Metal and metalloid exposure in Cape Town's caracals

24/04/2023

The use of human-associated landscapes and the consumption of food resources typical of the marine food web determine metal and metalloid exposure in Cape Town's caracals

Wildlife inhabiting around large cities is exposed to potentially toxic pollutants such as metals and metalloids, most of which are derived from human activities. The severity of this exposure, the pathways by which it occurs, and the degree of bioaccumulation of these chemicals vary depending on various factors, dietary habits, habitat use, and the wildlife species involved.

Among the groups of fauna, carnivores are especially vulnerable to bioaccumulation of metals and metalloids owing to their position in food webs, thus they are good sentinel species for environmental monitoring and to assess the risks of such exposure for the biodiversity conservation.

A research work led by the University of Cape Town and the Cape Leopard Trust (South Africa), in collaboration with the Research Group in Wildlife Toxicology of the Instituto de Investigación en Recursos Cinegéticos (IREC – CSIC, UCLM, JCCM), has studied the exposure of caracals (Caracal caracal) to metals and metalloids in the peri-urban environment of Cape Town (South Africa) through the analysis of blood samples.

The caracal (Caracal caracal) is an adaptable medium-sized carnivore that feeds in the peri-urban fringe of Cape Town (South Africa), being a good indicator species of its environmental status that can be used in pollution monitoring programs to mitigate exposure and promote biodiversity conservation in human-associated landscapes (Photo: Sebastian Wiedemann).

Although there are no specific toxicity thresholds for the caracal, the levels of arsenic (As) and chromium (Cr) in the blood of several individuals were compatible with sublethal health effects. On the other hand, the use of human-transformed landscapes, particularly urban areas, roads and vineyards, was associated with increased exposure to metals such as aluminum (Al), cobalt (Co), and lead (Pb).

The results also showed that caracals foraging closer to the coast and within aquatic food webs had higher blood levels of mercury (Hg), selenium (Se) and As, likely because of regular predation on seabirds and waterbirds facilitates the transfer of metals from aquatic to terrestrial food webs.

Finally, blood levels of several elements (such as Cr and Hg) were associated with lower levels of hemoglobin, whereas other elements (such as Hg and Se) were associated with elevated levels of infection-fighting cells, which suggests possible impacts on the immune system in caracals with higher rates of exposure to metals and metalloids.

In a previous study, researchers found that caracals in the peri-urban and agricultural environment of Cape Town are more exposed to organochlorine pollutants, and that such exposure was linked to haematological changes (Photo: Scott Clarkson).

This research work highlights the importance of anthropogenic activities as the main environmental sources of metal contamination in terrestrial wildlife, including exposure across the land-ocean interface, and highlights the fact that cities are particularly toxic areas for wildlife. Exposure to a 'cocktail' of toxic elements may threaten the long-term health and persistence of Cape Town's caracal population in unexpected ways, particularly when it interacts with additional exposure to other contaminants and pathogens.