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Degradation and detoxification of the wood preservatives creosote and pentachlorophenol in water by the photo-Fenton reaction
PII: S0043-1354(98)00323-6
Wat. Res. Vol. 33, No. 5, pp. 1151±1158, 1999 # 1999 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0043-1354/99/$ - see front matter
DEGRADATION AND DETOXIFICATION OF THE WOOD PRESERVATIVES CREOSOTE AND PENTACHLOROPHENOL IN WATER BY THE PHOTOFENTON REACTION M MARGARET A. ENGWALL12, JOSEPH J. PIGNATELLO12** and 2* M DOMENICO GRASSO
Department of Soil and Water, The Connecticut Agricultural Experiment Station, P.O. Box 1106, New Haven, CT 06504, U.S.A. and 2Department of Civil and Environmental Engineering, The University of Connecticut, 261 Glenbrook Rd., U-37, Storrs, CT 06269-2037, U.S.A.
1
(First received March 1998; accepted in revised form July 1998) AbstractÐPentachlorophenol (PCP) and the organic compounds in creosote often contaminate groundwater at wood preserving facilities. Since many of these compounds are toxic, eective water treatment technologies must be identi®ed. In laboratory scale experiments saturated aqueous solutions of creosote and PCP were treated by the photo-assisted Fenton reaction, Fe3+/H2O2/UV ([Fe3+] = 1 mM, [H2O2] = 10 mM, 1.4 10ÿ3 M hn minÿ1 black lamp ultraviolet light (UV), pH = 2.75 and 258C). The disappearance of 37 polycyclic aromatic hydrocarbons (PAHs), O, N and S-heterocyclic aromatic compounds and phenolic compounds and their mineralization products were monitored during a 180 min reaction period. Substantial (>90%) transformation of all compounds except a few 4- and 5-ring PAHs was achieved in 5 min, with more extensive transformation occurring thereafter. The reactivity followed the order: 2 ring PAHs>heterocyclics>phenolics>3 ring PAHs>4±5 ring PAHs. Complete dechlorination of PCP required only 10±20 min. Within 180 min the total organic carbon concentration declined by about 80% and added 9-14 C-phenanthrene or 4,5,9,10-14 C-pyrene were mineralized by 93% and 35%, respectively. About 33% of the organic nitrogen was converted to a 2:1 mole ratio of NH+ 4 and HNO3 and trace amounts of HNO2. An undetermined yield of sulfate was also generated. The acute toxicity of the treated solution to fathead minnows (Pimephales promelas) was nearly eliminated and the acute toxicity to daphnia (Daphnia pulex) was reduced. These results demonstrate the ecacy of Fe3+/H2O2/UV for removing creosote and PCP in water. # 1999 Elsevier Science Ltd. All rights reserved Key wordsÐcreosote, pentachorophenol, polycyclic aromatic hydrocarbons, phenols, heterocyclic aromatic compounds, Fenton reagent, water treatment, advanced oxidation processes
INTRODUCTION
Creosote and pentachlorophenol (PCP) are used as wood preservatives, often in combination. The organic constituents of creosote include polycyclic aromatic hydrocarbons (PAHs, 85%), phenolic compounds (10%) and N-, S- and O-heterocyclic aromatic compounds (5%) (Mueller et al., 1989). Due to past handling and disposal practices the soil and groundwater at many wood preservation facilities have become contaminated with these substances. Although the ``pump-and-treat'' approach is losing favor as a stand-alone remediation technology for aquifers, extraction wells are often utilized as a method of plume containment and require concomitant aqueous phase treatment. A need exists, therefore, to develop economical methods to *Author to whom all correspondence should be addressed. [Tel.: +1-203-974-8518; Fax: +1-203-974-8502; Email, [email protected]].
remove creosote and PCP in the contaminated water. Previous eorts have employed microorganisms (Mueller et al., 1991) or photocatalysis (Serpone et al., 1994). In this study, we investigated the photo-assisted Fenton (photo-Fenton) reaction for its ability to oxidize PCP and creosote and reduce the toxicity of the water. The photo-Fenton reaction employs ferric ion (Fe3+), hydrogen peroxide (H2O2) and UV light and has been shown eective in mineralizing a wide variety of organic pollutants in water (Pignatello, 1992; Sun and Pignatello, 1993; Pignatello and Sun, 1995; Sarazadeh-Amiri et al., 1996). After determining the identity and concentrations of the compounds that partition into water from a nonaqueous creosote/PCP phase we determined the extent of transformation of each compound, the degree of total organic carbon removal and the yield of selected inorganic ions. Finally, we measured the reduction in toxicity of the solution to two dierent organisms.
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Margaret A. Engwall et al. BACKGROUND
Creosote is a distillate of coal tar (United States Environmental Protection Agency, 1984). As of May, 1997 there were 59 sites on the U.S. Environmental Protection Agency (USEPA) Final National Priorities List involving past creosote/PCP wood preserving operations. Creosote contaminated sites have been identi®ed in Denmark, Canada, Greenland, Sweden and the United Kingdom, as well. Coal tar, formed during the high temperature carbonization of coal (United States Environmental Protection Agency, 1984), was produced in large quantities as a byproduct of coal gasi®cation until the early 1900s when it was replaced by natural gas. Coal tar is similar in composition to creosote in that it is a complex mixture mainly of PAHs. It has been estimated that there are at least 1000 (Peters and Luthy, 1993) and potentially as many as 32,600 (Hatheway, 1997) former manufactured gas plant sites that produced coal tar. The present study focuses on those organic compounds that partition into water from the creosote phase because of their potential to contaminate both surface and groundwater. Single-component water solubilities of the compounds studied range from 0105 mg/l for phenol to 010ÿ3 mg/l for benzo[b]¯uoranthene (Mackay et al., 1992a,b). Biodegradation of creosote/PCP in water is slow and incomplete; Mueller et al. (1991) found that after 14 d only 42% of the monitored creosote constituents in groundwater were completely converted. Lantz et al. (1997) found that certain creosote components either inhibited or were toxic to a ¯uoranthene-degrading microorganism and concluded that these eects may have contibuted to the limited extent of bioremediation. Advanced oxidation pro. cesses based on hydroxyl radical ( OH) chemistry, such as hydrogen peroxide based systems, ozone based systems and photocatalysis, can eciently oxidize many organic compounds in water (Legrini et al., 1993) and therefore are a logical alternative to biodegradation. Hydroxyl radicals, which are formed in solution or on the surface of the photocatalyst, react non-selectively with organic compounds via H-abstraction and addition to C±C unsaturated bonds. Mills and Homann (1993) reported that PCP is approximately 96% mineralized photocataytically by TiO2 in 90 min. Serpone et al. (1994) applied photocatalysis to the treatment of separate-phase creosote in water. The investigated compounds appeared to be 100% mineralized in 6±15 h, depending on the initial creosote concentration (Serpone et al., 1994). Previous research has shown success in degrading various organic compounds in water using the photo-assisted Fenton reaction (Pignatello, 1992; Sun and Pignatello, 1993; Pignatello and Sun, 1995; Sarazadeh-Amiri et al., 1996). Critical steps in the photo-Fenton process are:
. ÿ4Fe OH ÿ 2 OH, Fe2 H2 O2 ÿ
1
. 2 Fe OH2 hÿ ÿ4Fe ÿ OH:
2
The classical Fenton reaction in equation 1 is assisted by the photoreduction step in equation 2 which takes place in the near UV region and results in the regeneration of Fe(II) and production of . OH. The full sequence of inorganic reactions . involved in formation and decay of OH has been discussed elsewhere (Chen and Pignatello, 1997). While direct photolysis of hydrogen peroxide also . yields OH, hydrogen peroxide absorbs weakly in the ultraviolet range. The extinction coecient at 254 nm is 19.6 Mÿ1 cmÿ1 and approaches zero as the wavelength increases to 0320 nm. Hence, hydrogen peroxide direct photolysis is inhibited by absorbing organics. The aqueous saturated creosote/PCP solution used in the present study begins to absorb appreciably at about 340 nm and reaches an absorbance of 1.0 at about 300 nm and 1.4 at about 250 nm. Thus, the solution blocks most of the light at wavelengths required for hydrogen peroxide direct photolysis. PCP and many of the organic compounds found in creosote are acutely toxic, may produce animal and human cell mutations and may be teratogenic or exhibit other reproductive eects (Lewis, 1992). Reduction in toxicity of the treated water is a critical measure of the success of any treatment method, since the formation of toxic organic by-products is possible. In this study, we determined the LD50 (the statistically determined dose that causes 50% mortality in a given exposure period) of the aqueous creosote solution before and after photo-Fenton treatment using Pimephales promelas (fathead minnows) and Daphnia pulex (Daphnia) as test organisms. Such data is an indication of acute toxicity reduction resulting from treatment. MATERIALS AND METHODS
All reagents were used as received: perchloric acid (J.T. Baker), sodium perchlorate (99%, GFS Chemical), hydrogen peroxide (30% solution, Fisher), phenanthrene-9-14 C (59.5 mCi/mmol, 99% radiolabel purity, Sigma), pyrene4,5,9,10-14 C (58.7 mCi/mmol, 99% radiolabel purity, Sigma), tetralin (1,2,3,4-tetrahydronaphthalene, 99%, Aldrich), 2-chlorophenol (100%, Kodak), PCP (85%, ICN Biomedicals, Inc.), Bovine catalase (Thymol-free, Sigma) and ethanolamine (Laboratory grade, Fisher). American Creosote-P2, historically used to treat railroad ties, was provided by the American Wood-Preserver's Association. Glassware was rinsed three times with ethanol, washed with detergent and rinsed three times each with Type I distilled/deionized (DI) water, acetone and hexane prior to drying. Glassware exposed to Fe3+ was rinsed with 1 M HClO4. Aqueous solutions were prepared with Type I distilled/deionized water. Photo-assisted Fenton Reactions Test solutions were prepared by contacting 2 g of American Creosote-P2 and 2 g of PCP with 2 l of DI water for at least 10 d in the dark at laboratory ambient
Degradation of wood preservatives temperatures with stirring for the ®rst 24 h. Initial experiments indicated that 10 d was sucient to achieve saturation. After ®ltering through glass wool to remove any separate phase, the test solution was stored in a Te¯onsealed screw-top glass ¯ask at 48C in the dark. No phase separation of the creosote was observed during storage. The test solution (360 ml) was transferred to a covered 400 ml cylindrical double-walled borosilicate reaction vessel (Huston and Pignatello, 1996) by siphoning with a Te¯on tube. The vessel was then sealed with a Te¯on-lined screw cap and allowed to temperature equilibrate for at least 25 min at 2520.18C, which was maintained by circulating water from an external bath through the vessel jacket. Henry's Law calculations indicated that R0.1% of each compound would partition into the vessel headspace. Next, freshly prepared ferric perchlorate (Fe(ClO4)3) solution was added to the vessel to achieve 1 mM Fe3+ and the pH adjusted to 2.7520.05 using 0.1 M HClO4 or 0.1 M NaHCO3 solution. (The perchlorate salt of Fe(III) was chosen in this research to avoid metal ion complexation, light absorption and chemical and photochemical reactions involving the counterion (Pignatello, 1992); although the sulfate, chloride and nitrate salts are less desirable with respect to these considerations, it should be noted that they are more available and less expensive to use on a commercial scale and possibly more desirable because they exist naturally). Finally, iodometrically-standarized H2O2 solution was added to a concentration of 10 mM. The mole ratio of hydrogen peroxide to total organics was about 40:1. The vessel was then re-sealed, placed under an atmosphere of oxygen and inserted into a Rayonet RPR-200 chamber with 16 14-W ¯uorescent black lamps that emit at wavelengths between 300 and 400 nm. The light intensity was 1.4 10ÿ3 M photons minÿ1, as determined by ferrioxalate actinometry. The lamps were turned on at least 10 min in advance to insure constant output. The contents of the vessel were stirred using a magnetic stirrer. Samples were taken at intervals and quenched with methanol (0.5 ml CH3OH per 50 ml solution) containing analytical internal standards. Analytical techniques Parent compound transformation. A modi®ed acid/baseneutral fractionation method (EPA Method 625) was used to extract and quantify 37 parent compounds. The phenolic compounds (acid fraction) were derivatized to their acetate esters by addition of 1 ml of saturated K3PO4 and 200 ml of acetic anhydride to a 10 ml aliquot of sample initially at pH0 2. The sample was shaken for 10 s and then extracted with 10 ml of hexane for 2 min. The hexane layer was removed and concentrated to 1 ml with a stream of N2. The base-neutral fraction was obtained by dichloromethane extraction of samples adjusted to pH0 10. Extracts were analyzed using a Hewlett-Packard 5890 gas chromograph (GC) with a ¯ame ionization detector (FID) on a Supelco PTE-5 fused silica capillary column (0.25 mm diameter, 30 m long and 0.25 mm ®lm thickness). The GC conditions were: injector, 2908C; FID, 3008C; oven initially at 508C held for 1 min and then ramped at 58C/min to 3008C and held for 10 min. Peaks were identi®ed using a Hewlett-Packard 5970B mass selective detector (MS) modi®ed with the addition of a Galileo Channeltron 5772 electron multiplier. The electron impact mode was set at 7 eV. The MS was attached to a HewlettPackard 5890, Series 1 gas chromograph. Internal standards used for both MS identi®cation and peak quantitation were 2-chlorophenol (acid fraction) and tetralin (base/neutral fraction). The percent recoveries were (mean2standard deviation): 2-chlorophenol, 100 222; tetralin, 124231. Mineralization. The extent of organic carbon mineralization was monitored using a Shimadzu TOC-5000 organic carbon analyzer. Samples taken at prescribed times for
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TOC analysis were acidi®ed to pH 1 (to essentially quench the reaction), shaken to partition CO2 into the container's headspace and immediately frozen on dry ice until analysis. The TOC analysis on the timepoint samples was done without instrument sparging to avoid volatization of unreacted creosote components or their byproducts. Mineralization of added 14 C-phenanthrene and 14 C-pyrene (about 105 and 106 dpm, respectively) was determined by liquid scintillation counting after adding 2.00 ml of reaction solution to 15.0 ml Opti¯our1 scintillation cocktail (Packard Instrument Co., Meridan, CT). After the reaction was completed, the solution in the reaction vessel was sparged with air for 30 min at approximately 10 ml/ min and the air stream was passed ®rst through a Tenax1-®lled cartridge to trap 14 C volatile organic compounds (14 C-VOCs) and then through two 1 M ethanolamine solutions (10 ml) in series to trap 14 CO2. The 14 CVOC traps were subsequently eluted with hexane. The ethanolamine and hexane solutions were counted by liquid scintillation. Mineral acids (HNO3, HNO2, HCl, H2SO4) and organic acids (acetic, formic and oxalic) formation was monitored using a Dionex Ion Chromograph with an ASA-4 column. Ammonium ion concentration was determined by a modi®ed indophenol blue method (Pignatello and Sun, 1995). Toxicity. Toxicity bioassays of reaction and ``reagent water'' samples were completed by the Water Toxics Program Laboratory, Connecticut Department of Environmental Protection. ``Reagent water'' samples consisted of DI water amended with 1 mM Fe3+ and HClO4, pH 2.8. The pH of each sample was raised to 6±7 using 1M NaHCO3 to precipitate the Fe3+. Bovine catalase was added to destroy residual H2O2. (In reaction samples, H2O2 was found to be 00.5 mM by iodometric titration in the presence of NaF (Pignatello, 1992).) Established procedures (United States Environmental Protection Agency, 1995) were used to determine 48 h and 96 h acute toxicity to fathead minnows and to determine 48 h acute toxicity to Daphnia. Conditions speci®c to this study were: temperature, 208C2 18C; minimum analysis volume, 50 ml; minnow age, 14 d; Daphnia age, R24 h. RESULTS AND DISCUSSION
Parent compound transformation Data on PCP and the 36 identi®ed creosote components are listed in Table 1. In saturated aqueous solutions before treatment, naphthalene was present in the highest concentration (16.7 mg/l) and benzo[a]pyrene in the lowest concentration (0.019 mg/l) of all the compounds. The mole fraction composition of the solution with respect to the organic compounds followed the order: 2 ring PAHs (0.49)>phenolics (0.26; for PCP, 0.08)>heterocylics (0.21)>3 ring PAHs (0.03)>4±5 ring PAHs (0.01). Table 1 indicates that within 5 min 18 of the 37 compounds declined to values at or below their detection limits and all of the remaining compounds except phenanthrene, ¯uoranthene, 2,3-benzo[b]¯uorene, chrysene, benzo[b]¯uoranthene and benzo[a]pyrene were at least 90% transformed. By 180 min, 24 of the 37 compounds declined to values at or below their detection limits and all the rest except for chrysene and benzo[a]pyrene were at least 90% transformed. No new peaks appeared in the chromatograms.
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Margaret A. Engwall et al.
Table 1. Initial concentrations of 37 parent compounds identi®ed in creosote/PCP saturated water and transformation of the 37 parent compounds Compound 2 ring PAHs indane indene napththalene methylnapththalene (isomer) methylnapththalene (isomer) biphenyl dimethylnaphthalene (isomer) 3 ring PAHs acenaphthylene acenaphthene phenanthrene anthracene ¯uorene 4±5 ring PAHs ¯uoranthene pyrene 2,3-benzo[b]¯uorene chrysene benzo[b]¯uoranthene benzo[a]pyrene Heterocycles benzofuran benzo[b]thiophene quinoline isoquinoline methylquinone (isomer) dibenzofuran dibenzothiophene acridine carbazole Phenolics phenol o-cresol m-cresol p-cresol xylenol (isomer) xylenol (isomer) xylenol (isomer) 2,3,5-trimethylphenol naphthanol (isomer) pentachlorophenol
Weight fraction in P2-Creosote standarda,b
Initial conc. (mg/l) in saturated solution
Fraction transformed in 5 min
Fraction transformed in 180 min
0.00630 0.00998 0.10400
0.407 (0.327±0.487)c 2.10 (1.67±2.53) 16.7 (14.9±18.4) 2.70 (1.78±3.61) 0.651 (0.595±0.704) 0.213 (0.180±0.245) 0.080 (0.072±0.087)
1.00 1.00 1.00 0.997 (0.996±0.999)c 0.996 (0.988±1.00) 0.995 (0.986±1.01) 1.00
1.00 1.00 1.00 1.00 (0.999±1.00)c 0.999 (0.997±1.00) 1.00 1.00
0.01300 0.00322 0.53000 0.14100 0.01560 0.03900
0.947 0.567 0.485 0.101 0.467
(0.124±1.77) (0.000±1.34) (0.473±0.497) (0.081±0.120) (.437±0.497)
0.989 (0.978±1.00) 0.990 (0.970±1.01) 0.870 (0.813±0.927) 1.00 (0.964±1.05) 0.942 (0.915±0.969)
1.00 0.987 (0.965±1.01) 0.994 (0.963±1.03) 1.00 (0.913±1.12) 0.973 (0.931±1.02)
0.07870 0.03460 0.00968 0.00965 0.00496 0.00437
0.095 0.040 0.062 0.032 0.015 0.009
(0.071±0.120) (0.000±0.137) (0.038±0.085) (0.009±0.056) (0.000±0030) (0.000±0.022)
0.718 0.993 0.665 0.893 0.572 0.376
0.931 (0.845±1.02) 1.00 (0.723±2.32) 1.00 0.789 (0.154±1.42) 0.971 (0.913±1.03) 0.673 (0.013±1.33)
0.00101 0.00511 0.01540 0.00268
0.289 (0.224±0.355) 0.312 (0.264±0.361) 1.81 (1.50±2.11) 0.412 (0.344±0.479) 0.057 (0.049±0.064) 0.281 (0.247±0.315) 0.014 (0.000±0.029) 0.029 (0.029±0.030) 0.376 (0.343±0.409)
1.00 1.00 1.00 1.00 0.999 (0.968±1.03) 0.983 (0.971±0.996) 0.912 (0.739±1.09) 1.00 (0.998±1.38) 0.979 (0.963±0.996)
1.00 1.00 0.999 (0.998±1.00) 1.00 0.984 (0.957±1.01) 0.989 (0.965±1.01) 1.00 1.00 (0.953±1.33) 0.999 (0.997±1.00)
2.29 (0.979±3.59) 0.633 (0.078±1.189) 1.01 (0.407±1.61) 0.588 (0.230±0.945) 0.205 (0.177±0.234) 0.199 (0.112±0.285) 0.459 (0.402±0.517) 0.112 (0.094±0.130) 1.43 (0.847±2.017) 7.95 (2.05±13.9)
1.00 1.00 1.00 1.00 1.00 1.00 1.00 (0.996±1.01) 1.00 0.974 (0.898±1.05) 0.906 0.(0.876±0.936)
1.00 1.00 1.00 1.00 1.00 1.00 1.00 (0.988±1.04) 1.00 1.00 (0.966±1.033) 0.997 (0.991±1.00)
0.02990 0.00943 0.00202 0.00528 0.00209 0.00034 0.00154
(0.613±0.824) (ÿ1.478±3.464) (0.405±0.924) (0.787±0.998) (0.437±0.707) (0.000±0.794)
a Data supplied with the P2-Creosote standard, American Wood-Preserver's Association. bAbsence of a value means that the compound's weight fraction was less than 0.0001 or that compound isomers were not identi®ed during GC/MS analysis. Pentachlorophenol was not present in the P2-Creosote standard.c95% con®dence intervals, n = 3.
Figure 1 displays the average concentration remaining among the compounds in each class as a function of time. The reaction seems to slow down or stop after about 1 h; this could be due to depletion of H2O2. The reactivity of the creosote components followed the order: 2 ring PAHs>heterocyclics>phenolics (including PCP)>3 ring PAHs>4±5 ring PAHs. This order is approximately the same as the initial mole fraction composition of the solution. If the rate-limiting step for loss of a parent compound is its elementary . reaction with OH, the solution phase concentrations of any two components i and j at time t normalized to their concentrations at time zero are related to the ratio of their rate constants ki/kj by: ln
Ci t ki Cj t ln : Ci 0 kj Cj 0
3
Few rate constants are available for the compounds present in the creosote mixture. There is
good reason to believe, however, that PAH rate constants are close to the diusion limit in water and do not greatly dier with ring size Ð certainly not over three orders of magnitude, as Fig. 1 suggests. Hence, it is not possible to explain the . order in reactivity of the PAHs in terms of OH rate constants. Adsorption of creosote components to the vessel must be ruled out since they were absent in a solvent rinse performed at the end of the reaction. Alternatively, the dierences in reactivity may due to the presence of organic colloids in solution. Indeed, particles around 1 mm in size were detected in saturated creosite solutions that were absent in a distilled water control (Hiat Royco Particle counter); however, further studies are necessary to con®rm their nature. Partitioning of PAH into such colloids might be expected to segre. gate them from OH, which is presumably generated only in the aqueous phase and which has such a short lifetime that its concentration in non-aqueous
Degradation of wood preservatives
Fig. 1. Transformation under photo-assisted Fenton conditions of 37 parent compounds identi®ed in the creosote/ PCP saturated water classi®ed into 2-ring PAHs, 3-ring PAHs, 4- and 5-ring PAHs, heterocyclic aromatic compounds or phenolic compounds.
phases is negligible. The extent of PAH partitioning into the colloids is expected to be inversely related to their water solubility, which decreases with increasing number of rings. This expected correlation is thus consistent with the data. No reaction occurred in a control experiment carried out in the dark with a solution containing all components except H2O2; from this solution we recovered 86±132% of PAHs, 88±104% of heterocyclics and 95±99% of phenolics. Previous studies showed that transformation of pesticides in the partial systems Fe3+/H2O2, H2O2/UV and Fe3+/UV is much slower than in the complete system Fe3+/ H2O2/UV (Pignatello, 1992; Pignatello and Huang, 1993; Pignatello and Chapa, 1994; Pignatello and Sun, 1995). By comparing our results with those of Mueller et al. (1991), it is evident that the photo-Fenton reaction results in greater and far faster transformation of creosote/PCP than the microbial process. The percent photo-Fenton transformation after 3 h compared with the percent biotransformation after 14 d are as follows: 2 ring PAHs, 100%, 100%; heterocyclics, 100%, 90%; phenolics excluding PCP, 99%, 100%; 3 ring PAHs, 99%, 95%; and 4±5 ring PAHs, 85%, 65%. Very little biotransformation was detected in 1 d, whereas the photo-Fenton reaction caused signi®cant transformation in 5 min. No PCP was biotransformed, whereas we observed 99% transformation.
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Fig. 2. Mineralization of creosote components and PCP in water under photo-assisted Fenton conditions as measured by the change in the total organic carbon. Error bars represent the 95% con®dence intervals based on three separate determinations. [TOC]t and [TOC]t = 0 are the TOC concentrations at the sample time and initial time.
concentration of 7.8 2 0.9 mg/l, an 83% reduction. Figure 2 is actually a conservative estimate of mineralization because no attempt was made to sparge the solution of CO2 for fear of losing volatile organics. In order to investigate carbon mineralization of speci®c compounds, we supplemented the saturated solution with phenanthrene-9-14 C or pyrene4,5,9,10-14 C and monitored solution-phase 14 C during the reaction. Upon completion of the experiment, the solution was sparged with air that was subsequently passed through a VOC trap and two
Mineralization Figure 2 shows photo-Fenton mineralization of creosote/PCP in the saturated solution. The average initial TOC was 46.6 2 2.3 mg/l (triplicates). Within 30 min, the TOC was reduced by more than 50%. After 180 min, the TOC was reduced to an average
Fig. 3. Mineralization of phenanthrene-9-14 C amended to creosote/PCP saturated water under photo-assisted Fenton conditions. Stacked bar graph indicates mass balance: clear bar, 14 C remaining in solution after 30 min air sparge; shaded bar, 14 CO2 trapped.
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CO2 traps in series. In the case of phenanthrene-914 C (Fig. 3), the solution radioactivity was reduced to 7% of its initial value in 180 min; 94% of the radioactivity was recovered as 14 CO2 and R0.2% was recovered as 14 C-VOCs. Thus, all of the initial 14 C was accounted for at the end of the experiment. These results, together with the gas chromatographic results showing complete loss of parent compound, indicate that the 9-carbon of phenanthrene is largely mineralized and that the remainder is present in non-volatile compounds other than phenanthrene. In the case of pyrene-4,5,9,10-14 C (Fig. 4), the solution radioactivity declined to 65% of its initial value, 27% was recovered as 14 CO2 and R0.2% was recovered as 14 C-VOCs after the 180-min reaction period. Thus, 96% of the initial 14 C was accounted for at the end of the experiment. Like phenanthrene, oxidation of pyrene resulted in partial conversion of the labelled carbons to CO2 and partial conversion to nonvolatile organic products. However, the 4,5,9 and 10 carbons of pyrene collectively were mineralized less extensively than the 9-C of phenanthrene. Figure 5 shows that PCP was completely dechlorinated within 20 min. Total chloride recovery from PCP under photo-Fenton conditions suggests that toxic chlorinated by-products are not likely to be of concern in the treated water. By contrast, direct photolysis of PCP leads to chlorinated phenolic byproducts (Wong and Crosby, 1981). Mills and Homann (1993) found signi®cant dechlorination of PCP by TiO2 photocatalysis; however, it is not possible to compare our results with
Fig. 5. Formation of chloride from creosote/PCP saturated water under photo-assisted Fenton conditions. Error bars represent the 95% con®dence intervals based on ®ve separate determinations. Dashed line is the theoretical yield based on GC determination of initial PCP and dotted lines are the 95% con®dence intervals of the theoretical yield.
theirs quantitatively because the conditions are quite dierent. The presence of N- and S-heterocyclic aromatic compounds in creosote prompted us to monitor reactions for evolution of the expected inorganic nitrogen and sulfur ions. About 30% of the initial organonitrogen in solution was converted to a 2:1 + mole ratio of NH+ 4 and HNO3. Both NH4 and HNO3 are possible terminal products of organonitrogen compounds under hydroxyl radical-initiated conditions and their ratio depends in a complex manner on structure of the starting material, concentration and irradiation time (Low et al., 1991). The average ®nal NH+ 4 and HNO3 concentrations were 24.5 2 6.1 mM (n = 4) and 9.62 1.6 mM (n = 5), respectively. Nitrite ion appeared during the ®rst hour at relatively low concentrations (0.2± 6.4 mM) but then subsequently disappeared. The ®ve identi®ed N-heterocyclic parent compounds were transformed by 92±100% within 180 min (Table 1). For such compounds, ring opening is required before the nitrogen can be released in an inorganic form. Sulfate was also produced in low concentrations (0.007±0.009 mM); however, the initial concentration of organosulfur in the creosote sample was not determined. We did not detect evolution of acetate, formate, or oxalate ions. Toxicity reduction
Fig. 4. Mineralization of pyrene-4,5,9,10-14 C amended to creosote/PCP saturated water under photo-assisted Fenton conditions. Stacked bar graph indicates mass balance: clear bar, 14 C remaining in solution after 30 min air sparge; shaded bar, 14 CO2 trapped.
Results of the acute toxicity assays are given in Table 2. For the fathead minnows, photo-Fenton treatment of the saturated creosote/PCP solution for 10 min resulted in a 23-fold increase in the 48-h LD50 and a 25-fold increase in the 96-h LD50 compared to the untreated solution. Photo-Fenton oxi-
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Table 2. Toxicity to Fathead Minnows (Pimephales promelas) and Daphnia pulex of aqueous creosote/PCP solution before and after photo-assisted Fenton oxidation 48-h LDa50 A. Pimephales promelas untreated sample reagent water 10 min treated sample 180 min treated sample B. Daphnia pulex untreated sample reagent water 10 min treated sample 180 min treated sample
48-h NOALb
96-h LD50 0.006 (0.005±0.007) 0.71 (0.50±1.0) 0.15 (0.12±0.17) ND
0.01 0.71 0.23 0.56
(0.008±0.015)c (0.50±1.0) (0.19±0.26) (0.48±0.67)
ad b c b
0.008 0.50 0.12 0.10
0.03 0.16 0.34 0.55
(0.015±0.13) (0.14±0.19) (0.30±0.38) (0.10±1.0)
a b c abc
0.005 0.06 0.25 ND
96-h NOAL a b c
0.004 0.50 0.06 ND
a LD50: lethal dose to 50% of test population. Number is fraction of the original solution in the diluted test solution. bNOAL: no observed acute toxicity level. cValues in parentheses are the 95% con®dence intervals. dDown a column (a,b and c) represent signi®cant dierence at the 95% con®dence interval.
dation for 180 min resulted in a 56-fold increase in the 48-h LD50. Moreover, in each case the treated solution's toxicity was only slightly greater than that of the ``reagent water'' blank. For Daphnia, photo-Fenton treatment for 10 min resulted in an 11-fold increase in the 48-h LD50 compared to the untreated solution. Photo-Fenton treatment for 180 min resulted in an 18-fold increase in the 48-h LD50 compared to the untreated solution; although the increase was not statistically signi®cant, the trend is in the expected direction. The No Observed Acute toxicity Level (NOAL) for Daphnia followed a similar trend as the LD50. In the Mueller et al. (1991) study referred to earlier, signi®cant reduction in toxicity determined by the Microtox1 test was observed after 14 d of biological oxidation. SUMMARY
Photo Fenton oxidation eectively reduces the aqueous concentrations of 2 and 3 ring PAHs, heterocyclics and phenolic parent compounds including PCP in creosote/PCP contaminated water. Transformation of 4 and 5 ring PAHs was less complete than the other compounds. Extensive mineralization of organic carbon and complete dechlorination of PCP was observed. Major toxicity reduction to Pimephales promelas and Daphnia pulex indicates that signi®cant concentrations of toxic products are not formed. The parent compounds are transformed within minutes and extensively mineralized within a few hours starting with low hydrogen peroxide concentrations. These results indicate that photo-Fenton oxidation may be an eective treatment for creosote/PCP contaminated water. AcknowledgementsÐFunding for this project was provided by the National Science Foundation (Contract No. BES9414594). We would like to thank: Lee Dunbar and Rosemarie Gatter-Evarts at the Connecticut Department of Environmental Protection Water Toxics Program for arranging and completing, respectively, the toxicity analysis; Suzanne E. Lantz of the U.S. EPA Research Laboratory, Gulf Breeze, FL for assistance with the modi-
®ed Method 625 for PAH analysis; Dr. John Butala and the American Wood-Preserver's Association for providing the P2 creosote standard; Ruzhong Chen and Susan Devin for assistance with the photo-Fenton experiments; and Harry Pylypiw for completing GS/MS analysis of the P2 creosote and creosote/PCP contaminated water. REFERENCES
Chen R. and Pignatello J. J. (1997) Role of quinone intermediates as electron shuttles in Fenton and photoassisted Fenton oxidations of aromatic compounds. Environ. Sci. Technol. 31(8), 2399±2406. Hatheway A. W. (1997) Estimated number of manufactured gas and other coal-tar sites in the United States. Environ. Eng. Geosci. 3(1), 141±142. Huston P. L. and Pignatello J. J. (1996) Reduction of perchloroalkanes by ferrioxalate-generated carboxylate radical preceding mineralization by the photo-Fenton reaction. Environ. Sci. Technol. 30(12), 3457±3463. Lantz S. E., Montgomery M. T., Schultz W. W., Pritchard P. H., Spargo B. J. and Mueller J. G. (1997) Constituents of an organic wood preservative that inhibit the ¯ouranthene-degrading activity of Spingomonas paucimobilis strain EPA 505. Environ. Sci. Technol. 31(12), 3573±3580. Legrini O., Oliveros E. and Braun A. M. (1993) Photochemical processes for water treatment. Chem. Rev. 93, 671±698. Lewis, R. J. (1992). Sax's Dangerous Properties of Industrial Materials. Van Nostrand Reinhold, New York. Low G. K.-C., McEvoy S. R. and Mathews R. W. (1991) Formation of nitrate and ammonium ions in titanium dioxide mediated photocatalytic degradation of organic compounds containing nitrogen atoms. Environ. Sci. Technol. 31(12), 3573±3580. Mackay, D., Shiu, W. Y. and Ma, K. C. (1992a). Illustrated Handbook of Physical-Chemical Properties and Environmental Fate for Organic Chemicals. Lewis Publishers, Chelsea. Mackay, D., Shiu, W. Y. and Ma, K. C. (1992b). Illustrated Handbook of Physical-Chemical Properties and Environmental Fate for Organic Chemicals. Lewis Publishers, Chelsea. Mills G. and Homann M. R. (1993) Photocatalytic degradation of pentachlorophenol on TiO2 particles: identi®cation of intermediates and mechanism of reaction. Environ. Sci. Technol. 27(8), 1681±1689. Mueller J. G., Chapman P. J. and Pritchard P. H. (1989) Creosote-contaminated sites Ð Their potential for bioremediation. Environ. Sci. Technol. 23(10), 1197±1201. Mueller J. G., Middaugh D. P., Lantz S. E. and Chapman P. J. (1991) Biodegradation of creosote and pentachlor-
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ophenol in contaminated groundwater: chemical and biological assessment. Appl. Environ. Microbiol. 57(5), 1277±1285. Peters C. A. and Luthy R. G. (1993) Coal tar dissolution in water-miscible solvents: experimental evaluation. Environ. Sci. Technol. 27(13), 2831±2843. Pignatello J. J. (1992) Dark and photoassisted Fe3+-catalyzed degradation of chlorophenoxy herbicides by hydrogen peroxide. Environ. Sci. Technol. 26(5), 944± 951. Pignatello J. J. and Chapa G. (1994) Degradation of PCBs by ferric ion, hydrogen peroxide and UV light. Environ. Toxicol. Chem. 13(3), 423±427. Pignatello J. J. and Huang L. Q. (1993) Degradation of polychlorinated dibenzo-p-dioxin and dibenzofuran contaminants in 2,4,5-T by photoassisted iron-catalyzed hydrogen peroxide. Water Res. 27(12), 1731±1736. Pignatello J. J. and Sun Y. (1995) Complete oxidation of metolachlor and methyl parathion in water by the photoassisted Fenton reaction. Water Res. 57(8), 1837± 1844. Sarazadeh-Amiri A., Bolton J. R. and Cater S. R. (1996)
The use of iron in advanced oxidation processes. J. Adv. Oxid. Technol. 1, 18±26. Serpone N., Terzian R., Lawless D., Pelletier A. M., Minero C. and Pellzzetti E. (1994). Photocatalyzed destruction of water contaminants: mineralization of aquatic creosote phenolics and creosote by irradiated particulates of the white paint pigment titania. In Aquatic and Surface Photochemistry, ed. G. R. Helz, R. G. Zepp and D. G. Crosby, pp. 387±398. Lewis Publishers, Boco Raton, FL. Sun Y. and Pignatello J. J. (1993) Photochemical reactions involved in the total mineralization of 2,4-D by Fe3+/ H2O2/UV. Environ. Sci. Technol. 27(2), 304±310. United States Environmental Protection Agency. (1984). Creosote - Special Review Position Document 2/3. U.S. Government Printing Oce, Washington, D.C. United States Environmental Protection Agency. (1995). Whole Euent Toxicity: Guidelines Establishing Test Procedures for the Analysis of Pollutants, Final Rule. Federal Register, 40 CFR Part 136. Wong A. S. and Crosby D. G. (1981) Photodecomposition of pentachlorophenol in water. J. Agric. Food Chem. 29, 125±130.
Wat. Res. Vol. 33, No. 5, pp. 1151±1158, 1999 # 1999 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0043-1354/99/$ - see front matter
DEGRADATION AND DETOXIFICATION OF THE WOOD PRESERVATIVES CREOSOTE AND PENTACHLOROPHENOL IN WATER BY THE PHOTOFENTON REACTION M MARGARET A. ENGWALL12, JOSEPH J. PIGNATELLO12** and 2* M DOMENICO GRASSO
Department of Soil and Water, The Connecticut Agricultural Experiment Station, P.O. Box 1106, New Haven, CT 06504, U.S.A. and 2Department of Civil and Environmental Engineering, The University of Connecticut, 261 Glenbrook Rd., U-37, Storrs, CT 06269-2037, U.S.A.
1
(First received March 1998; accepted in revised form July 1998) AbstractÐPentachlorophenol (PCP) and the organic compounds in creosote often contaminate groundwater at wood preserving facilities. Since many of these compounds are toxic, eective water treatment technologies must be identi®ed. In laboratory scale experiments saturated aqueous solutions of creosote and PCP were treated by the photo-assisted Fenton reaction, Fe3+/H2O2/UV ([Fe3+] = 1 mM, [H2O2] = 10 mM, 1.4 10ÿ3 M hn minÿ1 black lamp ultraviolet light (UV), pH = 2.75 and 258C). The disappearance of 37 polycyclic aromatic hydrocarbons (PAHs), O, N and S-heterocyclic aromatic compounds and phenolic compounds and their mineralization products were monitored during a 180 min reaction period. Substantial (>90%) transformation of all compounds except a few 4- and 5-ring PAHs was achieved in 5 min, with more extensive transformation occurring thereafter. The reactivity followed the order: 2 ring PAHs>heterocyclics>phenolics>3 ring PAHs>4±5 ring PAHs. Complete dechlorination of PCP required only 10±20 min. Within 180 min the total organic carbon concentration declined by about 80% and added 9-14 C-phenanthrene or 4,5,9,10-14 C-pyrene were mineralized by 93% and 35%, respectively. About 33% of the organic nitrogen was converted to a 2:1 mole ratio of NH+ 4 and HNO3 and trace amounts of HNO2. An undetermined yield of sulfate was also generated. The acute toxicity of the treated solution to fathead minnows (Pimephales promelas) was nearly eliminated and the acute toxicity to daphnia (Daphnia pulex) was reduced. These results demonstrate the ecacy of Fe3+/H2O2/UV for removing creosote and PCP in water. # 1999 Elsevier Science Ltd. All rights reserved Key wordsÐcreosote, pentachorophenol, polycyclic aromatic hydrocarbons, phenols, heterocyclic aromatic compounds, Fenton reagent, water treatment, advanced oxidation processes
INTRODUCTION
Creosote and pentachlorophenol (PCP) are used as wood preservatives, often in combination. The organic constituents of creosote include polycyclic aromatic hydrocarbons (PAHs, 85%), phenolic compounds (10%) and N-, S- and O-heterocyclic aromatic compounds (5%) (Mueller et al., 1989). Due to past handling and disposal practices the soil and groundwater at many wood preservation facilities have become contaminated with these substances. Although the ``pump-and-treat'' approach is losing favor as a stand-alone remediation technology for aquifers, extraction wells are often utilized as a method of plume containment and require concomitant aqueous phase treatment. A need exists, therefore, to develop economical methods to *Author to whom all correspondence should be addressed. [Tel.: +1-203-974-8518; Fax: +1-203-974-8502; Email, [email protected]].
remove creosote and PCP in the contaminated water. Previous eorts have employed microorganisms (Mueller et al., 1991) or photocatalysis (Serpone et al., 1994). In this study, we investigated the photo-assisted Fenton (photo-Fenton) reaction for its ability to oxidize PCP and creosote and reduce the toxicity of the water. The photo-Fenton reaction employs ferric ion (Fe3+), hydrogen peroxide (H2O2) and UV light and has been shown eective in mineralizing a wide variety of organic pollutants in water (Pignatello, 1992; Sun and Pignatello, 1993; Pignatello and Sun, 1995; Sarazadeh-Amiri et al., 1996). After determining the identity and concentrations of the compounds that partition into water from a nonaqueous creosote/PCP phase we determined the extent of transformation of each compound, the degree of total organic carbon removal and the yield of selected inorganic ions. Finally, we measured the reduction in toxicity of the solution to two dierent organisms.
1151
1152
Margaret A. Engwall et al. BACKGROUND
Creosote is a distillate of coal tar (United States Environmental Protection Agency, 1984). As of May, 1997 there were 59 sites on the U.S. Environmental Protection Agency (USEPA) Final National Priorities List involving past creosote/PCP wood preserving operations. Creosote contaminated sites have been identi®ed in Denmark, Canada, Greenland, Sweden and the United Kingdom, as well. Coal tar, formed during the high temperature carbonization of coal (United States Environmental Protection Agency, 1984), was produced in large quantities as a byproduct of coal gasi®cation until the early 1900s when it was replaced by natural gas. Coal tar is similar in composition to creosote in that it is a complex mixture mainly of PAHs. It has been estimated that there are at least 1000 (Peters and Luthy, 1993) and potentially as many as 32,600 (Hatheway, 1997) former manufactured gas plant sites that produced coal tar. The present study focuses on those organic compounds that partition into water from the creosote phase because of their potential to contaminate both surface and groundwater. Single-component water solubilities of the compounds studied range from 0105 mg/l for phenol to 010ÿ3 mg/l for benzo[b]¯uoranthene (Mackay et al., 1992a,b). Biodegradation of creosote/PCP in water is slow and incomplete; Mueller et al. (1991) found that after 14 d only 42% of the monitored creosote constituents in groundwater were completely converted. Lantz et al. (1997) found that certain creosote components either inhibited or were toxic to a ¯uoranthene-degrading microorganism and concluded that these eects may have contibuted to the limited extent of bioremediation. Advanced oxidation pro. cesses based on hydroxyl radical ( OH) chemistry, such as hydrogen peroxide based systems, ozone based systems and photocatalysis, can eciently oxidize many organic compounds in water (Legrini et al., 1993) and therefore are a logical alternative to biodegradation. Hydroxyl radicals, which are formed in solution or on the surface of the photocatalyst, react non-selectively with organic compounds via H-abstraction and addition to C±C unsaturated bonds. Mills and Homann (1993) reported that PCP is approximately 96% mineralized photocataytically by TiO2 in 90 min. Serpone et al. (1994) applied photocatalysis to the treatment of separate-phase creosote in water. The investigated compounds appeared to be 100% mineralized in 6±15 h, depending on the initial creosote concentration (Serpone et al., 1994). Previous research has shown success in degrading various organic compounds in water using the photo-assisted Fenton reaction (Pignatello, 1992; Sun and Pignatello, 1993; Pignatello and Sun, 1995; Sarazadeh-Amiri et al., 1996). Critical steps in the photo-Fenton process are:
. ÿ4Fe OH ÿ 2 OH, Fe2 H2 O2 ÿ
1
. 2 Fe OH2 hÿ ÿ4Fe ÿ OH:
2
The classical Fenton reaction in equation 1 is assisted by the photoreduction step in equation 2 which takes place in the near UV region and results in the regeneration of Fe(II) and production of . OH. The full sequence of inorganic reactions . involved in formation and decay of OH has been discussed elsewhere (Chen and Pignatello, 1997). While direct photolysis of hydrogen peroxide also . yields OH, hydrogen peroxide absorbs weakly in the ultraviolet range. The extinction coecient at 254 nm is 19.6 Mÿ1 cmÿ1 and approaches zero as the wavelength increases to 0320 nm. Hence, hydrogen peroxide direct photolysis is inhibited by absorbing organics. The aqueous saturated creosote/PCP solution used in the present study begins to absorb appreciably at about 340 nm and reaches an absorbance of 1.0 at about 300 nm and 1.4 at about 250 nm. Thus, the solution blocks most of the light at wavelengths required for hydrogen peroxide direct photolysis. PCP and many of the organic compounds found in creosote are acutely toxic, may produce animal and human cell mutations and may be teratogenic or exhibit other reproductive eects (Lewis, 1992). Reduction in toxicity of the treated water is a critical measure of the success of any treatment method, since the formation of toxic organic by-products is possible. In this study, we determined the LD50 (the statistically determined dose that causes 50% mortality in a given exposure period) of the aqueous creosote solution before and after photo-Fenton treatment using Pimephales promelas (fathead minnows) and Daphnia pulex (Daphnia) as test organisms. Such data is an indication of acute toxicity reduction resulting from treatment. MATERIALS AND METHODS
All reagents were used as received: perchloric acid (J.T. Baker), sodium perchlorate (99%, GFS Chemical), hydrogen peroxide (30% solution, Fisher), phenanthrene-9-14 C (59.5 mCi/mmol, 99% radiolabel purity, Sigma), pyrene4,5,9,10-14 C (58.7 mCi/mmol, 99% radiolabel purity, Sigma), tetralin (1,2,3,4-tetrahydronaphthalene, 99%, Aldrich), 2-chlorophenol (100%, Kodak), PCP (85%, ICN Biomedicals, Inc.), Bovine catalase (Thymol-free, Sigma) and ethanolamine (Laboratory grade, Fisher). American Creosote-P2, historically used to treat railroad ties, was provided by the American Wood-Preserver's Association. Glassware was rinsed three times with ethanol, washed with detergent and rinsed three times each with Type I distilled/deionized (DI) water, acetone and hexane prior to drying. Glassware exposed to Fe3+ was rinsed with 1 M HClO4. Aqueous solutions were prepared with Type I distilled/deionized water. Photo-assisted Fenton Reactions Test solutions were prepared by contacting 2 g of American Creosote-P2 and 2 g of PCP with 2 l of DI water for at least 10 d in the dark at laboratory ambient
Degradation of wood preservatives temperatures with stirring for the ®rst 24 h. Initial experiments indicated that 10 d was sucient to achieve saturation. After ®ltering through glass wool to remove any separate phase, the test solution was stored in a Te¯onsealed screw-top glass ¯ask at 48C in the dark. No phase separation of the creosote was observed during storage. The test solution (360 ml) was transferred to a covered 400 ml cylindrical double-walled borosilicate reaction vessel (Huston and Pignatello, 1996) by siphoning with a Te¯on tube. The vessel was then sealed with a Te¯on-lined screw cap and allowed to temperature equilibrate for at least 25 min at 2520.18C, which was maintained by circulating water from an external bath through the vessel jacket. Henry's Law calculations indicated that R0.1% of each compound would partition into the vessel headspace. Next, freshly prepared ferric perchlorate (Fe(ClO4)3) solution was added to the vessel to achieve 1 mM Fe3+ and the pH adjusted to 2.7520.05 using 0.1 M HClO4 or 0.1 M NaHCO3 solution. (The perchlorate salt of Fe(III) was chosen in this research to avoid metal ion complexation, light absorption and chemical and photochemical reactions involving the counterion (Pignatello, 1992); although the sulfate, chloride and nitrate salts are less desirable with respect to these considerations, it should be noted that they are more available and less expensive to use on a commercial scale and possibly more desirable because they exist naturally). Finally, iodometrically-standarized H2O2 solution was added to a concentration of 10 mM. The mole ratio of hydrogen peroxide to total organics was about 40:1. The vessel was then re-sealed, placed under an atmosphere of oxygen and inserted into a Rayonet RPR-200 chamber with 16 14-W ¯uorescent black lamps that emit at wavelengths between 300 and 400 nm. The light intensity was 1.4 10ÿ3 M photons minÿ1, as determined by ferrioxalate actinometry. The lamps were turned on at least 10 min in advance to insure constant output. The contents of the vessel were stirred using a magnetic stirrer. Samples were taken at intervals and quenched with methanol (0.5 ml CH3OH per 50 ml solution) containing analytical internal standards. Analytical techniques Parent compound transformation. A modi®ed acid/baseneutral fractionation method (EPA Method 625) was used to extract and quantify 37 parent compounds. The phenolic compounds (acid fraction) were derivatized to their acetate esters by addition of 1 ml of saturated K3PO4 and 200 ml of acetic anhydride to a 10 ml aliquot of sample initially at pH0 2. The sample was shaken for 10 s and then extracted with 10 ml of hexane for 2 min. The hexane layer was removed and concentrated to 1 ml with a stream of N2. The base-neutral fraction was obtained by dichloromethane extraction of samples adjusted to pH0 10. Extracts were analyzed using a Hewlett-Packard 5890 gas chromograph (GC) with a ¯ame ionization detector (FID) on a Supelco PTE-5 fused silica capillary column (0.25 mm diameter, 30 m long and 0.25 mm ®lm thickness). The GC conditions were: injector, 2908C; FID, 3008C; oven initially at 508C held for 1 min and then ramped at 58C/min to 3008C and held for 10 min. Peaks were identi®ed using a Hewlett-Packard 5970B mass selective detector (MS) modi®ed with the addition of a Galileo Channeltron 5772 electron multiplier. The electron impact mode was set at 7 eV. The MS was attached to a HewlettPackard 5890, Series 1 gas chromograph. Internal standards used for both MS identi®cation and peak quantitation were 2-chlorophenol (acid fraction) and tetralin (base/neutral fraction). The percent recoveries were (mean2standard deviation): 2-chlorophenol, 100 222; tetralin, 124231. Mineralization. The extent of organic carbon mineralization was monitored using a Shimadzu TOC-5000 organic carbon analyzer. Samples taken at prescribed times for
1153
TOC analysis were acidi®ed to pH 1 (to essentially quench the reaction), shaken to partition CO2 into the container's headspace and immediately frozen on dry ice until analysis. The TOC analysis on the timepoint samples was done without instrument sparging to avoid volatization of unreacted creosote components or their byproducts. Mineralization of added 14 C-phenanthrene and 14 C-pyrene (about 105 and 106 dpm, respectively) was determined by liquid scintillation counting after adding 2.00 ml of reaction solution to 15.0 ml Opti¯our1 scintillation cocktail (Packard Instrument Co., Meridan, CT). After the reaction was completed, the solution in the reaction vessel was sparged with air for 30 min at approximately 10 ml/ min and the air stream was passed ®rst through a Tenax1-®lled cartridge to trap 14 C volatile organic compounds (14 C-VOCs) and then through two 1 M ethanolamine solutions (10 ml) in series to trap 14 CO2. The 14 CVOC traps were subsequently eluted with hexane. The ethanolamine and hexane solutions were counted by liquid scintillation. Mineral acids (HNO3, HNO2, HCl, H2SO4) and organic acids (acetic, formic and oxalic) formation was monitored using a Dionex Ion Chromograph with an ASA-4 column. Ammonium ion concentration was determined by a modi®ed indophenol blue method (Pignatello and Sun, 1995). Toxicity. Toxicity bioassays of reaction and ``reagent water'' samples were completed by the Water Toxics Program Laboratory, Connecticut Department of Environmental Protection. ``Reagent water'' samples consisted of DI water amended with 1 mM Fe3+ and HClO4, pH 2.8. The pH of each sample was raised to 6±7 using 1M NaHCO3 to precipitate the Fe3+. Bovine catalase was added to destroy residual H2O2. (In reaction samples, H2O2 was found to be 00.5 mM by iodometric titration in the presence of NaF (Pignatello, 1992).) Established procedures (United States Environmental Protection Agency, 1995) were used to determine 48 h and 96 h acute toxicity to fathead minnows and to determine 48 h acute toxicity to Daphnia. Conditions speci®c to this study were: temperature, 208C2 18C; minimum analysis volume, 50 ml; minnow age, 14 d; Daphnia age, R24 h. RESULTS AND DISCUSSION
Parent compound transformation Data on PCP and the 36 identi®ed creosote components are listed in Table 1. In saturated aqueous solutions before treatment, naphthalene was present in the highest concentration (16.7 mg/l) and benzo[a]pyrene in the lowest concentration (0.019 mg/l) of all the compounds. The mole fraction composition of the solution with respect to the organic compounds followed the order: 2 ring PAHs (0.49)>phenolics (0.26; for PCP, 0.08)>heterocylics (0.21)>3 ring PAHs (0.03)>4±5 ring PAHs (0.01). Table 1 indicates that within 5 min 18 of the 37 compounds declined to values at or below their detection limits and all of the remaining compounds except phenanthrene, ¯uoranthene, 2,3-benzo[b]¯uorene, chrysene, benzo[b]¯uoranthene and benzo[a]pyrene were at least 90% transformed. By 180 min, 24 of the 37 compounds declined to values at or below their detection limits and all the rest except for chrysene and benzo[a]pyrene were at least 90% transformed. No new peaks appeared in the chromatograms.
1154
Margaret A. Engwall et al.
Table 1. Initial concentrations of 37 parent compounds identi®ed in creosote/PCP saturated water and transformation of the 37 parent compounds Compound 2 ring PAHs indane indene napththalene methylnapththalene (isomer) methylnapththalene (isomer) biphenyl dimethylnaphthalene (isomer) 3 ring PAHs acenaphthylene acenaphthene phenanthrene anthracene ¯uorene 4±5 ring PAHs ¯uoranthene pyrene 2,3-benzo[b]¯uorene chrysene benzo[b]¯uoranthene benzo[a]pyrene Heterocycles benzofuran benzo[b]thiophene quinoline isoquinoline methylquinone (isomer) dibenzofuran dibenzothiophene acridine carbazole Phenolics phenol o-cresol m-cresol p-cresol xylenol (isomer) xylenol (isomer) xylenol (isomer) 2,3,5-trimethylphenol naphthanol (isomer) pentachlorophenol
Weight fraction in P2-Creosote standarda,b
Initial conc. (mg/l) in saturated solution
Fraction transformed in 5 min
Fraction transformed in 180 min
0.00630 0.00998 0.10400
0.407 (0.327±0.487)c 2.10 (1.67±2.53) 16.7 (14.9±18.4) 2.70 (1.78±3.61) 0.651 (0.595±0.704) 0.213 (0.180±0.245) 0.080 (0.072±0.087)
1.00 1.00 1.00 0.997 (0.996±0.999)c 0.996 (0.988±1.00) 0.995 (0.986±1.01) 1.00
1.00 1.00 1.00 1.00 (0.999±1.00)c 0.999 (0.997±1.00) 1.00 1.00
0.01300 0.00322 0.53000 0.14100 0.01560 0.03900
0.947 0.567 0.485 0.101 0.467
(0.124±1.77) (0.000±1.34) (0.473±0.497) (0.081±0.120) (.437±0.497)
0.989 (0.978±1.00) 0.990 (0.970±1.01) 0.870 (0.813±0.927) 1.00 (0.964±1.05) 0.942 (0.915±0.969)
1.00 0.987 (0.965±1.01) 0.994 (0.963±1.03) 1.00 (0.913±1.12) 0.973 (0.931±1.02)
0.07870 0.03460 0.00968 0.00965 0.00496 0.00437
0.095 0.040 0.062 0.032 0.015 0.009
(0.071±0.120) (0.000±0.137) (0.038±0.085) (0.009±0.056) (0.000±0030) (0.000±0.022)
0.718 0.993 0.665 0.893 0.572 0.376
0.931 (0.845±1.02) 1.00 (0.723±2.32) 1.00 0.789 (0.154±1.42) 0.971 (0.913±1.03) 0.673 (0.013±1.33)
0.00101 0.00511 0.01540 0.00268
0.289 (0.224±0.355) 0.312 (0.264±0.361) 1.81 (1.50±2.11) 0.412 (0.344±0.479) 0.057 (0.049±0.064) 0.281 (0.247±0.315) 0.014 (0.000±0.029) 0.029 (0.029±0.030) 0.376 (0.343±0.409)
1.00 1.00 1.00 1.00 0.999 (0.968±1.03) 0.983 (0.971±0.996) 0.912 (0.739±1.09) 1.00 (0.998±1.38) 0.979 (0.963±0.996)
1.00 1.00 0.999 (0.998±1.00) 1.00 0.984 (0.957±1.01) 0.989 (0.965±1.01) 1.00 1.00 (0.953±1.33) 0.999 (0.997±1.00)
2.29 (0.979±3.59) 0.633 (0.078±1.189) 1.01 (0.407±1.61) 0.588 (0.230±0.945) 0.205 (0.177±0.234) 0.199 (0.112±0.285) 0.459 (0.402±0.517) 0.112 (0.094±0.130) 1.43 (0.847±2.017) 7.95 (2.05±13.9)
1.00 1.00 1.00 1.00 1.00 1.00 1.00 (0.996±1.01) 1.00 0.974 (0.898±1.05) 0.906 0.(0.876±0.936)
1.00 1.00 1.00 1.00 1.00 1.00 1.00 (0.988±1.04) 1.00 1.00 (0.966±1.033) 0.997 (0.991±1.00)
0.02990 0.00943 0.00202 0.00528 0.00209 0.00034 0.00154
(0.613±0.824) (ÿ1.478±3.464) (0.405±0.924) (0.787±0.998) (0.437±0.707) (0.000±0.794)
a Data supplied with the P2-Creosote standard, American Wood-Preserver's Association. bAbsence of a value means that the compound's weight fraction was less than 0.0001 or that compound isomers were not identi®ed during GC/MS analysis. Pentachlorophenol was not present in the P2-Creosote standard.c95% con®dence intervals, n = 3.
Figure 1 displays the average concentration remaining among the compounds in each class as a function of time. The reaction seems to slow down or stop after about 1 h; this could be due to depletion of H2O2. The reactivity of the creosote components followed the order: 2 ring PAHs>heterocyclics>phenolics (including PCP)>3 ring PAHs>4±5 ring PAHs. This order is approximately the same as the initial mole fraction composition of the solution. If the rate-limiting step for loss of a parent compound is its elementary . reaction with OH, the solution phase concentrations of any two components i and j at time t normalized to their concentrations at time zero are related to the ratio of their rate constants ki/kj by: ln
Ci t ki Cj t ln : Ci 0 kj Cj 0
3
Few rate constants are available for the compounds present in the creosote mixture. There is
good reason to believe, however, that PAH rate constants are close to the diusion limit in water and do not greatly dier with ring size Ð certainly not over three orders of magnitude, as Fig. 1 suggests. Hence, it is not possible to explain the . order in reactivity of the PAHs in terms of OH rate constants. Adsorption of creosote components to the vessel must be ruled out since they were absent in a solvent rinse performed at the end of the reaction. Alternatively, the dierences in reactivity may due to the presence of organic colloids in solution. Indeed, particles around 1 mm in size were detected in saturated creosite solutions that were absent in a distilled water control (Hiat Royco Particle counter); however, further studies are necessary to con®rm their nature. Partitioning of PAH into such colloids might be expected to segre. gate them from OH, which is presumably generated only in the aqueous phase and which has such a short lifetime that its concentration in non-aqueous
Degradation of wood preservatives
Fig. 1. Transformation under photo-assisted Fenton conditions of 37 parent compounds identi®ed in the creosote/ PCP saturated water classi®ed into 2-ring PAHs, 3-ring PAHs, 4- and 5-ring PAHs, heterocyclic aromatic compounds or phenolic compounds.
phases is negligible. The extent of PAH partitioning into the colloids is expected to be inversely related to their water solubility, which decreases with increasing number of rings. This expected correlation is thus consistent with the data. No reaction occurred in a control experiment carried out in the dark with a solution containing all components except H2O2; from this solution we recovered 86±132% of PAHs, 88±104% of heterocyclics and 95±99% of phenolics. Previous studies showed that transformation of pesticides in the partial systems Fe3+/H2O2, H2O2/UV and Fe3+/UV is much slower than in the complete system Fe3+/ H2O2/UV (Pignatello, 1992; Pignatello and Huang, 1993; Pignatello and Chapa, 1994; Pignatello and Sun, 1995). By comparing our results with those of Mueller et al. (1991), it is evident that the photo-Fenton reaction results in greater and far faster transformation of creosote/PCP than the microbial process. The percent photo-Fenton transformation after 3 h compared with the percent biotransformation after 14 d are as follows: 2 ring PAHs, 100%, 100%; heterocyclics, 100%, 90%; phenolics excluding PCP, 99%, 100%; 3 ring PAHs, 99%, 95%; and 4±5 ring PAHs, 85%, 65%. Very little biotransformation was detected in 1 d, whereas the photo-Fenton reaction caused signi®cant transformation in 5 min. No PCP was biotransformed, whereas we observed 99% transformation.
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Fig. 2. Mineralization of creosote components and PCP in water under photo-assisted Fenton conditions as measured by the change in the total organic carbon. Error bars represent the 95% con®dence intervals based on three separate determinations. [TOC]t and [TOC]t = 0 are the TOC concentrations at the sample time and initial time.
concentration of 7.8 2 0.9 mg/l, an 83% reduction. Figure 2 is actually a conservative estimate of mineralization because no attempt was made to sparge the solution of CO2 for fear of losing volatile organics. In order to investigate carbon mineralization of speci®c compounds, we supplemented the saturated solution with phenanthrene-9-14 C or pyrene4,5,9,10-14 C and monitored solution-phase 14 C during the reaction. Upon completion of the experiment, the solution was sparged with air that was subsequently passed through a VOC trap and two
Mineralization Figure 2 shows photo-Fenton mineralization of creosote/PCP in the saturated solution. The average initial TOC was 46.6 2 2.3 mg/l (triplicates). Within 30 min, the TOC was reduced by more than 50%. After 180 min, the TOC was reduced to an average
Fig. 3. Mineralization of phenanthrene-9-14 C amended to creosote/PCP saturated water under photo-assisted Fenton conditions. Stacked bar graph indicates mass balance: clear bar, 14 C remaining in solution after 30 min air sparge; shaded bar, 14 CO2 trapped.
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Margaret A. Engwall et al.
CO2 traps in series. In the case of phenanthrene-914 C (Fig. 3), the solution radioactivity was reduced to 7% of its initial value in 180 min; 94% of the radioactivity was recovered as 14 CO2 and R0.2% was recovered as 14 C-VOCs. Thus, all of the initial 14 C was accounted for at the end of the experiment. These results, together with the gas chromatographic results showing complete loss of parent compound, indicate that the 9-carbon of phenanthrene is largely mineralized and that the remainder is present in non-volatile compounds other than phenanthrene. In the case of pyrene-4,5,9,10-14 C (Fig. 4), the solution radioactivity declined to 65% of its initial value, 27% was recovered as 14 CO2 and R0.2% was recovered as 14 C-VOCs after the 180-min reaction period. Thus, 96% of the initial 14 C was accounted for at the end of the experiment. Like phenanthrene, oxidation of pyrene resulted in partial conversion of the labelled carbons to CO2 and partial conversion to nonvolatile organic products. However, the 4,5,9 and 10 carbons of pyrene collectively were mineralized less extensively than the 9-C of phenanthrene. Figure 5 shows that PCP was completely dechlorinated within 20 min. Total chloride recovery from PCP under photo-Fenton conditions suggests that toxic chlorinated by-products are not likely to be of concern in the treated water. By contrast, direct photolysis of PCP leads to chlorinated phenolic byproducts (Wong and Crosby, 1981). Mills and Homann (1993) found signi®cant dechlorination of PCP by TiO2 photocatalysis; however, it is not possible to compare our results with
Fig. 5. Formation of chloride from creosote/PCP saturated water under photo-assisted Fenton conditions. Error bars represent the 95% con®dence intervals based on ®ve separate determinations. Dashed line is the theoretical yield based on GC determination of initial PCP and dotted lines are the 95% con®dence intervals of the theoretical yield.
theirs quantitatively because the conditions are quite dierent. The presence of N- and S-heterocyclic aromatic compounds in creosote prompted us to monitor reactions for evolution of the expected inorganic nitrogen and sulfur ions. About 30% of the initial organonitrogen in solution was converted to a 2:1 + mole ratio of NH+ 4 and HNO3. Both NH4 and HNO3 are possible terminal products of organonitrogen compounds under hydroxyl radical-initiated conditions and their ratio depends in a complex manner on structure of the starting material, concentration and irradiation time (Low et al., 1991). The average ®nal NH+ 4 and HNO3 concentrations were 24.5 2 6.1 mM (n = 4) and 9.62 1.6 mM (n = 5), respectively. Nitrite ion appeared during the ®rst hour at relatively low concentrations (0.2± 6.4 mM) but then subsequently disappeared. The ®ve identi®ed N-heterocyclic parent compounds were transformed by 92±100% within 180 min (Table 1). For such compounds, ring opening is required before the nitrogen can be released in an inorganic form. Sulfate was also produced in low concentrations (0.007±0.009 mM); however, the initial concentration of organosulfur in the creosote sample was not determined. We did not detect evolution of acetate, formate, or oxalate ions. Toxicity reduction
Fig. 4. Mineralization of pyrene-4,5,9,10-14 C amended to creosote/PCP saturated water under photo-assisted Fenton conditions. Stacked bar graph indicates mass balance: clear bar, 14 C remaining in solution after 30 min air sparge; shaded bar, 14 CO2 trapped.
Results of the acute toxicity assays are given in Table 2. For the fathead minnows, photo-Fenton treatment of the saturated creosote/PCP solution for 10 min resulted in a 23-fold increase in the 48-h LD50 and a 25-fold increase in the 96-h LD50 compared to the untreated solution. Photo-Fenton oxi-
Degradation of wood preservatives
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Table 2. Toxicity to Fathead Minnows (Pimephales promelas) and Daphnia pulex of aqueous creosote/PCP solution before and after photo-assisted Fenton oxidation 48-h LDa50 A. Pimephales promelas untreated sample reagent water 10 min treated sample 180 min treated sample B. Daphnia pulex untreated sample reagent water 10 min treated sample 180 min treated sample
48-h NOALb
96-h LD50 0.006 (0.005±0.007) 0.71 (0.50±1.0) 0.15 (0.12±0.17) ND
0.01 0.71 0.23 0.56
(0.008±0.015)c (0.50±1.0) (0.19±0.26) (0.48±0.67)
ad b c b
0.008 0.50 0.12 0.10
0.03 0.16 0.34 0.55
(0.015±0.13) (0.14±0.19) (0.30±0.38) (0.10±1.0)
a b c abc
0.005 0.06 0.25 ND
96-h NOAL a b c
0.004 0.50 0.06 ND
a LD50: lethal dose to 50% of test population. Number is fraction of the original solution in the diluted test solution. bNOAL: no observed acute toxicity level. cValues in parentheses are the 95% con®dence intervals. dDown a column (a,b and c) represent signi®cant dierence at the 95% con®dence interval.
dation for 180 min resulted in a 56-fold increase in the 48-h LD50. Moreover, in each case the treated solution's toxicity was only slightly greater than that of the ``reagent water'' blank. For Daphnia, photo-Fenton treatment for 10 min resulted in an 11-fold increase in the 48-h LD50 compared to the untreated solution. Photo-Fenton treatment for 180 min resulted in an 18-fold increase in the 48-h LD50 compared to the untreated solution; although the increase was not statistically signi®cant, the trend is in the expected direction. The No Observed Acute toxicity Level (NOAL) for Daphnia followed a similar trend as the LD50. In the Mueller et al. (1991) study referred to earlier, signi®cant reduction in toxicity determined by the Microtox1 test was observed after 14 d of biological oxidation. SUMMARY
Photo Fenton oxidation eectively reduces the aqueous concentrations of 2 and 3 ring PAHs, heterocyclics and phenolic parent compounds including PCP in creosote/PCP contaminated water. Transformation of 4 and 5 ring PAHs was less complete than the other compounds. Extensive mineralization of organic carbon and complete dechlorination of PCP was observed. Major toxicity reduction to Pimephales promelas and Daphnia pulex indicates that signi®cant concentrations of toxic products are not formed. The parent compounds are transformed within minutes and extensively mineralized within a few hours starting with low hydrogen peroxide concentrations. These results indicate that photo-Fenton oxidation may be an eective treatment for creosote/PCP contaminated water. AcknowledgementsÐFunding for this project was provided by the National Science Foundation (Contract No. BES9414594). We would like to thank: Lee Dunbar and Rosemarie Gatter-Evarts at the Connecticut Department of Environmental Protection Water Toxics Program for arranging and completing, respectively, the toxicity analysis; Suzanne E. Lantz of the U.S. EPA Research Laboratory, Gulf Breeze, FL for assistance with the modi-
®ed Method 625 for PAH analysis; Dr. John Butala and the American Wood-Preserver's Association for providing the P2 creosote standard; Ruzhong Chen and Susan Devin for assistance with the photo-Fenton experiments; and Harry Pylypiw for completing GS/MS analysis of the P2 creosote and creosote/PCP contaminated water. REFERENCES
Chen R. and Pignatello J. J. (1997) Role of quinone intermediates as electron shuttles in Fenton and photoassisted Fenton oxidations of aromatic compounds. Environ. Sci. Technol. 31(8), 2399±2406. Hatheway A. W. (1997) Estimated number of manufactured gas and other coal-tar sites in the United States. Environ. Eng. Geosci. 3(1), 141±142. Huston P. L. and Pignatello J. J. (1996) Reduction of perchloroalkanes by ferrioxalate-generated carboxylate radical preceding mineralization by the photo-Fenton reaction. Environ. Sci. Technol. 30(12), 3457±3463. Lantz S. E., Montgomery M. T., Schultz W. W., Pritchard P. H., Spargo B. J. and Mueller J. G. (1997) Constituents of an organic wood preservative that inhibit the ¯ouranthene-degrading activity of Spingomonas paucimobilis strain EPA 505. Environ. Sci. Technol. 31(12), 3573±3580. Legrini O., Oliveros E. and Braun A. M. (1993) Photochemical processes for water treatment. Chem. Rev. 93, 671±698. Lewis, R. J. (1992). Sax's Dangerous Properties of Industrial Materials. Van Nostrand Reinhold, New York. Low G. K.-C., McEvoy S. R. and Mathews R. W. (1991) Formation of nitrate and ammonium ions in titanium dioxide mediated photocatalytic degradation of organic compounds containing nitrogen atoms. Environ. Sci. Technol. 31(12), 3573±3580. Mackay, D., Shiu, W. Y. and Ma, K. C. (1992a). Illustrated Handbook of Physical-Chemical Properties and Environmental Fate for Organic Chemicals. Lewis Publishers, Chelsea. Mackay, D., Shiu, W. Y. and Ma, K. C. (1992b). Illustrated Handbook of Physical-Chemical Properties and Environmental Fate for Organic Chemicals. Lewis Publishers, Chelsea. Mills G. and Homann M. R. (1993) Photocatalytic degradation of pentachlorophenol on TiO2 particles: identi®cation of intermediates and mechanism of reaction. Environ. Sci. Technol. 27(8), 1681±1689. Mueller J. G., Chapman P. J. and Pritchard P. H. (1989) Creosote-contaminated sites Ð Their potential for bioremediation. Environ. Sci. Technol. 23(10), 1197±1201. Mueller J. G., Middaugh D. P., Lantz S. E. and Chapman P. J. (1991) Biodegradation of creosote and pentachlor-
1158
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ophenol in contaminated groundwater: chemical and biological assessment. Appl. Environ. Microbiol. 57(5), 1277±1285. Peters C. A. and Luthy R. G. (1993) Coal tar dissolution in water-miscible solvents: experimental evaluation. Environ. Sci. Technol. 27(13), 2831±2843. Pignatello J. J. (1992) Dark and photoassisted Fe3+-catalyzed degradation of chlorophenoxy herbicides by hydrogen peroxide. Environ. Sci. Technol. 26(5), 944± 951. Pignatello J. J. and Chapa G. (1994) Degradation of PCBs by ferric ion, hydrogen peroxide and UV light. Environ. Toxicol. Chem. 13(3), 423±427. Pignatello J. J. and Huang L. Q. (1993) Degradation of polychlorinated dibenzo-p-dioxin and dibenzofuran contaminants in 2,4,5-T by photoassisted iron-catalyzed hydrogen peroxide. Water Res. 27(12), 1731±1736. Pignatello J. J. and Sun Y. (1995) Complete oxidation of metolachlor and methyl parathion in water by the photoassisted Fenton reaction. Water Res. 57(8), 1837± 1844. Sarazadeh-Amiri A., Bolton J. R. and Cater S. R. (1996)
The use of iron in advanced oxidation processes. J. Adv. Oxid. Technol. 1, 18±26. Serpone N., Terzian R., Lawless D., Pelletier A. M., Minero C. and Pellzzetti E. (1994). Photocatalyzed destruction of water contaminants: mineralization of aquatic creosote phenolics and creosote by irradiated particulates of the white paint pigment titania. In Aquatic and Surface Photochemistry, ed. G. R. Helz, R. G. Zepp and D. G. Crosby, pp. 387±398. Lewis Publishers, Boco Raton, FL. Sun Y. and Pignatello J. J. (1993) Photochemical reactions involved in the total mineralization of 2,4-D by Fe3+/ H2O2/UV. Environ. Sci. Technol. 27(2), 304±310. United States Environmental Protection Agency. (1984). Creosote - Special Review Position Document 2/3. U.S. Government Printing Oce, Washington, D.C. United States Environmental Protection Agency. (1995). Whole Euent Toxicity: Guidelines Establishing Test Procedures for the Analysis of Pollutants, Final Rule. Federal Register, 40 CFR Part 136. Wong A. S. and Crosby D. G. (1981) Photodecomposition of pentachlorophenol in water. J. Agric. Food Chem. 29, 125±130.