Bio-accumulation and bio-magnification
-Some pesticides, especially organochlorides and some organophosphates, are readily taken up into and remain in the fatty tissue of animals. Single doses may not reach lethal levels, however, because these pesticides are very persistent, the poison can accumulate if the animal is exposed to the poison over a longer period of time. Each time an organism is exposed to the pesticide, the concentration increases.
So basically the more they eat the more ,in this case, DDT is accumulated.
-In other situations, organisms low in the food chain may not have accumulated lethal levels of the pesticides, however, due to the persistence of the pesticides, animals higher in the food chain feeding on these organisms may accumulate lethal pesticide levels. An example is the accumulation of DDT, which causes bird’s egg shells to be thin due to the bird having eaten small mammals exposed to DDT. The mammals had not been sprayed but the insects they ate had been sprayed.
I hope this helps in some way?!
(taken from
http://hsc.csu.edu.au/earth_environmental/core/caring/9_4_4/944net.html)
