MadSci Network: Environment & Ecology

Re: Does non-biodegradable chemicals hurt animals if eatten.

Date: Wed May 3 12:36:01 2000
Posted By: Steven Korenstein, Grad student, Environmental/Occupational Health, Cal. State Un. Northridge
Area of science: Environment & Ecology
ID: 954197894.En


You ask if certain chemicals can cause problems with animals if they eat 
plants or animals that that have been treated with these products.  The 
answer is definitly YES.  The most famous example is that of DDT.  DDT was 
used extensivly in the 1950's as a pesticide.  It effectivly killed 
mosquitos and other pest insects.  The trouble was that the DDT would then 
get into the food chain( or web).  Imagine an insect gets sprayed with 
DDT, the insect then lands on a lake.  A fish in the lake eats the insect 
( actually many, many insects).  This fish gets eaten by a larger fish, 
who then gets eaten by an eagle.  An eagle is a large, meat eating bird 
called a Raptor.  After so many steps in the Foodchain the eagle ( who now 
sits at the top of the chain) gets a lot of the DDT ( a process called 
BIOACUMULATION). DDT effects the bird by interfering with calcium 
absorbption.  Which means the eagle can not use the calcium in its body.  
Remember that bird lay eggs, and an important part of the egg is calcium.  
It is the calcium that makes the egg hard.  When a mother eagle sits on 
her eggs to keep them warm the egg need to be hard enough to support her 
weight.  If the egg does not have enough calcium, when the eagle tries to 
incubate the egg, it will crack and the baby will die.  Thus, if to much 
DDT gets into the environment many types of birds will not be able to have 
surviving offspring.  An this is exactly what happened in the 1950's-
1970's .  Many types of birds almost went extict because of the use of 
DDT.  When this chemical was banned these species began to recover.

Another problem with chemcials like DDT is that they do not brake down 
very fast.  They stay in the environment for many years.  Even though DDT 
has not been used in the United States for almost 30 years we can still 
find it in the environment so it still possible that it may be causing 
wildlife problems.

If you would like to know more about this subject there is a famous book 
by Rachel Carson called "Silent Spring".  This book is credited with 
starting the environmental movement in the USA and is must read for anyone 
interested in the subject.

Good luck on your project!

Steven Korenstein
Environmental Health Specialist

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