Biomedical subjects

K G Karthikeyan

Publications and source records attributed to K G Karthikeyan.

14 recordsLinked to original sources

PubMed2006

Complexation of the antibiotic tetracycline with humic acid.

The effect of solution chemistry and sorbate-to-sorbent ratio on the interaction of the antibiotic tetracycline with Elliott soil humic acid (ESHA) was investigated using equilibrium dialysis and FITEQL modeling. Tetracycline speciation strongly influenced its sorption to ESHA. Sorption was strongly pH-dependent with a maximum around pH 4.3, and competition with H+ and electrolyte cation (Na+) was evident. The pH-dependent trend was consistent with complexation between the cationic/zwitterionic tetracycline species and deprotonated sites in ESHA (mainly carboxylic functional groups). Modification of ESHA by Ca2+ addition increased tetracycline sorption suggesting that ternary complex formation (ESHA-metal-tetracycline) may be important at higher concentrations of multivalent metal cations. The macroscopic data (pH-envelope and sorption isotherms) were successfully modeled using a discrete logK function with the FITEQL 4.0 chemical equilibrium program indicating that ESHA-tetracycline interaction could be reasonably represented as complex formation of a monoacid with discrete sites in humic acid. Sorption-desorption hysteresis was observed; both sorption and desorption isotherms were well described by the Freundlich equation.

Adsorption↗

PubMed2006

Adsorption mechanism of cadmium on juniper bark and wood.

In this study the capacity of sorbents prepared from juniper wood (JW) and bark (JB) to adsorb cadmium (Cd) from aqueous solutions at different pH values was compared. Adsorption behavior was characterized through adsorption kinetics, adsorption isotherms, and adsorption edge experiments. Results from kinetics and isotherm experiments showed that JB (76.3-91.6 micromol Cdg(-1) substrate) had 3-4 times higher adsorption capacity for Cd than JW (24.8-28.3 micromol Cdg(-1)). In addition to higher capacity, JB exhibited a higher strength of adsorption (45.3 versus 9.1 Lmmol(-1)) and faster uptake kinetics (0.0119 versus 0.0083 g micromol(-1)min(-1)) compared to JW. For both these adsorbents, increasing Cd adsorption with increasing solution pH in the range of 2-6 suggests that surface carboxyl groups (RCOOH) might be involved in interaction with Cd. Diffuse reflectance infrared Fourier transform (DRIFT) spectra showed that the surface concentration of carboxyl groups was higher on JB compared to JW. The ratio of Ca released to Cd adsorbed was 1.04 and 0.78 for JB and JW, respectively, indicating that Ca-Cd ion-exchange was the primary mechanism involved. The higher Ca content in JB (15 times more) and the surface RCOOH concentration (2.5 times more) can be attributed to the observed differences in Cd adsorption behavior between the two lignocellulosic adsorbents.

Adsorption↗

PubMed2006

Instrumentation for measuring runoff, sediment, and chemical losses from agricultural fields.

This work describes a simple, passive sampling system for measuring runoff, sediment, and chemical losses from typical agricultural fields. The sampler consists of a 5 to 7 m wide runoff collector connected to a series of multislot divisors. These divisors split the flow into aliquots, providing a continuous sampling during the runoff event. Divisors were located in a wooden box below ground level. With an adequate pump, this system can operate in fields with a slope gradient as low as 2%, and can stay in the field during winter to record first snowmelt-generated runoff. A radio transmitter reports by telemetry the occurrence and magnitude of any runoff event, and indicates when the system should be sampled and emptied. This article includes a description of the equipment, advantages, and disadvantages based on 2 yr of operation, and examples of data collected.

Agriculture↗

PubMed2005

Sorption of the antimicrobial ciprofloxacin to aluminum and iron hydrous oxides.

Solution chemistry (pH, ionic strength (I), and sorbate-to-sorbent ratio) effects on ciprofloxacin sorption to hydrous oxides of Al (HAO) and Fe (HFO) were investigated using macroscopic and spectroscopic analyses. Sorption to both HAO and HFO showed a strong pH-dependent behavior, following the fraction of zwitterionic species over the entire pH range studied. Increase in I from 0.01 to 0.5 M had an insignificant effect on the extent of ciprofloxacin sorption, and isotherms were well-described by the Langmuir model. HFO possessed a higher sorption capacity (0.066 mmol kg(-1)) than HAO (0.041 mmol kg(-1)). Ligand-promoted dissolution of hydrous oxides, more pronounced for HAO, was observed in the presence of ciprofloxacin, but at a fairly high initial concentration (0.5 mM). Attenuated total reflectance Fourier transform infrared spectroscopy analysis indicated that different types of ciprofloxacin surface complexes are formed with HAO and HFO; while a monodentate mononuclear complex (with -COO-) appears likely between ciprofloxacin and HAO, keto O and one O from COO- seem to be involved in the formation of a six-membered ring with Fe on the HFO surface. The study results are expected to increase our understanding of the environmental reactivity of fluoroquinolones, an important class of antimicrobial compounds.

Adsorption↗

PubMed2005

Orthophosphate sorption onto lanthanum-treated lignocellulosic sorbents.

Inorganic/organic hybrid adsorbents for removing orthophosphate from water were prepared by lanthanum (La) treatment of bark fiber, a lignocellulosic material obtained from juniper (Juniperus monosperma). The La was anchored to the juniper bark (JB) fiber by ion exchange with Ca in the bark and was responsible for removing orthophosphate. Two La concentrations (0.01 and 0.1 M) were used that resulted in loadings of 0.198 (La/JB01) and 0.302 (La/JB02) mmol of La g(-1) of fiber, respectively. At circumneutral pH conditions, La exhibited a strong affinity for bark, but significant La desorption occurred under acidic conditions (pH < 4.5). For La/JB02, 86% of the initial La loading was released at pH 2.5, and only 0.1% at pH 7.3. Initial La loading in the bark fiber significantly influenced its orthophosphate sorption capacity, which was determined for La/JB01 and La/JB02, respectively, to be 0.188 and 0.233 mmol of P g(-1) (sorption envelopes) and 0.211 and 0.351 mmol of P g(-1) (sorption isotherms when surface site saturation occurred). The P-to-La molar ratio on the bark surface was extremely high (0.12-1.77for La/JB01 and 0.13-2.58 for La/JB02), implying that orthophosphate removal occurred by other mechanisms in addition to surface complexation. From the orthophosphate surface loading levels and the shape of the sorption isotherms, it appears that adsorption occurred at low sorbate-to-sorbent (P-to-La-treated JB) ratios and transitioned to surface precipitation at higher ratios. When surface precipitation occurred, orthophosphate uptake continued to increase with increasing initial P levels. Results from X-ray diffraction and infrared spectrometric analyses are also suggestive of the occurrence of surface precipitation during the interaction of orthophosphate with La-treated lignocellulosic materials.

Adsorption↗

PubMed2005

Corn residue level and manure application timing effects on phosphorus losses in runoff.

Growing interest in corn (Zea mays L.) silage utilization on Wisconsin dairy farms may have implications for nutrient losses from agricultural lands. Increasing the silage cutting height will increase residue cover and could reduce off-site migration of sediments and associated constituents compared with conventional silage harvesting. We examined the effects of residue level and manure application timing on phosphorus (P) losses in runoff from no-till corn. Treatments included conventional corn grain (G) and silage (SL; 10- to 15-cm cutting height) and nonconventional, high-cut (60-65 cm) silage (SH) subjected to different manure application regimes: no manure (N) or surface application in fall (F) or spring (S). Simulated rainfall (76 mm h(-1); 1 h) was applied in spring and fall for two years (2002-2003), runoff from 2.0- x 1.5-m plots was collected, and subsamples were analyzed for dissolved reactive phosphorus (DRP), total phosphorus (TP), and P mass distribution in four particle size classes. Total P and DRP loads were inversely related to percent residue cover, but both TP and DRP concentrations were unaffected by residue level. Manure application increased DRP concentrations in spring runoff by two to five times but did not significantly affect DRP loads, since higher concentrations were offset by lower runoff volumes. Spring manure application reduced TP loads in spring runoff by 77 to 90% compared with plots receiving no manure, with the extent of reductions being greatest at the lower residue levels (<24%). The TP concentration in sediments increased as particle size decreased. Manure application increased the TP concentration of the 0- to 2-microm fraction by 79 to 125%, but elevated the 2- to 10- and 10- to 50-microm fractions to a lesser extent. Recent manure additions were most influential in enriching transported sediments with P. By itself, higher residue cover achieved by high-cutting silage was often insufficient to lower P losses; however, the combination of manure application and higher residue levels significantly reduced P losses from corn fields harvested for silage.

Agriculture↗

PubMed2005

Occurrence of antibiotics in wastewater treatment facilities in Wisconsin, USA.

Samples from several wastewater treatment facilities in Wisconsin were screened for the presence of 21 antibiotic compounds. These facilities spanned a range of community size served (average daily flow from 0.0212 to 23.6 million gallons/day), secondary treatment processes, geographic locations across the state, and they discharged the treated effluents to both surface and ground waters (for ground water after a soil passage). A total of six antibiotic compounds were detected (1-5 compounds per site), including two sulfonamides (sulfamethazine, sulfamethoxazole), one tetracycline (tetracycline), fluoroquinolone (ciprofloxacin), macrolide (erythromycin-H(2)O) and trimethoprim. The frequency of detection of antibiotics was in the following order: tetracycline and trimethoprim (80%)>sulfamethoxazole (70%)>erythromycin-H(2)O (45%)>ciprofloxacin (40%)>sulfamethazine (10%). However, the soluble concentrations were in the parts-per-billion (ppb) range (<or=1.3 microg/L), and importantly were unaffected by the size of the wastewater treatment facility. The concentrations detected were within an order of magnitude of those reported for similar systems in Europe and Canada: they were within a factor of two in comparison to those reported for Canada but generally lower relative to those measured in wastewater systems in Europe. Only sulfamethoxazole and tetracycline were detected in groundwater monitoring wells adjacent to the treatment systems. Future intensive wastewater monitoring programs in Wisconsin may be limited to the six antibiotic compounds detected in this study.

Anti-Bacterial Agents↗

PubMed2005

Residue level and manure application timing effects on runoff and sediment losses.

There is growing interest in evaluating the effects of corn silage harvesting methods on erosion control. Increasing the silage cutting height will increase residue cover and could conceivably minimize off-site migration of sediments compared with conventional silage harvesting. The effects of residue level and manure application timing on runoff and sediment losses from no-till corn were examined. Treatments included conventional corn grain (G) and silage (SL) and nonconventional, high-cut (60-65 cm) silage (SH). Corn harvesting treatments were subjected to different manure application regimes: no manure (N) or surface application in fall (F) or spring (S). Simulated rainfall (76 mm/h; 1 h) was applied in spring and fall for two years (2002-2003), runoff from 2.0- x 1.5-m plots collected, and a subsample analyzed for sediment concentration and aggregate size distribution. Runoff volume was inversely related to residue cover. Manure addition to silage plots reduced spring runoff by 71 to 88%, attributable to an increase in soil organic matter content, compared with SH-N and SL-N. Differences in sediment concentration between SH and SL were not significant. For silage plots, spring-applied manure had the greatest influence on sediment export reducing it by 84 to 93% in spring runoff compared with corresponding N plots. Sediment loads were also 85 to 97% lower from SH-S compared with SL-N in all four seasons. Except for spring 2003, sediment export was lower from G compared with SL. The combination of manure and higher residue associated with high-cut silage often lowered sediment export compared with low-cut silage. Nearly identical aggregate size distributions were observed in sediments from SH and SL plots. High residue levels combined with spring-applied manure led to enrichment in the clay-sized fraction of runoff sediment. Recently applied manure and higher residue levels achieved by high-cutting silage can substantially lower sediment losses in spring runoff when soil is most susceptible to erosion.

Agriculture↗

PubMed2005

Interaction of tetracycline with aluminum and iron hydrous oxides.

The effect of solution chemistry (pH, sorbate-to-sorbent ratio, ionic strength (/)) and reaction time on the sorption of tetracycline to the hydrous oxides of Al (HAO) and Fe (HFO) was examined. Sorption to HAO increased with increasing pH upto pH 7 (no such trend for HFO) above which it decreased at higher pH values for both the hydrous oxides. Experimental results indicate that ligand-promoted dissolution is occurring during tetracycline sorption to these hydrous oxides. Ligand-promoted dissolution was more significantfor HAO than HFO attributable to the difference in labile surface sites between these two sorbents. The ability of tetracycline to form strong complexes with Al and Fe will increase the solubility of these minerals. Sorption of tetracycline was quite rapid and equilibrium was achieved after 8 h. However, soluble metal (Me: Al or Fe) concentrations attained equilibrium only after 24 h. Ligand-promoted dissolution appears to be a two-step process; initially, 1:1 Me-tetracycline soluble complexes are formed and as the reaction progresses 2:1 complexes existed. Increasing / (from 0.01 to 0.5 M) decreased the sorption extent only at higher sorbate-to-sorbent ratios suggesting the dominance of inner-sphere type complexes at low equilibrium tetracycline concentrations. Spectroscopic evidence indicates that tricarbonylamide and carbonyl functional groups of tetracycline could be responsible for sorption to mineral surfaces. Our research findings will increase understanding of the environmental occurrence, fate, and transport characteristics of antibiotics, which are considered as emerging organic contaminants.

Adsorption↗

PubMed2004

Solution chemistry effects on orthophosphate adsorption by cationized solid wood residues.

Adsorption of orthophosphate anions in aqueous solution by cationized milled solid wood residues was characterized as a function of sorbate-to-sorbent ratio (approximately equal to 0.001-2.58 mmol of P/g substrate), pH (3-9), ionic strength, I (no I control; 0.001 and 0.01 M NaCl), reaction time (4 min to 24 h), and in the presence of other competing anions (0.08-50 mM SO4(2-); 0.08-250 mM NO3-). Sorption isotherms revealed the presence of two kinds of adsorption sites corresponding to high and low binding affinities for orthophosphate anions. Consequently, a two-site Langmuir equation was needed to adequately describe the data over a range of solution conditions. In addition to higher sorption capacity, cationized bark possessed a higher binding energy for orthophosphate anions compared to cationized wood. The sorption capacity and binding energy for bark were 0.47 mmol of P g(-1) and 295.7 L mmol(-1), respectively, and for wood, the corresponding values were 0.27 mmol g(-1) and 61.4 L mmol(-1). Both the sorption capacity and binding energy decreased with increasing I, due to competition from Cl- ions for the available anion-exchange sites. The surface charge characteristics of cationized bark (pHzpc = 7.9) acted in concert with orthophosphate speciation to create a pH-dependent sorption behavior. Orthophosphate uptake was quite rapid and attained equilibrium levels after 3 h. Both SO4(2-) and NO3- influenced percent removal but required high relative competing anion to H2PO4- molar ratios, i.e., 2.5-3 for SO4(2-) and 25 for NO3-, to cause appreciable reduction. These results support our hypothesis that adsorption of orthophosphate anions on cationized bark involves ion exchange and other specific Lewis acid-base interactions.

Adsorption↗

PubMed2003

Linking cesium and strontium uptake to kaolinite weathering in simulated tank waste leachate.

Weathering behavior of kaolinite was studied in batch systems under geochemical conditions characteristic of tank waste released to the vadose zone at the Hanford Site, WA (0.05 M Al(T), 2 M Na+, 1 M N03-, pH approximately 14, Cs+ and Sr2+ present as co-contaminants). Time series experiments were conducted from 0 to 369 d, with initial Cs+ and Sr2+ concentrations ranging from 10(-5) to 10(-3) M. Dissolution of kaolinite increased soluble Si and Al to maximum levels at 7 d (Cs and Sr concentrations of 10(-5) and 10(-4) M) or 33 d (Cs and Sr concentrations of 10(-3) M). Subsequent precipitation of Si and Al was coupled to the formation of oxalate-extractable solids that incorporated Cs and Sr. Strontium sorption was nearly complete within 24 h for initial Sr concentrations (Sr0) < or = 10(-4) whereas Cs uptake increased over the full year of the experiment for all initial Cs concentrations. Spectroscopic analyses revealed neoformed solids including the zeolite Na-Al silicate (Al-chabazite), and feldspathoids sodium aluminum nitrate silicate (NO3-sodalite), and sodium aluminum nitrate silicate hydrate (NO3-cancrinite), which can incorporate Cs. Single-pulse 27Al solid-state nuclear magnetic resonance (NMR) spectroscopyyielded first-order rate constants (k)for mineral transformation that decreased from 3.5 x 10(-3) to 2 x 10(-3) d(-1) as Cs and Sr concentrations were increased from 10(-5) to 10(-3) M. Discrete strontium silicate solids were also observed. The incongruent dissolution of kaolinite promoted the sequestration of contaminants into increasingly recalcitrant solid phases over the 1-yr time period.

Adsorption↗

PubMed2002

Cesium adsorption on clay minerals: an EXAFS spectroscopic investigation.

Cesium adsorption on the clay minerals vermiculite and montmorillonite is described as a function of surface coverage using extended X-ray adsorption fine structure spectroscopy (EXAFS). Cesium (Cs) possessed a variable coordination environment consisting of Cs-O distances between 3.2 and 4.3 A; however, disorder typical of the Cs coordination environments prevented the resolution of all oxygen shells. On the basis of the influence of Cs loading and exchangeability on this structural arrangement, we could recognize both inner-sphere and outer-sphere adsorption complexes. The shorter Cs-O bond distance belongs to outer-sphere complexes typical of hydrated ions. In inner-sphere complexes, partially or fully dehydrated Cs coordinates directly to siloxane groups of the clay minerals forming longer Cs-O bonds. The inner-sphere adsorption complexes may have occurred within the interlayer or at frayed edge sites and were less extractable than the outer-sphere complexed Cs. Both coordination number ratios and linear combination fitting of EXAFS spectra were useful in estimating the fractions of inner-sphere and outer-sphere adsorption complexes. Our results show that X-ray absorption spectroscopy (XAS), and particularly EXAFS, is a valuable technique for exploring the type of Cs binding in environmental samples.

Adsorption↗

PubMed2002

Humic acid complexation of basic and neutral polycyclic aromatic compounds.

Complexation by humic acid (HA) of basic (quinoline) and neutral (naphthalene) polycyclic aromatic compounds (PACs) was compared using fluorescence spectroscopy and equilibrium dialysis (ED). These compounds sorb to HA via cation exchange and hydrophobic interactions, respectively. Ionization of quinoline strongly affects its sorption to HA; maximum sorption is observed at pH close to logKb (4.92), and competition with H+ and electrolyte cation (Li+) is evident. Spectroscopic experiments indicate that quinolinium (QH+) cation fluorescence is quenched via a static mechanism (i.e., a dark complex is formed) when the protonated form is adsorbed via ion exchange to HA. The extent of sorption, calculated from fluorescence data using the Stern-Volmer equation, was compared to independent ED measurements. Although both methods indicated the same trends with solution chemistry, fluorescence quenching data suggested more extensive complexation than that measured using ED. In contrast to ionizable PACs, studied here and previously, interaction of naphthalene with HA is unaffected by changes in solution conditions (pH, ionic strength).

Adsorption↗

PubMedDate not supplied

Phosphorus dynamics in soils receiving chemically treated dairy manure.

Chemical treatment of animal manure with Al, Fe, and Ca salts appears capable of concentrating P in a smaller volume, thereby providing increased manure management options. However, little information is available on the fate of nutrients in soils receiving chemically treated manure. An incubation study (1 d to 2 yr) was conducted with three soils (Soils I, II, and III with 12, 66, and 94 mg kg(-1) Bray-1 P, respectively) and four manure treatments (one untreated and three chemical including Al-, Fe-, and Ca-treated) at two rates (12.5 and 25 mg P kg(-1)), and a control (no manure). Subsamples were analyzed for Bray-1 P and water-extractable phosphorus (WEP) after eight incubation time periods. Phosphorus distribution among different fractions (soluble and loosely bound; Al-, Fe-, and Ca-bound; organic P; and residual) was also determined after 1 d and 1 yr. Water-extractable P increased when soils received untreated or Ca-treated manure in proportion to P application rate. Water-extractable P, however, decreased (compared with control) for Soils II and III or slightly increased for Soil I with addition of Al- or Fe-treated manure. Water-extractable P decreased sharply between 1 d and 1 to 2 wk and then remained relatively constant or increased slightly up to 2 yr depending on treatment and soil type. Bray-1 P increased for all treatment types and soils in the following order: Ca-treated > Al-treated >/= untreated > Fe-treated > control. Within each treatment, Bray-1 P decreased between 1 d and 1 to 2 wk and then gradually increased for up to 3 mo (Soils II and III) or 6 mo (Soil I). Application of Al- or Fe-treated manure decreased P solubility with the effect being more pronounced in soils with high background P. Since the application of Ca-treated manure increased both WEP and Bray-1 P, it should be recommended for soils where the objective is to increase P availability. Several years of P input through fertilizer and manure contributed mainly to aluminum-bound phosphorus (Al-P) and to a lesser degree to other fractions. Only soluble and loosely bound P (all soils) and Al-P (Soil I) exhibited treatment-type effects after receiving chemically treated manure. The study results will help bridge the gap between our knowledge of chemical treatment systems for animal manure and the ultimate fate of P when the treated manure is land-applied.

Aluminum↗