Plastics Cause Concern

Plastics chemical harms eggs in unborn mice

* 13:01 12 January 2007
* NewScientist.com news service
* Roxanne Khamsi
http://www.newscientist.com/article/dn10946-plastics-chemical-harms-eggs-in-unborn-mice.html

Female mice exposed to a common chemical found in plastics while in the
womb develop abnormal eggs, according to a new study. Based on this
finding, researchers speculate that the chemical, bisphenol A, might
increase the risk of spontaneous abortion and genetic disorders in humans,
such as Down's syndrome.

Bisphenol A, or BPA, is commonly found in hard plastics and the lining of
tin cans. The chemical has come under scrutiny before because it can mimic
the hormone oestrogen.

Patricia Hunt at Washington State University in Pullman, US, and
colleagues exposed pregnant mice to 20 micrograms of BPA per kilogram of
their bodyweight each day over a one-week period. During this same period,
the reproductive cells of female mice developing inside in the womb begin
a process of division known as meiosis.

Meiosis ultimately yields mature eggs, which have half the number of
chromosomes as other cells in the body. But the process is gradual. In
humans, for example, cells only reach the end of this division process
before ovulation.
Scrambled eggs

Researchers followed the female mouse pups that had been exposed to BPA in
the womb. When these mice reached adulthood, Hunt's team examined their
eggs. More than one in every 20 cells taken from those mice had unpaired
chromosomes – an abnormal trait. This trait was completely absent in cells
taken from the BPA-free control mice.

An analysis of slightly more mature eggs taken from another group of
females exposed to BPA in utero found that 10 eggs out of 56 sampled had
one or more extra chromosomes than normal. In contrast, only one out of 57
such cells from a control group showed the same defect.

By staining the cells, the researchers found that the chromosomes in eggs
from BPA-exposed mice connect in odd places during cell division. This
might explain why they do not segregate properly during meiosis.

The embryos of mice exposed to BPA in utero also show abnormalities,
suggesting that the chemical affects the grandchildren of exposed mice – a
"grandmaternal" impact.
Human concern

Hunt is concerned that BPA might disrupt egg development in humans as
well. The types of chromosomal defects seen in her mice are known to
increase the risk of spontaneous abortion and genetic disorders such as
Down's syndrome.

"It's very concerning," agrees Dorothy Warburton at Columbia University in
New York, who was not involved in the study. But she notes that measuring
exposure to BPA in humans "is a not an easy thing to do".

The US Environmental Protection Agency has declared that exposure to 50
micrograms or less of BPA per kilogram of bodyweight is safe for humans.

Steve Hentges of the American Plastics Council in Arlington, Virginia, US,
stresses that this guideline refers to eating or drinking BPA. He believes
that the unborn mice were exposed to higher levels of BPA because they
received it through implanted pellets rather than through their food.

For this reason, Hentges argues against drawing conclusions about human
health from the study: "These results do not seem to be relevant for
reproduction and in particular fertility." He adds that other mouse
studies that involved BPA levels similar to those used in Hunt's
experiments did not show an increased risk of genetic abnormalities across
generations.

However, Hunt is convinced that the BPA amounts used in her study are
equivalent to current human exposure. She notes that previous research has
found that mice exposed to the chemical in utero have abnormal prostate
and breast tissue development that could put them at greater risk of
developing cancer in these tissues.