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 learned 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 (ppm).
? 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 = amount algae consumed × concentration of DDT in algae So
DDT consumed by shrimp = 10 galgae × 0.0002 mgDDT per galgae = 0.002 mgDDT
Since a shrimp weighs 1 gram, the concentration of DDT in the shrimp is 0.002 mgDDT per gshrimp, or about 2 ppm
This assumes that ALL of the DDT consumed by the shrimp stays in its body (a "worst case" assumption that is probably not true).
Now, use this same methodology to estimate the potential concentration of DDT in fish and in humans (male and females), given the following:
An average fish eats 1.4 kg of shrimp as it grows to weigh 150 grams when consumed
An average female (weighing 69 kg) consumes 2 fish per day over a 60 year life
An average male (weighing 83 kg) consumes 1 fish per day over a 60 year life
You will have the following solutions
a. What is the concentration of DDT in an average fish (when consumed)?
b. How many grams of fish would both females and males consume over 60 years?
c. What is the concentration of DDT in an average female after 60 years?
d. What is the concentration of DDT in an average male after 60 years?
Hint: concentration of accumulated toxins tends to be expressed as mg/g, g/kg, kg/kg, etc.