Development and application of diffusive gradients in thin films for in situ sampling of the organic UV filter 4-methylbenzylidene camphor (4-MBC) in waters

Abstract

4-Methylbenzylidene camphor (4-MBC), a typical organic UV filter (OUVF) in personal care products, is considered to be a potential endocrine disruptor due to its estrogenic activity and bioaccumulation. Although 4-MBC residues have been extensively identified in aquatic waters, little is known about their occurrence, levels, and potential risk in coastal waters. This study developed a reliable sampling approach, based on diffusive gradients in thin films (DGT) with XAD-2 as the binding agent, for monitoring 4-MBC in coastal waters. The diffusion coefficients of 4-MBC in freshwater and artificial seawater were 3.65 × 10⁻⁶ cm²/s and 3.83 × 10⁻⁶ cm²/s, respectively. XAD-2 binding gel showed rapid adsorption to 4-MBC. The accumulated masses of 4-MBC in XAD-2 DGT increased linearly with deployed time for 7 days in freshwater and seawater, which agreed well with theoretical predictions. The sampling performance was independent of ionic strength (0.0001–0.5 M), pH (4.0–8.5), and dissolved organic matter (0–20 mg/L). Field deployment in the river estuary and bathing beach showed that DGT-measured 4-MBC concentrations were consistent in comparison with grab sampling. Environmental risk assessment showed that 4-MBC may pose a medium risk to aquatic organisms based on computed risk quotient (RQ) values. Sewage discharge is the main source of 4-MBC risk, while the residue in recreation beaches contributes more significantly in summer. The established DGT sampling is suitable for seasonal monitoring, source identification, and risk assessment of 4-MBC in coastal waters.