(Paleo)toxicological analyses of the mammalian skeleton: Environment, chemicals and health

(Paleo)toxicological analyses of the mammalian skeleton: Environment, chemicals and health


Good morning everyone, my name is
Sabrina Sholts, I am a new curator in Anthropology and I’m going to talk fast.
Ok, so I changed the first word in my title. Sorry, really what I wanted to talk about,
the concept that I wanted to discuss today is paleotoxicology. I define paleotoxicology
simply as the study of toxins in preindustrial populations. This is a unifying theme of
one of the projects that I’m doing right now and so I wanted to talk a little bit
about three of those in order to give you a sense of what I’m doing, where I’m
headed, and I’m going to actually then start with where I’ve been. On the background of this slide you
can see Santa Barbara, California, which is where I did my PhD and off
the coast of Santa Barbara you’ll see the California Channel Islands, which
were the focus of my dissertation research. These Islands were occupied by
people for about 13,000 years and I was studying changes and
craniofacial morphology over time. I was using collections of archaeological
skeletal remains that were in museums but you know if you go out to the Islands
and you actually experience this place where these people lived, you can’t help but
see so many ways in which human biology may have responded to this environment.
And so what I see here and think about the most is pollution. Actually everywhere
you look on the beaches of the Islands, you see petroleum which seeps
naturally from cracks in the ocean floor and floats to the surface. And the oil
platforms that you see you in Santa Barbara Channel those signify that this
is very rich area for petroleum seepage. So if you an archaeologist on the Islands
you see petroleum everywhere in the archaeological record because people that
lived on these Islands used it extensively in just about everything they made
including containers for food and water. And so I became very interested in how
the chemicals in petroleum, known as PAH’s, and they have actually impacted
human growth and development, and health over time, in the past because
in the present we know that these chemicals are highly hazardous. PAH’s are actually the top of the list
prior to pollutants that are regulated by the EPA and they outrank a number
of man-made synthetic chemicals that are highly persistent in the environment. And so, some colleagues and I propose
that increased reliance on petroleum may have actually been a factor in
declines in head size and stature and health that we see on the skeletal
collections from these Islands. However there are a lot of factors
that contribute to and explain these patterns and so in order to adequately
test this hypothesis we need to do a lot more work. It’s very difficult to quantify
exposure in the past and to identify effects of exposure when really all you got to work
with are bone and teeth. And so I’m just going to share with you a few different
ways that we’re approaching this problem and I think are promising avenues
for paleotoxicology in the future. Our projects deal a lot with metals
because metal does accumulate. It’s stored in bone tissue, and also
there’s a number of potentially very serious effects of chemical, of metal
exposure such as near neurodegeneration and endocrine disruption. And I think as
we understand more about these effects that metals are going to go up on this list.
At the bottom of the list, under the metals, what you see is a chemical, a synthetic
chemical, known as TCDD, which is probably best known as the chemical
that was used in the attempted assassination of Viktor Yushchenko
in 2004 and besides the chloracne that he experienced as, as a result of this
episode, there are many other effects that can occur from TCDD exposure at much
lower doses. It’s the most potent chemical in the dioxin family and it can serve as
a model compound for understanding mechanisms of dioxin-like
compounds such as PAH’s. So we used TCDD as a model compound
to understand dioxin-like effects in cranial growth in laboratory rats. Of the model
organisms that are used to understand human development, rodents provide
probably the best reflection of human head development and so it was nice
way to actually look at the dioxin-related effects in a controlled dose-response
experiment. In a sample of two rat strains, one that had a mutation, that provided
resistance to TCDD and the other that had a natural sensitivity to dioxin.
We found that craniofacial form was altered by exposure to TCDD during
adulthood. What we saw most significantly was a shortening of the face which is
because anterior facial growth is really the dominant process that continues to
occur in adulthood and so the results of this study show that timing is a critical
factor in toxicity. Had Viktor Yushchenko been a child or an infant when he received
that dose of TCDD and not a grown man he probably would not have
recovered or even survived. In another study where we’re
continuing this exploration of the timing, effects in toxicity, we’re
comparing the adult exposure sample to a sample of rats that were exposed
before birth and, and immediately afterwards through the dosing of
the mothers. And so on the left in the blue you see the shortening of
the face, well on the right in the red, in the prenatal exposure sample, what
you see is really the cranial dimensions haven’t been affected in the, in the adult,
in the adult rats but there’s more of a movement of the intersections of the
sutures. And it’s probably because these sutures fuse during the
first two weeks of life and high concentrations of TCDD in the mother’s
milk provided probably the highest level exposure that was received
by the nursing offspring. And our results suggest that TCDD may have
some sort of role or function in the expression of non-metric cranial trait
known as the interfrontal bone what you see below. And actually … that’s
very interesting because non-metric cranial traits are generally perceived to
be… in the presence or absence of hereditary trait or they might be affected
by mechanical function, but certainly not something that you’d expect to see
with toxicity. So this should shed more light on, on looking at
cranial remains in the future. And so I’m actually going to very
quickly say that another avenue for looking at paleotoxicology is
genetics. A way our colleagues in Sweden actually found that you
got these higher frequencies of this genetic variant that provides
some resistance to arsenic when you’re living in an arsenic rich
environment. And we’ll be exploring the antiquity of that human
adaptation to chemical exposure. And then finally on the Channel Islands
going back there and looking at some sort of environmental monitoring.
We’re going to be analyzing trace elements concentrations of metals
in fox bones which will allow us to understand how these levels have
changed and may have been the cause by and also influenced human
populations on the Islands. So, thank you. [ applause ] A Question for Sabrina. You ended
your talk with a tantalizing reference to evolution and arsenic, [yes], could
say a little bit more about that please? So, yeah, there’ve been a number of
studies that have come out from a group of scientists in Sweden, based
near Uppsala and Stockholm and they have found that focusing specifically
on the Andes in the Altiplano region, in northern Chile and midwestern Bolivia,
that the living populations in this region that the they actually they show these
higher frequencies of these genetic variance that do allow them to metabolize
arsenic more efficiently that actually there’s changes in the pattern of methylation
and that’s actually conferred some protection against the arsenic in the environment that
allowed them to lived there for so long and so really what we want to do because it
is, is quite a novel idea that this arose in these populations and we do have some
archaeological evidence showing that the mummies, the Chinchorro mummies
for example in the same region that they are showing elevated concentrations of arsenic
and so the exposure was probably there. But we don’t have any ancient DNA to
actually prove that we had similar frequencies going back into the past and when that may
have actually began and so we have started to sample on some mummies from northern
Chile to start this work and we’ll be continuing on with this hopefully and looking at other
regions of the world to better understand. Yeah this question and shed more
light on the history of this adaptation. So, Sabrina I have a question for you
as well, that’s sort of falling on Kay’s question, so are there any other
potentially morphological effects that you can imagine from the toxins
that you’re studying whether in, you know a rat model or something else,
are there predictions that you can make about that. About any of the toxins? Do you
mean for example the petroleum, like on the Channel Islands? There
are certain diseases that have been associated with exposure to certain
to PAH’s, and polycyclic aromatic hydrocarbons is what we’re talking
about and there a lot of them, it’s a huge class of chemicals and so when
you’re talking about petroleum you’re talking about a whole mixture and you
can look at, … specific effects of single compounds, such as naphthalene. And
this is something that my colleagues and I have been looking at that that naphthalene
in particular and that’s the kind of chemical that you get in moth balls, that’s been
associated with anemia, hemolytic anemia for example and so that’s simply one
example. I think with the hydrocarbons in general they act the way a lot of
harmful chemicals act and that they just disrupt growth and development and
so it’s going to be a systemic effect more than something localized or specific but it’s
certainly, it would be difficult to characterize anything as a smoking gun, nonetheless I
think that we can at least build support for this hypothesis and really think about these
health factors that are certainly important and relevant today and are equally
so would have been in the past.