Examining toxic trace element exposure in American alligators

Abstract

Toxic trace element exposure occurs through release of the ubiquitous and naturally occurring elements arsenic (As), cadmium (Cd), lead (Pb), and mercury (Hg). The unique environmental conditions of the wetland ecosystems along the southeastern Atlantic coast of the United States lead to the accumulation of Hg which is greater than in most other ecosystems in the country. There are also point sources of As, Cd, and Pb in this region. To effectively monitor trace element concentrations, and consequently the potential human exposure, accessible local sentinel species are needed. In this study, concentrations of As, Cd, Pb, Hg and six other trace elements (Al, Ni, Cu, Zn, Se, Mo) were examined in American alligators (Alligator mississippiensis) from seven wetland sites in South Carolina and Florida and assessed for their utility as a sentinel species for human trace element exposure. Alligators were chosen as a potential sentinel as they share a common exposure with the local human population through their aquatic diet, and they are directly consumed commercially and through recreation hunting in this region. Sex was significantly related to the concentration of Zn, Mo, and Al, but not As, Pb, Hg, Cd, Se, or Cu. Site specific differences in element concentrations were observed for As, Pb, Hg, Cd, Se, Zn, and Mo. Size/age was significantly related to the element Hg and Pb concentrations observed. The observed concentration ranges for the four toxic elements, As (6–156 ng/g), Cd (0.3–1.3 ng/g), Pb (3–4872 ng/g), and Hg (39–2765 ng/g), were comparable to those previously reported in diverse human populations. In this region alligators are hunted recreationally and consumed by the local community, making them a vehicle of direct human toxic element exposure. We propose that the similarity in As, Cd, Pb, and Hg concentrations between alligators observed in this study and humans underscores how alligators can serve as a useful sentinel species for toxic element exposure.

Relationships between stable isotopes and trace element concentrations in the crocodilian community of French Guiana

“…Crocodilians can be used to monitor the environmental contamination through trace elements (Nilsen et al, 2019). They have a lifespan of several decades leading to long-term accumulation of contaminants.…”

Cadmium Pollution in the Tourism Environment: A Literature Review

“…Scientifically correct approaches of this problem are not really common in the literature. An example of this was provided by Nilsen et al [113], who were able to relate Cd accumulation in alligators to tourist exposure to this toxic metal. The explanations of tourism contribution to Cd pollution are often restricted to stating various activities like traffic as a source of Cd.…”

Variation of Total Mercury Concentrations in Different Tissues of Three Neotropical Caimans: Implications for Minimally Invasive Biomonitoring

“…Crocodilians bioaccumulate Hg at various concentrations, depending on the species and on the location (Elsey et al 1999;Rumbold et al 2002;Campbell et al 2010;Vieira et al 2011;Nilsen et al 2017a;Lemaire et al 2021a). However, interspecific variability across the whole group remains still poorly understood to date as most of the available studies on Hg concentrations have disproportionately focused on two species, the American Alligator, Alligator mississippiensis and the Morelet's Crocodile, Crocodylus moreletii (Yanochko et al 1997;Jagoe et al 1998;Elsey et al 1999;Burger et al 2000;Rainwater et al 2007;Horai et al 2014;Trillanes et al 2014;Nilsen et al 2017a;Buenfil-Rojas et al 2018;Nilsen et al 2019;Buenfil-Rojas et al 2020). Some recent studies, however, have focused on several other species (Almli et al 2005;Vieira et al 2011;Lázaro et al 2015;Schneider et al 2015;Marrugo-Negrete et al 2019;Lemaire et al 2021a,b).…”