Assessment of the exposure to heavy metals in Griffon vultures (Gyps fulvus) from the Iberian Peninsula

Abstract

Griffon vultures (Gyps fulvus), by virtue of their position at the top of the food chain and as obligate scavengers, are at risk of accumulating and concentrating heavy metals in their tissues and may be more predisposed to their toxic effects. The aim of this study is to investigate heavy metal concentrations in Griffon vultures in Portugal and Catalonia, Spain and to determine if heavy metal concentrations in the blood of weak and/or injured Griffon vultures admitted to wildlife rehabilitation centres (WRC) reflect contamination profiles in the local, free-living and outwardly healthy population. Whole-blood samples taken from 121 Griffon vultures caught in the wild or admitted to WRC in Portugal and Catalonia, Spain were examined for cadmium (Cd), mercury (Hg) and lead (Pb) by inductively coupled plasma mass spectrometry (ICP-MS). Cd and Hg were not detected in most samples (98.3% and 95%, respectively), while Pb was detected in all birds in concentrations ranging between 4.97 and 300.23µg/dl. Birds admitted to WRC had significantly lower Pb concentrations (24.15±15.07 and 25.98±18.04µg/dl in Portugal and Catalonia, Spain, respectively) than animals caught in the wild (29.67±13.19 and 42.22±50.08µg/dl in Portugal and Catalonia, Spain, respectively) (p<0.05). This may be explained by the fact that malnutrition was the main cause of admission of Griffon vultures to WRC, as ingestion has been described as the most significant pathway for Pb exposure in raptors. Therefore Griffon vultures admitted to WRC do not seem to be representative of the local, free-flying populations, so it remains necessary to continue catching when one intends to monitor Pb exposure in this species. The population of vultures captured in Catalonia, Spain showed the highest mean blood Pb concentration, perhaps due to the municipal rubbish dump located near the feeding station, with rubbish providing a significant fraction of their trophic needs. The ingestion of game meat with bullet fragments in carcasses or with Pb shots embedded in their flesh could also be the cause of the high blood Pb concentrations found in some vultures. The potential risk of Pb exposure in Griffon vulture populations must be given consideration, since most individuals evaluated had Pb concentrations between 20 and 100µg/dl, which is considered to be subclinical exposure to Pb, and which is above the threshold level at which Pb can affect antioxidant system in this species (15µg/dl).