Field evaluation of metal bioaccumulation in the gastropod Helix aspersa at agricultural and industrial sites in Lebanon.

Juvenile Helix aspersa Müller exposed in field microcosms were used to assess the spatial and temporal bioaccumulation of Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn at two agricultural and two industrial sites in Lebanon. The study was performed over a 12-week period where caged snails were sampled once every 3 weeks and assessed for metal bioaccumulation and partitioning between soft tissue and shells. Results showed that metal bioaccumulation by snails was site dependent, with Fe and Cd being the greatest and least accumulated metals, respectively. Significant differences between bioaccumulation in each of the matrices (soft tissue and shells) were also observed. Time-dependent bioaccumulation results showed an increasing accumulation trend at both agricultural sites, while a slight decline was observed at the end of the sampling campaign for the industrial sites. The study of the bioaccumulation factors (BAF) revealed that tested H. aspersa were macroconcentrators for Zn and Cd (BAF > 2) and deconcentrators for all other analyzed elements (BAF < 1). The high partitioning factor values obtained for Cu and Zn indicate an affinity of these two elements for the soft tissues of the snails. The results of this field study indicate that H. aspersa are well suited for active biomonitoring and could provide reliable information on metal pollution and bioavailability.

Role of phosphogypsum and NPK amendments on the retention or leaching of metals in different soils.

Column leaching tests were conducted to investigate the effects of soil physicochemical characteristics on metal mobility in the subsurface. The metals investigated originated from disposed industrial waste byproducts and from agrochemicals spread over the farmlands. Soil column tests can provide insights into leaching of metals to underlying water compartments. The findings of this study can be used for prevention strategies and for setting risk assessment approaches to land-use and management, and soil and water quality and sustainability. Soils collected from an industrial (IS) watershed and an agricultural (AQ) hydrographic basin were used in soil column leaching experiments. The soil samples were characterized for mineralogy, functional groups, grain size, surface charge, soil type, porosity, and cation exchange capacity (CEC) along with elemental composition. Varying concentrations of phosphogypsum industrial waste or agrochemical (NPK fertilizer) was then added to the surface of the packed columns (n = 28). The columns were subjected to artificial rain over a period of 65 days. Leachates were collected and analyzed for dissolved Na(+), K(+), and Cd(2+) throughout the experimental period, whereas residual Cd content in the subsurface soil was measured at the end of the experiment. Physicochemical characterization indicated that the AQ soil has a higher potential for metal retention due to its fine clay texture, calcareous pH, high organic matter content and CEC. Metal release was more prominent in the IS soil indicating potential contamination of the surrounding soil and water compartments. The higher metal release is attributed to soil physicochemical characteristics. High calcium concentrations of phosphogypsum origin is expected to compete for adsorbed bivalent elements, such as Cd, resulting in their release. The physicochemical characteristics of the receiving media should be taken into consideration when planning land-use in order to achieve sustainable development. Soil physiochemical characteristics play a key role in determining the behavior and fate of elements upon application of amendments. Sandy soils should not be assigned to industrial zones or landfills due to their high permeability, unlike fine clay soils. Furthermore, application of fertilizers on sandy soils can threaten groundwater quality, whereas their extensive use on clayey soil can cause soil salinisation.

Reservoir sediments: a sink or source of chemicals at the surface water-groundwater interface.

This study delineates the physical, chemical, and biological effects resulting from anthropogenic and endogenic activities in a sensitive dammed reservoir situated in a semi-arid region. The reservoir is characterized by two major flow regimes: a wet fill hydrologic regime and a dry spill one. A seasonal sampling campaign was carried out over a period of 2 years (2011-2013) where water samples were collected across the water column and from piezometers just outside the perimeter of the reservoir. Similarly, sediments were collected from the corresponding areas beneath the water column. The water samples were analyzed for environmental isotopic ratios, elemental composition, and physical, biological and chemical parameters, whereas the sediment and algal samples were subjected to physical, mineralogical, spectroscopic, and microscopic analyses. This investigation indicated that the dam had resulted in the alteration of the biogeochemical cycle of nutrients as well as the degradation of the sediment and water quality. The hydrological and biogeochemical processes were found to induce vertical downward transport of chemicals towards the fine grained calcareous sediments during the fill mode, whereas the sediments acted as a source of a chemical flux upward through the water column and downward towards the groundwater during the spill mode. The geomorphological characteristics of the reservoir enhanced the strong hydrological connectivity between the surface water and the groundwater where the reservoir responded quickly to natural and anthropogenic changes in the upper watershed. The water and sediments in the sensitive spill mode were of poor quality and should receive more attention due to the potential hazard for the associated hydro-project and the sustainability of the agricultural soil in the long term. Thus, a safe water and sediment management plan should be implemented in order to improve the dam functionality and to safeguard the precious water resources.

Biomonitoring of PAHs and PCBs in industrial, suburban, and rural areas using snails as sentinel organisms.

There is a worldwide concern about the presence of persistent organic pollutants (POPs) in the environment because of their toxicity, bioaccumulation, and resistance to degradation. Various conventional monitoring techniques have been used to assess their presence in diverse environmental compartments. Most currently available methods, however, have limitations with regards to long-term monitoring. In the present work, juvenile Cornu aspersum (O. F. Müller, 1774) snails were tested in field microcosms as biomonitors for two major classes of organic pollutants, namely, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). The study assessed their deployment in one suburban, one rural, and two industrial sites over an 18-week period and monitored for temporal variations of 16 PAHs and 22 PCBs. Sampling was conducted once every 3 weeks. Targeted pollutants were extracted from the caged snails using the QuEChERS extraction procedure and subsequently analyzed using gas chromatography coupled to tandem mass spectrometry (GC-MS/MS). The results showed that the bioaccumulation of specific pollutants was site dependent; significantly higher levels of PCBs were observed at the industrial sites as compared to the suburban and rural ones. PAHs were bioaccumulated by the snails via ingestion of air and soil whereas PCBs were mainly bioaccumulated via soil contact and ingestion. The findings of this study indicate that C. aspersum is a reliable model organism for the biomonitoring of organic pollutants in air and soil compartments and can be used as part of an integrated environmental assessment.

Assessment of Opuntia ficus-indica (L.) Mill. extracts for the removal of lead from soil: the role of CAM plant harvest phase and soil properties.

Extensive research to date has focused on the coagulation-flocculation and biosorption properties of the invasive Opuntia ficus-indica (L.) Mill. to remove metals from water. However, no studies have reported on the use of O. ficus-indica extract as a leaching agent to remove metals from contaminated soil. In the present work, a new environmentally friendly method for lead-contaminated soil remediation is evaluated. The method involves the use of cladode extract from O. ficus-indica as a soil washing agent. This new technique can serve to mitigate against the potential deterioration of soil quality and other secondary environmental impacts that result from the use of inorganic acids and/or chelating agents. Extractions from cladodes harvested during both day and night crassulacean acidic metabolism (CAM) phases were evaluated for treatment of lead contamination in three different soils including kaolinite, montmorillonite and a field-natural soil sample. Lead removal rates, which ranged from 44 to 100%, were significantly impacted by the intrinsic properties of the soils, the leachate dosage, the plant harvest phase, and the soil washing duration. Fourier-transform infrared spectroscopy (FTIR) characterization of the leachates indicated that functional groups present in the O. ficus-indica extracts played an essential role in the removal process. Results suggest that this species possesses promising potential to be used as a sustainable basis for the abatement of lead contaminated soil.

Particle size and pH effects on remediation of chromite ore processing residue using calcium polysulfide (CaS5).

A long-term bench scale treatability study was performed to assess the ability to remediate chromite ore processing residue (COPR) using calcium polysulfide (CaS(5)). COPR materials were characterized with respect to particle size, pH, curing period and mineralogy. A stoichiometric ratio of sulfide species to hexavalent chromium (Cr(6+)) of 2 was used for the long-term treatment of COPR. The effectiveness of CaS(5) treatment was assessed using the toxicity characteristic leaching procedure (TCLP), alkaline digestion, and X-ray absorption near edge structure (XANES) analyses. The formation of ettringite, known as a heaving agent, was investigated following the treatment of CaS(5), using X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) along with an energy dispersive X-ray spectroscopy (EDX). Overall, after a curing period of 18 months, the TCLP total chromium (Cr) and alkaline digestion (Cr(6+)) results obtained from the treatability study showed that the concentrations were lower than 5 mg L(-1) and 9 mg kg(-1), respectively. However, XANES results obtained from samples cured for 18 months showed that all of the treated samples had higher Cr(6+) concentrations than shown using alkaline digestion. The lowest XANES Cr(6+) concentration of 610.2 mg kg(-1) was obtained from the sample with a particle size less than 0.075 mm and a pH value of 9. Particle size reduction prior to the addition of the reductant, along with pH reduction was found to be strongly associated with the treatment performance. Ettringite formation, due to pH increase over time in the samples, where the initial pH was adjusted to 9, was verified by XRPD and SEM-EDX analyses, indicating that a pH less than 9 should be maintained to avoid ettringite formation.

Application of an empirical transport model to simulate retention of nanocrystalline titanium dioxide in sand columns.

Nanocrystalline titanium dioxide was injected into sand columns to simulate subsurface injection for creation of a permeable treatment barrier. Past usage of this material as an ex situ pilot scale treatment filter has shown that it has a high adsorption capacity for a number of heavy metals and therefore would be a good candidate for injection technology. Three suspension concentrations (50, 75 and 100 mg l(-1)) were pumped through packed sand columns at different flow velocities (3.0, 6.8 and 14.1 cm min(-1)). Little to no particles was detected in the effluent. Most of the nanoparticles remained in the sand columns, with an increasing then decreasing retained solids pattern. Application of a one-dimensional advection-dispersion flow model, that included two empirical kinetic terms to account for particle retention in the porous media, produced data fits that followed the general trend of the data, but did not truly capture the concentration maxima in the data sets. Discussion of these results highlights the limited ability of existing models to aid in predicting particle retention of non-ideal materials for engineering purposes.

Leaching mechanisms of Cr(VI) from chromite ore processing residue.

Batch leaching tests, qualitative and quantitative x-ray powder diffraction (XRPD) analyses, and geochemical modeling were used to investigate the leaching mechanisms of Cr(VI) from chromite ore processing residue (COPR) samples obtained from an urban area in Hudson County, New Jersey. The pH of the leaching solutions was adjusted to cover a wide range between 1 and 12.5. The concentration levels for total chromium (Cr) and Cr(VI) in the leaching solutions were virtually identical for pH values >5. For pH values <5, the concentration of total Cr exceeded that of Cr(VI) with the difference between the two attributed to Cr(III). Geochemical modeling results indicated that the solubility of Cr(VI) is controlled by Cr(VI)-hydrocalumite and Cr(VI)-ettringite at pH >10.5 and by adsorption at pH <8. However, experimental results suggested that Cr(VI) solubility is controlled partially by Cr(VI)-hydrocalumite at pH >10.5 and by hydrotalcites at pH >8 in addition to adsorption of anionic chromate species onto inherently present metal oxides and hydroxides at pH <8. As pH decreased to <10, most of the Cr(VI) bearing minerals become unstable and their dissolution contributes to the increase in Cr(VI) concentration in the leachate solution. At low pH ( <1.5), Cr(III) solid phases and the oxides responsible for Cr(VI) adsorption dissolve and release Cr(III) and Cr(VI) into solution.

Assessment of cement kiln dust (CKD) for stabilization/solidification (S/S) of arsenic contaminated soils.

A stabilization/solidification (S/S) process for arsenic (As) contaminated soils was evaluated using cement kiln dust (CKD). Laboratory-prepared slurries, made of either kaolinite or montmorillonite, and field soils spiked with either As(3+) or As(5+) were prepared and treated with CKD ranging from 10 to 25 wt%. Sodium arsenite and sodium arsenate at 0.1 wt% were used to simulate arsenite (As(3+)) and arsenate (As(5+)) source contamination in soils, respectively. The effectiveness of treatment was evaluated at curing periods of 1- and 7-days based on the toxicity characteristic leaching procedure (TCLP). As-CKD and As-clay-CKD slurries were also spiked at 10 wt% to evaluate As immobilization mechanism using X-ray powder diffraction (XRPD) analyses. Overall, the TCLP results showed that only the As(5+) concentrations in kaolinite amended with 25 wt% CKD after 1 day of curing were less than the TCLP regulatory limit of 5mg/L. Moreover, at 7 days of curing, all As(3+) and As(5+) concentrations obtained from kaolinite soils were less than the TCLP criteria. However, none of the CKD-amended montmorillonite samples satisfied the TCLP-As criteria at 7 days. Only field soil samples amended with 20 wt% CKD complied with the TCLP criteria within 1 day of curing, where the source contamination was As(5+). XRPD and scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDX) results showed that Ca-As-O and NaCaAsO(4).7.5H(2)O were the primary phases responsible for As(3+) and As(5+) immobilization in the soils, respectively.

Assessment of calcium polysulfide for the remediation of hexavalent chromium in chromite ore processing residue (COPR).

Bench scale and pilot scale treatability studies were conducted to evaluate the remediation of hexavalent chromium [Cr(VI)] in chromite ore processing residue (COPR) using calcium polysulfide. The results from the bench scale study indicated that a calcium polysulfide dosage twice the molar stoichiometric requirement (2x) proved effective in meeting the New Jersey Department of Environmental Protection (NJDEP) total Cr(VI) and the Environmental Protection Agency (EPA) Toxicity Characteristic Leaching Procedure (TCLP) regulatory standards. The treatment results were more effective at pH 12 than at pH 9.5. X-ray powder diffraction (XRPD) and X-ray absorption near edge structure (XANES) spectroscopy were also used to assess the treatment performance. Based on the bench scale results, an ex-situ pugmill pilot program was implemented to evaluate the applicability of the calcium polysulfide treatment on a larger scale (1000-lb batch test). The pugmill treatment results met Cr(VI) and TCLP regulatory standards over a period of 15 months. XANES analysis indicated that approximately 62% of Cr(VI) was reduced by calcium polysulfide at stoichiometric ratio of 2x after a curing period of 10 months.

Long-term treatment issues with chromite ore processing residue (COPR): Cr(6+) reduction and heave.

A pugmill treatability study was conducted to remediate chromite ore processing residue (COPR) using ferrous sulfate heptahydrate (FeSO(4) x 7H(2)O) as a reductant. Two different types of COPR, with respect to particle size and mineralogy, were tested in this study. Two different stoichiometric ratios of FeSO(4) x 7H(2)O to Cr(6+) (5x and 8x) were applied to reduce Cr(6+) to Cr(3+). The effectiveness of FeSO(4).7H(2)O treatment was assessed using the toxicity characteristic leaching procedure (TCLP) tests and X-ray absorption near edge structure (XANES) analyses. TCLP results obtained from the pugmill treatability study showed that TCLP Cr concentrations were less than the TCLP regulatory limit of 5mg/L upon 8x FeSO(4) x 7H(2)O treatment for up to 420 days but may fail to meet this regulatory limit in the long-term. XANES results obtained from samples cured for 300 days showed that all of the treated samples failed the New Jersey Department of Environmental Protection (NJDEP) clean up level for Cr(6+) of 240 mg/kg. However, the Cr(6+) concentration from the sample with the smaller particle size approached 240 mg/kg (338 mg/kg), suggesting that particle size reduction prior to the addition of reductant may improve the effectiveness of the treatment. COPR heaving was investigated with unconfined swell tests upon 5x and 8x FeSO(4) x 7H(2)O treatment. The formation of ettringite, an expansive material, was investigated following the swell tests using X-ray powder diffraction (XRPD). Significant heaving (>50 vol%) was observed at curing times of 138 days for the 5x treatment and the ettringite formation was identified by XRPD analyses.

Carbonate effects on hexavalent uranium removal from water by nanocrystalline titanium dioxide.

A novel nanocrystalline titanium dioxide was used to treat depleted uranium (DU)-contaminated water under neutral and alkaline conditions. The novel material had a total surface area of 329 m(2)/g, total surface site density of 11.0 sites/nm(2), total pore volume of 0.415 cm(3)/g and crystallite size of 6.0 nm. It was used in batch tests to remove U(VI) from synthetic solutions and contaminated water. However, the capacity of the nanocrystalline titanium dioxide to remove U(VI) from water decreased in the presence of inorganic carbonate at pH > 6.0. Adsorption isotherms, Fourier transform infrared (FTIR) spectroscopy, and surface charge measurements were used to investigate the causes of the reduced capacity. The surface charge and the FTIR measurements suggested that the adsorbed U(VI) species was not complexed with carbonate at neutral pH values. The decreased capacity of titanium dioxide to remove U(VI) from water in the presence of carbonate at neutral to alkaline pH values was attributed to the aqueous complexation of U(VI) by inorganic carbonate. The nanocrystalline titanium dioxide had four times the capacity of commercially available titanium dixoide (Degussa P-25) to adsorb U(VI) from water at pH 6 and total inorganic carbonate concentration of 0.01 M. Consequently, the novel material was used to treat DU-contaminated water at a Department of Defense (DOD) site.

Spatial and temporal assessment of metal pollution in the sediments of the Qaraoun reservoir, Lebanon.

This study reports on metal (Cd, Cr, Cu, Ni, Pb, and Zn) pollution in the sediments of the Qaraoun reservoir over a span period of 9 years (2004, 2008, and 2013) along with key major environmental indicators. This time period corresponds with the onset of the rapid economic and industrial development of the reservoir region. For the first time, this study assessed the degree of environmental pollution by using indices such as enrichment factors (EF), contamination factors (CF), pollution load index (PLI), and geoaccumulation index (I geo). Moreover, sequential extraction was used to study the operationally determined chemical forms of the metals and their spatial and temporal distribution in the sediments. Correlation coefficients were also calculated to delineate the origin and association of the metals. Total metal concentrations and the environmental indices indicated increased pollution with time. Total organic carbon data showed a remarkable and significant increase in the organic fraction in 2013 relative to previous years. The increase in the organic fraction in the sediments was accompanied with a shift in cadmium [Cd] and lead [Pb] fractionation from the carbonate fraction to the organic fraction. The enrichment of the metal in the sediments along with the increased organic content is expected to exacerbate the metal bioavailability in the reservoir.

Phosphate removal from aqueous solution using ZVI/sand bed reactor: Behavior and mechanism.

This research reports on phosphate removal from aqueous solution using ZVI/sand packed columns. The influence of column preconditioning, consisting of ZVI pre-oxidation before feeding the columns with phosphate solution, revealed that a column aged for 1 day was more efficient than un-conditioned column, 5-days and 10-days preconditioned columns. The distribution of phosphate trapped inside the columns was evaluated by measuring phosphate concentration in the solids at different levels (P1, P2 and P3) along the depth of the columns. The distribution of phosphate inside the columns was determined for a time period up to 46 days, corresponding to column saturation. Results showed heterogeneous trapping along the column before saturation and homogeneous distribution upon saturation. The maximum cumulative trapped phosphate after column dismantling was determined before saturation (after 17 days running) at 130, 68 and 31 mgP/gFe at the inlet-P1, P1-P2 and P2-P3 layers, respectively, whereas the homogeneous distribution of phosphate upon saturation was determined at 132 mgP/gFe throughout the column. Solid supports were characterized using SEM, XRD and XPS. Lepidocrocite and maghemite/magnetite were the only iron oxidation products identified at the different layers inside the columns. XPS results confirmed the sorption of phosphate at the surface of ZVI and its oxidation products and highlighted the formation of an iron phosphate complex.

Assessment of ferrous chloride and Portland cement for the remediation of chromite ore processing residue.

Chromite Ore Processing Residue (COPR) is an industrial waste containing up to 7% chromium (Cr) including up to 5% hexavalent chromium [Cr(VI)]. The remediation of COPR has been challenging due to the slow release of Cr(VI) from a clinker like material and thereby the incomplete detoxification of Cr(VI) by chemical reagents. The use of sulfur based reagents such as ferrous sulfate and calcium polysulfide to detoxify Cr(VI) has exasperated the swell potential of COPR upon treatment. This study investigated the use of ferrous chloride alone and in combination with Portland cement to address the detoxification of Cr(VI) in COPR and the potential swell of COPR. Chromium regulatory tests, X-ray powder diffraction (XRPD) analyses and X-ray absorption near edge structure (XANES) analyses were used to assess the treatment results. The treatment results indicated that Cr(VI) concentrations for the acid pretreated micronized COPR as measured by XANES analyses were below the New Jersey Department of Environmental Protection (NJDEP) standard of 20 mg kg(-1). The Toxicity characteristic leaching procedure (TCLP) Cr concentrations for all acid pretreated samples also were reduced below the TCLP regulatory limit of 5 mg L(-1). Moreover, the TCLP Cr concentration for the acid pretreated COPR with particle size ⩽0.010 mm were less than the universal treatment standard (UTS) of 0.6 mg L(-1). The treatment appears to have destabilized all COPR potential swell causing minerals. The unconfined compressive strength (UCS) for the treated samples increased significantly upon treatment with Portland cement.

Evaluation of ettringite-related swelling mechanisms for treated chromite ore processing residue.

Accelerated one-dimensional unconfined swell tests were conducted for ferrous sulfate chromite ore processing residue (COPR) field-treated samples. The field-treated samples were subjected to wet and dry cycles over 100 days to accelerate the lithification of the samples. Parallel laboratory experiments were performed to investigate the effects of mineralogy on COPR swell under controlled conditions. The field and laboratory samples were treated with ferrous sulfate at a ferrous-to-Cr(6+) molar stoichiometric ratios of eight (8×) and five (5×). X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDX) analyses were used to investigate the mineralogical changes upon treatment. The swell results indicated that significant COPR swelling was observed in all of the tested samples. The swelling was more pronounced in the 5× treated COPR sample than in the 8× treated COPR sample. Moreover, the laboratory-treated samples showed greater swelling behavior as compared with the field-treated samples, which was most probably due to the high dry density of the COPR, indicating that dry density was a more dominant factor than lithification. XRPD and SEM-EDX results confirmed that significant ettringite formation occurred in all treated samples.

Stabilization of As-, Pb-, and Cu-contaminated soil using calcined oyster shells and steel slag.

In this study, As-, Pb-, and Cu-contaminated soil was stabilized using calcined oyster shells (COS) and steel slag (SS). The As-contaminated soil was obtained from a timber mill site where chromate copper arsenate (CCA) was used as a preservative. On the other hand, Pb- and Cu-contaminated soil was obtained from a firing range. These two soils were thoroughly mixed to represent As-, Pb-, and Cu-contaminated soil. Calcined oyster shells were obtained by treating waste oyster shells at a high temperature using the calcination process. The effectiveness of stabilization was evaluated by 1-N HCl extraction for As and 0.1-N HCl extraction for Pb and Cu. The treatment results showed that As, Pb, and Cu leachability were significantly reduced upon the combination treatment of COS and SS. The sole treatment of SS (10 wt%) did not show effective stabilization. However, the combination treatment of COS and SS showed a significant reduction in As, Pb, and Cu leachability. The best stabilization results were obtained from the combination treatment of 15 wt% COS and 10 wt% SS. The SEM-EDX results suggested that the effective stabilization of As was most probably achieved by the formation of Ca-As and Fe-As precipitates. In the case of Pb and Cu, stabilization was most probably associated with the formation of pozzolanic reaction products such as CSHs and CAHs.

Stabilization of Pb²âº and Cu²âº contaminated firing range soil using calcined oyster shells and waste cow bones.

Pb(2+) and Cu(2+) contamination at army firing ranges poses serious environmental and health risks to nearby communities necessitating an immediate and prompt remedial action. In this study, a novel mixture of calcined oyster shells (COSs) and waste cow bones (WCBs) was utilized to immobilize Pb(2+) and Cu(2+) in army firing range soils. The effectiveness of the treatment was evaluated based on the Korean Standard leaching test. The treatment results showed that Pb(2+) and Cu(2+) immobilization in the army firing range soil was effective in significantly reducing Pb(2+) and Cu(2+) leachability upon the combined treatment with COS and WCB. A drastic reduction in Pb(2+) (99%) and Cu(2+) leachability (95%) was obtained as compared to the control sample, upon treatment with 5 wt.% COS and 5 wt.% WCB. The combination treatment of COS and WCB was more effective for Pb immobilization, than the treatment with COS or WCB alone. The 5 wt.% COS alone treatment resulted in 95% reduction in Cu(2+) leachability. The SEM-EDX results suggested that Pb(2+) and Cu(2+) immobilization was most probably associated with the formation of ettringite, pozzolanic reaction products and pyromorphite-like phases at the same time.

Influence of Ca(2+) and Suwannee River Humic Acid on aggregation of silicon nanoparticles in aqueous media.

Silicon nanoparticles (NPs) have potential applications in many fields including microelectronics, biomedical imaging, and most recently energetics. Even though silicon NPs are thought to be harmless, their full impact on the environment and human health needs further investigation due to their potential increased use and recent toxicity data. Various techniques were used to characterize silicon NPs that are being considered for use in energetics. These techniques included dynamic light scattering (DLS), electron microscopy (EM), X-ray diffraction (XRD) and atomic force microscopy (AFM). Experiments were also conducted on the early stage aggregation kinetics of silicon NPs in the presence of Ca(2+) and Suwannee River Humic Acid (SRHA). The addition of SRHA in the presence of Ca(2+) resulted in increased attachment efficiencies and decreased critical coagulation concentration (from 0.4 to 0.1M). The enhanced aggregation was attributed to bridging generated by SRHA aggregates as evidenced by selected area electron diffraction (SAED) and energy dispersive spectroscopy (EDS). SAED verified the bridging to be amorphous phase comprised of humic substances rather than artifacts of silicon crystallites. Element distribution analyses were also used in the delineation of the silicon NP aggregation mechanisms in the absence and presence of SRHA.

Effects of natural organic matter on aggregation kinetics of boron nanoparticles in monovalent and divalent electrolytes.

Nano boron is a promising new propellant being considered for military and civilian applications; however, the impact of its release on the environment is largely not known. The early stage aggregation kinetics of boron nanoparticles was investigated in the presence of two kinds of natural organic matter-Suwannee River humic acid (SRHA) and sodium alginate-by dynamic light scattering and transmission electron microscopy (TEM). The addition of SRHA caused the boron nanoparticles to stabilize and resulted in (1) decreased attachment efficiency for the reaction-controlled regime and (2) an increase in the critical coagulation concentration, in CaCl(2) and MgCl(2) solutions. The increase in the electrostatic repulsion is suggested as a main cause of the induced stabilization as indicated by the electrophoretic mobility measurements. Similar behavior was observed in the presence of alginate and MgCl(2). However, the attachment efficiency kept increasing in the presence of CaCl(2) and alginate with the increase in the electrolyte concentration and was greater than unity at>4mM CaCl(2). The destabilization was attributed to bridging of the nanoparticles by the alginate-Ca(2+) system. Results from this study suggest that various NOM and electrolytes play significant and differing roles in the aggregation of boron nanoparticles in natural aquatic environments.