Experimental Study of Blood Lead Kinetics in Estuarine Crocodiles (Crocodylus porosus) Exposed to Ingested Lead Shot

Abstract

A previous study of lead (Pb) contamination in estuarine crocodiles (Crocodylus porosus) in Kakadu National Park, Australia, found elevated Pb levels in bone and flesh from individuals caught in habitats where hunting with lead ammunition had occurred. Lead shot was suspected as the potential source of Pb in these animals. An investigation was designed to determine if crocodiles are capable of retaining and dissolving lead shot in their stomachs and absorbing the ionic Pb into the blood. Four of the six juvenile crocodiles (C. porosus) used in the experiment were fed an initial dose of five or ten lead shot each. Most of the lead shot were retained in the stomach over the 20-week experimental period, as confirmed by stomach lavage and radiography of the stomach region. From 13 to 30% of the original weight of individual lead shot had been eroded in that time. In vitro experiments confirmed that lead shot could be dissolved under conditions simulating those known for the crocodilian stomach. Blood Pb concentrations increased by an order of magnitude within a week after dosing three crocodiles with five lead shot each, and then attained steady-state equilibrium 5-20 weeks after dosing, with blood Pb steady-state levels ranging from 278 to 363 microg/dL. The blood Pb concentration-time curves in these crocodiles followed a one-compartment model with first-order loss kinetics that yielded an apparent biological half-life for Pb in blood of about 3.4 days. Throughout the experiment, the crocodiles remained in apparent good physical condition and displayed no clinical signs of Pb toxicosis. These observations, together with the very high blood Pb levels that were sustained for several months, suggest that crocodilians may possess a relatively high degree of resistance to Pb toxicity.

Non-lethal sampling for mercury evaluation in crocodilians

“…Related studies suggest that, in general, Alligatoridae are able to accumulate high concentrations of metals, showing great resistance to the acute effects of these elements, but are susceptible to chronic effects, showing permanent health effects in the long term and in their reproductive cycles (Brisbin et al, 2002;Yoshikane et al, 2006;Hammerton et al, 2003;Camus et al, 1998;Peters, 1983;Guillette et al, 2000;Lance et al, 2006).…”

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

“…Pb concentrations, which appear to originate from natural sources, may be of concern as the metal is an extremely toxic element for human and wildlife that affects the crocodilian community of French Guiana reproductive systems, renal and hepatic functions, and endocrine processes (Wani et al, 2015;Pain et al, 2019, Lemaire et al, 2021c. As crocodiles efficiently assimilate Pb (Hammerton et al, 2003), they may suffer Pb poisoning. Future studies are required to determine the source of this contamination in French Guiana by using Pb stable isotopes and to further investigate the consequences of this toxic element in crocodilians.…”

Trace Element Concentrations in Blood and Scute Tissues from Wild and Captive Hawaiian Green Sea Turtles (Chelonia mydas)

“…Blood Pb concentrations of ≤200 ng/g are considered background levels in 3 orders of birds (Anseriformes, Falconifomes, and Columbiformes), and 500 ng/g is considered clinical poisoning in Anseriformes and Falconiformes (Stout et al 2010; Franson and Pain 2011). However, crocodiles ( Crocodylus porosus ) with sustained blood Pb concentrations of 3420 ng/g for several months showed no adverse effects (Hammerton et al 2003). All green sea turtle populations are well below these levels.…”