Environ. Sci. Technol. 1987, 21, 198-202
coal outcrops (22). This accounts for the high retene concentrations on the particulates in Commencement Bay. Retene, with a source function different from the combustion-derived PAH, provides a convenient marker for hydrocarbon transport. The likely somces of hydrocarbons to the water column in the middle of the central main basin, therefore, are the combined inputs of the Seattle and Tacoma metropolitan areas.
Conclusions (1)The highest hydrocarbon concentrations are found on particulates in the surface waters near Seattle. The distributions, therefore, although compositionally similar to the bottom sediments rather than individual sources (2)) do reflect the urban point sources. (2) Particulate hydrocarbon concentrations decrease with depth in the water column and with distance from Seattle. The residence time in the water column is not sufficient to mix these hydrocarbons throughout the estuary and out of the estuary. (3) Particulate PAH and UCM concentrations in the central basin of Puget Sound are uniform throughout the bottom nepheloid layer and the fine-grained surficial sediments. The sediments, except in industrialized embayments, do not reflect the sources. (4) The major particulate hydrocarbon transport processes in the central basin of Puget Sound, a dynamically mixed urban estuary, are a rapid vertical transport through the water column (>lo m/day) and resuspension and lateral transport in the bottom nepheloid layer. (5) Fjord-like estuaries, such as Puget Sound, act as traps for anthropogenic hydrocarbons. The subsequent accumulation of these compounds in the bottom sediments poses a potential threat to the health of the marine environment. Acknowledgments We thank S. Hamilton and D. Run0 for their analytical assistance. E. Baker and A. Paulson provided helpful review and discussions of the manuscript. Registry No. Retene, 483-65-8.
Literature Cited (1) Malins, D. C.; et al. Enuiron. Sci. Technol. 1984, 18, 705. (2) Bates, T. S.; Hamilton, S. E.; Cline, J. D. Enuiron. Sci. Technol. 1984, 18, 299.
(3) Cannon, G. A. “An Overview of Circulation in the Puget Sound Estuarine System”; NOAA Technical Memorandum ERL PMEL-48; NOAA Seattle, WA, 1983. (4) Bretschneider, D. E.; Cannon, G. A.; Holbrook, J. R.; Pashinski, D. J. J . Geophys. Res. 1985, 90, 11949. (5) Ebbesmeyer, C. C.; Barnes, C. A. Estuarine Coastal Mar. Sci. 1980, 11, 311. (6) Baker, E. T.; Feely, R. A,; Landry, M. R.; Lamb, M. Estuarine, Coastal Shelf Sci. 1985, 21, 859. (7) Cokelet, E. D.; Stewart, R. J.; Ebbesmeyer, C. C. “The Exchange of Water in Fjords: A Simple Model of Two-layer Advective Reaches Separated by Mixing Zones”; 19th Coastal Engineering Conference Proceedings, Sept 3-7, 1984, Houston, TX; ASCE: New York, 1984. (8) Baker, E. T. J. Geophys. Res. 1984,89, 6553. (9) Barrick, R. C. Enuiron. Sci. Technol. 1982, 16, 682. (10) Hamilton, S. E.; Bates, T. S.; Cline, J. D. Enuiron. Sci. Technol. 1984, 18, 72. (11) Baker, E. T.; Milburn, H. B. Cont. Shelf Res. 1983,1,425. (12) Baker, E. T.; Milburn, H. B.; Tennant, D. A. EOS Trans. AGU, 1985,66, 1307. (13) Bates, T. S.;Hamilton, S. E.; Cline, J. D. Estuarine, Coastal Shelf Sci. 1983, 16, 107. (14) Romberg, G. P.; Pavlou, S. P.; Shokes, R. F.; Hom, W.; Crecelius, E. A.; Hamilton, P.; Gunn, J. T.; Muench, R. D.; Vinelli, J. “Presence, Distribution, and Fate of Toxicants in Puget Sound and Lake Washington”; Toxicant Pretreatment Planning Study Technical Report C1; Municipality of Metropolitan Seattle (METRO): Seattle, WA, Oct 1984. (15) Barrick, R. C.; Hedges, J. I.; Peterson, M. L. Geochim. Cosmochim. Acta 1980, 44, 1349. (16) Prahl, F. G.; Bennett, J. T.; Carpenter, R. Geochim. Cosmochim. Acta 1980, 44, 1967. (17) Burns, K. A.; Villeneuve, J. P. Geochim. Cosmochim. Acta 1983, 47, 995. (18) Prahl, F. G.; Carpenter, R. Geochim. Cosmochim. Acta 1979, 43, 1959. (19) Lorenzen, C. J.; Welschmeyer, N. A. J. Plankton Res. 1983, 5, 929. (20) Thompson, S.; Eglinton, G. Geochim. Cosmochim. Acta 1978, 42, 199. (21) Prahl, F. G.; Carpenter, R. Geochim. Cosmochim. Acta 1983, 47, 1013. (22) Barrick, R. C.; Furlong, E. T.; Carpenter, R. Enuiron. Sci. Technol. 1984, 18, 846. Receiued for reuiew May 27,1986. Accepted September 17,1986. This work has been supported by the National Oceanic and Atmospheric Administration’s Section 202 Long-Range Effects Research Program.
Development of an On-Line Mercury Stream Monitor E. Ray Hinton, Jr.,” Leah K. Rawlins, and Edward 8. Flanagan Plant Laboratory, Oak Ridge Y-12 Plant, Martin Marietta Energy Systems, Inc., Oak Ridge, Tennessee 37831
An on-line, computer-controlled monitor for mercury in streams and aqueous discharges is described. The instrument is capable of unattended, continuous operation in the 0.5-10 ppb mercury concentration range and is able to sound an alarm from a remote location to a central monitoring facility.
Introduction Within the last few years, environmental concerns have been raised pertaining to the levels of mercury found in 198
Environ. Sci. Technol., Vol. 21, No. 2, 1987
the soil and water around the Oak Ridge Y-12 Plant (1). Since 1974, several studies have examined the mercury levels in soil, water, vegetation, and animals found in the Oak Ridge complex (2-4). The East Fork Poplar Creek originates within the Y-12 Plant. The numerous discharge points of the storm sewer system, shown in Figure 1, are located along the length of the creek, which flows into New Hope Pond. From the outfall of the pond, the creek flows through the city of Oak Ridge, TN. Several of the discharge points drain sumps located in buildings where mercury was used. During
0013-936X/87/0921-0198$01.50/0
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BETA 4
E L E X PRoDUCTlON PLANT 1953.1956
I.
ALPHA 5 COLEX PRODUCTION PLANT
RUST
,. DUMPING
'
STATION
ALPHA A COLEX PRODUCTlOh
MERCURY CONTINUEU B E L O W
UPPER EAST F O R K POPLAR CREEK
Y-12 PLANT AREA WEST OREX DEVELOPMENT 1951 1952
Y 12 PLANT AREA EAST ELEX DEVELOPMENT
OREX PILOT PLANT 1953 1954
ClPOLETTl WEIR
,x 'L-
PRIOR TO CONSTRUCTION OF NEW HOPE POND
COMPOSITE SAMPLER
NEW HOPE POND CONSTRUCTED IN 1963
Figure 1. Lithium isotope separation facilities at the Y-12 Plant, 1950-1963.
periods of wet weather, natural springs under the buildings fill the sumps, causing the contents to be pumped into the creek. A concentration gradient exists along the length of the creek. The mercury levels in the sumps vary considerably but are normally below 10 ppb at the entrance of New Hope Pond and approximately 2 ppb (the EPA drinking water limit) or below at the outfall of the pond. The residence time in the pond allows most of the mercury adsorbed on particulate matter to settle out, thus reducing the mercury levels that leave the pond. In an attempt to monitor the release of mercury from the discharge points and to gain data on the concentration variations at several points, an aggressive sampling program has been initiated. Grab sampling has been the normal sampling mode, but this type of sampling has several drawbacks that make it unsuitable for a rapid monitoring system. Several hours or days can pass before data are obtained from a central laboratory facility, and the method is also time consuming and expensive. In an attempt to overcome these deficiencies, an on-line monitor has been developed to provide remote, unassisted monitoring. The requirements for a prototype monitoring instrument were as follows: (1) Unattended continuous operation, providing 24-h coverage. (2) Multisite monitoring. The prototype instrument would be located near New Hope Pond and would monitor the mercury concentrations at the extrance and exit of the pond. (3) Routine operation in the 1-10 ppb Hg concentration range. Preliminary data indicated the mercury concen-
trations at these two points were normally in this range. (4)Capable of future operation below 0.1 ppb. This capability was desirable if stricter discharge limits were set for the plant. (5) Able to alarm in a remote central monitoring facility. The monitor would alarm if a preset level was exceeded at the exit to New Hope Pond.
Experimental Section Instrumentation. A prototype instrument has been fabricated around a Spectro Products HG-3 mercury analyzer (Spectro Products, Inc., North Haven, CT). The analyzer is a dual-wavelength spectrophotometer that ratios the intensity of a pulsed mercury hollow-cathode lamp (253.7 nm) against the intensity of an iron hollowcathode lamp (248.3 nm) to provide background correction. A modified Perkin-Elmer MHS-20 mercurylhydride generator (Perkin-Elmer Corp., Norwalk, CT) is used for sample preparation before reduction. The generator has been modified with an all-Teflon reaction vessel with tube fittings for sample and reagent introduction and a Hamilton 400 Series syringe pump (Hamilton Co., Reno, NV) for rapid and consistent introductions of reductant. Two other Hamilton syringe pumps are used. One pump injects KMnO, and H2SO,/HNO3 solutions, while the other adds samples, calibration standards, and blanks. Either 110 VAC Teflon or TFE solenoid valves (Fluorocarbon, Inc., Anahiem, CA) with l/*-in. orifices are used due to the highly corrosive nature of the reagents. A Hewlett-Packard HP9825 desktop computer (Hewlett-Packard, Palo Alto, CA) is used for control and data acquisition. Environ. Sci. Technol., Vol. 21, No. 2, 1987
199
Yv5
DRAIN
FLOW METER ORIFICE DIA. FLOW AT 20 psi 0 0035 105 ml/mtn F ? F2 0.006 316 mllmin F3 0 007 590 mllmtn
Figure 2. Schematic diagram of prototype instrument.
Two in-house fabricated, 1-L glass sampling reservoirs accept continuous flows from two sampling points in the pond. The reservoirs are constructed so that the sample streams enter the reservoirs tangentially, creating vortex mixing to minimize sediment settling. The system contains two in-house fabricated, printed circuit boards to interface the CPU to the various pumps, valves, and sensors. The first board is an ADC used to convert the 0-1-V output of the HG-3 analyzer to a 12-bit digital form that can be processed by the CPU. The second board is used to interface the TTL control lines from the CPU to the three syringe pumps and the ten solenoid flow valves. The second board also interfaces reagent-level indicators to the CPU so that the control softwave can be alerted when any reagent in the system becomes low or the reaction vessel overflows. A second instrument has been constructed that contains several modifications. The major modification consisted of replacing the HP9825 computer with a Micro-Link, single-board computer (Micro-Link, Carmel, IN). This computer features a 2-80 microprocessor with 64K RAM, 8K ROM, a serial interface, an 8-bit parallel port, and a battery-backed real-time clock, all of which are on a single, STD-bus-printed circuit board. A general purpose 110 board with one RS-232 interface and 32 bidirectional interface lines, a floating point processor board that performs BCD floating point arithmetic, and the two in-house 200
Environ. Sci. Technol., Voi. 21, No. 2, 1987
constructed interface boards described above complete the computer system. Reagents. A 7.5% v/v HNO,-7.5% v/v H2S04solution was prepared from reagent-grade acids obtained from J. T. Baker Chemical Co. (Phillipsburgh, NJ). A 0.5% w/v solution of KMn0, was prepared from reagent material also obtained from that company. The NaBH, obtained from either Sigma Chemical Co. (St. Louis, MO) or Alpha Products (Division of Morton-Thiokol, Danvers, MA) was used as the reductant. A 3% w / v solution was prepared by dissolving 98% NaBH4 in a 1%w/v NaOH solution. All mercury calibration standards were prepared by serial dilutions from a 1000 f 2 mg/L mercury standard solution (Hach Chemical Co., Ames, IA). The standards were preserved in solution with 0.5% w/v K,Cr207 and 5% v/v "OB. A solution that was 0.5% w/v K2Cr207and 0.5% v/v HNOBwas therefore used as a blank. Calibration. The instrument self-calibrates every 6 h. The calibration sequence is as followr, (see Figure 2): (1)Valves 8 and 9 open, and pump 2 dispenses 25 mL of reagent blank into the reaction vessel. (2) Valve 7 opens, and pump 1 sequentially dispenses 10 mL of acid solution and 10 mL of KMn04 solution. (3) Pump 3 dispenses 3 mL of NaBH, solution. (4) Argon is flushed through the solution to sweep the Hg vapor into the cell of the HG-3 analyzer. ( 5 ) No data are taken.
1
0 4 ppb RESPONSE
A
0.5 ppb RESPONSE
0
AVG = 4.2
* 0.3 ppb
Table I. Comparison of “Cold Digestion” with “Hot Digestion”
cold digestion hot digestion (ppb Hg)” (ppb Hg)” 3.3 5.9 4.2 3.8
3.3 i 0.1 5.3 f 0.1 4.0 f 0.1 3.1 f 0.1 2.7 f 0.1 2.9 i 0.0
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cold digestion hot digestion (ppb Hg)” (ppb Hg)”
f 0.2
3.5 2.5 2.7 2.7 3.5 3.2
k 0.5 f 0.1 f 0.1
3.1 f 0.2 2.8 f 0.1
3.7 2.8 2.6 2.7 3.1 3.3
f 0.1 f 0.1
i 0.1 f 0.1 f 0.1 f 0.2
f 0.1 f 0.0 i 0.0 f 0.1 k 0.1 f 0.1
Average of three aliauots.
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I
I
05
0
10
20
30
40
50
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70
80
90
100
110
120
130 140
SAMPLE NUMBER
Figure 3. Evaluation of on-line monitor with 0.5 and 4 ppb Hg standards.
(6) Valve 5 opens, and the reaction vessel is drained. (7) Steps 1-4 are repeated with the reagent blank. (8) The analog output of the HG-3 analyzer is digitized and integrated by the computer. This peak area is stored in the computer. (9) Steps 1-6 and 8 are repeated with an 8 ppb Hg standard. (10) The computer calculates the y intercept and slope of a line generated by the peak areas and stores this calibration curve. Sampling. Samples are analyzed on the hour. Steps 1-9 are repeated with the upstream and downstream samples, respectively. The peak areas are then compared to the calibration curve, and concentrations are calculated and printed. The cleaning and analysis sequence requires approximately 7 min to complete. If the calculated concentration of the downstream sample is above a preset level, the instrument automatically resamples the downstream point. If the second analysis is still above the preset level, an alarm is generated in a central monitoring facility. The instrument will continue to monitor the downstream point until the concentration drops below the alarm level or the instrument is manually reset.
Results and Discussion Evaluation. To evaluate the precision and accuracy of the instrument, the instrument was programmed to sequentially analyze 0.5 and 4 ppb standards over approximately an 8-day period. The concentration levels chosen represent the stated detection limit and a nominal stream value. The results of the evaluation are shown in Figure 3. As can be seen, the accuracy of the instrument is within 90%-95% of the actual values. The relative standard deviations at the 0.5 and 4 ppb levels are f18% and &7%, respectively. Digestion Comparison Study. A comparison study was made between samples analyzed manually on the monitor and also analyzed by the digestion method described in EPA Procedure 245.1 (5),which is an adaption of the procedure by Hatch and Ott (6). The EPA procedure uses a rigorous 2-h digestion of the samples in a water bath at 90 “C. The on-line procedure employs a “cold digestion” method. The cold digestion consists of adding a solution that is a mixture of HN03/H2SOIand a solution
0
1
2
3
4
5
6
7
8
8
10
ppb Hp LABORATORY
Flgure 4. Comparison of on-line vs. laboratory data.
of KMn04 to the stream samples before the reduction step. The study comparing the “hot” digestion with the “cold” digestion showed excellent correlation between the two techniques (as shown in Table I). On-Line vs. Laboratory Comparison Study. An extended comparison study between the on-line and the in-house EPA laboratory procedure was begun. The study consisted of randomly taking grab samples at the sample reservoir outlets immediately after the on-line instrument had drawn a sample. The samples were taken over a period of approximately 4 months. Figure 4 shows a graph of 108 comparison samples. Several factors influenced the plot. First, the plot compares single samples that were not exactly the same, therefore introducing potentially significant variations. The samples analyzed by the EPA method were integrated into other batches of samples; consequently, an extended time period may have elapsed before the samples were analyzed. The cold digestion procedure is generally sufficient for oxidation of most samples, but it is not sufficient for all samples (e.g., highly complexed), which could account for the points biased toward the EPA method. A 20% low bias for the laboratory using the EPA method was discovered for a time period that overlapped this study, which is reflected by the points biased high toward the on-line method. Considering these factors, it was felt that the on-line instrument generally reflected the standard method well enough to monitor the stream discharge, with the understanding that the monitor was not a replacement for the standard method but was a cost-effective and efficient method to monitor the fluctuations in the discharge concentrations leaving the plant. On-Line Data. Figure 5 shows a plot of a 20-h segment of both upstream and downstream data. As can be seen from the plot, the monitor detected two pulses of mercury entering New Hope Pond that were approximately 3 ppb above the nominal stream concentration of 2-3 ppb, which indicates the instrument is capable of detecting small Environ. Sci. Technol., Vol. 21, No. 2, 1987
201
Environ. Sei. Technol. 1987, 27, 202-208
charges from the Oak Ridge Y-12 Plant.
6 0 ppb Hg UPSTREAM
Acknowledgments
A ppb Hg DOWNSTREAM 5
E. R. Rogers, Jr., and P. Berlinski are acknowledged for their design assistance. R. J. McElhaney is also acknowledged for his discussions and advice. R. E. Carroll is recognized for helping prepare and edit the manuscript.
4
R e g i s t r y No. Mercury, 7439-97-6; water, 7732-18-5.
e”
%
Literature Cited
3
2
i
+-++A
P-+-
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1
1 0
2
4
6
8
10
12
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1 14
/
1 16
1 18
1
1
1
20
TIME (hl
Figure 5. Upstream/downstreamppb Hg at East Fork Poplar Creek.
concentration fluctuations in the stream. The downstream peak at 17:OO h is thought to be the 1O:OO h peak exiting the pond.
Conclusions The instrument described in this paper provides important stream monitoring data on mercury concentrations on a continuous basis. Continuous data of this type are needed to understand and allow control of mercury dis-
(1) “Testimony a t a Joint Hearing of the Subcommittee on Energy Research and Production and the Subcommittee on Investigations and Oversight of the U S . House Science and Technology Committee on the Impact of Mercury Releases at the Oak Ridge Complex”; July 11, 1983. (2) Reece, J. “Preliminary Aquatic Survey of East Fork Poplar Creek and Bear Creek, 1974”; Environmental Protection Branch, Safety and Environmental Control Division, Oak Ridge Operations, USAEC: Oak Ridge, TN, 1974. (3) Elwood, J. W. ORNL/CF/77/320, Oak Ridge, TN, 1977. (4) Van Winkle, W.; Counts, R. W.; Dorsey, J. G.; Elwood, J. W.; Lowe, V. W.; McElhaney, R.; Schlotzhauer, S. D.; Taylor, F. G.; Turner, R. R. ORNL/CF/82/257, Oak Ridge, TN, 1982. (5) Methods For Chemical Analysis of Water and Wastes;US. Environmental Protection Agency. U.S. Government Printing Office: Washington, DC, March 1983; EPA60014-79-020. (6) Hatch, W. R.; Ott, W. L. Anal. Chem. 1968, 40, 2085. Received for review March 25, 1986. Accepted August 25,1986.
Measurement of Henry’s Law Constants for C, and C2 Chlorinated Hydrocarbons James M. Gossett Environmental Engineering Department, Cornell University, Ithaca, New York 14853
A modification to the EPICS procedure for measuring Henry’s constants is proposed, wherein the original assumption of equal solute mass additions to bottle pairs has been eliminated via a gravimetric accounting, resulting in increased precision. The modified procedure was applied to 13 volatile C1 and C2 chlorinated hydrocarbons at temperatures from 10 to 35 “C, representing a range in dimensionless Henry’s constant (H,) of from 0.05 to 1.8. The mean coefficient of variation (CV) in Henry’s constant was 3-4% ; however, by employment of greater differentials in liquid volumes within bottle pairs, CV may be reduced to an estimated 2.5-3.5%. Precision deteriorates markedly at very low Henry’s constants (Le., H , < 0.1). Dilute aqueous mixtures of volatile solutes (with methanol also present) were employed in these measurements of Henry’s constant. Comparison with previous results from singlesolute assays supports the use of mixtures-at least within the range explored here. The effects of ionic strength on apparent Henry’s constants were evaluated for six of the compounds, with KC1 concentrations up to 1.0 M. The practical impact of ionic strength appears to be minimal. Salting-out coefficients ( k ) ranged from 0.107 to 0.213 L-mol-’ a t 20 “C. Introduction
The partition coefficient relating air and aqueous concentrations of a volatile substance is commonly referred 202
Environ. Sci. Technol., Vol. 21, Nu. 2, 1987
to as Henry’s constant. Values of Henry’s constant are required by design and performance models of air-stripping processes for the renovation of organic solvent contaminated waters, as well as by transport models that attempt to describe movement of volatile pollutants in the unsaturated zone of subsurface environments. Unfortunately, reliable values of Henry’s constant are often not available for solutes of environmental concern. Mackay and Shiu (I) have presented a comprehensive review of common methods for measuring Henry’s constants-along with their respective merits and deficiencies. There are three basic methods cited by Mackay and Shiu: (i) use of vapor pressure and solubility data; (ii) direct measurement of air and aqueous concentrations in a system at equilibrium; (iii) measurement of relative changes in concentration within one phase, while effecting a near-equilibrium exchange with the other phase. The first method suffers from lack of reliable solubility data. For example, reported solubility values (25 “C) for dichloromethane range from 13 200 to 19 400 mg/L (1). Additionally, in some instances, the vapor pressure of the water-saturated organic substance-the vapor pressure that should properly be used in the estimation of Henry’s constant-differs significantly from that of the p u r e organic, which is the value usually tabulated. The second method is difficult to carry out with accuracy at the low concentrations typical of environmental levels. The third
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