4-aminophenol

Additional information on environmental fate and behaviour

Administrative data

Endpoint:

additional information on environmental fate and behaviour

Type of information:

experimental study

Adequacy of study:

supporting study

Data source

Reference

Reference Type:

publication

Title:

Mechanism for the primary transformation of acetaminophen in a soil/water system.

Author:

Chuanzhou Liang, Zhonghui Lan, Xu Zhang, Yingbao Liu

Year:

2016

Bibliographic source:

Water Research 98 (2016) 215-224

Materials and methods

Principles of method if other than guideline:

The transformation of acetaminophen (APAP) in a soil/water system was systematically investigated by a combination of kinetic studies and a quantitative analysis of the reaction intermediates.

GLP compliance:

no

Type of study / information:

The primary aim of this work was to quantify the transformation products and identify the main transformation pathway of APAP in a soil/water system. The second objective was to determine to what extent and how soil residues were generated during the transformation of APAP in a soil/water system.

Test material

Test material information

Constituent 1

Reference substance name:

4-aminophenol

EC Number:

204-616-2

EC Name:

4-aminophenol

Cas Number:

123-30-8

Molecular formula:

C6H7NO

IUPAC Name:

4-aminophenol

Results and discussion

Any other information on results incl. tables

Transformation of APAP with high spiked concentrations (530 µМ) was conducted in an air-dried soil dispersion (m:v = 1:500). It was found that p-aminophenol was the predominant intermediate, especially during the fast transformation period (5-10 days) of APAP. It has been reported that p-aminophenol can be formed through the release of acetate from APAP, and the process can be catalyzed by amidohydrolase. In aerobic aquatic environments, p-aminophenol is not stable and can be rapidly oxidized to p-benzoquinone imine, with further oxidation leading to the formation of p-benzoquinone (Brown and Corbett, 1979; Lerner, 2011; Sousa et al., 2013). It has also been reported that p-benzoquinone is one of the main intermediates during the transformation of APAP in soils (Li et al., 2014a). The reduction of p-benzoquinone led to the formation of 1,4-hydroquinone.

Intermediates with a larger molecular weight were formed after a 5-day incubation. The accumulated concentration increased and reached a maximum concentration at different reaction times, but both were later than that for p-aminophenol.

An intermediate with molecular weight 321 (P8) was assigned as a hydroxyl analogue of Bandrowski's base (NN'-bis-(p-hydroxyphenyl)-2-hydroxy-5-amino-1,4-benzoquinone di-imine), which has been identified during the oxidation of p-aminophenol in aqueous solutions (Brown and Corbett, 1979; Lerner, 2011; Sousa et al., 2013). As the difference in molecular weights between these two intermediates was equal to that of p-benzoquinone imine (MW = 107), it was reasonable to propose the intermediate with MW = 426 (P9, structure not identified) was also an oxidation product of p-aminophenol.

The intermediates (P8, P9) might be further oxidized to form insoluble fused heterocyclic compounds, which were observed in the brown-red liquid at a later reaction stage.

Applicant's summary and conclusion

Conclusions:

Para-aminophenol is a transformation product of acetaminophen when the latter is present in high concentration in a soil/water system. Para-aminophenol can be rapidly oxidized to p-benzoquinone imine, with further oxidation leading to the formation of p-benzoquinone. Intermediates with a larger molecular weight were formed after a 5-day incubation. An intermediate with molecular weight 321 (P8) was assigned as a hydroxyl analogue of Bandrowski's base (NN'-bis-(p-hydroxyphenyl)-2-hydroxy-5-amino-1,4-benzoquinone di-imine), another one with a molecular weight of 426 was detected but the structure was not identified.
The results of this study indicated that parameters including the soil/water ratio, light irradiation, land soil pretreatment can significantly influence the transformation kinetics of APAP in a soil/water system, while the transformation pathway differed among different soil types and initial APAP concentrations.

Executive summary:

The transformation of acetaminophen (APAP) in a soil/water system was investigated by a combination of kinetic studies and a quantitative analysis of the reaction intermediates. The transformation pathways were strongly dependent on the initial concentration of APAP and type and conditions of soil/water systems. The concentration of APAP and its transformation products were analyzed by high-performance liquid chromatography (HPLC).

The main primary transformation products were APAP oligomers and p-aminophenol, with the initial addition of 26.5 and 530 µM APAP, respectively. With high spiked concentrations, it was found that p-aminophenol (P5) was the predominant intermediate, especially during the fast transformation period (5-10 days) of APAP. In aerobic aquatic environments, p-aminophenol is not stable and can be rapidly oxidized to p-benzoquinone imine, with further oxidation leading to the formation of p-benzoquinone.

Intermediates with a larger molecular weight were formed after a 5-day incubation. An intermediate with molecular weight 321 (P8) was assigned as a hydroxyl analogue of Bandrowski's base (NN'-bis-(p-hydroxyphenyl)-2-hydroxy-5-amino-1,4-benzoquinone di-imine), which has been identified during the oxidation of p-aminophenol in aqueous solutions. As the difference in molecular weights between these two intermediates was equal to that of p-benzoquinone imine (MW = 107), it was reasonable to propose the intermediate with MW = 426 (P9, structure not identified) was also an oxidation product of p-aminophenol.

The intermediates (P8, P9) might be further oxidized to form insoluble fused heterocyclic compounds, which were observed in the brown-red liquid at a later reaction stage.