NEW ORLEANS — An organic pesticide widely used on home-grown fruits and vegetables and for killing unwanted fish in the nation’s lakes and rivers produces all the classic symptoms of Parkinson’s disease in rats that receive steady amounts of the chemical in their bloodstream, scientists said.

While it is much too soon to say that the pesticide, rotenone, causes or contributes to Parkinson’s disease in humans, the scientists said the finding was the best evidence thus far that chemicals in the environment may be factors in the devastating disease.

Their study, the first to implicate rotenone in Parkinson’s disease, was described at a workshop on the neurobiology of disease, held in conjunction with the annual meeting of the Society for Neuroscience, the nation’s largest gathering of brain researchers. The workshop, sponsored by the National Institute of Neurological Disorders and Stroke, involved work by Dr Timothy Greenamyre and colleagues at Emory University in Atlanta. Results of the study were published in the December issue of the journal Nature Neuroscience.

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WASHINGTON, D.C. — A pesticide widely used in American homes and gardens will be pulled off the market over the next few years because of the risks it poses to the health of children and animals.

Beginning in March, the pesticide diazinon, used to control many insects, will no longer be made for use in homes. The federal Environmental Protection Agency reached an agreement to that effect in December with makers of the pesticide. The agreement provides that diazinon will no longer be sold for any household uses by 2004, including use outdoors to treat lawns and gardens.

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JOHANNASBURG — Negotiators for 122 nations have agreed on a global ban on 12 highly toxic chemicals that have been linked to cancer, birth defects, and other genetic abnormalities. The agreement calls for the elimination of PCBs, dioxins, and other chemicals intentially used or produced in manufacturing that have become known as the “dirty dozen.” They are persistent organic pollutants that dissolve slowly, travel easily, and are absorbed by living organisms, including humans. The treaty, which is to be signed in May in Stockholm, has been more than two and half years in the works after negotiations were begun in June 1998 in Montreal.

The treaty must be ratified by 50 nations before it can take effect. Brooks Yeager, head of the United States delegation, said he expected the ban to be approved by the coming Congress.

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A few extra pounds increase the likelihood of dangerous blood clots after hip replacement surgery, a study found. Researchers at the University of California at Davis Medical Center looked at California Medicare records of 25,388 patients who underwent hip replacement from 1993 through 1996. They found that 297 were re-admitted to the hospital within three weeks because a bit of blood clot had broken off and blocked a vein. Women were found to be more likely than men to develop the blockages, called embolisms. And people with a body mass index of 25 – the low edge of the overweight range – were more likely to develop them than people with normal body mass. Obese people, those who are extremely overweight, did not have a greater risk than those who were moderately overweight. The study was published in the New England Journal of Medicine. The blood thinner warfarin helped prevent the complication. So did use of a pneumatic compression device to reduce swelling in the legs, but only for people with a body mass index less than 25. Body mass is found by multiplying weight in pounds by 703, then dividing that by height in inches squared. Someone who is 5 -foot-1 and weighs 132 pounds has a body mass index of 25.

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DALLAS, TEXAS — Dieting to control cholesterol doesn’t work for everyone. Research conducted at the University of Texas Southwestern Medical Center in Dallas showed that people eating similar diets may have a wide variation in their cholesterol levels and that genes play a major role in the effectiveness of an unsaturated fat diet.

“The study demonstrates that there are people who, despite being very careful, can’t overcome their genetic predisposition,” said Dr Ronald M. Krauss, head of the molecular medicine department at Lawrence Berkeley National Laboratory at UC Berkeley.

This genetic trait is found in about 15% to 20% of Americans, according to Dr Krauss, who had done pioneering research suggesting a correlation between genetics and cholesterol levels.