Sperm, Pesticide Tie Found
* Missouri study marks the first time scientists have been able
to link environmental contaminants and semen quality.
exposed to pesticides widely used on crops are many times more likely
to have defective sperm and low sperm counts than males with little
or no exposure, according to a scientific study published today
study provides new evidence supporting a theory that pesticides
and other chemicals which mimic estrogen or block testosterone are
harming human reproductive systems. It is the first time that scientists
have shown a link between environmental contaminants in men's bodies
and large decreases in the number and quality of their sperm.
team led by University of Missouri-Columbia reproductive epidemiologist
Shanna Swan compared men from central Missouri who had higher concentrations
of two herbicides and one insecticide in their bodies with men from
Missouri and the Minneapolis area who had low levels.
Missouri, the pesticide score [of the men] was strongly associated
with semen quality," the authors reported in the journal Environmental
Health Perspectives, which is published by the National Institute
of Environmental Health Sciences.
of the men in the new study worked at or lived next to farms, where
the pesticides are most commonly used. They were most likely exposed
through drinking water supplied by aquifers, Swan said.
number of men tested for pesticides — 50 from Missouri and
36 from Minnesota — is considered small, but scientists said
the findings warrant close attention because some of those tested
were found to be 30 times more likely to have defective sperm. That
degree of risk is in the same range as the odds of contracting lung
cancer from a lifetime of smoking cigarettes.
the tested men, in their 20s and 30s, were fertile and recently
this means is that it's harder for these men to conceive. It takes
them longer," Swan said. "We also wonder what else it
is doing to these men, and what it is doing to the rest of the family,
the women and children?"
Perrault, a reproductive toxicologist at the U.S. Environmental
Protection Agency's national research lab, said the study "really
raises our antennae."
she said, Swan's team "hasn't proven that [the pesticides]
came from the water" and that more men should be tested before
the safety of the pesticides is questioned. "We should look
into this more, rather than drawing real definite conclusions now,"
scientific debate about sperm counts has been waged since 1992,
when Danish researchers reported that men on average have half as
much sperm as they did a half-century earlier, based on 61 sperm
count studies, mostly in Europe and North America. Some scientists
challenged the findings because there was no universal pattern.
sperm counts had been reported in European, but not American, men.
Since then, reproductive experts have tried to determine if chemical
exposures or geographic patterns could explain the differing sperm
fall, Swan broke new ground by reporting major differences in sperm
between rural and urban areas. Men in Columbia, Mo., have significantly
lower numbers of sperm — as much as 44% less — than
men in Minneapolis, New York and Los Angeles, according to her research.
had trouble finding men in Missouri with good sperm quality,"
Swan said in an interview. "The counts in Missouri are really
Hess, a reproductive toxicologist at University of Illinois-Urbana
who was not involved in the study, said the research was so well-documented
and found such a high risk that it leaves "no doubt in [his]
mind that there is a link" between semen and the three pesticides,
alachlor, atrazine and diazinon.
this means is if your sperm counts are low, [these pesticides] ought
to be a top candidate," he said. "Water is so important
that everybody ought to be conscious of this."
hope the study will increase pressure on the Bush administration
to adopt stricter regulations governing the use of herbicides and
insecticides. But the authors acknowledged that confirmation of
the results using larger numbers of men and those from other areas
the widespread use of these pesticides, if further study confirms
these findings, the implications for public health and agricultural
practice could be considerable," the researchers wrote in the
say it has already been well-documented over the last 20 years that
farm workers and herbicide sprayers have poor semen quality.
the new study is the first to note the condition in men who weren't
working directly with pesticides. "We're not looking at exposure
through home or occupational use. This is an environmental exposure
of which people had no knowledge," Swan said.
pesticide industry said Tuesday that the researchers "do not
provide clear evidence" that pesticides caused the sperm differences.
Instead, they could be within the normal, random variation found
in men, said Ray McAllister, vice president for science at CropLife
America, a group representing pesticide manufacturers.
Christina Wang, a co-author of the study from Harbor-UCLA Medical
Center, said it is "unlikely" that natural variation or
genetics would explain the large differences in sperm, but acknowledged
that she would need to see similar results in more men to confirm
her suspicion that pesticides are to blame. The research team is
now expanding its testing to another agricultural area, Iowa City.
main problem was that the study was done comparing only Missouri
and Minneapolis, mainly because those places showed the largest
difference in sperm counts," Wang said.
scientists wrote in the study that they adjusted the data for factors
known to affect sperm, including age, race, smoking, abstinence
and diseases, which they said left pesticide exposure as the only
known culprit. Seasonal temperature differences can also affect
sperm, but that effect would not be so large, Perrault and Wang
numerous studies during the last few years, researchers have found
evidence that estrogen-mimicking chemicals in the environment are
feminizing or emasculating wild animals. Laboratory tests also show
that when a male animal is exposed to high levels of pesticides
as a fetus, its sperm is affected.
people generally are exposed to much lower doses, and some scientists
are skeptical that the levels commonly found in the environment
can harm people.
human evidence has been growing, however. Other recent studies have
linked sperm quality of men with industrial compounds called PCBs
and chemicals found in plastics called phthalates.
highest risk was associated with alachlor, a popular weedkiller
in the Midwest used on primarily on corn, soybeans and peanuts,
the study said. About 20 million pounds of the weedkiller are used
annually in the United States.
rate of sperm defects was 30 times greater for Missouri men with
the highest levels of alachlor in their urine, compared to Missouri
men with low levels.
exposed to higher levels of the insecticide diazinon were 17 times
more likely to have poor semen quality. Diazinon, used widely on
lawns, was banned for residential use last year, but it is still
legal on many crops.
exposed to atrazine, used primarily on corn, were 11 times more
likely to have defective sperm, although fewer men had detectable
levels of atrazine than the other two chemicals.
everybody who had any atrazine in his body had very poor semen quality,"
January, after a review that lasted several years, the EPA announced
that atrazine, the country's most heavily used herbicide, could
still be used safely on crops, but that the manufacturer must monitor
some water systems in the Midwest and Southeast. Environmental groups
argue that the chemical should be banned because it exceeds federal
standards in some drinking water. They also want all commercial
use of diazinon eliminated.
of the EPA said the results of the new study are surprising and
important because the exposures to the three pesticides were fairly
low among the Missouri men and would be routine in many parts of