Cyclohexane

Cyclohexane was qualitatively found in 8 of 12 breath samples of subjects monitored in Bayonne and Elizabeth, NJ, and Research Triangle Park, NC, 1980(1). Cyclohexane was detected in 30 of 56 personal air samplers for outside attendants at gasoline stations at a mean concentration of 0.114 mg/cu m, 45 of 49 samples for transport drivers at a mean concentration of 0.739 mg/cu m, and 43 of 49 samples for service attendants at a mean concentration of 0.127 mg/cu m(2). The indoor air inhaled dose of cyclohexane for residents in 3 Italian cities, March, 1995, was 28.5, 22.5. and 28.0 ug/day(3).

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), cyclohexane, which has a vapor pressure of 96.9 mm Hg at 25 °C(2), is expected to exist solely as a vapor in the ambient atmosphere. Vapor-phase cyclohexane is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals(SRC); the half-life for this reaction in air is estimated to be 2.3 days(SRC), calculated from its rate constant of 6.97X10-12 cu cm/molecule-sec at 25 °C(3). Cyclohexane does not contain chromophores that absorb at wavelengths >290 nm(4) and, therefore, is not expected to be susceptible to direct photolysis by sunlight(SRC). Laboratory studies have suggested that adsorption from the gas-phase in the atmosphere to ambient...

Based on measured sorption isotherms in a high-organic soil(1), the Koc of cyclohexane can be estimated to be about 350(SRC). Using a structure estimation method based on molecular connectivity indices(2), the Koc for cyclohexane can be estimated to be about 150(SRC). According to a classification scheme(3), these estimated Koc values suggest that cyclohexane is expected to have moderate mobility in soil(SRC).

Microbial degradation of cyclohexane: Cyclohexane goes to cyclohexanol goes to cyclohexanone goes to 1-oxa-2-oxocycloheptane goes to 6-hydroxyhexanoate goes to adipic acid /From chart diagram/

Using carp (Cyprinus carpio) which were exposed over an 8-week period, the BCF of cyclohexane ranged from 31-102 at a concentration of 0.1 mg/L and 37-129 at a concentration of 0.01 mg/L(1). An experimental BCF of 158 has also been reported(2). According to a classification scheme(2), these BCF values suggest bioconcentration in aquatic organisms is moderate to high, provided the compound is not metabolized by the organism(SRC).

The Henry's Law constant for cyclohexane has been measured as 0.15 atm-cu m/mole at 25 °C(1). This Henry's Law constant indicates that cyclohexane is expected to volatilize rapidly from water surfaces(2). Based on this Henry's Law constant, the volatilization half-life from a model river (1 m deep, flowing 1 m/sec, wind velocity of 3 m/sec)(2) is estimated as 2.7 hours(SRC). The volatilization half-life from a model lake (1 m deep, flowing 0.05 m/sec, wind velocity of 0.5 m/sec)(2) is estimated as 3.6 days(SRC). Cyclohexane's Henry's Law constant indicates that volatilization from moist soil surfaces may occur(SRC). Cyclohexane is expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 96.9 mm Hg(3).

/Cyclohexane has a/ half-life of about 0.24-24 hr /in air/ according to the reactivity scale of Darnall et al.

SURFACE WATER: In a survey of 14 heavily industrialized river basins in the United States (240 sites), 1 site in the Hudson River Basin contained 1 ppb of cyclohexane and 13 sites in the Mississippi River Basin contained 1.0-4.0 ppb of cyclohexane(1). Grab samples of surface water in the Gulf of Mexico in which there was anthopogenic influence contained 0-0.26 ppb of cyclohexane(2). Open water and unpolluted coastal water did not contain detectable quantities of the chemical(2). Surface water at an offshore oil production operation in the Gulf of Mexico contained 0.47 ppb of cyclohexane(3). Cyclohexane concentrations of <0.1 to 1.6 ug/L were reported for surface waters of the Dutch Rhine, Meuse, Northern Delta area and Westerscheldt over the period of 1991-1997(4).

Muscat oil (from Muscat grapes) was qualitatively found to contain cyclohexane(1); it was suggested that this may have been due to its presence as a solvent in a pesticide sprayed on the grapes(1).

Studies from the exposure of the general population to cyclohexane revealed that human milk from five of eight mothers contained cyclohexane (concentrations not determined). /It was/ suggested that the cyclohexane in the milk resulted from the mothers' exposure to environmental pollutants since they resided near chemical manufacturing plants or industrial user facilities.

/OTHER TOXICITY INFORMATION/ Toxicity threshold, Pseudomonas putida (bacteria) >400 mg/L at a pH of 7 at 25 °C.

The shoot of catmint (Nepeta racemosa; species of flowering plant in the family Lamiaceae) is reported to contain cyclohexane concentrations of 0-3 ppm(1).

The average emission of cyclohexane from gasoline in S. California, 1987, was 0.37% of the total non-methane hydrocarbon concentration(1); in Chicago, 1990, it was 0.7%(2). Cyclohexane emissions were found to be 0.4% and 0% of total organic emission for catalyst and non-catalyst auto engines, respectively(3). It was detected in exhaust of 1975-1982 model passenger vehicles(4). Cyclohexane was detected as an emission from Oklahoma oil fields, 1988, at an average concentration of 2.1 ppbC(5). The emissions of wastewater sludge composting facility contained cyclohexane at a concentration of 327 ug/cu m(6). The average concentration of cyclohexane in the exhaust of 6 cars in the UK, 1988, was 82 ppb(7). Cyclohexane was qualitatively detected as an emission from 5 hazardous waste sites and a...

The substance is very toxic to aquatic organisms. The substance may cause long-term effects in the aquatic environment. It is strongly advised not to let the chemical enter into the environment.

Cyclohexane occurs in crude oil and as a plant volatile(1). It is also released into the atmosphere from volcanos(1). Cyclohexane occurs in US crude oil at a concentration of approximately 7,000 mg/L(2). Cyclohexane is present in all crude oils in concentrations of 0.1-1.0%(3,4).

Cyclohexane is found in straight-run gasoline.

SEDIMENT: Cyclohexane was not detected in 27 sediment samples from surface waters in Japan in 1979 (detection limit was 0.1-0.4 ug/kg dw)(1).

Cyclohexane occurs in crude oil at concentrations ranging from 0.5-1.0% (weight) and the concentration in gasoline ranges from 5-15% (volume)(1). The average concentration in the exhaust of 67 vehicles was 0.6% (weight)(2). One pesticide grade n-hexane sample used as a solvent contained 0.1-1.0% cyclohexane(3). Trace amounts were also identified in cigarette smoke(4). JP-4 synthetic jet fuel mixture contains 6.5% (weight) of cyclohexane(5).

Cyclohexane's production and use in producing nylons, as a solvent for lacquers, resins, paints and varnish removers and its presence in gasoline may result in its release to the environment through various waste streams. Cyclohexane is present in all crude oils in concentrations of 0.1-1.0% and it can be released to the environment in volcanic emissions, tobacco smoke and plant volatiles. If released to air, a vapor pressure of 96.9 mm Hg at 25 °C indicates cyclohexane will exist solely in the vapor phase in the atmosphere. Vapor-phase cyclohexane will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals; the half-life for this reaction in air is estimated to be 2.3 days. Some vapor-phase absorption to ambient surfaces may occur. If released to soil...

Petroleum distillate poisoning may cause nausea, vomiting, cough, pulmonary irritation progressing to pulmonary edema, bloody sputum, and bronchial pneumonia. At high amounts, central nervous system depression may also occur, with symptoms such as weakness, dizziness, slow and shallow respiration, unconsciousness, and convulsions. Petroleum distillates are also irritating to the skin. (A594)

Treatment is mainly symptomatic and supportive. Gastric lavage, emesis, and the administration of activated charcoal should be avoided, as vomiting increases the risk of aspiration. (A600)

Mice (33 males) received one 60 ul application of 0.3% DMBA in benzene followed by a 60 uL/ application of cyclohexane twice/week for 50 weeks. No promoting activity of cyclohexane was observed.

Eyes, skin, respiratory system, central nervous system

LD50: 1.30 g/kg (Oral, Mouse) (T21)

Petroleum distillates are aspiration hazards and may cause pulmonary damage, central nervous system depression, and cardiac effects such as cardiac arrhythmias. They may also affect the blood, immune system, liver, and kidney. (A600, L1297)

Occupational hepatotoxin - Secondary hepatotoxins: the potential for toxic effect in the occupational setting is based on cases of poisoning by human ingestion or animal experimentation.

Oral (L400); inhalation (L400); dermal (L400)

Petroleum distillates are central nervous system depressants and cause pulmonary damage. (A600)

Inhalation Subchronic Reference Concentration Reference: PPRTV Current

Cyclohexane is found in gasoline, which is possibly carcinogenic to humans (Group 2B). (L135)

LD50 Rat oral 8.0-39.0 mL/kg

Soil Saturation Concentration (mg/kg): 1.17e+02

Advanced treatment: Consider orotracheal or nasotracheal intubation for airway control in the patient who is unconscious, has severe pulmonary edema, or is in severe respiratory distress. Positive-pressure ventilation techniques with a bag-valve-mask device may be beneficial. Consider drug therapy for pulmonary edema ... . Monitor cardiac rhythm and treat arrhythmias as necessary ... . Start IV administration of D5W /SRP: "To keep open", minimal flow rate/. Use 0.9% saline (NS) or lactated Ringer's (LR) if signs of hypovolemia are present. For hypotension with signs of hypovolemia, administer fluid cautiously.Watch for signs of fluid overload ... . Treat seizures with diazepam or lorazepam ... . Use proparacaine hydrochloride to assist eye irrigation ... . /Aliphatic hydrocarbons and re...

Soil Saturation Concentration (mg/kg): 1.17e+02