Comparative Effects of Particle Sizes of Cobalt Nanoparticles to Nine Biological Activities

Abstract

The differences in the toxicity of cobalt oxide nanoparticles (Co-NPs) of two different sizes were evaluated in the contexts of the activities of bacterial bioluminescence, xyl-lux gene, enzyme function and biosynthesis of β-galactosidase, bacterial gene mutation, algal growth, and plant seed germination and root/shoot growth. Each size of Co-NP exhibited a different level of toxicity (sensitivity) in each biological activity. No revertant mutagenic ratio (greater than 2.0) of Salmonella typhimurium TA 98 was observed under the test conditions in the case of gene-mutation experiments. Overall, the inhibitory effects on all five bacterial bioassays were greater than those on algal growth, seed germination, and root growth. However, in all cases, the small Co-NPs showed statistically greater (total average about two times) toxicity than the large Co-NPs, except in shoot growth, which showed no observable inhibition. These findings demonstrate that particle size may be an important physical factor determining the fate of Co-NPs in the environment. Moreover, combinations of results based on various biological activities and physicochemical properties, rather than only a single activity and property, would better facilitate accurate assessment of NPs’ toxicity in ecosystems.

Evaluation of the Effects of Particle Sizes of Silver Nanoparticles on Various Biological Systems

“…The E. coli DH5α RB1436 mutant strain, producing bioluminescence during growth due to a plasmid with a constitutive promoter, was used. The preparation of this strain for the toxicity studies was as described in previous studies [ 75 ]. For the bioassay, AgNP solution (9 mL) was combined with the diluted bacterial suspension (1 mL), and bioluminescence activity (relative light units (RLU)) was measured every 30 min during incubation periods.…”

“…The procedure for the evaluation of the effect of AgNPs on enzyme biosynthesis was adopted based on the results of several preliminary tests. Detailed test protocols for the enzymatic and biosynthetic activity of enzyme were described in previous studies [ 75 ].…”

“…After 3 days of incubation, the growth inhibition was assessed by measuring three endpoints (cell counts, absorbance, and chlorophyll content). The preparation of the algal culture and test protocol for this assay was as described in previous studies [ 75 , 76 ].…”

Comparisons of the Effect of Different Metal Oxide Nanoparticles on the Root and Shoot Growth under Shaking and Non-Shaking Incubation, Different Plants, and Binary Mixture Conditions

“…Overall, slightly less soluble metals were observed with R. sativus (e.g., 156 ± 16 µg/L Ni for L. sativa vs. 37 ± 20 µg/L Ni for R. sativus at 5 mg/L NiO NPs), and there were no apparent differences in soluble metal concentrations in the different plant root growth experiments. Previous investigations in our laboratory using algae also revealed low concentrations of dissolved silver and cobalt (0.2–0.5 mg/L, corresponding to 0.1–0.5% of 20–100 mg/L Ag NPs) and Co (0.06–0.44 mg/L, corresponding to <0.02% of Co NPs), suggesting that dissolved metals had a low contribution to the toxicity of NPs in algae [ 51 , 52 ]. The control root length of R. sativus (115–152 mm) was approximately twice that of the L. sativa control (61–74 mm), providing a large surface area for contact with particles or soluble metals.…”

Metal Nano/Microparticles for Bioapplications

“…Kong et al reported a unique toxicity based on Co-NPs based on their sizes. Two different sizes of cobalt oxide nanoparticles were evaluated in the contexts of the activities of bacterial bioluminescence, enzyme function and biosynthesis of β-galactosidase, bacterial gene mutations, algal growth, and plant seed germination and root/shoot growth [ 13 ]. Han et al reported the stress response of mouse embryonic fibroblasts exposed to polystyrene (PS) nanoplastics.…”