Print

Print


Hello Harro,
Heterotrophs produce some metabolic water by "burning" food that may be 
isotopically very different from local meteoric water. Considering the 
fact that even some mammals in arid environment rarely or never drink 
and thus produce most or all of their body water metabolically, it can 
be expected that body water occasionally has little in common with local 
meteoric water. There is a nice graph depicting various mammalian 
sources and sinks of body water in terms of an oxygen isotope mass balance:
Ayliffe L.K. and Chivas A.R., 1990. Oxygen isotope composition of the 
bone phosphate of Australian kangaroos: Potential as a 
palaeoenvironmental recorder. Geochimica et Cosmochimica Acta 54, 
2603-2609. doi:10.1016/0016-7037(90)90246-H 
<http://dx.doi.org/10.1016/0016-7037%2890%2990246-H>
The same principles hold true for hydrogen.
Consequently diet has a major influence on the isotopic composition of 
animals' body water, in addition to the influence of drinking water and 
evapotranspiration (e.g., water vapor loss through lungs). Hydrogen and 
oxygen in food biomass are incorporated from water by autotrophs using 
different biosynthetic pathways, with fractionation for oxygen and 
hydrogen being independent from each other. Different biochemicals show 
different fractionations. Diets differ greatly among heterotrophs. These 
may be the chief reasons for your observations. In contrast, the 
isotopic exchange between body water and exchangeable organic hydrogen 
and oxygen in food and biomass has little to do with it.
Can you offer some more detailed information about which species' body 
water isotopic compositions exhibit strong deviation from that of 
regional meteoric water?
With best wishes,
Arndt

H.A.J. Meijer wrote:
> Dear colleagues,
>
> My estimate for the isotope values for blood (that is the water 
> component) in humans and animals would be that it has to be pretty 
> close to the local (drinking) water. It is possibly slightly enriched 
> due to evaporation processes in the body as well as in the open water 
> available in nature for animals to drink, but not by more than a few 
> per mil.
> In the "bakground" samples we process for doubly labelled water 
> studies, however, relatively high values for 2H occur regularly, 
> sometimes higher than + 50 o/oo. 18O is always in the local natural 
> range that I expect.
> Is this an artefact, i.e. contamination by memory effects in the lab, 
> or in the field, or during sample storage (samples are being stored in 
> flame-off capilaries)?. If so, why does it  never happen for 18O?
> Or is it real? We know that the hydrogen in body water interacts with 
> H in tissue to some extent, but can tissue be that highly enriched in 
> 2H? And if so, why is it so variable?
> Is there any experience with "blood water" isotopes in fields where 
> people do not use enriched water as well, f.i. in forensics?
>
> Thanks on forehand for helping!
>
> best regards,
>
> Harro


-- 
Arndt Schimmelmann, Ph.D.
Senior Scientist
Indiana University
Department of Geological Sciences
Biogeochemical Laboratories
1001 East 10th Street
Bloomington, IN 47405-1405
Ph   (812) 855-7645
home (812) 339-3708
FAX  (812) 855-7961
e-mail:   [log in to unmask]
personal home page:   http://www.indiana.edu/~geosci/people/faculty2.php?n=schimmelmann
home page of Biogeochemical Laboratories:
http://www.indiana.edu/~geosci/research/biogeochem/