Determining the Impacts of an Aquatic Copper Exposure to Ambystoma gracile (Northwestern Salamander)

This study investigated the acute and subchronic toxicity of copper on Northwestern Salamander (Ambystoma gracile) larvae under varying water hardness conditions. Acute exposure experiments demonstrated that larvae in soft water had lower LC50 values than those in moderately hard water, with LC50 values of 33.16 µg/L and 1383 µg/L, respectively. Subchronic exposure to copper resulted in delayed development, reduced survival, and growth inhibition, with a 35-day LC50 of 28.97 µg/L. Gene expression analysis was conducted for the acute copper exposures and revealed a significant increase in metallothionein 1 (mt1), a protein indicative of metal detoxification response in most vertebrates. However, expression levels of thyroid hormone receptor genes (thra, thrb) were unchanged. Additionally, there was no impact on the expression of an estrogen receptor (esr1α) and a deiodinase (dio1) gene. Comparisons with previous studies on anuran species highlighted both similarities and differences in copper sensitivity and developmental responses depending on the anuran species. This variation underscores the importance of species-specific studies in understanding the broader ecological impact of copper pollution on amphibians. Finally, this research provides critical data on a representative caudate amphibian species, a taxa that is typically not included in ecological risk assessments due to lack of toxicity data.