Environ. Sci. Technol. 1985, 19, 437-447
Taylor, G. E., Jr.; Selvidge, W. J. J. Enuiron. Qual. 1984, 13, 224-230. Heck, W. W.; Pires, E. G. "Growth of Plants Fumigated with Saturated and Unsaturated Hydrocarbon Gases and Their Derivatives"; Agriculture and Mechanical College of Texas: Texas AgriculturalExperiment Station, MP-603, College Station, TX, 1962;pp 1-12. Cameron, A. C.; Yang, S. F. Plant Physiol. 1982,70,21-23. Nassar, J.; Goldback, J. Znt. J. Enuiron. Anal. Chem. 1979, 6, 145-169.
Tingey, D. T.; Stadley, C.; Field, R. W. Atmos. Environ.
(26) Rao, A. M. M.; Netravalkar, A. J.; Arora, P. K.; Vohra, K. G. Atmos. Environ. 1983,17, 1093-1097. (27) Ferman, M.A. In "Atmospheric Biogenic Hydrocarbons.
Ambient Concentrations and Atmospheric Chemistry"; Bufalini, J. J.; Arnts, R. R., Eds.; Ann Arbor Science, Ann Arbor, MI, 1981;Vol. 2, pp 51-72. (28) Arnts, R. R.;Meeks, S. A. Atmos. Environ. 1981, 15,
1643-1651. (29) Lonneman, W. A.; Seila, R. L.; Bufalini, J. J. Environ. Sci. Technol. 1978,12,459-463. (30) Robinson, E.Pure Appl. Geophys. 1978, 116, 372-384.
1976,10,969-974.
Bressan, R. A.; LeCureaux, L.; Wilson, L. G.; Filner, P. L. Plant Physiol. 1979,63,924-930. Taylor, 0.C.; Cardiff, E. A.; Memereau, J. D. J.Air Pollut. Control Assoc. 1965,151,71-76. Nelson, P. F.; Quigley, S. M. Environ. Sci. Technol. 1982, 16,650-655.
Received for review July 16,1984.Revised manuscript received November 15, 1984. Accepted December 3, 1984. Research sponsored by the Office of Health and Environmental Research, U.S. Department of Energy, under Contract DE-AC05840R21400 with Martin Marietta Energy Systems, Znc.
Determination of Total Sulfur in Lichens and Plants by Combustion-Infrared Analysis Larry L. Jackson,* Edythe E. Engleman, and Janet L. Peard U.S. Geological Survey, MS 928, Denver Federal Center, Denver, Colorado 80225
rn Sulfur was determined in plants and lichens by combustion of the sample and infrared detection of evolved sulfur dioxide using an automated sulfur analyzer. Vanadium pentaoxide was used as a combustion accelerator. Pelletization of the sample prior to combustion was not found to be advantageous. Washing studies showed that leaching of sulfur was not a major factor in the sample preparation. The combustion-IR analysis usually gave higher sulfur content than the turbidimetric analysis as well as shorter analysis time. Relative standard deviations of less than 7% were obtained by the combustion-IR technique when sulfur levels in plant material ranged from 0.05 to 0.70%. Determination of sulfur in National Bureau of Standards botanical reference materials showed good agreement between the combustion-IR technique and other instrumental procedures. Seven NBS botanical reference materials were analyzed. The determination of sulfur in plants and lichens is an integral part of many environmental studies. In particular, lichens have proven to be viable air quality indicators for pollutants such as the heavy metals and sulfur. Numerous studies have shown correlations between the elemental content of lichens and that of anthropogenic sources (1-5). In environmental studies such as these the methodology used varies greatly both in the preparation and in the analysis of the lichens. Frequently the methodologic biases are not clearly understood, which makes broad interpretation of the data difficult, if not impossible. The determination of sulfur in plants has generally been restricted to turbidimetric procedures (6-8) and X-ray fluorescence spectroscopy (1, 9, 10). Combustion techniques with either photometric or titrimetric quantitation of evolved sulfur have also been used to a limited extent (11-1 4).
We have applied a combustion technique with infrared (IR) detection to the determination of sulfur in lichens and higher order plants and have examined the viability of using this procedure in long-range studies such as the detection of contaminants from emission sources over several years. The analytical methodology used in studies
of this nature must be both accurate and precise to detect small changes with time. Due to the increasing importance of lichens as air quality indicators and the heterogeneous nature of lichens, a symbiotic relationship of an algae and fungus, our experimental work emphasized the analysis of lichens. The effects on precision due to sample size, pelletization, and use of accelerator were examined. We also examined sample preparation techniques, washing and grinding, which may affect the determination of sulfur in lichens through leaching or inhomogeneity effects. Through detailed study of sample preparation and the analytical technique, we have attempted to define the methodologic biases and their effects on data interpretation. The following plant species (with common name where appropriate) are dealt with in this paper: Medicago sativa L. (alfalfa); Vitis labruscana Bailey (Concord grape); Festuca sp. (fescue grass);Fraxinus pennsylvanica Marsh. (green ash); Parmelia chlorochroa Tuck.; P. sulcata Tayl.; Juniperus scopulorum Sarg. (red juniper); Artemisia tridentata Nutt. (big sagebrush); Lycopersicum esculentum Mill. (tomato); Triticum compactum Host (soft-white wheatgrain); Agropyron smithii Rydb. (western wheatgrass); Salix pulchra Cham. (willow).
Experimental Section Instrumentation. A Leco combustion-IR sulfur analyzer, Model SC-132 (Leco Corp., St. Joseph, MI), was used in this work. The instrument is composed of a microprocessor control unit, an electronic balance, resistance furnace, and a solid-state infrared detector. The sample (0.25 g) was combusted in a stream of pure oxygen at 1370 OC for approximately 2 min. Thirty seconds after combustion was initiated oxygen was blown directly into the combustion crucible. The evolved SO2was detected and measured in an IR cell after the removal of water. The instrument was calibrated daily with National Bureau of Standards reference material 1572, citrus leaves (0.407% sulfur). A coal sample was combusted after every fourth sample to flush condensed organic matter through the combustion train. Also, several coal samples were
Not subject to U.S. Copyright. Published 1985 by the American Chemical Society
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combusted as conditioners after the changing of the Mg(ClOJz moisture trap which was replaced after 20-30 samples. Determination of Sulfur. An initial experiment was conducted to evaluate three factors that might influence the determination of sulfur. The factors were examined by using a balanced 23 factorial design: coarse- or fineground lichen material as the two levels of factor one; powdered or pelletized lichen material as the two levels of factor two; the absence or presence of an accelerator during combustion as the two levels of factor three (Table I). Parmelia sulcata colleded in Boulder County, CO, was washed with distilled water as described in the next section. The cleaned material was air-dried for 48 h at 40 “C and then ground in a Waring blender. This coarse-ground material was divided into two groups: the first group received no further grinding, and the second was ground to a finer and more uniformly sized powder in a Spex Industry mixer/mill. The finer material was obtained by grinding for 20 min in polystyrene vials with methacrylate balls. The coarse- and fine-ground groups were each divided into two parts: the first was analyzed as the powder, and the other was pelletized prior to analysis. Pellets were obtained by pressing 0.25 g of lichen in a 1.27-cm die under 700 kg/cm2. The powdered and pelletized groups were each further subdivided into two groups which were analyzed either with or without accelerator during combustion. One gram of vanadium pentaoxide (15)was spread evenly over the powdered or pelletized lichen sample. The eight treatment groups were analyzed 10 times each, randomizing both within and between groups. No instrumental memory effects were detected between analyses. Differences in the treatments were examined statistically by using factorial analysis of variance (AOV). Also, treatment means in which pelletizing and use of accelerator were not confounders (e.g., treatments (1)vs. b, (1)vs. c, and b vs. c, Table I) were compared by using the t test at the 95% confidence level (CL). To further examine the effects of pelletizing and the presence of accelerator, 31 lichen samples (Parmelia sulcata and P. chlorochroa), 14 samples of big sagebrush stems and leaves, and 17 samples of green ash leaves were analyzed as powdered material covered with accelerator and as pelletized material without accelerator. Differences in the treatment means were examined statistically by using paired t tests at the 95% CL. All subsequent plant and lichen samples were analyzed with a 0.25 g of sample without pelletization and with Vz05 as a combustion accelerator, except where otherwise indicated. The turbidimetric determination of sulfur was performed by the method of Tabatabai and Bremner (6). The plant material (0.25 g) was digested with nitric and perchloric acid. A barium chloride-gelatin mixture was added to the digest. The sulfur content was quantified by comparison of the barium sulfate turbidity in the sample solution to a calibration curve prepared from the analysis of standard solutions. Preparation and Cleaning of Lichens and Plants. Parmelia sulcata was collected from trunks, stumps, and downed logs of red juniper in Dunn County, ND. Thalli were broken into uniformly sized pieces, with diameters of about 2.5 cm. The pieces were floated in tap water, and adhering bark, moss, and other lichen species were removed with forceps. Pieces of thalli were randomly separated into three treatment groups, each to receive progressively more intense washings. Group 1 was set aside and labeled “grossly washed”. Groups 2 and 3 were re438
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Table I. Mean Apparent Sulfur Content ( % s)Found in 23 Factorial Experiment with Replication (n = 10) Using Samples of Parmelia sulcatan blender + mixer blender ground ground powdered pelletized powdered pelletized sample sample sample sample combusted without accelerator combusted with accelerator
0.139 (1) 0.141 (b) 0.139 (a)
0.142 (ab)
0.143 (c) 0.113 (bc) 0.142 (ac) 0.115 (abc)
Conventional abbreviated notation for treatment combinations and means are shown in parentheses.
combined and washed 8 times with distilled water. For each wash the material was floated in distilled water and stirred for about 15 s, and the floating lichen layer was removed. The thalli were randomly separated into two groups. Group 2 received no further washing and was labeled “distilled-water washed”. Group 3 was “ultrasonically washed” 4 times. For each wash the material was cleaned in distilled water by using an ultrasonic probe for 15 s, and the floating lichen layer was removed. Treatment groups 1-3 were dried overnight at 40 “C in a forced-air oven, ground in a Waring blender, and then shaken for 10 min by using a ceramic container and bead on a mixer/mill. Following thorough homogenization,each group was separated into 16 analytical splits of about 1.5 g each. One way analysis of variance was used to statistically determine differences between the treatment means. Duncan’s multiple range test (16) was used to make pairwise comparisons of these means. All other plant types were prepared by washing with distilled water and drying at 40 “C overnight. The samples were ground in a Wiley mill to pass a 1-mm mesh sieve.
Results and Discussion The sample combustion characteristics are the most important parameters with this analysis technique since the rate of sulfur evolution as well as incomplete conversion to SOz affects both the accuracy and the precision of the measurement. As described under Experimental Section, three factors, sample particle size, pelletizing, and the use of accelerator, were examined for their effects upon the sulfur determination in lichens. Particle size was chosen as a factor to test for inhomogeneity effects and possible size-related combustion effects. Pelletizing and the use of accelerator were also chosen as factors which might influence the rate of sulfur evolution or the formation of
soz.
The mean apparent sulfur content for each treatment group is shown in Table I. Evaluation of the AOV results shows an interaction between the pelletizing and use of accelerator treatments. When the lichen sample was both pelletized and combusted with accelerator, the apparent sulfur content decreased by 20%. Due to this interaction, interpretation of the effects of pelletizing and accelerator alone must be based on the examination of subsets of the data. Comparison of the treatment means in which these two factors were not used simultaneously indicated no apparent effect with pelletizing or the presence of accelerator. When lichen, sagebrush, and green ash samples were analyzed as powdered material covered with accelerator and as pelletized material without accelerator, paired t tests indicated that the means of the two treatments were significantly different. For the three sample types the sulfur
Table 11. Sulfur Content of Parmelia sulcata in Each Wash Treatment
grossly washed
treatments distilled water washed
Table 111. Analytical Variation, Day-to-Day sample
ultrasonically washed
range, % S relative standard deviation, %
0.153-0.163 2.4
0.136-0.169
4.8
0.141-0.149 1.7
mean,” % S (n = 16)
0.156
0.150
0.145
lichen (Parrnelia sulcata) sagebrush alfalfa fescue grass
Means underscored by the same lines are not significantly different (95% CL) when Duncan’s multiple range test is used.
content ranged from 5% to 13% higher without pelletizing. Since no detectable blank was found when Vz05was used, the small bias was attributed to minor differences during combustion, and pelletizing of the sample was not pursued further. Although the use of accelerator was not indicated as being necessary, we continued to use V205for routine analysis since it may suppress the formation of sulfur trioxide ( I 7). The factorial experiment revealed no sample inhomogeneity and combustion effects due to particle size, despite sieving experiments which showed that the additional grinding gave smaller and more uniform particle size. Simple grinding in a blender produced a particle size distribution that was not dramatically different from that of NBS citrus leaves. Sixty-six percent of the lichen sample was -60 mesh (0.25 mm) with blender grinding only compared to 80% with blender and mixef grinding, while 78% of the citrus leaves standard, as received, was -60 mesh. In all three cases more than 90% of the sample was -35 mesh (0.5 mm). Thus, blender grinding only was used for routine work. The excellent precision of the sulfur analyzer enhanced our ability to detect deleterious effects due to the two different grinding procedures (i.e., particle size effects), although none were found in the factorial experiment. It also allowed us to examine closely other factors in the sample preparation regimen, in particular, the washing of the sample. For environmental studies that are concerned with contaminant levels in plant tissue, some washing procedure may be required. However, it is difficult to determine when the washing procedure has removed the extraneous particulates but has not leached analyte from the plant itself. Goyal and Seaward (3) detected leaching of metals during their washing procedure but did not find it to be statistically significant. Lawrey and Hale (18)also found metal leaching due to washing when examining lichens for lead accumulation. Little (19) used deionized water and 1% HN03washes on aerially contaminated elm, oak, hawthorn, and willow leaves. He found lead and zinc present as surficial water-soluble and insoluble deposits which were distributed differently both within and between species. Water washing removed the majority of the surficial deposits, but the total amount removed was metal dependent. Thus, the sample preparation must be critically examined before environmental data can be interpreted. We examined three increasingly rigorous washing procedures and found a statistically significant difference between the washes. However, the difference could not be clearly attributed to improved removal of extraneous matter as opposed to leaching of sulfur. Table I1 shows the mean sulfur content of 16 analyses of each treatment category. The AOV of these data showed the three treatments to be significantly different (99% CL), while
NBS 1572 citrus leaves
mean, % day range, % S S (n = 5 ) RSD, % 1 2 1 2 1 2 1 2 1 2
0.067-0.080 0.065-0.076 0.178-0.192 0.182-0.193 0.339-0.354 0.352-0.359 0.232-0.255 0.242-0.256 0.387-0.408 0.400-0.411
0.074 0.071 0.184 0.186 0.349 0.356 0.244 0.247 0.399 0.406
7.0 6.5 3.3 2.2 1.8 0.8 3.4 2.2 2.1 1.2
the multiple range test showed there was no difference in mean percent S between the grossly washed material and the distilled water washed material or between the distilled water washed material and the ultrasonically washed material. There was a significant difference (95% CL) between the least rigorous and the most rigorous washes, that is, between the grossly washed and ultrasonically washed material. Although the decrease in sulfur content with rigor of washing may be due to leaching, it is possibly due to more effective removal of particulate matter since the ash content decreased with increased sample washing. The ash content was 14.9%, 11.6%, and 9.8% for the grossly washed, distilled water washed, and ultrasonically washed material, respectively. This decrease in ash content, however, could also be due to the leaching of calcium oxalate from the lichen sample (20). Regardless of the cause, the overall relative decrease in sulfur content of less than 10% was not considered important. In order to minimize sample preparation time yet provide an effective wash, the distilled water washing regimen was chosen for routine analysis and will be applied in all subsequent studies. Sample weight had no effect on the apparent sulfur content when a lichen sample was analyzed 5 times with 0.25 g and 0.5 g of material (0.071% and 0.073% S, respectively). However, the relative standard deviation (RSD)did improve from about 6% to 2% with the increase in sample size. Since the larger sample size caused more frequent changing of the water trap and a decrease in the number of samples analyzed per day, the improvement in precision did not warrant using the larger size on a routine basis. Analytical variation on a day-to-day basis was studied by analyzing several different plant types on two successive days. The results of replicate analyses on different days are shown in Table 111. Although differences of about 2% were detected between the days for each sample type, they were not statistically significant, and there was no consistent overall effect of day. Sulfur in 23 samples of lichens, sagebrush, alfalfa, wheatgrass, and a variety of other plants was determined by both the combustion-IR technique and the conventional turbidimetric procedure, and these data are plotted in Figure 1, one vs. the other. The combustion-IR technique gave sulfur contents that averaged more than 20% higher than those obtained by the turbidimetric analysis. Although the relative difference was large, on an absolute scale the difference was only 0.01-0.04% S. The NBS citrus leaves SRM and the lichen sample used in the factorial experiment were also analyzed by the turbidimetric procedure, 6 times each. The turbidimetrically determined sulfur contents were 0.36% and 0.14% for the citrus leaves and lichen, respectively. The sulfur content of the citrus leaves was 13% lower than the certified value (0.407% S), whereas for the lichen it compared Environ. Sci. Technol., Vol. 19,
No. 5, 1985 439
Table V. Sulfur Content of NBS 1571 Standard Reference Material, Orchard Leaves
0.361
methods of analysis
/'
neutron activation analysis neutron activation analysis X-ray fluorescence X-ray fluorescence X-ray fluorescence X-ray fluorescence photometric photometric combustion-titrator combustion-infrared combustion-infrared coal standard citrus leaves standard
o /
K
T 0.24
a
0 . 0 V "' ,4
o
L
81 ;8 l ' A 0 ~ T c0 (l 0Yl
l
2;
'I
CY; 2 2 ~
%S, Turbidimetric
Figure 1. Plot of sulfur determinations by combustion-IR analysis vs. turbMlmetric analysis. (-) Linear regression of 23 plant samples: Y = 1.12X-k 0.014, correlation coefficient of 0.97. (---) Y = X . (0) Parmelia chlorochroa; (0)alfalfa; (V)Concord grapes; (A)fescue grass; (0)sagebrush; (A) tomatoes; (H) wheatgraln; (V)wheatgrass; (X) willow.
Table IV. Analysis of NBS Botanical Reference Materials Using NBS 1572 Citrus Leaves SRM and a Leco Coal Standard for Instrumental Calibration NBS reference material
1567 wheat flour 1568 rice flour 1570 spinach leaves 1571 orchard leaves 1572 citrus leaves 1573 tomato leaves 1575 pine needles
Calibrating mean, % standard range, % S s (n = 5) RSD, % leaves coal leaves coal leaves coal leaves coal leaves coal leaves coal leaves coal
0.168-0.190 0.172-0.190 0.136-0.143 0.132-0.147 0.440-0.451 0.470-0.513 0.200-0.214 0.194-0.204 0.400-0.426 0.404-0.420 0.610-0.634 0.643-0.666 0.123-0.138 0.120-0.129
0.179 0.181 0.140 0.138 0.444" 0.486 0.204 0.196 0.414 0.416 0.626 0.655 0.129 0.124
,
5.4 4.0 1.9 4.3 1.4 3.3 2.7 2.2 2.5 1.6 1.6 1.4 4.2 2.6
n n = 3.
well with the combustion-IR result of 0.143%. The RSD for the turbidimetric analyses was 8% for both samples. The combustion-IR technique yielded slightly better precision, 2% and 4% RSD for the citrus leaves and lichen, respectively. Also an important improvement was obtained in the analysis time required: 60-80 samples per day by the combustion-IR technique compared to the 35 samples per day by the turbidimetric procedure. Several botanical reference materials are available from NBS; however, only 1572 citrus leaves SRM has a certified sulfur content, and only analyses of 1571 orchard leaves SRM are commonly found in the literature. Table IV shows the results obtained for seven of the NBS botanical SRM by using both 1572 citrus leaves SRM (% sulfur = 0.407 f 0.009) and a Leco coal standard (% sulfur = 0.47 f 0.02) for instrument calibration. The relative difference 440
Environ. Sci. Technol., Vol. 19, No. 5, 1985
% S
standard deviation
ref NBS"
0.19 0.23 0.17 0.212 0.212 0.215 0.195 0.195 0.186 0.12 0.190
0.005 0.038
0.003
21 21 21 21 21 13 13 13 12 14
0.196 0.204
0.004 0.006
this work this work
0.01 0.02
0.02 0.018
Noncertified information value only on certificate of analysis.
between the use of the two calibrating standards was less than 10%. Orchard leaves SRM has been analyzed by a variety of techniques as seen in Table V. The combustion-IR procedure was in excellent agreement with the other methods of analysis, except for the results of Jones and Isaac (12), obtained by using a Leco sulfur analyzer with an induction furnace and iodometric titrator. However, their results were substantially lower than those found by other investigators. The determination of sulfur using the combustion-IR analyzer proved suitable for the analysis of lichens and higher-order plants. The excellent precision and short analysis time meet the needs of environmental studies where small changes in sulfur content with time must be detected and where large numbers of samples must be analyzed. This method was successfully employed in a study of the sulfur levels in P. sulcata from Theodore Roosevelt National Park, ND, a class 1 air quality region (22). An andysis-of-variancesampling design allowed for estimation of both natural variation at several geographical distances and analytical variation due to methodology. Analytical error for the combustion-IR technique was only 0.7% of the total variance for sulfur. With this excellent precision, the natural variation in the sulfur content of P. sulcata was not obscured by the analytical variation. Acknowledgments
We thank Skip Snow of the National Park Service, Theodore Roosevelt National Park, for collecting the lichens, and Thelma Harms of the U.S.Geological Survey for providing the turbidimetric analyses. Registry No. Sulfur, 7704-34-9.
Literature Cited (1) Tomassini, F. D.; Puckett, K. J.; Nieboer, E.; Richardson, D. H. S.; Grace, B. Can. J. Bot. 1976,54,1591-1603. (2) Gough, L.P.;Erdman, J. A. Bryologist 1977,80,492-501. (3) Goyal, R.; Seaward, M. R. D. Lichenologist 1981, 13, 289-300. (4) Nygard, S.;Harju, L. Lichenologist 1983,15, 89-93. (5) Taylor, R. J.; Bell, M. A. Northwest Sci. 1983,57,157-166. (6) Tabatabai, M. A.; Bremner, J. M. Agron. J. 1970, 62, 805-806. (7) Basson, W.D.; Bohmer, R. G. Analyst (London) 1972,97, 266-270. (8) Chan, C. C. Y. Anal. Lett. 1975,8,655-663. (9) Alexander, G. V. Anal. Chem. 1965,37,1671-1674. (10) Norrish, K.;Hutton, J. T. X-Ray Spectron. 1977,6,6-17.
Environ. Scl. Technol. 1985, 19, 441-449
Tiedemann, A. R.; Anderson, T. D. Plant Soil 1971, 35, 197-200. Jones, J. B.; Isaac, R. A. J. Agric. Food Chem. 1972,20, 1292-1294. Bartels, U.; Pham, T. T. Fresenius' 2.Anal. Chem. 1982, 310, 13-15. Hem, J. L. Commun.Soil Sci. Plant Anal. 1984,15,99-109. Hagerman, D. B.; Faust, R. A. Anal. Chem. 1955, 27, 1970-1972. Duncan, D. B. Biometrics 1955, 11, 1-42. Ricke, W. Fresenius' 2.Anal. Chem. 1964,199,401-413. Lawrey, J. D.; Hale, M. E. Bryologist 1981, 84, 449-456. Little, P. Environ. Pollut. 1973, 5, 159-172.
(20) Erdman, J. A.; Gough, L. P.; White, R. W. Bryologist 1977, 80, 334-339. (21) Gladney, E. 1981, Los Alamos Scientific Laboratory Informal Report LA-8438-MS. (22) Uman, M. F. Environ. Sci. Technol. 1982,16,386A-393A.
Received for review August 13, 1984. Accepted November 19, 1984. This work was supported by the National Park Service Air Quality Division,Dr. James P. Bennett, project coordinator, through Interagency Agreement 475-83-02. The use of trade names is for descriptive purposes only and does not constitute endorsement by the US.Geological Survey.
Effects of Activated Carbon on the Reactions of Free Chlorine with Phenols Evangelos A. Voudrlas,t Richard A. Larson," and Vernon L. Snoeyink
Department of Civil Engineering and Institute for Environmental Studies, University of Illinois-Urbana, The use of prechlorination in drinking water treatment results in contact of free chlorine with activated carbon which has been added to remove organic compounds from water. The chlorine then reacts with the carbon and adsorbed compounds. Free chlorine reacts readily with a group of phenolic compounds (phenol, guaiacol, catechol, 2,6-dimethoxyphenol, and p-chlorophenol) in dilute aqueous solutions (10" M)to produce mono-, di-, or trichloro derivatives, but when it reacts with phenols adsorbed on granular activated carbon (GAC), many additional products are formed. GAC exposed to chlorine becomes capable of promoting reactions such as hydroxylation of the aromatic ring, oxidation to quinones, chlorine substitution, carboxylation, and oxidative coupling (dimer formation). The formation of chlorohydroxybiphenyls (hydroxylated PCBs) (in vivo metabolites of PCBs) is particularly important because of their potential toxicity. Such compounds are the main reaction products from chlorophenols, but they are also formed in smaller amounts from nonchlorinated phenols (phenol and guaiacol).
Introduction The application of both powdered and granular activated carbon (PAC and GAC) in drinking water treatment is very frequent. In use, it almost always contacts disinfectants such as HOC1, OC1-, "$21, etc. The addition of chlorine in the early stages of the treatment is known as prechlorination. Prechlorination is widely used for control of biological growths in the treatment units and oxidation of ammonia through breakpoint ehlorination (I). Several plants in the United States and Europe employ or have employed prechlorination along with PAC or GAC adsorption (2-5). Also, in wastewater treatment plants practicing advanced treatment, chlorinated tertiary effluent can contact activated carbon. $ome of the chlorine added is destroyed by satisfying the chlorine demand of the water. Possible products are trihalomethanes, other chlarinated organic compounds, and oxidation products. Some will reach the activated carbon and will react with activated carbon and compounds adsorbed on it. Recent research (6)has shown that compounds that readily reacted with HOC1 in dilute Present address: Environmental Engineering and Science, Department of Civil Engineering, Stanford University, Stanford, CA 94305. 0013-936X/85/0919-0441$01.50/0
Urbana, Illinois 6 1801
aqueous solutions also reacted when adsorbed, but different and unusual reaction products were formed. The same was observed for reactions with chlorine dioxide (7). Therefore, it is important to characterize the compounds formed from the surface reaction and their adsorption properties, to determine if they will be released to the treated water (and if so, the health hazard involved to those who drink this water). Factors that affect the surface reactions must also be determined so that the formation of health hazards can be controlled. This research was designed to study the reactions of aqueous free chlorine with phenols, both in aqueous solution and adsorbed on granular activated carbon, by using conditions approximating those encountered in drinking water treatment practice. The compounds selected for study were phenol, guaiacol, 2,6-dimethoxyphenol, catechol, and p-chlorophenol. They were selected because guaiacol, catechol, and 2,6-dimethoxyphenol are representatives of the aromatic substitution patterns known to exist in degradation products of lignin and humic acids (8). Phenol and p-chlorophenol are present in polluted waters; chlorophenols are largely responsible for unpleasant tastes and odors in waters supplies (9). All compounds belong to the same general family of phenols and react readily with chlorine.
Materials and Methods Materials. Chlorine solution was prepared by bubbling high purity chlorine gas (Linde Specialty Gas, Union Carbide, New York, NY) into distilled, deionized water made alkaline with NaOH. An appropriate amount of stock solution was added to distilled, deionized water to achieve a chlorine solution of required concentration for column or batch experiments. Chlorine solutions were buffered at the desired pH with 0.001 M phosphate salt. The solution concentration was checked by using the DPD titrimetric procedure (10). The carbons used in the experimepts were a 20 X 30 U.S. standard mesh fraction of F-400 GAC (Calgon Corp., Pittsburgh, PA), a 30 X 40 mesh fraction of HD-3000 GAC (IC1 America Inc., Wilmington, DE), and a 6 X 16 mesh fraction of Carborundum 616GA (Ceca, Inc., Tulsa, OK). The GACs were prepared by grinding the particles and sieving them to the desired mesh size fraction. Fines were removed by washing with distilled, deionized water. The sieved and washed carbon was baked at 175 "C for 1week to remove volatile impurities and then was kept continuously at 105 "C.
0 1985 Amerlcan Chemical Society
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