William C. Koskinen

Sorption of atrazine on Soil Clay Components.

Distribution coefficients for sorption and desorption of atrazine were determined for all combinations of three chemical treatments and four particle size fractions prepared from a typical soil clay. Organic and inorganic components were 11 and 89% of the mass and contributed 63 and 32% of the affinity of the soil clay for atrazine, respectively. Organic matter associated with the coarse clay had substantially greater affinity for atrazine and exhibited greater sorption-desorption hysteresis than organic matter associated with the fine clay. Silicate minerals had a moderate affinity for atrazine and exhibited little sorption-desorption hysteresis. Free Fe compounds interacted with silicate minerals in the coarse and medium clay to reduce affinity of the silicate minerals for atrazine (.)

Dicamba adsorption–desorption on organoclays

The adsorption–desorption of the herbicide dicamba (pKa=1.9, water solubility, 6.5 g kg−1) by organoclays (OCls) was studied at different concentrations and pH levels. Two smectites (SAz and SWy), varying in surface properties, were reacted with amounts of different alkylammonium cations [octadecyl(C18)-, hexadecyl-trimethyl(HDT)- and dioctadecyldimethyl(DOD)ammonium] equal to 50% or 100% of the clays CEC. Adsorption isotherms of dicamba on diverse OCl were some of L-type and others of S-type, but both resulted in sigmoid form when extended to higher concentration. Adsorption was greater for OCls with high-layer charge, basal spacing, alkylammonium size and organocation saturation close to CEC. Dicamba adsorption by OCls seems to involve hydrophobic and polar interactions for which the availability of interlayer room between organocations is very important. Adsorption data at different pH levels and two different concentrations (0.05 and 1 mM) indicated that molecular dicamba is the main adsorbing species, especially at high concentration. Desorption isotherms were reversible, except in OCls with primary alkylammonium (C18) and largest quaternary (DOD), for which there were moderate hysteresis as a result of stronger polar contribution in the primary alkylammonium and the difficulty for diffusion in the case of the quaternary, bulky OCl. The treatment of an artificially dicamba-contaminated soil with highly adsorptive OCls rendered a dramatic decrease in the CaCl2-released- or mobile dicamba, suggesting these OCls as potential immobilising agents. The amount of herbicide immobilised by the OCl was partially extractable with methanol/CaCl2 solution, suggesting its biovailability and hence, its possible combination with bioremediation technique.

Contaminants of Emerging Concern: Mass Balance and Comparison of Wastewater Effluent and Upstream Sources in a Mixed-Use Watershed

Understanding the sources, transport, and spatiotemporal variability of contaminants of emerging concern (CECs) is important for understanding risks and developing monitoring and mitigation strategies. This study used mass balances to compare wastewater treatment plant (WWTP) and upstream sources of 16 CECs to a mixed-use watershed in Minnesota, under different seasonal and hydrological conditions. Three distinct CEC groups emerged with respect to their source proportionality and instream behavior. Agricultural herbicides and daidzein inputs were primarily via upstream routes with the greatest loadings and concentrations during high flows. Trimethoprim, mecoprop, nonprescription pharmaceuticals, and personal care products entered the system via balanced/mixed pathways with peak loadings and concentrations in high flows. Carbaryl, 4-nonylphenol, and the remaining prescription pharmaceuticals entered the system via WWTP effluent with relatively stable loadings across sampling events. Mass balance analysis based on multiple sampling events and sites facilitated CEC source comparisons and may therefore prove to be a powerful tool for apportioning sources and exploring mitigation strategies.

Kinetics of atrazine hydrolysis in water

Abstract This study determined the kinetics of decomposition of atrazine in well water and deionized water refrigerated (4°C) and at slightly above room temperature (30°C.) When water samples containing normal groundwater pHs and dissolved organic carbon levels were brought to a known concentration of atrazine (400 nmol L‐1) and stored 19 weeks, no significant loss in atrazine concentration occurred. First‐order rate constants ranged from ‐2.4 × 10‐3 to ‐3.7 × 10‐3 weeks‐1. These results indicate that those quality assurance/quality control protocols that require holding times of less than 48 hours in the laboratory prior to extraction should be updated to allow flexibility dependent on the pesticide provided that the appropriate controls and documentation are in place.

Analysis of glyphosate and aminomethylphosphonic acid in water, plant materials and soil

There is a need for simple, fast, efficient and sensitive methods of analysis for glyphosate and its degradate aminomethylphosphonic acid (AMPA) in diverse matrices such as water, plant materials and soil to facilitate environmental research needed to address the continuing concerns related to increasing glyphosate use. A variety of water-based solutions have been used to extract the chemicals from different matrices. Many methods require extensive sample preparation, including derivatization and clean-up, prior to analysis by a variety of detection techniques. This review summarizes methods used during the past 15 years for analysis of glyphosate and AMPA in water, plant materials and soil. The simplest methods use aqueous extraction of glyphosate and AMPA from plant materials and soil, no derivatization, solid-phase extraction (SPE) columns for clean-up, guard columns for separation and confirmation of the analytes by mass spectrometry and quantitation using isotope-labeled internal standards. They have levels of detection (LODs) below the regulatory limits in North America. These methods are discussed in more detail in the review.

Pesticide sorption and leaching potential on three Hawaiian soils

On the Hawaiian Islands, groundwater is the principal source of potable water and contamination of this key resource by pesticides is of great concern. To evaluate the leaching potential of four weak acid herbicides [aminocyclopyrachlor, picloram, metsulfuron-methyl, biologically active diketonitrile degradate of isoxaflutole (DKN)] and two neutral non-ionizable herbicides [oxyfluorfen, alachlor], their sorption coefficients were determined on three prevalent soils from the island of Oahu. Metsulfuron-methyl, aminocylcopyrachlor, picloram, and DKN were relatively low sorbing herbicides (K(oc) = 3-53 mL g(-1)), alachlor was intermediate (K(oc) = 120-150 mL g(-1)), and oxyfluorfen sorbed very strongly to the three soils (K(oc) > 12,000 mL g(-1)). Following determination of K(oc) values, the groundwater ubiquity score (GUS) indices for these compounds were calculated to predicted their behavior with the Comprehensive Leaching Risk Assessment System (CLEARS; Tier-1 methodology for Hawaii). Metsulfuron-methyl, aminocyclopyrachlor, picloram, and DKN would be categorized as likely leachers in all three Hawaiian soils, indicating a high risk of groundwater contamination across the island of Oahu. In contrast, oxyfluorfen, regardless of the degradation rate, would possess a low and acceptable leaching risk due to its high sorption on all three soils. The leaching potential of alachlor was more difficult to classify, with a GUS value between 1.8 and 2.8. In addition, four different biochar amendments to these soils did not significantly alter their sorption capacities for aminocyclopyrachlor, indicating a relatively low impact of black carbon additions from geologic volcanic inputs of black carbon. Due to the fact that pesticide environmental risks are chiefly dependent on local soil characteristics, this work has demonstrated that once soil specific sorption parameters are known one can assess the potential pesticide leaching risks.

Isolation and Characterization of a Novel Imidacloprid-Degrading Mycobacterium sp. Strain MK6 from an Egyptian Soil

Thus far, only a small number and types of bacteria with limited ability in degrading imidacloprid have been reported. Also, genes regulating imidacloprid (IMDA) degradation have yet to be discovered. To study this in more detail, an enrichment technique was used to isolate consortia and pure cultures of IMDA-degrading bacteria. Through this approach, we successfully isolated a novel bacterium capable of completely degrading IMDA as a sole nitrogen source. The bacterium was subsequently identified as Mycobacterium sp. strain MK6 by sequence analysis of its 16S rRNA gene (Genbank accession number KR052814 ). BLASTn searches indicated that 16S rRNA gene from Mycobacterium sp. strain MK6 was 99% identical to several Mycobacterium spp. Mycobacterium sp. strain MK6 transformed 99.7% added IMDA (150 μg mL(-1)) in <2 weeks (t1/2 = 1.6 days) to 6-chloronicotinic acid (6-CNA) as its major metabolite. Although the isolated strain and mixed bacterial consortia were able to degrade IMDA, they failed to grow further on 6-CNA, indicating a lack of IMDA mineralization to carbon dioxide. Small amounts of the desnitro-olefin and desnitro-degradates of IMDA were observed during the incubation but did not accumulate in culture medium.

Analysis of Glyphosate and AMPA in Water, Plant materials, and Soil: A Review

There is a need for simple, fast, efficient and sensitive methods of analysis for glyphosate and its degradate aminomethylphosphonic acid (AMPA) in diverse matrices such as water, plant materials and soil to facilitate environmental research needed to address the continuing concerns related to increasing glyphosate use. A variety of water-based solutions have been used to extract the chemicals from different matrices. Many methods require extensive sample preparation, including derivatization and clean-up, prior to analysis by a variety of detection techniques. This review summarizes methods used during the past 15 years for analysis of glyphosate and AMPA in water, plant materials and soil. The simplest methods use aqueous extraction of glyphosate and AMPA from plant materials and soil, no derivatization, solid-phase extraction (SPE) columns for clean-up, guard columns for separation and confirmation of the analytes by mass spectrometry and quantitation using isotope-labeled internal standards. They have levels of detection (LODs) below the regulatory limits in North America. These methods are discussed in more detail in the review.

Atrazine sorption in field-moist soils : Supercritical carbon dioxide density effects

Abstract Supercritical carbon dioxide (SF-CO 2 ) has been recently introduced for use in determining sorption coefficients of atrazine (6-chloro-N-ethyl-N′-(1-methyl)-1,3,5-triazine-2,4-diamine) in field-moist soils. In this study we determined the effects of SF-CO 2 density modification on atrazine-soil sorption coefficients. As the density of SF-CO 2 increased, the SF-CO 2 soil/water partition coefficient (K d ) decreased. K d values for the first desorption equilibration (K d D1) obtained with the SF-CO 2 technique at an SF-CO 2 density of 0.25 g mL −1 were linearly related to soil organic carbon content, clay content, and batch Freundlich coefficients (K f values). The log of K d for each soil was linearly related to the log of the SF-CO 2 density for densities 0.25 through 0.45 g mL −1 . The SF-CO 2 Kd value predicted using the batch K f / SF-CO 2 K d relationship obtained in this study, and an experimental batch K f value for a Minnesota (USA) soil from the literature, was consistent with the SF-CO 2 K d values predicted using organic carbon and clay content relationships obtained from this study.

Sorption-desorption of imidacloprid onto a lacustrine Egyptian soil and its clay and humic acid fractions.

Sorption–desorption of the insecticide imidacloprid 1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolidinimine onto a lacustrine sandy clay loam Egyptian soil and its clay and humic acid (HA) fractions was investigated in 24-h batch equilibrium experiments. Imidacloprid (IMDA) sorption–desorption isotherms onto the three sorbents were found to belong to a non-linear L-type and were best described by the Freundlich model. The value of the IMDA adsorption distribution coefficient, Kdads, varied according to its initial concentration and was ranged 40–84 for HA, 14–58 for clay and 1.85–4.15 for bulk soil. Freundlich sorption coefficient, Kfads, values were 63.0, 39.7 and 4.0 for HA, clay and bulk soil, respectively. The normalized soil Koc value for imidacloprid sorption was ∼800 indicating its slight mobility in soils. Nonlinear sorption isotherms were indicated by 1/nads values <1 for all sorbents. Values of the hysteresis index (H) were <1, indicating the irreversibility of imidacloprid sorption process with all tested sorbents. Gibbs free energy (ΔG) values indicated a spontaneous and physicosorption process for IMDA and a more favorable sorption to HA than clay and soil. In conclusion, although the humic acid fraction showed the highest capacity and affinity for imidacloprid sorption, the clay fraction contributed to approximately 95% of soil-sorbed insecticide. Clay and humic acid fractions were found to be the major two factors controlling IMDA sorption in soils. The slight mobility of IMDA in soils and the hysteresis phenomenon associated with the irreversibility of its sorption onto, mainly, clay and organic matter of soils make its leachability unlikely to occur.