Common Weed Killers Affect Developing Fetus

Damage to Fetus Can Happen in Early Pregnancy

From the WebMD Archives

May 24, 2004 -- Common lawn care products can cause developmental problems in early pregnancy -- just days after conception, new research shows.

Exposure to newly treated lawns and golf courses -- before the recommended waiting period is over -- could harm the developing embryo, researchers say. Weed-B-Gon, Scott's 4XD, and Atrazine are just three products found to cause harm.

"Even extremely low concentrations of these pesticides -- concentrations thought to not cause any harm if the person ingests it -- could interfere with both conception and an embryo's implantation in the uterus," researcher Anne Greenlee, PhD, a research scientist with the Reproductive Toxicology Laboratory at the Marshfield Clinic Research Foundation in Wisconsin, tells WebMD.

Her study appears in the May issue of Environmental Health Perspectives. Findings 'Unquestionably Worrisome'

The EPA has asked to review her findings. The information may be included in new labeling for products containing 2,4-Dichlorophenoxyacetic acid (2,4-D), a commonly used lawn care herbicide.

"They realized they had very little information about these products on the fetus in [early pregnancy], and want to include the information we had on the package," Greenlee says.

At the EPA, Mark Seaton, PhD, is a chemical review manager heading up re-registration of herbicide 2,4-D. "Any time I see something about 2,4-D, I pay attention. I've made the team's toxicologist aware of the study."

"This is yet another in a worrisome, very substantial series of reports which suggest the in utero effects of these quite common pesticides and herbicides," Roberta Ness, MD, MPH, chair of epidemiology at the University of Pittsburgh Graduate School of Public Health, tells WebMD. She commented on Greenlee's findings.

"A number of animal studies have shown congenital malformations, abortion, and interference with neurological development," Ness says.

"This has been shown in a less rigorous way in humans -- in migrant farmer workers and other occupations where exposures have been more extreme. There has been very, very few good human studies that have allowed us to look at normal levels of pesticide exposure."

Greenlee's findings are "unquestionably worrisome but not completely surprising," she adds.

Women who are trying to get pregnant need to do homework: Find out what products their neighbors and greenskeepers use, says Greenlee.

For specific information about hazards of specific herbicide products, Greenlee advises checking the National Pesticide Information Center web site provided by Oregon State University and the EPA at npic.orst.edu.

Continued

Common Herbicide

Herbicides such as 2,4-D are used to control broad-leaf weeds in agriculture and for control of woody plants along roadsides, railways, and utilities' rights of way, according to the EPA. They are also widely used on such crops as wheat and corn, and on pasture- and rangelands.

Home lawns and golf greenways are all treated with similar herbicides, Greenlee adds.

Pesticide manufacturers are required to conduct health studies of the effects of these herbicides on reproduction. The safest exposures and safety hazards are provided on product labels. However, this very early time period in fetal development has not been investigated, she tells WebMD.

Studies have detected these pesticides in human ovarian fluid, fluid from semen, human amniotic fluid, and even in fluids that surround the human newborn, she notes.

In a previous two-year study, Greenlee investigated effects of pesticides and fungicides in women who mix and apply these chemicals. She found that women doing this kind of work were 27 times more likely to have fertility problems compared with pregnant women who didn't work with these chemicals.

In her current study, Greenlee sought to explain how the chemicals affected early pregnancy.

Mouse Embryos Mirror Humans

Newly conceived mice -- embryos that were just five days old -- were the subjects of her study.

In the first week after fertilization, the fetus has not yet become implanted in the mother's uterus. It's a phase of development that is similar to early pregnancy in humans, Greenlee explains. During the first to seventh day of pregnancy, the embryo is rapidly dividing and preparing to implant in the mother.

In a series of experiments, Greenlee exposed these tiny fetuses to extremely low doses of herbicides, insecticides, fungicides, and fertilizers used in lawn care and agriculture. She exposed them to individual chemicals and to mixtures of chemicals.

The exposures simulated typical human exposures when the chemicals are touched or inhaled.

Her discovery: 12 of 13 chemicals and all six chemical mixtures caused developmental injury prior to implantation, she writes. Some chemicals slowed embryonic development while others decreased the numbers of cells produced in the embryo. "These embryos wouldn't develop normally," she tells WebMD.

Only one chemical -- permethrin -- had no measurable effects on early pregnancy, Greenlee adds.

Greenlee stresses it is important that additional work be done to validate these findings in humans and to assess the real risks to pregnancy.

Continued

Advice for Mothers-to-Be

"It's going to be difficult to come up with hard-and-fast advisories for women," Greenlee tells WebMD.

All herbicides go through two risk reviews at the EPA -- a human health and an environmental "fate and effects" assessment that includes plant life, other mammals, and aquatic life, says Seaton. Those reviews are scheduled for public comment in late June.

Bottom line: Whatever can be done to minimize exposure, do it. If you're planning to conceive, or trying to conceive, minimize your exposure during early pregnancy. Read product labels and adhere to safety guidelines.

"Women considering or trying to conceive should make every effort to minimize their exposure to lawn care and agrochemical products," Greenlee writes. "Applying these products according to label guidelines and wearing protective gear, such as masks or gloves, can help reduce exposure. It's also important to adhere to the length of time manufacturers recommend you stay off your lawn or field after using pesticides, herbicides, and fertilizers" she advises.

SOURCES: Greenlee, A. Environmental Health Perspectives, May 2004; volt 112: pp 703-709. Anne Greenlee, PhD, research scientist, Reproductive Toxicology Laboratory at the Marshfield Clinic Research Foundation, Wisconsin. Mark Seaton, PhD, chemical review manager, Environmental Protection Agency. EPA.

WebMD Health News
© 2004 WebMD, Inc. All rights Reserved.

Pagination