Tuna for Lunch?
A Case Study Examining Mercury
Bioaccumulation and Biomagnification
By
Caralyn B. Zehnder
Department of Biological and Environmental Sciences
Georgia College and State University, Milledgeville, GA
Coal-burning power plants are the most common source of
mercury pollution.
Coal contains mercury naturally, and when it is burned, the
mercury travels up the smokestack and is released into the
air.
Mercury Methylation
Bacteria convert inorganic mercury (Hg) to the organic form methylmercury (MeHg)
Hg – in emissions (smoke)
Hg - Deposited on
land and into water
50-75% from
anthropogenic
(human) sources
Bacteria
Methyl-mercury
(MeHg)
Methylmercury (MeHg)
•Highly toxic
•Gets into the food web
Snail
Largemouth bass
Herbivorous
fish
Phytoplankton (algae)
Zooplankton
Small fish
Hg – in emissions (smoke)
Hg - Deposited on
land and into water
50-75% from
anthropogenic
(human) sources
Bacteria
Methyl-mercury
(MeHg)
MeHg
Zooplankton
Large fish
MeHg
MeHg
Small fish
MeHg
Phytoplankton (algae)
Report Objectives:
Describe the nationwide
occurrence and distribution of
mercury in fish tissue.
Evaluate mercury in streambed
(bed) sediment and stream water.
Scudder, B.C., Chasar, L.C., Wentz, D.A., Bauch, N.J., Brigham, M.E., Moran,
P.W., and Krabbenhoft, D.P., 2009, Mercury in fish, bed sediment, and water from
streams across the United States, 1998–2005: U.S. Geological Survey Scientific
Investigations Report 2009–5109, 74 p.
Methods
Fish
Sediment
A plastic scoop was used to
remove the upper 2 to 4 cm of
bed sediment from 5 to 10
depositional areas; samples
Largemouth bass were
were composited into a single
targeted for collection; but
sample for each site.
34 different fish species
were collected.
Each sample was
homogenized and mercury
Fish caught by
levels were measured.
electrofishing, rod & reel,
and gill nets.
291 fish from streams
nationwide.
Fish fillet analyzed for
mercury
Water
Stream-water samples
were collected by dipping
Teflon® or PETG
(Nalgene) bottles in the
centrer of streamflow by
use of trace-metal clean
techniques.
Samples analyzed for
mercury.
Figure 1: Mercury concentrations (ug/g) found in fish tissues of commonly
sampled fish species.
US EPA criterion for human
health.
Concern level for piscivorous
mammals
Each and every fish tested from nearly 300 water streams
in the U.S. was found to contain mercury.
Hg concentrations in fish were several orders of
magnitude higher than in stream water.
Bioaccumulation: the buildup of substances, such
as pesticides or heavy metals, in an organism.
Bioaccumulation occurs when an organism absorbs a
substance faster than it excretes it.
Bioaccumulation results in the organism having a higher
concentration than the surrounding environment.
Mercury out
Mercury in
Where in the U.S. were
the highest concentrations
of mercury in fish found?
http://www.usgs.gov/corecast/details.asp?ep=102
EPA Fish Advisories
http://www.epa.gov/waterscience/fish/states.htm
The relationship between trophic position and mercury in the food
web of Lake Washington.
Lake Washington
Methods – collect fish, crustaceans, & zooplankton and measure
methylmercury levels.
Mysid
Daphnia
(zooplankton)
Crayfish
Stickleback
Trout
Pikeminnow
Caddisfly
Sockeye salmon (fry)
Smallmouth bass
Table 3
Fish
Arthropods
Zooplankton
Species
Food
Methylmercury (ug / kg)
Northern pikeminnow
Cutthroat trout
Smallmouth bass
Juvenile sockeye
Stickleback
Mysids (small shrimp)
Signal crayfish
Caddisfly larvae
Bulk zooplankton
Other fish
Other fish
Other fish
Zooplankton and arthropods
Zooplankton and arthropods
Zooplankton
Zooplankton and phytoplankton
Phytoplankton
Phytoplankton
413 ± 45
194 ± 32
261 ± 13
46 ± 2
39 ± 1.3
15 ± 2
23 ± 4
6 ± 0.6
4 ± 0.4
*Arthropods are organisms with segmented bodies, hard exoskeletons and multiple
pairs of jointed legs. Aquatic examples include shrimp, crayfish, crabs, and insect
larvae including caddisflies.
Trout
Pikeminnow
Smallmouth bass
Stickleback
Mysid
Sockeye salmon (fry)
Crayfish
Daphnia
(zooplankton)
Caddisfly
Algae (phytoplankton)
Trout
Hg
Pikeminnow
Smallmouth bass
Stickleback
Hg
Mysid
Hg
Sockeye salmon (fry)
Crayfish
Daphnia
(zooplankton)
Caddisfly
Algae (phytoplankton)
Biomagnification: An increase in
concentration of a pollutant from one link in
a food chain to another.
If a substance can biomagnify, then animals
(predators) at the top of the food chain will
have higher concentrations than animals
lower on the food chain.
Even small concentrations of chemicals in
the environment can find their way into
organisms in high enough dosages to cause
problems.
Image credits
Licensed photo of school of tuna: ©Tommy Schultz | Fotolia.com, #4843675.
Coal fired power plant: http://commons.wikimedia.org/wiki/File:Dominion_Power_Plant.jpg
Bacteria: : www.nature.com/.../v2/n2/full/ngeo428.html
Water sampling: http://www.usgs.gov/themes/factsheet/146-00/
Largemouth bass: www.dfw.state.or.us/.../largemouth_bass.asp
Herbivorous fish: http://en.wikipedia.org/wiki/Rutilus
Fish electroshocking: www.epa.gov/esd/land-sci/water/fig9.htm
Lake Washington: .: www.fs.fed.us/r6/mbs/photo_gallery/index.php?...
Sockeye salmon fry: http://cybersalmon.fws.gov/sockeye.htm
Daphnia magma: http://upload.wikimedia.org/wikipedia/commons/c/c0/Daphnia_magna.png
Signal crayfish: www.tdsfb.org/crayfish.htm
Mysid shrimp: reefkeeping.com/issues/2004-02/rs/index.php
Stickleback: pond.dnr.cornell.edu/.../stickleback.html
Cutthroat trout: www.usbr.gov/mp/lbao/native_american.html
Northern pikeminnow: fishandgame.idaho.gov/ifwis/fishingplanner/ht...
Smallmouth bass: pond.dnr.cornell.edu/.../smallmouth_bass.html
Caddisfly larvae: www.slnnr.org.uk/sitedescription/freshwater.html
Mercury biomagnification: pubs.water.usgs.gov/fs-216-95
Vermont mercury fish advisory: www.neiwpcc.org/mercury/advisories_materials.asp