Inorganic elements in live vs dead nesting olive ridley marine turtles in the Mexican Pacific: Introducing a new statistical methodology in ecotoxicology

This study reports the largest inorganic elements database in the blood of live marine turtles (Lepidochelys olivacea), with 241 live as well as 38 dead nesting turtles sampled and analyzed for 26 inorganic elements, including essential (Al, As, B, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Se, S, V, and Zn) and non-essential elements (Cd, Li, Pb, Sr, Ti, Tl, and Hg). We compared inorganic element concentrations in live and dead olive ridleys from the arribada beach “La Escobilla” located on the Pacific coast of southeastern Mexico. The most outstanding result of our study is the higher Cd concentration in dead (mean 4.27 μg g−1 ww: min 0.01-max 81.5) compared with live animals (mean 0.14 μg g−1 ww: min 0.02-max 0.52). This population has been previously reported to have the highest Cd concentration worldwide in kidney and liver samples from marine turtles (with 150.88 ± 110.99 and 82.88 ± 36.65 μg g−1 ww, respectively). Other important findings of this study include the low Hg concentration along with the decrease in Pb over the years in this population. The study also uses a new statistical method – the iconography of correlations – in which all available information is used without removing individuals or variables with missing information for the whole analysis, which is a common problem in ecotoxicology. A major advantage of this method compared to other multivariate methods is that the missing information can be easily handled, because the correlations (2 variables) and partial correlations (3 variables) are estimated only with the available data using a one-at-a-time strategy.3,25