Biology Reference
In-Depth Information
and those that do not, as a failure to report this ratio does not allow for authentication of
the results.
Tissue Extraction: Biological Apatite
Besides bone collagen, researchers have recognized that the mineral portion of bone, as
well as tooth enamel, also contains useful isotopic information, particularly for the analysis
of carbon, strontium, and oxygen isotopes. This inorganic component of bone, comprising
approximately 70% of dry bone weight, is dominated by a mineral called
hydroxyapatite
(see Trammell and Kroman [Chapter 13], this volume). The mineral component of tooth
enamel is even higher, as nearly 96% is hydroxyapatite. Often termed bioapatite, apatite
carbonate, or bone carbonate, scholars agree that biological apatite has a propensity to
survive various depositional contexts, even when bone collagen is too far degraded to be
of much use for isotopic analysis. For example, Sponheimer and colleagues (2006) reported
isotopic results derived from biological apatite in 1.8-million-year-old
Paranthropus robustus
teeth. Such findings reiterate the importance of the mineral component of bones and teeth
in isotopic analysis. Techniques for isolating biological apatite are widely known and have
been reported by numerous authors (e.g.,
Lee-Thorp et al., 1989
;
Lee-Thorp and van der
Merwe, 1991
;
Balasse et al., 2002; Garvie-Lok et al., 2004
). In these methods, samples are
soaked in sodium hypochlorite (household bleach) and then treated with an acetic acid solu-
tion to remove external carbonate. Moreover, skeletal biologists have recognized that biolog-
ical apatite derived from tooth enamel provides a unique snapshot of enamel formation
during childhood while biological apatite extracted from bone is indicative of an individual's
last few years of life (
Knudson et al., 2009
).
If researchers' questions involve carbon, nitrogen, or oxygen isotopes, then no further
processing is necessary once biological apatite has been extracted. Workers interested in
strontium isotopes, on the other hand, are required to complete an additional step before
those isotopes can be analyzed. This step requires the separation of strontium under
clean-lab circumstances. In my experience, few skeletal biologists maintain such laborato-
ries (with the exception of ancient
DNA
labs) and often are required to collaborate with
experts from the geological sciences. While many skeletal biologists often ship samples of
extracted biological apatite to these experts for strontium isotope analysis, it should be
noted that many colleagues in geology are eager to work with skeletal biologists and will
gladly provide training on strontium extraction procedures. Regardless, skeletal biologists
must keep these special considerations in mind when planning any project on strontium
isotope analysis.
Laboratory Considerations
In ideal circumstances, skeletal biologists would be equipped with the laboratory capabil-
ities to extract both collagen and biological apatite. Both extraction methodologies can be
applied in standard laboratories equipped with one or more fume hoods, chemical storage
capabilities, and a source of distilled water. Collagen extraction typically requires glassware,
so interested skeletal biologists should consider the number of samples they hope to analyze
when preparing equipment orders or budgeting for grant proposals. An important consider-
ation for collagen preparation involves residual carbon that may adhere to glassware
