Detection of p-aminophenol and sub-products formed during oxidative process in water and hair salon effluent

Permanent hair dyeing is a popular process adopted by millions of people in the the world. Complex oxidative reactions are involved between precursor agents (aromatic amines) and couplers (phenolic compounds) in oxidizing alkaline medium inside the hair strand1. As result of these reactions colorful compounds are formed known as the proper hair dye. Simultaneously the reaction can also produce polynuclear by-products recognized for its high toxicity and mutagenic properties1. Thus, effluents from beauty salons can produce many contaminants that are commonly discarded in the sewer, contaminating water supply source, when the conventional sewage treatment system are not efficiently to treat this type of waste. The aim of this work is the investigation of the detection of p-aminophenol (PAF) a precursor of permanent hair dyeing and its oxidative sub-products formed in alkaline condition. In order to monitor its occurrence in hairdressing salon effluents collected after to receive wastewater from dyeing hair process, as well as to quantify the content of PAF in samples of surface water and tap water after treatment process in the drinking water plant. The effect of hydrogen peroxide at PAF was monitored by spectrophotometry UV-Vis and infrared spectrometry PAF in 0.1 mol L-1 ammonium buffer at pH 8.0. The intermediates and by-products generated during the polymerization side reaction of PAF were analyzed using mass spectrometry and hydrogen nuclear magnetic resonance spectroscopy. Previous extraction was used by thin layer chromatography and a mixture of chloroform, ethyl acetate and methanol in the ratio of 6:2:1 (v/v), respectively as the mobile phase. Quantitative analysis were carried out using high performance liquid chromatography with diode array detector for samples collected from surface water, tap water and hairdressing salon effluent. Under oxidizing alkaline medium, currently used in dyeing process it was observed a polymerization mechanism of PAF, forming the semi-quinoneimine radical as intermediate. Further oxidation generates the quinoneimine, which reacts subsequently with original PAF forming dimers, trimer and tetramer, respectively. The mass spectra obtained for the sample of hair salon effluents confirmed the presence of PAF and its reaction products as subproducts formed during the hair dyeing process. For the determination of PAF, analytical curve was constructed Area = 51914C(PAF) – 100.2 (R2 = 0.9994), with linearity to 300.0 mg L-1. Limits of detection and quantification were de 0.01 e 0.05 mg L-1, respectively. The recuperation of method was 97.4% and the relative standard deviation intra and interday were 3.6 and 6.8%, respectively. The residual concentrations of PAF in surface water, tap water and hairdressing salon effluent samples were 1,0x10-2 mg L-1, 5,78x10-3 mg L-1 and 3,4x10-2 mg L-1 of PAF, respectively. Therefore, the results obtained indicate that PAF is oxidized in peroxide medium commonly used in hair dyeing process without coupler presence and can forms many by-products identified by mass spectra and hydrogen nuclear magnetic resonance spectroscopy. Both, original PAF and their sub-products are found in hairdressing salon effluent. Taking into account, that PAF is considered highly toxic compounds when discarded in common sewage, and not properly treated could contaminate drinking and non-drinking water sources. The method proposed is able to detect the PAF and also their polynuclear by-products