Oahus urban streams are contaminated with DDT residue and have the highest levels in the nation of the toxic pesticides chlordane and dieldrin, according to a just-released federal monitoring study.
The persistent, man-made chemicals, now banned but once commonly used to control insects such as termites and mosquitoes, are found in the mud at the bottom of streams and also in creatures that live there.
"I wouldnt eat fish from the urban streams," said Barbara Brooks, a toxicologist with the state Health Departments hazard evaluation and emergency response office.
The new federal study of five Oahu urban streams suggests virtually any stream flowing through areas developed before 1980 can be expected to contain dangerous pesticides in both streambed sediment and in the fish, crabs and other forms of life found there.
A second survey of 19 other Oahu streams is under way to confirm the level of danger there, said hydrologist Stephen Anthony, associate district chief for Hawaii and the Pacific with the U.S. Geological Survey.
The state Department of Health is studying the new data. Officials there say people should assume any urban stream life is potentially hazardous and should not eat it.
"People should be very cautious eating crayfish, tilapia, crabs and even oopu," said Gary Gill, deputy director for the environment in the Department of Health.
State officials already have posted warnings about contaminated fish and shellfish at Pearl Harbor and the Ala Wai Canal, as the result of earlier tests of those areas. Health authorities are now trying to determine how best to warn people, and whether simply posting more and more signs is practical.
"How we continue to get the word out is something we continue to be discussing," Gill said.
The pesticide DDT was widely used in urban areas for control of pest insects, and was sometimes broadcast through the neighborhood streets by spray trucks to control mosquitoes. DDT also was used in agricultural insect control before being banned in 1972. It breaks down into products known as DDE and DDD, both of which are toxic and slow to break down.
Chlordane was Hawaiis termite ground treatment chemical of choice until it was banned for commercial use in 1988. Another termite pesticide used in the Islands, aldrin, breaks down readily into toxic dieldrin.
These compounds, known as organochlorides, bind to the soil and are washed into streams through soil erosion from urban areas.
They are associated with a range of health risks to animals and humans, and are considered possible human cancer risks and chemicals that may alter hormone balance.
Anthony and USGS aquatic ecologist Anne Brasher studied Kaneohe, Manoa, Nuuanu, Poamoho, and Waikele streams. As a control, they also took samples from the waters of Windward Oahus Waihee Stream in a forested region mauka of any houses or agricultural areas. No pesticides were detected in Waihee Stream samples, Anthony said.
"We expected that there would be relatively high concentrations in urban streams," Anthony said.
But the levels were surprising, he said. When compared with nationwide surveys in the National Water Quality Assessment Program, each of the Hawaii urban streams had higher levels of chlordane and dieldrin than any Mainland stream tested. DDT levels were comparable to average Mainland levels.
Anthony and Gill both said the high levels of the termite chemicals, compared with lower Mainland levels, is understandable.
The Islands, lacking freezing winters that limit termite activity, required dramatically more treatment to prevent the insects from destroying homes and other structures.
Hawaiian termite control has moved on to less-persistent chemical treatments and to nonchemical control means, but the toxic chemicals of decades ago remain.
"These organochlorines do not disappear. They persist for decades, and they are still with us," Gill said.
Anthony said comparisons with various tests done in Manoa Stream fish starting in the early 1970s suggest that levels of toxicity are declining, though slowly.
Both he and Gill said one way to prevent further stream contamination is to control runoff, since DDT, chlordane and dieldrin enter the waterways attached to eroding soil.
"One message should be that people should try to control soil erosion from urban areas, to prevent those soils from getting into streams," Anthony said.