Environ. Sci. Technol. 1989, 23, 480-484
Sorption of 2,3,7,8-Tetrachlorodibenzo-p-dioxin from Water by Surface Soils Richard W. Walters, *,+ Stanley A. Ostazeski,+ and Annette Guiseppi-Eliez
Department of Civil Engineering, University of Maryland, College Park, Maryland 20742, and Environmental Affairs and Toxicology, Mobil Oil Corporation, Princeton, New Jersey 08540 H The sorption of l4C-labeled 2,3,7,8-tetrachlorodibenzo-
p-dioxin (TCDD) from water by two uncontaminated surface soils from the Times Beach, MO, area was evaluated by using batch shake testing. Sorption isotherm plots for the soil with the lower fraction organic carbon ),f( were linear, and regression analysis was used to determine a value of the sorption coefficient (KD)of 30400 mL/g. This value corresponds to a value of log KO,of 6.66,where KO, is the partition coefficient normalized on the basis of soil organic carbon content. Significant interferences attributed to the presence of nonseparable suspended particles (NSP) were apparent in the measurement of the waterphase concentrations of TCDD for experiments involving the high-f,, soil. Prewashing this soil from one to five consecutive times with water appeared to reduce these interferences, as individual-point distribution ratios approached the K , value determined for the low-f, soil. The measured value of log K, agrees with the reported estimate of log K , of 6.6for TCDD made by applying the cosolvent theory to isotherm data generated with water/methanol mixtures.
Introduction The compound 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is one of the most toxic compounds known to man. Experimental studies of the toxicity of TCDD using guinea pigs have shown that the LDbOis as low as 0.6-2.0 bg/kg of body weight (1). TCDD as an environmental contaminant has perhaps received most widespread national attention because it was present in waste oils that were applied to roads and horse arenas for dust control in Missouri (2). However, TCDD contamination of soils and sediments has been documented in numerous locations throughout the United States and in other countries (3-5). Marple et al. (6, 7 ) have recently reported experimental determinations of the water solubility and the octanolwater partition coefficient (K0J of TCDD. These parameters have been found to be useful in predicting the environmental behavior and fate of hydrophobic organic contaminants (8). The soil-water partition coefficient normalized on the organic carbon content of the sorbent (K0J is also an important environmental parameter (9). Walters and Guiseppi-Elie (10) have applied the cosolvent theory of Rao et al. (11)to estimate a value of log K, for TCDD of 6.6by using log-linear extrapolation of K , data obtained for the sorption of TCDD by soils from water/ methanol mixtures. TCDD detection limits and interferences from nonseparable suspended particles (NSP) precluded the direct determination of the water-phase K,. This paper presents the results obtained by using a modified experimental procedure to determine a K , value for sorption of TCDD from water by surface soils. The validity of using log-linear extrapolation on the basis of the cosolvent theory to obtain estimates of log KO,for highly hydrophobic organic contaminants such as TCDD is also assessed. f
t
University of Maryland. Mobil Oil Corp.
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Environ. Sci. Technol., Vol. 23, No. 4, 1989
Table I. Characterization and Identification Information for Surface Soils soil no. sampling location EPA site no. PH CEC," mequiv/100 g fo,"
91 Sontag Road 04114B 6.8 5.4 0.0066
96 Piazza Road 06126B 5.8 15.3 0.077
texture, 70 sand silt clay
44 42 14
38 40 22
"CEC is cation-exchange capacity, and f, is fraction organic carbon.
Experimental Section Materials. Radiolabeled [I4C]TCDD with specific activity of 117.54 mCi/mmol was obtained from Cambridge Isotope Laboratories (Cambridge, MA). The radiolabeled TCDD had chemical and radiochemical purities of >99% and >99.99%, respectively, and was used as received without further purification. A TCDD working solution was prepared by dissolving the TCDD in methanol. The sorbents were uncontaminated surface soils from the Times Beach, MO, area. Characterization and identification information for these soils presented by Walters and Guiseppi-Elie (10) are summarized in Table I. The methods used for soil characterization are presented elsewhere (10). Methanol and methylene chloride were pesticide grade and were obtained from Fisher. These solvents were used as received without further purification. Water was generated by using a treatment system obtained from Hydro (Chapel Hill, NC), which consisted of a reverse osmosis unit, activated carbon cartridge, and a pair of mixed-bed deionizers. Water from this system was dosed with 0.01% by weight NaN3 as a biocide and the ionic strength was adjusted to 0.01 M with CaC12. The pH of the water was adjusted to 7.0 with NaOH. Insta-gel liquid scintillation cocktail obtained from United Technologies was used for radiochemical analysis. Sorption Experiments with Soil 91. Three separate experiments involving batch shake testing were conducted to generate data for sorption of TCDD by soil 91. All experiments were conducted in 50-mL, round-bottom, glass centrifuge tubes fitted with Teflon-lined screw caps. The first experiment involved single-point determinations, while the other two experiments were focused on generating sorption isotherm data. The first experiment was conducted to assess the POtential to reduce interferences in water-phase TCDD determinations caused by NSP. The occurrence and characteristics of NSP and the effects of NSP on sorption experiments have been documented by Gschwend and WU (12). This experiment was conducted by using duplicate tubes dosed with approximately 600 mg of soil and 35 mL of water. A soil prewash procedure similar to that of Gschwend and Wu (12)was used to remove water-phase NSP. The procedure consisted of (1)contacting the soil
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and water without TCDD for 24 h, (2) separating the soil and water by centrifuging a t 2000 rpm (740g) for 6 min, and (3) withdrawal and replacement of the supernate with fresh water. Centrifugation was accomplished by using a Model HN-SI1 centrifuge obtained from IEC (Needham Heights, MA). The prewash procedure was performed five times, after which tubes were dosed with 1.3 pg of TCDD. The contents of the tubes were then contacted for 5 days on a shaking table, after which the tubes were centrifuged at 3500 rpm (2300g) for 30 min. Triplicate 1-mL aliquots of the supernate water phase were then withdrawn from each tube and added to 10 mL of counting cocktail for analysis by liquid scintillation counting (LSC). The second and third experiments were conducted to generate sorption isotherm data and to assess the effects of contact time and soil prewashing on the observed sorptive characteristics of TCDD. Soil and water doses in these experiments were approximately 50 mg and 40 mL, respectively. Each isotherm determination consisted of duplicate tubes which were dosed with one of three TCDD doses ranging from 0.0074 to 0.0203 pg/tube. TCDD doses were delivered to the tubes by direct injection of 10-30 pL of the working solution. In the second experiment, tubes were dosed with water, TCDD, and soil that had not been prewashed, and the contents were contacted for 2 days on a shaking table. Tubes were then centrifuged by using a Model GPR temperature-controlled centrifuge equipped with a GH-3.7 horizontal rotor obtained from Beckman (Columbia, MD). Tubes were centrifuged at 3000 rpm (2100g) for 10 min, and the water phase was then removed for analysis. The third experiment was conducted using soil that was prewashed as in the first experiment. The prewash procedure consisted of (1)contacting the soil and water for 2 days, (2) separating soil and water by centrifuging at 1800 rpm (740g) for 30 min, and (3) withdrawal and replacement of the supernate with fresh water. This prewash procedure was performed five times, after which tubes were dosed with TCDD. The contents of the tubes were then contacted for 10 days, after which the tubes were centrifuged a t 3000 rpm (2100g) for 60 min. The supernate water phase was then withdrawn for analysis. The water-phase analysis for the latter two experiments involved withdrawing 30 mL of supernate by using a 15mL class A Kimax pipet. Each water sample was delivered to a 125-mL glass separatory funnel and was extracted four times with 5 mL of methylene chloride by applying a gentle swirling action to the funnel. Each 5-mL volume of extract was drained into a counting vial, and the total 20-mL volume was reduced to -5 mL by evaporating the methylene chloride into a gentle stream of nitrogen gas. Counting cocktail (10 mL) was added to the vials, and the mixture was analyzed by LSC. Sorption Experiments with Soil 96. Single-point sorption experiments involving soil 96 were conducted by using an experimental procedure similar to that used for the single-point sorption experiments with soil 91. Experiments were conducted using both 15-mL, conical, glass centrifuge tubes (with soil, water, and TCDD doses of 13 mL, 50 mg, and 1.3 pg, respectively) and 50-mL, roundbottom, glass centrifuge tubes. Soil in duplicate pairs of tubes was washed from one to five consecutive times prior to dosing the tubes with TCDD. The contents of the tubes were then contacted for 5 days, after which the tubes were centrifuged a t 3500 rpm (2300g) for 30 min. One-milliliter volumes of the water phase were then withdrawn and added to 10 mL of counting cocktail, and the mixture was analyzed by LSC.
Liquid Scintillation Counting. Liquid scintillation counting (LSC) analyses were performed by using a Model 1219 Rackbeta liquid scintillation counter obtained from LKB Instruments (Gaithersburg, MD). Samples consisting of water or methylene chloride were combined with 10 mL of counting cocktail and counted for a minimum of 10 min. Quench correction using an external standard and fluorescence correction was applied to all samples. Method Checks. Experiments were conducted to assess both the water-phase extraction efficiency of TCDD and losses of TCDD to tube walls and the cap liner associated with the methodology used to generate sorption isotherm data for soil 91. Water-phase TCDD extraction efficiency was evaluated by extracting a 30.0-mL volume of water containing no soil that was dosed with a 10-pL aliquot of the TCDD working solution. The sample obtained from this extract, and a sample that consisted of a 10-pL aliquot of the working solution delivered directly to counting cocktail, were analyzed by LSC. The results of this experiment indicated that TCDD recoveries were 92-100%. On the basis of these results, extraction efficiency corrections were not applied to the measured water-phase concentrations of TCDD. Experiments to measure losses of TCDD to the tube walls and the Teflon cap liner were conducted by using each of the tubes involved in the second isotherm experiment with soil 91. Following the withdrawal of the water-phase sample, the remaining water and soil phases were withdrawn from the tubes by using a Pasteur pipet, and the emptied tubes were rinsed three times with 5 mL of methanol followed by one rinse with 5 mL of methylene chloride. The rinses for each tube were collected in a counting vial, and the volume was reduced to 5 mL by evaporating the solvent mixture into a stream of nitrogen gas. Counting cocktail was added to the rinse, and the sample was analyzed by LSC. The results of this experiment indicated that 3.5 f 0.8% (average and 95% confidence limits of the six values) of the TCDD dosed to the tubes was associated with the tube walls and/or the Teflon liner. No attempt was made to determine the fraction of this TCDD that was associated with soil fines, which were observed to be retained by the walls and liner, and experimental values were not corrected to account for these apparent losses. Data Analysis. Isotherm data were analyzed by linear regression according to the equation S = KDC. In this equation, C is the water-phase concentration of TCDD (pg/mL) determined from the results of LSC analyses, and S is the soil-phase concentration of TCDD (pg/g) determined by the difference between total TCDD dosed to the tube and total TCDD in the water phase (CV),where V is the volume of water (mL) in the tube. In all experiments, essentially all of the TCDD dosed to the tubes was sorbed by the soil. The best-fit estimate of the sorption coefficient KD was determined from KD = CCiSi/xC? (13).
Results and Discussion Soil 91. The results of the single-point sorption experiments involving soil 91 indicated a distribution ratio (S/C)of 27 700 f 6500 mL/g (noted values are the average and standard deviation of the duplicate determinations). When normalized on soil fraction organic carbon content (foe), this distribution ratio corresponds to a value of log (S/Cf,)of 6.62, which is in good agreement with the value of log KO,of 6.6 estimated by Walters and Guiseppi-Elie (IO). On the basis of this observation, it was concluded that direct experimental evaluation of K , for TCDD might Environ. Sci. Technol., Vol. 23,No. 4, 1989
481
Table 11. Isotherm Data for Sorption of TCDD by Soil for a Contact Period of 2 Days mass soil, g total TCDD dose, Fg 0.0521 0.0074 0.0546 0.0074 0.0511 0.0129 0.0554 0.0129 0.0521 0.0160 0.0523 0.0160
91
0.5
s, rg/g
C, rg/mL 8.40 X lo4 8.30 X lo4 1.40 x 10-5 1.60 x 10-5 1.38 x 10-5 1.37 x 10-5
0.136 0.129 0.241 0.221 0.305 0.303
0.4
0.3
s, Mg/g 0.2
Table 111. Isotherm Data for Sorption of TCDD by Prewashed Soil 91 for a Contact Period of 10 Days mass soil, g total mass TCDD, pg 0.0325 0.0116 0.0537 0.0116 0.0544 0.0164 0.0510 0.0164 0.0496 0.0203 0.0504 0.0203
C, rg/mL 1.02 x 10-5 6.90 X 10+ 1.07 x 10-5 1.02 x 10-5 1.35 X 1.21 x 10-5
S? Pg/g 0.324 0.211 0.294 0.314 0.398 0.392
Table IV. Results of Isotherm Regression Analysis for Sorption of TCDD by Soil 91 from Water parametera
KD,mL/g F2 S
K,? mL/g 1% KO, log K,,
0.1
0.0 0.0
1.5
18000 0.96 0.048 2.73 X lo6 6.44 5.18
30 400 0.99 0.020 4.61 X 6.66 5.41
,
log(Ko,)
7.0 -
2.5
f o r Soil O i
- - - - - - - - - - - - - - - - - --
lo6
0
6.0 log(-
S/foc
C
0
0 0
0
a
5.0 -
S/f,,=* c
0
1,
9 0
4.0 -
3.0
be possible with soil 91; hence, sorption isotherm data for TCDD and this soil were consequently generated. The sorption isotherm data obtained for soil 91 by using each of the two experimental procedures are summarized in Tables I1 and 111. Values of KD and the regression statistics determined from linear regression analysis of each isotherm data set are summarized in Table IV. The isotherm data in Tables I1 and I11 are plotted in Figure 1. The plotted data, and the statistical parameters for the regression analyses of these data in Table IV, indicate that the sorption data for TCDD are well represented by a linear isotherm. For reference purposes, the maximum water solubility of TCDD determined by Marple et al. (6) of 19.3 ng/L is indicated in Figure 1,which shows that the water-phase concentrations correspond to roughly 30-70% of the reported water solubility of TCDD. The observation of isotherm linearity is generally consistent with the observation of Karickhoff (9) that isotherms for the sorption of hydrophobic organics by soils are generally linear for water-phase concentrations up to -50% of water solubility. As shown in Table IV, the measured values of K Ddetermined from the results of experiments for the 2- and 10-day contact periods were 18000 and 30 400 mL/g, respectively. These values are in fair agreement (within a factor of 2) despite the differences in the contact period and use of prewashing for the respective experiments. It is unclear whether either the increased contact period or the prewashing was responsible for the greater K Dvalue determined from the second experiment. However, the general linearity of the isotherm data and the absence of Environ. Sci. Technol., Vol. 23, No. 4, 1989
2.0
C, pg/mL Figure 1. Isotherm data plot for sorption of TCDD from water by soil 91.
2-day isothermb 10-day isothermC
aValue of K , determined by dividing K D by fraction organic carbon content of the soil (0.0066). Value of Km,,determined by dividing K , by molar volume of water (18 mL/mol). Values of r2 and s determined from r2 = KD CCiS,/CS,Z and s = [C(S,KDCJ2/(n - 1)]0.6. *Tabulated values based on regression of isotherm data in Table 11. Tabulated values based on regression of isotherm data in Table 111.
482
1 .o
0.5
l
l
l
l
l
any anomalous data points (e.g., data with unexpectedly high C values) suggest minimal interference attributed to NSP in experiments involving soil 91. The kinetics for sorption of TCDD by soil 91 can be qualitatively evaluated by considering the results of the 10-day isotherm experiment and the 5-day, single-point experiment. The value of KDdetermined from the former experiment was 30400 mL/g and the average distribution ratio ( S / C ) determined from the latter experiment was 27 700 mL/g. The agreement between these values (only 10% variability), both of which were obtained from experiments that utilized soil prewashing, suggests that equilibrium for sorption of TCDD by soil 91 may be attained within roughly a 5- to 10-day contact period. Soil 96. The results of individual-point sorption experiments involving soil 96 are plotted in Figure 2. Plotted in Figure 2 is the logarithm of the distribution ratio normalized on fa, (S/Cf,,,) versus the number of prior prewashes of the soil. A value off, of 0.077 was used for purposes of normalizing the data plotted in Figure 2. Also shown in Figure 2 is the value of the logarithm of the distribution ratio corresponding to the value of log KO, observed for soil 91. The data shown in Figure 2 clearly indicate that the distribution ratio varied significantly (by more than 2 orders of magnitude) as a function of the number of pre-
I
0
0.25
I
0.50
I
0.75
J 1 .0
Volume fraction solvent, f ,
Figure 3. Log-linear plot of Km,= values versus f , determined for sorption of TCDD by soils 91 and 96 from waterhethanol mixtures.
washes prior to the sorption experiment. These results suggest that NSP contributed significant experimental interferences in the determination of C values for soil 96. The logarithm of the distribution ratio increases with increasing number of prewashes and appears to approach the value of log K , determined for soil 91 at five consecutive prewashes (6.66 for soil 91 compared to 6.43 for soil 96). On the basis of this observation, the data for soil 96 appear to support the value of log KO,determined from the isotherm experiments with soil 91. However, because of the apparent problems with NSP, isotherm data for TCDD and soil 96 were not generated. It is suspected that the differences in interferences caused by NSP observed for soil 91 and 96 may be attributed to differences in the organic matter of these soils. The organic matter content of soil 96 is significantly greater than that of soil 91, and on the basis of qualitative observations, it is suspected that a portion of the NSP from soil 96 had a density similar to or less than that of water. For these reasons, NSP in experiments involving soil 96 continued to be present even after repeated prewashes. Assessment of the Cosolvent Theory. The cosolvent theory (11)predicts a log-linear relationship between the mole-based partition coefficient (Km,mol/g) and the volume fraction solvent (f,). Walters and Guiseppi-Elie (10)have applied the cosolvent theory to data generated for the sorption of TCDD by soils 91 and 96 from water/methanol mixtures to obtain an estimate of the water-phase log KO,of 6.6. The value of K Dof 30 400 mL/g determined from the isotherm data for soil 91 generated by using the 10-day contact period, when normalized on the fraction organic carbon content of the soil (0.0066), corresponds to a value of KO,of 4.61 X lo6 (log KO,= 6.66). This experimental value of K , was converted to units of moles per gram by dividing by the molar volume of water (18 mL/mol), resulting in a value of Km,ocof 2.56 X lo5 (log K,, = 5.41). This value is plotted in Figure 3 along with the cosolvent data of Walters and Guiseppi-Elie (10) obtained from experiments involving sorption of TCDD by soils 91 and 96 from water/methanol mixtures. The experimental value of log Km,, is in excellent agreement with the value
of log Km,mestimated by log-linear extrapolation using the cosolvent data presented in Figure 3 (estimated log Km,, = 5.23). On the basis of this observation, it is apparent that the cosolvent theory proposed by Rao et al. (11)to describe sorption of hydrophobic organic contaminants by soils from water/miscible solvent systems is applicable to the sorption of TCDD by surface soils from water/methanol mixtures over the entire range off, (0.0-1.0). This observation extends the applicability of the cosolvent theory for sorption by soils from water/methanol mixtures to sorbates spanning a wide range of hydrophobicity. Nkedi-Kizza et al. (14) were the first to note that the cosolvent theory applies to sorbates of relatively “intermediate” hydrophobicity (viz., log KO,of roughly 3.0-4.5. Fu and Luthy (15) demonstrated that the theory applies to sorbates of “lower” hydrophobicity (viz., log KO,of 2.0-3.4). The data presented here and by Walters and Guiseppi-Elie (10) for TCDD extend the theory to “highly” hydrophobic sorbates such as TCDD [log KO,of 6.6 (7)]. This provides support for the observation of Nkedi-Kizza et al. (14) that log-linear extrapolation could be used to estimate waterphase KO,values for hydrophobic solutes by using water/methanol cosolvent data. This latter observation is particularly significant for compounds such as polychlorodibenzo-p-dioxins (PCDDs), because it is often difficult or impossible to make direct water-phase determinations of KO,for PCDDs and other “highly” hydrophobic contaminants. Conclusions The sorption of TCDD from water by surface soils from the Times Beach, MO, area has been evaluated by batch shake testing. A procedure that employed a 10-day contact period and prewashing of the soil with water to reduce water-phase concentrations of nonseparable suspended particles (NSP) was used to determine a value of the sorption coefficient (KD)for TCDD of 30 400 mL/g. This value corresponds to a value of log K , of 6.66, which is in good agreement with the estimate of log KO,of 6.6 made by log-linear extrapolation of sorption isotherm data generated by using water/methanol mixtures, in accord with the cosolvent theory. This observation has significant implications for the determination of KO,for PCDDs and other highly hydrophobic organic contaminants, for which direct water-phase measurements of K , are complicated or impossible owing to the presence of suspended material that can not be separated from the water phase even by using extreme centrifugation. Acknowledgments Marvin D. Piwoni and Carl G. Enfield served as technical project officers for this work, and both have contributed to various technical aspects of this project. Jay C. Means has also contributed to various technical aspects of the project. Registry No. TCDD, 1746-01-6.
Literature Cited Esposito, M. P.; Tiernan, T. 0.; Dryden, F. E. Dioxins; NTIS: Washington, DC, 1980; EPA Report EPA-600/280-197. Exner, J. H. In Solving Hazardous Waste Problems: Learning f r o m Dioxin; Exner, J. H., Ed.; ACS Symposium Series 338; American Chemical Society: Washington, DC, 1987; pp 1-17. Rappe, C. In Solving Hazardous Waste Problems: Learning from Dioxin; Exner, J. H., Ed.; ACS Symposium Series 338; Environ. Sci. Technol., Vol. 23,
No. 4, 1989 483
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American Chemical Society: Washington, DC, 1987; pp
20-33. ( 4 ) Exner, J. H.; Alperin, E. S.; Groen, A.; Morren, C. E.; Kalcevic, V.; Cudahy, J. J.; Pitts, D. M. In Chlorinated Dioxins & Dibenzofurans i n the Total Environment II; Keith, L. H., Rappe, C., Choudhary, G., Eds.; Butterworth Stoneham, MA, 1985; pp 47-56. ( 5 ) Pereira, W. E.; Rostad, C. E.; Sisak, M. E. Environ. Toxicol. Chem. 1985,4, 629-639. ( 6 ) Marple, L.; Brunck, R.; Throop, L. Environ. Sci. Technol. 1986,20, 180-182. ( 7 ) Marple, L.; Berridge, B.; Throop, L. Environ. Sci. Technol. 1986,20, 397-399. ( 8 ) Handbook o f Chemical Property Estimation Methods; Lyman, W. J., Reehl, W. F., Rosenblatt, D. H., Eds.; McGraw-Hill: New York, 1982. ( 9 ) Karickhoff, S . W. J . Hydraul. Eng. 1984, 110, 707-735. (10) Walters, R. W.; Guiseppi-Elie, A. Environ. Sci. Technol. 1988,22,819-825. (11) Rao, P. S. C.; Hornsby, A. G.; Kilcrease, D. P.; Nkedi-Kizza,
P. J. Environ. Qual. 1985,14, 376-383. (12) Gschwend, P. M.; Wu, S. Environ. Sci. Technol. 1985,19, 90-96. (13) Gillingham, R.; Heien, D. A m . Stat. 1971, 25, 54-55. (14) Nkedi-Kizza, P.; Rao, P. S. C.; Hornsby, A. G. Environ. Sci. Technol. 1985, 19, 975-979. (15) Fu, J.; Luthy, R. G. J . Environ. Eng. (N.Y.) 1986, 112, 346-366. Received for review: May 9,1988. Accepted November 14, 1988. This research was supported in part by cooperative agreements CR-811743-01-0 and CR813601-01-0 with the R. S. Kerr Environmental Research Laboratory, Ada, OK. Although the research described i n this paper has been funded in part by the U.S. Environmental Protection Agency through assistance agreements CR-811743-01-0 and CR813601-01-0 to the University of Maryland, it has not been subjected to Agency review and therefore does not necessarily reflect the views of the Agency, and no official endorsement should be inferred.
NOTES Determination of Amines in Indoor Air from Steam Humidification Sylvia A. Edgerton,+Donald V. Kenny,* and Darrell W. Joseph Battelle, Columbus Division, 505 King Avenue, Columbus, Ohio 43201
During the winter season, buildings are often humidified with steam which may come from a boiler system that is being treated with volatile neutralizing amines to prevent corrosion. In this study, a room at Battelle Columbus Division, in Columbus, OH, was selected as a typical steam-humidified room. The Battelle boiler system is treated with a mixture of cyclohexylamine (Cyclo) and (diethy1amino)ethanol (DEAE) for corrosion control. The concentrations of both Cyclo and DEAE were measured in indoor air in the study room with a Trace Atmospheric Gas Analyzer (TAGA). The concentrations of both the Cyclo and the DEAE measured in indoor room air during normal operation of the boiler and humidification systems remained very low compared with any established health standards. The concentrations averaged about 0.6 ppb for DEAE and 0.7 ppb for Cyclo at 42% relative humidity and 2.4 ppb for DEAE and 0.8 ppb for Cyclo at 61% relative humidity. The detection limits for these compounds measured by the TAGA were 0.1 ppb for both amines. The primary fate of the amines that are introduced into room air through steam humidification appears to be removal to surfaces. Introduction
To prevent corrosion and subsequent deterioration of steam pipes and other equipment, neutralizing amines are often used as corrosion inhibitors in steam boiler systems. These compounds volatilize with the steam from the boiler water and react with gases such as carbon dioxide to neutralize the acidity of the condensate and prevent the 'Present address: Environment and Policy Institute, East-West Center, Honolulu, HI 96848. 484
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corrosion of iron. The three most common amines used for this purpose are morpholine (C4H,NO), cyclohexylamine (Cyclo, C6HllNH2), and (diethy1amino)ethanol [DEAE, (C2H6),NCH2CH,0H]. These amines minimize the corrosive effects of dissolved gases such as carbon dioxide and sulfur dioxide on metals in feedwater heaters and piping. Recently there has been some concern over the potential for adverse health effects from elevated concentrations of these amines in indoor air that is humidified by steam from boilers treated with these compounds. The National Research Council (1)has noted in a recent report that a major gap exists in information concerning the ambient levels of DEAE and other amines in humidified, ambient indoor air. Morpholine, cyclohexylamine, (diethylamino)ethanol, and octadecylamine have been measured previously in condensed stream samples in systems in which these amines were added continuously to the boiler feedwater (2). The National Institute of Occupational Safety and Health (NIOSH) has conducted a Health Hazard Evaluation Report (HETA) of DEAE exposure in indoor steam-humidified air in response to complaints of eye irritation (46% of the 40 employees) and skin problems (37% of employees) from workers inside a museum in Ithaca, NY (3). Limited measurements of DEAE in room air were conducted by using a modified NIOSH method. Of 14 samples, DEAE was detected in only 2, a t concentrations of 8 and 10 ppb with a detection limit of 8 ppb. DEAE was detected in higher concentrations on the art work and the plastic surfaces of the display cases, and the authors postulate that skin contact exposure, rather than the inhalation exposure, may be associated with the health effects. In this paper, we report the first real-time measurements of the concentrations of DEAE and cyclo-
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