Metal levels in bat guano from Brazilian caves: insights into environmental contamination

Bats, with more than 1450 species worldwide, roost in caves, and colonies can produce guano deposits. Guano analysis reveals bat diets and indicates environmental contamination, since bats interact and accumulate metals through food, water, and airborne particulate matter. This study examined guano from caves in Rio Grande do Norte (RN-27 samples) and Pará (PA-24 samples), Brazil, to assess metal levels. Samples were taken from different depths, locations, and species, including the omnivorous Phyllostomus discolor, insectivorous Pteronotus gymnonotus, and nectarivorous Glossophaga soricina. Microwave-assisted acid digestion was used, and a 23 factorial design optimized acid digestion conditions based on residual acidity (RA) and dissolved organic carbon (DOC). Optimal parameters were 10.0 mL of 1.5 mol L⁻1 HNO₃, 3.0 mL H₂O₂, and 35 min digestion. Cd, Co, Cr, and Pb were detected in samples from RN, with concentrations reaching 2.3, 5.2, 18.6, and 30.7 mg kg⁻1. In PA, Pb concentrations of 20.0 and 19.4 mg kg⁻1 were observed in two samples, and Cd concentrations ranged from 0.2 to 2.3 mg kg⁻1. By contrast, Cu was detected at concentrations ranging from 64.9 to 283.0 mg kg⁻1 in RN and 10.4 to 645.6 mg kg⁻1 in PA. Such levels likely reflect bioaccumulation, as Cu is an essential nutrient, but are not explained solely by physiological regulation and may also reflect environmental conditions at the sampling sites, while Pb indicates environmental exposure. These findings highlight the need to monitor metal contamination, with bat guano proving a useful indicator.