In the Laboratory
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Rapid Determination of Mercury in Seafood in an Introductory Environmental Science Class Jeanette K. Rice,* J. David Jenkins, A. Citabria Manley, Eric Sorel, and C. Jimmy Smith Department of Chemistry, Georgia Southern University, Statesboro, GA 30460-8064; *
[email protected] Experimental All samples were analyzed using a Milestone Scientific DMA-80 (Milestone Scientific, Inc., Monroe, CT) mercury analyzer in autosample mode. The autosampler loads a nickel boat containing the sample into a furnace, where it is dried, ashed, and carried via a stream of molecular oxygen into a catalyst tube, which passes only the mercury. This mercury enters a second furnace where it is collected on a gold composite amalgam for a set period of time to allow all of the mercury from the sample to be processed through the catalyst. The amalgam is then heated, releasing the mercury into an aluminum cuvette block where the concentration is dewww.JCE.DivCHED.org
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LCP site
Ma
health advisory area Blythe Island
cKay R ive r
Purvts Creek
Turtle River
St. Simons Island
un R sw iv ic er k
Andrews Island
Georgia
Br
All students at Georgia Southern University are required to take a core-curriculum course in environmental science through the chemistry, geology, biology, or physics departments. We have previously reported on the need for laboratory experiences appropriate for nonmajor students, the educational impact of regional relevance, and the suitability of direct mercury analysis for this target group (1). Traditional mercury-determination methods of sample digestion in concentrated acids followed by atomic absorption and cold vapor deposition are not appropriate for students with minimal laboratory skills. The experiment described here allows easy, rapid determination of mercury levels in commercially available seafood samples and comparison with samples from a contaminated area. Environmental mercury pollution has received national media coverage in recent years, particularly warnings of human health risks associated with consumption of contaminated seafood (2), including respiratory failure, central nervous system and kidney damage, gastrointestinal ulceration, circulatory collapse, which can lead to coma and death. Mercury contamination is an especially relevant issue to our students because of Georgia Southern University’s proximity to Brunswick, in Glynn County, GA, site of four Environmental Protection Agency National Priority Listings (3). This coastal town borders Georgia’s “Golden Isles”: St. Simons, Little St. Simons, and Jekyll Islands and is economically important for commercial shrimp and crab harvest, as well as tourists seeking sport fishing. The sources of mercury contamination were various industrial tenants at the Linden Chemical and Plastics (LCP) site, a 550-acre property composed largely of tidal marsh. In excess of 400,000 pounds of elemental mercury was released into the surrounding salt water estuary between 1968 and the mid-to-late 1980s, resulting in one of the worst environmental catastrophes in the country, and Georgia’s highest remediation priority (4). The cleanup of the upland area was completed in 1997 (5). Despite this, there remains a fishing ban on the adjacent Purvis Creek and portions of the Turtle River (Figure 1).
Atlantic Ocean
Figure 1. Map of LCP site showing area where fish were harvested (6).
termined based on atomic absorption. Interference from other species is not an issue as (a) nonmercury species remain in the catalyst tube and (b) a key advantage to atomic absorbance is its specificity (i.e., using a mercury lamp as the excitation source excludes species that do not absorb at that specific wavelength).1 This instrument is cost-effective and has a small footprint. The system software is user-friendly, allowing for rapid student training. Each analysis requires approximately five minutes, with zero wait time between runs. Total mercury is quantified based on a calibration curve prepared using a fish tissue standard.2 Students provide store-bought fish samples, and Brunswick samples are supplied to the class for comparison. Hazards Students should wear gloves when handling the fish tissue standard. The exhaust from the instrument should be passed through a packed carbon filter and vented at all times during operation. Results and Discussion Each team of two students analyzed their own seafood sample and a Brunswick sample of their choice, performing four replicate measurements of each. All data are presented to the entire class, which each student graphs and turns in with their report. Typical student data for both commercial and Brunswick samples, with numerical results and associated error, are shown in Figure 2, Table 1, Figure 3, and Table 2, respectively.
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In the Laboratory 500
[Hg] (ppb)
400
Figure 2. Mercury levels in commercially available canned seafood samples.
300 200 100
rri ng he
ui d sq
ke re l St ar tu ki na st
m ac
to pu s C hi th ck e e tu Se n o na a f
oc
lu m cr p ab
sh tiny rim Bu p m bl tu e B na ee
st er s oy
lm on sa
sa
rd in e
s
0
Table 1. Average Total Mercur y, Standard Deviation, and Relative Standard Deviation (RSD) for Four Replicate Measurements of Commercial Seafood Sample
[Hg] (ppb)
RSD (%)
Brunswick Brand Sardines
21.75
0.75
3.45
Chicken of the Sea Boneless Pink Salmon
24.64
1.56
6.35 15.74
Chicken of the Sea Whole Oysters
24.92
3.92
Chicken of the Sea Tiny Shrimp
46.86
3.30
7.05
Bumble Bee Tuna
84.41
22.25
26.36
Chicken of the Sea Lump Crab
118.27
3.97
3.36
Vigo Brand Octopus
140.70
8.70
6.18
Chicken of the Sea Tuna
144.88
13.85
9.56
Roland Brand Mackerel Fillets
243.53
23.27
9.56
Starkist Tuna
264.39
67.76
25.68
Vigo Brand Squid in Ink Sauce
288.84
29.12
10.08
King Oscar Smoked Herring
373.56
17.93
4.80
While waiting for the instrument to return their data, students use the Internet to research and determine the EPA consumption guidelines, for example, 0.1 µg mercury兾(kg body weight兾day) for their fish samples and to calculate the quantity they could safely ingest per week based on their body weight. As the Brunswick samples illustrate, the current fishing ban is justified, and consequently, no safe-consumption limit calculations were required for those samples. It should be noted that all of the fish samples taken from the Brunswick region, with the exception of the large stingray, were small for their species. None of the perch caught exceeded 6 inches in length, although much larger samples are regularly caught and ingested by local residents.3 The spot was 6.5 inches in length, a very small sample considering specimens 15–20 inches long are common.3 Despite the fishing ban, many residents rely on local seafood as a dietary staple. The area’s demographics are such that 38.3% of the residents in the census tract in which the contamination sites are located fall below the national poverty line (7). Fishing is a common method for supplementing family food supplies with high protein meals.3 This information, combined with the history of the site, corporate disregard for environmental health, and the students’ experimental data set the stage for an extremely meaningful classroom discus266
Standard Deviation
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sion on bioaccumulation, long-term effects of mercury exposure, corporate ethics, risk–benefit analysis regarding fish consumption, and lack of public awareness. As many students are from the Glynn County region, this laboratory and lecture experience became very personal to them. All students were enthusiastic about this unit of the course and were particularly gratified to learn of the extended prison sentences handed down against the corporate individuals responsible for the disaster (8). Conclusions Incorporation of a regional environmental disaster into a nonmajors course has resulted in student exposure to novel, modern analysis methods for a key contaminant of global concern. Using direct-analysis methods, mercury determination is readily available to a basic science course. Students gain experience in the preparation of a calibration curve, the determination of unknown concentrations, and risk assessment based on experimentally determined data. Perhaps most important for a nonmajors chemistry course is stimulation of a meaningful classroom discussion of experimental results in the larger framework of societal roles and responsibilities toward the environment.
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In the Laboratory
[Hg] (ppb)
2000
Figure 3. Total mercury content in flesh of samples taken near the contamination site in Brunswick, GA.
1500
1000
500
to fis ad h
ot sp
ab 2 st in (s gr m ay al l st ) i (la ngr rg ay e) Am er ee ica l n s pe ilve rc r h 1 s pe ilve rc r h 2 s pe ilv rc er h 3 pe silv e rc r h 4 pe silv rc er h 5 pe silv rc er h 6
cr
cr
ab
1
0
Table 2. Average Total Mercur y, Standard Deviation, and Relative Standard Deviation for Four Replicate Measurements of Fish from Pur vis Creek/Turtle River, Brunswick Sample
[Hg] (ppb)
Standard Deviation
RSD (%)
Crab 1
181.74
42.40
23.32
Crab 2
711.62
29.96
4.21
Stingray (small)
447.01
43.17
9.66
606.67
74.44
12.27
1776.52
92.84
5.23
Stingray (large) American Eel
WSupplemental
Silver Perch 1
791.61
29.80
3.76
Silver Perch 2
272.65
11.48
4.21
Silver Perch 3
1493.17
136.47
9.14
Silver Perch 4
531.18
7.97
1.50
Silver Perch 5
527.34
11.50
2.18
Silver Perch 6
590.96
88.23
15.19
Spot
571.05
15.03
2.63
Toad Fish
307.59
3.57
1.13
Material
Literature Cited
Instructions for the students and notes for the instructor are available in this issue of JCE Online. Acknowledgments Awards from the National Science Foundation, Division of Undergraduate Education, funded this work: NSF Award #9752602 and #0127065. The authors thank Steve Vives (Georgia Southern University Department of Biology) for his valuable assistance in acquiring and dissecting fish samples. The support provided by Georgia Southern University in the form of a second mercury analyzer is deeply appreciated. Notes 1. Additional information on this experimental technique may be found at http://www.milestonesci.com (accessed Nov 2004). 2. The fish standard is DORM-2, Dogfish muscle, National Research Council, Institute for Environmental Chemistry, Ottawa, Canada, 4.640 ppm mercury. 3. Personal communication with local residents while on-site.
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1. Jenkins, J. D.; Orvis, J. N.; Smith, C. J.; Manley, C.; Rice, J. K. J. Chem. Educ. 2004, 81, 22–23. 2. (a) Judd, C. S. J. Chem. Educ. 2001, 78, 570–572. (b) O’Connor, Anahad. Federal Draft Advisory Warns Some People To Limit Tuna. New York Times, Dec 12, 2003, Sec. A, p 32. (c) O’Neil, John. New Look at Fish and Pregnancy. New York Times, May 20, 2003, Sec. A, p 32. (d) FDA Sharply Lowers ‘Safe’ Mercury Levels. New York Times, April 5, 2003, Sec. A, p 14. (e) Motavalli, Jim. Effort To Remove Mercury Light Switches. New York Times, Nov 18, 2001, Sec. 12, p 4. (f ) Vergano, Dan. FDA Fish Warning Is Called ‘Lacking’. USA Today, Mar 1, 2002, p A01. (g) Boyles, Fred. Mercury Thermometers Taking Heat for Toxic Risks. USA Today, Nov 21, 2000, p A12. (h) Heiman, Diane. Pass New Laws To Make Fish Safer. USA Today, Dec 1, 1987, p A10. (i) Kelly, Erin. A Quick Look at the Clean Air Issue. USA Today, Jul 17, 2002, p 1. (j) Howlitt, Debbie. Aging Utility Plants Under Fire: Coalition Asks EPA To Impose Stricter Rules on Emissions. USA Today, Jun 14, 2000, p A7. (k) Pianin, Eric. Federal Ban on Tuna Planned; Mercury Danger to Fetuses, Children. Washington Post, Dec 11, 2003, p A01. (l) Huslin, Anita. Household Mercury Complicates EPA Rule. Washington Post, Aug 26, 2000, p BO2.
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In the Laboratory (m) U. S. Plans New Rules for Seafood. Washington Post, Jan 21, 1994, p A16. (n) Pianin, Eric. EPA Issues New Rules for Mercury; Aim Is To Prevent Spills but Tons of Toxics Are Unaccounted For. Washington Post, Dec 20, 2003, p A7. (o) Pianin, Eric. Mercury Rules Work, Study Finds. EPA, Florida Cite Emissions Regulations. Washington Post, Nov 6, 2003, p A10. (p) Pianin, Eric. EPA Announces Cap and Trade Plan To Cut Mercury Pollution. Washington Post, Dec 16, 2003, p A35. 3. U. S. Environmental Protection Agency, Georgia NPL/NPL Caliber Cleanup Site Summaries. http://www.epa.gov/region4/ waste/npl/nplga/lcpincga.htm (accessed Nov 2004). 4. Emory University Public Health Newsletter. http:// www.emory.edu/WHSC/HSNEWS/PUB/PH/PHFall97/ toxic.html (accessed Nov 2004). 5. U. S. Environmental Protection Agency, Cleanup Overview,
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LCP, Brunswick, GA, Congressional District 1. http:// www.epa.gov/region4/waste/errb/lcp.htm (accessed Nov 2004). 6. Coastal Hazardous Waste Site Review. http:// response.restoration.noaa.gov/cpr/wastesites/PDFs/1997/ Brunswic.pdf (accessed Nov 2004). 7. Environmental Justice Resource Center. http:// www.ejrc.cau.edu/final4.html (accessed Nov 2004). 8. (a) Hg-WG: Env crimes at LCP (chlor-alk) http:// yosemite.epa.gov/opa/admpress.nsf/0/ bd048b2330fe314d85256701006f04a0?OpenDocument (accessed Nov 2004). (b) U. S. Environmental Protection Agency, National News, Headquarters Press Release, Three Officials of LCP Chemicals Convicted. http://yosemite.epa.gov/opa/ a d m p re s s . n s f / 0 1 6 b c f b 1 d e b 9 f e c d 8 5 2 5 6 a c a 0 0 5 d 7 4 d f / bd048b2330fe314d85256701006f04a0?OpenDocument (accessed Nov 2004).
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