M. E. Doumer, S. J. Giacomini, C. A. P. Silveira, D. A. Weiler, L. M. Bastos, and L. L. de Freitas, “Microbial and enzymatic activities in the soil after application of retorted oil shale”, PAB, vol. 46, no. 11, pp. 1538–1546, Jan. 2012.