Study Suggests Weak Link Between Male Genital Birth Defect and Agricultural Pesticides

After an analysis of several hundred chemicals used in pesticides, researchers from Stanford University Medical Center suggest that there are only weak links between exposure to pesticides and the birth defect hypospadias in male infants.

The researchers conducted a study of expecting mothers and infants in eight counties in California's Central Valley --a heavily agricultural region of the state.

The research team sought to determine whether children were at increased risk of hypospadias if their mothers had lived in relatively close proximity to where pesticides were used while pregnant. Hypospadias is a genital malformation in which the urethral opening is on the underside of the penis rather than on the tip. About 5 male infants per 1,000 are born with the condition, but the cause remains widely unknown.

A set of 292 individual chemicals and 57 groups of structurally similar chemicals were included in the study, which Stanford reports is the most detailed study of the largest data sets done to date.

Of all the chemicals included in the study, only 15 were shown to have possible associations with hypospadias, but the research teams says additional studies must be done.

The counties included in the study, which comprise both the San Joaquin and Sacramento valleys, have one of the highest rates of pesticide use in the nation, a consequence of the area being a main supplier of many fruits and vegetables grown in America.

"We didn't see many chemicals that suggested an increased risk, and of those that did, most of them were infrequently used," said Suzan Carmichael, an associate professor of pediatrics and lead author of the study. "It is good news that such exposures are rare, but at the same time, when exposures are rare, it makes studies harder to do."

The study population included all male infants born in the counties of Fresno, Kern, Kings, Madera, Merced, San Joaquin, Stanislaus and Tulare between 1991 and 2004. The study sample comprised 690 cases of hypospadias, as well as 2,195 controls randomly selected for comparison.

"These results extend what we know, but at the end of the day they need to be replicated before we can really be sure whether there is, or is not, a real risk associated with these chemicals," said Gary Shaw, professor of pediatrics at Stanford and a co-author of the study.

The research is published in the journal Pediatrics.