Exposure and Childhood Development in the Yaqui Valley
Monitoring Type: Human Health
to pesticides has been linked to developmental health effects,
but this is rarely demonstrated with field studies and the
linkage can be difficult to document.
develop and demonstrate the use of simple methods for detecting
subtle health impacts, and to document these health impacts
in a comparative way in two communities with different pesticide
Yaqui community where the study took place did not participate
extensively in the study design or execution.
evidence of motor skill and developmental impairment gathered
by simple diagnostic methods. There is a striking contrast
between drawings made by children less exposed to pesticides
and by children who were more exposed to pesticides. Also,
there is a manual widely available to community researchers
showing how to employ the simple, low-cost methods used
by Dr. Guillette in Sonora Mexico and elsewhere. The manual
can be downloaded at: http://www.oztoxics.org/cmwg/library/documents_1/
Pesticides in two Yaqui Communities in Sonora Mexico
the 1950s, the indigenous Mayan people living in the Yaqui Valley
in the Mexican state of Sonora hit a philosophical divide. Some
wanted to adopt the so-called ćGreen Revolutionä modern farming
techniques, including the use of pesticides and tractors, while
others wanted to continue with traditional farming and ranching
methods. Those wishing to adopt the modern techniques (including
use of pesticides and tractors) moved to the valley of their
region, and those who did not occupied the foothills.
Valley is now one of the largest agricultural areas in Mexico
(31,000 hectares / 76,600 acres) and annually produces 1/2 million
tons of fruits and vegetables annually, mainly for export to
the U.S. and Canada. Along with increased production has come
greatly increased pesticide use in all other respects, even
genetic, the communities of the valley and the foothills do
the late 1980ās, the Institute for Technology in Sonora (ITSON)
conducted studies in the Yaqui Valley and found high levels
of pesticides in cord blood and breast milk. In the early 1990s,
Dr. Jose Luiz Perez Gonzales conducted a health effects study
in the Yaqui Valley and found that children had extremely high
levels of pesticides in their porous organs that in some cases
had led to death. Unfortunately, because of the political climate
of the time, his team was not allowed to expand or even continue
the study. Elizabeth Guillette, an anthropologist and research
scientist, learned about these studies in the mid-1990s and
obtained permission from the Mexican government to continue
testing on the condition that she not use the word Īpesticide,ā
which the Mexican government thought would create undue alarm
among the residents of the communities. She agreed to conduct
a generic ćenvironmental study.ä
STUDY: Yaqui Valley Mothers Suspect Chemicals Are Harming Children
Guillette and Maria Mercedes Meza, a chemist for Institute of
Technology in Sonora (ITSON) carried out the study, entitled
ćAn Anthropological Approach to the Evaluation of Preschool
Children Exposed to Pesticides in Mexico,ä funded by the U.S.
Government and printed in the scientific journal, Environmental
Health Perspectives in June 1998.
study was conducted in farming communities of the Yaqui Valley
and in Tescopaco. Tescopaco, in the Sierra Madre foothills,
is the 'control site' because it is the town furthest from the
farms, about 80 km away (approximately 50 miles). These towns
are considered interesting communities to compare because the
people in these areas are very similar genetically.
They also eat the same food source, have the same education,
same economy, customs, and the same housing facilities, yet
there are significant differences in the health of the children
in the two communities.
who farm in the valley use a wide mix of pesticides so it is
impossible to tell what specific pesticides they have been exposed
to. There is strong evidence of DDT usage and exposure, among
dozens of other chemicals. Farmers would not reveal information
about specific pesticides, in part because pesticides are tied
to bank loans, and the banks are not willing to reveal what
is being used with certain crops. However, they did tell Dr.
Guillette and Ms. Meza that pesticides were applied thirty to
forty times a season - about three times the number of applications
reported by experts in the U.S. and Canada. The families under
study lived in towns surrounded by farms. The children are exposed
to aerial and ground spraying in their environment where they
play and from the food they eat. Many of the valley families
told the researchers that they are often showered with pesticides
that come into their homes and cause problems like headaches
Guillette was initially interested in cancer - the dramatic,
obvious outcome, like that found in laboratory rats subjected
to huge amounts of chemicals. But mothers in the valley insisted
that the researchers search for broader, perhaps subtle effects.
The mothers already suspected that chemicals were affecting
their children, but could not identify specific health effects.
To uncover hidden impacts, the researchers used common intelligence
and developmental diagnostics ö for example asking children,
ages four and five, to perform a series of play activities corresponding
to developmental levels. Tests consisted of simple tasks such
as catching a ball, and dropping raisins into a bottle cap.
Pediatricians to measure development in children use these same
tests. Children of age three should have been able to accomplish
these tasks. The research team noticed right away that the Valley
children showed deficits in energy levels and in hand and eye
coordination. The 4 and 5-year-old Valley children weren't performing
at the level of a three year old.
Drawings Dramatically Illustrate Problem
One of Dr. Guilletteās findings stood out hauntingly above the
others; the ability to draw a person (see
figures below). This is a pediatrician's method to measure
a child's development of perceptual and motor abilities. The
foothills children at ages 4 and 5 could draw a complete person.
Among the exposed children, most 4-year-olds just scribbled,
and the 5-year-olds could draw a head and a line or a circle
and a line. She also noted evidence that the valley children
were getting sick more often
were also differences in behavior. The foothill children were
observed to be busy with group play, whereas the valley children
were more apt to play alone. Local teachers also complained
that the valley children were much more difficult to teach,
as they have trouble remembering and often have behavioral problems.
They Yaqui mothers from the valley also reported more problems
getting pregnant and higher rates of miscarriage, stillbirth,
neonatal death and premature birth.
Guillette made a second trip to the region two years after the
first to follow up on the developmental progress and health
of the children. In the second trip she noted that the valley
children had continued developmental and mental deficits, including
poor, sense of balance, and poorer general health. The exposed
children lacked the balance to turn around on a 2x4 plank and
walk back to the starting location whereas the lesser exposed
could. She also found that the 7-year-old valley (exposed) children
were only drawing at the 4-year-old level. The 7-year-old lesser-exposed
were identifying people by gender, with a dress or pants, appropriate
hair, fingers, facial features and shoes.
this second trip to Sonora, she also surveyed the children for
illness during the past three months and found that the valley
children had been ill about six times more often than the lesser-exposed
children in the foothills. The valley children had high rates
of upper respiratory infection and other symptoms such as allergies.
Some of the illnesses in the valley children were associated
with direct pesticide exposure, such as rashes and gastrointestinal
Elizabeth Guilletteās husband, Louis, was one of the first scientists
to discover that many pesticides can disrupt the endocrine system
that controls animal hormone production (see case study on Lake
Apopka). Scientists now suspect that pesticides have similar
effects on humans. Knowing this, Elizabeth Guillette noticed
that the Valley children appeared to be maturing more rapidly
than those in the foothills. . She has recently completed a
study on breast development in 8 to 10 year old girls and found
the valley girls generally have a decrease, or lack of, mammary
tissue in the developing breast. Dr. Guillette found that mothers
experienced higher levels of birth defects, spontaneous abortion,
premature birth, and stillborns that were more than double in
the valley town than in the foothill town of Tescopaco. Although
Elizabeth couldn't prove conclusively that pesticides were the
reasons for the deficiencies, the results are alarming and strongly
suggest the possibility of a connection to the pesticide contamination,
as other variables are limited.
ON THE PROJECT: Simple Methods Generate Powerful Data
methods used in this study are attractive because they are simple
and inexpensive. For example, the team Dr. Guillette is now
working with in a similar study using three community researchers.
A diagnostic test for a single child takes about 30 minutes.
An interview with the parent of the child also takes about 30
minutes. Compared to other monitoring techniques discussed in
this handbook, these methods require little technical expertise.
Essentially, one merely has to follow the directions in the
handbook developed by Dr. Guillette (see below). Dr. Guillette
will review your interview forms, data analysis and help solve
related problems using e-mail. Typical equipment includes: tape
measure, tennis balls, a 2x4 plank, raisins to drop into a bottle
cap, and gallon jugs.
Dr. Guilletteās study was so widely read and well received,
many researchers are now looking at how children function, especially
mentally. The studies have been used mainly in the context of
decreasing exposures (for example, pesticide bans in Canada
resulted from this type of study). Also, through the UN convention
for the elimination of POPS (Stockholm Convention), similar
diagnostic methods are being used in India and elsewhere in
the developing world.
is important to keep in mind that the diagnostic techniques
described in this case study are not a magic bullet. As with
all health effects monitoring, these methods are not sufficient
evidence that the results seen are the result of any particular
contaminant. They can, however, be used in conjunction with
other evidence to build such a case. Researchers must also be
careful not to exclude the community in designing or executing
the study. Lack of community involvement in this study occurred
because this monitoring study was the first of its kind and
basic testing methodologies were being adapted for use at the
community level. And, of course, the study was directed in response
to mothersā concerns about their childrenās health. Collaboration
with the community at all phases will enrich any similar studies
and ensure that the best possible results are achieved.
Guillette has produced a manual outlining the simple and elegant
diagnostic methods used in her Yaqui research and elsewhere.
It is available for download at: http://www.oztoxics.org/cmwg/library/documents_1/Community%20Health%20Assessment%20Manual.pdf
links and contact info
of Elizabethās work in Mexico:
Elizabeth A. Guillette, Ph.D.
Asst. Research Scientist, Anthropology
University of Florida
32 SW 43rdTerrace
Gainesville, FL 32607
(352) 375-5929 (tel)
(352) 392-6929 (fax)
These are pictures of people drawn by Yaqui children. Notice
the incredible contrast in the representations performed
by the lesser-exposed foothill children (left) and more-exposed
valley children (right). (Back to
4 Year Olds
5 Year Olds
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