Page 381 - Environment: The Science Behind the Stories

THE SCIENCE BEHIND THE STORY

Testing the Safety the eggs of mice in the control cages
of Bisphenol A were normal.
In another round of tests, Hunt’s
team gave sets of female mice daily
Of the many studies documenting
health impacts of bisphenol A on lab oral doses of BPA over 3, 5, and 7
animals, one of the first came about days. They observed the same meiotic
because a lab assistant reached for the abnormalities in these mice, although at
wrong soap. lower levels (Figure 2). The mice given
At a laboratory at Case West- dr. Patricia hunt, Washington State BPA for 7 days were most severely
ern Reserve University in Ohio in university affected.
1998, geneticist Patricia Hunt (now at
Washington State University) was mak- in a controlled experiment, Hunt 12
ing a routine check of her female lab instructed researchers in her lab to
mice. As she extracted and examined wash polycarbonate cages and water 10
developing eggs from the ovaries, she bottles using varying levels of the harsh
began to wonder what had gone wrong. soap. They then compared mice kept in
About 40% of the eggs showed prob- damaged cages with plastic water bot- 8
lems with their chromosomes, and 12% tles to mice kept in undamaged cages
had irregular amounts of genetic mate- with glass water bottles. Percent mice with chromosomal problems 6
rial, a dangerous condition called ane- The developing eggs of mice
uploidy, which can lead to miscarriages exposed to BPA through the delib-
or birth defects in mice and people alike. erately damaged plastic showed 4
A bit of sleuthing revealed that a lab significant problems during meiosis,
assistant had mistakenly washed the the division of chromosomes during 2
lab’s plastic mouse cages and water bot- egg formation—just as they had in the
tles with an especially harsh soap. The original incident (Figure 1). In contrast, 0
soap damaged the cages so badly that 0 20 40 60 80 100
parts of them seemed to have melted. Dose of bisphenol A (ng/g)
The cages were made from
polycarbonate plastic, which contains Figure 2 in this dose-response experiment,
bisphenol A (BPA). Hunt knew at the the percentage of mice showing chromo-
time that BPA mimics estrogen and that somal problems during cell division rose
with increasing dose of bisphenol A. In the
some studies had linked the chemical to United States and Europe, regulators have
reproductive abnormalities in mice, such set safe intake levels for people at a dose
as low sperm counts and early sexual (a) (b) of 50 ng/g of body weight per day. Data from
development. Other research indicated Hunt, P.A., et al., 2003. Bisphenol A exposure causes
that BPA leaches out of plastic into Figure 1 exposure to bisphenol A meiotic aneuploidy in the female mouse. Current
water and food when the plastic is affects cell division in mice. In normal Biology 13: 546–553.
cell division (a), chromosomes (red) align
treated with heat, acidity, or harsh soap. properly. Exposure to bisphenol A causes Using the figure, predict the percent
Hunt wondered whether the chem- abnormal cell division (b), whereby of mice in the study that would
ical might be adversely affecting the chromosomes scatter and are distrib- likely suffer chromosomal problems when
mice in her lab. Deciding to re-create uted improperly and unevenly between exposed to a bisphenol A dosage of
the accidental cage-washing incident daughter cells. 70 ng/g. What would this percentage be?

Disease is a major focus heart disease, and respiratory disorders have some genetic
of environmental health basis, but they are influenced by environmental factors. For
instance, whether a person develops asthma depends not only
Among the hazards people face, disease stands preeminent. on his or her genes, but also on environmental conditions.
Despite all our technological advances, we still find ourselves Studies have shown that pollutants from fossil fuel combus-
battling disease, which causes the vast majority of human tion worsen asthma, and children raised on farms suffer less
380 deaths worldwide (Figure 14.3a). Major killers such as cancer, asthma than children raised in cities. Malnutrition (p. 264),

M14_WITH7428_05_SE_C14.indd 380 12/12/14 3:04 PM