Chronic toxicity of parabens and their chlorinated by‐products in Ceriodaphnia dubia

The chronic toxicity of 12 compounds of parabens and their chlorinated by‐products was investigated using 7‐day Ceriodaphnia dubia test under static renewal condition in order to generate information on how to disinfect by‐products of preservatives that are discharged in aquatic systems. The mortality and inhibition of reproduction tended to increase with increasing hydrophobicity and decreased with the degree of chlorination of parabens. The EC₅₀ values for mortality, offspring number, and first brood production ranged between 0.30–3.1, 0.047–12, and 1.3–6.3 mg L^?1, respectively. For the number of neonates, the most sensitive endpoint, the no‐observed‐effect concentration (NOEC) and lowest‐observed‐effect concentration (LOEC) values ranged from 0.63 to 10 mg L^?1 and from 1.2 to 19 mg L^?1, respectively. Methylparaben (MP), benzylparaben (BnP), and dichlorinated BnP (Cl₂BnP) elicited a significant decrease in offspring numbers even at their lowest concentration tested; the NOEC for these compounds was determined to be less than the lowest test concentration (1.3, 0.04, and 0.63 mg L^?1 for MP, BnP, and Cl₂BnP, respectively). Propylparaben (PP), chlorinated PP, isopropylparaben (iPP), and chlorinated iPP exhibited nonmonotonic concentration‐dependent response; their NOEC and LOEC values could not be determined. The multivariate approach involving principal component analysis and hierarchical cluster analysis revealed four groups that corresponded to the toxicological profiles of parabens. Our results suggested that disinfection of parabens by chlorination could reduce aquatic toxicity of original compounds. The findings obtained in our study together with the data available on paraben concentrations in aquatic systems can be used to perform preliminary risk assessment by comparing the predicted environmental concentration (PEC) with the predicted no‐effect concentration (PNEC) for the marine aquatic environment. The calculated PEC/PNEC ratios ranged from 0.0012 to 0.2, with the highest value observed in MP. This suggested that there are negligible environmental risks for aquatic organisms at current use levels. © 2013 Wiley Periodicals, Inc. Environ Toxicol 30: 664–673, 2015.     

Chronic toxicity of chlordane to Daphnia magna and Ceriodaphnia dubia: A comparative study

Chronic toxicity of chlordane, an organochlorine insecticide, was assessed on Ceriodaphnia dubia under standardized conditions of testing. Results were compared to Daphnia magna to determine the sensitivity of the two freshwater cladoceran species to this persistent organic pollutant (POP) and to explore the possibility of using the 7‐day C. dubia test as an alternative to the 21‐day D. magna test in chronic toxicity assessment of POPs. The NOEC‐7d value of chlordane on reproduction of C. dubia (2.9 μg/L) was much higher than the NOEC‐21d value of D. magna (0.18 μg/L), attesting that the 7‐day test on C. dubia was less sensitive than the 21‐day reproduction test on D. magna to chlordane. However, extending the period of exposure of C. dubia to chlordane from 7 to 14 days led to a NOEC‐14d value similar to the NOEC‐21d value in D. magna (0.18 μg/L). This study highlights the usefulness of prolonging the exposure time of the reproduction test in C. dubia from 7 to 14 days to increase the performances of the reproduction test on C. dubia for assessing chronic toxicity of POPs. © 2010 Wiley Periodicals, Inc. Environ Toxicol, 2012.     

银模板法制备中空金纳米粒及其质量评价

目的 制备并表征一种可用于载药的中空金纳米粒载体.方法 以银纳米粒为模板,通过模板置换法使氯金酸与银纳米粒反应生成金壳,并裹覆于银纳米粒表面,最后形成一种中空结构的金纳米粒,通过单因素考察对中空金纳米粒的制备进行初步探究.使用透射电镜对中空金纳米粒进行结构观察,紫外全波长扫描考察其吸收情况,体外光热转化试验考察载体的光热转化能力,以及四甲基偶氮唑蓝(MTT)试验考察载体细胞毒性.结果 氯金酸的加入方式为逐滴加入,制备温度为60 ℃,氯金酸(25 mmol·L-1)的加入量为128 μL,中空金纳米的粒径为35~55 nm,壳厚4~6 nm,最大吸收波长750~800 nm,具备较强的光热转化能力.细胞毒性结果表明,中空金纳米粒对人皮肤成纤维细胞(HDF)没有明显的细胞毒性.结论 经过优化制备得到的中空金纳米粒具备较好的中空结构,以及优异的光热转化能力和较低的细胞毒性.     

Acute toxicity of commonly used forestry herbicide mixtures to Ceriodaphnia dubia and Pimephales promelas

Because many herbicides selectively control specific species or types of vegetation, they are often applied as mixtures to achieve better control over undesirable vegetation. When herbicides are applied in forest ecosystems, streams, ponds, and other bodies of water are typically protected by buffer zones in which no herbicide is applied. However, in some landscapes, small wetlands and streams are difficult to see and avoid, thus the potential acute toxicity of herbicide mixtures to aquatic organisms is of interest, yet it has not been well‐studied. We examined the acute toxicity of 23 different herbicide mixtures to Ceriodaphnia dubia and fathead minnows (Pimephales promelas) at environmentally relevant concentrations, and, where possible, characterized mixture interactions using Marking's Additive Index. Maximum exposure concentrations were equivalent to applying the maximum allowable rate for each component directly to the surface of a 6‐in. deep pond with no dissipation following application. Under the conditions of this study, herbicide formulations containing Accord Concentrate (glyphosate), Arsenal AC (imazapyr), Chopper (imazapyr), Escort (metsulfuron methyl), Oust XP (sulfometuron methyl), and Velpar L (hexazinone) were not associated with appreciable acute toxicity to fathead minnows or C. dubia when used alone or in mixtures with each other and various surfactants and adjuvants. Herbicide mixtures for which Additive Indexes could be calculated exhibited primarily antagonistic or simple additive toxicity. In the few cases where synergistic toxicity was observed, the degree of synergism was slight, never exceeding approximately twice the effect estimated based on additive toxicity. Based on the results of this study, neither acute toxicity nor enhanced acute aquatic toxicity due to synergistic mixture effects appears to be a significant concern for applications of the herbicide mixtures most commonly used in forestry. © 2011 Wiley Periodicals, Inc. Environ Toxicol 2012.     

Teratogenic hazard of BPEI-coated silver nanoparticles to Xenopus laevis

Silver nanoparticles (AgNPs) are among the most exploited antimicrobial agents and are used in many consumer products. Size and surface reactivity are critical physico-chemical properties responsible for NPs toxicity, and surface coatings, often used to functionalize or stabilize AgNPs, can influence their toxic profile and biocompatibility. In the current study the developmental toxicity of (1) negatively charged citrate-coated AgNPs (Cit-AgNPs), (2) positively charged branched polyethylenimine-coated AgNPs (BPEI-AgNPs), and (3) Ag⁺ (from 0.0625 to 0.75?mg Ag/L) was investigated by the standard Frog Embryo Teratogenesis Assay – Xenopus (FETAX). In order to identify the most sensitive developmental phase, embryos were also exposed during different embryonic stages. Morphological and bio-physical studies were performed to characterize tissue lesions and NP uptake. The results suggest that Ag⁺ was strongly embryo-lethal. Contrary to Cit-AgNPs, the positively charged BPEI-AgNPs exert a concentration-dependent effect on lethality and malformations of embryos. The BPEI-AgNPs showed the highest teratogenic index (TI?=?1.6), pointing out the role of functional coating in determining the developmental hazard. The highest susceptibility to BPEI-AgNPs was during early embryogenesis, when embryos are still enclosed in the fertilization envelope, and the post-stomodeum opening stages, when NPs ingestion occurs. In BPEI-AgNPs treated larvae, the histological examination revealed irregular intestinal diverticula coupled with edematous connective tissue. Small NPs aggregates are mapped throughout the intestinal mucosa and secondary target organs by two-photon excitation microscopy. We conclude that a teratogenic risk may be associated with BPEI-AgNPs exposure, but the modality of NP-tissue interactions and the teratogenic mechanism need further investigations to be better defined.     

Effects of oral exposure to silver nanoparticles on the sperm of rats

It has been demonstrated that exposure to silver nanoparticles (AgNPs) can induce toxicological effects in rodents. In this study, we investigated whether sub-chronic oral exposure to different doses of polyvinil pyrrolidone (PVP)-coated AgNPs (PVP-AgNPs) (50, 100 and 200 mg/kg/day) could induce harmful effects on epididymal sperm rat parameters. Sperm motility, viability and morphology were examined. Moreover, a histological evaluation of testis and epididymis was also performed. High doses of PVP-AgNPs showed higher sperm morphology abnormalities, while a progressive, but not significant effect, was observed in other sperm parameters. The current results suggest that oral sub-chronic exposure to PVP-AgNPs induces slight toxicological effects in sperm rat parameters.     

载阿霉素金纳米粒的制备和细胞毒性研究

目的 构建载阿霉素（DOX）的甲氧基聚乙二醇（mPEG）修饰的金纳米粒AuNPs-mPEG@DOX，以降低DOX的毒副作用。方法 制备AuNPs-mPEG@DOX，通过粒径、电位和紫外可见光吸收光谱（UV-Vis）进行表征。考察连接巯基的DOX（HS-DOX）投药浓度对AuNPs-mPEG@DOX吸附率和载药量的影响。建立未吸附HS-DOX含量测定的高效液相色谱法（HPLC），对专属性、线性、精密度、稳定性和加样回收率进行考察。采用CCK-8法检测AuNPs-mPEG@DOX对MCF-10A和MCF-7细胞的毒性作用。结果 成功制备了AuNPs-mPEG@DOX，粒径为（46.12±0.49） nm，电位为（18.60±1.51） mV，最大吸收波长为530 nm。建立了可用于检测AuNPs-mPEG@DOX未吸附HS-DOX含量的HPLC方法，测定最佳投药浓度11.18 μg/ml，HS-DOX条件下的吸附率为（9.21±2.88）%，载药量为（2.01±0.62）%。细胞毒性实验表明AuNPs-mPEG@DOX可明显降低DOX对正常乳腺细胞的毒副作用；DOX在≥4.75 μmol/L时，AuNPs-mPEG@DOX与游离DOX对乳腺肿瘤细胞的细胞毒性作用一致。结论 AuNPs-mPEG@DOX可有效降低DOX的毒副作用，为后续AuNPs连接药物降低其毒副作用的研究提供参考。     

Aquatic toxicity of four alkylphenols (3-tert-butylphenol, 2-isopropylphenol, 3-isopropylphenol, and 4-isopropylphenol) and their binary mixtures to microbes, invertebrates, and fish

The acute and chronic toxicity of four simple alkylphenols with butyl and propyl substitutions was evaluated with aquatic microbes, invertebrates, and fish. These alkylphenols-3-tert-butylphenol, 2-isopropylphenol, 3-isopropylphenol, and 4-isopropylphenol-have been detected in various environmental media, but their impact on aquatic fauna has seldom been evaluated. Relative susceptibility to each phenolic varied by test species. The marine bacterium Vibrio fischeri was the most susceptible to the alkylphenols, up to 3 orders of magnitude more sensitive than species of higher trophic levels. For 4-isopropylphenol, the 5-min Microtox EC(50) value was 0.01 mg/L, whereas the EC(50) for Ceriodaphnia after a 48-h exposure was 10.1 mg/L. Notable differences in sensitivity to the alkylphenols was also observed with the Microtox assay: 4-isopropylphenol was > 200 times more toxic to V. fischeri than was 2-isopropylphenol (EC(50) = 2.72 mg/L). For V. fischeri, the mixture toxicity of the alkylphenols was additive in nature and was predicted by a concentration addition model. The energy of the lowest unoccupied molecular orbital (ELUMO) explained the observed toxicity of the individual alkylphenols to V. fischeri (r(2) = 0.92, p < 0.05). These results suggest that the mode of action of polar narcotic alkylphenols to V. fischeri is different than that of other test organisms, possibly because of the differences in the cell structure of the prokaryotic V. fischeri.     

Time-resolved toxicity study reveals the dynamic interactions between uncoated silver nanoparticles and bacteria

It is still unclear whether the toxicity of silver nanoparticles (AgNPs) can be attributed solely to the release of Ag⁺ or whether dissolved and nanoparticulate Ag act in parallel; this is due to the difficulty in distinguishing Ag⁺- from AgNP-effects. Also, AgNPs undergo changes during toxicity tests. This is the first study to investigate the influence of AgNP dissolution over time on viable counts at high time resolution and low cell density, avoiding the apparently reduced toxicity at higher cell densities identified in our study. Uncapped AgNPs were synthesized to avoid any interference from surface coatings. The transformations of AgNPs during storage were reduced. Lowering the concentration of AgNPs reduced their aggregation in Davis minimal medium (DMM). Also, AgNPs dissolved more slowly in DMM than in water. The minimum inhibitory concentrations (MICs) of Ag⁺ and AgNPs increased with cell density according to a power law, suggesting that binding to cells decreased effective concentrations. However, AgNPs acted as a reservoir of Ag, releasing new Ag⁺ to maintain the Ag stress. The toxicity of AgNPs was dominated by dissolved Ag. Combining controlled conditions, high time-resolution and low cell density, we could demonstrate different roles of ionic and nano Ag in bacterial death caused by AgNPs.     

Comparison of the Ceriodaphnia dubia and MicrotoxR inhibition tests for toxicity assessment of industrial and municipal wastewaters

Toxicity tests on effluents from industrial production facilities, municipal and industrial wastewater treatment plants, and stormwater runoff were conducted with the freshwater invertebrate, Ceriodaphnia dubia, and the marine luminescent bacterium, Vibrio fischeri in the Microtox^R test system (Microtox is a registered trademark of AZUR Environmental, Carlsbad, CA.). Percent mortalities of C. dubia in whole effluent, generated in 24- and 48-h exposure periods during the conductance of static-renewal acute and chronic tests were compared with percent reductions in light output by V. fischeri after 15-min exposure periods in the Microtox Inhibition test. A total of 16 effluent and stormwater samples from seven sources were used in tests conducted over a 3-month period. Results of the Microtox Inhibition tests correctly predicted the results of C. dubia tests for all eight nontoxic samples after both 24- and 48-h exposure periods. Of three samples that were toxic to C. dubia within 24 h, the Microtox test also detected toxicity in two of those samples. Results from tests on the remaining five samples showed that while the Microtox Inhibition test indicated the presence of toxic components after 15 min exposure, C. dubia required exposure to potentially toxic samples for 48 h before producing a toxic response. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 375–382, 1999     

Assessment of the toxicity of silver nanoparticles in vitro: A mitochondrial perspective

The major toxicological concern associated with nanomaterials is the fact that some manufactured nanomaterials are redox active, and some particles transport across cell membranes, especially into mitochondria. Thus, evaluation of their toxicity upon acute exposure is essential. In this work, we evaluated the toxicity of silver nanoparticles (40 and 80 nm) and their effects in rat liver mitochondria bioenergetics.Wistar rat liver mitochondria demonstrate alterations in respiration and membrane potential capacities in the presence of either 40 or 80 nm silver nanoparticles. Our data demonstrated a statistically significant decrease in mitochondrial membrane potential, ADP-induced depolarization, and respiratory control ratio (RCR) upon exposure to silver nanoparticles.Our results show that silver nanoparticles cause impairment of mitochondrial function, due mainly to alterations of mitochondrial membrane permeability. This results in an uncoupling effect on the oxidative phosphorylation system. Thus, mitochondrial toxicity may have a central role in the toxicity resulting from exposure to silver nanoparticles.     

Cellular uptake, intracellular trafficking and cytotoxicity of silver nanoparticles

Silver nanoparticles (Ag NPs) are used in consumer products and wound dressings due to their antimicrobial properties. However, in addition to toxic effects on microbes, Ag NPs can also induce stress responses as well as cytotoxicity in mammalian cells. We observed that Ag NPs are efficiently internalized via scavenger receptor-mediated phagocytosis in murine macrophages. Confocal and electron microscopy analysis revealed that internalized Ag NPs localize in the cytoplasm. Ag NPs cause mitochondrial damage, induce apoptosis and cell death. These effects were abrogated in presence of Ag ion-reactive, thiol-containing compounds suggesting the central of Ag ions in Ag NP toxicity. Quantitative image analysis revealed that intracellular dissolution of Ag NPs occurs about 50 times faster than in water. In conclusion, we demonstrate for the first time that Ag NPs are internalized by scavenger receptors, trafficked to cytoplasm and induce toxicity by releasing Ag ions.     

Effects of silver and gold nanoparticles of different sizes in human pulmonary fibroblasts

Abstract

Silver and gold nanoparticles (Ag–AuNPs) are currently some of the most manufactured nanomaterials. Accordingly, the hazards associated with human exposure to Ag–AuNPs should be investigated to facilitate the risk assessment process. In particular, because pulmonary exposure to Ag–AuNPs occurs during handling of these nanoparticles, it is necessary to evaluate the toxic response in pulmonary cells. The aim of this study was to evaluate the in vitro mechanisms of toxicity of different sizes of silver (4.7 and 42?nm) and gold nanoparticles (30, 50 and 90?nm) in human pulmonary fibroblasts (HPF). The toxicity was evaluated by observing cell viability and oxidative stress parameters. Data showed that AgNPs-induced cytotoxicity was size-dependent, whereas the AuNPs of the three sizes showed similar cytotoxicity. Silver nanoparticles of 4.7?nm were much more toxic than the large silver nanoparticles and the AuNPs. However, the pre-treatment with the antioxidant, N-acetyl-l-cysteine, protected HPF cells against treatment with Ag–AuNPs. The oxidative stress parameters revealed significant increase in reactive oxygen species levels, depletion of glutathione level and slight, but not statistically significant inactivation of superoxide dismutase, suggesting generation of oxidative stress. Hence, care has to be taken while processing and formulating the Ag–AuNPs till their final finished product.     

Toxicity of differently sized and charged silver nanoparticles to yeast Saccharomyces cerevisiae BY4741: a nano-biointeraction perspective

Abstract

In the current study, we evaluated the modulatory effects of size and surface coating/charge of AgNPs on their toxicity to a unicellular yeast Saccharomyces cerevisiae BY4741 – a fungal model. For that, the toxicity of a set of 10 and 80?nm citrate-coated (negatively charged) and branched polyethylenimine (bPEI) coated (positively charged) AgNPs was evaluated in parallel with AgNO₃ as ionic control. Yeast cells were exposed to different concentrations of studied compounds in deionized water for 24?h at 30?°C and evaluated for the viability by the post-exposure colony-forming ability. Particle-cell interactions were assessed by SEM, TEM and confocal laser scanning microscopy (CLSM) in the reflection mode. AgNPs toxicity to yeast was size and charge-dependent: 24-h IC₅₀ values ranged from 0.04 (10nAg-bPEI) up to 8.3?mg Ag/L (80nAg-Cit). 10?nm AgNPs were 5–27 times more toxic than 80?nm AgNPs and bPEI-AgNPs 8–44 times more toxic than citrate-AgNPs. SEM and TEM visualization showed that bPEI-AgNPs but not citrate-AgNPs adsorbed onto the yeast cell’s surface. However, according to CLSM all the studied AgNPs, whatever the size and coating, ended up within the yeast cell. Toxicity of citrate-AgNPs was largely explained by the dissolved Ag ions but the bPEI-AgNPs showed mainly particle-driven effects leading to the cellular internalization and/or to more pronounced dissolution of AgNPs in the close vicinity of the cell wall. Therefore, the size, and especially the coating/charge of AgNPs can be efficiently used for the design of new more efficient antifungals.     

Ecotoxicological effects of bisphenol A and nonylphenol on the freshwater cladocerans Ceriodaphnia silvestrii and Daphnia similis

Toxicities of bisphenol A (BPA) and nonylphenol (NP) to the neotropical freshwater cladocerans Ceriodaphnia silvestrii and Daphnia similis were studied under laboratory conditions. Acute exposures to BPA generated mean 48-h EC₅₀ values of 14.44 (6.02–22.85) mg L^?1 for C. silvestrii and 12.05 (1.73–22.37) mg L^?1 for D. similis. When the organisms were exposed to acute doses of NP, mean 48-h EC₅₀ values were 0.055 (0.047–0.064) mg L^?1 (C. silvestrii) and 0.133 (0.067–0.200) mg L^?1 (D. similis). Ceriodaphnia silvestrii was also tested in chronic bioassays, which resulted in mean 8-d IC₂₅ values of 2.43 (2.16–2.69) mg L^?1 BPA [no observed effect concentration (NOEC): 1.38?mg L^?1] and 0.020 (0.015–0.026) mg L^?1 NP (NOEC: 0.015?mg L^?1). These laboratory tests are valuable to broaden the understanding of the environmental threat posed by BPA and NP in aquatic ecosystems, and to increase the knowledge about the sensitivity of neotropical indigenous species to these contaminants. In addition to the laboratory bioassays, species sensitivity distributions were used to suggest protective concentrations of BPA and NP to prevent adverse effects on freshwater organisms. According to the obtained results, concentrations lower than 36.47?µg L^?1 BPA and 1.39?µg L^?1 NP are not expected to adversely impact aquatic organisms in natural ecosystems.     

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 © 2012 John Wiley & Sons, Ltd.     

Influence of silver and titanium dioxide nanoparticles on in vitro blood-brain barrier permeability

An in vitro blood-brain barrier (BBB) model being composed of co-culture with endothelial (bEnd.3) and astrocyte-like (ALT) cells was established to evaluate the toxicity and permeability of Ag nanoparticles (AgNPs; 8 nm) and TiO₂ nanoparticles (TiO₂NPs; 6 nm and 35 nm) in normal and inflammatory central nervous system. Lipopolysaccharide (LPS) was pre-treated to simulate the inflammatory responses. Both AgNPs and Ag ions can decrease transendothelial electrical resistance (TEER) value, and cause discontinuous tight junction proteins (claudin-5 and zonula occludens-1) of BBB. However, only the Ag ions induced inflammatory cytokines to release, and had less cell-to-cell permeability than AgNPs, which indicated that the toxicity of AgNPs was distinct from Ag ions. LPS itself disrupted BBB, while co-treatment with AgNPs and LPS dramatically enhanced the disruption and permeability coefficient. On the other hand, TiO₂NPs exposure increased BBB penetration by size, and disrupted tight junction proteins without size dependence, and many of TiO₂NPs accumulated in the endothelial cells were observed. This study provided the new insight of toxic potency of AgNPs and TiO₂NPs in BBB.     

Three-layered silver nanoparticles to trace dissolution and association to a green alga

Abstract

Core-shell silver nanoparticles (NPs) consisting of an inner Ag core and successive layers of Au and Ag (Ag@Au@Ag) were used to measure the simultaneous association of Ag NPs and ionic Ag by the green alga Chlamydomonas (C.) reinhardtii. Dissolution of the inner Ag core was prevented by a gold (Au) layer, while the outer Ag layer was free to dissolve. In short-term experiments, we exposed C. reinhardtii to a range of environmentally realistic Ag concentrations added as AgNO₃ or as NPs. Results provide three lines of evidence for the greater cell-association of NPs compared to dissolved Ag over the concentration range tested, assuming that cell-association comprises both uptake and adsorption. First, the cell-association rate constants (k_uw) for total Ag (Ag_NP+D), NPs (Ag_NP) and Au_NP were similar and 2.2-fold higher than the one from Ag_D exposure, suggesting predominant association of the particles over the dissolved form. Second, model calculations based on Ag fluxes suggested that only 6–33% of algal burden was from Ag_D. Third, the significantly lower Ag_NP/Au ratio measured with the algae after exposure (2.1?±?0.1) compared to the Ag_NP/Au ratio of the NPs in the media (2.47?±?0.05) suggests cell-association of NPs depleted in Ag. Core–shell NPs provide an innovative tool to understand NP behavior and to directly delineate Ag accumulation from ion and NPs in aquatic systems.     

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

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.