Lawn care herbicide link Lawn care herbicide linked to reproductive ...

cias.wisc.edu

Lawn care herbicide link Lawn care herbicide linked to reproductive ...

CIASLawn care herbicide linked toreproductive problems in miceCenter for Integrated Agricultural Systems • UW-Madison College of Agricultural and Life Sciences • July, 2003ResearchBrief#64CIAS-sponsoredresearch onsustainable,integrated, andalternativeagricultural systemsResearchers at UW-Madison found that exposureto low levels of a common lawn herbicide mixtureled to reduced litter sizes in laboratory mice. Thisresearch builds on other studies showing possiblelinks between pesticide exposure and reproductiveand/or developmental problems in animals andhumans.While previous epidemiological studies havelinked herbicide exposure and birth defects,others have found no link between pesticides andreproductive problems. UW-Madison ZoologyProfessor Warren Porter says, “The present studyshows that there may be cause for concern.Further study on the effects of low doses ofoff-the-shelf herbicide mixtures on reproductiveperformance are needed. Levels that were previouslyassumed safe by the EPA have now beenshown to have possible biological effects. Sincethe greatest effects were at the lowest dose, westill don’t know how low an exposure can be andstill induce effects.”The herbicide mixture tested was composed of2,4-D (7.59%), mecoprop (3.66%), dicamba(0.84%), and inert ingredients (87.91%), asreported by the manufacturer. These chemicalsare also used in agriculture to control broadleafweeds, although application rates are typicallylower for agriculture than for lawns.Of mice and herbicidesUW-Madison Zoology researchers James Jaegerand Warren Porter and University of Valparaíso,Chile, faculty member María Fernanda Cavieresexposed pregnant female mice to the commercialherbicide mixture via drinking water in 2000-01.The mice were assigned to four groups receivingdifferent dosage levels, and a control group. Alldose levels were confirmed by State of Wisconsinlab analysis. The researchers closely monitoredwater consumption to make sure that water intakedid not differ significantly between the groups ofmice and that each mouse received the right dose.At birth, each litter of mice was checked for thetotal number of live pups. Pups born dead andcannibalized pups were not included. Oncecounted, the litters were culled to 8 pups toensure comparable growth. These pups wereweaned at three weeks and kept until they were 6weeks old for additional studies. The researchersalso examined each female mouse to determinehow many embryos it carried at the beginning ofthe pregnancy.All experiments were conducted in accordancewith laboratory animal use and care protocols asestablished by the UW-Madison Research AnimalResource Center.Effects of herbicide exposure“We found that herbicide doses at all levels causeda decrease in the number of embryos in earlypregnancy and live born pups compared to thecontrol group,” says Porter. These decreases weresignificant in the low and very low dosage groups(ANOVA, Bonferroni p


“These data do not fit with the commoncurrently accepted toxicology models fordose-response relationships—one wouldexpect that litter size would decrease as dosageincreases,” states Porter. However, U-shapeddose response curves (greatest effects at lowerdoses) have been reported for neurological,endocrine, and immune functions. Porter says,“We speculate that the greatest effect occurs atthe lower dosage levels because of the interactionbetween hormones.” For example, theremay be negative feedbacks between hormones,or responses to subtly different levels may bevery different, or there may be subtle shifts inthe chemical environment of the enzymescreating the hormones.In the world of endocrinology and immunology,it is well established that the body’senzymes, hormones and other chemicals tend tobe controlled over very narrow concentrationranges—often in the parts per trillion. Most ofthe reproductive problems that occurred in thisstudy were produced by doses at which otherenvironmental chemicals have been shown toproduce similar effects.More research is needed to replicate these results.Seasonal variationsThere were seasonal differences in the responsesto varying herbicide doses. In fall, the largestdecrease in litter size occurred at the high doselevel; in all other seasons, the largest decreaseoccurred at low and very low doses.The researchers speculate that these seasonaldifferences may be due to normal seasonalinfluences on animal hormone levels, even thoughthe mice were kept under controlled laboratoryconditions. “Extreme care was taken in our proceduresto minimize inter-experimental variation sothat the animal supplier, the age of the animals,the sources of food and water, room temperatureand humidity, and length of daylight were alwaysthe same in all experiments,” says Porter. Hereports that other studies have found seasonalvariations in the release of reproductive hormonesin experimental animals.Initial litter size and # live born pups at 4 dosage levels10Numberof pups50Controlgroup# Live born pups # Embryos in early pregnancy12.0810.7110.38 10.78.71Very lowdosage*8.64Lowdosage*11.59.42Interm.dosageLinks to human healthMice, as mammals, provide a model system onwhich to test the effects of toxic compounds, butthere are differences in how mice and peoplereact to some chemicals. However, these findingsare significant enough to cause concerns aboutherbicide exposure and reproductive problems inhumans.People can be exposed to chemicals like those inthe study by drinking contaminated groundwater,breathing air containing the chemicals, or havingtheir skin come into contact with a treated lawn.“All three chemicals in this mixture are found ingroundwater, which is why EPA has establishedstandards for each of them,” Porter notes. Certainsubstances in commercial herbicide formulationsallow the rapid movement of chemicalsthrough the skin, bypassing the body’s primarydefenses in the liver. “Due to the ability of thesechemicals to pass through fat, once in the bloodthey have the potential of crossing the bloodbrainbarrier and gaining access to the brain,”according to Porter. “Once the chemicals gainaccess to the brain, the potential for reproductiveproblems like infertility and miscarriages arises.”11.8410.05HighdosageSee text for explanation of largest effect at very low and low dosages.*Statistically significant: p

More magazines by this user
Similar magazines