Estimate Bioaccumulation: DDT in a Lake-(this is a hypothetical example) A mediu

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Estimate Bioaccumulation: DDT in a Lake-(this is a hypothetical example) A medium sized lake can serve as a major food source for a subsistence community. Suppose that a community of about 100 people gets much of its protein from fishing on such a lake. Every day, each person eats one or two fish, which weigh on average about 150 grams. The fish feed primarily on shrimp, as well as insects and other small animals. You have leamed that an alga that is one of the primary food sources for shrimp in the lake is contaminated with DDT, a persistent organic pesticide that farmers upstream have begun using to control ants in food crops. You want to know how much of this DDT might eventually end up in members of the community The following shows how to calculate the concentration of DDT in the shrimp, given the concentration in algae and the eating habits of the shrimp. Knowns: Algae contain about 0.0002 mg of DDT per gram of algae. That is about 0.2 parts per million . Over its (short) life, a shrimp will grow to weigh about 1 gram .The average shrimp eats about 10 grams of contaminated algae during its life. The amount of DDT consumed by the shrimp can then be calculated: DDT consumed by shrimp-armount algae consumed x concentration of DDT in algae So DDT consumed by shrimp = 10 galgae x 0.0002 mgDOT per gague = 0.002 mgoor Since a shrimp weighs 1 gram, the concentration of DDT in the shrimp is 0.002 mgOOr per gahremp, or about 2 ppm

Explanation / Answer

Solution:

a) DDT in average fish = DDT consumed by fish = 1.4 kg of shrimp * 0.002 DDT per gm of shrimp

                                 = 1400 gm * 0.002 mg = 28 mg of DDT per 150 gm of fish

b) Grams of fish consumed over 60 years by males and females,

Males = 60 years * 365 days * 1 fish per day * 150 gm of fish = 3285000 gm of fish consumed for 60 yrs by male Female= 60 years * 365 days * 2 fish per day * 150 gm of fish = 6570000 gm of fish consumed for 60 yrs by female

c) concentration of DDT in female = 6570000 gm of fish * (28 mg DDT / 150 gm fish) = 1226.4 gm of DDT after 60 yr

d) concentration of DDT in male = 3285000 gm of fish * (28 mg DDT/150gm fish) = 613.2 gm of DDT after 60 yrs

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