Indole

4 of 46 human adipose tissue samples, collected in 1982, contained indole (3 in age category 45+, 1 in age category 15-44 years)(1).

PERSONAL AIR: Expired air from control (n= 20), but not prediabetic (n= 14) or diabetic (n= 28) human study populations contained indole at unreported concns(1).

TERRESTRIAL FATE: Based on a recommended classification scheme(1), an estimated Koc value of 350(SRC), determined from a measured log Kow(2) and a recommended regression-derived equation(3), and a measured Koc of 187 from a synthetic soil with 0-2% added humic acid(4), indicate that indole will have moderate mobility in soil(SRC). Volatilization of indole should not be important from moist soil surfaces(SRC) given an estimated Henry's Law constant of 5.3X10-7 atm-cu m/mole(SRC), calculated from experimental values for vapor pressure(5) and water solubility(6). Indole is expected to readily biodegrade under both aerobic and anaerobic conditions in soil(SRC). Indole, added to Chernozem soil at 1 and 10 g/kg soil, was completely biodegraded in 19 and 135 days, respectively(7). Indole was completely biodegraded by suspensions of an organic soil (Carlisle muck) under methanogenic and denitrifying conditions within 67 and 144 days, respectively; oxindole was reported as a metabolite of this process(8).

AQUATIC FATE: Based on a recommended classification scheme(1), an estimated Koc value of 350(SRC), determined from a measured log Kow(2) and a recommended regression-derived equation(1), and a measured Koc value of 187(3) indicate that indole may adsorb to suspended solids and sediment in water(SRC). Indole is not expected to volatilize from water surfaces(1,SRC) based on an estimated Henry's Law constant of 5.3X10-7 atm-cu m/mole(SRC), calculated from experimental values for vapor pressure(4) and water solubility(5). According to a classification scheme(6), an estimated BCF value of 25(1,SRC), from a measured log Kow(2), suggests that bioconcentration in aquatic organisms is low(SRC). Indole is expected to readily biodegrade under both aerobic and anaerobic conditions in water(SRC). At 10 °C, aerobic groundwater containing a mixture of aromatic compounds completely biodegraded indole in 310 hours, including an acclimation period of 130 hours(7). Complete metabolism of indole by methanogenic sediments from the shore, edge, and bottom of Buffalo Run stream, PA, occurred within 33 days; oxindole was formed during this process(8). Indole was completely biodegraded under denitrifying conditions in 7 days using a sewage inoculum(8).

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), indole, which has a measured vapor pressure of 0.0122 mm Hg at 25 °C(2), will exist solely as a vapor in the ambient atmosphere. Vapor-phase indole is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals, nitrate radicals, and ozone(SRC); the half-lives for these reactions in air are estimated to be about 2 to 3 hours, < 1 minute, and 6 hours, respectively(3,SRC).

Different samples of Beaufort cheese from the French Alps contained indole at unreported concns(1). Indole, at unreported concns, was reported as a volatile flavor compound in fried bacon(2), roasted filbert nuts(3), short-necked clams and corbicula(4), and pork(5). Water-boiled duck meat and duck fat contained indole at 1.72 and 2.28 ppb, wet basis, respectively(6).

Indole was detected in industrial wastewaters from the following industries: timber products, leather tanning, iron and steel manufacturing, inorganics and plastics, synfuels, and publicly owned treatment works(1). Process water derived from the Fischer Assay retorting of oil shale from Rundle, Australia contained indole at 3 mg/l(2). A grab sample of final effluent from the Addison, IL publicly-owned treatment works in April 1980 contained indole at unreported concns(3). Wastewater obtained during the gasification of Indian Head lignite contained indole at an estimated concn of 1 mg/l(4). Wastewater and sludge from the Iona Island Sewage Treatment plant, Vancouver, British Columbia contained indole at unreported concns(5).

Untreated coke plant wastewater contained indole from 23 to 26,000 ug/l(1). Volatile components in poultry manure contained indole at concns of 5.08 and 10.4 mg/kg(2). Indole was identified in creosote oil extracts at 7700 ug/g(3). Basin floodwater, taken from Fort Devens, MA, following primary treatment, contained indole at 11 ug/l(4,5). Chlorinated still bottom extract contained indole at unreported concns(6).

A Koc of 187 was measured for indole on a synthetic soil consisting of 88-90% sand, 10% clay and 0-2% humic acid(1). The Koc of indole is estimated as approximately 350(SRC), using a measured log Kow of 2.14(2) and a regression-derived equation(3,SRC). According to a recommended classification scheme(4), these Koc values suggest that indole has moderate mobility in soil(SRC).

INDOOR AIR: Indoor air from 11% of the sampled private homes in the Chicago, IL area contained indole at unreported concns (n= 36)(1).

URBAN AIR: Both vapor phase and aerosol fractions of urban air contained indole at unreported concns(1). Indole was identified on aerosols collected from the Southern North Atlantic Ocean at a mean concn of 0.18 ng/cu m(2).

Indole's production and use as a chemical intermediate(1,2), a perfume fixative(2), a synthetic flavor(3) and its possible use as a kairomone (a volatile chemical released by a plant to attract phytophagus insects - used for insect control of adult rootworms)(4) may result in its release to the environment through various waste streams(SRC). Indole is released directly to the environment as a component of tobacco smoke(5). High-temperature coal tar contains on average just under 0.2% indole(6).

Groundwater containing a mixture of aromatic hydrocarbons and aromatic nitrogen-, sulfur-, and oxygen-containing heterocyclics, including indole initially present at 0.2 to 1 mg/l, gave an aerobic degradation time (defined as the total time from the start of the experiment until a concn less than 1 ug/l is reached) for indole of 310 hours including an acclimation time of 130 hours at 10 °C(1). Indole, in a 5 day BOD test, reached 49.5% of the theoretical BOD using a mixed microbial inoculum obtained from an enrichment culture(2). A 5 day BOD test gave a BOD of 2.07 g/g for indole using a sewage inoculum(3). First order biodegradation rate constants of 4.3X10-2 BOD/hr and 7.7X10-2 spec/hr were measured for indole at 1.6, 2.5, and 3.2 mg/l for a BOD and a UV spectrophotometry detection method, respectively; the inoculum used was a mixed culture obtained from an enrichment culture technique(3). A reaction pathway for the aerobic biodegradation of indole was proposed: indole to indoxyl to dihydroxyindole to isatin to formylanthranilic acid to anthranilic acid to catechol(5). Indole, added to Chernozem soil at 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 g/kg soil, was completely biodegraded in 19, 37, 62, 72, 84, 92, 102, 131, and 135 days, respectively(6).

Indole was completely biodegraded in 10 days under methanogenic conditions using a 9% anaerobic sewage sludge inoculum forming oxindole as an intermediate metabolite; the concn of indole in the sterile control over this time remained unchanged(1). Throughout the incubation period, net methane production increased, indicating that indole was mineralized(1). Complete metabolism of indole by methanogenic sediments from the shore, edge, and bottom of Buffalo Run stream, PA, occurred within 33 days. As indole disappeared, stoichiometric amounts of oxindole appeared in the sediment suspensions and persisted for over 4 weeks and was completely eliminated over 110 days(2). Complete biodegradation of indole was reported in 24 days using a 9% digested sludge inoculum at 22 °C under methanogenic conditions(2). Indole was completely biodegraded by suspensions of an organic soil (Carlisle muck) under methanogenic conditions within 67 days; concurrently, oxindole appeared, and persisted in near stoichiometric amounts for about 3 weeks(2). No oxindole accumulated under denitrifying conditions, using a soil inoculum, during the 144 days which were required for indole to disappear(2). This pattern was again seen using a 9% sewage sludge inoculum under methanogenic and denitrifying conditions; both conditions required 7 days for complete disappearance of indole; however, oxindole accumulated temporarily in the methanogenic culture but was not seen in the denitrifying culture probably due to rapid metabolism of this compound(2).