- Good evening and welcome to
the Pioneer Room of the Portage County Public Library.
I'm Todd Good.
I'm the Associate Dean in the College of Letters and Science
at the University of Wisconsin-Stevens Point.
Welcome to the April installment of the community lecture series
which is co-sponsored by the Portage County Public Library
and by UWSP and the College of Letters and Science.
Tonight's speaker is Heather Molenda-Figueira,
an Assistant Professor of Psychology at UWSP.
Dr. Molenda-Figueira has been at UWSP since 2011,
is an alum of the University of Michigan
and the University of Massachusetts at Amherst,
where she received her Ph.D.,
and was a postdoctoral fellow at Michigan State University
before joining us.
Her presentation tonight addresses
Problematic Plastics: Effects on Brain and Behavior,
and this talk will provide a look at how
these hormone disrupting chemicals
can alter brain development as well as behavior.
Please join me in welcoming Dr. Heather Molenda-Figueira.
(audience applause)
- Thank you.
To give a little bit of background
on how I got interested in this topic,
it started out in graduate school
when I attended several seminars
that talked about how wildlife biologists
were noticing some changes
in reproductive structure and function in animals
and how they suggested that maybe this was due
to endocrine-disrupting chemicals that these animals
were being exposed to in their environment.
I also noticed that as my friends
started to think about having families
a lot of them were struggling with fertility issues
and I was wondering if maybe some of these same chemicals
that were causing difficulties in the animals
were causing them troubles with reproduction as well.
So then when I decided to start my own family,
I completely freaked out about all of these
chemicals that we were potentially exposed to.
So I started buying
organic cotton mattresses for the crib,
organic cotton sheets and bedding,
BPA free bottles and organic baby food,
because I knew that some of these chemicals
could be harmful to my child
and I wanted to limit her exposure as much as possible.
However I didn't know the full extent
of how these endocrine-disrupting
chemicals could impact our biology, our physiology,
as well as the brain and behavior.
So I decided that this would be the focus of my research
at UWSP.
So what exactly is an endocrine-disrupting chemical?
Well according to the CDC,
an endocrine-disrupting chemical is an exogenous agent,
meaning coming from outside the body,
that interferes with synthesis, secretion, transport,
metabolism, binding action, or elimination of natural
blood-borne hormones that are responsible for
homeostasis, reproduction, and developmental processes.
So as you can see,
exposure to these endocrine-disrupting chemicals
can cause things to go array at many different levels.
Exposure to endocrine-disrupting chemicals
can disrupt things like lactation, sexual maturation,
also reduce fertility,
as well as potentially increase the risk
for psychological disorders.
So how do these chemicals work
once they get into our body?
Once these endocrine-disrupting chemicals enter our body,
their next step is to enter into our endocrine cells.
So I have a very, very, basic, rudimentary diagram
of how this mechanism works.
Here we have our lovely endocrine cell.
So these endocrine-disrupting chemicals, or EDCs for short,
enter through the membrane of that cell
where they interact with hormone receptors.
These can be receptors for hormones for
estrogen and androgens, like testosterone as an example.
Once these EDCs bind to our hormone receptors...
Once these hormones bind to their receptors
they double up with other hormone bound receptors
to create what is known as a hormone dimer.
Now, many of these receptors for hormones
are classified as nuclear receptors,
and this is because once they bind those hormones
they then move in to the nucleus of the cell
where they interact with small pieces of DNA
called hormone response elements.
Once this interaction takes place,
they then turn on things like
expression of hormone dependent genes,
the production of proteins,
as well as hormone dependent behaviors.
So how do we study
endocrine-disrupting chemicals' actions?
Well there are first are a couple of in vitro,
or outside of a physiological body,
couple of different tests that we can do in vitro.
So first are hormone binding assays.
These in general tell us about the strength of interactions
between these endocrine-disrupting chemicals
and hormone receptors.
Then we can compare the strength of those interactions
between hormones and EDCs
with natural hormones and receptors as well.
Next we can use reporter gene assays,
and this gives us an idea of how easily EDCs
can activate genes regulated by our endogenous hormones.
And usually this is measured by measuring fluorescence
that is present in proteins in cells.
Finally, we can also look at cell proliferation studies.
This can assess whether EDCs increase cell numbers.
For example we might want to investigate
whether one of these EDCs causes cancerous tumors,
so cell proliferation assays would be a way
that we can do this.
Next we can also do in vivo studies.
In this case we can
conduct behavioral or physiological assessments in animals.
So in these studies what usually happens is that
we expose animals, usually rodents like rats or mice,
to endocrine-disrupting chemicals
at different time points in development,
or maybe even at different dosages,
and see how this affects their physiology and behavior
in comparison to untreated animals.
Then finally we can look at correlation studies in humans.
So we can look for the relationship between exposure levels
and outcomes for physiology
as well as behavior and development.
All right.
So how are we exposed to these
endocrine-disrupting chemicals?
One of the main routes is through our foods.
Not all endocrine disruptors come from man-made chemicals.
There are natural endocrine disruptors as well.
So genistein is an estrogenic component
that is present in soy products, in soy foods.
This chemical can bind to estrogen receptors
and mimic some of estrogen's activity in the body.
Other foods are also large sources for exposure to EDCs,
and in particular canned foods.
Acids in these foods can help to leach out
some of these endocrine-disrupting chemicals
that typically line the inside of cans.
And water sources.
So lakes and rivers and oceans all have
detectable levels of endocrine-disrupting chemicals
and so this again is one way in which wildlife
becomes exposed to endocrine disruptors.
Okay.
Other products also contain EDCs as well,
including phthalates and bisphenols,
like BPA which you guys might have heard of previously.
So one of those major sources is plastics.
This comes in the form of plastic bottles,
so containers that we use for water,
sodas, as well as some baby bottles.
It also comes from plastics used in medical supplies,
including syringes as well as medical tubing.
So of course when endocrine disruptors
leach out of these plastics into the fluids
that pass through these medical supplies
they're going right into your blood stream,
so probably not such a good thing.
Another source within plastics is in plastic toys.
Children's toys, a lot of them are made out of plastic,
and they likely contain levels of bisphenol-A,
although there are some toys that are now on the market
that are BPA free.
Also cosmetics and personal care products.
So things like lotions and shampoos and soaps
all have endocrine-disrupting,
many of them have endocrine-disrupting chemicals
in them as well.
In this case we kind of get a double whammy,
because a lot of these products also
are housed within plastic bottles, so that's one source,
and then the products themselves often contain fragrances,
and fragrances is another source of phthalates,
one of those endocrine-disrupting chemicals.
So what disorders are associated
with these endocrine-disrupting chemicals?
Number one, it can affect pregnancy outcomes.
In humans, some but not all studies have shown
that exposure to endocrine-disrupting chemicals
can cause lower birth rates
and others have found that
exposures to EDCs like BPA and phthalates
correlates with preterm birth.
It also affects various hormone-dependent
physiological functions.
Some studies have shown that exposure
to endocrine-disrupting chemicals
can advance puberty in girls,
and this is problematic because advances in puberty
have been associated with reproductive cancers
as well as the development of
psychological disorders like depression.
It also can alter hormone release,
so many endocrine disruptors can alter
the release of hormones in the brain
as well as the rest of the body.
It's also been associated with problems
in reproductive structures in males.
Particularly when it comes to phthalates,
phthalate exposure has been associated with
smaller penis size,
also undescended testes, lower testosterone,
and also gynecomastia, or the development of breasts.
It also is associated with decreases in fertility
for both men and women.
It also alters neural development,
so one of the most harmful time points for exposure
to these EDCs tends to be during in utero development.
This is a time point when there's a lot of
changes in the brain going on,
and one area in which some of these EDCs
can affect development is the hippocampus,
which some of you might already know
is important for memory.
We have seen in animal studies that are problems with memory
with exposure to some of these chemicals.
Also it's been suggested that some of these EDCs
might play a role in development of ADHD.
EDC exposure has shown to alter
dopamine function in the brain, causing hyperactivity.
And finally, EDCs are also associated
with lower IQ in humans.
One last note is it also affects the risk of cancer,
particularly hormone-dependent cancers
like breast cancer, prostate cancer, and testicular cancer.
Okay, so why are plastics problematic?
Well one of the reasons is that they are
one of the main sources for
the endocrine disruptor bisphenol-A, or BPA.
In the U.S. it's one of the
highest volume chemicals produced
and it is found in a variety of products,
including plastics, where it's used to make
plastics more heat resistant and clear.
So it's found, again, in water bottles
and containers that are used to house food,
plastic food packaging.
BPA is also
a component of PVC,
and it also is part of the epoxy resins that line
food cans and beverage cans.
So again as I mentioned earlier,
some of this BPA can leach out into our food products,
particularly if those food products are high in acid.
It's also found in a couple other
products including dental sealant
and also thermal receipts.
So again, because a lot of our foods
are contained in plastic as well as in cans,
a major route of exposure of course is our diet.
In one study by Liao and Kannan,
shown here,
they looked at the content of different bisphenols
in several different categories of foods.
BPA is shown in the red bars on this figure,
so over 40% of foods in these categories
had detectable levels of BPA,
with the highest rates being in things like fats and oils,
fish and seafood, meats and meat products, and vegetables.
So again, particularly those canned vegetables.
This study also looked at
and estimated the daily exposure
to bisphenol-A from these food products
across different age groups.
What they found was the highest levels of exposure
actually occurred in infants, toddlers, and children.
Although these were very minute doses,
so in the case of toddlers,
which had the highest rate of exposure,
estimated rate of exposure,
it was only about 243 nanograms,
which is much, much, lower
than what has been deemed safe by the CDC.
So what is that safe dose?
Well the CDC suggests that a safe dose of exposure
is about 50 micrograms per kilogram of body weight per day.
So in nanograms this would be 50,000 nanograms.
And BPA clears the body in about six hours.
But what's important to note here
is that a lot of animal studies that have shown
adverse effects with exposure to BPA
come at doses much lower than what is
acceptable for human exposure.
BPA is also found throughout many different
tissues and fluids in the body,
including the blood,
urine, so one study conducted by the CDC
showed that in 93% of human participants
they had detectable levels of BPA in their urine.
It's also present in amniotic fluid and placental tissue
and can actually cross the placenta,
so this is one way in which a developing fetus
can be exposed to BPA.
It also is found in breast milk,
so this is one source for infants to be exposed to BPA,
and it is also found in fat tissue.
BPA is found in higher levels in infants and children
as we saw in the previous slide,
and another source beyond breast milk
that some infants can find themselves being exposed to BPA,
again, is if they have spent any time in the NICU.
So again, if children are in the NICU
they'll likely be hooked up with IVs,
and possibly feeding tubes, etcetera,
again which are sources of bisphenol-A.
So they've noticed that in urine of children
who've spent time in the NICU,
they have higher levels of BPA
compared to children who have not spent time in the NICU.
In terms of children, as we noticed on the previous slide,
they have the highest estimated
dietary intake of BPA.
And this is likely due to a couple factors.
Number one is they typically eat more
per kilogram of body weight than adults do,
and also they are more likely to consume foods
that might be a source of BPA exposure.
So BPA also has estrogen
or estrogen-mimicking effects within the body,
and also anti-androgenic effects.
So what I mean by this term is that it
blocks the effects of androgens such as testosterone
and a related hormone
called dihydrotestosterone.
Both of these androgens are important
for sexual differentiation of the brain,
as well as the body, in males.
So how does BPA exposure effect our physiology?
Number one, it reduces fertility
in both men and women.
So in women it increases the risk
for polycystic ovarian syndrome.
It also increases the
risk of endometriosis,
or build up of the tissue that lines the uterus,
and also increases risk for miscarriage.
And in men, it increases testosterone,
and this might seem like a good thing at first,
more testosterone, more manly,
but in fact it's more likely an indication
that there are problems in the regulation
of release of hormones within the body.
It also causes a decrease in sperm motility in men.
So it's also associated with preterm birth and
lower birth weights.
In one study they looked at
maternal levels of BPA in urine
in women that gave birth prematurely
or those that gave birth on time,
and higher levels are found in those women
who gave birth preterm.
Again, as with some of the other EDCs,
this associated with a higher risk
of breast, prostate, and testicular cancer,
and then also with other disorders
such as obesity and diabetes,
indicating that bisphenol-A exposure
may affect metabolism and homeostasis in the body,
and is also associated with cardiovascular disease.
So numerous animal studies have also demonstrated
that BPA exposure can alter brain function
and related behaviors.
Typically in these studies what occurs
is that animals are exposed to BPA
either during gestation,
through administration to the mom,
or shortly after birth.
These are important time points for
the development and organization of brain circuits,
including organization in the brain in terms of
circuits that are necessary for learning, memory,
and social behaviors.
It is also during this time point
that their sex differences in the brain
become apparent.
So next I'm gonna walk you through
a couple changes that have been observed in the brain
as a result of BPA exposure,
and some associated behavioral changes
that have been found with BPA exposure.
So first we have the overproduction
of neurons in the hypothalamus,
and the hypothalamus is an important area of the brain
for regulating a wide variety of things,
including hormone release,
reproduction, social behaviors, homeostasis, etcetera.
And there's also been shown to be an overproduction
of neurons in the cortex,
which is necessary for some of our
higher order cognitive functions
as well as things like sensation and perception.
Now you might think that having more neurons is a good thing
but it's actually not,
particularly when it occurs during development.
If we have an excess of neurons
we might have problems when
our brain is developing in utero
in terms of pruning of those neurons.
So it's normal over the course of development prior to birth
that the brain loses some neurons
and loses some connections.
What's going on during this process
is they're making more efficient and better connections.
So with an excess of neurons
we might not have proper pruning,
and this could potentially lead to problems in behaviors.
So because this is occurring in the hypothalamus,
it could alter reproduction
and it could also, overall,
in terms of improper pruning,
potentially lead to problems from mental health in humans.
In fact, some of the changes that take place in the brain
with BPA exposure,
are similar to those that we find in humans
that have ADHD or schizophrenia.
We also find that there are
decreases in dendritic spines,
particularly in an area of the brain called the hippocampus,
which is important for memory.
So what is a dendritic spine?
Well to back up even further,
a dendrite is a part of the structure of the neuron
which receives information from neighboring neurons.
Dendritic spines are small projections on these dendrites
that kind of offer more areas of connection
for neighboring neurons,
so essentially more input to those neurons.
With the loss of these dendrites in the hippocampus
it can impact memory function.
Another thing that can impact memory function
is a decrease in acetylcholine activity.
Acetylcholine is a neurotransmitter, or chemical,
that is released in the brain
that is important for memory as well.
Okay.
Also, with BPA exposure,
we have a loss of sex differences in the brains of animals.
This in particular takes place in the hypothalamus.
So there's one region called
the sexually dimorphic nucleus of the preoptic area.
You guys of course don't need to remember that,
there will not be a quiz on this.
But this nucleus typically is larger in size in males,
and there's another nucleus within the hypothalamus,
called the AVPV, that is typically larger in females.
And with BPA exposure, the size of these nuclei decreases.
This can impact things like social behaviors, reproduction,
and the regulation of hormone release,
which these nuclei are responsible for.
So some of the related behavior changes
that are found in animals,
is that it alters social behaviors.
In both males and females it increases aggressive behaviors,
and in females it's shown to increase exploratory behaviors.
So typically female rodents are a little bit more shy
than their male counterparts
and don't really want to explore that much,
particularly if they are in an unfamiliar environment,
but BPA seems to somewhat reverse this typical behavior
in the females.
It also alters oxytocin receptors.
These are receptors in the brain that are important for
oxytocin actions.
Oxytocin is a hormone that is also important
for social behaviors as well as parental behaviors.
So with a decrease in these receptors,
we see that there's an alteration in sexual behaviors
in rats.
So females are more sexually receptive,
and more motivated to engage in sex.
The opposite is true of males,
so it decreases their interest in sex.
Also in terms of maternal behaviors,
we see a decrease in maternal behaviors in rats.
So rat mothers are less likely to spend
time in contact with their pups following BPA exposure.
BPA also alters dopamine function.
Dopamine is involved
in a lot of different things in the brain,
including the regulation of mood, movement,
and also plays a role with reward systems in the brain.
With alterations to dopamine function with BPA exposure
we see that there's an increase in movement,
so hyperactivity in animal models.
And we also see that there are
greater rewarding effects with drugs,
including methamphetamine and morphine.
Finally,
we see that there's a decrease in glutamate function.
Glutamate is an excitatory neurotransmitter,
kind of speeds things up and gets things going in the brain,
and what we find with BPA exposure is that there
is an alteration in the levels of glutamate
in the amygdala as well as the hippocampus.
These are two structures that are important
for processing the emotion of fear.
So what we see as a result is, in BPA-treated rats,
there's an increase in anxiety and depression-like behaviors
in rodent models.
Okay.
So that's a lot that we've seen in rat studies,
but how can BPA impact
functions and behaviors in humans?
There have been a few studies that have
looked at prenatal exposure to BPA
as measured in the mother's urine,
and how this level of BPA in the urine
correlates with later behaviors in young children.
So using the Child Behavior Checklist,
or the Behavioral Assessment System for children,
they found that with higher levels of BPA exposure
there is an increase in anxiety and depression.
Also there is an increase in social problems.
So in one study they showed that BPA exposure
was associated with higher levels of aggression
and also emotional reactivity in males,
but the opposite was found for females.
A separate study on the other hand,
did find that there was an increase in aggressive behaviors
and disruptive behaviors in females.
This was particularly associated
with the levels of BPA in the mother's urine
around 16 weeks of gestation,
so kind of the beginning of the second trimester.
Also with higher levels of BPA exposure
there's an association with
hyperactivity and attention problems.
So this is one of those suggestions
that this particular endocrine-disrupting chemical
may potentially play a role in the development of ADHD.
And also, higher levels of BPA exposure
are associated with problems in reading, writing, and math,
in both males and females.
Now there are some discrepancies in some of these studies,
as some produce different sex-dependent results,
and in many cases girls were more negatively affected
by BPA exposure prenatally than boys,
so this might suggest that potentially
female fetuses are more sensitive
to these potentially negative effects of BPA.
Because of all of these concerns
about health and development with BPA,
it's been removed from a lot of products,
but it has been replaced
with a structurally similar chemical BPS.
BPS has mainly replaced
BPA in a lot of plastic products,
it's more heat stable than BPA is,
and that's thus maybe a little bit less likely to leach out
of plastics and into your food supply for example.
But another negative of BPS is that it's less biodegradable,
so it might have more negative effects
on the environment in general.
So it's been found in the urine in different studies
in anywhere between 81-97% of participants,
and again, as with BPA,
it's found in higher levels in children
and also adolescents.
Like BPA it's found in bottles,
but also pesticides, leather tanning agents,
cleaning products,
personal care products, and thermal paper as well.
It is found in lower levels in foods
compared to BPA,
so it's only in about 10%
of foods from those previous slides.
However, like BPA, some of the highest levels of BPS
were found in meats, fish, and seafood.
Okay.
So how does BPS affect our physiology?
We know that it has estrogenic effects
at two of those nuclear estrogen receptors,
estrogen receptor alpha and beta.
It also has anti-androgenic effects, so again,
blocking the effects of androgens like testosterone and DHT.
It may also alter cell survival,
so some studies have shown that
BPS exposure increases enzymes that promote cell death.
And it can affect physiology in vivo as well.
So many of the studies on
effects of BPS in vivo
have come from studies of Zebrafish
in which their water has been treated with BPS.
And we found, in terms of compromising their reproduction,
is that number one we see an increase in estrogen
in males and females,
and a decrease in testosterone in male fish,
and this indicates that, again,
there might be problems with regulation of hormone release.
We also find that there is
a decrease in gonad weight
in these fish that have been exposed to BPS.
They also produce fewer viable offspring
and more of those offspring are malformed.
Also, in terms of brain development,
we see that BPS exposure in these fish
resulted in a 240% increase
in neurogenesis in the hypothalamus.
So again, with more neurons
we have more chances for miswiring
and then later problems with
physiological function and behavior.
In terms of rodents,
exposure to BPS alters reproduction.
It decreases testosterone production
and also impairs spermatogenesis,
or the production of new sperm.
This is also occurring at doses lower than
what has been deemed safe for BPS exposure,
which like BPA is around 50 micrograms per kilogram per day.
Finally, BPS exposure has shown to
increase uterine growth in rats.
So like BPA, it's potentially a chemical that could promote
a disorder like endometriosis.
Okay, so what do we know
about the effects of BPS on behavior?
The answer is pretty much nothing.
So I had,
after reading these studies on BPA
and how it affects anxiety,
I was wondering if potentially exposure to BPS
could impact levels of anxiety as well.
Why I chose to look at anxiety is,
is because it's one of the most prevelant
psychiatric illnesses in the U.S. population
with about 16 million people suffering from the disorder.
So in our study we used a rat model.
So pregnant rats were administered BPS-treated water
that resulted in daily exposures of about 15 micrograms,
and then we had a group of control rats
that received untreated water.
This treatment began at 12 days of gestation,
so equivalent to kind of
the end of the second trimester in humans,
and it continued until 45 days of life in the pups.
So they were exposed to BPS
in the water consumed by their mothers,
transferred through the milk,
and then also from their water bottles
once they were old enough to consume water
and actually reach the spouts on their own.
So it continued until 45 days of life,
and this is just past puberty.
Yes, rats do go through puberty,
in case you were all wondering.
So this is just past puberty,
because puberty is another important time point
where hormones organize and change circuits in the brain.
We wanted to make sure we covered that time point as well.
So we had four experimental groups.
We were also interested in looking at whether there are
potentially sex differences in levels of anxiety,
so we had males and females
that were treated with BPS or controlled water.
Following treatment with this, or also I guess,
during some of the treatment with this water,
we assessed anxiety using the three most common tests
used to quantify anxious behavior in rodent models.
Number one was the elevated plus maze,
also the open field test,
and lastly the light-dark box.
And I'll explain what these tests are in a moment.
So testing
of these three different assessments
took place on three consecutive days
and tests were run at three different
developmental time points.
So first it was starting at 21 days of age,
so this was a juvenile testing point,
37 days, which is around the time of puberty in rats,
and at 56 days or older for their adult testing point.
Okay, so what do these tests look like?
First of all we have the elevated plus maze,
and as the name suggests it has a plus confirmation,
and it's elevated off of the floor about a foot and a half.
It has two open arms and two closed arms.
So if rats are more anxious,
what they do is they will spend more time
in those closed arms, 'cause rodents tend to
feel more secure in dark, cozy, little places.
The next test is the open field test,
which simply is a square box that is divided into
nine different squares.
Here in order to assess anxiety,
we see what duration of time they spent
in the very center of the chamber
versus the corners and sides.
So the more anxious the animals are,
the more time they will spend in those corners and sides
versus the center of the chamber.
Lastly, we have the light-dark box.
This has two adjoining chambers with a door in the middle
so they can pass through from side to side.
The light side of the compartment has white walls
that's illuminated by a bright, white, light,
and the dark side has black walls and a lid,
so not too much illumination penetrates in to that side.
So for each of these assessments
the duration of the test was five minutes,
we recorded all of these behaviors,
and then myself as well as my team of five or six students
analyzed the tapes with a computer aided program
to determine duration spent in the various areas
within these testing chambers.
So what we found was,
first of all, with the elevated plus maze
that we didn't see an effect of BPS treatment
or any sex differences,
but as they aged they did tend to spend
less time in those open arms,
so essentially becoming a little bit more anxious
as they got older.
We found similar effects for the open field test,
so no treatment effects and no sex differences,
but in this case they seemed to be a little more anxious
around the time of puberty,
so around that pubertal time point they spent
less time in the middle of that chamber.
Then lastly we found completely nothing
with the light-dark box.
And the reason for this is
that the light side is very, very, aversive.
So usually within 10 seconds they flew into the dark side
and they did not exit for the remainder of the test.
So, as a scientist, finding negative results
kind of is a disappointing thing,
but for the rest of humanity,
it might not be such a bad thing.
There are some reasons why we might not have found
an association between BPS treatments
and levels of anxiety.
The good news could be that there simply is
no association between BPS and levels of anxiety
as has been observed in previous studies with BPA.
Second, we might have used
too low of a dose of BPS treatment
to elicit any changes in levels of anxiety.
So currently what we are doing in the lab
is we are going to be increasing our dose
and also using a different administration paradigm
where we are more directly feeding the animals
BPS in corn oil.
Apparently rats really like to drink corn oil.
So this will also help us to get a better idea
of direct dosing
rather than having to estimate it
based on water consumption.
Okay.
My second to last question for everyone is
is bisphenol exposure safe?
In my mind this still is a little bit up for debate.
While exposure to one of these
endocrine-disrupting chemicals such as BPA
at doses deemed to be safe
as determined by the CDC might be okay.
This is certainly not the only endocrine-disrupting chemical
we're exposed to on a daily basis.
So there have been studies that have shown
that these mixtures of EDCs that we take in through
environmental exposures, through our diet, etcetera,
can have detrimental effects
on health and animal models.
Also, maybe because we are exposed
to so many of these different chemicals,
we might need to reevaluate what is considered
a safe dose for individual chemical exposure.
This is something that has occurred recently in Europe.
They have lowered their daily exposure dose for BPA
from 50 micrograms to four micrograms.
So quite a bit different.
So according to the National Toxicology Program
at the National Institutes of Health,
they do suggest that there is some concern
for effects on brain behavior and the prostate gland,
for exposures to fetus, infants,
and young children.
They also suggest that there is minimal concern
for adverse effects for mammary gland
and early puberty in females,
as well as reproductive toxicity in workers.
So for example, those individuals that work as cashiers
and are exposed to BPA through those cash register receipts.
Finally, negligible concern for reproductive toxicity
in adult men and women,
and malformation in newborns.
But again, this is based on fairly limited studies
that have looked at the associations
between exposure levels
and health outcomes in humans.
I also think that it's important to further investigate
exposure and whether there are
particular times in development
where exposure to endocrine-disrupting chemicals in general
might be more harmful to development
and later behaviors and physiology.
So, what can we do to reduce our exposure?
Number one, we can avoid plastics
that have their recycling labels
numbered three, six, and seven.
Safer bets are numbers one, two, three, and four.
We can also look for glass or metal containers
for our food and drink.
Next we can avoid microwaving our food
in plastic containers
or washing plastic containers in dishwashers
with harsh detergents, so again,
heating up these plastic components or plastic products
is one way to promote the leaching of these chemicals
into your food sources.
Next we can reduce or eliminate
the consumption of canned foods
and try to eat more fresh foods or frozen foods.
And finally, with concerns for exposure to children,
you can look for BPA and BPS free baby bottles,
as well as toys.
There are quite a few
BPA free bottles on the market, as well as some toys.
Looking for BPS free items
currently is a little bit more challenging
but hopefully as more research comes about
and suggests that there might be some harm
with exposure to this chemical as well,
we'll start removing BPS from products as well.
All right.
Thank you all for being such good listeners.
(audience applause)