Black mambas (Dendroaspis polylepis) as novel bioindicators of urban heavy metal pollution

Biomonitoring studies have documented the presence of contaminants in various urban wildlife species, but research has predominantly focused on avian and mammalian species. Despite snakes possessing several traits that make them excellent subjects for ecotoxicological studies, knowledge on their capacity to serve as bioindicators remains limited, particularly in African ecosystems where their utility has not previously been assessed. In this study, we investigated the use of black mambas (Dendroaspis polylepis), a large-bodied snake species native to sub-Saharan Africa, to serve as a bioindicator for heavy metal pollution within an urban environment. We examined concentrations of arsenic, cadmium, lead, and mercury in ventral scale clippings and compared these to concentrations in internal tissue samples from dead specimens opportunistically collected around the city of Durban, South Africa. Our findings demonstrated that black mambas are exposed to and accumulate heavy metals within their tissues. Metal concentrations tended to be higher in scales than liver and muscle tissue and displayed substantial variability, which was not strongly linked to body size or sex. We found a clear association between land use and heavy metal exposure in black mambas. Snakes living in connected green spaces around the city generally had significantly lower heavy metal concentrations in their scales compared to those in more industrial and commercial areas. Our findings indicate that black mambas can act as valuable sentinels of heavy metal pollution, enabling the detection of fine-scale local patterns. This suggests that snakes could be valuable models for environmental monitoring elsewhere in Africa.