Study On The Phytotoxicity Of Coking Wastewater

Coke plant wastewater is generated in the coal coking, coal gas purification, and by-product recovery processes of coke factory, and referred as coking wastewater. The pollution caused by coking wastewater has been a severe problem for decades in China as coal is its main energy resource. Most of the compounds in coking wastewater are refractory, highly concentrated and toxic, such as phenolics, heterocyclic compounds and polycyclic aromatic hydrocarbons (PAHs). However, the exposure route and toxicity of the wastewater has not been well known.Therefore, it has become important to study the toxicity of the mixture of coking wastewater in the environment to organism.The physical and chemical characteristics of coking wastewater in and/or out of the Biochemical Station were analyzed, and the coking wastewater-induced toxicity to seed germination and plant growth was also investigated using plant-test system. The results indicated that the coking wastewater contained high concentration of organic metter, phenolics are the main organic constituents, other organics present include polynuclear aromatic hydrocarbons (PAHs) and nitrogen, oxygen and sulfur-containing heterocylic compounds. Most of the physical and chemical indicators cann't conform to the standards of National Institute, even though it has be treated using biochemical mothods.The genotoxicity of coking wastewater was also studied using Vicia faba L. and Hordeum vulgare L. root tip cytogenetic bioassay. Results show that the tested coking wastewater decreased the mitotic index (MI) and caused significant increases of micronuclei (MCN), sister chromatid exchange (SCE) and pycnotic cell (PNC) frequencies in concentration-dependent manners. The decrease of mitotic index and cell cycle delay were also found in coking-wastewater groups and they were positive correlative to MCN frequencies. After exposure to the same concentration wastewater, the increasing ratios of MCN, SCE and PNC frequencies were higher in V. faba than that in H. vulgare. The results confirm that coking wastewater is a genotoxic agent in plant cells and imply that exposure to the wastewater in environment may pose a potential genotoxic risk to organisms.Although our data are still insufficient, this is the first experimental evidence that sulfur dioxide induces MCN, binucleated cells, pycnosis and nuclear disintegration in plant cells in a dose-dependent manner. The frequencies of various abnormal cells in root tips were in relation to treated concentration and duration and duration time. The experimental results came to the same conclusion as our previous observation that coking wastewater is a clastogenic and genetoxic agent. In this research the use of the V. faba-MCN test showed good correlation with data obtained from H. vulgare-MCN test.In brief, coking wastewater is the toxicity factor of DNA molecule, and the genetic damage of plant system could show indirectly us damage of the animal cells under the same condition, so we could use both V. faba and H. vulgare bioassays as efficient genotoxicity tests of coking wastewater and as the monitors of its pollution in the environment, but the V. faba assay is more sensitive than H. vulgare assay during the process.