Biochemical stress response in tetradifon exposed Daphnia magna and its relationship to individual growth and reproduction

Environmental risk assessment of chemicals toxicity requires the use of costly and labor-intensive chronic data and short-term tests provide additional information. Energy budget is used by the animals for their growth, reproduction, and metabolism and it is reduced in case of toxic stress. Tetradifon acaricide is frequently used in the European Mediterranean region and it is implicated in aquatic environmental pollution. Previous studies showed that the EC₅₀-24 h of tetradifon on Daphnia magna was 8.92 mg/L. Based on that, D. magna were exposed to sublethal tetradifon concentrations of 0.10, 0.18, 0.22 and 0.44 mg/L for five days in order to investigate their effect on intermediate metabolism. Caloric content was determined as biomarker of tetradifon toxicity. Results were analyzed using one-way analysis of variance (ANOVA) and Duncan's significant difference test was used to find differences between groups (α was set at p = 0.05). Daphnids energy content decreased as tetradifon concentration increased. At 120-h caloric content was depleted > 51% at pesticide concentrations of 0.18 mg/L and higher. In order to determine a possible link between the 5-d test and the 21-d chronic test, animals under short-term test were exposed to the same pesticide concentrations known to cause adverse effects on reproduction, growth and survival. Results from the present study indicated a good correlation between the proposed 5-day test and daphnid energy budget. Comparison between both, caloric content results and the chronic effect values obtained using life-table studies, suggested a good fit between them. These studies can be used as earlier, predictive and useful tests with comparable results to the classic chronic ones. Our results indicate that caution must be done about the use of tetradifon in the aquatic environment.     

Bacterial responses to Cu-doped TiO2 nanoparticles

The toxicity of Cu-doped TiO₂ nanoparticles (NPs, 20 nm), synthesized by a flame aerosol reactor, to Mycobacterium smegmatis and Shewanella oneidensis MR-1, is the primary focus of this study. Both doped and non-doped TiO₂ NPs (20 nm) tended to agglomerate in the medium solution, and therefore did not penetrate into the cell and damage cellular structures. TiO₂ particles (< 100 mg/L) did not apparently interfere with the growth of the two species in aqueous cultures. Cu-doped TiO₂ NPs (20 mg/L) significantly reduced the M. smegmatis growth rate by three fold, but did not affect S. oneidensis MR-1 growth. The toxicity of Cu-doped TiO₂ NPs was driven by the release of Cu²⁺ from the parent NPs. Compared to equivalent amounts of Cu²⁺, Cu-doped TiO₂ NPs exhibited higher levels of toxicity to M. smegmatis (P-value < 0.1). Addition of EDTA in the culture appeared to significantly decrease the anti-mycobacterium activity of Cu-doped TiO₂ NPs. S. oneidensis MR-1 produced a large amount of extracellular polymeric substances (EPS) under NP stress, especially extracellular protein. Therefore, S. oneidensis MR-1 was able to tolerate a much higher concentration of Cu²⁺ or Cu-doped TiO₂ NPs. S. oneidensis MR-1 also adsorbed NPs on cell surface and enzymatically reduced ionic copper in culture medium with a remediating rate of 61 µg/(liter?OD₆₀₀? hour) during its early exponential growth phase. Since the metal reducing Shewanella species can efficiently “clean” metal-oxide NPs, the activities of such environmentally relevant bacteria may be an important consideration for evaluating the ecological risk of metal-oxide NPs.     

Photocatalytic inactivation of E. coli in surface water using immobilised nanoparticle TiO2 films

Photocatalysis is a promising method for the disinfection of potable water in developing countries where solar irradiation can be employed, thus reducing the cost of treatment. In addition to microbial contamination, water normally contains suspended solids, dissolved inorganic ions and organic compounds (mainly humic substances) which may affect the efficacy of solar photocatalysis. In this work the photocatalytic and photolytic inactivation rates of Escherichia coli using immobilised nanoparticle TiO₂ films were found to be significantly lower in surface water samples in comparison to distilled water. The presence of nitrate and sulphate anions spiked into distilled water resulted in a decrease in the rate of photocatalytic disinfection. The presence of humic acid, at the concentration found in the surface water, was found to have a more pronounced affect, significantly decreasing the rate of disinfection. Adjusting the initial pH of the water did not markedly affect the photocatalytic disinfection rate, within the narrow range studied.     

DNA can sediment TiO2 particles and decrease the uptake potential by mammalian cells

Titanium dioxide (TiO₂) is an important material used in a broad range of industries. As TiO₂ particles used in industries have recently become smaller as technology develops, problems specific to small size are increasing. One such problem is the difficulty of recovering TiO₂ particles suspended in solution. Particles not recovered during their manufacture would be released in the environment and might be taken up by living organisms, leading to “small-size specific toxicity”, which has recently become a concern in numerous industries. To prevent environmental release of small-size TiO₂, separation and complete recovery of the particles are important. In this study, we showed that DNA could be used to separate TiO₂ particles (60-500 nm) from an aqueous solution. Although TiO₂ particles (20 mg/10 ml) were kept in suspension in a standing solution for 72 h, addition of small amounts of DNA (25-100 μg/10 ml) completely sedimented all particles within 4 h. Analysis with transmission electron microscopy suggested that the enhanced sedimentation with DNA was due to the formation of aggregates of TiO₂ particles with DNA. Conveniently, DNA-treated TiO₂ particles had difficulty translocating into human cell lines (keratinocytes and skin fibroblasts), suggesting that “small-size specific toxicity” can be prevented. DNA is a useful tool for separating TiO₂ particles which would prevent “small-size specific toxicity” by allowing quick and complete recovery and suppression of uptake by living organisms.     

Degradation of diclofenac by TiO2 photocatalysis: UV absorbance kinetics and process evaluation through a set of toxicity bioassays

In the present study the degradation kinetics and mineralization of diclofenac (DCF) by the TiO₂ photocatalysis were investigated in terms of UV absorbance and COD measurements for a wide range of initial DCF concentrations (5-80 mg L⁻¹) and photocatalyst loadings (0.2-1.6 g TiO₂ L⁻¹) in a batch reactor system. A set of bioassays (Daphnia magna, Pseudokirchneriella subcapitata and Artemia salina) was performed to evaluate the potential detoxification of DCF. A pseudo-first-order kinetic model was found to fit well most of the experimental data, while at high initial DCF concentrations (40 and 80 mg L⁻¹) and at 1.6 g TiO₂ L⁻¹ photocatalyst loading a second-order kinetic model was found to fit the data better. The toxicity of the treated DCF samples on D. magna and P. subcapitata varied during the oxidation, probably due to the formation of some intermediate products more toxic than DCF. Unicellular freshwater algae was found to be very sensitive to the treated samples as well as the results from D. magna test were consistent to those of algae tests. A. salina was not found to be sensitive under the investigated conditions. Finally, UV absorbance analysis were found to be an useful tool for a fast and easy to perform measurement to get preliminary information on the organic intermediates that are formed during oxidation and also on their disappearance rate.     

TiO2 nanoparticles aggregation and disaggregation in presence of alginate and Suwannee River humic acids. pH and concentration effects on nanoparticle stability

The behavior of manufactured TiO₂ nanoparticles is studied in a systematic way in presence of alginate and Suwannee River humic acids at variable concentrations. TiO₂ nanoparticles aggregation, disaggregation and stabilization are investigated using dynamic light scattering and electrophoretic experiments allowing the measurement of z-average hydrodynamic diameters and zeta potential values. Stability of the TiO₂ nanoparticles is discussed by considering three pH-dependent electrostatic scenarios. In the first scenario, when pH is below the TiO₂ nanoparticle point of zero charge, nanoparticles exhibit a positively charged surface whereas alginate and Suwannee River humic acids are negatively charged. Fast adsorption at the TiO₂ nanoparticles occurs, promotes surface charge neutralization and aggregation. By increasing further alginate and Suwannee River humic acids concentrations charge inversion and stabilization of TiO₂ nanoparticles are obtained. In the second electrostatic scenario, at the surface charge neutralization pH, TiO₂ nanoparticles are rapidly forming aggregates. Adsorption of alginate and Suwannee River humic acids on aggregates leads to their partial fragmentation. In the third electrostatic scenario, when nanoparticles, alginate and Suwannee River humic acids are negatively charged, only a small amount of Suwannee River humic acids is adsorbed on TiO₂ nanoparticles surface. It is found that the fate and behavior of individual and aggregated TiO₂ nanoparticles in presence of environmental compounds are mainly driven by the complex interplay between electrostatic attractive and repulsive interactions, steric and van der Waals interactions, as well as concentration ratio. Results also suggest that environmental aquatic concentration ranges of humic acids and biopolymers largely modify the stability of aggregated or dispersed TiO₂ nanoparticles.     

Effects of nickel on daphnia magna during chronic exposure and alterations in the toxicity to generations pre-exposed to nickel

Daphnia magna was cultured at sublethal nickel concentrations. The mean life expectancy was significantly less when exposed to 40 ppb Ni. Statistically significant reductions of the number of offspring, maximum body length of adults and of neonates were caused by 80 ppb Ni. The length and brood size of primiparous animals were significantly less when exposed to 120 ppb Ni. The intrinsic rate of population growth (r) was inversely proportional to nickel concentrations. During seven successive generations exposed to 160 ppb Ni, both the mean life span and the length of primiparous animals decreased significantly with increasing time. The progeny of nickel pre-exposed generations exhibited no adaptation towards nickel except an altered reproduction pattern which induced an increase of r. After the transfer into nickel-free water, the progeny of nickel pre-exposed generations showed an increase of body length, mean life span, number of offspring, brood size and brood number as well as the maximum body length of neonates. However, the progeny of pre-exposed generations remained smaller than the progeny of an untreated generation.     

Arsenic sorption on TiO2 nanoparticles: Size and crystallinity effects

Single solute As (III) and As (V) sorption on nano-sized amorphous and crystalline TiO₂ was investigated to determine: size and crystallinity effects on arsenic sorption capacities, possible As (III) oxidation, and the nature of surface complexes. Amorphous and crystalline nanoparticles were prepared using sol-gel synthesis techniques. For amorphous TiO₂, solute pH in the range of 4-9 had a profound impact on only As (V) sorption. As (III) and As (V) sorption isotherms indicated that sorption capacities of the different TiO₂ polymorphs were dependent on the sorption site density, surface area (particle size) and crystalline structure. When normalized to surface area, As (III) surface coverage on the TiO₂ surface remained almost constant for particles between 5 and 20 nm. However, As (V) surface coverage increased with the degree of crystallinity. X-ray absorption spectroscopic analysis provided evidence of partial As (III) oxidation on amorphous TiO₂ rather than crystalline TiO₂. The data also indicated that As (III) and As (V) form binuclear bidentate inner-sphere complexes with amorphous TiO₂ at neutral pH.     

Life history responses of Daphnia magna feeding on toxic Microcystis aeruginosa alone and mixed with a mixotrophic Poterioochromonas species

The toxic effects of a mixotrophic golden alga (Poterioochromonas sp. strain ZX1) and a cyanobacterium Microcystis aeruginosa grazed by Poterioochromonas to a cladoceran were investigated through life history experiments using Daphnia magna. Poterioochromonas cultured in two ways (fed M. aeruginosa in an inorganic medium or grown in an organic medium) both induced starvation-like effects on D. magna, indicating that Poterioochromonas is neither acutely toxic nor a good food for D. magna. Despite a microcystin-LR content of 10⁻⁸ μg cell⁻¹ in M. aeruginosa, no toxins were accumulated in Poterioochromonas fed the cyanobacterium. The toxic effect of M. aeruginosa to D. magna was significantly reduced in the presence of Poterioochromonas, which may be performed in two ways: decrease M. aeruginosa cells ingestion of D. magna by grazing on M. aeruginosa; and decrease the toxicity of the medium by degrading the toxins released by M. aeruginosa. This study provides new information on the interactions between a cyanobacterium and its grazer under laboratory conditions and may increase our understanding of the ecological significance of such interactions in the aquatic food webs.     

Combination of one-dimensional TiO2 nanowire photocatalytic oxidation with microfiltration for water treatment

This paper proposed the fabrication of two different diameter one-dimensional TiO₂ nanowires, 10 nm TNW₁₀ and 20-100 nm TNW₂₀, via hydrothermal process using different alkaline sources. TNW₁₀ and TNW₂₀ were used as photocatalysts for the degradation of humic acid (HA), the major natural organic matters (NOMs) in surface and ground water, followed by microfiltration. The evaluation of photocatalytic activities of them showed that TNW₁₀ was superior to the commercial P25 TiO₂ while TNW₂₀ was as good as P25. The membrane filtration verified that the two types of nanowires could be completely reclaimed. The membrane fouling caused by TNW₁₀ and TNW₂₀ was much less than that of P25 due to more porous cake and less pore plugging. No apparent decrease on their photocatalytic activity was observed in repeated reuse experiments. These one-dimensional TiO₂ nanowires would provide a new route for the combination of photocatalytic oxidation and membrane filtration for water treatment.     

Electro-photocatalytic degradation of acid orange II using a novel TiO2/ACF photoanode

A novel photoanode was prepared by immobilizing TiO₂ film onto activated carbon fibers (TiO₂/ACF) using liquid phase deposition (LPD) to study the electro-photocatalytic (EPC) degradation of organic compounds exemplified by an azo-dye, namely, Acid Orange II (AOII). Results demonstrated that by applying a 0.5 V bias (vs. SCE) across the TiO₂/ACF electrode, the AOII degradation rate was increased significantly compared to that of photocatalytic (PC) oxidation. The application of an electric field promotes the separation of photogenerated electrons and holes as confirmed by electrochemical impedance spectroscopy (EIS) measurements. The structural and surface morphology of the TiO₂/ACF electrode was characterized by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). SEM images showed that TiO₂ was deposited on almost every carbon fiber with an average thickness of about 200 nm with the inner space between neighboring fibers being maintained unfilled. The morphological features of the photo-anode facilitated the passage of solution as well as UV light through the felt-form electrode and created a three-dimensional environment favorable to EPC oxidation. Both the large outer surface area of the 3D electrode and the good organic adsorption capacity of the ACF support promoted high contact efficiency between AOII and TiO₂ surface. Anatase was the major crystalline TiO₂ deposited. UV-vis spectrophotometry, TOC (total organic carbon) analysis, and HPLC technique were used to monitor the concentration change of AOII and intermediates as to gain insight into the EPC degradation of AOII using the TiO₂/ACF electrode.     

Norovirus and MS2 inactivation kinetics of UV-A and UV-B with and without TiO2

Germicidal ultraviolet, such as 254-nm UV-C, is a common method of disinfection of pathogenic enteric viruses. However, the disinfection efficacies of UV-A or -B in terms of inactivating waterborne viruses such as norovirus have not been characterized. We evaluated the inactivation kinetics of MS2 bacteriophage and murine norovirus (MNV), a surrogate of human norovirus (NoV), by UV-A and -B. In addition to UV disinfection, we further investigated whether the presence of TiO₂ could enhance the virus inactivation kinetics of UV-A and -B. Both MS2 and MNV were highly resistant to UV-A. However, the addition of TiO₂ enhanced the efficacy of UV-A for inactivating these viruses. UV-A dose of 1379 mJ/cm² resulted in a 4 log₁₀ reduction. In comparison, UV-B alone effectively inactivated both MS2 and MNV, as evidenced by the 4 log₁₀ reduction by 367 mJ/cm² of UV-B. The addition of TiO₂ increased the inactivation of MS2; however, it did not significantly increase the efficacy of UV-B disinfection for inactivating MNV. When these treatments were applied to field water such as groundwater, the results were generally consistent with the laboratory findings. Our results clearly indicated that UV-B is useful for the disinfection of waterborne norovirus. However, MNV was quite resistant to UV-A, and UV-A effectively inactivated the tested viruses only when used in combination with TiO₂.     

Use of a mathematical model in the analysis of survival curves of Daphnia magna exposed to toxicants

Chronic toxicity tests carried out on species of the genus Daphnia (Crustacea: Cladocera) are bioassays commonly used in ecotoxicology. Mortality in the cohorts exposed to toxicants can be examined by the analysis of survival curves. The shape of these curves may be very different because of inter-individual heterogeneity: the less rectangular is the shape the more different is the probability of dying of daphnids in the cohort. Aim of this paper is to analyze the characteristics-in particular the shape-of survival curves of cohorts of Daphnia magna exposed to heavy metals in chronic toxicity tests. Experimental curves were fitted by a mathematical model recently proposed, which puts emphasis just on this heterogeneity, described by the parameter of the model S(0). The information contained in S(0) is very useful for the present purposes: the higher the value of S(0) the less rectangular the shape of the curve and, as a consequence, the higher the age-at-death heterogeneity of the cohort is thought to be. The model contains a second parameter, omega, representing the maximum potential ability of the individuals to survive in a specific environment and is related with the maximal life span. The model fitted well the survival curves in most cases and both S(0) and omega showed statistically different values between treatments, useful for comparisons. It was concluded that S(0) provides a quantitative estimation of curve "rectangularization", useful to check different sensitivities to a specific toxicant concentration among daphnids belonging to the same cohort, while omega provides an estimate of maximal life span.     

Heterogeneous photocatalytic removal of toluene from air on building materials enriched with TiO2

This paper reports the potential of heterogeneous photocatalysis as an advanced oxidation technology for removal of toluene from air using TiO₂ as a photocatalyst in building materials. First, the photocatalytic activity of two types of TiO₂ containing building materials, i.e. roofing tiles and corrugated sheets, has been investigated at ambient conditions (T=25.0 °C; relative humidity RH=47%; toluene inlet concentration [TOL]_in=17–35 ppbv). Toluene removal efficiencies up to 63% were observed at a gas residence time (τ) of 17 s. Second, the effect of RH (1–77%), [TOL]_in (23–465 ppmv) and τ (17–115 s) on toluene removal has been systematically investigated using TiO₂ containing roofing tiles as photocatalytic building materials. Results revealed lower toluene removal efficiencies at higher RH and [TOL]_in, whereas a positive effect was observed with increased τ. Under optimal conditions, toluene removal efficiencies up to 78±2% and elimination rates higher than 100 mg h⁻¹ m⁻² roofing tile were obtained. A decline in photocatalytic activity by a factor of 2 was observed after operation at gas residence times shorter than 69 s and [TOL]_in higher than 76 ppmv. Washing the building materials with deionized water, simulating rainfall, could partially (i.e. by a factor 1.3) regenerate the catalyst activity.     

Toxicity of nanoparticles of CuO, ZnO and TiO2 to microalgae Pseudokirchneriella subcapitata

Toxicities of ZnO, TiO₂ and CuO nanoparticles to Pseudokirchneriella subcapitata were determined using OECD 201 algal growth inhibition test taking in account potential shading of light. The results showed that the shading effect by nanoparticles was negligible. ZnO nanoparticles were most toxic followed by nano CuO and nano TiO₂. The toxicities of bulk and nano ZnO particles were both similar to that of ZnSO₄ (72 h EC50 ~ 0.04 mg Zn/l). Thus, in this low concentration range the toxicity was attributed solely to solubilized Zn²⁺ ions. Bulk TiO₂ (EC50 = 35.9 mg Ti/l) and bulk CuO (EC50 = 11.55 mg Cu/l) were less toxic than their nano formulations (EC50 = 5.83 mg Ti/l and 0.71 mg Cu/l). NOEC (no-observed-effect-concentrations) that may be used for risk assessment purposes for bulk and nano ZnO did not differ (~ 0.02 mg Zn/l). NOEC for nano CuO was 0.42 mg Cu/l and for bulk CuO 8.03 mg Cu/l. For nano TiO₂ the NOEC was 0.98 mg Ti/l and for bulk TiO₂ 10.1 mg Ti/l. Nano TiO₂ formed characteristic aggregates entrapping algal cells that may contribute to the toxic effect of nano TiO₂ to algae. At 72 h EC50 values of nano CuO and CuO, 25% of copper from nano CuO was bioavailable and only 0.18% of copper from bulk CuO. Thus, according to recombinant bacterial and yeast Cu-sensors, copper from nano CuO was 141-fold more bioavailable than from bulk CuO. Also, toxic effects of Cu oxides to algae were due to bioavailable copper ions.To our knowledge, this is one of the first systematic studies on effects of metal oxide nanoparticles on algal growth and the first describing toxic effects of nano CuO towards algae.     

Photosynthesis and oxidative stress in the restinga plant species Eugenia uniflora L. exposed to simulated acid rain and iron ore dust deposition: Potential use in environmental risk assessment

The Brazilian sandy coastal plain named restinga is frequently subjected to particulate and gaseous emissions from iron ore factories. These gases may come into contact with atmospheric moisture and produce acid rain. The effects of the acid rain on vegetation, combined with iron excess in the soil, can lead to the disappearance of sensitive species and decrease restinga biodiversity. The effects of iron ore dust deposition and simulated acid rain on photosynthesis and on antioxidant enzymes were investigated in Eugenia uniflora, a representative shrub species of the restinga. This study aimed to determine the possible utility of this species in environmental risk assessment. After the application of iron ore dust as iron solid particulate matter (SPM_Fe) and simulated acid rain (pH 3.1), the 18-month old plants displayed brown spots and necrosis, typical symptoms of iron toxicity and injuries caused by acid rain, respectively. The acidity of the rain intensified leaf iron accumulation, which reached phytotoxic levels, mainly in plants exposed to iron ore dust. These plants showed the lowest values for net photosynthesis, stomatal conductance, transpiration, chlorophyll a content and electron transport rate through photosystem II (PSII). Catalase and superoxide dismutase activities were decreased by simulated acid rain. Peroxidase activity and membrane injury increased following exposure to acid rain and simultaneous SPM_Fe application. Eugenia uniflora exhibited impaired photosynthetic and antioxidative metabolism in response to combined iron and acid rain stresses. This species could become a valuable tool in environmental risk assessment in restinga areas near iron ore pelletizing factories. Non-invasive evaluations of visual injuries, photosynthesis and chlorophyll a fluorescence, as well as invasive biochemical analysis could be used as markers.     

Effect of sunlight irradiation on photocatalytic pyrene degradation in contaminated soils by micro-nano size TiO2

The enhanced catalytic pyrene degradation in quartz sand and alluvial and red soils by micro-nano size TiO₂ in the presence and absence of sunlight was investigated. The results showed that the synergistic effect of sunlight irradiation and TiO₂ was more efficient on pyrene degradation in quartz sand and red and alluvial soils than the corresponding reaction system without sunlight irradiation. In the presence of sunlight irradiation, the photooxidation (without TiO₂) of pyrene was very pronounced in alluvial and red soils and especially in quartz sand. However, in the absence of sunlight irradiation, the catalytic pyrene degradation by TiO₂ and the photooxidation (without TiO₂) of pyrene were almost nil. This implicates that ultra-violet (UV) wavelength range of sunlight plays an important role in TiO₂-enhanced photocatalytic pyrene degradation and in photooxidation (without TiO₂) of pyrene. The percentages of photocatalytic pyrene degradation by TiO₂ in quartz sand, alluvial and red soils under sunlight irradiation were 78.3, 23.4, and 31.8%, respectively, at 5 h reaction period with a 5% (w/w) dose of the amended catalyst. The sequence of TiO₂-enhanced catalytic pyrene degradation in quartz sand and alluvial and red soils was quartz sand > red soil > alluvial soil, due to different texture and total organic carbon (TOC) contents of the quartz sand and other two soils. The differential Fourier transform infrared (FT-IR) spectra of degraded pyrene in alluvial soil corroborate that TiO₂-enhanced photocatalytic degradation rate of degraded pyrene was much greater than photooxidation (without TiO₂) rate of degraded pyrene. Based on the data obtained, the importance for the application of TiO₂-enhanced photocatalytic pyrene degradation and associated organic contaminants in contaminated soils was elucidated.     

Antifungal capability of TiO2 coated film on moist wood

Photocatalytic oxidation by TiO₂ has been shown to deactivate biological pollutants. Most previous studies evaluated TiO₂'s antimicrobial performance using bacteria, with Escherichia coli most commonly applied as the test microbe. There have not been concentrated studies focusing on the photocatalytic disinfection of fungi which widely exist in buildings and cause health problems. In this study, the antifungal activity of TiO₂ photocatalytic reaction against Aspergillus niger was investigated for moist wood boards during periods of several weeks. TiO₂ coated film in the presence of UVA (365 nm) irradiation exhibited antifungal capability. No visible growth was observed on specimens during the photo-process. Re-growth appeared in subsequent dark, indicating that the photocatalytic reaction was not sufficient for total disinfection against mold fungi but did suppress fungi growth. The study sheds light on conditions and potential applications of photocatalytic deactivation of fungi.     

Lethal synergy of solar UV-radiation and H2O2 on wild Fusarium solani spores in distilled and natural well water

Environmentally-friendly disinfection methods are needed in many industrial applications. As a natural metabolite of many organisms, hydrogen peroxide (H₂O₂)-based disinfection may be such a method as long as H₂O₂ is used in non-toxic concentrations. Nevertheless, when applied alone as a disinfectant, H₂O₂ concentrations need to be high enough to achieve significant pathogen reduction, and this may lead to phytotoxicity. This paper shows how H₂O₂ disinfection concentrations could be significantly reduced by using the synergic lethality of H₂O₂ and sunlight the first time for fungi and disinfection. Experiments were performed on spores of Fusarium solani, the ubiquitous, pytho- and human pathogenic fungus. Laboratory (250-mL bottles) and pilot plant solar reactors (2 × 14 L compound parabolic collectors, CPCs) were employed with distilled water and real well water under natural sunlight. This opens the way to applications for agricultural water resources, seed disinfection, curing of fungal skin infections, etc.     

Release of phosphorous impurity from TiO2 anatase and rutile nanoparticles in aquatic environments and its implications

Phosphorus-bearing materials as an additive have been popularly used in nanomaterial synthesis and the residual phosphorus within the nanoparticles (NPs) can be of an environmental concern. For instance, phosphorus within pristine commercial TiO₂ NPs greatly influences the surface charge and aggregation behavior of the host TiO₂ in aquatic environments; however, it is unknown whether and how fast phosphorus is released. In this study, we focus on the phosphorus release kinetics from five types of TiO₂ NPs (i.e., 5, 10, and 50 nm anatase and 10 × 40, 30 × 40 nm rutile) under the influence of varying solution chemistries. The 50 nm anatase has the highest quantity of P (8.05 g/kg) and most leachable P dissolves within the first 2 h (i.e., 5.01 g/kg), which presents a potential pollutant source of P. Higher pH favors the phosphorus release (release order: pH 11.2 > pH 8.2 > pH 2.4), while variations in the environmentally relevant ionic strengths (0.01 M NaCl + 0.01 M NaHCO₃ and 0.04 M NaCl + 0.01 M NaHCO₃) and the presence of dissolved natural organic matter (10 mg/L) do not affect release rate greatly. X-ray Absorption Near Edge Structure results suggest that phosphate adsorbed on the pristine 50 nm anatase desorbs, and some dissolved phosphate again re-sorbs as a surface precipitate. The findings from this research may have important environmental implications such as accidental release of TiO₂ NPs and other nanomaterials that are synthesized using phosphorus containing chemicals as an ingredient.