Phthalic acid esters (PAEs) are often detected in remediated groundwater using appropriate oxidant materials by in situ groundwater treatment. The study compares zero-valent iron–persulfate with a pyrite–persulfate system to degrade three PAEs—di(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), and dimethyl phthalate (DMP). Column experiments were conducted, and rapid oxidation occurred in a pyrite–persulfate system due to sulfate radical generation. DMP concentration was found at about 60.0% and 53.0% with zero-valent iron (ZVI) and pyrite activation of persulfate, respectively. DBP concentration was measured as 25.0–17.2% and 23.2–16.0% using ZVI–persulfate and pyrite–persulfate systems, respectively. However, DEHP was not detected. The total organic carbon concentration lagged behind the Ʃ₃ PAEs. Persulfate consumption with ZVI activation was half of the consumption with pyrite activation. Both systems showed a steady release of iron ions. Overall, the oxidation–reduction potential was higher with pyrite activation. The surface morphologies of ZVI and pyrite were investigated using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and XPS. Intensive corrosion occurs on the pyrite surface, whereas the ZVI surface is covered by a netting of iron oxides. The pyrite surface showed more oxidation and less passivation in comparison with ZVI, which results in more availability of ${\mathrm{Fe}}^{2+}$ for persulfate activation. The pyrite–persulfate system is relatively preferred for rapid PAE degradation for contamination.

Stable isotopes are natural tracers that can provide quantitative information about the surface water/groundwater interactions and sources of pollutants in water. In this study, we measured δ18Owater and δ2Hwater and δ18Onitrate and δ15Nnitrate of the samples from the Hun River and groundwater in Shenyang City, China, where the water from the Hun River has a strong discharge and recharge connection with the groundwater. δ18Owater and δ2Hwater were used to determine the amount of surface water that was discharged into groundwater, while δ18Onitrate and δ15Nnitrate were employed to determine the sources of nitrate and ammonium in groundwater, which are the main contaminants in the study area. The reducing environment in groundwater may result from the prevailing iron and manganese, occurring from weathering of minerals and rocks, which prevents the ammonium being oxidized into nitrate. Results show that the amount of recharge from the Hun River into groundwater accounts for around 55.56–86.60% of the total groundwater in the dry season, and the ratio changed to 30.97–63.79% in the wet season. Multiproxy analysis (stable isotope analyses in combination with chemical and hydrogeological data of the study area) indicates that human activities, such as manure and sewage discharge, are the prevailing source of nitrogen in the waters.