Monday, January 17, 2011

Testing for Mercury in Amazonian Turtles

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. 

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.

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