Martha J. M. Wells

Solid-phase extraction of acidic herbicides.

A discussion of solid-phase extraction method development for acidic herbicides is presented that reviews sample matrix modification, extraction sorbent selection, derivatization procedures for gas chromatographic analysis, and clean-up procedures for high-performance liquid chromatographic analysis. Acidic herbicides are families of compounds that include derivatives of phenol (dinoseb, dinoterb and pentachlorophenol), benzoic acid (acifluorfen, chloramben, dicamba, 3,5-dichlorobenzoic acid and dacthal--a dibenzoic acid derivative), acetic acid [2,4-dichlorophenoxyacetic acid (2,4-D), 4-chloro-2-methylphenoxyacetic acid (MCPA) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)], propanoic acid [dichlorprop, fluazifop, haloxyfop, 2-(4-chloro-2-methylphenoxy)propanoic acid (MCPP) and silvex], butanoic acid [4-(2,4-dichlorophenoxy)butanoic acid (2,4-DB) and 4-(4-chloro-2-methylphenoxy)butanoic acid (MCPB)], and other miscellaneous acids such as pyridinecarboxylic acid (picloram) and thiadiazine dioxide (bentazon).

Log DOW: Key to Understanding and Regulating Wastewater-Derived Contaminants

Environmental Context. Worldwide, surface water is a source of drinking water and is a recipient of wastewater effluents and pollutants. Many surface water bodies undergo a natural, cyclical, diurnal variation in pH between 7 and 9. Most drinking water and wastewater treatment in the United States is conducted between pH 7 and 8. The pH of water undergoing treatment processes directly impacts the ratio of nonionized to ionized chemical form(s) present, which in turn impacts the success rate of contaminant removal. Many organic wastewater-derived contaminants are very water soluble at pH 7–8 and are inadequately treated. Abstract. Wastewater-derived contaminants (WWDCs) occur in surface water due to inadequate wastewater treatment and subsequently challenge the capabilities of drinking water treatment. Fundamental chemical properties must be understood to reduce the occurrence of known WWDCs and to better anticipate future chemical contaminants of concern to water supplies. To date, examination of the fundamental properties of WWDCs in surface water appears to be completely lacking or inappropriately applied. In this research, the hydrophobicity–ionogenicity profiles of WWDCs reported to occur in surface water were investigated, concentrating primarily on pharmaceuticals and personal care products (PPCPs), steroids, and hormones. Because most water treatment is conducted between pH 7 and 8 and because DOW, the pH-dependent n-octanol–water distribution ratio embodies simultaneously the concepts of hydrophobicity and ionogenicity, DOW at pH 7–8 is presented as an appropriate physicochemical parameter for understanding and regulating water treatment. Although the pH-dependent chemical character of hydrophobicity is not new science, this concept is insufficiently appreciated by scientists, engineers, and practitioners currently engaged in chemical assessment. The extremely hydrophilic character of many WWDCs at pH 7–8, indicated by DOW (the combination of KOW and pKa) not by KOW of the neutral chemical, is proposed as an indicator of occurrence in surface water.

Analysis of amphetamine and methamphetamine as emerging pollutants in wastewater and wastewater-impacted streams.

The identification and quantitation of the non-ecstasy amphetamine-type stimulants (ATSs) amphetamine and methamphetamine in lakes, rivers, wastewater treatment plant influents, effluents, and biosolids are reviewed. Neither monitoring nor reporting is required of these ATSs, which are considered emerging pollutants, but they have been identified in the environment. Amphetamine and methamphetamine enter our water supply by human excretion after legal or illegal consumption and via manufacturing in clandestine laboratories. Analytical methodology for sampling, sample preparation, separation, and detection of ATSs is discussed. Reported occurrences of ATSs in the environment and their use in municipal sewage epidemiology are noted. Future research needs that challenge applications of analytical techniques are discussed. The review focuses on research reported from 2004 to 2009.

Diffusion Coefficients and Molecular Weight Distributions of Humic and Fulvic Acids Determined by Flow Field-Flow Fractionation

Abstract The ability to characterize molecules whose physical and chemical properties are intimately linked to their diffusion coefficients and molecular weight is important to further understanding of chemical transport in the environment. Flow field-flow fractionation (flow FFF) was used to obtain separations of water-soluble macromolecules of varying molecular weight, including polystyrene sulfonates and humic substances. The separation occurs due to differing diffusion rates for chemical species of differing molecular weight in aqueous solution. Flow FFF uses fluid flow as the mechanism of separation. A model that yields liquid phase diffusion coefficients as a function of molecular weight was utilized to determine molecular weights from degree of separation. Separations of polystyrene sulfonates, a humic acid, and two fulvic acids of known molecular weight were accomplished using flow FFF. The separations obtained were used to develop a relationship between flow FFF separation and species molecular w...

Development and optimization of a solid-phase extraction scheme for determination of the pesticides metribuzin, atrazine, metolachlor and esfenvalerate in agricultural runoff water

Abstract Concomitant determination of the pesticides metribuzin, atrazine, metolachlor and esfenvalerate in agricultural runoff water was developed utilizing solid-phase extraction (SPE). A 2 5 factorial experimental design compared relative importance for extraction efficiency of the five variables sample pH, elution solvent strength, ionic strength of the sample, addition of organic modifier to the sample, and elution by gravity or vacuum. The protocol was further optimized with respect to sorbent mass, sample volume, elution volume and concentration. The approach offers optimal recoveries, low detection limits, rapid extraction, and final determination by either gas or high-performance liquid chromatography.

Abiotic reversible self-assembly of fulvic and humic acid aggregates in low electrolytic conductivity solutions by dynamic light scattering and zeta potential investigation.

The aggregation of humic substances and their interaction with filtration media (membranes, soils) has implications for our understanding of membrane fouling during water treatment, the facilitated transport of contaminants, and the transport of organic matter through the microbial loop. To investigate the aggregation of fulvic and humic acids in low electrolytic conductivity solutions, laboratory studies of simulated environmental water samples as well as actual environmental water samples were examined. Intensity-, volume-, and number-based particle size distributions (PSDs) were obtained by dynamic light scattering. Aggregates were categorized into three ranges, i.e., 10-100 nm, 100-1000 nm, and >1 μm. Individual biomacromolecules and the aggregates between 10 nm and 1 μm were presumed to be precursors for the formation of a large 5-μm-sized-particle. The self-assembly of the large-in-volume, few-in-number, 5-μm-sized particle was observed in real-time and occurred in unfiltered samples and in samples filtered (0.45 μm) at a nominal size one order of magnitude smaller. The supramicrometer-sized particle formed, dissipated, and spontaneously re-formed over turbulent/quiescent cycles in the presence of sodium azide indicating reversible abiotic self-assembly. Zeta potential analyses demonstrated that colloidal stability increased as concentration increased. DLS studies of the environmental water samples were comparable to those of the simulated laboratory samples. The operational range of the instrumentation used in these experiments was 0.6 nm-6 μm; therefore, aggregates larger than 6 μm may exist in these solutions.

Determination of oil and grease in waste water by solid-phase extraction

Solid-phase extraction (SPE) protocols were developed for the determination of oil and grease in waste water. SPE was found to be an efficient alternative to standard methods. Both synthetically spiked samples and environmentally contaminated samples were examined. Analysis times and organic solvent consumption were decreased by the SPE procedure compared with liquid–liquid extraction (LLE). Recovery and variability studies of environmentally contaminated samples indicated that SPE results using methylene chloride as an extractant were comparable to those obtained by continuous liquid–liquid extraction using a chlorofluorocarbon (CFC). Extractions performed by manually shaken separating funnel LLE with CFCs were found to be matrix dependent when compared with SPE results. Suitable alternative elution solvent systems for SPE, including hexane, hexane–diethyl ether, ethyl acetate and methyl tert-butyl ether, were also examined.

Preferential adsorption of fluorescing fulvic and humic acid components on activated carbon using flow field-flow fractionation analysis

Activated carbon treatment of drinking water is used to remove natural organic matter (NOM) precursors that lead to the formation of disinfection byproducts. The innate hydrophobic nature and macromolecular size of NOM render it amenable to sorption by activated carbon. Batch equilibrium and minicolumn breakthrough adsorption studies were performed using granular activated carbon to treat NOM-contaminated water. Ultraviolet (UV) absorption spectroscopy and flow field-flow fractionation analysis using tandem diode-array and fluorescence detectors were used to monitor the activated carbon sorption of NOM. Using these techniques, it was possible to study activated carbon adsorption properties of UV absorbing, fluorescing and nonfluorescing, polyelectrolytic macromolecules fractionated from the total macromolecular and nonmacromolecular composition of NOM. Adsorption isotherms were constructed at pH 6 and pH 9. Data were described by the traditional and modified Freundlich models. Activated carbon capacity and adsorbability were compared among fractionated molecular subsets of fulvic and humic acids. Preferential adsorption (or adsorptive fractionation) of polyelectrolytic, fluorescing fulvic and humic macromolecules on activated carbon was observed. The significance of observing preferential adsorption on activated carbon of fluorescing macromolecular components relative to nonfluorescing components is that this phenomenon changes the composition of dissolved organic matter remaining in equilibrium in the aqueous phase relative to the composition that existed in the aqueous phase prior to adsorption. Likewise, it changes the composition of dissolved organic matter remaining in equilibrium in the aqueous phase relative to the adsorbed phase. This research increases our understanding of NOM interactions with activated carbon which may lead to improved methods of potable water production.

Trihalomethane formation potential of aquatic and terrestrial fulvic and humic acids: Sorption on activated carbon

Humic substances (HSs) are precursors for the formation of hazardous disinfection by-products (DBPs) during chlorination of water. Various surrogate parameters have been used to investigate the generation of DBPs by HS precursors and the removal of these precursors by activated carbon treatment. Dissolved organic carbon (DOC)- and ultraviolet absorbance (UVA254)-based isotherms are commonly reported and presumed to be good predictors of the trihalomethane formation potential (THMFP). However, THMFP-based isotherms are rarely published such that the three types of parameters have not been compared directly. Batch equilibrium experiments on activated carbon were used to generate constant-initial-concentration sorption isotherms for well-characterized samples obtained from the International Humic Substances Society (IHSS). HSs representing type (fulvic acid [FA], humic acid [HA]), origin (aquatic, terrestrial), and geographical source (Nordic, Suwannee, Peat, Soil) were examined at pH6 and pH9. THMFP-based isotherms were generated and compared to determine if DOC- and UVA254-based isotherms were good predictors of the THMFP. The sorption process depended on the composition of the HSs and the chemical nature of the activated carbon, both of which were influenced by pH. Activated carbon removal of THM-precursors was pH- and HS-dependent. In some instances, the THMFP existed after UVA254 was depleted.

Supercritical fluid extraction coupled with enzyme immunoassay analysis of soil herbicides

Supercritical fluid extraction (SFE) was coupled with enzyme immunoassay analysis (EIA) for the analysis of the following herbicides, 2,4-phenoxyacetic acid (2,4-D), 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), 2-chloro-4-ethylamino-6-propylamino-s-triazine (atrazine) and 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor) in soil and compared with liquid vortex extraction (LVE). Five soils, ranging in texture from sandy loam to silty clay were fortified with 500 ng g–1 of herbicide, allowed to air dry, and extracted using supercritical fluid or LVE. Atrazine and alachlor were also fortified at 50 ng g–1. Field-weathered soils, with incurred residues from field application, were also extracted. EIA of herbicides using a microtitre plate format were in good agreement with GC and HPLC results (r2= 0.95). SFE was performed using a Dionex (Sunnyvale, CA, USA) Model 703 extractor in the dynamic mode at 20.3 MPa and 66 °C for 3 min, followed by 34.4 MPa extraction for 17 min. SFE recoveries with unmodified CO2 were 7, 56, 57, and 83%, respectively, for 2,4-D, simazine, atrazine and alachlor. Recoveries improved to 101, 79, 90, and 88% for 2,4-D, simazine, atrazine and alachlor, respectively, by adding 1.5 ml of triethylamine to a 100 ml acetone–water (9 + 1) modifier. Collection of analytes by SFE was improved by using C18 solid-phase traps (90% recovery) compared to liquid acetone collection results (65% recovery).