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'New' pesticides affect immune system, study finds

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USA: April 10, 2002

 

 

WASHINGTON - Pesticides developed in the hope that they may be safer than older

chemicals known to cause cancer may be only slightly better, researchers said

yesterday.

 

 

They found the compounds, used to protect crops such as pecans, potatoes and

sugar beets, as well as protect boats and wood, can damage cells that seek out

and destroy microbes and cancer cells.

A one-hour exposure to one of the chemicals, triphenyltin, reduces the

tumor-killing ability of natural killer cells by 50 to 60 percent, biochemist

Margaret Whalen of Tennessee State University in Nashville, who led the study,

reported.

 

And the cells did not work properly again for six days after the exposure,

Whalen and graduate student Sharnise Wilson 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.

 

Whalen's team did the study in laboratory dishes, and now she says they are

going to 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. " It is

not a chemical that the majority of us are going to be exposed to. "

 

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,

targeting and killing cells that do not carry a flag, called the major

histocompatibility complex, that marks them as " good guys " .

 

Whalen decided 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.

 

" I took lymphocytes from normal human donors ... and exposed them in a test tube

to varying levels of the compound, " Whalen said in a telephone interview.

 

" The compound limited one immune function of the natural killer cells which is

to kill tumor cells. What was startling to us was that if we removed the

compound, the inability to kill tumor cells continued. "

 

Whalen said her team will try and test farm workers and will also do lab tests

to see if the body can get around the damage caused by the pesticides.

 

" Is it possible in any way to reverse this? " she asked. Perhaps signaling

chemicals called interleukins can have an effect, she believes.

 

Of more than a dozen chemicals she screened, only two groups, triphenyltins and

the related tributyltins, had this effect on the natural killer cells, Whalen

said.

 

" These chemicals were made to replace things that are more toxic, " she said.

" This was considered an improvement on things that were used in the past. "

 

Whalen said she did not want to worry the public but believes her findings merit

further studies to see if agricultural workers may be at risk.

 

 

 

Story by Maggie Fox, Health and Science Correspondent

 

 

REUTERS NEWS SERVICE