Traces of the banned pesticide DDT and the man-made PCB chemicals have been found in dolphins in Gladstone Harbour, in the Whitsundays and the Fitzroy River near Rockhampton, a long-time dolphin researcher said.

Daniele Cagnazzi, a post-doctoral researcher with Southern Cross University's Marine Ecology Research Centre, has published his findings on contaminants found in dolphins.

Humpback dolphin. Credit:Southern Cross University

Dr Cagnazzi said his findings suggest the chemicals were washed from fertilised fields and have been slowly absorbed by dolphins at the other end of the food chain.

"During the floods, all the sediment gets washed from the grazing land and the agricultural land and ends up in the coastal waters," he said.