Study Of The Ecotoxicological Effects Of Compound Pollution Of Metalaxyl And Cadmium On Tobacco Planting Soil

Residues of metalaxyl and cadmium pollution often exist in tobacco fields,which have become an urgent issue in tobacco production.Learning the effects of compound pollution of metalaxyl and cadmium on growth and development of tobacco and clarifying their ecotoxicological effects,understanding the toxicity differences of single and compound pollution on different organisms,which will be of great theoretical and practical value to ecological environmental risk assessment and control strategy in the agricultural field.The main conclusions are as follows:1.Effects of single and combined pollution of metalaxyl and cadmium on tobacco growth and development.Pot experiment were carried out to study the effects of metalaxyl and cadmium on the growth and photosynthetic performance of tobacco.The results showed that the treatment of 20 mg/kg metalaxyl addition had different inhibitions on the tobacco root biomass,chlorophyll content,photosynthetic rate,stomatal conductance and transpiration rate.But had a certain stimulation effect on the growth of stem and leaf.And the treatment of 20 mg/kg cadmium addition had different inhibition effects on tobacco main root length,biomass,chlorophyll content,carotenoid content,net photosynthetic rate,stomatal conductance and transpiration rate.Under the combined pollution of metalaxyl and cadmium,the length,biomass,net photosynthetic rate,stomatal conductance and transpiration rate of tobacco were significantly inhibited and the two pollutants had synergistic effect;while they had synergistic and then antagonistic effect on the root activity,chlorophyll content and carotenoid content with the growth stage of tobacco.And the inhibitory effect of cadmium in combined pollution was stronger than that of single addition.Under the combined pollution condition,the cadmium addition inhibited the absorption and degradation of metalaxyl in tobacco leaves While the metalaxyl addition promoted the absorption and transport of cadmium in tobacco leaves.2.Acute toxicity of single and combined pollution of metalaxyl and cadmium to earthworms.The 14 days acute toxicity of the compound pollution of metalaxyl and cadmium to Eisenia foetida was studied through natural soil test.The results showed that the LC₅₀ value of the single pollution of metalaxyl to earthworms was 112.76 mg/kg,and the LC₅₀ value of the single cadmium pollution of cadmium was 763.79 mg/kg.The acute toxicity of metalaxyl pollution to earthworms was significantly higher than that of cadmium.Under the compound pollution condition,middle and low concentration of cadmium addition?380 mg/kg,760 mg/kg?inhibited the toxicity of metalaxyl.The combined toxicity of two pollutions were antagonistic,and the high concentration of cadmium addition?1520 mg/kg?enhanced the toxicity of metalaxyl,and the two pollutions were synergistic.Meanwhile,the middle and low concentration of metalaxyl addition?55 mg/kg,110 mg/kg?inhibited the toxicity of cadmium,and the combined toxicity of two pollutions were antagonistic,while the high concentration of metalaxyl addition?220 mg/kg?increased the toxicity of cadmium,and both of them were synergistic.3.Acute toxicity of single and combined pollution of metalaxyl and cadmium to luminescent bacteria.The acute toxic effects of compound pollution of metalaxyl and cadmium on the luminescent bacteria?Photobacterium phosphoreum T3 spp.?were studied.The results showed that the 15min EC₅₀value of metalaxyl to luminescent bacteria was 51.65 mg/kg and the 15min EC₅₀ value of cadmium to luminescent bacteria was 0.99 mg/kg,which indicated that the acute toxic effect of cadmium to luminescent bacteria was significantly higher than that of metalaxyl.Under the combined pollution condition,the acute toxicity of metalaxyl and cadmium to luminescent bacteria with different molar ratios showed antagonistic effect.4.The response of tobacco development to the improvement of combined pollution of metalaxyl and cadmium.Pot experiment were carried out to study the response of tobacco development and photosynthetic performance to the compound pollution of metalaxyl and cadmium after adding the soil amendment?sepiolite and biochar?.The results showed that the addition of sepiolite and biochar to the compound polluted soil could improve the root activity,the content of chlorophyll,chlorophyll a and chlorophyll b and the content of carotenoid in tobacco.And meanwhile,the addition of sepiolite and biochar could also promote the photosynthetic parameters of tobacco leaf,which showed that the two kinds of soil amendments had good improvement effect on the growth and development of tobacco under the combined polluted conditions.