The research was conducted in Mexico, but many of these pesticides, although they go by a different name, have the same ingredients and are used in the United States, potentially giving Americans the same risks, said Elizabeth Guillette, a UF anthropology professor who led the research.
The connection from mother to child was found among Sonoran Mayan girls whose mothers were exposed to chemical spraying. They did not develop the ability to produce milk, unlike their counterparts who lived a more organic lifestyle, she said.
“The results underscore the importance of women protecting themselves from manufactured chemicals beginning at birth because they stay in the body,” said Guillette, whose research is published in the March issue of Environmental Health Perspectives.
The study found changes in breast development when comparing pre-adolescent girls whose mothers grew up in an agricultural valley where heavy doses of pesticides were sprayed with those who were raised in surrounding foothills where none were used. Some of the girls in the agricultural valley had no mammary tissue or a minimal amount.
Although several studies have examined the effects of pesticides on when puberty begins, none have looked at how exposure influences the development of mammary gland tissue, she said. To investigate the question, Guillette found two population samples about 50 miles apart in the northwestern Mexican state of Sonora’s Yaqui Valley that were almost identical except for their exposure to pesticides.
The Sonoran Mayan people of the valley split philosophically over the use of pesticides and other modern agricultural techniques during the country’s Green Revolution of the early 1950s, when large-scale pesticide-based agriculture came into practice. Valley residents embraced pesticides, herbicides and other agricultural chemicals, including spraying in homes, while the other group, which moved to the foothills, avoided them entirely.
“These groups were the same in every respect, culturally, genetically and socio- economically, except for their use of pesticides,” Guillette said. “They had the same diet, the same child-rearing practices and the same school system.”
Although the farmers in the valley and the ranchers in the foothills had cousins and other extended family members living in the other community, they never intermarried because of their strong differences over pesticides, she said.
Guillette began her research in 1966, comparing the physical coordination and mental development in preschool children from the two communities. In an earlier published study, she found that valley children were less adept at catching a ball, reflecting poor eye-hand coordination, and showed dramatic differences in their ability to draw a person.
Her more recent study focused on breast development in girls between the ages of 8 and 10 and involved 30 girls from the valley and 20 girls who lived in the foothills. Guillette and local nurses measured total breast diameter and mammary diameter.
While breast size was much larger in the girls in the valley, they had much less mammary tissue, and sometimes none at all, than the girls in the foothills, Guillette said.
Mammary tissue could not be palpated in about 19 percent of the girls from valley towns who showed signs of breast development. In contrast, none of the girls from the foothills who had reached this stage lacked mammary tissue.
“With the foothill girls, there was a direct correlation between breast size and mammary development, whereas with the pesticide-exposed girls there was none,” Guillette said. “In fact, we saw girls who were fairly well developed with absolutely no mammary glands.”
Because the Yaqui Valley was in its fifth year of a drought at the time of the study, with most farmers moving into ranching and stopping pesticide use, the results point to earlier exposure, probably transferred from the mother before birth, she said.
Various pesticides, mainly organophosphates and organochlorines, were used extensively to farm the Yaqui Valley near the time of the girls’ birth, between 1992 and 1994, and many of these compounds are known to cross a pregnant woman’s placenta to the developing child, Guillette said. A study of newborn children from the valley that was done close to the time these children were conceived found elevated pesticide levels, she said.
“Many of these pesticides are popular in the United States, both for agriculture and for home use and lawn care,” she said. “We know the age for breast development in girls is occurring earlier and there is the potential that pesticides may be playing a similar role in the United States as found in Mexico.”