Review of biomonitoring metals in rivers using bullfrog tadpoles: an applicability study of exposed animals to Sorocaba River

Abstract: Aim This study reviewed recent literature on the use of the bullfrog species (Aquarana catesbeiana, Shaw, 1802) as an environmental bioindicator of pollution. Additionally, the total concentration of metals in the skin of bullfrog tadpoles exposed to the Sorocaba River was evaluated to explore the potential of this tissue as a biomonitoring tool and assess the bioavailability of metals in the river to aquatic organisms. Methods A bibliographic review was conducted using the Scopus and PubMed platforms with the search terms “Lithobates catesbeianus biomarkers,” “Aquarana catesbeiana biomarkers,” and “Rana catesbeiana biomarkers.” Tadpoles were exposed for 96 hours to water from two points along the Sorocaba River: Point Ibiúna (PI), representing the river's source, and Point Itupararanga Reservoir (PIR), a key water supply location for the Sorocaba-SP region. Deionized, contaminant-free water served as the control. Metal concentrations (Ba, Cu, Mn, Sr, and Zn) in skin samples (n=30) were analyzed after sample digestion using HNO3 and HCl, with determination via Microwave Plasma Atomic Emission Spectrometer (MP-AES). Results A review of the last 10 years of bibliographic production revealed 35 articles, where metals were the second most studied contaminant using this species (approximately 34% of articles), following agricultural pesticides (43%). Metal concentrations of Ba and Zn in the PI group varied compared to the control group. For the PIR group, Mn concentrations varied significantly relative to both the control and PI groups. No significant variation in Cu and Sr concentrations was observed across the groups. Conclusions Existing literature supports the use of various bullfrog tissues as bioindicators of environmental pollution. In this study, Ba concentrations increased by 12% and Mn by 54% in the PIR group compared to the PI group. No differences were observed for Cu, Sr, and Zn across groups. Metals such as As, Cd, Co, Mo, Ni, and Pb were below the quantification limit in all groups. The increased Mn concentration in PIR-exposed tadpoles suggests metal accumulation, pointing to a potential decline in water quality downstream from the river's source.