Endocrine-disrupting nonylphenols

Abstract

Nonylphenols (NPs) are degradation products of 4-nonylphenol ethoxylates (NPEs). NPEs are non-ionic surfactants that have been used for decades in cleaning agents and industrial processes due to their surfactant activity. As a result, NPs are ubiquitously detectable in many environmentally relevant matrices and biological samples. Theoretically, 550 different isomers can be derived. A possible grouping based on chain length and a numbering system based on this was proposed by Guenther et al. (2006). <br/> Nonylphenols are persistent, toxic, and endocrine disruptors. The structural features of various alkylphenols are known to influence estrogenic activity. Therefore, the use of NPEs and NPs was regulated throughout Europe in 2005 by Directive 2003/53/EC. Since then, the sale and use of products/formulations containing more than 0.1% NPE or NP have been prohibited. <br/> Nonylphenols can be extracted from food using steam distillation with integrated liquid-liquid extraction. Adding an isotopically labeled internal standard (¹³C₆-NP₁₁₂) before extraction allows the quantification of nonylphenols present in food as a sum parameter. After analyzing selected foods from different countries by high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS), NPs were detected in 30 of the 35 food samples. The concentration of NPs, based on fresh weight, ranged from 0.1 to 18.9 µg kg⁻¹. <br/> The highest NP contents were found in coffee samples, and therefore an isomer-specific analysis was carried out by comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GCxGC-TOF). Fourteen pure isomers of NP were used as standards for cross-referencing the NP isomers. We identified the two main NP isomers in the coffee samples as 4-[3-ethyl-1,1-dimethylpentyl]-phenol and 4-[1-ethyl-1,3-dimethylpentyl]-phenol or NP₁₂₈ and NP₁₁₁ (Juelich nomenclature), respectively. The GCxGC-TOF system with a liquid nitrogen cryogenic modulator used in this study is suitable for the isomer-specific analysis of NP and can be applied and further optimized for future routine analysis in food control.