Hurta, V., and M. Kmeťová. “A Contribution to the Knowledge of Selected Ele-Ment Contents in Food Products and Sycamore Leaves Near the Paper Mill Industry”. Oecologia Montana, Vol. 26, no. 2, Dec. 2017, pp. 55-58, http://om.vuvb.uniza.sk/index.php/OM/article/view/302.