Presentation on theme: "Bellringer How much seafood do you eat in the average week? What types? Are there any dangers associated with eating seafood?"— Presentation transcript:
Bellringer How much seafood do you eat in the average week? What types? Are there any dangers associated with eating seafood?
Mercury The Minimata Disease
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 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
Key Questions to answer How does mercury get into the food chain? What is the EPA limit for mercury? What are the factors that determine how much mercury an animal has in it? What part of the population needs to be the most careful about ingesting mercury? Is mercury the only substance with this type of problem?
How does mercury get into the food chain? ___________is the most common source of mercury pollution Natural sources of mercury are: _____
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 Small fish Large fish
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 Methods to study mercury contamination Fish SedimentWater 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 was homogenized 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.
Each and every fish tested from nearly 300 water streams in the U.S. was found to contain mercury.
Figure 1: Mercury concentrations (ug/g) found in fish tissues of commonly sampled fish species.
US EPA criterion for human health.
What are the primary factors that determine how much mercury an animal has in it? How much food containing mercury the animal eats – Eating food without mercury How long the animal has lived – Biaccumulation How high in the food chain it is – Biomagnification
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 in Mercury out Bioaccumulation
Biomagnification: An increase in concentration of a pollutant from one position in the food chain (trophic level) to the next. If a substance can biomagnify, then animals (predators) at the top of the food chain can have higher concentrations than animals lower on the food chain. Biomagnification
Producers Algae/Plankton Consumers Invertebrates Consumers small fish Consumers Large fish Humans?? What happens to contamination level for each organism as you move up the food chain? 30ppb 300ppb 700ppb 2000ppb
Just another way to look at it… What does the relative size of each rectangle represent in this diagram?
An anchovy eats zooplankton that have tiny amounts of mercury in them. The anchovy eats many zooplankton, accumulating the mercury of each over its life. A tuna then eats many of these anchovies over its life, accumulating the mercury of each of those anchovies into its body. This continues up the food chain, with the concentration increasing each time.
Size vs. Trophic level Why might two types of animals that are very different in size have the same level of contamination? They are on the same level of the food chain
Bioaccumulation vs. Biomagnification Bioaccumulation is the increase of toxins within an organism Biomagnification is the increase of toxins between organisms of different trophic levels.
How much mercury do you have in you? Calculate your mercury intake: calculator/start.asp
Is Mercury the only example of bioaccumulation? DDT was an insecticide that built up in birds that ate infected bugs. The largest birds were harmed the most Eagle Egg shells too weak to protect the growing eaglet.