Determination Of Sorption Coefficients Research Articles

Sorption of pyrene to dissolved humic substances and related model polymers. 1. Structure--property correlation.

Solid-phase microextraction (SPME) was employed to determine sorption coefficients for pyrene on dissolved humic substances (DHS) of various origins and also on model polymers to gain a better understanding of the relationships between sorption potential and sorbent structures. The sorption potential of DHS from very different sources is described by an empirical two-parameter correlation involving the polarity (O/H atomic ratio) and the aromaticity (epsilon 280 nm) as descriptors. On the other hand, sorption experiments with well-defined model polymers, poly(acrylic acid) esters, led to the conclusion that aliphatic chains may be more effective than aromatic moieties in binding PAHs. The molecular weight of the model sorbents was found to have a significant influence on the sorption potential.

Fluorescence quenching of polycyclic aromatic compounds by humic substances. Part 1. Methodology for the determination of sorption coefficients.

An introduction to the methodology of fluorescence quenching measurements as an experimental tool for investigating the sorption of hydrophobic organic substances by dissolved organic matter (OM) is given. Special attention is paid to the implications of inner-filter effects (IFEs) on the determination of sorption coefficients. The essential aspects of the theoretical description of IFEs are outlined and various procedures for the IFE correction of fluorescence quenching measurements in the presence of dissolved OM are presented. Geometric parameters relevant for the quantitative description of IFE applying a 90 degrees arrangement between fluorescence excitation and detection are determined by different methods, newly developed or adapted from the literature, for the fluorescence spectrometer used in this work. Moreover, an experimental validation of the applicability of different IFE correction procedures is performed. In order to evaluate the variations of sorption coefficients that result from the use of different IFE correction procedures, the quenching of the fluorescence of the well-known polycyclic aromatic compound pyrene by a commercially available humic substance in aqueous solution is investigated. Compared to the apparent sorption coefficient, which is obtained without any IFE correction, the sorption coefficients determined with the correction of primary IFE or with the correction of primary and secondary IFE are on average ca. 40 or 60% lower. The application of different IFE correction procedures allows the determination of sorption coefficients with appropriate precision of +/- 15%.

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

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 dD1) 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.

Carbon Tetrachloride Retention by Modern and Buried Soil A Horizons

Carbon tetrachloride (CCl4) was commonly used as a fumigant for stored corn (Zea mays L.) and other grains. This practice and other industrial uses have resulted in instances of soil and groundwater contamination. To better understand the potential for downward CCl4 movement, retention by a buried soil A horizon was compared with that of the modern A horizon in that same location and its loess C parent material. Batch equilibration was used to determine sorption coefficients (Kd) to compare retention among horizons. Mean Kd values were 0.83 (standard deviation [SD] = 0.18) for the modern A, 0.36 (SD = 0.10) for the loess C and 0.41 (SD = 0.07) for the buried A. Mean organic carbon (OC) contents were 14.9 g kg−1 (SD = 2.6) for the modern A, 1.3 g kg−1 (SD = 0.50) for the loess C, and 5.3 g kg−1 (SD = 0.60) for the buried A. Sorption coefficients were most strongly related to percent OC (R = 0.91 across all soils). Log OC coefficients (log Koc) were 1.74 (SD = 0.04) for the modern A, 2.43 (SD = 0.18) for the loess C, and 1.89 (SD = 0.10) for the buried A. The OC coefficient varied with OC content of the horizons. This variation may be attributed to qualitative chemical differences in the organic matter fractions. This may also be caused by the increased importance of the clay mineral fraction at low OC contents, leading to falsely high Koc values. The presence of a buried A horizon may help retard movement of CCl4 to groundwater.

Experimental problems in determining sorption coefficients of organic chemicals; an example for chlorobenzenes

Sorption of five chlorinated benzenes have been determined for a lake sediment. Sorption isotherms are linear over the tested aqueous concentrations ranges (three orders of magnitude), which supports the sorption partitioning model. Sorption coefficients of the chlorobenzenes are compared to the results of other sorption studies on the basis of sorption coefficient ratios and are consistent with literature data. In this study emphasis is on the experimental problems in determining sorption coefficients. Sediment extractions and experimental conditions such as equilibrium period, water-sediment separation and water/sediment ratio may influence sorption results. These possible experimental artefacts are investigated in this study in order to have better insight in the influence of the experimental artefacts and consequently in the spread of the experimental sorption coefficients.

Attenuation and Biodegradation of Chlorophenols in Ground Water at a Former Wood Treating Facility

AbstractThis communication describes novel methods to measure site‐specific sorption data, and to determine if biodegradation of pentachlorophenol (PCP) in complex technical‐grade formulations occurs at industrial facilities. Ground‐water slurry samples containing between 0.012 and 230 mg/l PCP were collected from a former wood treating site, the liquid and solid fractions separated, and both fractions analyzed for PCP using selective ion monitoring to determine sorption coefficients (Kd(PCP)). Although field sorption coefficients could not be represented by simple Freundlich and Langmuir isotherms, an empirical hyperbolic function (Kd(PCP)) = 0.054 + 0.086/Caq) fit the isotherm (r > 0.99), demonstrating that for PCP > 10 mg/l, no measurable retardation occurred in the aquifer. Biodegradation of PCP in ground water was apparent when PCP concentrations were < 20 mg/1, while at higher concentrations, PCP in the technical‐grade formulation appeared to break down less readily. The results imply that, at the plume periphery, PCP in the subsurface will be attenuated and degrade, while at higher concentrations (i.e., at the source), PCP is mobile, and more recalcitrant to degradation.

Estimation of Sorption Coefficients for Fungicides in Soil and Turfgrass Thatch

AbstractEnvironmental fates of turf‐applied fungicides are not well understood. The role of thatch as a sorptive surface for fungicides has not been evaluated. Thatch may decrease mobility of fungicides and decrease their potential to be transported off‐site. Batch type sorption studies were conducted to determine sorption coefficients (Kf) for the fungicides triadimefon, [1‐(4‐chlorophenoxy)‐3,3‐dimethyl 1‐1‐(1H‐1,2,4‐triazol‐1‐g‐1) butanone], vinclozolin [3‐(3,5‐dichlorophenyl)‐5‐methyl‐5‐vinyl‐1,3‐oxazolidine‐2,4‐dione], and chloroneb (1,4‐dichloro‐2,5‐dimethoxybenzone) in thatch and in the underlying soil. The Kf values also were derived from octanol/water partitioning coefficients (Kow) for these and five other compounds. All Kow values were determined with reverse‐phase high pressure liquid chromatography (HPLC) and calculated from physical properties of the fungicides. The Kf values [µmol(l‐n) Ln kg−1] determined from isotherm data for thatch and soil (respectively) were 90 and 10 for triadimefon, 163 and 21 for chloroneb, and 431 and 47 for vinclozolin. When Kf values were adjusted for organic C content of the sample, the resulting Kow values were similar for thatch and soil. The Koc values estimated from HPLC‐derived Kow values were consistently less than those obtained using batch isotherm methods. The Kow values calculated from physical properties of the fungicides were poorly correlated with measured values. The HPLC method appears to be useful for determining sorption coefficients. Results indicate that thatch substantially increases fungicide sorption, which, in turn, decreases the potential for these compounds to migrate off site.

Sorption of nonpolar organic chemicals on low‐carbon‐content aquifer materials

AbstractSorption isotherms were measured by batch equilibration methods for three nonpolar organic sorbates on seven subsurface, low‐carbon sedimentary aquifer materials. Radiolabeled (14C) 1‐methylnaphthalene, o‐dichlorobenzene and naphthalene were separately equilibrated with the sorbents to determine sorption coefficients (K). Chemical and physical properties of the aquifer materials were determined.Possible relationships between sorption coefficients and organic carbon (OC) content and other sorbent properties were investigated using multivariate statistics. Sorbent properties used in the statistical analysis were sorption coefficients, percentage OC, percentage sand, percentage clay, percentage silt, specific surface area, cation exchange capacity, percentage 1:1 clay, percentage 2:1 clay and percentage iron content. No predictive relationships between sorption coefficients and aquifer material properties were found. The sorption coefficient does not correlate with any of the properties of the aquifer materials, including OC content for aquifer materials with OC content of less than 0.10%. It is recommended that sorption coefficients be determined experimentally on each different aquifer material for use in ground water transport calculations.

SORPTION OF NONPOLAR ORGANIC CHEMICALS ON LOW-CARBON-CONTENT AQUIFER MATERIALS

Sorption isotherms were measured by batch equilibration methods for three nonpolar organic sorbates on seven subsurface, low-carbon sedimentary aquifer materials. Radiolabeled (14C) 1-methylnaphthalene, o-dichlorobenzene and naphthalene were separately equilibrated with the sorbents to determine sorption coefficients (K). Chemical and physical properties of the aquifer materials were determined. Possible relationships between sorption coefficients and organic carbon (OC) content and other sorbent properties were investigated using multivariate statistics. Sorbent properties used in the statistical analysis were sorption coefficients, percentage OC, percentage sand, percentage clay, percentage silt, specific surface area, cation exchange capacity, percentage 1:1 clay, percentage 2:1 clay and percentage iron content. No predictive relationships between sorption coefficients and aquifer material properties were found. The sorption coefficient does not correlate with any of the properties of the aquifer materials, including OC content for aquifer materials with OC content of less than 0.10%. It is recommended that sorption coefficients be determined experimentally on each different aquifer material for use in ground water transport calculations.