Tuna for Lunch? A Case Study Examining Mercury Bioaccumulation and BiomagnificationByCaralyn B. ZehnderDepartment of Biological and Environmental SciencesGeorgia 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)

50-75% from anthropogenic (human) sources

Hg - Deposited on land and into water

Methyl-mercury (MeHg)

Bacteria

Methylmercury (MeHg)

•Highly toxic•Gets into the food web

Phytoplankton (algae)

Zooplankton

Snail

Largemouth bass

Herbivorous fish

Small fish

Hg – in emissions (smoke)

50-75% from anthropogenic (human) sources

Hg - Deposited on land and into water

Methyl-mercury (MeHg)

Bacteria

Phytoplankton (algae)

MeHg

Zooplankton

MeHg

MeHg

MeHg

Small fish

Large fish

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.

291 fish from streams nationwide.

Largemouth bass were targeted for collection; but 34 different fish species were collected.

Fish caught by electrofishing, rod & reel, and gill nets.

Fish fillet analyzed for mercury

MethodsFish Sediment Water

A plastic scoop was used to remove the upper 2 to 4 cm of bed sediment from 5 to 10 depositional areas; samples were composited into a single sample for each site.

Each sample washomogenized and mercury levels were measured.

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 inMercury out

http://www.usgs.gov/corecast/details.asp?ep=102

Where in the U.S. were the highest concentrations of mercury in fish found?

http://www.epa.gov/waterscience/fish/states.htmEPA Fish Advisories

Lake Washington

The relationship between trophic position and mercury in the food web of Lake Washington.

Methods – collect fish, crustaceans, & zooplankton and measure methylmercury levels.

Daphnia (zooplankton)

Mysid

Stickleback

Pikeminnow

Trout

Smallmouth bass

Caddisfly

Crayfish

Sockeye salmon (fry)

Table 3  Species Food Methylmercury (ug / kg)

Northern pikeminnow Other fish 413 ± 45 Cutthroat trout Other fish 194 ± 32 Smallmouth bass Other fish 261 ± 13 Juvenile sockeye Zooplankton and arthropods 46 ± 2 Stickleback Zooplankton and arthropods 39 ± 1.3 Mysids (small shrimp) Zooplankton 15 ± 2

Arthropods Signal crayfish Zooplankton and phytoplankton 23 ± 4 Caddisfly larvae Phytoplankton 6 ± 0.6

Zooplankton Bulk zooplankton Phytoplankton 4 ± 0.4

Fish

*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.

Algae (phytoplankton)

Daphnia (zooplankton)

Stickleback

Trout

Caddisfly

Crayfish

Mysid Sockeye salmon (fry)

Smallmouth bassPikeminnow

Hg

Hg

Hg

Algae (phytoplankton)

Daphnia (zooplankton)

Stickleback

Trout

Caddisfly

Crayfish

Mysid Sockeye salmon (fry)

Smallmouth bassPikeminnow

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.  

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.htmlWater sampling: http://www.usgs.gov/themes/factsheet/146-00/Largemouth bass: www.dfw.state.or.us/.../largemouth_bass.aspHerbivorous fish: http://en.wikipedia.org/wiki/RutilusFish electroshocking: www.epa.gov/esd/land-sci/water/fig9.htmLake Washington: .: www.fs.fed.us/r6/mbs/photo_gallery/index.php?...Sockeye salmon fry: http://cybersalmon.fws.gov/sockeye.htmDaphnia magma: http://upload.wikimedia.org/wikipedia/commons/c/c0/Daphnia_magna.pngSignal crayfish: www.tdsfb.org/crayfish.htmMysid shrimp: reefkeeping.com/issues/2004-02/rs/index.phpStickleback: pond.dnr.cornell.edu/.../stickleback.htmlCutthroat trout: www.usbr.gov/mp/lbao/native_american.htmlNorthern pikeminnow: fishandgame.idaho.gov/ifwis/fishingplanner/ht...Smallmouth bass: pond.dnr.cornell.edu/.../smallmouth_bass.htmlCaddisfly larvae: www.slnnr.org.uk/sitedescription/freshwater.htmlMercury biomagnification: pubs.water.usgs.gov/fs-216-95Vermont mercury fish advisory: www.neiwpcc.org/mercury/advisories_materials.asp

Image credits