Fluoroquinolones, a class of antibiotics, have been detected in various aquatic environments, including those experiencing freeze-thaw cycles. This study investigated the adsorption of ciprofloxacin (CIP) in frozen (-21 degrees C) and aqueous (25 degrees C) solutions under varying pH levels, electrolyte types, and ionic strengths. CIP sorption on goethite was found to be transient, as freezing re-establishes equilibrium, nearly doubling CIP loadings at acidic to circumneutral pH values. The original equilibrium was restored by thawing. Our investigation reveals that ion pairs, formed between the positively charged piperazine group of CIP and anions (Cl-, Br-, and NO3-), create a charge-shielding effect, explaining the transient nature of CIP sorption equilibrium at goethite-water interfaces. In situ ATR-FTIR observations and model predictions further confirm the significant role of ion-paired surface complexes in transient CIP sorption. The transience of CIP sorption equilibrium in frozen and aqueous solutions is attributed to the local concentrations of anions, which undergo freeze-concentration into liquid intergrain boundaries and dilution by reversible ice nucleation and thawing. As the interaction between the hydrosphere and cryosphere intensifies with climate change, these findings have significant implications for evaluating the fate of contaminants in both terrestrial and aquatic environments.

Layers of permafrost developed during the 1950s and 1960s incorporated tritium from the atmosphere that originated from global nuclear weapons testing. In regions underlain by substantial permafrost, this tritium has been effectively trapped in ice since it was deposited and subject to radioactive decay alone, which has substantially lengthened its environmental half-life compared to areas with little or no permafrost where the weapons-test era precipitation has been subject to both decay and hydrodynamic dispersion. The Arctic is warming three times faster than other parts of the world, with northern regions incurring some of the most pronounced effects of climate change, resulting in permafrost degradation. A series of 23 waterbodies across the Canadian sub-Arctic spanning the continuous, discontinuous and isolated patches permafrost zones in northern Manitoba, Northwest Territories and Labrador were sampled. Surface water and groundwater seepage samples were collected from each lake and analyzed for tritium, stable isotopes (delta O-18 and delta H-2) and general water chemistry characteristics. Measured tritium was significantly higher in surface waters (SW) and groundwater seepage (GW) in water bodies located in the sporadic discontinuous (64 +/- 15 T U. in SW and 52 +/- 9 T U. in GW) and extensive discontinuous (53 +/- 7 T U. in SW and 61 +/- 7 T U. in GW) permafrost regions of the Northwest Territories than in regions underlain by continuous permafrost in northern Manitoba (< 12 T U. in both SW and GW) or those within isolated patches of permafrost in Labrador (16 +/- 2 T U. in SW and 21 +/- 4 T U. in GW). The greatest tritium enrichment (up to 128 T U.) was observed in lakes near Jean Marie River in the Mackenzie River valley, a region known to be experiencing extensive permafrost degradation. These results demonstrate significant permafrost degradation in the central Mackenzie River basin and show that tritium is becoming increasingly mobile in the sub-Arctic environment-at concentrations higher than expected-as a result of a warming climate. A better understanding of the cycling of tritium in the environment will improve our understanding of Arctic radioecology under changing environmental conditions.