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Some second generation chemicals have proved to be unexpectedly toxic to many organisms, Johnson continued. Residue from DDT used to combat Dutch Elm disease went from the leaves that fell from the trees to earthworms and caused death in birds that ate the worms. Likewise, DDT used to control mosquitoes on a California lake showed up in ever increasing concentrations in first plankton, then fish and reached lethal levels of concentration in the birds that fed on the fish. “We were not prepared for the persistence” of hydrocarbons like DDT, said Johnson.
Science was also not prepared for the world wide spread of some of these chemical residues either, Johnson continued. He reported that DDT had been fou. d in the liver oil of sharks caught 500 miles out at sea and in the fat of penguins and caribou in the arctic regions. However, he noted that decreased use of DDT i had resulted ,»n a drop in the residue found in humans from 13 to five parts per million.
Johnson acknowledged that industrial and individual carelessness chemical use is becoming more controlled. He maintained that the outlook for the future was improved thanks to better education for chemical applicators, better equipment and better technique in using chemical controls. "We’re moving in the right direction but we’re moving slowly...Complete reliance on chemicals is not promising for the future,” he concluded.
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