Physico-chemical behaviour and algal toxicity of nanoparticulate CeO2 in freshwater

Abstract

Environmental context. It cannot be assumed that nanomaterials entering aquatic environments will have the same impacts on aquatic biota as their macroscopic particle equivalents. If their toxicities are different, this will have implications for the way in which nanomaterial usage is regulated. Algae, at the bottom of the food chain, are likely to be a sensitive indicator of toxic effects. Understanding the physical and chemical factors controlling nanoparticle toxicity to algae will assist in evaluating their ecological risk. Abstract. In assessing the risks posed by nanomaterials in the environment, the overriding research challenges are to determine if nanomaterials are more toxic than the bulk forms of the same material, and the extent to which toxicity is governed by particle size and reactivity. In this study, the toxicity of nanoparticulate CeO2 (nominally 10–20 nm) to the freshwater alga Pseudokirchneriella subcapitata was compared to the same material at the micron size (nominally <5 μm). Growth inhibition experiments revealed inhibitory concentration values, giving 50% reduction in algal growth rate after 72 h (IC50), of 10.3 ± 1.7 and 66 ± 22 mg L–1 for the nanoparticles and bulk materials respectively. Cells exposed to CeO2 particles were permeable to the DNA-binding dye SYTOX® Green in a concentration-dependent manner indicating damage to the cell membrane. Screening assays to assess the oxidative activity of the particles showed that the light illumination conditions used during standard algal bioassays are sufficient to stimulate photocatalytic activity of CeO2 particles, causing the generation of hydroxyl radicals and peroxidation of a model plant fatty acid. No oxidative activity or lipid peroxidation was observed in the dark. These findings indicate that inhibitory mode of action of CeO2 to P. subcapitata is mediated by a cell-particle interaction causing membrane damage. The effect is most likely photochemically induced and is enhanced for the nanoparticulate form of the CeO2.

Ecotoxicity test methods for engineered nanomaterials: Practical experiences and recommendations from the bench

“…Lighting is essential for algal growth, but too much light may promote ROS generation from ENMs. For example, the energy from ultraviolet light especially can promote free radical reactions on the surface crystal structure of nano titania [49] and nanoceria [50]. Notably, the rates of ROS production can be substantial (mmol/h levels for the final CO 2 product [49]) and are strongly dependent on the presence of organic matter to facilitate the movement of electrons on the surface of the ENM.…”

Manufactured nanoparticles in the environment

“…Further research in more complex but less easily interpreted conditions is required alongside these important laboratory based experiments. The next two papers by Scown et al [11] and Rogers et al [12] show further ecotoxicological data for fish and algae respectively using commercially available but well characterised metal oxides nanoparticles and discuss mechanisms of action (algae) and uptake (fish). Domingos et al [13] then discuss the impacts of environmentally relevant conditions such as pH, ionic strength, phosphate concentration and humic substances on the surface properties and aggregation of commercially available inorganic nanoparticles.…”

Beneficial Effects of Cerium Oxide Nanoparticles in Development of Chondrocyte-Seeded Hydrogel Constructs and Cellular Response to Interleukin Insults

“…[24][25][26][27][28][61][62][63][64][65][66][67][68][69][70] Specifically, nanoceria has been reported to be toxic to microbial and algal cells, which is correlated with the nanoparticle adsorption on the cell membrane. [64][65][66]68 It can also be toxic to mammalian cells, although the nanotoxicity mechanism appears to be different, including a rapid intracellular uptake 15 . A statistically significant downregulation of mechanical properties and GAG content was observed due to 0.5 ng/mL IL-1a in control and experimental samples.…”