Researchers zero in on leukemia risks. (Cancer Causer?).

Kids may be protected from some diseases when parents use insecticides to keep homes free of cockroaches and other infection-bearing insects. However, these chemicals may cause damage in other ways, even contributing to the incidence of childhood leukemia, according to a new study revisiting a suspected link between pesticides and the disease.

There is evidence that radiation and certain genetic conditions increase the risk of leukemia, says study leader Xiaomei Ma of the University of California, Berkeley. Besides these, the causes are largely unknown.

Anecdotal links between pesticides and childhood leukemia emerged in the late 1970s. Since then, surveys have shown a modest statistical association connecting the disease with agricultural and household pesticides. However, scientists have not been able to specify the riskiest types of pesticide exposure nor have they determined the ages when children are most vulnerable. Researchers estimate that U.S. residents deposit about 62.7 million pounds of pesticides indoors each year.

Ma and her colleagues interviewed Northern Californians to compare exposure levels between children with and without leukemia. Between 1995 and 1999, the scientists queried the families of 324 children age 14 and under about household-pesticide use. Half of the children had already been diagnosed with the disease, primarily acute lymphoblastic leukemia. The survey focused on whether pesticides were used inside or outside the house and at what points--during a pregnancy and the resulting child's first three years--the pesticides were applied. The survey also noted the use of professional exterminators.

In the September Environmental Health Perspectives, Ma and her coauthors report that the families of children with leukemia were nearly three times as likely to have used a professional exterminator than were families with a child free of the cancer. The team also found that exposure to the professionals' pesticides during the child's second year was associated with the highest risk.

The data show that a mother's exposure to any type of pesticide in her home during pregnancy coincided with twice as much risk of her child developing leukemia, compared with mothers reporting no pesticide exposure. The researchers found no association of leukemia risk with pesticides used outside the house.

Susan Preston-Martin of the University of Southern California in Los Angeles says the finding that exposure during pregnancy seems to double leukemia risk fits well with her own research on childhood brain cancer and pesticide exposure.

Many pesticides are carcinogenic, says Susan E. Carozza of the Texas A&M University System Health Science Center in Bryan. The study by Ma's team is one of several suggesting that exposure to pesticides in the home is more important than exposure to agricultural sources, she says. The next step in proving a pesticide-leukemia link will be identifying specific chemicals that can cause the disease.