Pesticides developed in the hope that they may be safer than older chemicals known to cause cancer may be only slightly better, researchers said on Tuesday.
Scientists found the compounds, used to protect crops such as pecans, potatoes and sugar beets, can damage cells that seek out and destroy microbes and cancer cells.
A one-hour exposure to one of the chemicals, triphenyltin, reduces the tumour-killing ability of natural killer cells by 50 to 60 per cent, lead researcher biochemist Margaret Whalen of Tennessee State University in Nashville.
According to the study the cells did not work properly again for six days after the exposure, Whalen and colleagues told a meeting of the American Chemical Society in Orlando.
"The results indicate that brief exposures to triphenyltin can cause persistent suppression of human immune system function," Whalen said.The study was carried out in vitro and now Whalen's team will test agricultural workers who have used the pesticide to see if they have any in their blood.
"It's hard to know what real-life levels for phenyltins are," she said.
A related group of chemicals called tributyltins have similar effects on natural killer cells, Whalen said.Natural killer cells are one of the arsenal of white blood cells called lymphocytes. They are a first line of defense in the human immune system. Whalen set out to test the effects of various chemicals on these cells, and chose from a list of compounds found to cause cancer and hormone disruption in rats and mice. Phenyltins have been found to contaminate water, sediment, and fish.