Therapeutic effect of Nepenthes kampotiana Lecomte ethanol extract (Nk-EE) on androgenic alopecia through the inhibition of apoptosis and 5α-reductase activity.

There is increasing interest in hair loss treatment because a growing number of people affected. Nepenthes kampotiana Lecomte is known for its anticancer effects, but its potential for preventing hair loss has not been researched. Therefore, this study focused on the hair loss prevention effects of N. kampotiana Lecomte ethanol extract (Nk-EE). The results showed that Nk-EE had a proliferative effect on human follicle dermal papilla cells and inhibited cell death. In vivo experiments using androgenic areata models showed that Nk-EE had a positive effect on a variety of biomarkers such as hair-to-skin ratio, hair type frequency, and hair thickness. The results of this study suggest that Nk-EE has potential as an effective treatment for androgenic alopecia.

Anti-oxidative, anti-apoptotic, and anti-inflammatory activities of Connarus semidecandrus Jack ethanol extract in UVB-irradiated human keratinocytes.

ETHNOPHARMACOLOGICAL RELEVANCE: Connarus semidecandrus Jack (Family: connaraceae) is a medicinal plant known for its wide distribution throughout Southeast Asia. Renowned for its diverse therapeutic properties, it has been traditionally used for treating fever, skin irritation, and colic. AIM OF THE STUDY: Numerous individuals suffer from skin issues, including wrinkles, hyperpigmentation, and inflammation, due to environmental factors. Although many drugs are available to treat skin problems, chemical drugs have many shortcomings and side effects. Therefore, natural products are attractive potential medicines for alleviating skin troubles. We recently showed that Connarus semidecandrus Jack ethanol extract (Cs-EE) has anti-alopecia potential. This paper aims to explore the potential skin-protective effects and underlying molecular mechanisms of Connarus semidecandrus Jack in UVB-induced human keratinocytes (HaCaT). MATERIALS AND METHODS: Before utilization, Cs-EE was dissolved in dimethyl sulfoxide (DMSO) and was preserved at a temperature of -20 °C. The phytochemical constituents of Cs-EE were detected by gas chromatography-mass spectrometry analysis (GC-MS). Sequentially, HaCaT cells were exposed to varying concentrations of Cs-EE prior to ultraviolet B (UVB) irradiation. Evaluations of cellular responses in HaCaT cells, including assessments of cell viability, deoxyribonucleic acid (DNA) damage, and gene and protein expressions, were carried out. To explore the specific signaling pathway involved, we conducted a luciferase assay in addition to validating these pathways using Western blot analysis. RESULTS: Nitric oxide (NO) and intracellular reactive oxygen species were decreased. Melanin production through the activation of melanocytes by α-melanocyte-stimulating hormone (MSH) was also inhibited by Cs-EE. Furthermore, the mRNA expression levels of key factors such as cyclooxygenase-2 (COX-2), tumor necrosis factor-α (TNF-α), interleukin 6 (IL-6), MMP-1, MMP-3, and MMP-9 exhibited a remarkable decrease. In addition, the phosphorylation of TAK1 within the signaling cascade exhibited a decline, and the activities of the transcription factor AP-1 were decreased according to a luciferase reporter assay. CONCLUSIONS: Taken together, these findings suggest that the anti-inflammatory, anti-aging, and anti-apoptotic effects of Cs-EE indicate the compound's potential usefulness as a natural component in pharmaceutical and cosmetic products.

Strategies to control the growth of cyanobacteria and recovery using adsorption and desorption.

In this study, adsorption strategy using diethylenetriamine-modified cotton fiber (DETA-cotton) was investigated to control the target cells in aqueous phase. Adsorptive removal of M. aeruginosa using the DETA-cotton showed decrease in cell concentration from (100 ± 4.0) × 104 cells/mL to (32.1 ± 0.7) × 104 cells/mL in 24 h, and the concentration of microcystin did not increase during the removal process. Also, an increase in the amine groups on the surface was confirmed through the surface characterization by FT-IR and XPS. Desorption process was performed to analyze total lipid and fatty acid contents for potential use as bio-energy resources. About 90 % of the adsorbed cells were recovered through desorption, and the lipid content and composition were more suitable for use as biodiesel raw materials. Our adsorption-based approach might provide feasible solution not only to counteract environmental issue HABs but also to recover energy-resources from the harmful cyanobacterial species.

Acute and developmental toxic effects of mono-halogenated and halomethyl naphthalenes on zebrafish (Danio rerio) embryos: Cardiac malformation after 2-bromomethyl naphthalene exposure.

Polyhalogenated polycyclic aromatic hydrocarbons (HPAHs) represent a major environmental concern due to their persistency and toxicity. Among them, mono-halogenated (HNs) and halomethyl naphthalenes (HMNs) are not well-studied, and the toxicity of many HNs to fishes has not been reported. In this study, we exposed zebrafish (Danio rerio) embryos to naphthalene and five HNs at concentrations ranging from 0.25 to 2.0 mg L-1 to assess acute toxicities and developmental effects. Among them, 2-bromomethyl naphthalene (2-BMN) produced moderate lethal effects (96-h LC50 = 1.4 mg L-1) and significantly reduced hatchability. Abnormal phenotypes, including pericardial edema, spine curvature, and shortened body length, were also induced by 2-BMN (96-h EC50 = 0.45 mg L-1). Treatments of 0.5-2.0 mg L-1 2-BMN evoked cardiac malformations via significant down-regulation of the cacna1c gene, which codes the voltage-dependent calcium channel, at 72 hpf and up-regulation of the nppa gene, responsible for the expression of natriuretic peptides, at 96 hpf in zebrafish. One presumable toxic photo-dissociated metabolite of 2-BMN, the 2-naphthylmethyl radical, may be responsible for the toxic effect on zebrafish embryos. HPAHs must be monitored and managed due to their adverse effects on living organisms at low concentrations.

Temperature and Aging Affect Glyphosate Toxicity and Fatty Acid Composition in Allonychiurus kimi (Lee) (Collembola).

Glyphosate is the most used herbicide worldwide, but enormous use of glyphosate has raised concerned about its environmental loadings. Although glyphosate is considered non-toxic, toxicity data for soil non-target organisms according to temperature and aging are scarce. This study examined the toxicity of glyphosate with the temperature (20 °C and 25 °C) and aging times (0 day and 7 days) in soil using a collembolan species, Allonychiurus kimi (Lee). The degradation of glyphosate was investigated. Fatty acid composition of A. kimi was also investigated. The half-life of glyphosate was 2.38 days at 20 °C and 1.69 days at 25 °C. At 20 °C with 0 day of aging, the EC50 was estimated to be 93.5 mg kg-1. However, as the temperature and aging time increased, the glyphosate degradation increased, so no significant toxicity was observed on juvenile production. The proportions of the arachidonic acid and stearic acid decreased and increased with the glyphosate treatment, respectively, even at 37.1 mg kg-1, at which no significant effects on juvenile production were observed. Our results showed that the changes in the glyphosate toxicity with temperature and aging time were mostly dependent on the soil residual concentration. Furthermore, the changes in the fatty acid compositions suggest that glyphosate could have a chronic effect on soil organisms.

The complete mitochondrial genome of Yuukianura szeptyckii Deharveng & Weiner 1984 (Collembola: Neanuridae).

The complete mitochondrial genome of Yuukianura szeptyckii Deharveng & Weiner 1984 was sequenced, assembled, and annotated. The mitochondrial genome of Y. szeptyckii has a length of 15,771 bp and contains 13 protein-coding genes (PCGs), 22 transfer (tRNA) genes, and 2 ribosomal RNA (rRNA) genes. Y. szeptyckii was closely clustered with the following species of Neanuridae: Bilobella aurantiaca and Friesea grisea.

The complete mitochondrial genome of Allonychiurus kimi (Lee, 1973) (Collembola: Onychiuridae).

The complete mitochondrial genome of Allonychiurus kimi (Lee, 1973) was sequenced, assembled, and annotated. The mitochondrial genome of A. kimi is 14,386 bp in length and contains 13 protein-coding, 22 transfer RNA, and 2 ribosomal RNA genes. A. kimi was closely clustered with the following species of the family Onychiuridae: Onychiurus orientalis, Orthonychiurus forlsomi, and Tetrodontophora bielanensis.

Quantitative prediction of mixture toxicity of AgNO3 and ZnO nanoparticles on Daphnia magna.

Once metal-based engineered nanoparticles (NPs) are released into the aquatic environment, they are expected to interact with other existing co-contaminants. A knowledge gap exists as to how the interaction of NPs with other co-contaminants occurs. Here we selected ZnO NPs among various NPs, with Ag ion existing as a contaminant in the aquatic environment by Ag NPs widely used. A novel modeling strategy was demonstrated enabling quantitative and predictive evaluation of the aqueous mixture nanotoxicity. Individual and binary mixture toxicity tests of ZnO NPs and silver (as AgNO3) on Daphnia magna were conducted and compared to determine whether the presence of Ag ions affects the toxicity of ZnO NPs. Binary mixture toxicity was evaluated based on the concentration addition (CA) and independent action models. The CA dose-ratio dependent model was found to be the model of best fit for describing the pattern of mixture toxicity. The MIX I and MIX III suspensions (higher ratios of ZnO NPs to AgNO3) showed a synergism, whereas the MIX II suspension (lower ratio of ZnO NPs to AgNO3) showed an antagonism. The synergistic mixture toxicity at higher ratios of ZnO NPs to AgNO3 was caused by either the physiological or metabolic disturbance induced by the excessive ionic Zn or increased transport and accumulation in D. magna via the formation of complex of ionic Ag with ZnO NPs. Therefore, the toxicity level contributed via their aggregation and physicochemical properties and the dissolved ions played a crucial role in the mixture toxicities of the NPs.

Effect of HNO3 and H2SO4 on the Paddy Ecosystem: A Mesocosm Study with Exposure at PNEC and HC50 Levels.

Paddy mesocosms comprising of rice (Oryza sativa), snail (Pomacea canaliculata), and worm (Tubifex tubifex) were used to assess the damage caused by two acids (HNO3 and H2SO4) at predicted no-effect concentration (PNEC) and hazardous concentration for 50% of species (HC50) levels. In the fourth week, the fresh weight and shoot height of O. sativa at H2SO4-HC50 were reduced by 83.2% and 30.3%, respectively. Wilted leaves (%) at HC50 were approximately twice that at PNEC. No P. canaliculata and T. tubifex were recovered at HC50. At H2SO4-PNEC, the length and weight of P. canaliculata were reduced by 7.4% and 25.9%, respectively, whereas fewer adult (46.5%) and juvenile (84%) T. tubifex were recovered. In the 20th week, rice growth and productivity were correlated with initial pH (pHi) and nitrogen levels. Poor correlation with chlorophyll at the active tillering stage suggests the disturbance of nutrient uptake by roots. Partial least squares path modeling (PLS-PM) results further supported that the pHi directly affects grain yield and quality, as well as plant growth. The indirect effect via intervening fourth-week-variables was also substantial. Therefore, it is important to measure initial pH upon acid spill to estimate the risk to the paddy ecosystem. Information on the change in soil properties associated with acidity will also aid in predicting the yield and quality of grain to be harvested.

Temperature-dependent competitive advantages of an allelopathic alga over non-allelopathic alga are altered by pollutants and initial algal abundance levels.

In the context of climate warming, the dominance of allelopathic algae that cause ecosystem disturbances is an important topic. Although the hypothesis that an increase in temperature will be favorable to the dominance of allelopathic algae has been increasingly supported by many studies, it is still unclear how other factors can affect the influence of temperature. In this study, the effects of copper exposure and initial algal abundance on the competition between Pseudokirchneriella subcapitata (non-allelopathic alga) and Chlorella vulgaris (allelopathic alga) were investigated during temperature changes. The results showed that increased temperatures enhanced the competitive advantage of C. vulgaris only in the absence of copper exposure. Our data confirmed that copper exposure along with increased temperature (20-30 °C) may change the competitive advantage of C. vulgaris from favorable to unfavorable. The initial algal abundance was found to affect competition outcome by controlling copper toxicity. This study suggests that pollutants and initial abundance can alter the effects of increased temperature on the allelopathic interaction. Given the temporal dynamics of algal abundance and the pollutants in natural ecosystems, these findings should be considered in the prediction of temperature influence on an algal community.

Contributions of egg production and egg hatching to the total toxicity of teflubenzuron in Yuukianura szeptyckii (Collembola) in soil toxicity test.

In the standard ISO soil toxicity test using Collembola, adult survival and juvenile production are the only endpoints that can be attainable. The information on egg production and egg hatching cannot be investigated in the ISO test. To overcome this limitation, in this study, the effects of teflubenzuron on life history parameters of Yuukianura szeptyckii (Collembola) were investigated with a compressed soil test. Teflubenzuron is an insect growth regulator and has a negative effect on egg production, and egg hatching process of arthropods. LC50 decreased with increases in exposure period from 6.97 mg/kg in the third week to 3.60 mg/kg in the fourth week. The EC50 for egg and juvenile production was 0.57 mg/kg and 0.26 mg/kg, respectively. The hatching rate decreased significantly from 46 to 7% as the concentration increased from 0.25 to 1.00 mg/kg, respectively, and the molting frequency was significantly affected only at > 4 mg/kg. The toxic contribution rate (TCR) was defined as the ratio of juvenile production at an exposure concentration compared with the control, and a simple life history model was developed for TCR estimations. At the lower concentrations (< 0.3 mg/kg), the hatching rate reduction was a main contributor to the total toxicity, but the adult mortality and egg production reduction were the main contributors at the higher concentrations (> 2.0 mg/kg). The contribution of egg production reduction remained relatively constant. Since collembolan populations in the soil can be composed of various developmental stages, the differences in the sensitivity to chemicals depending on the developmental stages should be included in the assessment of the toxic impact on soil ecosystems.

Screening level ecological risk assessment of abandoned metal mines using chemical and ecotoxicological lines of evidence.

In the present study, a screening level site-specific ecological risk assessment (ERA) was conducted on 10 abandoned metal mines in Korea to determine the ecological risk and prioritize the mines requiring further investigation. A cost-saving approach was adopted by combining both the chemical (ChemLoE) and the ecotoxicological (EcotoxLoE) lines of evidence for the evaluation of integrated risk (IR), rather than applying the full spectrum of Triad, including ecological LoE. The risk values for ChemLoE were derived by calculating the toxic pressure based on the total and 0.01 M CaCl2 extractable metal(loid) concentrations. The risk values for EcotoxLoE were based on the mortality and reproduction of the collembolan species Paronychiurus kimi in the mine soils. A response surface model with a central composite design (CCD) was constructed to standardize the effects of soil physicochemical properties (i.e., organic matter content, clay content, and soil pH) on the reproduction of P. kimi. The predicted number of offspring was used as a reference for the calculation of risk value for reproduction. The ChemLoE and EcotoxLoE values ranged from 0.34 to 1.00 and 0.12 to 0.49, respectively, in the surveyed mines. The contribution of the ChemLoE value to the IR was higher than that of the EcotoxLoE value for all mines. Overall, two of the 10 mines were classified as high-risk soils with high IR values (IR > 0.76), but large deviations were also observed between the LoEs in these mines, suggesting the need for further studies to confirm the potential risks. The future investigations of these mines should focus particularly on providing additional evidence to reduce the degree of uncertainty for risk assessment.

Transfer and biological effects of arsenate from soil through a plant-aphid system to the parasitoid wasp, Aphidius colemani.

The accumulation of metalloid elements during transfer from contaminated soil to higher trophic levels may potentially result in the exposure of parasitic arthropods to toxic concentrations of these elements. This study examined the transfer of arsenate (As(V)) to aphids (Myzus persicae) from pepper plants cultivated in As(V) contaminated soils of two concentrations (2 and 6 mg As(V)/kg dry soil), and the subsequent biological effects on the aphid parasitoid, Aphidius colemani. Results showed that considerable quantities of As(V) were transferred to the plant in a concentration-dependent manner and were partitioned in the plant parts in the order of roots > stems > leaves. The accumulation of As(V) in the aphids increased with the concentrations in the plants; however, the transfer coefficient of As(V) from leaf to aphid was relatively similar and constant (0.07-0.08) at both soil As(V) concentration levels. Increased levels of As(V) significantly affected fecundity and honeydew production in aphids, but survival and developmental time were unaffected. Fecundity (mummification rate) of the parasitoid was not impaired by host As(V) contamination; however, vitality (eclosion rate) was significantly affected. Results are discussed in relation to possible ecological risks posed by the transfer of soil As(V) via the plant-arthropod system to parasitoid arthropods in agroecosystems.

Toxicity effects and biomarkers of tebufenozide exposure in Yuukianura szeptyckii (Collembola: Neanuridae).

Tebufenozide is an insect growth regulator used to control pest caterpillar populations. As an ecdysone agonist, tebufenozide is equally toxic to several non-target arthropod species, binding the receptor sites of the molting hormone 20-hydroxyecdysone and causing premature and lethal molting. In this study, the toxic effects of tebufenozide were assessed, and biomarkers of tebufenozide exposure were identified, in the non-target soil collembolan species Yuukianura szeptyckii. Adult mortality and reproduction in Y. szeptyckii exposed to tebufenozide were evaluated after 28 days of exposure and were used to calculate LC50 and EC50, respectively. The LC50 could not be determined, because the mortality values observed were below 50%, even when exposed to the highest concentration tested (700 mg/kg), but the EC50 was 95.5 mg/kg. Effects on hatching and molting rates were evaluated using compressed soils, to prevent experimental individuals from burrowing; thus, all eggs and exuviae were detectable on the soil surface. Significant negative effects of tebufenozide exposure on the hatching rate and molting frequency were observed only at the highest concentration tested (700 mg/kg). Proteomic analyses were conducted to detect the cryptic effects of toxicity in adult collembolans exposed for 28 days to 43.8 mg/kg of tebufenozide, a concentration at which no toxicity effects were observed. The production rates of two ribosomal proteins, as well as proteins involved in apoptotic cell signaling, were higher in collembolans exposed to tebufenozide than in the control group. However, the production of proteins involved in glycolysis and energy production was downregulated. Therefore, the ecotoxicoproteomic approach is a promising tool for measuring the cryptic effects of tebufenozide exposure in Y. szeptyckii at low concentrations.

Bioavailability and Toxicity of Copper, Manganese, and Nickel in Paronychiurus kimi (Collembola), and Biomarker Discovery for Their Exposure.

Bioavailability and toxicity of Cu, Mn, and Ni in Paronychiurus kimi were investigated after 28 days of exposure to OECD artificial soil spiked with these metals. Uptake and effect of Cu, Mn, and Ni on the reproduction of P. kimi were related to different metal fractions (water-soluble, 0.01 M CaCl2-extractable or porewater metal concentrations). Cu and Mn concentrations in P. kimi increased with increasing Cu and Mn concentrations in the soil, while Ni contents in P. kimi reached a plateau at a concentration higher than 200 mg/kg in soil. Both uptake and juvenile production related well to different metal fractions, suggesting that these metal fractions are suitable for assessing bioavailability and toxicity of metals in P. kimi. When toxicity for reproduction was compared, as reflected by EC50 values, the order of metal toxicity varied depending upon how exposure concentration was expressed. Moreover, the results of proteomic analysis showed that several proteins involved in the immune system, neuronal outgrowth, and metal ion binding were up-regulated in P. kimi following short-term (7 days) exposure to sublethal level (corresponding to 50% of the EC50) of Cu, Mn, or Ni, respectively. This suggests that the ecotoxicoproteomic approach seems to be a promising tool for early exposure warnings below which significant adverse effects are unlikely to occur. This study demonstrated that a combination of chemical and biological measures can provide information about metal bioavailability and toxicity to which P. kimi has been exposed.

Joint toxic action of binary metal mixtures of copper, manganese and nickel to Paronychiurus kimi (Collembola).

The joint toxic effects of binary metal mixtures of copper (Cu), manganese (Mn) and nickel (Ni) on reproduction of Paronhchiurus kimi (Lee) was evaluated using a toxic unit (TU) approach by judging additivity across a range of effect levels (10-90%). For all metal mixtures, the joint toxic effects of metal mixtures on reproduction of P. kimi decreased in a TU-dependent manner. The joint toxic effects of metal mixtures also changed from less than additive to more than additive at an effect level lower than or equal to 50%, while a more than additive toxic effects were apparent at higher effect levels. These results indicate that the joint toxicity of metal mixtures is substantially different from that of individual metals based on additivity. Moreover, the close relationship of toxicity to effect level suggests that it is necessary to encompass a whole range of effect levels rather than a specific effect level when judging mixture toxicity. In conclusion, the less than additive toxicity at low effect levels suggests that the additivity assumption is sufficiently conservative to warrant predicting joint toxicity of metal mixtures, which may give an additional margin of safety when setting soil quality standards for ecological risk assessment.

Influence of surface chemical properties on the toxicity of engineered zinc oxide nanoparticles to embryonic zebrafish.

Zinc oxide nanoparticles (ZnO NPs) are widely used in a variety of products, thus understanding their health and environmental impacts is necessary to appropriately manage their risks. To keep pace with the rapid increase in products utilizing engineered ZnO NPs, rapid in silico toxicity test methods based on knowledge of comprehensive in vivo and in vitro toxic responses are beneficial in determining potential nanoparticle impacts. To achieve or enhance their desired function, chemical modifications are often performed on the NPs surface; however, the roles of these alterations play in determining the toxicity of ZnO NPs are still not well understood. As such, we investigated the toxicity of 17 diverse ZnO NPs varying in both size and surface chemistry to developing zebrafish (exposure concentrations ranging from 0.016 to 250 mg/L). Despite assessing a suite of 19 different developmental, behavioural and morphological endpoints in addition to mortality in this study, mortality was the most common endpoint observed for all of the ZnO NP types tested. ZnO NPs with surface chemical modification, regardless of the type, resulted in mortality at 24 hours post-fertilization (hpf) while uncoated particles did not induce significant mortality until 120 hpf. Using eight intrinsic chemical properties that relate to the outermost surface chemistry of the engineered ZnO nanoparticles, the highly dimensional toxicity data were converted to a 2-dimensional data set through principal component analysis (PCA). Euclidean distance was used to partition different NPs into several groups based on converted data (score) which were directly related to changes in the outermost surface chemistry. Kriging estimations were then used to develop a contour map based on mortality data as a response. This study illustrates how the intrinsic properties of NPs, including surface chemical modifications and capping agents, are useful to separate and identify ZnO NP toxicity to zebrafish (Danio rerio).

Effect of pH and ionic strength on exposure and toxicity of encapsulated lambda-cyhalothrin to Daphnia magna.

Encapsulation of pesticide active ingredients in polymers has been widely employed to control the release of poorly water-soluble active ingredients. Given the high dispersibility of these encapsulated pesticides in water, they are expected to behave differently compared to their active ingredients; however, our current understanding of the fate and effects of encapsulated pesticides is still limited. In this study, we employed a central composite design (CCD) to investigate how pH and ionic strength (IS) affect the hydrodynamic diameter (HDD) and zeta potential of encapsulated λ-cyhalothrin and how those changes affect the exposure and toxicity to Daphnia magna. R(2) values greater than 0.82 and 0.84 for HDD and zeta potential, respectively, irrespective of incubation time suggest those changes could be predicted as a function of pH and IS. For HDD, the linear factor of pH and quadratic factor of pH×pH were found to be the most significant factors affecting the change of HDD at the beginning of incubation, whereas the effects of IS and IS×IS became significant as incubation time increased. For zeta potential, the linear factor of IS and quadratic factor of IS×IS were found to be the most dominant factors affecting the change of zeta potential of encapsulated λ-cyhalothrin, irrespective of incubation time. The toxicity tests with D. magna under exposure conditions in which HDD or zeta potential of encapsulated λ-cyhalothrin was maximized or minimized in the overlying water also clearly showed the worst-case exposure condition to D. magna was when the encapsulated λ-cyhalothrin is either stable or small in the overlying water. Our results show that water quality could modify the fate and toxicity of encapsulated λ-cyhalothrin in aquatic environments, suggesting understanding their aquatic interactions are critical in environmental risk assessment. Herein, we discuss the implications of our findings for risk assessment.

Effects of water quality parameters on agglomeration and dissolution of copper oxide nanoparticles (CuO-NPs) using a central composite circumscribed design.

Once released into the aquatic environment, nanoparticles (NPs) are expected to interact (e.g., dissolve, agglomerate, settle), with important consequences for particle fate and toxicity. However, a clear understanding of how environmental factors influence the toxicity and fate of NPs in the environment is still in its infancy. In this study, a second order central composite circumscribed design (CCCD) was employed to systematically explore how different combinations of pH, hardness, and natural organic matter (NOM) in receiving water affect the hydrodynamic diameter, surface charge (zeta potential), and release of free Cu(2+) from CuO-NPs under a range of environmentally realistic conditions. The results clearly showed that all three CuO-NP properties varied markedly as functions of pH, hardness and dissolved NOM, confirming that agglomeration and the extent of release of free Cu(2+) largely depend on the surrounding environmental conditions. The response of hydrodynamic diameter, but not zeta potential, to water quality parameters was highly time dependent, showing very different patterns on day 2 and day 10. The approach used in this study can contribute to improving understanding of how, and to what extent, environmental factors affect the physicochemical properties of CuO-NPs once they enter aquatic environments. This understanding can help to predict the conditions under which CuO-NPs are likely to become problematic, which can inform management and mitigation actions.

Interactions between suspension characteristics and physicochemical properties of silver and copper oxide nanoparticles: a case study for optimizing nanoparticle stock suspensions using a central composite design.

The preparation of a stable nanoparticle stock suspension is the first step in nanotoxicological studies, but how different preparation methods influence the physicochemical properties of nanoparticles in a solution, even in Milli-Q water, is often under-appreciated. In this study, a systematic approach using a central composite design (CCD) was employed to investigate the effects of sonication time and suspension concentration on the physicochemical properties (i.e. hydrodynamic diameter, zeta potential and ion dissolution) of silver (Ag) and copper oxide (CuO) nanoparticles (NPs) and to identify optimal conditions for suspension preparation in Milli-Q water; defined as giving the smallest particle sizes, highest suspension stability and lowest ion dissolution. Indeed, all the physicochemical properties of AgNPs and CuONPs varied dramatically depending on how the stock suspensions were prepared and differed profoundly between nanoparticle types, indicating the importance of suspension preparation. Moreover, the physicochemical properties of AgNPs and CuONPs, at least in simple media (Milli-Q water), behaved in predictable ways as a function of sonication time and suspension concentration, confirming the validity of our models. Overall, the approach allows systematic assessment of the influence of various factors on key properties of nanoparticle suspensions, which will facilitate optimization of the preparation of nanoparticle stock suspensions and improve the reproducibility of nanotoxicological results. We recommend that further attention be given to details of stock suspension preparation before conducting nanotoxicological studies as these can have an important influence on the behavior and subsequent toxicity of nanoparticles.