Eco-friendly method for the analysis of the soluble fraction of parabens leached from sludge of a hospital wastewater treatment plant—proof of concept

Developing eco-friendly analytical methods is crucial for monitoring emerging pollutants in complex matrices. This study presents a methodology based on green chemistry for determining the bioavailable fraction of methylparaben (MeP), ethylparaben (EtP), propylparaben (PrP), and butylparaben (BuP) in hospital wastewater treatment plant sludge. The approach combines in situ leaching with rotating-disk sorptive extraction (RDSE) in reverse mode, followed by direct-immersion solid-phase microextraction (DI-SPME) and headspace (HS-SPME) with on-fiber derivatization. GC-MS analysis identified the DVB/CAR/PDMS fiber as the most effective due to its high analyte affinity. Derivatization was successfully performed at room temperature in 10 min, with mass spectral match factors above 85%. The active analytical workflow (SPME extraction, on-fiber silylation, and GC-MS analysis) is completed in under 60 min per sample, enabling high-throughput screening once the parallel overnight leaching is completed. The method shows high sensitivity (LODs: 2.1-5.2 ng/g), good reproducibility (RSD < 9%), and accuracy (recoveries: 80-96% at 800 ng/g, n = 3). The four parabens were quantified in real sludge samples; MeP, EtP, and BuP were detected below their limits of quantification (< LOQ), while PrP was quantified at 20.0 ± 2.4 ng/g. Significant matrix effects (50% signal reduction) necessitated a standard additions protocol. The method's greenness, practicality, and innovation were validated using AGREEprep (score 0.54), BAGI (score 75.0), and VIGI (score 75) metrics, confirming its high sustainability, routine feasibility, and innovative character for complex environmental sample preparation.