Estimation of Apparent Rate Coefficients for Phenanthrene And

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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

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 measure 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

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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 5 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). Although the 0.5:30, 1.0:30, 1.0:30, for phenanthrene sorption, and use of PCP has decreased during recent years, it still 1.0:30, 0.5:30, 2.0:30, 0.5:30, 0.5:30, 1.0:30, 2.0:30 and causes environmental problems at many locations, for 2.0:30 (wt:wt), respectively, for PCP sorption. The vials instance, contaminating sediments and even groundwa- were stored at 20 (C in the dark and shaken at 200 rpm. ter. Understanding the behavior of phenanthrene and Measurements were taken at various time intervals. PCP requires an assessment of the processes influencing Before analysis the samples were centrifuged at constant their fate, transport and bioavailability in sediments. temperature of 20 (C at 3000 rpm for 20 min. The In this experiment, model compounds were dissolved concentrations of phenanthrene and PCP in supernatant in methanol to form a 100 mg/ml stock solution. Before were determined with HPLC system. use, the stock solution was diluted to a set concentration with an electrolyte matrix, which was composed of 2.4. Irreversible sorption amount measured 1 mM CaCl2, 0.1 mM MgCl2, and 0.5 mM Na2- B4O710H2O. Sodium azide (NaN3) was added at a After the sorption experiments, desorption was concentration of 200 mg/ml to minimize bacterial growth induced by the successive replacement of 90% superna- and biodegradation during batch experiments. All the tant with a model compound free electrolyte solution glass vials containing sediments and model compound (actual amounts were determined by weight), and the solutions were shaken in darkness until the measure- vials were sealed and shaken for 24 h at 200 rpm at ment time was reached. For each batch experiment, 20 (C in the dark. The desorption period of 24 h was blank samples were prepared and monitored (i.e., model chosen after a preliminary desorption kinetic experiment compound solutions without sediment). The blank sam- was conducted for 72 h. The data revealed a concentra- ples did not indicate any significant degradation or sorption plateau after 18 h. For a more convenient opera- tive losses on the glassware during the course of the tion, the desorption period was set at 24 h. At the end of experiment, so the missing model compounds from the desorption period, the vials were centrifuged at the solution phase can be considered safely sorbed onto 3000 rpm for 20 min, and the supernatant was analyzed the sediment solid phase. Aqueous phase model com- for solution-phase model compound concentration by pound concentrations were determined with the Agilent HPLC. The desorption procedure was repeated until the 1100 serials HPLC system. The HPLC system was model compound concentration in the supernatant was equipped with a vacuum degasser, quaternary pump, below the detection limit. After the successive de- autosampler, column compartment, diode array and sorption steps, the solution was decanted and the wet multiple wavelength detectors (DAD), and a hypersil sediment was left in the vial (actual amounts were reversed-phase ODS-C-18 column made by the Agilent determined by weighing). Purified methanol solution Company, U.S.A. The conditions for measuring phen- (30 ml) was added into the vials to extract the model anthrene were: a mobile phase made of purified water compounds from the sediment solids in the water bath (10%) and methanol (90%) at a flow rate of 1.00 ml/ (60 (C) for 4 d. The extracted quantities of model com- min, signal wavelength of 250 nm with 20 nm band- pounds were determined by HPLC. width, and a reference wavelength of 330 nm with 50 nm bandwidth. The conditions for measuring PCP were: 2.5. Data analysis a mobile phase made of 1% acetic acid (10%) and methanol (90%) at a flow rate of 1.00 ml/min, signal wave- In the sorption experiments, the mass of PCP, which length of 220 nm with 20 nm bandwidth, and a reference disappeared from the solution phase at the end of the 中国科技论文在线 http://www.paper.edu.cn

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sorption experiment, was assumed to adsorb onto constants, k21 was the biggest for phenanthrene, fol- sediment: lowed by k12, while k32 was apparently smaller than the other three constants. That suggested the irreversible Vw qadsorbed ¼ðCinitial CsolutionÞ ð1Þ sorption existence for phenanthrene sorption in sedi- Ws ments. For PCP sorption, the same trend was observed, but the k23 value was near k32, suggesting more mass where qadsorbed is the mass of solute adsorbed onto the exchanging between irreversible and reversible compart- sediment (mg/g), Cinitial is the initial concentration of ment for PCP than that for phenanthrene, i.e., the solute (mg/ml), Csolution is the solution-phase solute concentration at the end of the sorption experiment (mg/ irreversible compartment capacity of PCP was smaller than that of phenanthrene. ml), Vw is the volume of solution (ml), and Ws is the mass of the sediment (g). With the sorption rate constants presented in Table 2, To gain information about the kinetics of model the amounts of reversible sorption (cr(t)) and the compounds to reversible and irreversible (or slowly irreversible sorption (ci(t)) were calculated with the reversible) binding sites in the sediment, the amount of integration of Eq. (2), and the results are plotted in Figs. the model compounds associated with the sediment 3 and 4. From the results, for phenanthrene sorption, in phase was divided into two groups, i.e., reversible frac- the initial sorption period, the concentration in water tion and irreversible fraction. To model the kinetic inter- phase decreased rapidly, then reached a plateau after actions, three-compartment model was used (Fig. 1). 10 d. The concentration of phenanthrene in the reversible The exchange reactions for the model are described by: compartment increased rapidly in first 10 d, then decreased slowly, while the concentration in the irreversible dcwðtÞ compartment increased during the whole sorption time. ¼k c ðtÞCk c ðtÞCf dt 12 w 21 r 10 That suggested that the real equilibrium of sorption was dc ðtÞ not reached in the experiment (100 d). In fact, the trans- r ¼ k c ðtÞðk Ck Þc ðtÞCk c ðtÞð2Þ dt 12 w 21 23 r 32 i portation of phenanthrene from reversible compartment dc ðtÞ into irreversible compartment continued, so that the real i ¼ k c ðtÞk c ðtÞ dt 23 r 32 i equilibrium of sorption should take more time. So did the PCP sorption. With smaller irreversible compart- where cw(t), cr(t), ci(t) are the concentrations in the ment capacity, sorption of PCP can reach equilibrium water (mg/ml), reversibly associated fraction, and faster than that of phenanthrene. irreversibly (or slowly reversibly) associated fraction (mg/g), respectively. The apparent rate coefficients can be 3.2. Irreversible sorption amount estimated by fitting Eq. (2) to the experimental data using numerical optimization methods. The results of continuous desorption were applied to validate the modeling data. When the endpoint of 3. Results and discussion desorption experiment was reached, the amount adsorbed in the sediment was taken as the irreversible 3.1. Sorption kinetics fraction, while the desorbed amount was the reversible amount. So these data were applied to validate the Fig. 2 is the result of sorption capacity versus model. In this study, only contact 1 d and 5 d experi- sorption time. Model compound concentration in ment were carried out, and the results are shown in aqueous phase decreased rapidly versus sorption time. Table 3. The calculated data with the model are After 10 d sorption, aqueous phase concentration presented in Table 3 as well. almost reached equilibrium. After 40 d sorption, the Take the data of phenanthrene sorption on Dongqian aqueous phase concentration keep constant. Based on Lake sediment as an example. After 1 d sorption, the 1 the experiment data, sorption rate constants (k12, k21, total adsorbed amount was 58.22 mgg , and after 7 1 k23, k32) were calculated and the results are presented in steps desorption, the desorbed amount, 15.93 mgg , Table 2. The results showed that among the four was the reversible fraction, so the residual amount,

k12 k23 f10 Water Reversible Irreversible (or slowly fraction sites reversible) sites k21 k32 (cw(t)) (cr(t)) (ci(t))

Fig. 1. The wateresediment system described by three-compartment model. The sediment is divided into two compartments; operationally divided into a ‘‘reversibly bound fraction’’ and ‘‘irreversible (or slowly reversibly associated) fraction’’. The interactions between the compartments are

described by apparent rate coefficients (k12, k21, k23, k32) defined by first order linear differential equations. 中国科技论文在线 http://www.paper.edu.cn

H.-L. Chen et al. / Environmental Pollution 131 (2004) 223e231 227

1.4 1.4 PCP 1.2 1.2 PCP 1

-1 -1 1 0.8 0.8 0.6 /µg•ml /µg•ml 0.6 c 0.4 c 0.4 0.2 0.2 0 0 0 20 40 60 80 100 120 0 20 40 60 80 100 120 Contact time/d Contact time/d Dongqian Dianchi West Lake after dredging Great Canal Yongjiang Taihu West Lake before dredging Qiantang CK CK

1.4 1.4 phenanthrene 1.2 1.2 phenanthrene 1 1 -1 -1 0.8 0.8 0.6

/µg•ml /µg•ml 0.6 c 0.4 c 0.4 0.2 0.2 0 0 0 20406080100120 0 20 40 60 80 100 120 Contact time/d Contact time/d Dongdian Dianchi West Lake after dredging Great Canal Yongjiang Taihu West Lake before dredging Qiantang CK CK Fig. 2. The sorption rate curves of phenanthrene and PCP on eight sediments. CK = control.

43.29 mgg1, was the irreversible fraction, while the irreversible compartment during the whole sorption modeling data were 57.79 mgg1 for total amount, time. The model compound continuously transport from 32.97 mgg1 for reversible sorption, and 26.82 mgg1 reversible compartment into irreversible compartment, for irreversible sorption. It is obvious that for irrevers- so based on the desorption operation procedure, the ible amount the modeling data were smaller than the reversible and irreversible amounts after 1 d sorption were experiment data. The diﬀerence was caused by the not really the values for 1 d sorption due to the dynamic desorption operations. Figs. 3 and 4 showed the mass course of sorption. In fact, in the continuous desorption transformation between reversible compartment and time (6 d), the model compound continuously transport

Table 2 The sorption rate constantd of phenanthrene and PCP on sediments (d 1) Sedimente Phenanthrene PCP

k12 k21 k23 k32 k12 k21 k23 k32 DQ 0.1294 0.3483 0.2132 0.0091 0.2357 0.2367 0.0512 0.0255 WLA 0.0896 0.2628 0.1227 0.0009 0.1102 0.1169 0.0644 0.0191 YJ 0.2360 0.4931 0.0456 0.0083 0.0452 0.0219 0.0580 0.0363 WLB 0.0609 0.1278 0.0817 0.0017 0.2455 0.2168 0.0364 0.0224 DC 0.1182 0.1502 0.0217 0.0021 0.0418 0.0608 0.0478 0.0577 GC 0.1208 0.2622 0.0921 0.0040 0.0613 0.0909 0.0729 0.0740 TH 0.1176 0.1798 0.0656 0.0051 0.0739 0.2116 0.0647 0.0299 QT 0.1216 0.2024 0.0524 0.0222 0.0864 0.2300 0.0057 0.0300 d Rate constants in sorption course are given in Fig. 1. e Abbreviations of sediments are explained in Table 1. 中国科技论文在线 http://www.paper.edu.cn

228 H.-L. Chen et al. / Environmental Pollution 131 (2004) 223e231

0.8 Dongqian Lake 20 0.8 West Lake after dredging 50

40 0.6 15 0.6 1 1 1 - - 1 - -

30 g 0.4 10 0.4 • µg µg µg / / /•ml /•ml 20 qµg•g q c c 0.2 water 5 0.2 water reversible reversible 10 irreversible irreversible 0 0 0 0 0 20 40 60 80 100 120 020406080100120 Contact time/d Contact time/d

1.2 Yo n g jian g 5 0.9 West Lake before dredging 40 1 4 30 1 1 1 1 -

- 0.6 0.8 - - g

3 ml • 0.6 • 20 µg µg µg µg / /•g / /•ml 2 q q c

c water 0.4 0.3 water reversible 10 0.2 1 reversible irreversible irreversible 0 0 0 0 0 20406080100120 020406080100120 Contact time/d Contact time/d

0.9 Dianchi Lake 30 1 Grand Canal 14 12 25 0.8 10 1 1 1 - 1 - l 0.6 20 - 0.6 - m 8 15 µg µg µg µg /•g /•g /•ml /• 0.4 6 q q

c water 0.3 10 c water reversible 4 0.2 reversible irreversible 5 irreversible 2 0 0 0 0 0 20406080100120 0 20406080100120 Contact time/d Contact time/d

0.9 Taihu Lake 7 1.4 Qiantang River 6 6 1.2 5 1 1 5 1 1 - 4

0.6 - 0.8 4 •g-1 •ml- 3

Water µg µg µg /•g µg /

3 /•ml 0.6 / q q c c 0.3 water Reversible 2 2 0.4 reversible Irreversible irreversible 1 0.2 1 0 0 0 0 0 20406080100120 0 20 40 60 80 100 120 Contact time/d Contact time/d Fig. 3. Kinetics of PCP added to the wateresediment system according to the three-compartment model in Fig. 1.

from reversible compartment into irreversible compart- difference existed, while for PCP, the difference was ment, so when the desorption experiment reached small. That suggested it was a good way to apply the endpoint, the irreversible amount should be the amount compartment model to PCP sorption in sediments. For of sorption after the whole contact time, i.e., sorption phenanthrene sorption, the validation method for time before desorption (1 d) and desorption time (6 d), model needs to be improved. 7 d. The modeling irreversible sorption values after 7 d In this study, the values of irreversible sorption were sorption are listed in Table 3. Comparing the 7 d calculated with reversible amount subtracted from total modeling irreversible amount to the 1 d sorption experi- sorption amount. That can lead to overestimation of the ment data, we can find that for phenanthrene, the irreversible sorption amount because the amount lost via 中国科技论文在线 http://www.paper.edu.cn

H.-L. Chen et al. / Environmental Pollution 131 (2004) 223e231 229

0.3 Dongqian Lake 70 0.18 West Lake after dredging 210 0.25 60 0.15 180 Water 50 150 1 1 1 1 - 0.2 - 0.12 - Reversible - 40 Water 120 0.15 Irreversible 0.09 µg µg µg µg /•g Reversible /•g /•ml 30 /•ml 90 q q c 0.1 c 0.06 Irreversible 20 60 0.05 10 0.03 30 0 0 0 0 020406080100120 0 20406080100120 Contact time/d Contact time/d

0.6 Yongjiang River 25 0.25 West Lake before dredging 180

0.5 20 0.2 150 1 1 1 - 1

0.4 - 120 - 15 - 0.15 Water 0.3 Reversible 90 µg µg µg µg /•g /•g /•g /•ml 10 0.1 q

c Irreversible q c 0.2 Water 60 0.1 Reversible 5 0.05 30 Irreversible 0 0 0 0 0 20406080100120 0 20406080100120 Contact time/d Contact time/d

0.6 Water 140 0.35 Great Canal 70 Reversible 120 0.5 Irreversible 0.3 60 100

1 0.25 50 1 1 -

0.4 1 - - Water - 80 g 0.2 40 0.3 Reversible µg µg µg /• µ /•g

/•ml 60 /g•ml 0.15 Irreversible 30 q q c 0.2 c 40 0.1 20 Dianchi Lake 0.1 20 0.05 10 0 0 0 0 020406080100120 0 20406080100120 Contact time/d Contact time/d

0.5 Taihu Lake 35 0.8 Qiantang River 21 30 18 0.4 25 0.6 15 1 1 1 - 1 - - -

Water g

0.3 ml 20 12 •g Reversible • 0.4 µg µg µg / µg /• / /•ml Irreversible 15 9 0.2 q q c c Water 10 0.2 6 0.1 Reversible 3 5 Irreversible 0 0 0 0 0 20406080100120 020406080100120 Contact time/d Contact time/d Fig. 4. Kinetics of phenanthrene added to the wateresediment system according to the three-compartment model in Fig. 1.

volatilization and photodegradation was mistaken for desorption experiment, so the modeling data were smaller irreversible sorption. In the sorption course, the amount than measured data. lost via volatilization and photodegradation was smaller than that in desorption course, because sorption opera- 3.3. Extraction eﬃciency of sorbed model compounds tion only contained one step, while desorption operation contained many steps as described in Section 2.4. For Because the eight sediment samples used in this study irreversible sorption amount, modeling data came from did not contain a detectable quantity of phenanthrene sorption experiment, while measured data came from and PCP extracted with hot methanol before sorption 中国科技论文在线 http://www.paper.edu.cn

230 H.-L. Chen et al. / Environmental Pollution 131 (2004) 223e231

experiment, the extracted amount for model compounds after the sorption experiment could be regarded as the

reversible sorption amount. The results showed that the extraction efficiency of sorbed model compounds in sorption course with hot methanol ranged from 36% to 103% for phenanthrene, and from 65% to 101% for PCP. The efficiency decreased with sorption time. The difference among the sediments showed that the efficiencies of sediments with high organic matter contents, such as sediment in West Lake and Dianchi Lake, were slower that that of sediments with low organic matters contents, such as in Taihu Lake, Qiantang River, and Yongjiang River. This suggested that the organic matter content attributed to irreversible sorption heavily. In the literature, Karapanagioti et al. (1999) obtained the extraction efficiency of phenanthrene sorption in soil after 100 d in the range of 26e76%. So the irreversible fraction may be underestimated due to incomplete recovery (Hatzinger and Alexander, 1995).

4. Conclusion Irreversible 7 d Irreversible Total Reversible Irreversible 12 d Ir The sorption experiments showed that phenanthrene and PCP sorption in most sediments reached equilibrium after 20 d. The modeling data calculated with compartment model showed that at the premise of equilibrium of aqueous phase concentration with total solid phase adsorbed amount, the model compound ) 1

continuously transport from reversible compartment g m

( into irreversible compartment. The results of modeling f data compared to those of experiment data showed that the irreversible amount modeling was smaller than experiment data. To validate the calculated data, hot methanol extraction was carried out at the end of sorption experiment. The recovery of phenanthrene ranged from 36% to 103%, and of PCP from 65% to 101%. . Acknowledgements Table 1 This research has been conducted under the auspices of the Hangzhou Environmental Protection Bureau.

References

Experiment dataContact 1 dTotal Reversible Irreversible Total Reversible Irreversible Total Reversible Contact 5 d Contact 1 Modeling d data Abrahamsson, K., Klick, Contact 5 d S., 1991. Degradation of halogenated phenols in anoxic marine sediments. Mar. Pollut. Bull. 22, 227e233. DQWLA 158.8 58.22YJ 15.93 12.8WLB 151.9DC 23.49GC 23.1 8.53 111.7 43.29TH 146.0 12.38 63.92QT 13.71 27.26 128.8 14.96DQ 65.03 178.8 14.58 8.56 12.71WLA 91.32 5.33 15.82YJ 9.0 31.58 50.21 162.0 26.51WLB 8.41 9.94 18.70 16.3 149.0DC 52.32 2.88 27.58 3.60GC 13.9 14.41 169.8 9.25 67.49 1.66 23.72TH 12.14 21.64 7.41 30.87 11.57 145.7 11.62QT 59.79 23.63 32.97 9.69 135.1 13.17 6.15 163.6 22.14 6.20 55.35 88.06 1.94 1.59 41.41 2.38 22.28 2.91 12.15 153.4 21.27 14.01 11.59 26.82 1.78 13.63 21.18 81.49 110.0 46.24 5.47 21.75 75.59 57.73 64.50Ball, 20.55 30.40 4.51 32.29 3.29 27.40 34.49 10.69 14.52 71.92 24.33 2.19 7.64 0.60 W.P., 16.17 13.95 45.50 24.49 85.07 15.99 25.44 8.56 30.35 16.15 7.99 15.88 9.84 76.02 Roberts, 18.60 11.42 10.38 9.38 2.32 2.99 3.28 48.90 25.31 65.32 29.54 19.73 1.26 7.61 179.0 33.80 24.89 11.75 6.15P.V., 4.74 12.14 13.84 3.79 98.34 169.8 4.71 31.51 5.58 2.25 1.73 12.30 148.4 26.381991a. 15.79 96.39 11.06 7.48 80.72 66.73 7.14 101.2 17.65 7.40 39.02 6.53 41.03 10.36 73.41Long-term 1.54 30.38 1.54 3.83 10.45 47.2 8.73 96.17 19.08 5.16 27.71 1.46 44.73 84.33 22.13 25.16 1.79 11.30 30.86 2.70 10.91 15.27 sorption 53.96 45.86 34.16 18.80 0.08 5.54 37.36 30.32 13.87 14.40 6.86 19.99 3.13 6.35 of 0.18 8.50halogenated 5.07 21.00 10.33 15.97 9.11 3.41 9.79 10.78 14.70 11.39 8.42 1.66 4.24 5.18 5.51 4.08 2.14 2.91 6.66 0.14 4.51 0.28 organic chemicals by aquifer material: 1. Equilibrium. Environ. Sci.

g Technol. 25, 1223e1236. Ball, W.P., Roberts, P.V., 1991b. Long-term sorption of halogenated Abbreviations of sediments are explained in The content is given on moisture-free basis.

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