Novel flame retardants detected in marine plastic litter in coastal areas in Central Chile.

Flame retardants (FRs) are released throughout the plastic life cycle, potentially impacting the environment, biodiversity, and human health. This study analyzed novel flame retardants (NFR) in marine plastic litter (MPL) from six coastal areas in central Chile in November 2017. Target chemicals (n = 19) were analyzed using ultrasonic extraction with hexane, gas chromatography, and mass spectrometry (GC-MS). From all nineteen NFRs analyzed, only ten (53 %) were routinely detected. BTBPE (1,2-bis(2,4,6-tribromophenoxy) ethane) showed the highest concentrations at the Bellavista site (618 to 424,000 pg g-1), and HBB (Hexabromobiphenyl), banned since 1970, was detected in Coliumo (2630 to 13,700 pg g-1). These results show emerging transport patterns and underscore the critical need for enhanced waste management practices for MPL in coastal regions to prevent adverse impacts on marine biodiversity.

Biofouling potential of surface-enhanced Raman scattering-based seawater quality sensors by Ulva spp.

This study investigated the biofouling potential of surface-enhanced Raman scattering (SERS)-based sensor materials in the context of marine environments. Uncoated and monolithic commercial gold (Au) silicon nanopillar array SERS substrates, Au-coated carbon black nanoparticle (AuCB NP) substrates, uncoated and Au sputter-coated in-house SERS, and uncoated and Au sputter-coated glass controls were tested for biofouling potential using Ulva spp. as model biofouling organisms. The mean percentages of Ulva spp. zoospores that adhered per mm2 (×103) on the uncoated and coated Au silicon nanopillar array, AuCB NP, uncoated and Au sputter-coated in-house, and uncoated and Au sputter-coated glass substrates were 10.28%, 5.45%, 10.49%, 3.25%, 24.84%, 12.86% and 7.78%, respectively. Results indicated that surface properties such as hydrophobicity, roughness, Au sputter-coating and the presence of micro-refuges on nano- and microstructured substrates were critical to the biofouling formation.

Electric Potential Induced Prevention and Removal of an Algal Biofoulant from Planar SERS Substrates.

Ulva zoospores are widespread marine macroalgae and a common organism found in biofouling communities due to their strong adhesive properties and quick settlement times. Using Ulva as a model organism, a strategy is presented where direct-current (DC) electric potentials are applied in conjunction with surface-enhanced Raman spectroscopy (SERS) to characterize, remove, and prevent Ulva from forming a biofilm on gold-capped nanopillar SERS substrates. Experiments were conducted within a poly(tetrafluoroethylene) (PTFE) flow channel device where the SERS substrates were used as an electrode. Ulva density, determined in situ by SERS and ex situ by electron and fluorescence microscopy, decreased under successively increasing low negative potentials up to -1.0 V. The presence of damaged Ulva suggests that the applied potential led to spore rupture. At the highest negative applied potential (-1.0 V), microparticles containing copper, which is known for its antimicrobial properties, were associated with Ulva on the SERS substrate and the lowest Ulva density was observed. These findings indicate that (1) SERS can be employed to study biofilm formation on nanostructured metal surfaces and (2) applying low-voltage electric potentials may be used to control Ulva biofouling on SERS marine sensors.

Fouling Resistance of Brush-Modified Elastomers.

The most effective antifouling coatings are designed to slowly release biocides that target a broad spectrum of marine organisms. However, as biocides have a deleterious effect on marine life, there is demand for environmentally friendly coatings that resist fouling through physical interactions. We propose a simple platform for the development of such coatings based on bottlebrush-modified elastomers. The bottlebrush additives were synthesized to have side chain chemistries that are known to be fouling-resistant, and these were incorporated in a commercial elastomer through blending and/or covalent attachment. The fouling performance of these coatings was highly variable, with area coverages of hard and soft foulants ranging from 1.4% to 7.2% and 29.1% to 64.0%, respectively, across a set of eight materials. The origin of these differences was explained by examining the structure of the coating surface through chemical imaging by time-of-flight secondary ion mass spectrometry (TOF-SIMS) and topographic imaging by atomic force microscopy (AFM). We found that fouling by certain soft and hard fouling organisms was primarily influenced by surface composition, which was controlled by both the chemistry and loading level of the bottlebrush additive, and was independent of the inherent surface roughness. While no type of coating could resist all soft and hard foulants, a formulation based on a bottlebrush copolymer additive with both siloxane and fluorinated monomers was effective against nearly all organisms encountered in the study.

Prediction of the Limiting Flux and Its Correlation with the Reynolds Number during the Microfiltration of Skim Milk Using an Improved Model.

Limiting flux (JL) determination is a critical issue for membrane processing. This work presents a modified exponential model for JL calculation, based on a previously published version. Our research focused on skim milk microfiltrations. The processing variables studied were the crossflow velocity (CFV), membrane hydraulic diameter (dh), temperature, and concentration factor, totaling 62 experimental runs. Results showed that, by adding a new parameter called minimum transmembrane pressure, the modified model not only improved the fit of the experimental data compared to the former version (R2 > 97.00%), but also revealed the existence of a minimum transmembrane pressure required to obtain flux (J). This result is observed as a small shift to the right on J versus transmembrane pressure curves, and this shift increases with the flow velocity. This fact was reported in other investigations, but so far has gone uninvestigated. The JL predicted values were correlated with the Reynolds number (Re) for each dh tested. Results showed that for a same Re; JL increased as dh decreased; in a wide range of Re within the turbulent regime. Finally, from dimensionless correlations; a unique expression JL = f (Re, dh) was obtained; predicting satisfactorily JL (R2 = 84.11%) for the whole set of experiments.

A Critical Review of Extraction and Identification Methods of Microplastics in Wastewater and Drinking Water.

This critical review analyzes methodologies used to collect, quantify, and characterize microplastics in both wastewater and drinking water. Researchers used different techniques at all stages, from collection to characterization, for quantifying microplastics in urban water systems. This represents a barrier to comprehensively assess the current loads of microplastic and to compare the results obtained by such assessments. The compiled studies address microplastic contamination using four types of sample collection techniques, four methods for processing samples, and four techniques for characterizing microplastics. This results in significant discrepancies in each of the following: (1) reported concentrations in both wastewater effluents and drinking water, (2) microplastic characteristics (i.e., size, color, shape, and composition), and (3) quality control and assurance procedures. Finally, this review qualitatively evaluated the reports by the completeness of their data based on a ranking system using five criteria: sample collection, sample processing, quality control, identification technique, and results. The results of this ranking system clarify disparities between the studies.

Synthesis of silver nanoparticles using a modified Tollens' method in conjunction with phytochemicals and assessment of their antimicrobial activity.

BACKGROUND: Silver nanoparticles (AgNPs) have attracted great attention due to their outstanding electrical, optical, magnetic, catalytic, and antimicrobial properties. However, there is a need for alternative production methods that use less toxic precursors and reduce their undesirable by-products. Phyto-extracts from the leaves of olive and rosemary plants can be used as reducing agents and (in conjunction with Tollens' reagent) can even enhance AgNP antimicrobial activity. METHODS: Conditions for the proposed hybrid synthesis method were optimized for olive leaf extracts (OLEs) and rosemary leaf extracts (RLEs). The resultant AgNPs were characterized using UV-visible spectroscopy, an environmental scanning electron microscope, and Dynamic Light Scattering analysis. An atomic absorption spectrophotometer was used to measure AgNP concentration. Fourier transform infrared spectroscopy (FTIR) was used to determine the specific functional groups responsible for the reduction of both silver nitrate and capping agents in the leaf extract. Additionally, the antimicrobial properties of the synthesized AgNPs were assessed against Gram-negative bacteria (Escherichia coli and Salmonella enterica) and Gram-positive bacteria (Staphylococcus aureus), by using both the Kirby-Bauer and broth microdilution methods on Mueller-Hinton (MH) agar plates. RESULTS AND DISCUSSION: A simple, feasible, and rapid method has been successfully developed for silver nanoparticle synthesis by reducing Tollens' reagent using leaf extracts from olive and rosemary plants (widely available in Jordan). Scanning electron microscopy images showed that the method produces AgNPs with a spherical shape and average core sizes of 45 ± 2 and 38 ± 3 nm for OLE and RLE, respectively. A negative zeta potential (ζ) of -43.15 ± 3.65 mV for OLE-AgNPs and -33.65 ± 2.88mV for RLE-AgNPs proved the stability of silver nanoparticles. FTIR spectra for AgNPs and leaf extracts indicated that the compounds present in the leaf extracts play an important role in the coating/capping of synthesized nanoparticles. The manufactured AgNPs exhibited an antibacterial effect against Escherichia coli and Staphylococcus aureus with minimum inhibitory concentrations (MIC) of 9.38 and 4.69 µl/ml for OLE-AgNPs and RLE-AgNPs, respectively. The MIC for Salmonella enterica were 18.75 µl/ml for both OLE-AgNPs and RLE-AgNPs. Furthermore, our results indicated that the RLE-AgNPs exhibited a stronger antibacterial effect than OLE-AgNPs against different bacteria species. These results contribute to the body of knowledge on nanoparticle production using plant-mediated synthesis and performance. They also offer insights into the potential for scaling up this production process for commercial implementation.

Nanofiller Presence Enhances Polycyclic Aromatic Hydrocarbon (PAH) Profile on Nanoparticles Released during Thermal Decomposition of Nano-enabled Thermoplastics: Potential Environmental Health Implications.

Nano-enabled products are ultimately destined to reach end-of-life with an important fraction undergoing thermal degradation through waste incineration or accidental fires. Although previous studies have investigated the physicochemical properties of released lifecycle particulate matter (called LCPM) from thermal decomposition of nano-enabled thermoplastics, critical questions about the effect of nanofiller on the chemical composition of LCPM still persist. Here, we investigate the potential nanofiller effects on the profiles of 16 Environmental Protection Agency (EPA)-priority polycyclic aromatic hydrocarbons (PAHs) adsorbed on LCPM from thermal decomposition of nano-enabled thermoplastics. We found that nanofiller presence in thermoplastics significantly enhances not only the total PAH concentration in LCPM but most importantly also the high molecular weight (HMW, 4-6 ring) PAHs that are considerably more toxic than the low molecular weight (LMW, 2-3 ring) PAHs. This nano-specific effect was also confirmed during in vitro cellular toxicological evaluation of LCPM for the case of polyurethane thermoplastic enabled with carbon nanotubes (PU-CNT). LCPM from PU-CNT shows significantly higher cytotoxicity compared to PU which could be attributed to its higher HMW PAH concentration. These findings are crucial and make the case that nanofiller presence in thermoplastics can significantly affect the physicochemical and toxicological properties of LCPM released during thermal decomposition.

Synergistic effects of engineered nanoparticles and organics released from laser printers using nano-enabled toners: potential health implications from exposures to the emitted organic aerosol.

Recent studies have shown that engineered nanoparticles (ENPs) are incorporated into toner powder used in printing equipment and released during their use. Thus, understanding the functional and structural composition and potential synergistic effects of this complex aerosol and released gaseous co-pollutants is critical in assessing their potential toxicological implications and risks. In this study, toner powder and PEPs were thoroughly examined for functional and molecular composition of the organic fraction and the concentration profile of 16 Environmental Protection Agency (EPA)-priority polycyclic aromatic hydrocarbons (PAH) using state of the art analytical methods. Results show significant differences in abundance of non-exchangeable organic hydrogen of toner powder and PEPs, with a stronger aromatic spectral signature in PEPs. Changes in structural composition of PEPs are indicative of radical additions and free-radical polymerization favored by catalytic reactions, resulting in formation of functionalized organic species. Particularly, accumulation of aromatic carbons with strong styrene-like molecular signatures on PEPs is associated with formation of semivolatile heavier aromatic species (i.e., PAHs). Further, the transformation of low molecular weight PAHs in the toner powder to high molecular weight PAHs in PEPs was documented and quantified. This may be a result of synergistic effects from catalytic metal/metal oxide ENPs incorporated into the toner and the presence/release of semi-volatile organic species (SVOCs). The presence of known carcinogenic PAHs on PEPs raises public health concerns and warrants further toxicological assessment.

Polycyclic Aromatic Hydrocarbon Contamination in Soils of San Mateo Ixtatán, Guatemala: Occurrence, Sources, and Health Risk Assessment.

Exposure to high concentrations of carcinogenic pollutants in soils and sediments can result in increased health risks. Determining the levels and sources of contamination in developing communities is important for helping to reduce pollution and mitigate the risk of exposure. In the Mayan community of San Mateo Ixtatán, Guatemala, 24 samples of topsoil from urban, peri-urban, and agricultural sites and six samples of river sediment were collected and analyzed for 17 polycyclic aromatic hydrocarbons (PAHs). The sum of the concentrations of these PAHs at the urban and peri-urban sites ranged from 460 to 3251 µg kg (mean, 1401 µg kg), whereas at agricultural sites the range was 350 to 2087 µg kg (mean, 1038 µg kg). Analysis to identify and apportion the source showed that the PAHs emitted from wood stoves contributed 71 and 76% of the total PAHs in urban and agricultural areas soils, respectively. The calculated incremental lifetime cancer risk due to the ingestion of soil, dermal contact, and dietary intake through corn consumption was greater than the acceptable level of 10 established by the USEPA. Our findings suggest that the residents of rural communities can be at increased cancer risk despite little or no industrial activity in the local area. Alternate domestic fuel sources should be considered to reduce the health risk in local communities.

Comparative study between chemostat and batch reactors to quantify membrane permeability changes on bacteria exposed to silver nanoparticles.

Continuous and batch reactors were used to assess the effect of the exposure of casein-coated silver nanoparticles (AgNPs) on Escherichia coli (E. coli). Additionally, E. coli membrane extracts, membrane permeability and Langmuir film balance assays were used to determine integrity and changes in lipid composition in response to AgNPs exposure. Results showed that batch conditions were not appropriate for the tests due to the production of exopolymeric substances (EPS) during the growth phase. After 5h of contact between AgNPs and the used growth media containing EPS, the nanoparticles increased in size from 86nm to 282nm reducing the stability and thus limiting cell-nanoparticle interactions. AgNPs reduced E. coli growth by 20% at 1mg/L, in terms of Optical Density 670 (OD670), while no effect was detected at 15mg/L. At 50mg/L of AgNPs was not possible to perform the test due to aggregation and sedimentation of the nanoparticles. Membrane extract assays showed that at 1mg/L AgNPs had a greater change in area (-4.4cm(2)) on bacteria compared to 15mg/L (-4.0cm(2)). This area increment suggested that membrane disruption caused by AgNPs had a stabilizing/rigidifying effect where the cells responded by shifting their lipid composition to more unsaturated lipids to counteract membrane rigidification. In chemostats, the constant inflow of fresh media and aeration resulted in less AgNPs aggregation, thus increased the AgNPs-bacteria interactions, in comparison to batch conditions. AgNPs at 1mg/L, 15mg/L, and 50mg/L inhibited the growth (OD670 reduction) by 0%, 11% and 16.3%, respectively. Membrane extracts exposed to 1mg/L, 15mg/L, and 50mg/L of AgNPs required greater changes in area by -0.5cm(2), 2.7cm(2) and 3.6cm(2), respectively, indicating that the bacterial membranes were disrupted and bacteria responded by synthesizing lipids that stabilize or strengthen membranes. This study showed that the chemostat is more appropriate for the testing of nanotoxicological effects when testing bacteria at growing conditions.

New Antimicrobially Amended Media for Improved Nonpoint Source Bacterial Pollution Treatment.

Nonpoint source pollution (NPS) such as stormwater runoff may introduce high loads of bacteria, impairing surface water bodies. The existing filter materials in stormwater best management practices (BMP) are typically not designed to inactivate bacteria. Herein, novel filtration media were extensively tested for microbial load reduction in stormwater runoff. Red cedar wood chips (RC) were amended with different loadings of either 3-(trihydroxysilyl) propyldimethyloctadecyl ammonium chloride (TPA) or silver nanoparticles (AgNP). Under batch conditions at 25 °C, log10 removal values (LRV) up to 3.71 ± 0.38 (mean ± standard error) for TPA-RC and 2.25 ± 1.00 for AgNP-RC were achieved for Escherichia coli (E. coli), whereas unmodified RC achieved less than 0.5 LRV. Similar trends were observed at 17.5 °C, however at low temperature (10 °C) no statistically significant difference in E. coli inactivation between modified and unmodified RC was detected. Inactivation kinetic studies show that TPA-RC has higher inactivation rate constants compared to AgNP-RC. Under dynamic flow conditions a mass balance approach indicates that even after remobilization up to 99.8% of E. coli removal using 9 mg/g TPA-RC compared to 64.8% for unmodified RC. This study demonstrates that RC wood chips amended with antimicrobial compounds show promising applications as filtration material for the reduction of microbiological contamination load in stormwater runoff.

Ceramic water filters impregnated with silver nanoparticles as a point-of-use water-treatment intervention for HIV-positive individuals in Limpopo Province, South Africa: a pilot study of technological performance and human health benefits.

Waterborne pathogens present a significant threat to people living with the human immunodeficiency virus (PLWH). This study presents a randomized, controlled trial that evaluates whether a household-level ceramic water filter (CWF) intervention can improve drinking water quality and decrease days of diarrhea in PLWH in rural South Africa. Seventy-four participants were randomized in an intervention group with CWFs and a control group without filters. Participants in the CWF arm received CWFs impregnated with silver nanoparticles and associated safe-storage containers. Water and stool samples were collected at baseline and 12 months. Diarrhea incidence was self-reported weekly for 12 months. The average diarrhea rate in the control group was 0.064 days/week compared to 0.015 days/week in the intervention group (p < 0.001, Mann-Whitney). Median reduction of total coliform bacteria was 100% at enrollment and final collection. CWFs are an acceptable technology that can significantly improve the quality of household water and decrease days of diarrhea for PLWH in rural South Africa.

Disinfection action of electrostatic versus steric-stabilized silver nanoparticles on E. coli under different water chemistries.

The capping layer stabilizing silver nanoparticles (AgNPs) affects its aggregation, dissolution, and net disinfection action, especially under conditions of varying water composition, such as, pH, ionic strength and organic matter content. Herein, we correlate the silver ion (Ag(+)) release and reactive oxygen species (ROS) generation rates for AgNPs of varying functionalization to their net disinfection coefficient on Escherichia coli, under conditions of differing water chemistries. For electrostatically stabilized citrate-capped AgNPs, the rate of ROS generation, as measured using a fluorescent dye, is found to dominate over that of Ag(+) release, especially for smaller sized AgNP suspensions (~10nm) at low pH (~6.2). For these AgNPs, the ROS disinfection mechanism is confirmed to dominate net disinfection action, as measured by the live/dead assay, especially at low levels of organic matter. Steric stabilization of AgNPs by protein or starch-capped layers enables disinfection through reducing AgNP aggregation and promoting silver dissolution over ROS generation. We suggest the involvement of protons and dissolved oxygen in causing the independent formation of Ag(+) and ROS, regardless of the AgNP capping layer. While protein-capping layers effectively stabilize AgNPs, the generated ROS is likely dissipated by interference with the bulky capping layer, whereas the interference is lower with citrate-capping layers. Steric stabilization of AgNPs enables disinfection within a wide range of water chemistries, whereas effective disinfection can occur under electrostatic stabilization, only at low NaCl (<1 mmol/L) and organic matter (<5 mg/L) levels.

Comparison of the bacterial removal performance of silver nanoparticles and a polymer based quaternary amine functiaonalized silsesquioxane coated point-of-use ceramic water filters.

This study compares the disinfection performance of ceramic water filters impregnated with two antibacterial compounds: silver nanoparticles and a polymer based quaternary amine functiaonalized silsesquioxane (poly(trihydroxysilyl) propyldimethyloctadecyl ammonium chloride (TPA)). This study evaluated these compounds using ceramic disks manufactures with clay obtained from a ceramic filter factory located in San Mateo Ixtatan, Guatemala. Instead of using full size ceramic water filters, manufactured 6.5 cm diameter ceramic water filter disks were used. Results showed that TPA can achieve a log bacterial reduction value of 10 while silver nanoparticles reached up to 2 log reduction using a initial concentration of bacteria of 10(10)-10(11)CFU/ml. Similarly, bacterial transport demonstrated that ceramic filter disks painted with TPA achieved a bacterial log reduction value of 6.24, which is about 2 log higher than the values obtained for disks painted with silver nanoparticles (bacterial log reduction value: 4.42). The release of both disinfectants from the ceramic materials to the treated water was determined measuring the effluent concentrations in each test performed. Regarding TPA, about 3% of the total mass applied to the ceramic disks was released in the effluent over 300 min, which is slightly lower than the release percentage for silver nanoparticles (4%). This study showed that TPA provides a comparable disinfection performance than silver nanoparticles in ceramic water filter. Another advantage of using TPA is the cost as the price of TPA is considerable lower than silver nanoparticles. In spite of the use of TPA in several medical related products, there is only partial information regarding the health risk associated with the ingestion of this compound. Additional long-term toxicological information for TPA should be evaluated before its future application in ceramic water filters.

The effect of natural water conditions on the anti-bacterial performance and stability of silver nanoparticles capped with different polymers.

This study evaluated the effect of natural water composition onto the bactericidal and physicochemical properties of silver nanoparticles (AgNPs) stabilized with three different polymeric compounds. All the nanoparticles behaved similarly in the water conditions tested. Compared to solutions with low organic matter content and monovalent ions, lower disinfection performances of AgNPs suspensions were obtained in the following order seawater ≤ high organic matter content water ≤ high divalent cations content synthetic water. Suspension of AgNPs in seawater and water with divalent cations (Ca(2+) and Mg(2+)) formed larger AgNPs aggregates (less than 1400 nm) compared to other solutions tested (up to approximately 38 nm). The critical coagulation concentration (CCC) of AgNPs was determined to quantitatively evaluate the stability of the nanoparticle suspension in different water conditions. When the concentration of dissolved organic matter was increased from 0 mg/L to 5 mg/L, the CCC increased by a factor in the range of 2.19 ± 0.25 for all AgNPs in divalent solutions, but a smaller increase occurred, in the range of 1.54 ± 0.21 fold, when monovalent solutions were used. The concentration of ionic silver released indicated that the dissolved Ag(+) (3.6-48.2 ppb) was less than 0.5% of the total mass of Ag(0) added. At all the conditions tested, the concentration of silver ions in solution had a negligible contribution to the overall anti-bacterial performance of AgNPs. This study demonstrated that the anti-bacterial performance of AgNPs at selected natural water conditions decreases in the presence of dissolved natural organic matter or divalent ions, such as humic acid and calcium carbonate. These results may be helpful in understanding the toxicity of AgNP in various natural water conditions and in explaining the risk associated with discharging AgNP in natural aquatic systems.

Sustainable colloidal-silver-impregnated ceramic filter for point-of-use water treatment.

Cylindrical colloidal-silver-impregnated ceramic filters for household (point-of-use) water treatment were manufactured and tested for performance in the laboratory with respect to flow rate and bacteria transport. Filters were manufactured by combining clay-rich soil with water, grog (previously fired clay), and flour, pressing them into cylinders, and firing them at 900 degrees C for 8 h. The pore-size distribution of the resulting ceramic filters was quantified by mercury porosimetry. Colloidal silver was applied to filters in different quantities and ways (dipping and painting). Filters were also tested without any colloidal-silver application. Hydraulic conductivity of the filters was quantified using changing-head permeability tests. [3H]H2O water was used as a conservative tracer to quantify advection velocities and the coefficient of hydrodynamic dispersion. Escherichia coli (E. coli) was used to quantify bacterial transport through the filters. Hydraulic conductivity and pore-size distribution varied with filter composition; hydraulic conductivities were on the order of 10(-5) cm/s and more than 50% of the pores for each filter had diameters ranging from 0.02 to 15 microm. The filters removed between 97.8% and 100% of the applied bacteria; colloidal-silver treatments improved filter performance, presumably by deactivation of bacteria. The quantity of colloidal silver applied per filter was more important to bacteria removal than the method of application. Silver concentrations in effluent filter water were initially greater than 0.1 mg/L, but dropped below this value after 200 min of continuous operation. These results indicate that colloidal-silver-impregnated ceramic filters, which can be made using primarily local materials and labor, show promise as an effective and sustainable point-of-use water treatment technology for the world's poorest communities.

Simultaneous sorption of benzene and heavy metals onto two organoclays.

An experimental study was performed to determine the feasibility of using hexadecyltrimethylammonium bentonite clay (HDTMA-clay) and benzyltriethylammonium bentonite clay (BTEA-clay) for simultaneous sorption of benzene and one of four heavy metals (Pb, Cd, Zn and Hg). Specifically, the role of competition between benzene and each heavy metal was studied. The sorption of Pb, Cd, and Zn on both BTEA- and HDTMA-clay decreases in the presence of benzene relative to the sorption obtained without benzene present. This indicates that there is competition between Pb, Cd, and Zn and organic compounds during sorption onto both organoclays. On BTEA-clay, Cd, Pb and Zn sorption was reduced by 24, 37, and 51%, respectively. On HDTMA-clay, Cd, Pb, and Zn sorption was reduced by 25, 30, and 57%, respectively. Hg sorption was not affected either by the presence of benzene or by the organoclays used. The sorption of benzene onto BTEA-clay in the presence of Hg, Zn, Pb, and Cd was less than the sorption observed when no heavy metal was present. The presence of Hg resulted in the most significant decrease in sorption, causing a 59% reduction in benzene sorption. The presence of Zn, Pb, and Cd caused a 41, 35, and 31% reduction in benzene sorption, respectively. In general, sorption of benzene onto HDTMA-clay was not affected by the presence of the heavy metals, indicating there are no competitive effects observed with Zn, Cd, and Hg when HDTMA-clay was the sorbent. However, the presence of Pb did cause a 20% reduction in benzene sorption to HDTMA-clay. Both organoclays tested had dual sorptive properties for both heavy metals and an organic contaminant. While the competitive effects were greater for the BTEA clay, both organoclays are capable of simultaneously removing benzene and either Zn, Cd, Hg, or Pb from aqueous solution.

Effect of quaternary ammonium cation loading and pH on heavy metal sorption to Ca bentonite and two organobentonites.

Sorption of four heavy metals (Pb, Cd, Zn and Hg) to calcium bentonite (Ca bentonite), hexadecyltrimethylammonium bentonite (HDTMA bentonite) and benzyltriethylammonium bentonite (BTEA bentonite) was measured as a function of the quaternary ammonium cation (QAC) loading at 25, 50 and 100% of the clay's cation-exchange capacity (CEC). The effects of pH on the surface charge of the clays and heavy metal sorption were also measured. Sorption of Cd, Pb, and Zn was non-linear and sorption of all three metals by HDTMA and BTEA bentonites decreased as the QAC loading increased from 25 to 100%. In most cases, sorption of these metals to 25% BTEA and 25% HDTMA bentonite was similar to or greater than sorption to Ca bentonite. Hg sorption was linear for both HDTMA and BTEA bentonite. No significant effect on Hg sorption was observed with increasing QAC loading on BTEA bentonite. However, an increase of Hg sorption was detected with increasing QAC loading on HDTMA bentonite. This behavior suggests that a process different than cation exchange was the predominant Hg sorption mechanism. Cd, Pb, and Zn sorption decreased with pH. However, this effect was stronger for Cd and Pb than Zn. Hg sorption varied inversely with pH. QAC loading affected the surface charge of the clays. Twenty-five and 50% loading of BTEA cations increased the negative charge on the clay's surface relative to the untreated clay, without affecting the zero point of charge (ZPC) of the clay. Increased QAC loading on HDTMA bentonite causes the surface charge to become more positive and the ZPC increased. One hundred percent of HDTMA bentonite maintained a positive surface charge over the range of pH values tested. The organoclays studied have considerable capacity for heavy metal sorption. Given that prior studies have demonstrated the strong sorption capacity of organoclays for nonionic organic pollutants, it is likely that organoclays can be useful sorbents for the treatment of effluent streams containing both organic contaminants and heavy metals.