost all of the illnesses suffered by Air Corps Chemical Abuse Survivors is of course vigilance. Don’t delay going to your doctor.