Some of Africa’s most iconic herbivores may be more exposed to toxic elements in soil than others, not because of what they eat, but because of how and where they feed. New research from South Africa’s Kalahari desert shows that grazing and digging animals ingest significantly more soil than tree-browsing species, increasing their potential exposure to harmful metals such as arsenic, lead and chromium.
The study, led by Andrea Webster of the University of Pretoria examined 16 herbivore species at the Tswalu Kalahari Reserve. It highlights how feeding behaviour plays a crucial role in determining wildlife exposure to soil-borne toxins, with important implications for conservation, rewilding and habitat restoration projects.
Feeding close to the ground increases exposure
All herbivores ingest some soil while feeding, but the amount varies widely between species. Animals that graze on grass or dig for roots are far more likely to swallow soil particles than those that browse leaves higher up in trees. Grazers such as white rhinoceros, African buffalo and blue wildebeest were found to ingest large quantities of soil, especially in dry conditions when grass is coated with dust.
Burrowing species like warthogs and porcupines showed the highest soil intake of all. Their feeding and digging behaviour brings them into constant contact with surface sediments, where toxic elements are often most concentrated. In contrast, browsers like giraffes, which feed mainly in the tree canopy, had much lower exposure because their food is largely free from soil contamination.
Tracing toxins from soil to animals
Over two years, researchers collected soil and vegetation samples from 25 waterpoints across the reserve to map where toxic elements were most concentrated. They then analysed animal faeces to understand short-term exposure and fur samples to assess how much of those elements were absorbed into the body over time.
The results showed that several toxic elements, including vanadium, aluminium, lead, chromium, tin, cobalt and arsenic, were more concentrated in soil than in plants. Grazing and mixed-feeding species were therefore more exposed than strict browsers. Black rhinos, which primarily browse on shrubs and trees, showed comparatively low levels of exposure and retention.
Mixed feeders such as eland and springbok, which switch between grazing and browsing depending on the season, fell somewhere in between. When grazing during dry periods, they ingest more soil and face higher exposure than during times when they rely more on leaves and shoots.
Teeth offer clues to long-term risk
The study also found that tooth structure can reveal which species are most vulnerable to soil-borne toxins. Grasses naturally contain abrasive silica, and in dry environments they are often coated with dust and fine soil. Over time, this wears down teeth.
Species that regularly consume abrasive, soil-covered food have evolved high-crowned teeth with thick enamel to cope with heavy wear. Researchers found a strong link between these tooth traits and higher levels of toxic elements in faeces and fur, suggesting that dental structure can act as a biological indicator of long-term soil ingestion and exposure.
This insight could help conservation managers identify at-risk species without relying solely on chemical testing, allowing for more targeted monitoring in sensitive landscapes.
Why the findings matter for conservation
Soil naturally contains trace amounts of toxic elements, and animals have evolved to tolerate low levels. The presence of metals in wildlife tissue does not automatically signal pollution or ecological harm. However, human activities such as mining, agriculture, industrial emissions and altered water management can sharply increase concentrations in soil.
Species that already ingest large amounts of soil are therefore more vulnerable when landscapes are disturbed. As conservation efforts increasingly focus on restoring ecosystems and reintroducing large herbivores, understanding these differences becomes critical.
The study provides a framework to help conservationists distinguish between natural exposure and human-driven contamination, reducing the risk of misinterpreting data and ensuring better-informed decisions. Ultimately, it shows that animals are not passive victims of their environment. Their behaviour, anatomy and evolutionary history shape how they interact with the soil beneath their feet and how much risk they carry as landscapes continue to change.