Environ. Sci. Technol. 1990, 24, 1059-1069
New Source Identification of Mercury Contamination in the Great Lakes Gary E. Glass,*.+John A. Sorensen,t Kent W. Schmldt,t and George R. Rapp, Jr.t Environmental Research Laboratory-Duluth, U.S. EPA, 620 1 Congdon Boulevard, Duluth, Minnesota 55804 and College of Science and Engineering, University of Minnesota, Duluth, Minnesota 55812 Investigations of two Great Lakes estuaries for new sources of mercury contamination revealed previously unmeasured high concentrations in water, sediments, and precipitation. For the St. Louis River estuary, the highest water and sediment mercury concentrations occurred near a regional wastewater treatment facility. Analysis of waste streams showed that the highest levels were associated with the incineration process where sewage sludge is burned by using refusederived fuel from municipal garbage, and from municipal wastewater inputs. The total mass of mercury entering the St. Louis River estuary (Minnesota and Wisconsin) is estimated from upstream, wastewater, and precipitation sources. Drought conditions and lake seiche combined to push elevated mercury concentrations “upstream”, exposing more than 80% of the estuary to mercury contamination. The highest water concentrations in the Fox River/Green Bay (Wisconsin) estuary occurred immediately downstream from the DePere Dam and originated from sediment sources and/or unidentified discharges. Investigation of contamination of water samples by Kemmerer and Van Dorn water samplers showed that plastic components contained up to 0.2% mercury that leached into the samples. A new sampler was devised to correct the problem. The detection limit for US.EPA methodology for mercury analysis of water (No. 245) has been lowered from 25 ng of Hg/L to an average of 2 ng of Hg/L by using a standardized protocol of standard solutions and blanks and by prescreening reagents for the lowest mercury content to achieve a reagent blank value of -4 ng of Hg/L. These low detection limits create opportunities to identify new sources of mercury contamination. The identification of incineration of municipal refuse as a major source of mercury emissions to the environment may lead to additional discoveries across the United States, where more than 150 facilities have been built.
Introduction Mercury contamination of the fishery affects hundreds of lakes and rivers in the Upper Midwest and around the Great Lakes (1-4); see Figure 1. In Minnesota, fish consumption advisories restricting full utilization of the resource because of elevated levels of mercury have been issued for 285 water bodies compared to the limited database of 22 water bodies 10 years ago. Six years ago in Wisconsin, five inland lakes were found to have elevated levels of mercury; now several hundred have been studied and 154 water bodies have restrictions on fish consumption because of known high levels of mercury residues. In December 1988 in the broadest health warning issued on inland lakes, Michigan’s Department of Public Health announced that people should limit consumption of fish from all of the state’s 10000 inland lakes because of mercury contamination. In the Great Lakes the International Joint Commission (IJC) identified 42 areas of concern for the development of plans for mitigation of pollution problems (5). In 34 of these areas of concern, U.S. EPA.
* University of Minnesota. 0013-936Xl90l0924-1059$02.50/0
mercury pollution or contamination is listed as an issue (ref 6; Figure 1). Are these examples of increasing mercury contamination or are they a result of the widespread knowledge about mercury contamination of the freshwater fishery in the upper midwestern states, or both? What are the sources and causes of this contamination? What can be done to mitigate the problem? In order to examine these questions we have selected the St. Louis River estuary (Minnesota) as a primary study area and the Fox River/Green Bay (Wisconsin) as a secondary study area. These are shown in Figure 1 along with other locations identified by the IJC ( 4 ) as having mercury problems. The St. Louis River is an important water body shared by Minnesota and Wisconsin where fish consumption is severely restricted because of mercury, PCB, and dioxin contamination. Fish consumption advisories have been issued by health departments of both Minnesota and Wisconsin (1,2).The Wisconsin Department of Natural Resources (WDNR) states that no one should eat walleyes larger than 66 cm, and walleyes 46 cm or larger should not be consumed by children under 18, pregnant or breastfeeding women, or women who plan to have children (2, 7). The Minnesota Department of Health (MDH) states that all fish species from the mouth of the St. Louis River to a distance of 50 km upstream are moderately contaminated with mercury and PCBs and consumption should be restricted to one meal per month, and that high-risk individuals should not eat any fish from the river (1). The problem of toxic levels of contaminants in fish persists in spite of major improvements in water quality such as increased oxygen, reduced noxious wastes and odors, and decreased concentrations of nutrients and suspended solids. These improvements were achieved by the construction and operation of the Western Lake Superior Sanitary District (WLSSD) in 1978 and have resulted in the reestablishment of a large sport fishery in the estuary, indicating the potential for a renewed commercial fishery. Although this is the largest estuary on the US. side of Lake Superior (4700 ha), its importance as a nursery area for the fishery of the western arm of Lake Superior has been overlooked (8). The estuary is also an important seaport with -30 million tons of cargo, mostly iron ore and grain shipped annually and more than 3000 vessel visits per year. The 50 km of ship channels in the estuary are maintained by dredging to a depth of 9 m. This creates 150 000 m3 of sediment each year that must be disposed of on land because of elevated contaminant concentrations (5). The Fox River is located in northeastern Wisconsin and flows into the Green Bay region of Lake Michigan. The river has a history of former mercury discharges to it from the large number of paper mills. I t also is an important sport fishery area. Identification of the sources and causes of the continued contamination of these and other water bodies is the major objective of this study. Once the sources and causes are identified, options for mitigation can be developed and implemented to reduce toxic compound residue levels in fish and other biota.
0 1990 American Chemical Society
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Environ. Sci. Technol., Vol. 24, No. 7, 1990
1050
DEGRADED AREAS IN THE GREAT LAKES BASIN
@ No mercury found
0 Mercury problem
0
Mercury identified
0
Incinerator sewage sludge
-
Figure 1. Laurention Great Lakes and watershed map showing the location of the IJC 42 areas of concern, degraded areas due to mercury contamination, and the locations of sewage sludge incinerators. From Hartig and Thomas (5) and Great Lakes Water Quality Board ( 4 ) .
Methods Analytical Methodology. Mercury measurement methodology utilizes cold vapor atomic absorption spectrometry (CVAA) approved by the US. Environmental Protection Agency (US.EPA) (9). This method was used with modifications (IO)for standardizing operating procedures and screening reagents for lowest levels of mercury content to reduce the blank to the lowest value. By employment of quality assurance monitoring procedures for each batch of samples analyzed, a significant improvement in the detection limit was achieved. The following is a list of reagents and manufacturers that were used: H2S0,, HN03, and NaC1-Fisher Scientific, Fair Lawn, NJ; KPCr207,KMnO,, and (NH20H)2-H2S04-Baker Inc., Phillipsburg, NJ; K2S208-Matheson, Coleman, & Bell Manufacturing Chemists, Norwood, O H SnS04-EM (Science) Industries, Inc., Cherry Hill, NJ. The analytical instrumentation used included PerkinElmer atomic absorption spectrophotometers (Models 403 and 5OOO) equipped with deuterium background correctors, electrodeless discharge lamp (ME-782), and power supply (APR) and a Heath Schlumberger (SR-206) multirange variable-speed chart recorder. A slit width of 1 mm (spectral band width 0.7 nm) was used at a wavelength of 253.7 nm. The instruments were operated in the concentration mode (lox) with the integration set at 10 average (10 samples of the signal are averaged as one value per 1080 Environ. Sci. Technol., Vol. 24, No. 7, 1990
second). The concentration readout of the signal was recorded on the strip chart at 5 and 20 mV/25 cm chart width for water and sediment samples, respectively. The elemental mercury analyte was circulated (1 L/min) through an 18- X 1.8-cm cylindrical absorption cell by means of a Neptune Dyna Pump (Neptune Co., Dover, NJ). After the atomic absorption resulting from the presence of mercury vapor reached a maximum in about 0.5-1.0 min, the pump was turned off and the absorption rose to its final value. The sample size for water samples was usually 150 mL and the total volume of the flask (250 mL) contents was 172 mL after reagents had been added. Standardized analytical calibration was obtained by analyzing three standard solutions and two reagent blank samples at the beginning and end of each batch of samples. National Bureau of Standards (NBS) certified samples were also included in each batch. Unknown sample concentrations were computed by using a standardized linear regression analysis program (copy available upon request) that also records the run number, date, analyst, chart scale, and number of standards and blanks and computes t.2 for recorder response vs Hg added in nanograms and the intercept for 0.0 ng of Hg added. The average blank response is subtracted from all recorder responses before the regression is performed. The characteristics of a run were monitored for quality assurance by comparing results with the previous runs for changes in sensitivity, blank con-
6
/ 0
f
f
lo-
1
Flgufs 2. Comparison of mercury concentrationsin water, determined by using two alternate methods vs the standard US. EPA cold vapor atomic absorption method. 0,water, sediment, etc; A, ash, X, Wiklco leachate (deuterium background corrected); 0,gold film resistance mercury analyzer.
tamination, precision, and accuracy. Time trend plots of run parameters were used to judge the performance of the analytical instrumentation, reagent purity, and overall performance of the analytical operation. The median detection limit (11) with the standardized procedure was 2 ng/L for water and precipitation samples and 8 ng/g of sample for sediments. The gold gauze amalgam accessory was used with the CVAA system to check for interferences. It was used in conjunction with a set of relay-activated Teflon gas valves to aerate the sample, collect the analyte on the gold gauze, flush air past the heated gauze, which releases the previously trapped analyte into the absorption cell, and finally, exhaust the system into an acid permanganate (gas scrubbing) mercury collection vessel for wastes. Sediment analysis for mercury concentrations was conducted using U S . EPA methods (9),with two modifications: (1)After removal and cooling, deionized water was added to a total volume of 150 mL before adding 6 mL of NaC1-hydroxylamine sulfate solution, and (2) The headspace in the flask was flushed with room air for 20-30 s to remove possible gaseous interferents (Cl,) before the SnSO, solution was added and the flask was connected to the absorption cell and recirculating pump system. The standard calibration and blank samples are carried through the same procedure as the sediment samples. As in the water method, identical seta of standards and blanks for calibration are analyzed both before and after the unknown samples to monitor any change in instrument sensitivity during the analyses. Glassware and utensils used in the homogenization and transfer of samples and the analysis are cleaned by rinsing with deionized water (prepared with a Millipore Super-Q filtered, deionized water system, Millipore Corp., Bedford, MA), soaking in 30% HNOB,and rinsing three times with deionized water. All new glassware and reagents are checked by running through the analysis before use to check for contamination. Deuterium background correction tests were conducted to assure the accuracy of the mercury analysis and to check for positive interferences by the possible presence of nonmercurial compounds that could absorb UV radiation a t 253.7 nm. In addition, gold film mercury vapor analyzers (Models 511 and 431), Jerome Instrument Corp., Jerome, AZ, were used as independent checks on the accuracy of the atomic absorption (AA) methods (12).These instruments were found to be especially useful and convenient in the field for monitoring ambient air concentrations with gold film mercury collectors (13). A summary
of the data from the various methods of analysis used on selected samples is shown in Figure 2. Sampling Methods. The plastic Kemmerer sampler (and Van Dorn sampler both manufactured by Wildco Wildlife Supply Co., Saginaw, MI) designed for water sampling, commonly used for limnologic studies, was found to severely contaminate water samples with 20-250 ng/L mercury depending on how rapidly the sample was taken. The mercury originated primarily from the polyurethane plastic used as ring seals on the movable end pieces that close the main barrel of the sampler. After the problem was identified in the field, laboratory tests were conducted to determine the maximum extent of contamination when this type of sampler is used. The blue plastic bands used as end seals on Wildco samplers (Models 1520 and 1540) were removed from the original equipment and soaked for varying periods of time in distilled water and separately in dilute acid. Concentrations of mercury as high as 300000 ng/L could be observed in the water leachate after a few days. These are shown in Figure 2 as hourglass symbols. To avoid this problem, a new water sampler was designed and built that used a removable Pyrex stopper and replaceable square 300-mL Nalgene polyethylene bottles to collect the samples. The sampler bottle itself could be immersed in the water body to be sampled and lowered to the desired depth and the stopper loosened with a jerk of the lowering line. The sampler was immersed several times at a new site without the sampling bottle to assure that nothing would carry over from the previous sample from the Pyrex stopper. Tests showed this procedure to be effective. The air bubbles released by the filling bottle served to indicate the direction and relative speed of water currents. Before sampling, an acid dichromate preservative (6 mL of 2.5% K,Cr20, and 25% HNO,) was added to new bottles that had been rinsed with deionized water. Replicate water samples were taken at every fifth site on the average. Unused sampling bottles (with preservative) were filled with distilled water on the day of analysis to use as a blank. With this technique, blank values for the sample bottles alone and many samples from remote lakes and streams showed less than the detection limit of 2 ng/L, indicating that systematic sampling contamination had been eliminated. Suspended Particulates and Plankton. Large-volume (20-L) samples were taken by immersion of stainless steel pressure filtration vessels to determine dissolved and particulate forms of mercury. These samples were kept at 4 "C and pressure filtered by using compressed nitrogen and 0.45-pm membrane filters. Smaller sample volumes (up to 300 mL) were filtered by using a Buchner funnel apparatus and membrane filters. Both filtrate and filter were analyzed and compared with whole water total mercury analysis. Good agreement was obtained, indicating no significant contamination or sorption of mercury by the sampling or filtration techniques. Plankton samples (>80pm) were obtained from vertical tows by using a Wisconsin-style net (Wildco) and a "Minnesota plankton bucket" (J.Shapiro, U. of Minnesota, Minneapolis, MN). The net was soaked in dilute acid before use to reduce the leachable mercury content of the mesh. The Minnesota bucket was tested with dilute acid and did not leach significant amounts of mercury. Samples were analyzed by using the same methodology as for water. Sediments. Sediment samples were obtained with Hongve and Wildco corers and push rods (14). The surface portions (surface 3-6 cm) of the cores were collected in zip-lock polyethylene bags that were previously tested and Environ. Sci. Technol., Vol. 24, No. 7, 1990
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Table I. Statistical Summary of Analytical Characteristics for the Analysis of Mercury in Water by CVAA for 68 Runs run characteristic sensitivity, cm/ppt r2 a S bcm ,::(I cmc blank concn, ppt detection limit, ppt NBS water: ppt NBS sediment! ppm
mean
median
SD
N
min
max
0.141 0.994 0.251 -0.0174 4.20 2.32 58.7 1.35
0.139 0.996 0.222 -0.0240 3.85 2.15 58.8 1.34
0.022 0.0070 0.131 0.061 1.85d 1.34 4.13 0.092
68 68 68 68
0.068 0.967 0.074 -0.149
68
0.80 0.00
0.192 1.000 0.768 0.134 9.70 6.90 68.9 1.49
68 71 8
44.9 1.21
a ? is the coefficient of determination ("goodness"of fit). * S is the standard error of the regression line, [x.(predicated - measured)*/N - 2]1/2;chart recorder response is measured in centimeters. .TK'e Y intercept is the recorder response for 0.0 ng of added Hg as determined
by the regression line. The average blank response is subtracted from all recorder responses before the regression is performed. "The average standard deviation of blanks within individual runs is 0.77 ppt. 'NBS certified (No. 1641B): 60 f 1.6 ppt at 1:25300 dilution. fNBS certified (No. 2704): 1.44 f 0.07 ppm. Laboratory duplicate precision equals field replicate precision, 1 ppt.
shown to contribute no detectable quantities of mercury to the sample. Composite sediment samples obtained from Minnesota Pollution Control Agency (MPCA) staff who used an Eckman dredge were also analyzed. The sediment samples were kept at 4 "C until analyzed. In Situ Measurements. Profiles of in situ water column measurements of conductivity, turbidity, temperature, pH, and dissolved oxygen were made throughout the St. Louis River estuary with an Interocean Water Quality monitoring probe (Model 512). The influence from major sources of water to the estuary on these parameters vary depending on location, flow rates, and meteorologic conditions. The location of the mixing zones of these sources can change but the characteristics of each can be measured. The St. Louis River is high in conductivity; the Nemadji River is high in turbidity because of red clay; and Lake Superior is colder, more dilute, lower in conductivity, and least turbid. Atmospheric Inputs. Precipitation was monitored near the mouth of the Lester River in Duluth, MN. Sampling was accomplished by using an automatic sensing collector with a double sensor head (40 cm2) to activate the movable roof that covers a Teflon-lined funnel with 0.212 m2 of collection area (MIC Co., Thornhill, Ontario, Canada). The bottom surface of the funnel is heated in winter with a 60-W surface heater to melt the snow samples. The precipitation passes out the bottom of the funnel through a Teflon fitting and tubing into a l-L sample collection bottle (Nalgene, polyethylene) containing acid dichromate preservative located inside the enclosed, heated base (4 "C) of the MIC sampler. Sample collection bottles were changed manually at intervals corresponding to individual precipitation events or several times during heavy events. Collection times, sample volumes, and meteorologic observations were recorded. Air sampling was accomplished by drawing air through gold film dosimeters, two or three in series (Jerome Instrument Co., Jerome, AZ) and a flowmeter by use of a pressure-vacuum pump (Neptune Dyna Pump). These samples were analyzed daily with a gold film resistance mercury analyzer (Model 431, Jerome Instrument Co.). Additional samples were taken by using gas scrubbing chambers that contained acid dichromate absorbent and were analyzed by CVAA techniques. Gas emissions from the sludge and municipal refuse derived fuel (RDF) incinerator at WLSSD were sampled with a heated probe positioned at several points across the 1.5-m diameter of the stack. A Peterson Instrument Co. sampler equipped with a glass particulate filter chamber, three bubblers in series, and a drying chamber were used to collect particulates and mercury from the gases emitted over three l-h periods according to EPA procedures (15). 1062 Environ. Sci. Technol., Vol. 24, No. 7, 1990
Each of the bubblers was analyzed separately to check for capture efficiency.
Results and Discussion Analytical Methodology. Table I shows a statistical summary of results for 68 runs of the analytical determinations of mercury using EPA methodology as described above. These results indicate that the detection limits for the EPA method can be substantially improved over the lower limits of 25 (9)and 8 ng/L (10). The most significant factor in improving the detection limit is the reduction of the blank value by prescreening reagents to select those with the lowest mercury content. Routine blank values of 4 ng/L can be observed. The importance of reproducibility of the blank values is seen in the definition of the detection limit used (11), which is 3 times the standard deviation of the four blank values used (averaging 0.77 ppt for each run) in our standardized procedure. Thus, a detection limit of 2 ng of Hg/L can be routinely achieved. Comparisons of the results using different analytical techniques for the same samples are shown in Figure 2. The analytical determinations for the different samples were performed on differing sample dilutions corresponding to the chosen range of analytical standards that were usually between 15 and 120 and 60 and 480 ng/L for water and sediment samples, respectively. For a mixture of sample types over a large range of concentrations, these results show a slope of 1.0, indicating little or no positive interference for the CVAA from non-mercury-absorbing compounds. Highest concentrations were observed for the Kemmerer polyurethane leaching tests, followed by samples from municipal incinerator ash leachate, stack gas scrubber water, various wastewater streams, and river and precipitation water. The polyurethane used in the manufacture of Wildco Kemmerer and Van Dorn samplers was made with a urethane catalyst containing an organomercurial at 20% mercury calculated as metal (16). The polyurethane was formulated at 0.5-1.0% catalyst, making the mercury concentration of the final product about 0.1-0.2% mercury. All four of the Wildco plastic Kemmerer samplers that were used to collect surface water samples in this and other studies resulted in sample contamination. In two instances, the samples were collected by personnel of other agencies who had no knowledge of the contamination problem. For example, water samples from Wisconsin lakes were collected in 1983 with a Wildco sampler and sent to US.EPA for analysis. A summary of these results for lake water samples (now known to be contaminated) were published by Glass et al. (ref 10, p 43, Table 2). It is estimated that 300400 samplers per year have been sold over the last 15 years, resulting in a great potential for
Table 11. Mercury Concentrations in Water, Plankton, Suspended Solids, and Surface Sediment Samples from Sites in the Lower St. Louis River during 1988” sampling site upstream reservoirs Whiteface Res. Wolf Lake Boulder Res Wild Rice Lake Island Lake (east) Island Lake (west) Fish Lake Cloquet R., Hwy 7 St. Louis R. Brookston Hwy. 33 USG Potlatch Dam Scanlon Dam 1-35 Bridge Thomson Res. Thomson Dam Forbays L. FdL Dam Hwy 23 (WI) Oliver Br. Spirit L. Riverside Kimbals Bay Grassey Pt. Br. St. Louis Bay WLSSD Pt. Globe El. Baltnik Br. Superior Bay 19th MN Ave. 27th MN Ave. 39th MN Ave. PP Rec. MN Bark. Is. Br., WI Nemadji R., WI Allouez Bay, WI Superior entry Duluth Ship Canal L. Superior, 6th MN Ave.
waterc
plankton
-177 -158 -129 -121 -119 -113 -100 -74
