Release of Adsorbed Polycyclic Aromatic Hydrocarbons Under Cosolvent Treatment: Implications for Availability and Fate

ArticleinEnvironmental Toxicology and Chemistry 27(1):112-8 · February 2008with5 Reads
DOI: 10.1897/07-170.1 · Source: PubMed
Abstract
During laboratory and field studies, a fraction of contaminants in soils or sediments often is observed to be highly resistant to desorption. This desorption-resistant fraction may have significant effects on long-term fate and exposure of soil/ sediment-bound contaminants in particular, causing much reduced availability and contaminant persistence. Previous work by many research groups has indicated that this nonideal desorption behavior could be better predicted with biphasic desorption models. The present study further investigated the release of naphthalene and phenanthrene from sediments during and after cosolvent treatment. Experimental results indicate that release of these two compounds under cosolvent conditions can be accurately predicted with a previously developed, biphasic desorption model when the solubility enhancement effect of cosolvent is accounted for using standard activity coefficient ratios. In addition, desorption of the residual contaminants after cosolvent treatment follows the original biphasic desorption model very well, suggesting that cosolvent treatment increases only the aqueous solubility and has little effect on the nature of the desorption-resistant fraction and that cosolvent desorption is a valuable analytical tool for quickly measuring the magnitude of the desorption-resistant fraction. The present findings might have important implications for the mechanisms controlling resistant desorption of hydrophobic organic compounds and for predicting the availability and long-term fate of contaminants in soils and sediments.
    • "The presence of black carbon hinders switching PAHs from less bioaccessible to bioaccessible sites. It is known that contaminants in the less bioaccessible phase make remediation difficult (Chen et al., 2008) since they are unavailable for treatment technologies that are dependent on mass transfer to the aqueous phase (Ghosh et al., 2000; Talley et al., 2002). However this less bioavailable phase may have a significant impact on the long-term fate and exposure of soil/sediment bound organic contaminants (Cornelissen et al., 2005) as they can be released slowly to the environment and are often tedious to treat. "
    [Show abstract] [Hide abstract] ABSTRACT: In this study, the effect of sonication on the distribution of polycyclic aromatic hydrocarbons (PAHs) in the bioaccessible and less bioaccessible fractions of three contaminated sediments (Little Scioto River, OH-LS; Gary, IN-GI; Eagle Harbor, WA-EH) was examined. After 60min sonication, the fractions of naphthalene, phenanthrene and pyrene remaining in the LS sediment were 0.76±0.18, 0.83±0.04 and 0.76±0.05, respectively, indicating ultrasonic degradation of PAHs in the sediment. In addition, there was a significant decrease in PAH concentration (i.e., up to 91.4%) in the less bioaccessible fractions for all three sediments with sonication. The bioaccessible fraction of phenanthrene and pyrene in LS and pyrene in EH increased by 12.9%, 48.3% and 27.8%, respectively, followed by a slight decrease due to degradation. The initial increase suggests that ultrasonic irradiation of sediment either transfers the PAHs from the less bioaccessible sites to the bioaccessible sites for treatment or transforms less bioaccessible sites into bioaccessible sites. A comparatively smaller reduction (i.e., 20.2%) in the less bioaccessible fraction in GI sediment is attributed to the larger fraction of black carbon in the organic carbon content of the sediment hindering the ability of ultrasound to switch the PAHs from the less to the more bioaccessible sites. Overall ultrasonic irradiation of contaminated sediments is a technique to enhance contaminant remediation by reducing the fraction of contaminants in less bioaccessible sites. Copyright © 2014 Elsevier Ltd. All rights reserved.
    Full-text · Article · Dec 2014
    • "The practical effect of the adsorption and desorption rates, is that it controls the overall reaction rate of degradation process. They are one of the primary factors which affect availability , mobility and toxicity of contaminants in the soil34567891011121314151617. They determine the measured concentration and the mechanism of distributing the contaminants into surfaces and into pores of individual soil particles1819202122 and are thus counteractive to efficient biodegradation. "
    [Show abstract] [Hide abstract] ABSTRACT: The sorption behaviour of benzene, toluene, ethyl benzene, xylene and naphthalene using clay and sand sediments under ambient conditions is examined in this study. Experimental results showed that, the time taken to attain adsorption equilibrium for naphthalene, and BTEX were 28, 30, 30, 32, 28 hrs and 20, 22, 22, 24, 22 hrs while the desorption equilibrium time were 10, 13, 12, 15, 12 hrs and 9, 9, 9, 11, 10 hrs in clay and sand respectively. All of the naphthalene, and BTEX were adsorbed at the different equilibrium times, using clay while the amount of naphthalene and BTEX ad-sorbed by sand, at different equilibrium times were 117, 121, 127, 123 and 134 mg. Following the results of the adsorp-tion/desorption experiments, quantitative measurements showed that sand exhibited higher affinity for the solute as retained more chemicals (as high as between 58%-66%) within it pores while nearly all the chemicals adsorbed by the clay were released at the attainment of equilibrium. The implication of this is that occlusion within the sand particles may likely be the resultant effect of continued sand-chemicals contact. The amount of contaminant solute adsorbed and desorbed affirmed that clay has a better capacity to retain naphthalene and BTEX than sand and this may not be unrelated to its large surface area, high porosity and higher hydraulic conductivity for the solutes arising from its good binding sites (small pore sizes) that tend to hold the adsorbates to its particles.
    Full-text · Article · Jan 2013
    • "Water-miscible organic cosolvents can be encountered in soils and groundwaters as a result of accidental spills during storage, disposal in landfill and cosolvent mediated remediation processes (Chen et al., 2008; Maturi and Reddy, 2008; Wan et al., 2009 ). Sorption by soil is an important natural process, which influences the bioavailability, mobility and overall fate of hydrophobic organic chemicals (HOCs) released onto a soil system. "
    [Show abstract] [Hide abstract] ABSTRACT: The effect of the sorption of phenanthrene and 2,2',5,5'-polychlorinated biphenyl (PCB52) by five differently weathered soils were measured in water and low methanol volume fraction (f(c)0.5) as a function of the apparent solution pH (pH(app)). Two weathered oxisols (A2 and DRC), and moderately weathered alfisols (Toronto) and two young soils (K5 and Webster) were used. The K(m) (linear sorption coefficient) values, which log-linearly decreases with f(c), were interpreted using a cosolvency sorption model. For phenanthrene sorption at the natural pH, the empirical constant (alpha) ranged between 0.95 and 1.14, and was in the order of oxisols (A2 and DRC)<alfisols (Toronto)<young soils (K5 and Webster). Smaller alpha values for highly weathered soils are indicative of smaller solute sorption reduction than those predicted from the increment of the solute's activity coefficient in the solution phase. A similar trend was observed for PCB52 sorption. The K(m) values measured at the range of pH 3-7 also showed an inversely log-linear relationship. The regression slope (alphasigma) calculated from the cosolvency sorption model as a function of pH(app) only varied within <5%, with the exception for phenanthrene sorption by two highly weathered soils, which had 10% greater alphasigma values obtained at acidic pH(app). This phenomenon is a result of the greater acid enhancement effect on phenanthrene sorption by the oxisols, which is reduced with increasing f(c). These results revealed an unexplored relationship between the cosolvent effect on the sorption and the properties of the soil organic matter (a primary sorption domain) as a function of the degree of soil weathering.
    Full-text · Article · Nov 2009
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