Occurrence, spatial distribution, and source implications of 1,4-dioxane and chlorinated solvents from streams to marine environments.

1,4-Dioxane is a cyclic ether with high water solubility and low biodegradability, enabling its persistence and dispersion in aquatic systems. Chlorinated solvents are widely used industrial chemicals and are frequently co-detected with 1,4-dioxane because of its historical use as a stabilizer. Although 1,4-dioxane and related chlorinated solvents have been detected in seawater near marine industrial facilities, reliable analytical methods for their simultaneous determination in seawater have not yet been established. This study evaluated a modified U.S. EPA Method 522-based SPE-GC/MS approach for seawater and applied it across the Masan Bay continuum, including rivers, coastal waters, and a WWTP outlet area. Target analytes were 1,4-dioxane and the chlorinated solvents, including 1,1-dichloroethene (1,1-DCE), trichloroethylene (TCE) and 1,1,1-trichloroethane (TCA). Performance met analytical criteria, with calibration linearity (R2 ≥ 0.99), method detection limit (MDL) (0.10-0.27 ng/L), limit of quantification (LOQ) (0.30-0.87 ng/L), accuracy (72-96%), and precision (5.9-9.4%). Field application revealed a decreasing spatial trend, with higher concentrations in the inner bay and lower concentrations seaward. Near the WWTP outlet, 1,1-DCE, TCE, and TCA declined more rapidly than 1,4-dioxane. Riverine concentrations and composition profiles of target compounds differed among watersheds, with elevated 1,1-DCE levels observed at sites near industrial complexes. 1,4-Dioxane showed only minor differences between surface and bottom waters, while the chlorinated solvents were higher at depth at several sites. Based on the observed concentration distributions and composition patterns, monitoring strategies should differ by compound: chlorinated solvents should be prioritized in near-field surveillance, whereas 1,4-dioxane requires wider-area and long-term monitoring.