Heavy metals in hair of small mammals from the cacao agroforestry and Brazilian Atlantic Forest

The current growing demand for resources, food production, and agricultural crops leads to a drastic reduction in biodiversity and ecosystem services. One of the options to mitigate the recurring effects of land use changes is the adoption of wildlife-friendly systems, such as cacao agroforestry systems, which integrates production with biodiversity conservation. Cacao management involves the frequent use of pesticides, such pesticides are comprised of heavy metals that are considered non-point sources of pollution. Animal hair is considered an excellent cumulative bioindicator of contamination. Small mammals are known as bioindicators of pollution, as they provide a warning of adverse effects on ecosystems. The main objective was to determine the concentrations of six heavy metals (Pb, Ni, Cr, Cd, Mn, and Cu) in hair of small mammals in traditional cacao agroforests and Atlantic Forest fragments in the southern region of Bahia, Brazil. The study covered 12 traditional cacao agroforests and 12 Atlantic Forest fragments. A total of 34 small mammals were captured in the traditional cacao agroforests, representing 12 species, while 18 were captured in the Atlantic Forest fragments, representing 6 species. We found that small mammals in both habitats had similar levels of lead in their hair. Heavy metals concentrations in the hair of small mammals were higher in individuals from traditional cacao agroforests than the Atlantic Forest fragments (Cacao agroforest (mg/Kg): Pb - 26.42 ± 16.42; Ni - 5.31 ± 4.3; Mn - 1.64 ± 2.63; Cu - 1.13 ± 1.15; Cd - 1.42; Atlantic Forest (mg/Kg): Pb - 19.28 ± 14.46; Ni - 0.18; Mn - 0.34 ± 0.40; Cu - 1 ± 2.05). Marsupials exhibited higher lead concentrations compared to rodents (Didelphimorphia (mg/Kg): Pb - 28.66 ± 18.73; Rodentia (mg/Kg): Pb - 18.44 ± 9.85), likely due to their distinct eating habits and habitat use. Body condition of the small mammals did not differ between the two habitat types, and there was no relationship between the bioaccumulation of heavy metals in small mammals and body condition. This is the first study to evaluate heavy metal contamination in small mammals in traditional cacao agroforests and Atlantic Forest fragments, thus providing important data that indicate the presence of heavy metals in the hair of the small mammals sampled, and consequently, the presence of these heavy metals in the environment where these small mammals lived.