Study On The Improvement Of The Soil Contaminated By Lead, Cadmium And Carbofuran Compound Pollution Using Photosynthetic Bacteria

The effect on the species distribution of heavy metals lead and cadmium and the degradation of carbofuran by photosynthetic bacteria was studied. The results showed that photosynthetic bacteria reduced the bioavailability of lead and cadmium and increased the degradation of carbofuran significantly. The effect of soil enzyme activity and the number of microorganisms by photosynthetic bacteria was studied. The results indicated that photosynthetic bacteria activated the activity of soil enzyme and improved the number of microorganisms. Under the laboratory conditions, the orthogonal experiment of lead, cadmium and carbofuran compound pollution was studied. The results of a pot experiment showed that photosynthetic bacteria lowered the accumulation of pollutants in vegetables and improved crop quality. The main conclusions were as follows:Ⅰ. At different pH, temperature and bacterial concentration, photosynthetic bacteria affected five species distribution of lead and cadmium in soil at different levels.①When pH was 7, compared with the control, the bioavailability of heavy metals lead and cadmium decreased 21.39% and 7.59% respectively in the plus photosynthetic bacteria group. At this time, there was the lowest bioavailability of heavy metals lead and cadmium.②When the temperature was 35℃, compared with the control, the bioavailability of heavy metals cadmium was reduced 7.57% and was the lowest in the plus photosynthetic bacteria group. When the temperature was 30℃, compared to the control, the bioavailability of heavy metals lead was reduced 18.59% in the plus photosynthetic bacteria group. At the same time, it was the lowest.③When the concentration of PSB was 10~6 bacteria / g·soil, the bioavailability of heavy metals cadmium in the plus PSB group was 22.39% less than the control. And the bioavailability was the lowest among the different concentration of PSB. When the concentration of PSB was 10~8 bacteria / g·soil, the bioavailability of heavy metals lead was decreased 8.18% compared to the control and was the lowest among the different concentration of PSB.Ⅱ. When the concentration of carbofuran was respectively 5mg/kg, 10mg/kg, 25mg/kg and 50mg/kg, with increasing the concentration of carbofuran contamination, the carbofuran degradation rate of the plus PSB group and the control was decreased. When the carbofuran concentration was 25mg/kg, photosynthetic bacteria on the degradation rate of carbofuran in the first 7 days was 96%. Under the high degradation rate and high concentration of carbofuran, the effect of photosynthetic bacteria on the degradation of carbofuran was the best at the concentration of 25mg/kg.Ⅲ. In this study, the results of using photosynthetic bacteria to increase enzyme activity in the soil of heavy metals and pesticides compound pollution showed that photosynthetic bacteria increased catalase, urease, invertase and phosphatase activity in soil. The best conditions were pH 7.0, temperature 30℃and the amount of 10~8 bacteria / g·soil. Photosynthetic bacteria improved the different effect of soil enzyme activity due to different types of enzymes. Photosynthetic bacteria increased urease and invertase activity obviously, phosphatase activity averagely and catalase activity slightly from the experiment.Ⅳ. Using RAPD random amplified polymorphic method, DNA sequence diversity of soil microbial community affected by lead, cadmium and carbofuran was studied. The results showed that lead, cadmium and carbofuran combined pollution had the greatest impact on the composition of DNA sequence diversity of soil microbial community. By cadmium, lead and carbofuran contamination of single or complex, DNA sequence diversity of soil microbial community was increased at different degrees. The results also showed that DNA sequence diversity of soil microbial community affected by cadmium, lead and carbofuran compound pollution was more serious than a single pollution. After photosynthetic bacteria was added in the soil of single and combined pollution, DNA sequence diversity of soil microbial community in the contaminated soil of adding PSB was closer to the control soil than without PSB. The similarity coefficient of adding PSB in the contaminated soil and the control soil was higher than without PSB in the contaminated soil and the control soil. This suggested that photosynthetic bacteria could improve DNA sequence diversity of soil microbial community in the contaminated soil.Ⅴ. According to the orthogonal experimental results of lead, cadmium and carbofuran contamination in soil, combined with the actual conditions of the experimental environment, the pot experiment conditions of lead, cadmium and carbofuran contamination was set. After one month of the pot experiment, the conclusions were presented:①When the concentration of cadmium, lead and carbofuran was 20mg/kg, 100mg/kg and 25mg/kg, the cabbage on the absorption of cadmium and lead was powerful, rape on the weakest absorption of cadmium and garland chrysanthemum on the weakest absorption of lead. In the control group, rape on the largest enrichment factor of carbofuran was 16.1%, the minimum of cabbage was 10.4%, radish was 13.3% and garland chrysanthemum was 11.5%. In the plus PSB group, radish on the largest enrichment factor of carbofuran was 6.1%, the minimum of cabbage was 4.8%, rape was 5.7% and garland chrysanthemum was 5.2%.②When the concentration of cadmium, lead and carbofuran was 10mg/kg, 500mg/kg and 50mg/kg, in the control group, the enrichment coefficient of Cd: radish > rape > cabbage > garland chrysanthemum, lead enrichment factor: cabbage > radish > rape > garland chrysanthemum. In the plus PSB group, the level of lead and cadmium enrichment factors: cabbage > radish > rape > garland chrysanthemum, radish > cabbage > rape > garland chrysanthemum. In the control group, garland chrysanthemum on the largest of carbofuran enrichment factor was 19.3%, the minimum of radish was 14.4%, rape was 17.5% and cabbage was 16.4%. In the plus PSB group, the maximum carbofuran enrichment factor of rape was 9.6%, the minimum of cabbage was 7.1%, radish was 8.2% and garland chrysanthemum was 8.9%.