Arsenic, cadmium, chromium, lead, mercury, and selenium levels in blood of four species of turtles from the Amazon in Brazil

Using blood as a method of assessing metal levels in turtles may be useful for populations that are threatened or endangered or are decreasing. In this study the levels of arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), mercury (Hg), and selenium (Se) in blood of four species of turtles from the tributaries of the Rio Negro in the Amazon of Brazil were examined. The turtles included the six-tubercled Amazon (river) turtle (Podocnemis sextuberculata), red-headed Amazon (river) turtle (Podocnemis erythrocephala), big-headed Amazon (river) turtle (Peltocephalus dumerilianus), and matamata turtle (Chelus fimbriatus). Blood samples were taken from the vein in the left hind leg of each turtle. There were significant interspecific differences in the sizes of the turtles from the Rio Negro, and in concentrations of Pb, Hg, and Se; the smallest species (red-headed turtles) had the highest levels of Pb in their blood, while Se levels were highest in big-headed turtles and lowest in red-headed turtles. Hg in blood was highest in matamata, intermediate in big-headed, and lowest in the other two turtles. Even though females were significantly larger than males, there were no significant differences in metal levels as a function of gender, and the only relationship of metals to size was for Cd. Variations in metal levels among species suggest that blood may be a useful bioindicator. Metal levels were not high enough to pose a health risk to the turtles or to consumers, such as humans.