Influence Of Exogenous Lead And Cadmium Pollution On Enzyme Activities And Organic Matter Degradation In River Sediment

With the development of industrialization and urbanization, a large number of industrial waste water, waste residue and sewage was discharged into river. That result in increasing heavy metal pollution and threat to human health. Lead and cadmium are two of the most widespread heavy metals in river sediment. The effects of exogenous lead and cadmium pollution on enzyme activities and organic matter degradation in the surface of river sediment with high moisture content were studied at laboratory-scale. The dynamic changes of urease, catalase, protease activities, organic matter content, exchangeable Pb/Cd or EDTA-extractable Pb/Cd concentration in sediment were monitored during different levels of exogenous lead and cadmium infiltrating into sediment.The results showed that concentration of exogenous heavy metal and time are important factors, which affected enzyme activities and degradation of organic matter and the interaction effect between the two factors on enzyme activities and degradation of organic matter was significant. At the early stage of experiment, the exogenous lead with low and medium concentration promoted urease activities and cadmium with high concentration inhibited urease activities. Catalase and protease activities were inhibited by exogenous lead and cadmium pollution. Urease, catalase, and protease activities were stimulated with low concentration of exogenous heavy metal during the middle and late stage of the experiment. At the end of the experiment, the inhibitory effect of heavy metals on enzymes had weakened. However, enzyme activities with high concentration of heavy metal pollution were still inhibited. The concentrations of exchangeable Pb/Cd increased at the early stage and then fall. The concentration of EDTA-extractable Pb/Cd increased with time. Pearson correlation analysis showed negative correlation between urease activities and exchangeable Pb/Cd or EDTA-extractable Pb/Cd. There were significant negative correlation between catalase activities and EDTA-extractable Pb on day 3, day 10 and day 30. Catalase and protease activities had significant negative correlation between exchangeable and EDTA-extractable Cd. There was no significant negative correlation between protease activities and EDTA-extractable Pb. Organic matter content in polluted sediment with exogenous lead was lower than control and decrease with time. The degration of organic matter had significant difference under different levels of exogenous lead and cadmium pollution. Under exogenous lead pollution, there was significant positive correlation between organic matter and urease activities on day 45, significant positive correlation between organic matter and catalase activities on day 30, negative correlation between protease activities and organic matter. Under exogenous cadmium pollution, there was significant positive correlation between organic matter and urease activities on day 7, day 15 and day 45, significant positive correlation between organic matter and catalase activities on day 45, significant positive correlation between protease activities and organic matter on day 7 and day 30. The present findings will improve the understandings about the ecotoxicological mechanisms in sediment.