Papers by Arturo A Keller
Journal of Nanoparticle Research, 2018
The increasing use of nanopesticides has raised concerns about their effects on crop plants and t... more The increasing use of nanopesticides has raised concerns about their effects on crop plants and the impact of human health as well as ecological effects. While increased uptake of metal ions has been observed before, to date, very few studies have demonstrated the presence of nanoparticles in edible tissues. Singleparticle inductively coupled plasma-mass spectrometry (sp-ICP-MS) has been suggested as a powerful tool to detect inorganic nanoparticles (NPs) in environmental samples. Here, we exposed edible plant tissues from lettuce, kale, and collard green to nano-CuO, simulating its use as a nanopesticide. We applied sp-ICP-MS to demonstrate the presence of nanoparticles, both in the water used to rinse crop leaf surfaces exposed to nano-CuO and within the leaf tissues. Lettuces retained the highest amounts of nCuO NPs on the leaf surface, followed by collard green and then kale. Surface hydrophilicity and roughness of the leaf surfaces played an important role in retaining nano-CuO. The results indicate that most of the nanoparticles are removed via washing, but that a certain fraction is taken up by the leaves and can result in human exposure, albeit at low levels.
Application of Probabilistic Collocation Method in the Uncertainty Analysis for Watershed Non-point Source Pollution Modeling
Journal of Agro-Environment Science, 2010
Agricultural non-point source pollution(NPSP)is now a severe problem.Watershed water quality mode... more Agricultural non-point source pollution(NPSP)is now a severe problem.Watershed water quality models could provide decision supports for managing NPSP,but their efficiency is limited by significant uncertainty involved in the simulation.Current uncertainty analysis techniques are mainly based on Monte Carlo Simulation(MCS),which are usually associated with high computation costs.In this study,the Probabilistic Collocation Method(PCM)was used to analyze the uncertainty in watershed NPSP modeling.The Diazinon pollution in Newport Bay watershed(USA)was chosen as the case study,and the WARMF model was used.It has been shown that,in many cases,PCM could achieve good uncertainty results comparable to those by traditional MCS,with a much less computational cost.It has also been revealed that management factors could have significant impact on the NPSP modeling and its uncertainty analysis.
Dispersivity of Colloids in Saturated Porous Media is a Function of Colloid Size
Colloid dispersion in porous media is a consequence of the different paths and velocities experie... more Colloid dispersion in porous media is a consequence of the different paths and velocities experienced by the colloids. This work represents a number of studies at the pore and column scales, as well as comparisons to field scale studies. At the pore scale we examined the effect of particle and pore size on colloid dispersion using water-saturated micromodels. Four sizes of colloids were transported at several pressure differences. Image analysis was used to determine particle trajectories, residence times and dispersion coefficients through the micromodels. The magnitude of the dispersion at any given flow rate was found to be controlled by the pore-space geometry and the relative size of colloids with regards to pore channels. Dispersion coefficient and dispersivity decrease with increasing colloid size. Dispersivity is thus not just a function of pore geometry, but depends on colloid characteristics. We corroborated these results with column-scale experiments to observe the effect...
Estimated Influent PFAS Loads to Wastewater Treatment Plants and Ambient Concentrations in Downstream Waterbodies: Case Study in Southern and Central California
ACS ES&T water, Jun 27, 2023
Adsorption of perchlorate and other oxyanions onto magnetic permanently confined micelle arrays (Mag-PCMAs)
Water Research, Mar 1, 2012
The removal of oxyanions found in drinking water sources -perchlorate, nitrate, phosphate, and su... more The removal of oxyanions found in drinking water sources -perchlorate, nitrate, phosphate, and sulfate- onto magnetic permanently confined micelle arrays (Mag-PCMAs) was studied. We determined the removal efficiency in both competitive and non-competitive environments, as many of these anions are present in these sources. Mag-PCMA removed over 98% of the aqueous perchlorate anions across a concentration range of 60-500 μg/L. Nitrate was absorbed 100% over a concentration range of 10-35 mg/L as nitrate. Removal of phosphate was 95.7% for 0.2-2.45 mg/L as phosphate. Sulfate was 100% absorbed across a concentration range of 5-20 mg/L and an average 75.7% for 5-50 mg/L. The sorption isotherms followed a Freundlich relationship with K(f) values of 2.00, 2.05, 1.9, and 3.86 mg/g for nitrate, perchlorate, phosphate, and sulfate respectively. Perchlorate and nitrate did not compete significantly for binding on Mag-PCMAs, with almost equal sorption, greater than 90%, for both anions in elevated concentrations. This is a distinguishing feature from ion exchange resins or activated carbon with cationic surfactants, where these anions have been shown to compete for sorption sites. At the concentrations studied, phosphate and sulfate also do not exhibit significant competition. Desorption for reuse was successful at pH 10. This reusable magnetic sorbent can thus be used to rapidly remove target anions such as perchlorate from water in the presence or absence of other oxyanions.
Climatic Change, May 1, 1996
Environmental Modeling & Assessment, Jan 16, 2008
Agriculture can be a major nonpoint source (NPS) of nutrient and pesticide contamination in the e... more Agriculture can be a major nonpoint source (NPS) of nutrient and pesticide contamination in the environment. Available databases do not provide accurate and dynamic data on fertilizer and pesticide application, which limits the ability of complex watershed models to simulate contaminant loads into impaired water bodies. A model for estimating agricultural nutrient and pesticide input for watershed modeling has been developed. Climate, soils, and major agricultural operations are considered within the model, so that it can be adapted to any watershed or subregion within a watershed. The timing of the agricultural operations is a function of the weather data, providing realistic results at daily, monthly, or annual application rates. The model also predicts irrigation demand and biomass production, which can be used to calibrate the model. Model output can be used in any watershed model that considers agricultural land uses. Two case studies were evaluated, using grape vineyards in the Napa River and strawberry production in Newport Bay as examples. The predicted time to maturity corresponded well with actual data. Irrigation and fertilizer needs were very sensitive to weather input. Although the model can generate weather from long-term averages, the simulated results are best when at least observed precipitation and temperature are provided, to capture extreme events. The model has data for 98 crops and 126 pesticides, based on the California Department of Pesticide Regulation database. The databases are easily modifiable by the user to adapt them to local conditions. The output from AgInput is much needed for watershed modeling and for development of total maximum daily loads (TMDLs), based on realistic targets of irrigation, nutrient, and pesticide inputs. The model is available for free download at .
Geophysical Research Letters, Jun 1, 1995
A single variable aperture fracture plane is the microscopic scale equivalent of a pore in a poro... more A single variable aperture fracture plane is the microscopic scale equivalent of a pore in a porous medium, with the advantage that it can be more easily characterized using a deterministic or stochastic description of the fracture aperture. Fracture aperture distributions can be measured in the laboratory for small fractured cores using Computed Tomography (CT) Xray scanning to a resolution of about 50 !xm. Using the small perturbation analysis developed by Gelhar (1987) based on a stochastic description of the fracture aperture distribution, we predict the breakthrough curve of a dissolved contaminant in an aqueous phase flowing through a single natural fracture, from the knowledge of the geostatistical description of the fracture aperture. The results of the stochastic analysis are compared to experimental results from the actual breakthrough curve of a nonsorbing solute flowing through a single fracture plane in a granite core at different flow rates, with a fracture aperture characterized using CT scanning. The measured effective transmissivity is 13% larger than the estimated value, and the measured dispersivity is 33% larger than the estimated value. Errors introduced by the boundary conditions, the first order approximation and heterogeneities not sampled by the CT scanner may account for the difference. The estimation method may be useful for predicting solute breakthrough at field sites if the required statistics are obtained from hydraulic and tracer tests at similar sites.
Water Research, Apr 1, 2008
Understanding the partitioning of hydrophobic organic compounds (HOCs) within soil-water-surfacta... more Understanding the partitioning of hydrophobic organic compounds (HOCs) within soil-water-surfactant systems is key to improving the use of surfactants for remediation. The overall objective of this study was to investigate the soil properties that influence the effectiveness of surfactants used to remediate soil contaminated with hydrophobic pesticides, as an example of a more general application for removing strongly sorbing HOCs from contaminated soils via in-situ enhanced sorption, or ex-situ soil washing. In this study, the partitioning of two commonly used pesticides, atrazine and diuron, within soil-water-surfactant systems was investigated. Five natural soils, one nonionic surfactant (Triton-100 (TX)) and one cationic surfactant (benzalkonium chloride (BC)) were used. The results showed that the cation exchange capacity (CEC) is the soil property that controls surfactant sorption onto the soils. Diuron showed much higher solubility enhancement than atrazine with the micelles of either surfactant. Within an ex-situ soil washing system, TX is more effective for soils with lower CEC than those with higher CEC. Within an in-situ enhanced sorption zone, BC works significantly better with more hydrophobic HOCs. The HOC sorption capacity of the sorbed surfactant (K ss ) was a non-linear function of the amount of surfactant sorbed. For the cationic surfactant (BC), the maximal K ss occurred when around 40% of the total CEC sites in the various soils were occupied by sorbed surfactant. Below a sub-saturation sorption range ($20 g/kg), under the same amount of BC sorbed, a soil with lower CEC tends to have higher K ss than the one with higher CEC.
Optimization of Targeted Plant Proteomics Using Liquid Chromatography with Tandem Mass Spectrometry (LC-MS/MS)
ACS agricultural science & technology, Apr 17, 2023
Elsevier eBooks, 2023
The application of nanotechnology in drinking water treatment and pollution cleanup is promising,... more The application of nanotechnology in drinking water treatment and pollution cleanup is promising, as demonstrated by a number of field-based (pilot and full scale) and bench scale studies. A number of reviews exist for these nanotechnology-based applications; but to better illustrate its importance and guide its development, a direct comparison between traditional treatment technologies and emerging approaches using nanotechnology is needed. In this review, the performances of traditional technologies and nanotechnology for water treatment and environmental remediation were compared with the goal of providing an up-to-date reference on the state of treatment techniques for researchers, industry, and policy makers. Pollutants were categorized into broad classes, and the most cost-effective techniques (traditional and nanotechnology-based) in each category reported in the literature were compared. Where information was available, cost and environmental implications of both technologies were also compared. Case studies were also provided where traditional technologies were directly compared with nanotechnology-based technologies for the similar pollutants. Although nanotechnology-based methods are generally believed to be more expensive, we found instances where they offer cheaper and more effective alternatives to conventional techniques. In addition, nano-based techniques may become extremely important in meeting increasingly stringent water quality standards, especially for removal of emerging pollutants and low levels of contaminants. We also discuss challenges facing environmental application of nanotechnology and offer potential solutions.
Cost Benefit Analysis for the Use of Mtbe and Alternatives
Innovation in procedures for human and ecological health risk assessment of engineered nanomaterials
Elsevier eBooks, 2019
Abstract The large data gaps in the hazards and potential exposure to engineered nanomaterials (E... more Abstract The large data gaps in the hazards and potential exposure to engineered nanomaterials (ENMs) make it challenging to assess their human and ecological health risks. Nevertheless, it is necessary to develop risk estimates, to assist decision-making with regard to product design, exposure reduction, alternative ENMs, and other options. In the past decade a number of increasingly more accurate approaches have been developed to estimate ENM hazard and exposure. While these predictive approaches have an associated uncertainty, they serve to highlight areas where more research is needed as well as develop strategies to minimize risk. These innovative approaches also serve to identify types of ENMs that are more likely to result in higher risk. For example, ENMs that dissolve rapidly release metal ions that may be at concentrations that are toxic, increasing both exposure and hazard. Most predicted environmental concentrations are below ecological hazard levels, although the predictions tend to reflect average release rates at constant levels, and may not reflect episodic or accidental spills that could lead to higher concentrations. On the hazard side, there is very little information on the effects of long-term exposure, and thus this represents a major challenge in predicting these risks. There are also some applications, such as ENMs in agriculture, which are likely to increase rapidly in the coming decades, and may present risks that have not yet been properly assessed.
Environmental science. Nano, 2017
We investigated the physiological and molecular response of cucumber plants to a CuIJOH) 2 nanopes... more We investigated the physiological and molecular response of cucumber plants to a CuIJOH) 2 nanopesticide. We demonstrated that foliar exposure to the nanopesticide increases the expression levels of several key antioxidant and detoxification related genes (SOD, GPX4, GPX, MDAR, POD, and WRKY6). This indicates that the CuIJOH) 2 nanopesticide induces oxidative stress and activates the antioxidant defense system in the plants. Exposure to Cu 2+ from CuSO 4 also increased the transcript production of the SOD, GPX4, GPX, MDAR, POD, and WRKY6 genes, and also increased transcription of WRKY30, GST, CAT, APX and GPX2 genes. In addition, Cu 2+ activated two regulatory genes (RBOH and MAP3K3), which was not observed in plants treated with CuIJOH) 2 nanopesticide. The up-regulation of the expression levels of those genes are a protective mechanism for cucumber plants. These results provide a deeper understanding of the antioxidant defense responses in plants exposed to CuIJOH) 2 nanopesticides and may be applicable to other plant/nanopesticide interactions.
Journal of Colloid and Interface Science, 2007
The goal of this research was to study wetting and adhesion processes between various petroleum p... more The goal of this research was to study wetting and adhesion processes between various petroleum products and solid surfaces. When a liquid interacts with a solid surface, wetting, spreading and adhesion processes determine its behavior. These processes are of great importance for understanding oil spill response as well as oil spill behavior on land and in near shore environments, and oil extraction from the reservoir rock. The current study aimed at analyzing oil affinity and adhesion to surfaces used in the mechanical recovery of oil spills. A number of crude oils and petroleum products were tested with the surface materials that are used or may potentially be used to recover oil spills. Through the study of contact angles and recovered mass, it was found that the behavior of the oils at the solid surface is largely determined by the roughness of the solid. For smooth solids, contact angle hysteresis is a good indicator of the ability of the solid to retain oil. For rougher elastomers, the advancing contact angle can be used to predict wetting and adhesion processes between oil and solid. This study showed that oleophilic elastomers (e.g., Neoprene and Hypalon) have higher oil recovery potential than smooth polymers.
Journal of Environmental Engineering, Oct 1, 2010
To remove natural organic matter (NOM) from water, magnetic permanently confined micelle arrays (... more To remove natural organic matter (NOM) from water, magnetic permanently confined micelle arrays (Mag-PCMAs) were synthesized by coating the surface of Fe 3 O 4 particles with a silica/surfactant mesostructured hybrid layer. An environmental scanning electron microscope (ESEM) was used to characterize the particle size and surface morphology of the Mag-PCMAs. The zeta potential was used to assess the surface charge. Batch experiments were performed to investigate the adsorption of NOM by Mag-PCMAs. It was determined that NOM removal efficiency by Mag-PCMAs could be as high as 80% at a wide range of initial pH values (∼6.0-10.0). The adsorption isotherm was fitted well by a Langmuir model. Although Fe 3 O 4 had a high positive charge and Mag-PCMAs a small negative charge, Mag-PCMAs had a higher removal efficiency of NOM than uncoated Fe 3 O 4 particles (which are also magnetic), which indicated that the adsorption of NOM onto Mag-PCMAs was not dominated by electrostatic interactions. Possible mechanisms of the adsorption of NOM onto Mag-PCMAs were hydrophobic interactions and hydrogen bonding. It was feasible to reuse Mag-PCMAs after regeneration. These results indicate that Mag-PCMAs can be very attractive for the removal of NOM from aqueous matrices.
Measurement of Henry's law constant for methyl<i>tert</i>-butyl ether using solid-phase microextraction
Environmental Toxicology and Chemistry, Aug 1, 2001
Increasing groundwater contamination with methyl tert‐butyl ether (MTBE) requires more efficient ... more Increasing groundwater contamination with methyl tert‐butyl ether (MTBE) requires more efficient remediation technologies. Accurate measurement of MTBE's air–water partitioning coefficient (Henry's law constant, H) is important for the design and optimization of removal efficiency for many treatment systems as well as for predicting its fate and transport. Previously published data for MTBE appear to have some unusual nonlinearity at lower temperatures (15–30°C), and a wide range of values exists for dimensionless H at 25°C, from 0.0216 to 0.1226 in the published literature. We measured H for MTBE using headspace solid‐phase microextraction (SPME) and a static method that considers equilibrium partitioning in a closed system, for temperatures between 15 and 40°C. To validate our methods, we measured H for benzene, toluene, and trichloroethylene and compared our results to previously published values, with excellent agreement. The Arrhenius plot for MTBE indicates that ln(H MBTE) = 6.85−2,900 T −1, with T in K. At 25°C, H MBTE = 0.0555 ± 0.0122.
NanoImpact, Jul 1, 2016
Copper-based nanopesticides are increasingly being used in the agriculture, especially in organic... more Copper-based nanopesticides are increasingly being used in the agriculture, especially in organic farming. This has triggered some concerns about their risk to environmental and human health. In this study, 24-day-old lettuce plants grown in soil were exposed via the leaves to different concentrations (0, 1050 and 1555 mg/L) of Cu(OH) 2 nanopesticides for one month. Results showed Cu was mainly localized in lettuce leaves (823-1111 and 1353-2008 mg/kg in vascular and photosynthetic tissues), which may potentially increase Cu intake and impact human health. In addition, foliar application of Cu(OH)2 nanopesticide significantly increased potassium concentration in lettuce leaves by 6-7% and 21-28%, in vascular and photosynthetic tissues. A Gas Chromatography-Time-of-Flight Mass Spectrometry (GC-TOF-MS) based metabolomics approach was applied to determine hundreds of organic compounds simultaneously. Using relative quantitation and Partial Least Squares-Discriminant Analysis (PLS-DA) clustering of all compounds, clear differences were observed in the metabolite profiles of control and Cu(OH) 2 nanopesticides treated leaves. Discriminating compounds include amino acids, organic acids, polyamines, vitamin C and polyphenols. Dehydroascorbic acid and cis-caffeic acid, which are important antioxidants, were significantly decreased (19-33% and 5-8%) due to foliar exposure to the nanopesticide. Total antioxidant capacity was significantly decreased 20-23% after exposure to Cu(OH) 2 nanopesticides. There was also up-and down-regulation of a number of amino acids, particularly 4-hydroxybutytic acid (GABA) which decreased 50% compared to the control, potentially affecting the overall nutritional value of lettuce leaves exposed to the Cu(OH) 2 nanopesticides. In future work, determining an appropriate level of nanopesticide will be important to obtain the antifungal benefits without resulting in a significant decrease in nutritional value.
Water Science and Technology, Oct 1, 2009
With Chemically Enhanced Primary Treatment (CEPT) as the short-term process, the capacity of Bail... more With Chemically Enhanced Primary Treatment (CEPT) as the short-term process, the capacity of Bailonggang Wastewater Treatment Plant accounts for almost 25% of the total capacity of wastewater treatment in Shanghai, China. However, shortly after this plant was placed in operation in 2004, it was found that the effluent of CEPT couldn't meet the new national discharge criteria. Although the removal of phosphate is almost 80%, chemical oxygen demand (COD) and ammonia nitrogen (NH 3 -N) in the effluent is frequently found to exceed the standards. The primary goal of this research is to investigate the possibility of optimizing the CEPT to make it meet the discharge criteria before it is upgraded to a secondary treatment. An oxidant is adopted to remove NH 3 -N, and a high performance polyaluminum chloride (HP-PACl) is synthesized to enhance the removal of COD. It is found that HP-PACl improves the removal of COD, and the oxidant enhances NH 3 -N removal effectively. However, to meet the requirement of a newly implemented stricter discharge standard, it is necessary to upgrade this CEPT to a secondary treatment. The results of this study provide scientific evidence for the upgrade of the Bailonggang Wastewater Treatment Plant.
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Papers by Arturo A Keller