Release of adsorbed polycyclic aromatic hydrocarbons under cosolvent treatment: Implications for availability and fate
College of Environmental Science and Engineering/Tianjin Key Laboratory of Environmental Remediation and Pollution Control, Nankai University, People's Republic of China. Environmental Toxicology and Chemistry
(Impact Factor: 3.23).
02/2008; 27(1):112-8. DOI: 10.1897/07-170.1
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.
Available from: Linda K Weavers
- "Sediment is composed of a continuum of pores ranging in size from micropores < 0.1 lm in diameter to macropores > 20 lm (Baldock et al., 2004) and a continuum of compartments ranging from rubbery (i.e., loose, flexible) to glassy (i.e., condensed, rigid) organic matter (Xing and Pignatello, 1997) ordered by their desorption rate constants (Pignatello and Xing, 1996) and degree of sorption (Braida et al., 2004). The release of contaminants from these sites is often considered to occur in biphasic stages: a fast desorbing contaminant fraction in equilibrium with the contaminant in solution and a slow desorbing contaminant fraction that is not in equilibrium with the contaminant in solution (Cornelissen et al., 1997; Chen et al., 2008). The fast desorbing fraction releases from amorphous materials (Huang et al., 1997; Cornelissen et al., 2005) and adsorption sites in the outer regions of the sediment aggregates which are in close contact with the aqueous phase (Cornelissen et al., 1997) allowing for rapid and reversible desorption (Qiu and Davis, 2004). "
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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.
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Available from: Bamidele Victor Ayodele
- "These chemicals due to their recalcitrant persistent nature have relatively low solubilities in water, but are highly lipophilic. The four and more condensed aromatic rings are considered to be more dangerous than the two and three rings PAHs   . The presence of these compounds which are listed as priority pollutants     in the environment is of considerable public health and ecological concern due to their toxicity to a wide range of biological systems. "
Available from: Kitae Baek
- "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. "
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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.
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