ZnO Nanoparticles: Synthesis, Characterization, and Ecotoxicological Studies

Abstract

The potential ecotoxicity of nanosized zinc oxide (ZnO), synthesized by the polyol process, was investigated using common Anabaena flos-aquae cyanobacteria and Euglena gracilis euglenoid microalgae. The photosynthetic activities of these microorganisms, after addition of ZnO nanoparticles, varied with the presence of protective agents such as tri-n-octylphosphine oxide (TOPO) and polyoxyethylene stearyl ether (Brij-76) used to control particle size and shape during the synthesis. In the case of Anabaena flos-aquae , the photosynthetic activity, after addition of ZnO, ZnO-TOPO, and ZnO-Brij-76, decreased progressively due to stress induced by the presence of the nanoparticles in the culture medium. After contact with ZnO-TOPO nanoparticles, this decrease was followed by cell death. On the other hand, after 10 days, a progressive increase of the photosynthetic activity was observed after contact with ZnO and ZnO-Brij-76 nanoparticles. In the case of Euglena gracilis , cell death was observed after contact with all nanoparticles. Transmission electron microscopy (TEM) analyses of ultrathin sections of microorganisms showed that polysaccharides produced by Anabaena flos-aquae avoid particle internalization after contact with ZnO and ZnO-Brij-76 nanoparticles. On the other hand, nanoparticle internalization was observed after contact with all nanoparticles in the presence of Euglena gracilis and also with ZnO-TOPO nanoparticles after contact with Anabaena flos-aquae .

Does the Process for Production Nanoparticulate ZnO Play a Role in its Ecotoxicity?

“…Indeed, the photosynthetic activity was found statistically decreased in the microalgae grown in both media since the first 24h of exposure to the ZnO nanoparticles, but there was a gradual negative trend along the days. This effect was already observed by Brayner et al [5], for their synthesized nanoZnO. The deregulation in the cells energetic metabolism can also be confirmed by the intracellular ATP content, a parameter related to the mitochondrial activity.…”

“…Although no zeta potential study was performed, which is a limitation of this study, previous works from our research group with ZnO from diverse synthesis routes showed that zero-point charge is generally expected to be around pH 9.0 [5,11]. According to these authors, this material tends to be slightly negative between pH 4 and 6, neutral between pH 8 and 10 and highly negative between pH 10 and 12.…”

“…Because it has been widely produced and applied in industry, concern about its ecotoxicity is raising, as evidenced by the increasing number of publications in this topic, specially the ones dealing with aquatic toxicology. To cite a few of these studies: Tang et al [3] explored the toxicity of ZnO nanoparticles to Anabaena sp, a cyanobacteria (EC 50 = 0.74 ± 0.01 mg L -1 ); Brayner et al [4] reported biocidal effects of ZnO nanoparticles on E. coli bacteria (concentrations between 3.0 x 10 -3 and 1.5 x 10 -3 M inhibited bacterial growth by 85%, but concentrations between 1.5 x 10 -3 and 10 -3 M promoted an increase of E. coli colony forming units); Brayner et al [5] also observed that ZnO killed A. flos-aquae and the euglenoid Euglena gracilis after 10 days of incubation in the presence of the nanoparticles; and Franklin et al [6] evaluated the toxicity using Pseudokirchneriella subcapitata freshwater alga (72-h IC 50 value near 60 g Zn L -1 ).…”

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

“…For example, theoretically, a lipid-soluble synthetic dispersant could interact with the cell membrane (also lipophilic) to deliver more ENM to the test organism inadvertently, thus increasing the apparent toxicity of the test. In such circumstances, this additional effect on toxicity would not be evident in the dispersion agent control [32,33].…”

ZnO materials and surface tailoring for biosensing

“…The potential ecotoxicity of nanosized zinc oxide, synthesized by the polyol process, was investigated using common Anabaena flos-aquae cyanobacteria and Euglena gracilis euglenoid microalgae (72). Via addition of ZnO nanoparticles, the photosynthetic activities of these microorganisms varied with the presence of protective agents such as tri-octylphosphine oxide (TOPO) and polyoxyethylene stearyl ether (Brij-76) which is used to control particle size and shape during ZnO synthesis.…”