Roman, Adam, and Ewa Popiela-Pleban. “Contamination of Propolis Used As a Dietary Supplement”. Potravinarstvo Slovak Journal of Food Sciences 6, no. 2 (March 6, 2012): 50–52. Accessed November 22, 2024. http://potravinarstvo.com/journal1/index.php/potravinarstvo/article/view/184.