Effects Of Tetracycline On The Bioavailability Of Copper And Zinc In Contaminated Soils

Heavy metal pollution and antibiotic residues in soil have attracted increasing attention with development of modern industrial and agricultural production.At the same time,accumulation of antibiotics and heavy metals such as copper and zinc in local environment and causing direct harm to the agricultural ecological environment according to the increasing popularity of large-scale farms,animal antibiotics and feed additives are widely used.Tetracycline antibiotics(TCs)are the main kind antibiotics used in breeding industry,while heavy metals remains in the environment for a long time,thus,both of them can greatly threat to human health through food chain.Present studies mainly focus on environmental toxicological effects of tetracycline antibiotics and copper-zinc respectively.Interaction and environmental effects of the two kind materials were rarely been reported.Therefore,experimental and mechanism discussion have been carried out on the bioavailability of tetracycline(TC)coexist with copper and zinc in contaminated soils.In this study,Pakchoi potted experiments were conducted by adding tetracycline into copper-zinc contaminated soil.The content of available copper zinc in the soil and plant,and Pakchoi growth level were detected.Soil physical-chemical properties and rhizosphere soil enzyme activity were studied.On the base of above studies,biological effectiveness of copper and zinc in the soil,were analyzed and the influence mechanism of tetracycline on copper zinc availability would been explored.This study has important practical significance for safety of vegetables production and protection of human health.The following research results were obtained through experimental research:(1)Effects of tetracycline on availability of copper and zinc in soilContent of available copper and zinc in soil increased with the addition of tetracycline.At the same level of tetracycline,zinc could promote the availability of copper,and the effect was enhanced with the coexistent of tetracycline and zinc.Similarly,copper in soil could also promote the availability of zinc,but the promoting effect of copper to zinc is stronger.Cation exchange capacity(CEC)of soil was decreased by the addition of tetracycline.And it went down with the concentration of tetracycline increased.The results showed that tetracycline could affect the adsorption of copper and zinc in soil and thus changed their availability.(2)Effects of tetracycline on the absorption of copper and zinc in PakchoiWhen soil copper and zinc content at 100 mg/kg and 250 mg/kg respectively,tetracycline promoted the growth of Pakchoi within the experimental concentration range(0-5 mg/kg).However,the growth of Pakchoi was inhibited in the presence of tetracycline together with higher concentrations of copper(200 mg/kg)and zinc(500 mg/kg).The effect of tetracycline on absorption of copper in Pakchoi was consistent with the content change of available copper in soil as tetracycline coexistent with copper-zinc.When tetracycline concentration was 2 mg/kg,copper content was the highest as 34.27 mg/kg and 50.20 mg/kg in plants and roots respectively.And the content of zinc in the underground part reached the maximum of 311.52 mg/kg with 2 mg/kg tetracycline in soil while there was no change in the upgroud part.(3)Effects of tetracycline on rhizosphere enzyme activity in soilWhen tetracycline coexisted with copper-zinc,the activities of soil catalase,urease and phosphatase were inhibited.And the inhibition was enhanced with the concentration of tetracycline increasing.The order of the inhibition on soil catalase activity by tetracycline was: tetracycline and copper and zinc > tetracycline and zinc > tetracycline and copper.The order of inhibition of soil urease activity was: tetracycline and copper > tetracycline and copper and zinc > tetracycline and zinc >tetracycline.With the addition of tetracycline,there was a negative correlation between catalase activity and zinc availability in soil as the correlation coefficient was-0.385.There was a significant negative correlation between urease activity and copper availability in soil(P<0.05)as the correlation coefficient was-0.678.There was a significant positive correlation between phosphatase activity and zinc availability in soil(P<0.05)as the correlation coefficient was 0.819.