Toxicity of ceria nanoparticles to the regeneration of freshwater planarian Dugesia japonica: The role of biotransformation

Cerium oxide nanoparticles (n-CeO₂) have wide applications ranging from industrial to consumer products, which would inevitably lead to their release into the environment. Despite the toxicity of n-CeO₂ on aquatic organisms has been largely reported, research on developing organisms is still lacking. In this study, we investigate the toxic effects of n-CeO₂ on the stem cells, tissue- and neuro-regeneration, using freshwater planarian Dugesia japonica as a model. Effects of bulk sized (μ-) CeO₂ and ionic Ce (Ce³⁺) were compared with that of n-CeO₂ to explore the origin of the toxic effects of n-CeO₂. No overt toxicity was observed in μ-CeO₂ treatment. n-CeO₂ not only impaired the homeostasis of normal planarians, but also inhibited the regeneration processes of regenerated planarians, demonstrated by the inhibited blastema growth, disturbed antioxidant defense system at molecular levels, elevated DNA-damage and decreased stem cell proliferation. Regenerating organisms are more susceptible to n-CeO₂ than the normal ones. Ce³⁺ exhibited significantly higher toxicity than n-CeO₂, even though the total Ce uptake is 0.2 % less in Ce³⁺ than in n-CeO₂ treated in planarian. X-ray absorption near edge spectroscopy (XANES) analysis revealed that 12.8 % of n-CeO₂ (5.95 mg/kg Ce per planarian) was transformed to Ce³⁺ after interaction with planarian, suggesting that biotransformation at the nano-bio interface might play an important role in the observed toxicity. Since the biotransformation of n-CeO₂ is a slow process, it may cause long-term chronic toxicity to planarians due to the slow while sustained release of toxic Ce³⁺ ions.

Using ammonium-tolerant yeast isolates: Candida halophila and Rhodotorula glutinis to treat high strength fermentative wastewater

Two ammonium-tolerant yeast strains were isolated from sludge samples contaminated with monosodium glutamate manufacturing wastewater and were identified as Candida haplophila and Rhodotorula glutinis. The tolerance of the two yeast isolates to ammonia and their chemical oxygen demand (COD) removal perfomances were evaluated under batch and bench-scale conditions. The mixture of the two isolates was found to grow well in an artificial medium containing 25% (NH4)2SO4 and could effectively remove COD from monosodium glutamate wastewater even when the concentrations of NH4+-N and free NH3-N reached as high as 18,977 and 879 mg l(-1) respectively. A fixed-bed yeast reactor, which was initially inoculated with the yeast mixture, permitted a constant COD removal rate of over 80% during a period of near 2-month continuous running even when the influent COD was increased from 8,000 to 25,000 mg l(-1). The effluent was accompanied with suspended solids (SS) of over 4,500 mg l(-1), which was mainly composed of yeast cells and could be considered as a source of animal forage additive. The residual COD of effluents from the yeast reactor could be further reduced to under 500 mg l(-1) by a combination process of activated sludge treatment and coagulation technologies.