Legacy of a Marine Disaster: Four-Year-Old Oil Fragments Pose Ecotoxicological Threat to Amphibian Life

Abstract

This study evaluated the ecotoxicological effects of weathered oil fragments (WOFs) collected four years after the 2019–2020 Brazilian oil spill on Scinax fuscovarius tadpoles, a species commonly found in mangrove-adjacent ecosystems. Tadpoles were exposed to WOFs at 1 g/L (WOF-I) and 4.5 g/L (WOF-II) for 21 days. Growth inhibition, oxidative stress, and genotoxicity were observed in both exposed groups. Compared to controls, WOF exposure resulted in up to 25.1% higher total petroleum hydrocarbon (TPH) accumulation in intestines, 400% more erythrocyte nuclear abnormalities, and significantly elevated DNA damage (tail DNA % and olive tail moment). Biochemical responses included increased reactive oxygen species (ROS), malondialdehyde (MDA), and corticosterone levels, along with altered antioxidant enzyme activities and upregulation of digestive enzymes. Principal Component Analysis (PCA) explained 75.1% and 24.9% of the variance in PC1 and PC2, respectively, highlighting oxidative stress, corticosterone, and genotoxicity as key factors in discrimination. Detrended Correspondence Analysis (DCA) confirmed group separation, with greater response variability in WOF-II. These findings demonstrate that WOFs remain toxic years after their release, posing a threat to amphibians in transitional ecosystems. The study highlights the importance of long-term monitoring and remediation efforts that extend beyond marine environments.