Amphibians are the most threatened class of vertebrates worldwide, according to the IUCN Red List. Habitat loss and degradation are considered to be major threats causing population declines. Even common and widespread species, such as the European Common toad (Bufo bufo), are facing gradual population declines. A minor decline of a common species results in a significant decrease in biomass, which is expected to have major effects on ecosystem functions and services. Therefore, it is crucial to understand the causes of toad population decline in order to formulate effective conservation strategies. In this research project, the presence of agricultural contaminants in the environment is linked to population decline. The exposure of different life stages to agricultural contaminants is assessed by analysing water samples from breeding ponds during larval development, as well as tissues from road-killed reproductive adult toads. In addition, a quantitative analysis of bufotoxins in skin samples is developed to serve as a biomarker of stress. Using this data, we can improve our understanding of the causes of toad population decline, in order to provide effective conservation strategies to mitigate threats to an ecologically valuable species.