Studying The Responses And Tolerance Mechanisms Of Plants To Coking Wastewater Pollution

Coking wastewater is a kind of high concentrated organic wastewater which is generated in the coal coking, coal gas purification, and byproduct recovery processes of coke factories.It is composed of ammonia, cyanide, thiocyanide, phenolic compounds, polynuclear aromatic hydrocarbons (PAHs), polycyclic nitrogen-containing aromatics, oxygen-and sulfur-containing heterocyclics, and the composition of the wastewater is complicated, mutative and toxic.Thus the refractory pollutants remains in effluents may cause serious threaten to the environment. Moreover, pollution caused by coking waster and security of effluents have been concerned universally. Therefore, it is extremely important to study the toxicity of coking wastewater to organisms, especially the effluent.For this reason, several physiological changes of Zea mays L. (maize) after exposure to coking wastewater were investigated in the present study, including growth,fresh biomass, oxidative stress and antioxidant capacity. The results are showed as follows:(1)The concentration of organic contaminants and ammonia are high in the crude coking wastewater and most of them are refractory, toxic and inhibitory. After treated by biochemical process, pollutants in effluent were significantly reduced.(2) Coking wastewater significantly inhibited the growth and fresh biomass of maize seedlings.The inhibition varied as a function of samples concentration and was more significant in root length.After being treated by biochemical process treatment, the growth inhibition caused by effluents was alleviated.(3)Coking wastewater inhibited cell division in root tips of maize seedlings,decreasing the mitotic index, while induced the increase in micronucleus (MCN) frequency. The results show that components of coking wastewater may be genotoxic in plant cells and the genotoxicity was relieved in effluents treated by biochemical process. (4) In maize seedlings exposed to the influents,MDA level did not show significant change, but PCO content significantly enhanced with the exposure concentration.Furthermore, both of MDA level and PCO content significantly increased in maize seedlings after the exposure of effluents. Moreover, changes in antioxidant enzyme activities (POD, SOD, CAT, APX, and GPX) and non-enzymatic antioxidants (AsA and GSH)contents were observed differently.The results indicate that coking wastewater inhibited the growth of maize seedlings and elevated the levels of protein oxidation and lipid peroxidation in leaf tissues in a time-dependent manner, accompanied by the changes in heredity and antioxidant status. The physiological responses that varied as a function of samples concentration may link to the tolerance mechanisms of plants.In addition, since composed of complex pollutants, the treated coking wastewater could still cause toxic effects on organisms,but the toxic effects had been alleviated.It is therefore implicated that the persistive and refractory pollutants remains in effluents may cause potential threaten to organisms, thus the ecological risks of effluents are still existed.