Ngumah, C., Orji, J., Akubuokwuoma, J., & Anoliefoh, U. (2019). Impacts of different concentrations of Copper and Zinc on in vitro responses of Azotobacter chroococum in biomass and nitrogen fixing outputs. Ecotoxicology and Environmental Contamination, 13(1), 79–83. https://doi.org/10.5132/eec.2018.01.09