Biosorption of uranium from aqueous solutions by Azolla sp. and Limnobium laevigatum

Bioavailability assessment of propiconazole to Limnobium laevigatum and zebrafish (Danio rerio) in aquatic microcosms

Residues of the triazole fungicide propiconazole (PCZ) in the environment can easily enter aquatic ecosystems through various pathways and accumulate in sediments, thus threatening ecosystem stability. The method of using passive sampling techniques to measure the freely dissolved concentration (Cfree) of pollutants in aquatic environments for assessing their bioavailability has been widely utilized in environmental risk assessments. This study employs oleic acid-embedded cellulose acetate membrane (OECAM) as a tool to determine the Cfree of PCZ in water. By establishing sediment spiking concentrations of 0.1 and 0.5 mg/kg in an aquatic microcosm, the distribution and bioaccumulation of PCZ in zebrafish (Danio rerio) and the aquatic plant Limnobium laevigatum (L. laevigatum) were examined over a 7-day period. During the experimental period, the concentrations of PCZ in the water for the 0.1 mg/kg and 0.5 mg/kg treatment groups remained approximately 0.9 μg/L and 10.0 μg/L, respectively. After 7 days, the PCZ content in the sediments decreased by 22.74% and 14.94%, respectively. In both zebrafish and L. laevigatum, the concentration of PCZ initially increased and then gradually stabilized, with both species exhibiting moderate accumulation ability for PCZ. The bioconcentration factor (BCF) for zebrafish in the 0.1 mg/kg and 0.5 mg/kg treatment groups ranged from 9.25 to 13.96 and 7.84-16.05, respectively, while those for L. laevigatum ranged from 28.17 to 31.40 and 23.01-36.11, respectively. By the end of the 7-day experiment, the total PCZ content in both treatment groups decreased by an average of 17.51%. Among them, L. laevigatum contributed significantly, highlighting its potential in accelerating the removal of PCZ from aquatic ecosystems.

A review of remediation technologies for uranium-contaminated water

Uranium is a naturally existing radioactive element present in the Earth's crust. It exhibits lithophilic characteristics, indicating its tendency to be located near the surface of the Earth and tightly bound to oxygen. It is ecotoxic, hence the need for its removal from the aqueous environment. This paper focuses on the variety of water treatment processes for the removal of uranium from water and this includes physical (membrane separation, adsorption and electrocoagulation), chemical (ion exchange, photocatalysis and persulfate reduction), and biological (bio-reduction and biosorption) approaches. It was observed that membrane filtration and ion exchange are the most popular and promising processes for this application. Membrane processes have high throughput but with the challenge of high power requirements and fouling. Besides high pH sensitivity, ion exchange does not have any major challenges related to its application. Several other unique observations were derived from this review. Chitosan/Chlorella pyrenoidosa composite adsorbent bearing phosphate ligand, hydroxyapatite aerogel and MXene/graphene oxide composite has shown super-adsorbent performance (>1000 mg/g uptake capacity) for uranium. Ultrafiltration (UF) membranes, reverse osmosis (RO) membranes and electrocoagulation have been observed not to go below 97% uranium removal/conversion efficiency for most cases reported in the literature. Heat persulfate reduction has been explored quite recently and shown to achieve as high as 86% uranium reduction efficiency. We anticipate that future studies would explore hybrid processes (which are any combinations of multiple conventional techniques) to solve various aspects of the process design and performance challenges.