While energy decreases and becomes more dispersed at each step in the food chain, some substances become more concentrated with each link in a process that has become known as biological magnification. The dramatic increase in concentration of four dangerous substances in four different ecosystems is shown in table 4 -1. In each case the amount in the water or soil (that is, the general environment ) at the time of measurement was extremely small and certainly ‘’harmless,’’ but by the time the poisonous substances reached the end of the food chain, concentrations were high enough to cause sickness and death. Physical, chemical, and biological processes may all contribute to the concentration process. DDT may be absorbed through the skin of a fish as well as be ingested with food. It becomes concentrated in vertebrates because it tends to become stored in fat deposits. Radio active phosphorus is concentrated simply because of the natural tendency of biota to concentrate and store this scarce but vital element, as noted earlier in this chapter. Strontium – 90 concentrates in bone, where its tadiation may damage sensitive blood – making tissue because of its chemical resemblance to calcium. In other cases reason for concentrations are unknown. We must observe, experiment with and model the ecosystem level because neither laboratory experiment nor general theory are adequate for predicting the behavior of each of the thousands of new chemicals that man is constantly introducing . concentration factors tend to be higher in aquatic than in terrestrial system since water is a more ‘’dilute’’ medium than soil.

Biological magnification has come as a great surprise to physical scientists and technologists who were enthusiastic about the idea that ‘’the solution to pollution is dilution’’ or, in other words, the belief that poisons would be quickly lost in the vast confines of nature. Because predatory birds are being wiped out by DDT and man himself threatened (since he cannot escape being part of food chains) society has been forced to consider reducing or banning outright, this pesticide that was once heralded as the solution to all insect pest problems. Likewise, the difficulty of dispersing or containing large amounts of radioactive wastes without contaminating man’s food chain is one major reason why you cannot as yet enjoy the peaceful uses of atomic energy.