Estimation of Apparent Rate Coefficients for Phenanthrene And

http://www.paper.edu.cn Environmental Pollution 131 (2004) 223e231 Estimation of apparent rate coefficients for phenanthrene and pentachlorophenol interacting with sediments Hua-Lin Chena,b, Ying-Xu Chena,*, Yun-Tai Xua, Meng-Wei Shena aDepartment of Environmental Engineering, Huajiachi Campus, Zhejiang University, Hangzhou 310029, PR China bDepartment of Environmental Sciences and Engineering, Sichuan Agricultural University, Ya’an 625014, PR China Received 11 August 2003; accepted 16 February 2004 ‘‘Capsule’’: A model was used to study time-dependent interactions of phenanthrene and PCP in collected sediments. Abstract To gain information on organic pollutants in wateresediment systems, a compartment model was applied to study the sorption course of phenanthrene and pentachlorophenol (PCP) in sediments. The model described the time-dependent interaction of phenanthrene and PCP with operationally defined reversible and irreversible (or slowly reversible) sediment fractions. The interactions between these fractions were described using first order differential equations. By fitting the models to the experimental data, apparent rate constants were obtained using numerical optimization software. The model optimizations showed that the amount of reversible phase increased rapidly in the first 10 d with the sorption time, then decreased after 10 d, while the amount of irreversible phase increased in the total sorption course. That suggested the mass transport between reversible phase and irreversible phase. The extraction efficiency with hot methanol ranged from 36% to 103% for phenanthrene and from 65% to 101% for PCP, with the trend of decreasing with sorption time. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Compartment model; Sediment; Phenanthrene; Pentachlorophenol (PCP); Sorption 1. Introduction choice of cleanup technology. Kinetics can also be an important mechanistic tool for understanding sorption Sorption to natural solids is an underlying process itself. affecting the transport, degradation, and biological activ- In most cases, the uptake or release of organics by ity of organic compounds in the environment (Pignatello natural particles is bimodal in that it occurs in fast and and Xing, 1996). Although often regarded as instanta- slow stages (Carroll et al., 1994; Pignatello and Huang, neous for modeling purposes, sorption may in fact 1993). The division between them is rather arbitrary, but require weeks to many months to reach equilibrium in many cases it occurs at a few hours to a few days. (Rugner et al., 1999; Ball and Roberts, 1991a). Fate, Desorption likewise often reveals a major slow fraction transport, and risk assessment models all contain terms (10e96%) following a comparatively rapid release. for sorption; therefore, an understanding of the dynamics Historically contaminated (aged) samples, where con- of sorption is crucial to their success. Ignoring slow tact time may have been months or years, can be kinetics can lead to an underestimation of the true extent enriched in the slow fraction owing to partial dissipation of sorption, false predictions about the mobility and or degradation of more labile fractions before collection. bioavailability of contaminants, and perhaps the wrong The slow fraction of some pesticides was found to increase with contact time in the environment (Chen * Corresponding author. Tel.: C86-571-86971159; fax: C86-571- et al., 2000). 86971898. For models describing the short- and long-term E-mail address: [email protected] (Y.-X. Chen). interactions of organic pollutants with natural particles 0269-7491/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2004.02.020 中国科技论文在线 http://www.paper.edu.cn 224 H.-L. Chen et al. / Environmental Pollution 131 (2004) 223e231 (sediment or soil), many parameters were put forward, with sediments collected in different lake and rivers, to such as diffusion coefficient in diffusion model (Ball and obtain apparent rate coefficients using compartment Roberts, 1991b), glassy and rubbery regions in organic models. Compartment model with first order linear matter diffusion (Brusseau and Rao, 1991). However, it kinetic expressions was used to fit the experimental data. is very difficult to gain these parameters and it is hard to To obtain the apparent rate coefficients the system of apply in experiment. Compartment model has been used linear differential equations was solved using numerical in medication research field for many years. It can integration. indirectly reflect the concentration variation in different compartment, the capacity of which is difficult to mea- sure directly. Organic pollutants adsorbed into sediment 2. Materials and methods or soil can be divided into two fractions: reversible and irreversible fraction (Kan et al., 1997). The part sorbed 2.1. Sorbent into reversible compartment was bound to sediment loosely and was easy to desorb into aqueous phase again Eight sediments sampled in the south of China were when desorption operation was carried out (Drouillard used in this study. The sediments were obtained with et al., 1996), while the irreversible part closely bound to a clam sampler from West Lake before dredging, from sediment was difficult to desorb into aqueous phase West Lake after dredging, from Grand Canal, Taihu again (Pignatello and Xing, 1996). So it is possible to Lake and Dianchi Lake, which are heavily contami- apply compartment model to estimate the reversible and nated, and from Dongqian Lake, Yongjiang River and irreversible amount in the sorption course of organic Qiantang River, which are relatively lightly contami- pollutants in sediments. nated. Abbreviations of sediment samples are presented Sediment was the sink or source of pollutants in in Table 1. The sampling depth was 1e10 cm from the natural water. For example, when outside sources were surface of the sediment. The fresh sediments were air cut out, pollutants in aqueous phase may mainly come dried, crushed, mixed thoroughly and sieved through from sediments (Bremle et al., 1995). So the characters a 0.25 mm mesh, and stored in a refrigerator at 4 (C. of transport of pollutants in sediment and water were The pH of the sediments was determined with a glass the key factors to control the harmful effect on biology. combination electrode (sediment:water ratio of 1:2.5 Phenanthrene and pentachlorophenol (PCP) are persis- W:V), the cation exchangeable capacity (CEC) was tent organic pollutants in the environment. As anaerobic measured by the NH4CleC2H5OH method, and the biodegradation of them is relatively slow, they are organic matter content by the K2Cr2O7 oxidation preserved in sediments for a very long time. The highest method. The physico-chemical properties of eight sedi- concentration of phenanthrene and PCP in aquatic ments are shown in Table 1. To determine the back- environments usually has been found in river and lake ground concentrations of phenanthrene and PCP in sediments (Maatela et al., 1990; Abrahamsson and sediments, the dried sediment samples were extracted Klick, 1991). Therefore, the toxicity of phenanthrene with hot methanol in water bath (60 (C). After 4 d, the and PCP to aquatic organisms will remain for a very sediments were separated from solution by centrifuga- long time. tion at 3000 rpm for 20 min, and the phenanthrene and The overall objectives of this research are to study PCP concentrations in supernate were analyzed with time-dependent interactions of phenanthrene and PCP HPLC. The result showed that the eight sediment Table 1 Basic physico-chemical properties of sediment samplesa Sampling site Sample code Moisture (%) pHb CECc (cmol/kg) Organic matters (g/kg) Dongqian Lake DQ 2.644 G 0.114 5.28 30.78 G 0.74 44.62 G 0.087 West Lake WLA 7.924 G 0.470 7.35 58.39 G 0.31 365.7 G 4.3 after dredging Yongjiang River YJ 2.847 G 0.438 8.15 14.03 G 0.05 11.16 G 0.25 West Lake WLB 3.807 G 0.235 7.68 35.39 G 0.24 218.0 G 1.98 before dredging Dianchi Lake DC 4.817 G 0.124 8.08 36.52 G 0.09 106.8 G 1.5 Great Canal GC 1.532 G 0.136 7.86 17.16 G 0.72 46.27 G 0.739 Taihu Lake TH 3.156 G 0.464 6.50 21.40 G 0.98 14.93 G 0.30 Qiantang River QT 0.400 G 0.054 7.90 5.435 G 0.815 5.428 G 0.257 a The content is given on moisture-free basis. Mean G SD. b Sediment:water 1:2.5 (w/v). c CEC = cation exchangeable capacity. 中国科技论文在线 http://www.paper.edu.cn H.-L. Chen et al. / Environmental Pollution 131 (2004) 223e231 225 samples used in this study did not contain a detectable wavelength of 300 nm with 50 nm bandwidth. The quantity of phenanthrene and PCP. phenanthrene and PCP concentrations were quantified with an external standard method. 2.2. Sorbate 2.3. Sorption kinetic experiments Phenanthrene and pentachlorophenol (PCP) were used as the model compounds in this study. Phenan- All sorption kinetic experiments were conducted in threne (C14H10) is a three ring polycyclic aromatic triplicate in 35 ml glass vials. Sediment was taken and hydrocarbon with (a) molecular weight: 178 g/mol, 30 ml model compound solution was added into the vial. (b) solubility: 1.29 mg/ml at 25 (C, (c) Henry’s law Different solid-to-water ratios were used due to the ÿ5 3 constant: 2.6 ! 10 atm m /mol, and (d) log Kow: 4.6 sediment samples having different sorption capacities (i.e. (Karapanagioti et al., 2000). Phenanthrene was chosen to achieve sufficient sorption so that it could be easily because of its high hydrophobicity (Kow), low volatility quantified while keeping the aqueous phase concentration (Henry’s law constant), and simplicity of analysis. PCP above the detection limit). For the sediments of DQ, (C6Cl5OH) is a pesticide with a molecular weight of WLA, YJ, WLB, DC, GC, TH, and QT, the solid-to- 266.5 g/mol, solubility of 3.0 mg/ml at 25 (C, and water ratios were 0.5:30, 0.2:30, 1.0:30, 0.2:30, 0.2:30, log Kow of 4.4 (De Paolis et al., 1997).

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