Toxicity of heavy metals and organic mineral processing agents to recombinant Escherichia coli

In mining activities, the substantial use of organic flotation agents leads to their co-discharge with heavy metals into the environment, resulting in forming heavy metal-organic composite pollution and exacerbating ecological risks in the surrounding mining areas. This study aims to investigate the toxic effects between Cd2+ and ethyl xanthate (EX) and diethyldithiocarbamate (DDTC). Determination of toxicity levels under individual and combined exposures was conducted using recombinant bioluminescent Escherichia coli HB101 pUCD607. Toxic effects were assessed, and the sources of synergistic toxicity were identified. The toxicity mechanism was explained at the cellular, enzymatic, and genetic levels. The results indicate that Cd2+ with EX and DDTC exhibit synergistic toxicity under mixed exposure. The half-effective mass concentrations of luminescent bacteria were 1.6 mg/L and 1.0 mg/L at mass concentration ratios of 1.02 and 1.14, respectively. The synergistic toxicity was due to the formation of Cd(EX)2 and Cd(DDTC)2 through chelation, and these formed particles were mainly distributed in the range of 100-300 nm. Cd(EX)2 and Cd(DDTC)2 lead to cell membrane damage and cell shrinkage in luminescent bacteria, causing secondary harm to cells by releasing hydrogen sulfide through decomposition. Cd(EX)2 and Cd(DDTC)2 micro/nanoparticles induce oxidative stress by affecting cellular ROS, LDH, SOD, GSH, and other enzyme activities, resulting in cell membrane rupture and structural damage. Micro/nanoparticles cause upregulation of gene expression, including umuD and yqhD, by causing DNA damage. This study reveals the toxic effects and mechanisms of heavy metal-organic composite pollution in mining areas, contributing to a comprehensive understanding of the impact of such composite pollution.