Cresol (mixed isomers)

Mixed cresols occur naturally in coal tar and are recovered as cresylic acids from coal tar distillation in the fractions above phenol (boiling range 190–205°C). They are also produced from petroleum by catalytic methylation of phenol or as byproducts of toluene and xylene processing. [1] The name 'cresol' without isomer specification typically refers to technical-grade cresylic acids — a mixture of all three isomers in proportions that vary depending on the source and manufacturing process. Commercial cresylic acid (from coal tar) has historically been approximately 35–40% o-cresol, 35–40% m-cresol, and 25–30% p-cresol. Cresol mixtures were the active ingredient in 'Lysol' when the product was introduced in 1889 by Gustav Raupenstrauch as a phenol-based disinfectant — a formulation that continued for decades until less toxic quaternary ammonium compounds largely replaced it in consumer products. [2] Creosote wood preservatives used to treat railroad ties, utility poles, and marine pilings contain substantial amounts of mixed cresols along with polycyclic aromatic hydrocarbons. Releases from wood treatment facilities, petroleum refineries, pharmaceutical plants, and chemical manufacturing operations make mixed cresols among the more commonly detected HAPs in industrial air emissions. [3] They are also released in wood smoke, vehicle exhaust, and tobacco smoke at lower levels.

Creosote workers in wood treatment facilities handling railroad tie and utility pole preservation are the primary occupational risk group for mixed cresol exposure from this source. Petroleum refinery workers encounter cresols in certain process streams. Chemical manufacturing workers producing disinfectants, synthetic resins, and specialty chemicals have direct exposures. The general public encounters very low levels from environmental background (traffic exhaust, wood smoke, tobacco smoke). People in communities near creosote wood treatment plants or petroleum refineries may have above-background air exposures.

Mixed cresols share phenol's mechanism of toxicity — rapid skin absorption, corrosive properties, CNS depression, and liver/kidney damage at significant doses. The OSHA PEL for mixed cresols is 5 ppm (ceiling). [3] Chronic occupational exposure has been associated with nervous system effects (including tremor and cognitive changes) in creosote workers. The EPA has classified the mixture as having carcinogenic potential. Aquatic toxicity is a significant concern — cresols are acutely toxic to fish and invertebrates at relatively low concentrations.

Creosote wood treatment workers, petroleum refinery workers, and chemical manufacturing workers are most at risk occupationally. Communities near creosote treatment facilities or sites with creosote-contaminated soil/groundwater have environmental exposures.

1. Creosote-treated wood should not be used in vegetable gardens, in indoor settings, or in contact with food or drinking water supplies. 2. Workers handling creosote-treated materials should wear chemical-resistant gloves, eye protection, and respiratory protection for dust. 3. Do not burn creosote-treated wood — combustion generates cresols and PAHs in smoke. 4. Chemical workers require local exhaust ventilation and continuous air monitoring with alarms set below the 5 ppm ceiling. 5. Communities near contaminated sites should monitor drinking water for cresols.