Sun-Hwa Nam

Interaction of Silver Nanoparticles with Biological Surfaces of Caenorhabditis elegans

Silver nanoparticles (AgNPs) are being used in an increasing number of industrial and commercial applications; this has resulted in an increased release of AgNPs into the environment. Understanding the interaction of AgNPs with biological surfaces is important, as such understanding will facilitate predictions of the further effects of nanoparticles on biological systems. This study highlights the interaction of citrate-coated silver nanoparticles (cAgNPs) with the biological surfaces of the nematode C. elegans. General toxicity, as proxied by factors such as mortality and reproduction, was evaluated in nematode growth medium (NGM), which provides a more homogeneous distribution of cAgNPs than in K-medium. The survival and reproduction of C. elegans evidenced a clear reduction in up to 100 mg/L and 10 mg/L of cAgNPs, respectively. We also noted significant interactions of cAgNPs with the biological surfaces of C. elegans. Severe epidemic edema and burst were detected in the exposure group, which may be associated with secondary infections in soil ecosystems. We observed no evidence of cAgNPs intake by C. elegans. This is, to the best of our knowledge, the first report to investigate the nanotoxicity of cAgNPs as related to biological surfaces of C. elegans; further research is needed to study the fate of cAgNPs inside of C. elegans.

No evidence of the genotoxic potential of gold, silver, zinc oxide and titanium dioxide nanoparticles in the SOS chromotest.

Gold nanoparticles (Au NPs), silver nanoparticles (Ag NPs), zinc oxide nanoparticles (ZnO NPs) and titanium dioxide nanoparticles (TiO2 NPs) are widely used in cosmetic products such as preservatives, colorants and sunscreens. This study investigated the genotoxicity of Au NPs, Ag NPs, ZnO NPs and TiO2 NPs using the SOS chromotest with Escherichia coli PQ37. The maximum exposure concentrations for each nanoparticle were 3.23 mg l–1 for Au NPs, 32.3 mg l–1 for Ag NPs and 100 mg l–1 for ZnO NPs and TiO2 NPs. Additionally, in order to compare the genotoxicity of nanoparticles and corresponding dissolved ions, the ions were assessed in the same way as nanoparticles. The genotoxicity of the titanium ion was not assessed because of the extremely low solubility of TiO2 NPs. Au NPs, Ag NPs, ZnO NPs, TiO2 NPs and ions of Au, Ag and Zn, in a range of tested concentrations, exerted no effects in the SOS chromotest, evidenced by maximum IF (IFmax) values of below 1.5 for all chemicals. Owing to the results, nanosized Au NPs, Ag NPs, ZnO NPs, TiO2 NPs and ions of Au, Ag and Zn are classified as non‐genotoxic on the basis of the SOS chromotest used in this study. To the best of our knowledge, this is the first study to evaluate the genotoxicity of Au NPs, Ag NPs, ZnO NPs and TiO2 NPs using the SOS chromotest. Copyright

Effects of antimony on aquatic organisms (Larva and embryo of Oryzias latipes, Moina macrocopa, Simocephalus mixtus, and Pseudokirchneriella subcapitata)

Antimony is widespread in aquatic environment. Trivalent forms of antimony are known to be more toxic than other chemical species of antimony. In the present study, antimony potassium tartrate (APT), the trivalent inorganic forms of antimony, was selected as a test antimony compound due to its high water solubility. The effects of antimony on Japanese medaka (Oryzias latipes), planktonic crustacea (Moina macrocopa and Simocephalus mixtus), and green algae (Pseudokirchneriella subcapitata) were evaluated. Larval survival and the embryonic development were measured for fish assay. APT was less toxic to larval medaka (24-h LC50, 261; 48-h LC50, 238 mg L(-1)). Simocephalus mixtus was killed by very low concentrations of APT (24-h LC50, 4.92 mg L(-1)), and antimony was also toxic to Moina macrocopa (24-h LC50, 12.83 mg L(-1)). Toxicities of APT to S. mixtus and Moina macrocopa were about 50 and 20 times more toxic to Oryzias latipes larvae, respectively, in terms of 24-h LC50 value. Growth inhibition of Pseudokirchneriella subcapitata was observed in the presence of APT (72-h EC50, 206 mg L(-1)). This study demonstrated that APT is more toxic to planktonic crustacea than fish and green algae, and planktonic crustacea appears a better indicator of antimony pollution in aquatic environment.

Multispecies toxicity test for silver nanoparticles to derive hazardous concentration based on species sensitivity distribution for the protection of aquatic ecosystems

Abstract With increasing concerns about the release of silver nanoparticles (AgNPs) into the environment and the risks they pose to ecological and human health, a number of studies of AgNP toxicity to aquatic organisms have been conducted. USEPA and EU JRC have published risk assessment reports for AgNPs. However, most previous studies have focused on the adverse effects of AgNPs on individual species. Hazardous concentration (HC) of AgNPs for protection of aquatic ecosystems that are based on species sensitivity distributions (SSDs) have not yet been derived because sufficient data have not been available. In this study, we conducted multispecies toxicity tests, including acute assays using eight species from five different taxonomic groups (bacteria, algae, flagellates, crustaceans and fish) and chronic assays using six species from four different taxonomic groups (algae, flagellates, crustaceans and fish). Using the results of these assays, we used a SSD approach to derive an AgNP aquatic HC5 (Hazard concentrations at the 5% species) of 0.614 μg/L. To our knowledge, this is the first report of a proposed HC of AgNPs for the protection of aquatic ecosystems that is based on SSDs and uses chronic toxicity data.

Research Trends of Ecotoxicity of Nanoparticles in Soil Environment

We are consistently being exposed to nanomaterials in direct and/or indirect route as they are used in almost all the sectors in our life. Nations across the worlds are now trying to put global regulation policy on nanomaterials. Sometimes, they are reported to be more toxic than the corresponding ion and micromaterials. Therefore, safety research of nanoparticles has huge implications on a national economics. In this study, we evaluated and analyzed the research trend of ecotoxicity of nanoparticles in soil environment. Test species include terrestrial plants, earthworms, and soil nematode. Soil enzyme activities were also discussed. We found that the results of nanotoxicity studies were affected by many factors such as physicochemical properties, size, dispersion method and test medium of nanoparticle, which should be considered when conducting toxicity researches. In particular, more researches on the effect of physico chemical properties and fate of nanoparticles on toxicity effect should be conducted consistently.

Paper-disc method: An efficient assay for evaluating metal toxicity to soil algae ☆

The probabilistic ecological risk assessment using terrestrial toxicity data has been mainly based on microfauna or mesofauna. Soil algae, which are food source for microfauna and mesofauna, may be alternatively used for assessing soil toxicity. However, there are no internationally recommended guidelines for soil algal bioassays, and the collection of algae from the test soils has some limitations. In this study, we suggested the paper-disc method as an easy-to-use alternative. This method has been widely used for testing the antibacterial toxicity of various chemicals in agar media by measuring the diameter of the inhibition zone around the disc. We adapted the paper-disc method for screening the toxicity of copper (Cu) and nickel (Ni) to the soil alga Chlorococcum infusionum using various evaluation endpoints, such as growth zone, chlorophyll fluorescence, and photosynthetic activity. Chlorophyll fluorescence and photosynthetic activity decreased with the increasing concentrations of Cu(+2) or Ni(+2) contaminated soils. Algal growth zone was analyzed visually and showed similar results to those of chlorophyll fluorescence. The direct ethanol extraction method and indirect culture medium extraction method were similarly effective; however, the former was easier to perform, while the latter might facilitate the analysis of additional endpoints in future studies. Overall, the results suggested that the paper-disc method was not only a user-friendly assay for screening soil toxicity, but also effective due to its association with indirect soil quality indicators.

Cell size and the blockage of electron transfer in photosynthesis: Proposed endpoints for algal assays and its application to soil alga Chlorococcum infusionum

This study evaluated multiple endpoints of algal assays to identify sensitive and easy to use endpoints that could be applied to evaluate algal toxicity in metal-polluted soil extracts. Soil algae play an important role in trophic levels; thus, Chlorococcum infusionum was selected as the test species. Soil extracts were used because they might help identify potential soil retention and ecological hazards caused by pollutants that are present in the soil aqueous phase. The multi-endpoints measured were growth yield, photosynthetic activities, and cell viabilities. Nine parameters were measured to evaluate photosynthetic activity; namely, specific energy fluxes per quinone A-reducing photosystem II reaction center (absorption flux, trapped energy flux, electron transport flux, and dissipated energy flux per reaction center), quantum yields (maximum quantum yield of primary photochemistry, quantum yield of electron transport, quantum yield of energy dissipation, and average quantum yield of primary photochemistry), and the blockage of electron transfer from the reaction center to the quinone pool. Cell viability was evaluated by measuring cell size, cell granularity, and the autofluorescence of chlorophyll using flow cytometry. The results showed that heavy metals reduced growth yield, cell viability, and the photosynthetic activity of C. infusionum in soil extracts. Out of the 13 tested endpoints, the blockage of electron transfer from the reaction center to the quinone pool and cell size represented the most sensitive endpoints. We propose that both endpoints should be measured, along with conventional growth yield, to determine the effect of soil pollutants and to lower pollutant concentrations in soils.

An efficient and reproducible method for improving growth of a soil alga (Chlorococcum infusionum) for toxicity assays.

This study evaluated five methods of soil inoculation using the soil alga Chlorococcum infusionum to determine the most efficient and reproducible method for promoting the growth of soil algae for toxicity testing. The five techniques included application of C. infusionum in a circle on top of the soil, to a central spot on top of the soil, to a central spot in the subsoil, to one side on top of the soil, and application divided between a circle and a central spot on top of the soil. Of these, the first method generated the greatest amount of chlorophyll fluorescence and was the method with the best reproducibility. We evaluated the applicability of this method in an assessment of the toxicity of copper and nickel to C. infusionum in two representative standard soils. Copper (20-75 mg/kg for OECD soil and 20-60 mg/kg Lufa 2.2 soil) and nickel (400-500 mg/kg for OECD soil and 60-100 mg/kg Lufa 2.2 soil) reduced the chlorophyll fluorescence of C. infusionum when the inoculation was delivered in a circle on top of both soil types. To our knowledge, this is the first study to assess the suitability of different soil algal inoculation methods for terrestrial toxicity testing.

Conducting a battery of bioassays for gold nanoparticles to derive guideline value for the protection of aquatic ecosystems

Abstract Gold nanoparticles (Au-NPs) are used in many applications, including the manufacture of products like cosmetics, paints, and electrochemical immunosensors, and in the detection, diagnosis, and treatment of tumors. However, there are no legal or recommended guidelines for protecting aquatic ecosystems from Au-NPs. In this study, we conducted a battery of bioassays and present toxicity values for two bacteria, one alga, one euglena, three cladoceran, and two fish species that were exposed to Au-NPs. Guideline values for protecting aquatic ecosystems from Au-NPs were derived using methods that are generally used to derive water-quality guidelines and are used in Australia, New Zealand, Canada, the European Community (EC), and the USA. Au-NPs had adverse effects on all test species, including growth inhibition of both bacteria, the alga, and the euglena; mortality and immobilization in the three cladocerans; and developmental malformations in the embryos and larvae of the two fish. Guideline values of 0.15 and 0.04 × 1010 particles/mL were derived for Au-NPs using a species sensitivity distribution (SSD) and assessment factor. The guideline value derived for Au-NPs using an assessment factor was more stringent than that derived using SSD. This is the first study to derive guideline values for nanoparticles in water environments.

Continuous ultraviolet irradiation increases the adverse effects of photoreactive nanoparticles on the early development of Oryzias latipes.

The present study investigated the toxicity of photoreactive nanoparticles (NPs) on the development of Oryzias latipes. Buoyant fish embryos are potentially vulnerable to sunlight-derived ultraviolet (UV) irradiation. Zinc oxide (ZnO) NPs in surface water easily absorb UV irradiation from transmitted solar light. In the present study, O. latipes were exposed to ZnO NPs under irradiation with UV or visible light. The ZnO NPs exhibited considerable toxicity toward embryos and sac fry following UV irradiation, and these toxic effects resulted in increased mortality and abnormalities. The UV irradiation induced more serious effects on embryos than did visible light irradiation, and embryonic exposure resulted in irreversible developmental impairment or death of sac fry. The adverse effects of ZnO NPs may result from Zn ions released from photoreactive ZnO NPs. The present study demonstrates photo-dependent developmental impairment of O. latipes embryos as a result of exposure to ZnO NPs. The results demonstrate that the toxicity of photoreactive ZnO NPs could vary under environmentally relevant UV irradiation. These data could serve as a guide for evaluation of the toxicity of photo-activated NPs in natural surface waters and could be useful for the ecological risk assessment of photoreactive NPs.