Impacts of aqueous extracts of wildfire ashes on aquatic life-stages of Xenopus laevis: Influence of plant coverage

Wildfires have emerged as a global ecological concern due to their wide-ranging off-site effects. One particular consequence is the adverse impact on aquatic environments, as wildfires are acknowledged as a significant source of aquatic contamination through ash runoffs containing toxic compounds. Yet, amphibian response to this source of contamination remains largely undocumented. This study assessed how ash runoffs from Eucalyptus sp. and Pinus sp. affect early aquatic life-stages of Xenopus laevis. Embryos and tadpoles were exposed, respectively, for 96 h and 14 days to serial concentrations (26.9% - 100%) of aqueous extracts of ashes (AEAs; 10 gL^-1) composed of eucalypt (ELS) and pine (PLS) ashes. Mortality and development were monitored, and biometric data (snout-to-vent, tail and total length, and weight) measured. Sub-individual endpoints regarding oxidative stress (catalase-CAT; total glutathione-TG; lipid peroxidation-TBARS), neurotoxicity (acetylcholinesterase-AChE), transformation metabolism (glutathione-S-transferase-GST) and energetic metabolism (carbohydrate, lipid and protein content and O₂ consumption), were also measured. The two AEAs induced no significant lethal effects on embryos or tadpoles. However, in general, AEAs caused a developmental delay in both life stages. Effects of AEAs on biometric endpoint were only reported for tadpoles, which showed a decreased body length (snout-to-vent, tail and total) and weight (embryos were not weighed), with PLS exerting higher effect than ELS. As for the sub-individual endpoints, embryos showed mostly no alterations on the activity of the monitored parameters, except for PLS, which reduced embryos' carbohydrate content (at ≥59.2%) and increased O₂ consumption (at ≥35.0%). Regarding tadpoles, AEA exposure decreased the activity of CAT and GST (at ≥26.0%) and decreased carbohydrate (at ≥26.0%) and lipid (at ≥45.5%), whereas oxygen consumption increased (at ≥26.0%) only on PLS. Overall, the tested AEAs differentially affected amphibians across life-stages, indicating that plant coverage might affect ash toxicity.