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| Giant River Turtle (Podocnemis expansa) | | |
Mercury (Hg) in the food webs of the Amazon
Basin have been studied since the 1980s and its presence was first attributed
to its uncontrolled use artesanal gold mining. However, in the early 1990s,
high levels of Hg were found in soil, fish, and hair of local individuals far from any anthropogenic
sources. In the upper Rio Negro, a small gold-mining operation developed in
1993, but was shut-down by the Brazilian Government. This basin, located on the
border of Brazil, Colombia, and Venezuela, is strongly protected and has no
mining activity or any other known anthropogenic Hg sources. Mercury concentrations in the soil are
naturally high and the metal is probably transported into river systems by runoff.
Turtles in this region have been an important commercial and protein source for
local residents for centuries and they continue to be exploited today. Rio
Negro Basin turtles also supply the markets in Manaus, the Amazonas state
capital. The species most often used are the podocnemidids: Podocnemis
expansa, P. erythrocephala, P. sextuberculata, P. unifilis,
and Peltocephalus dumerilianus. Podocnemis
are all listed in the IUCN Red
List of Threatened Species with P. expansa listed as in Low
Risk/Conservation Dependent species, and the other species listed as Vulnerable.
Schneider et al. (2011) determined the
concentrations of mercury (Hg) in four tissues of six species of turtles from
the Rio Negro. They
found two species that had mercury concentrations in blood and carapace tissues
that were correlated with concentrations in internal tissues. This serves as a
way to establish a non-lethal indicator of internal metal exposure or body
burden of Hg. Mercury levels were also correlated to turtle size and gender.
The liver in five species of turtles had the highest concentration, followed by
carapace, muscle, and blood. The exception was Chelus fimbriatus, which
had a higher metal concentration in the muscle than carapace. The use of
carapace tissue to infer internal concentrations of Hg is commonly used in freshwater
and sea turtles, but this study found that only blood might be a reliable
indicator of Hg concentrations in liver and muscle tissues for P. sextuberculata.
Thus blood may be used as a non-invasive method to study concentrations of Hg
in liver and muscle of P. sextuberculata. The entire article can be
found on-line.
Citation
Schneider,
L., L. Belger, J. Burger, R. C. Vogt, C. Jeitner, J.
R. P. Peleja. 2011. Assessment
of non-invasive techniques for monitoring mercury concentrations in species of
Amazon turtles. Toxicological
& Environmental Chemistry, 93(2):238-250.
Labels: Podocnemis, tesing for environmental contaminents
