Bačeva, K., T. Stafilov, and R. Šajn. “Biomonitoring of Nickel Air Pollution Near the City of Kavadarci, Republic of Macedonia”. Macedonian Journal of Ecology and Environment, vol. 12, no. 1-2, Dec. 2009, pp. 57-69, http://mjee.org.mk/index.php/mjee/article/view/91.