Occurrence of alkylphenols in drinking water samples by solid phase extraction gas chromatography-mass detection analysis

Aim: Alkylphenols (APs) are synthetic organic compounds widely used in the chemical industry and in consumer products such as detergents, cosmetics, plastics, pesticides, pharmaceuticals, and cleaning agents. These compounds are persistent in the environment, prone to bioaccumulation in aquatic organisms, and exhibit considerable toxicity. Their presence has been reported in a wide range of environmental matrices, including surface water, wastewater, drinking water, sediments, and biological tissues, with concentrations reaching up to 30 μg/L in surface waters. The aim of this work is to study the concentration of APs in drinking water samples from several locations across the Mediterranean basin of Spain in order to establish an assessment of the occurrence of these compounds in these samples. Methods: In this study, a solid-phase extraction (SPE) method followed by gas chromatography-mass spectrometry (GC-MS) was developed, validated, and applied to determine the presence of APs in water. Two sorbents (C18 and HLB) were evaluated for extraction efficiency, with C18 yielding the best recoveries. The method showed good linearity and low detection and quantification limits, achieving acceptable recovery and precision values across various concentrations. Results: A set of 64 tap water samples was collected across Spain between February and May 2025, and 4-nonylphenol (4-NP), 4-octylphenol (4-OP), and 4-tert-octylphenol (4-tOP) concentrations were determined. Among the compounds studied, 4-OP was the most frequently detected (73%), followed by 4-NP (34%) and 4-tOP (12%). All detected concentrations were below the legal threshold of 0.3 µg/L, although certain locations showed relatively higher levels. Conclusions: The results demonstrate the method’s suitability for environmental monitoring and highlight the continued presence of APs in drinking water despite existing regulations, with the 4-alkylphenol (4-AP) being the most prevalent found in the analyzed drinking water.