Lv, Pin, et al. “Heavy Metal Contamination in Soils of Greenhouse Vegetable Production Systems in a Cold Region of China”. International Journal of Agricultural and Biological Engineering, vol. 12, no. 2, Apr. 2019, pp. 98-102, https://www.ijabe.migration.pkpps06.publicknowledgeproject.org/index.php/ijabe/article/view/4306.