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Environmental fate & pathways

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4-aminophenol is soluble (6500 mg/L) and is inherently biodegradable in water with pre-adapted sludge. It has a low capacity to volatilise from solution to the air (Henry's law constant of 8.954E-005 Pa m3/mol-1) and undergoes rapid phototransformation in the atmosphere (half-life of 1.7 hours in the presence of hydroxyl radicals at1.5X10+6 hydroxyl radicals per cu assuming 12 hours daylight).

The partitioning coefficient (log Kow = -0.09) indicates that 4-aminophenol does not have a high potential for adsorption to soil or sediment (log Koc = 0.59). It has a low potential for bioaccumulation in aquatic and terrestrial habitats (BCF <=0.46 L/kg). Assuming predominate emissions to the water compartment, Mackay Level III fugacity predictions estimate 1.61%, 98.2%, 0.18% and 3.24e-007 % partitioning in the soil, water, sediment and air compartments, respectively.

4 -aminophenol is amphoteric with both amine and hydroxyl functional groups; pKa values for these groups are 5.48 and 10.46, respectively. At environmental pH values from 5 to 9, the substance is expected to exist primarily as the neutral species.

The rate constant for the vapor-phase reaction of 4-aminophenol with photochemically-produced hydroxyl radicals has been estimated as 74.2471 E-12cu cm/molecule-sec at 25 deg C using a structure estimation method (aopWin v1.92). This corresponds to an atmospheric half-life of about 1.7 hours at an atmospheric concentration of 1.5X10+6 hydroxyl radicals per cu cm (aopWin v 1.92).4-Aminophenol is expected to undergo fairly rapid oxidation in the presence of air and may directly photolyze due to its absorption in the environmental UV spectrum (max= 294 nm). Hence, the substance is unlikely to persist in air.  In addition, the vapour pressure (0.00053 Pa at 25°C) and the Henry's law constant (8.954E-005 Pa m3/mol) of the substance indicate that the substance is not likely to volatilize extensively from surfaces into air under dry conditions or from water.  Therefore, any concentrations of the substance in air are considered negligible.

4-Aminophenol is not expected to undergo hydrolysis in the environment due to the lack of hydrolyzable functional groups. Biodegradation is not expected to be a primary route of degradation in the environment. The substance is not readily biodegradable but can be considered inherently biodegradable with pre-adapted sludge. The substance is degraded at rates of 92%, 87% and 66% after 22d, 5d and 8d respectively when exposed to pre-adapted sludge (see section 4.1.2.1.2).This is an indication that the substance has the potential for degradation under favorable conditions, such as STP or biological treatment plant.  

The substance degrades primarily via abiotic processes and to a much lesser extent via biotic processes such as microbial degradation.  Abiotic degradation occurs rapidly when the substance is exposed to light and oxygen.