Preferential sorption of some natural organic matter fractions to titanium dioxide nanoparticles: influence of pH and ionic strength.

Natural organic matter (NOM) sorption to nanoparticles (NPs) can influence their transport and bioavailability in the aquatic environment. The sorption affinity of NOM to surfaces including NPs is size dependent, and depending on environmental conditions, NOM may enhance or mitigate NPs toxicity. The aim of this study was to investigate the preferential sorption of different-sized fractions of NOM to titanium dioxide (TiO2) NPs. We specifically investigated the influence of pH, ionic strength, and NOM concentration on the extent of this preferential sorption using a constant sorbent concentration (400 mg/L TiO2 NPs). Additionally, sorption of NOM to TiO2 NPs at varying pH was investigated. The nonsorbed NOM was separated from the sorbed, by 50 nm polycarbonate membrane filters and ultracentrifugation. High-performance size exclusion chromatography (HPSEC) was used to determine the average molecular weights of NOM (MWw). Corroborative evidence of preferential sorption of different-sized molecular weight fractions of NOM was obtained from optical techniques such as absorbance and fluorescence spectrophotometry. The total organic carbon was measured by the Total Organic Carbon Analyzer-Shimadzu (TOC-VCPH). The results indicated that there is preferential sorption of larger sized fractions of NOM to TiO2 NPs irrespective of NOM concentration. It was observed that the sorption of larger sized fractions of NOM was much enhanced at lower pH and at higher ionic strength. Both absorbance and fluorescence spectrophotometric techniques gave credible corroborative evidence on the extent of preferential sorption of lager sized fractions of NOM with respect to pH and ionic strength. The sorption results demonstrated higher sorption at lower pH than at higher pH. Overall, the results of this study suggest that the environmental conditions are key factors that can contribute to NOM's fractional preferential sorption to NPs in the aquatic environment.

Confined within a sugarcane monoculture: A participatory assessment of water pollution and potential health risks in the community of El Tiple, Colombia.

Communities neighboring monoculture plantations are vulnerable to different forms of pollution associated with agro-industrial operations. Herein, we examine the case of El Tiple, a rural Afro descendant community embedded within one of the largest sugarcane plantations in the Americas. We implemented a participatory approach to assess water pollution, exposure via water ingestion, and non-carcinogenic health risks associated with the use of local water sources available to the community. We conducted household surveys to unveil demographic characteristics and family dynamics linked to water consumption. Additionally, we measured water quality parameters and assessed the concentration glyphosate, its major metabolite (aminomethylphosphonic acid) and metals and metalloids. Drinking water El Tiple households is sourced from three primary sources: the local aqueduct system, water delivery trucks, and private deep wells. Tests on water samples from both the local aqueduct and delivery trucks showed no traces of pesticides, metals, or metalloids surpassing regulatory limits set by Colombian or EPA standards. However, we found concentration of contaminants of primary concern, including mercury (up to 0.0052 ppm) and lead (up to 0.0375 ppm) that exceed the permissible regulatory thresholds in water from groundwater wells. Residents of the peripheric subdivisions of El Tiple are four times more reliant on well water extraction than residents of the central area of the town due to lack of access to public drinking water and sanitation infrastructure. Finally, adult women and school-age children have a higher health risk associated with exposure to local pollutants than adult men due to their constant presence in the town. We conclude that expanding the coverage of clean water and sanitation infrastructure to include all households of the community would be the most recommended measure to minimize exposure and risk via ingestion of water pollutants.

Potential Environmental and Health Implications from the Scaled-Up Production and Disposal of Nanomaterials Used in Biosensors.

Biosensors often combine biological recognition elements with nanomaterials of varying compositions and dimensions to facilitate or enhance the operating mechanism of the device. While incorporating nanomaterials is beneficial to developing high-performance biosensors, at the stages of scale-up and disposal, it may lead to the unmanaged release of toxic nanomaterials. Here we attempt to foster connections between the domains of biosensors development and human and environmental toxicology to encourage a holistic approach to the development and scale-up of biosensors. We begin by exploring the toxicity of nanomaterials commonly used in biosensor design. From our analysis, we introduce five factors with a role in nanotoxicity that should be considered at the biosensor development stages to better manage toxicity. Finally, we contextualize the discussion by presenting the relevant stages and routes of exposure in the biosensor life cycle. Our review found little consensus on how the factors presented govern nanomaterial toxicity, especially in composite and alloyed nanomaterials. To bridge the current gap in understanding and mitigate the risks of uncontrolled nanomaterial release, we advocate for greater collaboration through a precautionary One Health approach to future development and a movement towards a circular approach to biosensor use and disposal.

Fast peroxyoxalate chemiluminescence for minimized analytical separation systems.

The maximum intensity, Imax, and time required to reach the maximum emission, taumax, for 1-aminopyrene monitored in 1,1'-oxalyldi-4-methylimidazole (OD4MI) chemiluminescence (CL) reactions are approximately 61 times higher and 16 times faster than their respective values for bis(2,4,6-trichlorophenyl)oxalate (TCPO) CL reactions in the presence of imidazole (ImH).

PAH degradation by UV/H2O2 in perfluorinated surfactant solutions.

Polycyclic aromatic hydrocarbons (PAHs) solubilized in perfluorinated surfactant (PFS) solutions were degraded by direct photolysis and UV/H2O2 process. The subsequent recovery and reuse of these surfactant solutions were also demonstrated. Phenanthrene and pyrene were selected as representative PAHs and an anionic PFS: ammonium perfluorooctanoate (APFO) was used. In our experiments, micellar APFO solutions retarded the phenanthrene photolysis and enhanced the pyrene photolysis. The results indicate that the photochemical reactivity of compound in micelles is strongly dependent on specific properties of the solubilizate, possibly due to the different excited state behaviors of compound. UV/H2O2 process exhibits a greatly enhanced rate of PAH photolysis in both water and APFO compared to direct photolysis. indicating that hydroxyl radicals may be generated or penetrated at the sites of PAHs solubilized in the micelles. Additionally. a smaller rate enhancement by UV/H2O2 in micelles than in water suggests that micelles provide some degree of protection from hydroxyl radical attack. The possibility of recovery and reuse of PFS has been demonstrated by measuring the solubilizing capacity of APFO after direct photolysis and UV/H2O2 process. Overall, this study demonstrates UV/H2O2 process can be an effective treatment method for not only PAH degradation but also surfactant recovery and reuse.

Solubilization of polycyclic aromatic hydrocarbons by perfluorinated surfactant micelles.

Due to their chemical and thermal stability, perfluorinated surfactants (PFSs) are promising materials for the development of novel environmental remediation applications. This stability also leads to the persistence of PFS in the environment; therefore, their properties and behavior should be well understood. This study focused on polycyclic aromatic hydrocarbon (PAH) and PFS interactions, particularly the solubilization of PAHs by PFS micelles. Naphthalene. phenanthrene, and pyrene were selected as representative PAHs and an anionic PFS, ammonium perfluorooctanoate (APFO) was used. Critical micelle concentration (CMC) values of APFO measured by surface tension, fluorescence probe, and solubility enhancement methods fell in the range of 20-30 mM at 22 +/- 1 degrees C. Apparent solubilities of molecular oxygen and PAHs in APFO micellar solutions depended linearly on the APFO concentration. Molar solubilization ratio (MSR) values were determined to be 9.50 x 10(-4), 4.17 x 10(-3), 2.31 x 10(-4), and 4.09 x 10(-5) and mole fraction micellar partition coefficient (Kmic) values were found to be 1.89 x 10(2), 9.50 x 10(2), 2.12 x 10(3), and 3.79 x 10(3) for oxygen, naphthalene, phenanthrene, and pyrene, respectively at 22 +/- 1 degrees C. log Kmic values for three PAHs were shown to be linearly correlated with the log values of octanol-water partition coefficients (log Kow).

Testing a surface tension-based model to predict the salting out of polycyclic aromatic hydrocarbons in model environmental solutions.

Molar-based Setschenow constants (Ks) for six alkali and alkaline earth metal-based inorganic salts were determined at 20 degrees C to evaluate their influence on the solubilities, and thus the aqueous activity coefficients, of three polycyclic aromatic hydrocarbons (PAHs). The six salts tested exhibited a wide range of Ks values, varying from 0.105 +/- 0.009 M(-1) (for NaClO4 and pyrene) to 1.29 +/- 0.17 M(-1) (for K2SO4 and perylene). In general, salting out effects with these electrolytes were observed in the order Ca2+ > Na+ > K+ and SO4(2-) > Cl- > ClO4-, consistent with previous reports. However, the expected salting out trend of perylene > pyrene > naphthalene was only observed with K2SO4. In CaCl2 solutions, the Ks value of pyrene was significantly lower than that of naphthalene. For NaCl, KCl and NaClO4, pyrene Ks values were found to be lower than, but not significantly different from, those of naphthalene. Setschenow constants for all six salts were predicted using a semi-empirical, thermodynamically-based equation that relates the standard free energy change associated with transferring solutes from water to a salt solution to the difference in surface tensions between the two solutions. With this equation, predicted Ks values were in reasonable agreement with observed Ks values (generally within +/- 50%). Lack of better agreement between predicted and observed values likely reflects the inability of the simple surface tension model to account for all interactions among the cations, anions, PAH molecules and water molecules in the respective systems.

Characterization of cation-pi interactions in aqueous solution using deuterium nuclear magnetic resonance spectroscopy.

Chemical interactions of aromatic organic contaminants control their fate, transport, and toxicity in the environment. Recent molecular modeling studies have suggested that strong interactions can occur between the pi electrons of aromatic molecules and metal cations in aqueous solutions and/or on mineral surfaces, and that such interactions may be important in some environmental systems. However, spectroscopic evidence for these so-called cation-pi interactions has been extremely limited to date. In this paper, cation-pi interactions in aqueous salt solutions were characterized via 2H nuclear magnetic resonance (NMR) spin-lattice relaxation times (T1) and calculations of molecular correlation times (tau(c)) for a series of perdeuterated (d6-benzene) benzene-cation complexes. The T1 values for d6-benzene decreased with increasing concentrations of LiCl, NaCl, KCl, RbCl, CsCl, and AgNO3, with the largest effects observed in the AgNO3 and CsCl solutions. Upon normalizing tau(c) values by solution viscosity effects, an overall affinity trend of Ag+ >> Cs+ > K+ > Rb+ > Na+ > Li+ was derived for the d6-benzene-cation complexes. The ability of Ag+ to complex d6-benzene was significantly reduced upon addition of NH3, which strongly coordinates Ag+ at high pH. Results with d6-benzene, d8-naphthalene, d2-dichloromethane, and d12-cyclohexane in 0.1 M methanolic salt solutions confirmed that spin-lattice relaxation rates are characterizing cation-pi interactions. The relatively strong cation-pi bonding observed between Ag+ and aromatic hydrocarbons probably results from covalent interactions between the aromatic pi electrons and the d orbitals of Ag+, in addition to the normal electrostatic interaction.

Cation-pi bonding: a new perspective on the sorption of polycyclic aromatic hydrocarbons to mineral surfaces.

Recent molecular modeling and spectroscopic studies have suggested that relatively strong interactions can occur between aromatic pi donors and metal cations in aqueous solutions. The objective of this study was to characterize potential cation-pi interactions between pi donors and exchangeable cations accumulated at mineral surfaces via both spectroscopic and batch sorption methods. Quadrupolar splitting in deuterium nuclear magnetic resonance ((2)H NMR) spectroscopy for d(2)-dichloromethane, d(6)-benzene, and d(8)-toluene (C(6)D(5)- moiety) in aqueous suspensions of a Na-saturated reference montmorillonite unambiguously indicated the ordering of solute molecules with respect to the clay surface. The half line broadening (Delta nu(1/2)) of (2)H NMR of d(6)-benzene in montmorillonite suspensions showed that soft exchangeable cations generally resulted in more benzene sorption compared with harder cations (e.g., Ag(+) > Cs(+) > Na(+) > Mg(2+), Ba(2+)). In batch sorption experiments, saturating minerals (e.g., porous silica gels, kaolinite, vermiculite, montmorillonite) with a soft transition metal or softer base cations generally increased the polycyclic aromatic hydrocarbon (PAH) sorption relative to harder cations (e.g., Ag(+) >> Cs(+) > K(+) > Na(+); Ba(2+) > Mg(2+)). Sorption of phenanthrene to Ag(+)-saturated montmorillonite was much stronger compared with 1,2,4,5-tetrachlorobenzene, a coplanar non-pi donor having slightly higher hydrophobicity. In addition, a strong positive correlation was found between the cation-dependent sorption and surface charge density of the minerals (e.g., vermiculite, montmorillonite >> silica gels, kaolinite). These results, coupled with the observations in (2)H NMR experiments with montmorillonite, strongly suggest that cation-pi bonding forms between PAHs and exchangeable cations at mineral surfaces and affects PAH sorption to hydrated mineral surfaces.

The induction of biochemical changes in Daphnia magna by CuO and ZnO nanoparticles.

Whilst a considerable number of studies have been reported on the acute toxicity of nanoparticles (NPs) on invertebrates such as Daphnia magna, few studies have been reported on the biochemical change (biomarkers) induction on these species by NPs, especially metal oxide NPs. The aim of this study was to investigate some biomarkers in D. magna induced by copper oxide (CuO) and zinc oxide (ZnO) NPs under controlled laboratory conditions. We exposed the 5 day old D. magna for 72 h to sublethal concentration of CuO and ZnO NPs in synthetic moderately hard water (MHW) with and without dissolved natural organic matter (NOM) and estimated the glutathione-S-transferase (GST) activity, formation of oxidized glutathione (GSSG), and amounts of thiobarbituric acid reacting substances (TBARS) and metallothionein (MT). Additionally, complementary short term dissolution studies on CuO and ZnO NPs were conducted. The results showed inactivation of GST enzyme by both metal oxide NPs. The results also showed increased production of oxidized GSH, increased generation of TBARS and increased induction of MT. In the presence of NOM, significant reduction (p<0.05) in these biochemical changes was observed. These results indicated that oxidative stress is one of the toxicity mechanisms for these metal oxide NPs. Furthermore, the results suggest that these metal oxide NPs compromise the health of D. magna, and possibly other aquatic organisms, and therefore have potential to affect ecosystem stability. The short term dissolution studies showed that the proportion of dissolved NPs is higher (1.2% and 70% of initial concentration for dissolved Cu and Zn, respectively) at low particle concentration and is lower (0.4% and 17% of initial concentration for dissolved Cu and Zn, respectively) at higher particle concentration. These results suggest that the observed toxicity may be caused by both metal oxide nanoparticles and metal ions dissociated from the nanoparticles.

Evidence of multiple pathways capable of emitting peroxyoxalate chemiluminescence using a charge coupled device spectrometer.

Peroxyoxalate chemiluminescence (PO-CL) spectra obtained simultaneously and continuously using a CCD spectrometer provide evidence of the complexity of PO-CL reactions.

Amendment of hydroxyapatite in reduction of tetrachloroethylene by zero-valent zinc: its rate enhancing effect and removal of Zn(II).

The effects of hydroxyapatite (HAP) on dechlorination of tetrachloroethylene (PCE) by zero-valent zinc (ZVZ) were examined in batch systems. PCE was primarily transformed to trichloroethylene by ZVZ, with 1,2-trans-dichloroethylene representing a minor product. Dechlorination of PCE was accelerated by the presence of HAP, and the pseudo-first order rate constants increased with increasing amount of HAP. Zn(II), mostly generated from oxidative dissolution of ZVZ by PCE, was effectively removed from the solution by HAP. Ion substitution, coprecipitation, and adsorption are proposed as the possible mechanisms for Zn(II) removal. These reactions appeared to occur simultaneously and the contribution of each reaction to overall removal of Zn(II) was primarily dependent on HAP loading at constant ZVZ loading. The results indicate that the use of HAP in combination with conventional zero-valent metals is promising in that it can achieve both degradation of organic contaminants and stabilization of inorganic contaminants.

Reduction of chlorinated ethanes by nanosized zero-valent iron: kinetics, pathways, and effects of reaction conditions.

Nanosized iron (< 100 nm in diameter) was synthesized in the laboratory and applied to the reduction of eight chlorinated ethanes (hexachloroethane (HCA), pentachloroethane (PCA), 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA), 1,1,1,2-tetrachloroethane (1,1,1,2-TeCA), 1,1,2-trichloroethane (1,1,2-TCA), 1,1,1-trichloroethane (1,1,1-TCA), 1,2-dichloroethane (1,2-DCA), and 1,1-dichloroethane (1,1-DCA)) in batch reactors. Reduction of 1,1,1-TCA increased linearly with increasing iron loading between 0.01 and 0.05 g per 124 mL solution (0.08-0.4 g/L). Varying initial concentrations of PCA between 0.025 and 0.125 mM resulted in relatively constant pseudo-first-order rate constants, indicating PCA removal conforms to pseudo-first-order kinetics. The reduction of 1,1,2,2-TeCA decreased with increasing pH; however, dehydrohalogenation of 1,1,2,2-TeCA became important at high pH. All chlorinated ethanes except 1,2-DCA were transformed to less chlorinated ethanes or ethenes. The surface-area-normalized rate constants from first-order kinetics analysis ranged from < 4 x 10(-6) to 0.80 L m(-2) h(-1). In general, the reactivity increased with increasing chlorination. Among tri- and tetrasubstituted compounds, the reactivity was higher for compounds with chlorine atoms more localized on a single carbon (e.g., 1,1,1-TCA > 1,1,2-TCA). Reductive beta-elimination was the major pathway for the chlorinated ethanes possessing alpha,beta-pairs of chlorine atoms to form chlorinated ethenes, which subsequently reacted with nanosized iron. Reductive alpha-elimination and hydrogenolysis were concurrent pathways for compounds possessing chlorine substitution on one carbon only, forming less chlorinated ethanes.

Solvent and pH effects on fast and ultrasensitive 1,1'-oxalyldi(4-methyl)imidazole chemiluminescence.

Solvent and pH effects on fast and ultrasensitive 1,1'-oxalyldi(4-methyl)imidazole chemiluminescence (OD4MI-CL) were studied. The influences of these two factors on the complex OD4MI-CL reaction are discussed within a conceptual prototype for developing aqueous and non-aqueous capillary electrophoresis (ACE and NACE) devices with OD4MI-CL detection. The reaction channel length and OD4MI yield from the reaction between bis(2,4,6-trichlorophenyl) oxalate (TCPO) and 4-methylimidazole in the channel will be influenced by pH, water volume fraction, and cosolvent properties of the solution. Optimum OD4MI-CL efficiency is observed at pH 6.5 when 1-propanol, which has a low dielectric constant (epsilon = 20.8), is used as the NACE solvent in the separation channel. Water (epsilon = 80.1), the solvent in the ACE separation channel, acts similarly to a high dielectric constant organic solvent in NACE because the disadvantages normally associated with TCPO-CL reactions in water disappear due to the faster OD4MI-CL reaction versus OD4MI decomposition in aqueous solution. Therefore, it is expected that the OD4MI-CL detection system can be used in both NACE and ACE devices without requiring detector modifications. We also conclude that OD4MI-CL detection in NACE and ACE devices will be much more sensitive than the TCPO-CL detection used in current NACE devices.